Landolt-Börnstein Numerical Data and Functional Relationships in Science and Technology New Series / Editor in Chief: W. Martienssen
Group III: Condensed Matter Volume 42
Physics of Covered Solid Surfaces Subvolume A Adsorbed Layers on Surfaces Part 2 Measuring Techniques and Surface Properties Changed by Adsorption
Editor H.P. Bonzel Authors K. Hermann, H. Ibach, K. Jacobi, M.A. Rocca, D. Sander, M.A. Van Hove, P.R. Watson, Ch. Wöll
13
ISSN 1615-1925 (Condensed Matter) ISBN 3-540-41224-7 Springer-Verlag Berlin Heidelberg New York Library of Congress Cataloging in Publication Data Zahlenwerte und Funktionen aus Naturwissenschaften und Technik, Neue Serie Editor in Chief: W. Martienssen Vol. III/42A2: Editor: H.P. Bonzel At head of title: Landolt-Börnstein. Added t.p.: Numerical data and functional relationships in science and technology. Tables chiefly in English. Intended to supersede the Physikalisch-chemische Tabellen by H. Landolt and R. Börnstein of which the 6th ed. began publication in 1950 under title: Zahlenwerte und Funktionen aus Physik, Chemie, Astronomie, Geophysik und Technik. Vols. published after v. 1 of group I have imprint: Berlin, New York, Springer-Verlag Includes bibliographies. 1. Physics--Tables. 2. Chemistry--Tables. 3. Engineering--Tables. I. Börnstein, R. (Richard), 1852-1913. II. Landolt, H. (Hans), 1831-1910. III. Physikalisch-chemische Tabellen. IV. Title: Numerical data and functional relationships in science and technology. QC61.23 502'.12 62-53136 This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilm or in other ways, and storage in data banks. Duplication of this publication or parts thereof is permitted only under the provisions of the German Copyright Law of September 9, 1965, in its current version, and permission for use must always be obtained from Springer-Verlag. Violations are liable for prosecution act under German Copyright Law. Springer-Verlag Berlin Heidelberg New York a member of BertelsmannSpringer Science+Business Media GmbH © Springer-Verlag Berlin Heidelberg 2002 Printed in Germany The use of general descriptive names, registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. Product Liability: The data and other information in this handbook have been carefully extracted and evaluated by experts from the original literature. Furthermore, they have been checked for correctness by authors and the editorial staff before printing. Nevertheless, the publisher can give no guarantee for the correctness of the data and information provided. In any individual case of application, the respective user must check the correctness by consulting other relevant sources of information. Cover layout: Erich Kirchner, Heidelberg Typesetting: Authors and Redaktion Landolt-Börnstein, Darmstadt Printing: Computer to plate, Mercedes-Druck, Berlin Binding: Lüderitz & Bauer, Berlin SPIN: 10783464
63/3020 - 5 4 3 2 1 0 – Printed on acid-free paper
Preface Surface Science is understood as a relatively young scientific discipline, concerned with the physical and chemical properties of and phenomena on clean and covered solid surfaces, studied under a variety of conditions. The adsorption of atoms and molecules on solid surfaces is, for example, such a condition, connected with more or less drastic changes of all surface properties. An adsorption event is frequently observed in nature and found to be of technical importance in many industrial processes. For this reason, Surface Science is interdisciplinary by its very nature, and as such an important intermediary between fundamental and applied research. The beginning of Surface Science may be placed around the years 1900-1928, connected with seminal works by J.W. Gibbs, I. Langmuir, M. Knudsen, O. Stern, M. Volmer, C. Davisson and L. Germer, H.S. Taylor, J.E. Lennard-Jones, I.N. Stranski and others. In modern times, research activities in this field have literally exploded worldwide. Consequently, enormous progress can be recognized and it is no exaggeration, to note a high degree of maturity in this well-established scientific discipline. Tribute is being paid to this effect by the renowned Series of Landolt-Börnstein whose editor-in-chief Werner Martienssen, Frankfurt am Main, has initiated several volumes of collected scientific data in the field of Surface Science. Indeed, the point in time has arrived where all quantitative data, that have been generated over so many years, are worth being collected in tables and figures for critical review and reference purposes as well. The beginning has been made with Landolt-Börnstein volume 24, entitled Physics of Solid Surfaces. This volume, consisting of four subvolumes, appeared in 1993-96 and covers the properties of clean solid surfaces. The present volume 42 is devoted to Covered Solid Surfaces and, in particular, to Adsorbed Layers on Surfaces. It is as such a collection of data obtained for adsorbates on well-defined crystalline surfaces. "Well-defined" means surfaces of known crystallographic structure and chemical composition. These conditions can in most cases be realized by careful sample preparation in ultra-high vacuum. Work on the present volume started in late 1997 when I was first contacted by W. Martienssen. An initial outline of the volume was written in January of 1998. At this point I want to express my sincere gratitude to George Comsa, Bonn, and Gerhard Ertl, Berlin, for their support by making valuable suggestions, concerning both the outline and the choice of possible authors. In fact, the choices made at the time proved to be excellent ones, and the consulting of G. Comsa and G. Ertl turned out to be extremely helpful for the evolution of the present volume. It was almost clear at the beginning, that the amount of general information and quantitative data on Adsorbed Layers on Surfaces is enormous, too large to fit into a single volume. Hence, again several subvolumes had to be planned. Unfortunately, the chapters anticipated for each of the subvolumes did not arrive synchronously with the production schedule, such that the sequence of chapters actually printed in the subvolumes deviates from that in the general outline of the whole volume. We apologize for this inconvenience, but in the age of electronic information distribution this problem will be solved, once all volumes are available electronically. Search routines will guide the reader to the data of his desire. Until that time, the index of each subvolume will have to do. The present subvolume III/42A2 deals with Measuring Techniques and Surface Properties Changed by Adsorption. Finally and most importantly, I would like to extend my deep appreciation to all authors of this volume for their excellent contributions, and to the editing and production offices of Springer-Verlag for efficient cooperation and general support. Jülich, January 2002
The Editor
Editor H.P. Bonzel Forschungszentrum Jülich Institut für Grenzflächenforschung und Vakuumphysik (IGV) 52425 Jülich Germany
Authors K. Hermann Fritz-Haber-Institut der Max-Planck Gesellschaft (MPG) Abteilung Theorie D-14195 Berlin Germany 4.1 Surface structure on metals and semiconductors H. Ibach Institut für Grenzfläch enforschung und Vakuumphysik (IGV) Forschungszentrum Jülich D-52425 Jülich Germany 4.4 Surface free energy and surface stress K. Jacobi Fritz-Haber-Institut der Max-Planck Gesellschaft (MPG) D-14195 Berlin Germany 4.2 Electron work function of metals and semiconductors M.A. Rocca Centro di Fisica delle Superfici e Basse Temperature del CNR Istituto Nazionale di Fisica della Materia I-16146 Genova Italy 4.5 Surface phonon dispersion D. Sander Max-Planck Institut (MPI) für Strukturphysik D-06120 Halle Germany 4.4 Surface free energy and surface stress
M.A. Van Hove Lawrence Berkeley National Laboratory Materials Science 66 Berkeley, CA 94720 and Department of Physics University of California-Davis Davis, CA 95616 USA 4.1 Surface structure on metals and semiconductors P.R. Watson Department of Chemistry Oregon State University Corvallis, OR 97331 USA 4.1 Surface structure on metals and semiconductors Ch. Wö ll Lehrstuhl für Physikalische Chemie I Ruhr-Universität Bochum D-44801 Bochum Germany 2 Characterization of adsorbate overlayers: Measuring techniques
Landolt-Börnstein Editorial Office Gagernstr. 8, D-64283 Darmstadt, Germany fax: +49 (6151) 171760 e-mail:
[email protected] Internet http://www.landolt-boernstein.com Helpdesk e-mail:
[email protected]
Contents III/42 Physics of Covered Solid Surfaces A: Adsorbed Layers on Surfaces Part 2: Measuring Techniques and Surface Properties Changed by Adsorption 1
Introduction to physical and chemical properties of adlayer/substrate systems (H.P. BONZEL) ................................................... see subvolume III/42A1
2 2.1 2.1.1 2.1.2 2.2 2.2.1 2.2.2 2.2.3 2.2.4 2.2.5 2.2.6 2.2.7 2.2.8 2.3 2.3.1 2.3.2 2.3.3 2.4 2.4.1 2.4.2 2.4.3 2.4.4 2.5 2.5.1 2.5.2 2.5.3 2.5.4 2.5.5 2.5.6 2.5.7 2.5.8 2.5.9 2.5.10 2.6 2.6.1 2.6.2 2.6.3 2.6.4 2.6.5 2.6.6 2.6.7
Characterization of adsorbate overlayers: measuring techniques (CH. WÖLL) .......... 2-1 Introduction .......................................................................... 2-1 Comparative information on techniques discussed in this chapter....................... 2-2 List of acronyms used in this chapter .................................................. 2-4 Direct methods ....................................................................... 2-4 Monitoring adsorption by calorimetry ................................................. 2-5 Quartz crystal microbalance .......................................................... 2-5 Chemiluminescence .................................................................. 2-5 Exoelectrons ......................................................................... 2-6 Adsorption-induced changes of surface stress ......................................... 2-6 Adsorption-induced changes in resistivity ............................................. 2-6 Reflectance ellipsometry ............................................................. 2-6 Change of work function ............................................................. 2-7 Techniques based on a mass spectrometer ............................................. 2-7 Determination of sticking coefficients using a molecular beam ......................... 2-7 Thermal Desorption Spectroscopy (TDS) ............................................. 2-8 Laser-induced Thermal Desorption (LITD) ............................................ 2-9 Techniques for a chemical analysis.................................................... 2-9 Secondary Ion Mass Spectroscopy (SIMS) ........................................... 2-10 Ion Scattering Spectroscopy (ISS) ................................................... 2-10 Auger Electron Spectroscopy (AES) ................................................. 2-10 X-ray Photoelectron Spectroscopy (XPS) ............................................ 2-11 Structural sensitive techniques ....................................................... 2-13 Low Energy Electron Diffraction (LEED) ............................................ 2-13 Diffuse Low Energy Electron Diffraction (DLEED) .................................. 2-14 Photoelectron Diffraction (PED) ..................................................... 2-15 Techniques employing X-ray standing waves (XSW) ................................. 2-16 Extended X-ray Absorption Fine-Structure Spectroscopy (EXAFS) ................... 2-16 He-atom scattering (HAS) ........................................................... 2-18 Scattering of Rare Gases and Molecules .............................................. 2-19 X-ray Diffraction .................................................................... 2-19 Neutron Scattering .................................................................. 2-20 Ion Scattering Spectroscopy (ISS) ................................................... 2-20 Imaging techniques .................................................................. 2-21 Field Ion Microscopy (FIM) and Field Electron Microscopy (FEM) ................... 2-21 Transmission Electron Microscopy (TEM) ........................................... 2-22 Low Energy Electron Microscopy (LEEM) ........................................... 2-22 Photoemission Electron Microscopy (PEEM) ........................................ 2-22 Miscellaneous ....................................................................... 2-23 Scanning Tunneling Microscopy (STM) ............................................. 2-23 Atomic Force Microscopy (AFM) ................................................... 2-24
2.7 2.7.1 2.7.2 2.7.3 2.7.4 2.8 2.8.1 2.8.2 2.8.3 2.8.4 2.9 2.9.1 2.9.2 2.10 2.10.1 3 3.1 3.1.1 3.1.2 3.2 3.2.1 3.2.2 3.3 3.3.1 3.3.2 3.4 3.4.1 3.4.2 3.4.3 3.4.4 3.5 3.6 3.7 3.7.1 3.7.2 3.7.3 3.7.4 3.8 3.8.1 3.8.2 3.8.3 3.8.4 3.8.5 3.8.6
Vibrational spectroscopy of adsorbed particles ....................................... 2-25 Electron Energy Loss Spectroscopy (EELS) .......................................... 2-26 Infrared Reflection-absorption spectroscopy (IRAS) .................................. 2-26 Surface Enhanced Raman Spectroscopy (SERS) ...................................... 2-27 Inelastic scattering of He-atoms ...................................................... 2-27 Techniques probing the electronic structure .......................................... 2-28 Ultraviolet Photoelectron Spectroscopy (UPS) ....................................... 2-28 Inverse photoemission (IPE) ......................................................... 2-29 Near Edge X-ray Absorption Fine-Structure Spectroscopy (NEXAFS) ................ 2-30 Resonant X-ray Emission Spectroscopy (XES) ....................................... 2-31 Nonlinear optical techniques ......................................................... 2-32 Second Harmonic Generation (SHG)................................................. 2-32 Sum Frequency Generation (SFG) ................................................... 2-33 Bulk techniques ..................................................................... 2-33 Nuclear Magnetic Resonance (NMR) and Electron Spin Resonance (ESR) ............ 2-33 References .......................................................................... 2-35 Data: Adsorbate properties ....................................... see subvolume III/42A1 Adsorption of noble gases ........................................ see subvolume III/42A1 Noble gases on metals and semiconductors (P. ZEPPENFELD) ....... see subvolume III/42A1 Noble gases on graphite, lamellar halides, MgO and NaCl (M. BIENFAIT) .................................................... see subvolume III/42A1 Adsorption of alkali metals ....................................... see subvolume III/42A1 Alkali metals on metals (R.D. DIEHL, R. McGRATH) ............... see subvolume III/42A1 Alkali metals on semiconductors (E.G. MICHEL, R. MIRANDA) ..... see subvolume III/42A1 Adsorption of metals ............................................. see subvolume III/42A1 Metals on metals (H. BRUNE) ..................................... see subvolume III/42A1 Metals on semiconductors (V.G. LIFSHITS, K.OURA, A.A. SARANIN, A.V. ZOTOV) ............ see subvolume III/42A1 Non-metallic atomic adsorbates on metals and semiconductors .... see subvolume III/42A3 Chemisorbed hydrogen on metals and semiconductors (K. CHRISTMANN) ............................................... see subvolume III/42A3 C, N, O on metals and semiconductors (H. OVER) ................ see subvolume III/42A3 Halogens on metals and semiconductors (E.I. ALTMAN) .......... see subvolume III/42A1 P, S, As, Sb on metals and semiconductors (M. ENACHESCU, M. SALMERON) ................................. see subvolume III/42A3 Surface segregation of atomic species (non-metal on metal) (H.-J. GRABKE, CH. UEBING, H. VIEFHAUS) ....................... see subvolume III/42A3 Molecules on graphite, BN, MgO (except noble gases) (H. WIECHERT, J. SUZANNE) ...................................... see subvolume III/42A3 Molecular diatomic adsorbates on metals and semiconductors...... see subvolume III/42A3 CO and N2 on metals (A. FÖHLISCH, A. NILSSON, H.P. BONZEL) ... see subvolume III/42A3 NO, CN, O2 on metals (W.A. BROWN) ........................... see subvolume III/42A3 Diatomic molecules on alloys (B. E. NIEUWENHUYS) .............. see subvolume III/42A3 Diatomic molecules on semiconductors (K. HORN) ................ see subvolume III/42A3 Molecular polyatomic adsorbates on metals and semiconductors ... see subvolume III/42A3 H2O and OH on metals (G. PIRUG) ............................... see subvolume III/42A3 H2O and OH on semiconductors (W. JAEGERMANN, T. MAYER) ... see subvolume III/42A3 NH3 and PF3 on metals and semiconductors (E. HASSELBRINK) .... see subvolume III/42A3 CO2, NO2, SO2, OCS, N2O, O3 (B.E. KOEL) ...................... see subvolume III/42A3 Substituted hydrocarbons on metals (W.T. TYSOE, D.R. MULLINS) see subvolume III/42A3 Linear hydrocarbons and CH4 on metals and semiconductors (G. SOMORJAI, G. RUPPRECHTER) ................................. see subvolume III/42A3
3.8.7 3.8.8 3.8.9 3.8.10 3.8.11 3.9 3.10 3.11 3.12 4 4.1 4.1.1 4.1.2 4.1.3 4.1.4 4.1.5 4.1.6 4.1.7 4.1.8 4.1.9 4.1.10 4.1.11 4.1.12 4.1.13 4.1.14 4.1.15 4.1.16 4.1.17 4.1.18 4.1.18 4.1.19 4.1.20 4.1.21
Cyclic hydrocarbons on metals and semiconductors (G. HELD, H.P. STEINRÜCK) ...................................... see subvolume III/42A3 Oxygenated hydrocarbons on metals and semiconductors (J. VOHS) . see subvolume III/42A3 Halogen-substituted hydrocarbons on metals and semiconductors (J. FIEBERG, J.W. WHITE) ........................................ see subvolume III/42A3 Polyatomic chain-like hydrocarbons on metals and semiconductors (M. GRUNZE) .................................................... see subvolume III/42A3 Large aromatic adsorbates on metals and semiconductors (M. SOKOLOWSKI, E. UMBACH) .................................. see subvolume III/42A3 Adsorption on oxides (H. KUHLENBECK, H.J. FREUND) ............ see subvolume III/42A3 Adsorption on alkali halides (J. HEIDBERG) ....................... see subvolume III/42A3 Surface diffusion on metals, semiconductors, and insulators (E.G. SEEBAUER, M.Y.L. JUNG) .................................. see subvolume III/42A1 Dynamics of activated adsorption (A.C. LUNTZ) .................. see subvolume III/42A3 Data: Adsorbate-induced changes of substrate properties ............................ 4.1-1 Surface structure on metals and semiconductors (M.A. VAN HOVE, K. HERMANN, P.R. WATSON) ................................... 4.1-1 Introduction................................................. 4.1-1 Relaxation vs. reconstruction ....................................................... 4.1-1 Notations and conventions .......................................................... 4.1-3 Organization of the tables .......................................................... 4.1-4 Organization of data for individual structures ........................................ 4.1-4 Adsorption on fcc(111) ............................................................. 4.1-6 Adsorption on hcp(0001) ........................................................... 4.1-6 Adsorption on bcc(110) ........................................................... 4.1-7 Adsorption on fcc (100) ............................................................ 4.1-7 Adsorption on bcc (100), pure or alloyed ............................................ 4.1-8 Adsorption on fcc (110) ............................................................ 4.1-8 Adsorption on hcp ( 10 1 0 ) ......................................................... 4.1-9 Adsorption on bcc (211) ............................................................ 4.1-9 Adsorption on bcc (111) ............................................................ 4.1-9 Adsorption on Si, Ge and C(111) ................................................... 4.1-9 Adsorption on Si and Ge(100) ..................................................... 4.1-10 Adsorption on diamond-like(311) .................................................. 4.1-10 Adsorption on zincblende(110) .................................................... 4.1-10 Adsorption on zincblende(110) .................................................... 4.1-10 Adsorption on zincblende(111) and (-1-1-1) ........................................ 4.1-11 Adsorption on zincblende(100) .................................................... 4.1-11 Adsorption on 6H-SiC(0001) ...................................................... 4.1-11 Acknowledgments ................................................................. 4.1-11 Tables ............................................................................ 4.1-12 Table 1. Techniques used for surface structure determination; listed by their acronyms ........ 4.1-12 Table 2. Structures of clean fcc(111) surfaces............................................ 4.1-14 Table 3. Adsorbate-induced structures on fcc(111) surfaces ............................... 4.1-15 Table 4. Structures of clean hcp(0001) surfaces ......................................... 4.1-31 Table 5. Adsorbate-induced structures on hcp(0001) surfaces. ............................. 4.1-31 Table 6. Structures of clean bcc(110) surfaces........................................... 4.1-43 Table 7. Adsorbate-induced structures on bcc(110) surfaces............................... 4.1-44 Table 8. Structures of clean fcc(100) surfaces ........................................... 4.1-45 Table 9. Adsorbate-induced structures on fcc(100) surfaces ............................... 4.1-47 Table 10. Structures of clean bcc(100) surfaces.......................................... 4.1-57
4.2 4.2.1 4.2.1.1 4.2.1.2 4.2.1.3 4.2.1.4 4.2.1.5 4.2.1.5.1 4.2.1.5.2 4.2.1.5.3 4.2.1.5.4 4.2.1.5.5 4.2.1.5.6 4.2.1.6 4.2.2 4.2.3 4.2.3.1 4.2.3.2 4.2.3.3 4.2.3.4 4.2.3.5 4.2.3.6 4.2.3.7
Table 11. Adsorbate-induced structures on bcc(100) surfaces.............................. 4.1-58 Table 12. Structures of clean alloyed bcc(100) surfaces ................................... 4.1-62 Table 13. Adsorbate-induced structures on alloyed bcc(100) surfaces....................... 4.1-63 Table 14. Structures of clean fcc(110) surfaces .......................................... 4.1-64 Table 15. Adsorbate-induced structures on fcc(110) surfaces .............................. 4.1-67 Table 16. Structures of clean hcp(10-10) surfaces........................................ 4.1-75 Table 17. Adsorbate-induced structures on hcp(10-10) surfaces............................ 4.1-76 Table 18. Structures of clean bcc(211) surfaces.......................................... 4.1-77 Table 19. Adsorbate-induced structures on bcc(211) surfaces.............................. 4.1-78 Table 20. Structures of clean bcc(111) surfaces.......................................... 4.1-79 Table 21. Adsorbate-induced structures on bcc(111) surfaces. ............................. 4.1-79 Table 22. Structures of clean Si; Ge and C(111) surfaces ................................. 4.1-80 Table 23. Adsorbate-induced structures on Si; Ge and C (111) surfaces ..................... 4.1-80 Table 24. Structures of clean Si and Ge (100) surfaces.................................... 4.1-86 Table 25. Adsorbate-induced structures on Si and Ge (100) surfaces........................ 4.1-87 Table 26. Structures of clean Si(311) surfaces ........................................... 4.1-91 Table 27. Adsorbate-induced structures on Si(311) surfaces ............................... 4.1-91 Table 28. Structures of clean zincblende(110) surfaces ................................... 4.1-92 Table 29. Adsorbate-induced structures on zincblende(110) surfaces ....................... 4.1-93 Table 30. Structures of clean zincblende(111) surfaces ................................... 4.1-95 Table 31. Adsorbate-induced structures on zincblende(111) surfaces ....................... 4.1-96 Table 32. Structures of clean zincblende(-1-1-1) surfaces ................................. 4.1-96 Table 33. Adsorbate-induced structures on zincblende(-1-1-1) surfaces ..................... 4.1-96 Table 34. Structures of clean zincblende(100) surfaces ................................... 4.1-97 Table 35. Adsorbate-induced structures on zincblende(100) surfaces ....................... 4.1-97 Table 36. Structures of clean 6H-SiC(0001) surfaces ..................................... 4.1-98 Table 37. Adsorbate-induced structures on 6H-SiC(0001) surfaces ......................... 4.1-98 Figures for 4.1 .................................................................... 4.1-99 References for 4.1 ................................................................ 4.1-109 Electron work function of metals and semiconductors (K. JAKOBI) ................... 4.2-1 Introduction ........................................................................ 4.2-1 List of abbreviations................................................................ 4.2-1 Definition of work function ......................................................... 4.2-1 Work function versus local potential ................................................ 4.2-2 Standardization of work-function change with coverage ............................. 4.2-3 Experimental methods .............................................................. 4.2-4 Thermionic emission (Therm) ..................................................... 4.2-4 Field electron emission (FEM) ..................................................... 4.2-4 Photoemission (PYS, ARUPS) ..................................................... 4.2-5 Secondary electron edge method (SE edge) ........................................ 4.2-6 Diode method (Diode) ............................................................. 4.2-6 Vibrating capacitor method (Kelvin) ............................................... 4.2-6 Data collection ..................................................................... 4.2-7 Rare gases ......................................................................... 4.2-7 Ne, Ar, Kr, Xe Atomically chemisorbed adsorbates ................................................ 4.2-13 Hydrogen, Deuterium ............................................................. 4.2-13 Carbon and C60.................................................................... 4.2-18 Nitrogen .......................................................................... 4.2-19 Oxygen ........................................................................... 4.2-20 Sulfur ............................................................................. 4.2-29 Selenium.......................................................................... 4.2-31 Tellurium ......................................................................... 4.2-31
4.2.3.8 4.2.3.9 4.2.3.10 4.2.4 4.2.4.1 4.2.4.2 4.2.4.3 4.2.4.4. 4.2.4.5 4.2.4.6 4.2.4.7 4.2.4.8 4.2.4.9 4.2.4.10 4.2.4.11 4.2.4.12 4.2.5
4.2.6
4.2.7
4.2.8
4.2.9 4.2.10 4.2.11 4.2.12 4.2.13 4.2.14 4.2.15
Chlorine .......................................................................... 4.2-32 Bromine .......................................................................... 4.2-34 Iodine ............................................................................ 4.2-35 Small molecules ................................................................... 4.2-35 H2 ................................................................................ 4.2-35 N2 ................................................................................ 4.2-36 O2 ................................................................................ 4.2-37 CO ............................................................................... 4.2-37 NO, N2O .......................................................................... 4.2-42 NH3, PH3, PF3, P(CH3)3, AsH3 ..................................................... 4.2-44 H2O, D2O ......................................................................... 4.2-46 H2S ............................................................................... 4.2-48 CO2, SO2, (CH3)2SO, (CH3)3PO3 ................................................... 4.2-48 C2N2, HCN ....................................................................... 4.2-49 CH3CN, HCOOH, HNCO ......................................................... 4.2-50 KOH, KCl, HCl, HBr ............................................................. 4.2-50 Nonpolar hydrocarbons............................................................ 4.2-51 Methane (CH4), Propane (C3H8), Ethylene (C2H4), Acetylene (C2H2), Propylene (CH3CH:CH2), Cyclopentane (C5H10), Pentadiene (C5H8), n-hexane (C6H14), Cyclohexane (C6H12), Cyclohexene (C6H10), 1,3-Cyclohexadiene (C6H8), Benzene (C6H6, C6D6), Toluene (C6H5-CH3), Ethylbenzene (C6H5C2H5), n-butylbenzene (C6H5C4H9), t-butylbenzen (C6H5C(CH3)3), m-xylene (C6H4(CH3)2), Biphenyle (C6H5C6H5), Naphtalene (C10H8), 2-Methylnaphtalene (C10H7CH3) Polar hydrocarbons ................................................................ 4.2-58 Methanol (CH3OH), Ethyleneoxide (C2H4O), Ethylenedioxide ((CH2)4O2), Acetone (C3H6O), Furan (C4H4O), Benzenethiol (C6H5SH), Pyridine (C6H5N), Aniline (C6H5NH2), Nitrobenzene (C6H5NO2), Cyanobenzene (C6H5CN) Halohydrocarbons ................................................................. 4.2-60 Chloro-methane (ClCH3), Chloro-ethane (ClC2H5), Di-chloro-methane (Cl2CH2), Tri-chloro-methane (Cl3CH), Tetra-chloro-methane (Cl4C), Bromo-methane (BrCH3), Di-bromo-methane (Br2CH2), Tetra-bromo-methane (Br4C), Iodo-methane (ICH3), Iodo-ethane (IC2H5), Chloro-tri-fluoro-methane (ClCF3), 1,2-di-chloro-ethane (ClCH2CH2Cl), 1,2-di-chloro-ethene (ClCH:CHCl), 1,2-chloro-bromo-ethane (ClCH2CH2Br), Iodo-benzene (IC6H5), Chloro-benzene (ClC6H5) Other hydrocarbons ............................................................... 4.2-62 Di-ethyl-zink ((C2H5)2Zn), glycine (α-amino acetic acid) (H2NCH2CO2H), Closo-1,2-di-carbado-decaborane (C2B10H12), TCNQ (Tetra-cyano-quino-dimethane) (C12N4H4) Alkali metals ...................................................................... 4.2-63 Li, Na, K, Rb, Cs Noble metals ...................................................................... 4.2-76 Cu, Ag, Au 3d transition metals................................................................ 4.2-83 Ti, V, Cr, Fe, Co, Ni 4d transition metals................................................................ 4.2-86 Zr, Nb, Mo, Rh, Pd 5d transition metals................................................................ 4.2-89 La, Hf, Ta, W, Re, Os, Ir, Pt Rare-earth metals.................................................................. 4.2-91 Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb Group IIa metals .................................................................. 4.2-93 Be, Sr, Ba
4.2.16 4.2.17 4.2.18 4.2.19
4.3 4.4 4.4.1 4.4.2 4.4.2.1 4.4.2.2 4.4.2.3 4.4.2.4 4.4.2.5 4.4.3 4.4.3.1 4.4.3.2 4.4.3.3 4.4.4 4.4.5 4.4.5.1 4.4.5.2 4.4.5.3 4.4.5.4 4.4.5.5 4.4.5.6 4.4.6 4.4.7 4.4.7.1 4.4.7.2 4.4.7.3 4.4.7.3.1 4.4.7.4 4.4.7.5 4.4.7.6 4.4.7.7 4.4.7.8 4.4.7.9 4.4.7.10 4.4.7.11 4.4.8 4.4.9 4.4.9.1 4.4.9.2 4.4.9.3
Group IIIa metals ................................................................. 4.2-95 Al, Ga, Group IVa elements ............................................................... 4.2-96 C, Si, Ge, Sn, Pb Group Va elements ................................................................ 4.2-98 N, P, As, Sb, Bi Other elements .................................................................... 4.2-99 Hg, U Figures for 4.2 ................................................................... 4.2-100 References for 4.2 ................................................................ 4.2-118 Electron binding energy of metals and semiconductors (R. DENECKE, N. MARTENSSON, A. NILSSON) ..................... see subvolume III/42A3 Surface free energy and surface stress (D. SANDER, H. IBACH) ....................... 4.4 -1 Introduction ........................................................................ 4.4 -1 Experimental determination of surface free energy................................... 4.4 -2 Cleavage experiments .............................................................. 4.4 -3 Pendant drop and drop weight method .............................................. 4.4 -4 Zero creep experiments ............................................................. 4.4 -5 Orientation dependence of the surface free energy ................................... 4.4 -6 Empirical relation between surface free energy and other quantities .................. 4.4 -8 Experimental determination of the absolute value of the surface stress ................ 4.4 -8 Lattice parameter of small particles ................................................. 4.4 -8 Surface phonons as indicator of surface stress ....................................... 4.4 -9 Absolute surface stress from the bending of thin crystal plates ....................... 4.4 -9 Experimental determination of changes of surface stress due to adsorption .......... 4.4 -10 Calculations of surface free energy and surface stress ............................... 4.4 -13 Inert gas crystals .................................................................. 4.4 -14 Ionic crystals ...................................................................... 4.4 -14 III-V compounds .................................................................. 4.4 -15 Group IV materials ................................................................ 4.4 -15 Metals ............................................................................ 4.4 -16 Calculated adsorbate-induced surface stress ........................................ 4.4 -16 Data .............................................................................. 4.4 -18 Clean surfaces .................................................................... 4.4 -19 Surface free energy from cleavage experiments ..................................... 4.4 -19 Surface free energy of metals near the melting point ................................ 4.4 -19 Temperature dependence of the surface free energy................................. 4.4 -21 Temperature dependence of the anisotropy of the surface free energy ............... 4.4 -22 Calculated surface free energy and surface stress for inert gas crystals ............... 4.4 -22 Calculated surface free energies and surface stress for alkali halides ................. 4.4 -23 Calculated surface free energy and surface stress of III-V compounds ............... 4.4 -23 Calculated surface free energy and surface stress for Si and Ge ..................... 4.4 -24 Calculated adsorbate-induced changes of stress on semiconductor surfaces .......... 4.4 -25 Calculated surface free energies of metals .......................................... 4.4 -26 Calculated surface stress ........................................................... 4.4 -32 Calculated adsorbate induced surface stress on Pt(111) ............................ 4.4 -34 Adsorbate-induced changes of surface free energy .................................. 4.4 -34 Adsorbate-induced changes of surface stress ....................................... 4.4 -36 Gas adsorption .................................................................... 4.4 -36 Alkali metal deposition ............................................................ 4.4 -40 Semiconductor and metal deposition ............................................... 4.4 -40 References for 4.4 ................................................................. 4.4 -44
4.5 4.5.1 4.5.1.1 4.5.1.2 4.5.1.3 4.5.1.4 4.5.1.4.1 4.5.1.4.2 4.5.1.5 4.5.1.6 4.5.2 4.5.2.1 4.5.2.2 4.5.2.3 4.5.2.4 4.5.2.5
4.6
Surface phonon dispersion (M.A. ROCCA) ........................................... 4.5-1 Introduction ........................................................................ 4.5-1 Background and general layout ..................................................... 4.5-1 Symmetry considerations, energy and momentum conservation and relevant selection rules in inelastic scattering ........................................ 4.5-3 Folding of the surface Brillouin zone by symmetry reduction, mode mixing, phonon crossing and opening of energy gaps ........................................ 4.5-3 Phonon anomalies .................................................................. 4.5-4 Effect of mass loading, modification of force constants and surface stress ............ 4.5-4 Kohn anomaly ..................................................................... 4.5-5 Dispersion of adsorbate induced modes ............................................. 4.5-6 Theoretical models ................................................................. 4.5-7 Data collection ..................................................................... 4.5-7 Correspondence of units ............................................................ 4.5-9 Metal surfaces ..................................................................... 4.5-9 Ag, Al, Cu, Mo, Ni, Pb, Pt, Rh, Ru, W Elemental semiconductors and insulators ........................................... 4.5-20 C, Ge, Si Compound semiconductors ........................................................ 4.5-22 GaAs, GaP, InAs, InP Oxides and Salts .................................................................. 4.5-23 MgO, NaCl Acknowledgements................................................................ 4.5-24 Figures for 4.5 .................................................................... 4.5-25 References for 5.4 ................................................................. 4.5-68 Surface optical properties (N. ESSER, W. RICHTER) ................ see subvolume III/42A3
2 Measuring techniques CH. WÖLL
2.1 Introduction Whereas the observation of molecular adsorption on a solid surface can be monitored by the naked eye (corrosion of e.g. iron surfaces, formation of patina on copper,...), more detailed investigations require the availability of rather sophisticated equipment. The diffraction of electrons represents the first method of its kind to portray the structure of single crystalline solid surfaces [27DAVa; 27DAVb]. Even in the first studies the adsorption of gases on the specimen has been noted and found to cause „anomalous“ beams [27DAVb], very likely the first observation of an ordered molecular adlayer on a solid substrate. Today electron diffraction prevails as the standard technique to characterize adsorbate covered surfaces of wellordered solids. As a result of the comparatively simple technical requirements this technique enjoys widespread distribution and tremendous success in the determination of structures and relaxation-effects on clean surfaces as well as in the investigation of adsorbate overlayers. The immense body of knowledge present today about the application of this technique is the source not only for ongoing research in surface science but also for the development of related techniques, e.g. the different versions of photoelectron diffraction. The diffraction of electrons is complemented by the oldest technique for structure determination of bulk matter, the diffraction of X-rays. Due to the very small (typ. 1015 part/cm2) scattering cross section of a monolayer this technique is not suitable for the determination of adsorbate structures on solid substrate surfaces in a straightforward fashion, which also holds true for neutron scattering, another standard technique in bulk structure determination. Despite the tremendous success of electrons in surface science studies other probe particles also generate diffraction patterns from surfaces. The application of neutral atoms and molecules with thermal energies for surface diffraction studies [30EST] had been preceded by electron scattering by only a few years. Although this method has been applied in numerous investigations, it has not developed into a widespread technique, mostly because of the considerable experimental efforts required to generate and detect molecular (and atomic) beams. Atoms at higher than thermal energies exhibit de Broglie wavelengths significantly smaller than the lattice-spacing of solids and can therefore not be used for diffraction studies. By going to even higher energies, however, the wavelength becomes so small that the motion of the particles can be treated classically. Subsequently, the scattering of low, medium and high energy ions has been used together with a classical trajectory analysis in a large number of works to investigate the structure of surfaces, clean and adsorbate-covered. In the following the different probe techniques suitable for structural analysis of adsorbed layers on surfaces will be briefly discussed. We will begin with the conceptually most simple and direct methods, which are principally also suited for designing sensor devices. We will proceed with slightly more complicated yet still straightforward techniques based on a mass spectrometer and then continue with diffraction and other structural sensitive techniques which make full use of the advanced technology available today. Subsequently, methods sensitive to adsorbate vibration and electronic structure will be presented. Together with a brief description of the respective technique, the major limitations will be briefly mentioned. The description of the rather large set of measuring techniques starts with a list of acronyms for the different methods and a table, which classifies the techniques according to a number of different criteria. The table should be used, however, only as a rough guide, a more detailed discussion of the respective merits and limitations will be provided in the related paragraphs.
Landolt -Börnst ein New Series III/42A2
2-2
2 Measuring techniques
[Ref. p. 2-35
2.1.1 Comparative information on techniques discussed in this chapter For the list of acronyms used in this chapter, see page 2-4 Elemental Chemical state LEED HREELS HAS SEM,TEM ISS TPD SIMS SHG SFG XPS AES UPS NEXAFS XES STM
(+) + + + + (no H) + (no H) + (no H) + (no H) -
+ (+) (+) + (+) (+) (+) ++ ++ (+)
AFM IRAS EXAFS LITD PED XSW XRD SERS IPE FIM FEM Φ, ∆Φ
(+) + (+) (+) (+)
+ (+) (+) (+) (+) (+)
-
-
Binding energy (1) ind. ind. ind. ind. +
ind.
ind.
Structural order, coh.length + + + +
Geometric structure (ordered) + (+) + + (+) (+) (+) (+) XPD (+) (+) (+) (+) +
+ -
-
+ -
+ (+) + + + + (+) -
-
-
(+) -
(ind.) ind.
Resol. [Å] 0.01
orient. 0.01 vert 0.2 hor orient. 0.01 0.01 0.01 0.01
Geometric structure (disordered) (+) (+) (+) + (+) XPD (+) (+) (+) (+) (+) + (+) + -
Resol. [Å] 0.05
orient.
orient.
(+)
Lando lt -Bö rnst ein New Series III/42A2
Ref. p. 2-35]
2 Measuring techniques
Phase Electronic Intertransitions structure pretation (valence) (2) LEED + + HREELS ++ HAS + + SEM,TEM (+) ISS (+) TPD + SIMS + SHG (+) SFG XPS (+) + AES UPS ++ + NEXAFS (+) + XES ++ + STM (+) (+) + AFM IRAS EXAFS LITD PED XSW XRD SERS IPE FIM FEM Φ, ∆Φ
(+)
(+)
(+)
Vibrations
Diffusion
++ + (FIR) (3) + (+) + (+) (+) (+)
2-3
Destructive
Synchrotron required
yes yes yes yes yes -
+
+ ++ + (+) + + + + +
++ + -
+ -
yes varies varies
-
-
-
-
-
yes yes
yes
yes helpful
-
(1) Basically all methods can be used to roughly determine the binding energy by determining the temperature where the molecule is desorbed from the surface.“ind“ is entered when the method is frequently applied for this purpose. (2) Many techniques require significant theoretical and computational effort to obtain the desired information. In this column ++ indicates that this effort is small, whereas – indicates that significant effort is required. (3) Mainly applied to vibrations in the Far-Infrared regime (< 200 cm-1 or < 25 meV)
Landolt -Börnst ein New Series III/42A2
2-4
2 Measuring techniques
[Ref. p. 2-35
2.1.2 List of acronyms used in this chapter AES AFM DLEED EXAFS HAS HREELS IPE IRAS ISS LEED LEEM LEIS LITD MEIS NEXAFS PEEM PED QCM QMS RBS SEM SERS SFG SHG SIMS STM TEM TDS TPD UPS XANES XES XPS XRD XSW Φ
Auger Electron Spectroscopy Atomic Force Spectroscopy Diffuse Low Energy Electron Diffraction Extended X-ray Absorption Fine Structure He-Atom Scattering High-Resolution Electron Energy-Loss Spectroscopy Inverse Photoemission Infrared Reflection Absorption Spectroscopy Ion Scattering Spectroscopy Low Energy Electron Diffraction Low Energy Electron Microscopy Low Energy Ion Scattering Laser-Induced Thermal Desorption Medium Energy Ion Scattering Near Edge X-ray Absorption Fine Structure Photoelectron Electron Microscopy Photoelectron Diffraction Quartz Crystal Microbalance Quadrupole Mass Spectrometer Rutherford Backscattering Scanning Electron Microscopy Surface Enhanced Raman Spectroscopy Sum Frequency Generation Second Harmonic Generation Secondary Ion Mass Spectrometry Scanning Tunneling Microscopy Transmission Electron Microscopy Thermal Desorption Spectroscopy Temperature Programmed Desorption Ultraviolet Photoelectron Spectroscopy X-ray Absorption Near Edge Structure, see NEXAFS X-ray Electron Spectroscopy X-ray Photoelectron Spectroscopy X-ray Diffraction X-ray Standing Wave Work Function
2.2 Direct methods The adsorption of a molecule on a surface, as schematically illustrated in Fig. 1, leads to changes of a number of different quantities and properties. The main problem in surface science is that these changes are restricted to the top substrate layer and are thus very small in relation to any changes of the bulk. As a result, rather complicated surface sensitive techniques have been developed in the past decades to gain information on the adsorption process and the nature of the substrate-adsorbate complex. Very often these Lando lt -Bö rnst ein New Series III/42A2
Ref. p. 2-35]
2 Measuring techniques
2-5
methods are rather indirect, and a significant computational effort is required to obtain e.g. precise information on adsorbate geometries from the experimental data. There are, however, a few general methods where the required information can be obtained in a rather direct way. Correspondingly, these techniques are in principle suited for applications as sensors. In the following we will briefly list the most important of these conceptually very simple methods before proceeding with the methods which have been designed for surface studies.
Fig. 1. Adsorption of a molecule on a solid substrate. In the case shown in the figure the process is called associative, since the molecule is not dissociated upon adsorption.
2.2.1 Monitoring adsorption by calorimetry One of the most direct ways to follow an adsorption process and to quantitatively determine the excess energy is by detection of the corresponding rise in substrate temperature. Although substrates with thicknesses in the mm range have heat capacities which are far too large, the preparation of very thin films makes such measurements possible. In the case of polycrystalline films evaporated onto thin glass substrates direct measurements of heats of adsorption have been reported for a number of different adsorbate/substrate combinations [78WED]. For single crystalline films, however, the task is considerably more difficult, since the growth of very thin films with high structural quality poses a huge experimental challenge. These problems, however, have in recent years been overcome and it was possible to apply the method e.g. to the case of oxygen on Ni(100), where temperature rises originating from the adsorption of amounts as small as 0.01 monolayers could be detected [91BOR]. Although this method is very elegant, the severe technological limitations restrict its application to but a few cases. Recently, a novel approach has been demonstrated for detecting the small temperature changes accompanying the adsorption of gases on metal surfaces. In a pioneering investigation the heat evolution in the adsorption and subsequent reaction of O2 and H2 to form water on a thin Pt-layer evaporated on a SFM bimetallic cantilever has been studied [94GIM].
2.2.2 Quartz crystal microbalance Another physical quantity which can in principle be used to detect adsorption is the corresponding increase in weight. The detection of such mass-changes via a precise measurement of the resonance frequency of a quartz crystal is a standard technique to monitor the deposition of metal films. The method is, however, only rarely applied to the investigation of adsorbates because of experimental problems and the difficulty to grow well-defined films on quartz substrates. Recently, however, a quartz crystal microbalance (QCM) has been used to monitor the adsorption of noble gases and simple hydrocarbons on surfaces of Ag-films [90KRI; 96DAL].
2.2.3 Chemiluminescence In principle the adsorption process can be viewed as a chemical reaction and several phenomena accompanying reactions in the gas-phase or the liquid also occur for surface reactions. One of these is Lando lt -Bö rnst ein New Series III/42A2
2-6
2 Measuring techniques
[Ref. p. 2-35
chemiluminescence, where electronically excited product molecules decay to their ground state by emission of photons. Of course this process requires that the adsorption energy is sufficiently large and that non-radiative processes do not come into play. Due to the fairly small number of surface reaction sites considerable experimental effort is required for detection. Nevertheless, chemiluminescence accompanying adsorption has been observed in a few cases, e.g. for the adsorption of chlorine on Ksurfaces [85AND].
2.2.4 Exoelectrons A very convenient way to follow adsorption is the detection of electrons generated during the adsorption process. Since the reaction with the surface must be sufficiently energetic for the emitted electrons being able to overcome the substrate work-function, the phenomenon has been observed only in a few cases, e.g. during the oxidation of Cs- and Na-surfaces [94GRO],[92BOE].
2.2.5 Adsorption-induced changes of surface stress The creation of a surface can give rise to significant mechanical stress, which can be related to the difference in chemical environment for surface atoms and bulk atoms. Generally, adsorption of particles is expected to change this stress. Since the absolute forces related to this phenomenon are rather small, significant experimental effort is required to detect the adsorption-induced changes in surface stress. Such measurements are, however, feasible and results have been reported for polycrystalline films evaporated onto specially designed cantilevers [86ABE]. Recently, it has been possible to extend these measurements to single crystalline substrates, including the oxidation of silicon [91SAN] and molecular adsorbates on Ni(100) [94GRO].
2.2.6 Adsorption-induced changes in resistivity One of the oldest and experimentally most straightforward ways to detect adsorption on metals – even for weak adsorbate-substrate interaction as in the case of N2-molecules adsorbed on Cu - is the measurement of the conductivity of thin metal films [72WIS; 87WIS]. Attaining a detailed understanding of the basic microscopic mechanism causing this effect has been hampered by the fact that the thin films used for these experiments generally exhibit rather poor structural quality. Recently, it has been shown theoretically, that the change in dc-resistivity upon molecular adsorption is related to the reduction of electron-hole lifetime in the top layers of the substrate through excitations of frustrated translations of the adsorbed molecules [91PER; 94PER].
2.2.7 Reflectance ellipsometry Adsorption of atomic or molecular species affects the electronic structure of the substrate and, as a consequence, the reflectivity (or color) of the surface. Although these changes are typically very small, independent measurements of the reflectivity for differently polarized light (s vs. p) and the phase delay between the two polarizations allow to monitor e.g. the adsorption of noble gas adlayers on graphite with submonolayer sensitivity [93YOU]. Recently, it has been demonstrated that the method can be combined with an optical microscope to image in-situ the patterns formed in surface reactions using visible light [95ROT; 96HAA].
Lando lt -Bö rnst ein New Series III/42A2
Ref. p. 2-35]
2 Measuring techniques
2-7
2.2.8 Change of work function In case of conducting samples adsorption events are typically accompanied by a change of the workfunction, Φ, i.e. the minimum energy required to remove an electron from the probe. The microscopic origin of this behavior is related to the formation of a dipole-adlayer, which is particularly strong if the molecule carries a significant dipole moment (e.g. in the case of the cyclic ether trioxane, C3H6O3, [94HOF]). But also in case of physisorbed noble gas atoms, e.g. Xe, noticeable changes in workfunction, ∆Φ, can be observed [87JAC]. A variety of methods has been used to detect these changes, some of which are conceptually rather simple and can be used also for sensor applications (e.g. vibrating capacitor method). Several methods for detecting work function changes are based on equipment primarily used for other methods (e.g. UPS). Since work-function changes are rather important for both monitoring the adsorption of adparticles and the understanding of adsorption–induced changes in electronic structure, chapter 4.2 is devoted to this topic.
2.3 Techniques based on a mass spectrometer 2.3.1 Determination of sticking coefficients using a molecular beam
molecular beam
F1 F2 open open
F2 to QMS sample
to pump
Pressure
flag F1
Time
Fig. 2. Schematics for determining the sticking coefficient using the King and Wells method [72KIN]. The diagram on the right hand shows the mass spectrometer (QMS) signal after first opening flag F1 and then flag F2.
An important question concerning a particular adsorbate/substrate combination is whether for a given substrate temperature the particle or molecule sticks to the surface, and what the sticking probability amounts to. The conceptionally most simple method to answer this questions is the so-called King and Wells method [72KIN] as illustrated in Fig. 2. A molecular beam containing either the pure substance or a mixture with an inert (e.g. He, Ar) carrier gas impinges on the substrate and the pressure in the recipient is measured using either a mass-insensitive pressure gauge (e.g. an ionization gauge) or a mass spectrometer. The experiment starts by determining the pressure inside the chamber containing the clean substrate with the molecular beam of the corresponding particle (e.g. CO) blocked by a flag (F2) with a chemically inert surface. After opening the flag the pressure drops due to adsorption on the sample surface. The pressure is recorded until saturation sets in. If the particle or molecule sticks to the surface with unity sticking coefficient, the pressure inside the chamber will initially drop to zero, since all incident particles are trapped by adsorption to the surface. If the number of free surface sites is reduced, particles are scattered back into the vacuum chamber, giving rise to an increase of the pressure. Measurements of this kind give rise to detailed information of the absolute value of the sticking coefficient and its dependence on coverage, defects and coadsorbates. Although the method requires substantial technical effort, preparation
Landolt -Börnst ein New Series III/42A2
2-8
2 Measuring techniques
[Ref. p. 2-35
of a well collimated molecular beam, it can be used to measure sticking probabilities on virtually all types of substrates. Structural order is not a prerequisite, and the method can be applied to metals and semiconductors as well as to insulators. For very small (<< 0.05) sticking coefficients the method becomes difficult to apply due to the long measuring times and the corresponding small changes in pressure. The method only monitors the adsorption on a surface, a combination with a more elaborate technique is required to find out whether adsorbates stick at the point where they first hit the surfaces or whether they are sufficiently mobile to diffuse to defect sites [00BEC].
2.3.2 Thermal Desorption Spectroscopy (TDS)
Fig. 3. Schematic illustration of a second order desorption process in thermal desorption spectroscopy, TDS. Upon heating the adsorbed atoms form molecules before they desorb from the surface and are detected in a mass spectrometer (MS).
One of the key issues when investigating adsorbate overlayers on solid substrates is the question whether the adsorption of a particle (atom, molecule) is reversible (i.e. whether the intact particle can be desorbed from the surface by e.g. heating) or whether the interaction between adparticle and substrate is so strong that adsorption is accompanied by fragmentation. Together with qualitative information on this behavior also quantitative information on binding energies and desorption kinetics is needed. The most powerful technique to answer this type of basic question is thermal desorption spectroscopy (TDS), frequently also referred to as temperature programmed desorption (TPD). Basically, the strength of the adsorbate-surface interaction is determined by linearly increasing the substrate temperature (typ. rate 5 K/s) and then detecting the particles desorbing from the surface using a mass spectrometer (see the schematic drawing in Fig. 3). Since the mass spectrometer can detect the mass of a desorbing particle, this technique can be employed to distinguish between the desorption of the intact adparticle or its fragments. More importantly,
Lando lt -Bö rnst ein New Series III/42A2
Ref. p. 2-35]
2 Measuring techniques
2-9
the determination of the temperature at which the desorption maximum is observed allows for a rough estimation of the energy by which the particle is bound to the surface. Although the technique is conceptionally rather simple, there are several difficulties, related to both data acquisition and data analysis. With regard to the former, a precise determination of binding energies requires a reliable temperature measurement. Although a precise determination of substrate temperature presents no major problem for metal substrates, for insulating or semiconducting materials (e.g. diamond and metal oxides) such a measurement can require a considerable effort. There are in fact cases where different groups have reported desorption temperatures for the same system differing by more than 100 K [97SCH]. A second important point is the linearity of the substrate temperature as a function of time. Even small deviations can significantly alter the shape of the TDS-curves and make a quantitative analysis very difficult if not impossible. Concerning the analysis of the thermal desorption spectra, a detailed understanding of the experimentally measured desorption rates requires precise modeling of all relevant interaction energies [99KRE]. Although in most cases the adsorbate-substrate interaction is dominant, the adparticle-adparticle interaction can also significantly affect position and shape of the desorption maxima. Since the desorption process is governed by thermodynamics, entropic contributions also become important. It should be noted that in addition to obvious contributions from configurational entropy for weakly adsorbed species, vibrational entropy plays an important role, too [97KRE].
2.3.3 Laser-induced Thermal Desorption (LITD) When raising the substrate heating rate by using an intense laser beam, the desorption of the particles becomes so fast that a detailed determination of binding energies is impossible. Nevertheless, laser induced thermal desorption (LITD) has become an important tool for investigations of diffusion processes on surfaces. For this purpose, the laser is focussed on a small spot of several µm diameter. With a first laser pulse all adparticles within the spot area are desorbed. After termination of the laser pulse, thermal diffusion along the surface leads to a repopulation which can be determined quantitatively using a second laser pulse. The amount of desorbed particles is measured using a mass spectrometer, and from the amount of particles detected within the spot after different times the diffusion coefficient can be obtained. A large number of different systems has been investigated, a few examples are alkanes [90BRA] or CO and K [96WES] adsorbed on Ru(0001). A major advantage of the method is the fact that it can be applied for a large number of substrates, including semiconductors and insulators.
2.4 Techniques for a chemical analysis When investigating adsorption phenomena a key requirement is to study the cleanliness of a given substrate before the adsorption process and to determine the chemical compositions of the products formed in the subsequent adsorption. For this purpose techniques which are sensitive to the presence of different elements on a substrate surface are required. Although virtually all of the methods discussed here can be used in one way or another to follow an adsorption process, a technique which provides direct information on the chemical composition of a surface is very often a necessary prerequisite for fully characterizing the behavior of a particular adsorption system. In the following we will discuss first secondary ion mass spectroscopy, or SIMS, and then two variants of photoelectron spectroscopy, X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES).
Landolt -Börnst ein New Series III/42A2
2-10
2 Measuring techniques
[Ref. p. 2-35
2.4.1 Secondary Ion Mass Spectroscopy (SIMS) When a beam of energetic (1-10 keV) particles, either charged or neutral, impinges on a surface, atoms and molecular fragments are emitted. A small fraction of the ejected species is charged (either positive or negative) and can be detected via mass spectrometer. The mass spectrum shows a distribution of fragments typical for a given substance. In connection with the characterization of adsorbates on solid substrates the technique is only useful when the primary flux is reduced to about 5x1012 atoms /cm2. In that case the method is referred to as static SIMS. Although most applications of static SIMS are restricted to polycrystalline substrates [85BEN], it occasionally finds use in the study of adsorption of molecules on single crystalline surfaces, e.g. propene on Ru(0001). At higher fluxes significant amounts of material are removed from the surface, and material from deeper regions of the substrate surface is ejected. The high flux variant is called dynamic SIMS and is an important analytical method [92BRU]. Although static SIMS is applied predominantly for material characterization [92BRU], true surface sensitivity can be achieved when combining the method with powerful and sensitive mass spectrometers (e.g. a time-of-flight mass spectrometer). A particular advantage of SIMS is that all elements (including H) can be detected.
2.4.2 Ion Scattering Spectroscopy (ISS) When medium energy ions (200-3000 eV) impinge on a surface the energy exchanged with the substrate depends on the mass of the substrate atoms hit in the collision processes. As a result the ion energy loss can be used to determine the mass of the collision partner and thus provides direct information on the elemental composition of the surface. For this ion scattering spectroscopy, or ISS, typically noble gas ions (frequently also 3He) are used. Since most electron-energy analyzers can be operated also with reversed polarity and the only additional component required for ISS-measurements is a sputter-gun, this technique is widely accessible. One major advantage of this method is the ability to detect H-atoms, e.g. in the case of hydrogen on a Ru(001)-substrate [93NIE]. Lateral order is not required for applying this technique. See also the chapter on the scattering of ions.
3.4.3 Auger Electron Spectroscopy (AES)
Kontinuum Continuum
e- to electron energy analyzer
h’
count rate h horfest high-energy e
Intensität
h’ Photonenenergie Kinetic energy
e-
Fig. 4. In Auger electron spectroscopy, AES, an electron is removed from a core level by either highenergy electrons or X-ray photons. The excited states decay via transition of a less strongly bound electron into the empty core-level and the emission of a third electron. The kinetic energy of the latter is determined using an electron energy analyzer.
One of the oldest experimental methods available for determining the electronic structure of solid substrates is based on the excitation of electrons from a core level state (binding energy Eb) to a continuum state either by collisions with high energy electrons (typically around 3 keV) or X-ray photons (see Fig. 4). The core-excited electronic state is highly unstable and decays by a transition of an electron with smaller binding energy E′b into the empty state. Two different variants of this process are observed. In the first type the electronic transition is accompanied by emission of a second electron, the Auger
Lando lt -Bö rnst ein New Series III/42A2
Ref. p. 2-35]
2 Measuring techniques
2-11
electron, from a state with binding energy E ′b′ . The Auger electron carries a kinetic energy of Ek = E ′b′ – ( E ′b – Eb). This Auger process competes with a second process where the first transition is accompanied by the emission of a photon with an energy corresponding to h⋅ν = E ′b – Eb. The final state thus carries a charge of +2 in Auger spectroscopy and of +1 in fluorescence spectroscopy. The fluorescence process dominates Auger electron emission for atoms with Z larger than ~ 20. Using high-energy electrons for the excitation process turns Auger electron spectroscopy (AES) into a versatile method for determining the composition of surfaces, since the generation of electrons with energies around 3 keV is rather straightforward. This type of excitation, however, is not well suited for the investigation of molecular adsorbates due to the low threshold levels for electron beam damage. Thus the more delicate adsorbates require the use of X-rays to initiate the primary excitation [76FUG; 82FUG]. The positions of the Auger-lines for the different elements are tabulated [78WAG]. The analysis of Augerspectra becomes very tedious, if information about details on the electronic structure of adsorbed molecules is sought. Nevertheless, Auger spectra of molecular adsorbate species are often rich in structure and reveal detailed information on the electronic properties of the adsorbate-substrate complex [76FUG] as well as on the geometries of molecular adsorbates [84UMB], e.g. the tilt-angle of CO on Ni(110) [93MAC]. In conventional Auger electron spectroscopy the adsorbate carries a charge of +2 in the final state, since two electrons have been removed. More recently a variant of the method has been employed, where the exciting X-ray photons are tuned to an energy where the primary photoelectron is not emitted but excited into an empty molecular level of the particle, resulting in a final charge of +1. This resonant Auger process can provide more detailed information on the molecular adsorbate than the nonresonant process [90POR; 94POR].
e-
to electron energy analyzer
Continuum
Intensity h fixed
Binding energy Eb
2.4.4 X-ray Photoelectron Spectroscopy (XPS)
Fig. 5 In X-ray photoelectron spectroscopy, XPS, a substrate is illuminated wit X-ray photons of fixed energy. The kinetic energy of the photoelectrons is determined using an electron energy analyzer. In a typical XPS-analysis only the energies of the coreelectrons are considered.
In X-ray photoelectron spectroscopy the information on the electronic structure of the specimen is obtained by carrying out an energy analysis of the photoelectrons emitted from a probe illuminated by Xray photons. The primary process of X-ray photon absorption in matter, see Fig. 5, consists of an excitation of a bound electron into an unoccupied electronic state. If this final state is a continuum state with a kinetic energy sufficiently high to overcome the substrate work function, the electron will be emitted from the probe. With an appropriate energy analyzer, the kinetic energy EK of the electron can be measured and used to compute the binding energy according to Eb = hν – Ek. X-ray photoelectron spectroscopy is particularly useful for determining the chemical composition of an adsorbate overlayer and, if the resolution of both X-ray source and analyzer is sufficient, information can also be obtained on the partial charge of that particular atom from which the core-electron originates. This chemical shift Landolt -Börnst ein New Series III/42A2
2-12
2 Measuring techniques
[Ref. p. 2-35
makes it possible to directly distinguish physisorbed O2-molecules from chemisorbed O-atoms on Ptsubstrates [89LUN], for example. X-ray photoelectron spectroscopy, or XPS, is less useful for obtaining detailed information on the electronic structure of a molecular adsorbate. The chemical shift of core-electrons is mainly determined by the partial charge of the corresponding atom and to a lesser extent by the nature of the chemical bond to adjacent atoms. For example the binding energies of the C1s core-level of carbon atoms in the saturated hydrocarbon ethane (C2H6), 284.4 eV, and the unsaturated ethylene (C2H4), 284.2 eV, differ by only 0.2 eV; the difference to acetylene (C2H2), 283.7 eV, is slightly larger [74DAV]. On the other hand, in favorable cases the chemical shift observed for the same atom or molecule bound at different adsorption sites can be sufficiently large to distinguish between them. In the case of CO adsorbed on Rh(110), for example, the difference in O1s binding energies between CO bound at a bridge and an on-top site amounts to 1.1 eV [93DHA]; in the case of CO coadsorbed with hydrogen on Ni(100) the difference in C1s binding energy between on-top and hollow sites also amounts to 1.1 eV [98FOE]. In connection with intense X-ray sources, e.g. a synchrotron, X-ray spectra can be recorded in very short times (< 6 s), enabling the determination of adsorbate coverage as a function of surface temperature in a fashion similar to thermal desorption spectroscopy [96BAR]. It should be noted, that some care has to be taken when interpreting the chemical shifts observed in XPS data. The common case is that these shifts are caused by differences in the partial charge at the respective atom, thus leading to differences in the core-level binding energies. This so-called initial state effect has to be distinguished from final state effects, where differences in the screening of the core-hole generated in the photoabsorption process come into play. For example in the case of simple saturated hydrocarbons adsorbed on Cu(100), a C1s-shift of about 1 eV is observed with respect to the gas-phase or multilayer data, an effect which is mainly related to the improved screening of the core-hole by the metal electrons in the vicinity of the substrate surface [95WIT]. With regard to molecular adsorbates the XPS-method has significant advantages over Auger electron spectroscopy, since the extraction of quantitative information from the experimental data can be carried out in a much more direct fashion. The X-ray absorption cross section for a given element does not depend on its chemical environment and the area of a given X-ray photoelectron peak thus provides a good measure of the concentration of the particular element in the probe material. The cross sections have been calculated theoretically for all elements (except H) and are readily available in tabulated form [76SCO]. If the transmission function of the electron energy analyzer is known, reliable information on the stoichiometry of an adsorbed molecule can be obtained from XP-spectra. Note, however, that diffraction effects can lead to a pronounced angular variation of the emitted photoelectron intensity; see the paragraph on photoelectron diffraction (PED). In some cases the primary excitation process is accompanied by rearrangements of the electronic configuration (so-called shake-up process), which give rise to satellites at the high-energy side of the core level lines, which can then be used to derive information on the adsorbed species (e.g. C, N and O atoms on Ni [91NIL], N2 molecules on Ni [81HER]). The XPS-method can be applied to all systems where charging represents no major problem. It is the method of choice for determining the chemical composition of an adsorbate layer. Among all techniques employed for the characterization of the chemical composition of surfaces this is the most common one. It is estimated that worldwide several thousand XPS-machines are currently being operated.
Lando lt -Bö rnst ein New Series III/42A2
Ref. p. 2-35]
2 Measuring techniques
2-13
2.5 Structural sensitive techniques 2.5.1 Low Energy Electron Diffraction (LEED)
Fig. 6. In low energy electron diffraction, LEED, electrons with energies between 10 eV and 1000 eV (schematically shown as plane waves, left side top) are scattered from the substrate atoms. In case of ordered substrates the interference of the scattered waves (approximated by spherical waves, left side bottom) yields sharp diffraction beams which give rise to characteristic diffraction patterns. The LEED pattern shown on the right side has been recorded for a c(4√3x2√3) overlayer of heptanethiolate (CH3-(CH2)6-S-) on n Au (111) substrate at an electron incident energy of 27 eV.
The penetration depth of electrons into solids exhibits - for a very large number of conducting or semiconducting materials - a minimum of about 1 nm for energies of 150 eV, corresponding to a wavelength of 0.1 nm or 1 Å. This fairly small penetration depth yields a pronounced surface sensitivity and presents the basis for all electron-based techniques in surface science. As schematically shown in Fig. 6, the electrons, which in this energy regime can be represented by a plane wave when penetrating into the solid, are mainly scattered from the ion cores. The superposition of spherical waves emitted from the atoms in the adlayer and in the deeper substrate layers leads to the formation of diffracted beams. An important issue for the application to adsorbed layers on solid substrates is the fact that the intensity of the emitted spherical wave depends on the scattering cross section of the particular type of atoms, which in turn increases with atomic number Z. Diffraction from adlayers consisting of elements with low Z on substrates consisting of elements with high Z-numbers thus yields small diffraction peaks on top of intense diffraction spots originating from the substrate. Therefore, the detection of the weak adsorbate-induced diffraction peaks represents a formidable experimental problem. In particular the structural characterization of atomic hydrogen overlayers on solid substrates with LEED has been a major challenge for experimentalists. Ideal cases for this type of analysis are overlayers consisting of large Z elements on low Z substrates, e.g. Xe overlayers on graphite substrates.
Lando lt -Bö rnst ein New Series III/42A2
2-14
2 Measuring techniques
[Ref. p. 2-35
While the position of peaks in an electron diffraction pattern only provides information on the size and the shape of the surface unit cell, LEED can also produce precise quantitative data on the position of the adsorbate relative to the substrate atoms. By recording the intensity of a given LEED-spot as a function of incident electron energy, so-called I(V)-curves can be measured. Today the most convenient experimental procedure is to record the intensity variations of all LEED-spots simultaneously with a Video-camera [84HEI; 88HEI]. The I(V)-curves typically show a rich structure arising from interference phenomena and contain detailed information on the precise geometrical arrangement of adsorbates on a single crystalline substrate. A structure determination based on the complete theoretical description of an experimental I(V)-curve represents a formidable computational effort, thus imposing severe limitations on the size of the unit cell. While overlayers with small unit cells, i.e. less than 5 atoms per substrate unit cell for a surface with low miller indices, can be studied in a routine fashion, overlayers of larger molecules or large unit cells are still difficult to handle. An example where a full I(V) structure analysis has been carried out for a larger adsorbate is the adsorption of benzene on a Ru-surface [95STE]. Note, however, that in this case only the position of the C-atoms could be determined. The scattering cross section of the H-atoms is so small that these contributions were omitted from the analysis. The fact that many molecular adsorbates exhibit non-zero cross sections for electron-induced damage poses an experimental limitation on the application of the technique. To account for this fact, single or double channel plates are used for recording the diffraction patterns in the most recent generation of LEED-systems. Such systems make it possible to record a single diffraction pattern with a dosage of less than one electron per 100 adsorbate molecules [95STE]. For diffraction studies the width of the electron energy distribution does not represent a major problem. Therefore, most instruments use thermal electron emission without any monochromator. In the case of adsorbates forming structures with large unit cells, resulting either from many particles per unit cell or from the large size of the adsorbed molecule [98UMB], a variant of the technique with a significantly enhanced angular resolution is used. In addition to the determination of diffraction peak positions and intensities, SPA-LEED (for spot profile analysis-LEED) [86SCH] allows the analysis of spot profiles. Today LEED is the standard technique for detecting lateral order in adlayers on single crystalline metal substrates and semiconductors. For insulators the application is not straightforward, but charging problems can be overcome by heating the substrate or by going to very low beam currents.
2.5.2 Diffuse Low Energy Electron Diffraction (DLEED) A structure analysis with LEED requires the presence of ordered structures, since principally geometric parameters are calculated from diffraction peak intensities. In the absence of order, e.g. in case of randomly distributed adsorbates, the standard analysis of LEED patterns cannot be applied. In order to overcome this limitation, in recent years a variant of LEED, namely diffuse low energy electron diffraction (DLEED), has been developed [96STA]. Here, the full angular distribution of scattered electron intensity is measured and subsequently analyzed theoretically. Although the technique requires a significantly greater effort it becomes possible to determine adsorbate geometries despite absence of lateral order. The technique has been applied to a number of atomic adsorbates [96STA], however, the investigation of larger molecules was restricted to only a few (ethylene/Pt(111) [97DOL], CO2/Ni(110) [88ILL]).
Lando lt -Bö rnst ein New Series III/42A2
Ref. p. 2-35]
2 Measuring techniques
2-15
2.5.3 Photoelectron Diffraction (PED)
Fig. 7. Schematics of photoelectron diffraction, PED. The primary photoelectron is scattered by the surrounding atoms and the subsequent superposition leads to interference and the formation of a diffraction pattern.
While in low-energy electron diffraction the electrons being used as probe particles come from outside the sample, diffraction phenomena can also be exploited with electrons generated inside the sample, e.g. by a photoabsorption process. For sufficiently high kinetic energies (>500 eV) the scattering of the photoelectron by the neighboring atoms is dominated by forward scattering, i.e. the scattered intensity is peaked in the direction of neighboring atoms (see Fig. 7). As a result, information on the local environment of a photo-ionized atom can be studied by experimentally determining the angular distribution of emitted photoelectrons [88FAD]. In a typical application the presence of perpendicular and tilted CO-molecules on clean and potassium-modified Ni(110) could be demonstrated by experimentally determining the angular distribution of the C1s photoelectrons [89WES]. For smaller photoelectron energies (< 300 eV), the forward scattering mechanism is no longer dominant and interference effects lead to a distribution of intensity over a much larger angular regime. As a result, data analysis is not as straightforward and requires significant theoretical support. However, if experimental photoelectron angular distributions are recorded for a series of different photon incident energies (so-called "scan energy photoelectron diffraction"), the theoretical analysis of the experimental spectra yields very detailed information on the position of the adsorbate atoms. It is of particular interest that in addition to the atomic positions, information on the type of atoms is also contained in the experimental data. Furthermore, this chemical sensitivity makes it possible to separately determine the positions of atoms of the same type, which are equivalent for the free molecule but become chemically distinct when adsorbed on a surface [99WEI]. Although the theoretical analysis of the experimental data is rather complex, recently a direct method has been proposed, which allows for a direct extraction of geometrical data from the experimental results [93SCHb]. The application of photoelectron diffraction has the same limitations as LEED, i.e. charging for insulating substrates requires additional effort. Note, that long-range order is not necessary for applying this method.
Lando lt -Bö rnst ein New Series III/42A2
2-16
2 Measuring techniques
[Ref. p. 2-35
2.5.4 Techniques employing X-ray Standing Waves (XSW) The availability of synchrotron sources of second and third generation have made possible the application of X-ray based techniques commonly used for bulk investigations for surface studies which were not feasible previously because of intensity problems. With regard to the determination of structural parameters on single crystalline substrates novel approaches employing X-ray standing waves (XSW) [93ZEG] are particularly interesting. In this technique the wavelength of the incident X-rays is chosen such that the superposition of the incident beam and one particular Bragg spot generate a standing wave at the surface. Atoms positioned in the node of this standing wave will absorb little or no radiation, while those placed at the corresponding maxima will show enhanced absorption. By slightly tuning the wavelength of the incident radiation the position of nodes and maxima shifts slightly, and a corresponding analysis of the photoabsorption cross section of the given atoms provides detailed information on the positions. By additionally employing a triangulation scheme the method can be used to precisely determine the absolute position of adatoms relative to the substrate atoms. With regard to practical aspects the most popular variant is the so-called normal-incidence XSW method, where the incident beam is normal to the corresponding Bragg planes [93ZEG]. Recently, the method has been combined with an energy-resolved detection of the corresponding photoelectrons, which makes it possible to determine the geometric position of one type of atom in different chemical environments separately. For example in the case of PF3 adsorbed on Ni(111) this so called chemical-shift normal incidence X-ray standing wave (CS-NIXSW) technique makes it possible to determine the position of three different P-species independently [99JAC].
2.5.5 Extended X-ray Absorption Fine-Structure Spectroscopy (EXAFS) In XPS the kinetic energy of photoelectrons emitted after excitation by photons with a fixed energy is determined, whereas in EXAFS (extended X-ray absorption fine structure) the photoabsorption cross section is measured as a function of X-ray photon energy. In contrast to NEXAFS (see below) in EXAFS the absorption is measured in a fairly large interval of electron energies (typ. several 100 eV). As schematically depicted in Fig. 8, an X-ray photon is absorbed by exciting an electron into a continuum state. This electron travelling away from the core-excited atom is scattered by the neighboring atoms as discussed in connection with X-ray photoelectron diffraction (XPD). Depending on the kinetic energy of the electron, which is given by the difference between the photon energy hν, the core-level binding energy Eb and the inner potential V of the electrons inside the probe, constructive or destructive interference will occur at the position of the core-excited atom. As a result the X-ray absorption cross section is modulated, it increases when the constructive interference dominates for the emitted photoelectron, and decreases when destructive interference takes place. As a result, the exact shape of the X-ray absorption edge depends on the geometric surrounding of the core-excited atom, and e.g. the distributions of distances to nearest neighbors can be determined by a procedure which essentially consists of a Fourier-transformation [95ARV; 96BAB]. The outgoing wave will in general be non-spherical. If, for example, the initial state is a p-type orbital, the orientation of the p-lobes will depend on the direction of the incident light. By varying the angle of incidence of the exciting X-rays the backscattering amplitude from neighbors in different directions can be changed, thus increasing the amount of information which can be extracted from the EXAFS-data. As an example, interatomic distances and molecular orientation could be determined for formate (HCOO–) on Cu(110) [85PUS].
Lando lt -Bö rnst ein New Series III/42A2
Ref. p. 2-35]
2 Measuring techniques
2-17
Fig. 8. In EXAFS, the absorption of X-ray radiation is determined as a function of photon energy. The photoelectrons generated in the photoabsorption process at an adsorbate-atom are backscattered from substrate atoms and lead to modulation of the absorption cross section through interference phenomena. In the center figure the lines of equal phase of the backscattered radiation go through the excited atom (see top) resulting in constructive interference, whereas in the bottom figure the photoelectron kinetic energy is slightly different, resulting in destructive interference at the position of the excited atom.
Although the EXAFS-method requires a tunable source for X-rays, which is most conveniently realized by a synchrotron, it has significant advantages because of the rather straightforward data analysis. If X-ray absorption is determined directly, e.g. in transmission using an X-ray sensitive detector, the method is not intrinsically surface sensitive. In fact, bulk EXAFS has found widespread application in the determination of interatomic distances in (disordered) bulk samples, in particular for compounds containing transition metals. Surface sensitivity is achieved by measuring X-ray absorption indirectly via detection of secondary electrons. This variant is frequently called SEXAFS (surface EXAFS). Note also that this method does not require single-crystalline substrates.
Lando lt -Bö rnst ein New Series III/42A2
2-18
2 Measuring techniques
[Ref. p. 2-35
2.5.6 He-Atom Scattering (HAS) Helium atom scattering (HAS) Octane / Cu(111) [112]
Relative intensity
1
20
0
-4
-2
0
2
4
K [Å-1]
Fig. 9. Left: He-atoms with thermal energies (10-60 meV) from a molecular beam source are scattered off the very top surface charge density (left), whereas electrons penetrate several layers. As a result, He-atom scattering, HAS, offers a unique surface sensitivity. Right: Due to the very low incident energy He-atoms are particularly well suited for the investigation of delicate adsorbate layers. The angular distribution has been recorded for ordered monolayers of octane (C8H18) on Cu(111).
In order to obtain well-resolved diffraction peaks from ordered adsorbate overlayers, the wavelength of the scattered particle is required to lie in the regime of 1-10 Å. Therefore, only slow and light atoms are well suited for this application, of which helium, the lightest readily available neutral atom, finds widespread use. A particular advantage of 4He atoms is the fact that an adiabatic expansion of He through a small (typ. 10-20 µm) nozzle results in the formation of a supersonic beam with a very narrow energy distribution (values of less than 2% of the initial spread can be reached [77TOE]), so that diffraction studies can be carried out without any monochromator. Inspection of a typical interaction potential between a surface and a He atom demonstrates dramatic differences in the interaction between a surface and noble gas atom on the one hand and electrons on the other. The steep repulsive branch of the gas-surface potential prohibits any penetration of the He-atoms into the substrate and limits the interaction to the first layer only. Electrons, on the other hand, penetrate several layers, see Fig. 9. This fundamental difference results in a tremendous enhancement of the surface sensitivity and makes it possible to detect single atomic and molecular adsorbates. In contrast to LEED, however, the cross section depends very sensitively on the electronic structure of the adsorbate surface complex. In many cases it is found that the cross-section of a molecular adsorbate like CO is significantly larger than the corresponding gas-phase value [88YIN]. The elastic diffuse scattering signal caused by the presence of adsorbed atoms and molecules or step edges could also be detected directly and was used to infer on size and location of such surface defects [87LAH; 92WOE]. The pronounced surface sensitivity of He-atom scattering can be exploited to directly determine whether adsorbates preferentially adsorb at defect sites by monitoring the He-atom reflectivity in the course of an adsorption experiment as a function of surface coverage [00BEC]. The high surface sensitivity of He-atom scattering is best demonstrated by the straightforward detection of hydrogen-atom overlayers. This has first been reported for the case of H-overlayers on Ni(110) [83RIE]. In this case the unit-cell of the adsorbate is several times larger than that of the substrate. The corresponding additional diffraction peaks are clearly visible in He-atom scattering [83RIE], but give rise to only weak electron diffraction (LEED) spots. The detection of such superspots is no problem for modern state-of-the–art LEED instruments, whereas for the straightforward detection of (1x1) H-atom overlayers on metal substrates the scattering of He-atoms is still the method of choice [95WIT]. Recently, it has been demonstrated that He-beams can be focussed to below 1 µm using Fresnel zone plates [99DOA] thus opening the route to spatially resolved studies and investigations of small particles. An advantage in connection with the investigation of molecular adlayers is the fact that light atoms with de-Broglie wavelengths in the 0.1 nm regime have incident energies which are so small that Lando lt -Bö rnst ein New Series III/42A2
Ref. p. 2-35]
2 Measuring techniques
2-19
scattering of thermal-energy He-atoms is strictly non-destructive. The method can thus be applied to characterize the surface geometry of the outer, CH3-terminated surface of self-assembled monolayers of alkanethiols [91CAM], which is difficult to study with other methods due to the small cross-section of Cand H-atoms for electrons and X-rays. The most striking advantage of using He-atoms as opposed to electrons is the fact that neutral atoms are not sensitive to electric or magnetic fields. As a result insulating substrates can be investigated in a straightforward fashion [99BRA].
2.5.7 Scattering of rare gases and molecules The use of noble gases other than He in atom-surface scattering suffers from the fact that the corresponding molecular beams are significantly inferior to He beams with regard to monochromaticity and intensity. In addition for noble gas atoms heavier than He the scattering process becomes dominated by multiphonon-excitations, thus reducing the flux in the elastic diffraction channels. Only in a few cases have other noble gas atoms been used in diffraction studies (Ne [94RIE], Ar [89SCH]). The scattering of molecules to obtain structural information on surfaces is generally hampered by the fact that the angular distributions obtained by scattering of molecules from a surface are to a large extent governed by rotational excitations. As a result, only in a few cases have molecules been used for structural characterizations of adlayers. Note, however, that recently it could be demonstrated that diffraction of hydrogen molecules in different rotationally excited states can provide interesting information about details of the charge distribution on compound surfaces [98BER]. Molecular beam techniques are a rather convenient way to obtain direct information on the atomsurface resp. molecule surface potentials by monitoring selective adsorption processes, which can be either mediated by diffraction [80HOI] or by rotational excitation [83YU].
2.5.8 X-ray diffraction Despite the fact that X-ray scattering constitutes the standard technique for bulk structure determination, quantitative studies at surfaces have so far only been carried out for selected systems. This results from the small cross section of single atoms for X-rays. Very bright X-ray sources like synchrotrons in connection with glancing incident angles can, however, be used to overcome these limitations and the required surface-sensitivity can be achieved. As a consequence, X-ray diffraction, or XRD, has in recent years become a very attractive method for obtaining detailed structural information on ordered molecular adsorbates, even in the case of larger molecules (n-alkane thiolates [93FEN]). Since X-ray induced damage is a general phenomenon observed for many adsorbate systems, the applicability of the technique to a given system has to be carefully examined in particular for molecular adlayers. Note, that in the case of metallic substrates the damage is typically not generated by the incident X-ray photons but is caused by the secondary electrons resulting from the absorption of X-rays in the substrate and the subsequent decay of core-excitations by primary and secondary Auger transitions. Only very recently it has become possible to also use laboratory sources for unraveling the structure of organic overlayers on metal surfaces. For example the ordering and the adsorption-induced intramolecular distortions have been determined in adlayers of end-capped quarterthiophene [99MEYa] and 2-thiouracil [99MEYb] on Ag(111).
Landolt -Börnst ein New Series III/42A2
2-20
2 Measuring techniques
[Ref. p. 2-35
2.5.9 Neutron Scattering Similar to the case of X-ray scattering the application of neutron scattering in surface science is severely hampered by the small scattering cross section of a surface adlayer. Nevertheless, neutron scattering is an important technique in association with the characterization of molecular adlayers of very different composition on graphite substrates. The successful application to this special surface is due to the availability of a particular type of graphite powder, grafoil, which consists of flat sheets of graphite particles oriented such that a large fraction (∼30%) of the surface-planes are coplanar. Diffraction studies have been carried out for a large number of adlayers ranging from adsorbed atoms (Ar, [77TAU]) and diatomics to larger molecules (hexane, C6H14, [92HAN]). Apart from graphite, the only other substrate for which neutron studies on adlayers supported by a single crystalline surface have been reported is MgO [91LAR; 98LAR].
2.5.10 Ion Scattering Spectroscopy (ISS) A major disadvantage of all diffraction techniques is the fact that a straightforward, direct determination of the geometric structure of an adlayer solely from the diffraction peak intensities is not possible. As a result, information on the structure in real space can only be obtained by various types of fitting procedures. In this context the scattering of particles with high energies and correspondingly small deBroglie wave-lengths offers the possibility to directly infer on real-space structures by, e.g. channeling and blocking. (See Fig. 10) The energy regime between 100 eV and 10 keV is commonly called low energy ion scattering (LEIS). In this regime the energy is sufficiently high to describe the interaction with solid substrates in terms of classical physics. The ions incident on the adsorbate-covered surface follow classical trajectories, and after one or more collisions the backscattered particle is detected. The determination of the surface composition from the energy-loss of the ion has been described in paragraph 3.4.2 on Ion Scattering Spectroscopy (ISS). For a fixed incident direction of the ions the analysis of the angular distribution of the backscattered ions allows for a precise determination of atomic positions. Generally, a direct determination of the structure from the angular distributions of the backscattered particles is not feasible. With the aid of computer programs, however, it is possible to simulate the angular distributions of the scattered ions by analysing the classical trajectories of a large number of ions scattered off a substrate with an assumed geometry [93NIE]. After comparing the theoretical results with those obtained experimentally the assumed geometry can be adjusted so as to minimize the deviation between experiment and simulation. In case of hydrogen atom overlayers on Ru(001), the analysis of the ions scattered from the H-atoms revealed that the H-atoms are adsorbed on threefold sites of the Ru-substrate, 1 Å above the plane of the surface atoms [93NIE]. Fig. 10. In ion scattering spectroscopy, ISS, charged atoms are accelerated towards a substrate. When the ions impinge on the surface, the atoms in the first layer generate a shadow cone which, depending an the precise geometry, can make atoms in deeper layers invisible. Whereas all atoms of the first substrate layer are visible for the scattering geometry depicted on the right, some substrate atoms are located in the shadowing cone for the scattering geometry shown on the left.
Lando lt -Bö rnst ein New Series III/42A2
Ref. p. 2-35]
2 Measuring techniques
2-21
Of course, the interaction of the high-energy ions with the substrate also causes damage due to sputtering. This is generally an unwanted effect in investigations of overlayers on solid substrates. Fortunately, the detection efficiency for ions is rather large, thus in most cases the total fluency can be reduced to below 10-3 ions per surface atom, a value for which the ion-induced damage can be safely neglected. The sputtering can, however, be employed to study depth profiles, e.g. to investigate whether dosing a substrate with another compound leads to excessive subsurface diffusion [93NIE]. When increasing the ion energies further, the scattering cross sections become smaller, resulting in a deeper penetration of the particles into the substrate. As a result, medium energy ion scattering (MEIS) and Rutherford back scattering (RBS) are less surface sensitive (and thus less well-suited for the investigation of adsorbate overlayers) but are the methods of choice when either information on deeper layers or a very high precision of the atomic positions is needed [93NIE]. From an experimental point of view the analysis of ions with higher energies has the disadvantage of requiring more expensive equipment (accelerator, energy analyzer). When applying the method to semiconductors and insulators, the appearance of charging phenomena can strongly affect the neutralization probabilities in the scattering process and thus significantly complicate a quantitative analysis [79Joi].
2.6 Imaging techniques 2.6.1 Field Ion Microscopy (FIM) and Field Electron Microscopy (FEM)
FEM
FIM
e-
- +
+
EVac EF
e-
-
Fig. 11. In field electron microscopy, or FEM, the negative voltage applied to a metal tip (left) is increased to the point where the electrons can tunnel from the tip into the vacuum (bottom left). In field ion microscopy, or FIM, the voltage is reversed and leads to the field-induced ionization of rare gas atoms trapped at the tip surface (right). Atomic resolution can readily be achieved with FIM.
In field electron microscopy (FEM) electrons are extracted from a metallic substrate by applying a very strong electric field, the emission pattern is recorded using a fluorescence screen. In order to reach the required field strengths (~ 100eV/nm) very sharp metal tips are employed, the fabrication of which poses a formidable task. Although the first real-space images of molecules adsorbed on metal surfaces have been obtained using field electron microscopy for a phthalocyanine molecule adsorbed on a tungsten surface Landolt -Börnst ein New Series III/42A2
2-22
2 Measuring techniques
[Ref. p. 2-35
[50MUE], the method has not found widespread application for direct imaging of molecular adsorbates, mainly due to technical difficulties in preparing the sharp metal tips. However, it has been demonstrated that the FEM-method is capable of monitoring adsorbate motion or diffusion on a substrate via fluctuations in the electron emission. In fact, the method has become one of the most important tools for measuring the diffusion coefficient of adsorbates on metal surfaces [90GOM]. In one experiment the temporal variation of the emitted electrons has been studied on the picosecond time-scale, thus allowing the observation of the motion of a single adsorbed atom [93HEI]. Recently the method has been extended to study fluctuations in the course of a surface chemical reaction in adsorbed molecular adlayers on a Pt-substrate [99SUC]. In field ion microscopy (FIM), basically the same setup is used as in FEM (see Fig. 11), but with a reversed polarity (positive tip) of the applied voltage. Imaging is carried out by introducing an appropriate gas (e.g. He, Ne) into the chamber. When the gas atoms come close to the metal tip they experience an electric field of increasing strength, which can be made strong enough to cause field ionization. The positive ions are then accelerated in the radially symmetric field and generate an image of the field desorption tip with atomic resolution. Although the method cannot be applied to image adsorbates directly, it has been the basis for one of the first methods used for chemical surface analysis, the atom probe [68MUE]. More recently an improved version of the method, pulsed field desorption mass spectrometry (PFDMS), has been applied to identify adsorbate products [89KRU] as well as to study surface reactions and to determine kinetic parameters, e.g. in the case of CO and NO on Rh-crystals [97KRU].
2.6.2 Transmission Electron Microscopy (TEM) So far investigations of the geometric structure of adsorbate overlayers by transmission electron microscopy have only been possible using the transmission and diffraction of very high energy electrons (several 100 keV). The method has been successfully applied for structure determination of metallic overlayers on semiconductor substrates (e.g. In/Si(111)[97COL], Ge/Si(111)[96LEG], (Au + Cu)/Si(111) [91HOM]). For molecular and organic adsorbates the applicability of the method is limited because of the rather low threshold for radiation induced damage (dissociation). For large molecules, e.g. proteins, however, the adlayer can be coated with thin metal overlayers which can then be imaged with electron microscopy [91AMR].
2.6.3 Low Energy Electron Microscopy (LEEM) The use of electrons with low energy (< 200 eV) to obtain structural information on adlayers by either direct imaging or rastering is limited by the fact that the performance of electron optical elements at such low energies is rather poor. Bauer and coworkers, however, have developed a special type of electron microscope, where the electrons are first accelerated to high kinetic energies, focussed, and subsequently decelerated to low energies before they impinge on the surface [98BAU]. After the interaction they are again accelerated to high energies and focussed on a channel plate using standard high-voltage electron optics. Although the lateral resolution is limited to about 100 Å, steps of monatomic height are clearly visible in the micrographs. Numerous works have been carried out for adsorbate overlayers [99LEEM], including the motion of reaction fronts on single crystalline surfaces.
2.6.4 Photoemission Electron Microscopy (PEEM) In conventional electron microscopy the imaged electrons are generated by reflection, diffraction or transmission of the primary electrons directed from an external source towards the specimen. In contrast, photoemission electron microscopy employs an external photon source to generate electrons internally by Lando lt -Bö rnst ein New Series III/42A2
Ref. p. 2-35]
2 Measuring techniques
2-23
photoemission. By combining an ultraviolet lamp, generating photons with an energy slightly less than the work-function of the substrate, with a conventional electron optical system, images of adsorbate-covered regions on a surface can be obtained by employing the adsorbate-induced lowering of the work-function: photoelectrons are emitted only on patches covered with an adsorbate, thus allowing for real-time studies of changes in the shape of the patterns, e.g. resulting from diffusion (see e.g. the case of K on Pd(111) [98SNA]) or reaction fronts running across a substrate surface, e.g. in the case of CO oxidation on Pd(100) [97ASA]. The imaging-contrast described above is based on the difference in work-function and thus is not intrinsically element-specific. When a photon source in the soft X-ray regime is available, however, maps showing the distribution of a specific element on the surface can be generated by first recording images for photon energies slightly above and below a characteristic absorption edge of the particular element and then computing the difference of the two maps. If the electron optics additionally are augmented by an energy-filter and the experiments are carried out using the high brilliance of a third-generation synchrotron, a large variety of new imaging techniques becomes available [98WIC], which is too expansive to be covered here in detail.
2.6.5 Miscellaneous Many of the optical techniques, e.g. SHG, can be converted into a microscopical technique by simply focussing the incident beam. For example in the case of SHG (see chapter on SHG) a resolution of 5 µm has been achieved in a study on the diffusion of Sb on Ge(111) [92SCH].
Piezo-tube
2.6.6 Scanning Tunneling Microscopy (STM)
Preamplifier
Adjustment of tunneling gap
Tunneling voltage
Computer and display
Fig. 12. In scanning tunneling microscopy, STM, the distance between a metal tip and a conductive substrate with a small potential difference (typ. 0.1 eV – 2 eV) is reduced until quantum mechanical tunneling leads to the flow of a small current. When the tip is scanned across the surface a feedback electronic readjusts the distance so as to keep the current constant. The corresponding feedback signal can then be used to generate a topographical image of the substrate.
Among the different microscopical techniques applied for the investigation of adsorbate layers, scanning tunneling microscopy has so far found the most widespread application, mostly due to its fairly straightforward implementation [93WIE]. In this technique the distance between a sharp metal tip and a substrate is decreased until quantum-mechanical tunneling generates small currents even for small (< 2V) voltages across the gap. When the tip is moved along the surface (see Fig. 12), this current will change due to variations of the gap between tip and surface. With the help of a feedback system the gap can be readjusted and the corresponding feedback signal is used to create an image of the surface. In case of clean metal surfaces these images contain mostly topographical information, and adsorbed particles can be imaged in a straightforward fashion provided that the motion of the particle along the surface is substantially slower than the scanning of the tip. Generally, lowering the temperature will decrease the diffusivity of adparticles and at cryogenic temperatures even noble gas atoms can be stably imaged [90EIG]. It has been demonstrated that the STM-tip can also be used as a tool to displace and move Landolt -Börnst ein New Series III/42A2
2-24
2 Measuring techniques
[Ref. p. 2-35
adsorbed particles in a controlled fashion (Xe atoms [90EIG], O2-molecules [97BRI], CO-molecules [97BAR]). The STM-tip has also been successfully used to assemble nanostructures, which in turn can be used for further experiments [93CRO], [96CRO]. In case of adsorbates it becomes important that the STM-images, when recorded in the so-called constant current mode, actually correspond to lines of constant electron density at the substrate Fermi level. As a result, atomic and molecular adsorbates which locally decrease the density of states at the Fermi level create depressions in the STM micrographs rather than protrusions as might be expected naively. In principle the STM can also be used to derive information on the electronic structure of the surface by measuring the current through the tip as a function of the applied voltage (so-called I(V)-curves). The method thus also offers the possibility to directly determine the local density of electronic states, both above and below the Fermi edge. By evaluation of the second derivative of the I(V)-curves it has very recently also become possible to measure molecular vibrations of adsorbed molecules. In the case of acetylene (C2H2) adsorbed on Cu(001) the C-H-stretch mode at 358 meV could be clearly identified [98STI]. Frequently, images recorded by STM are also used to determine information on surface crystallography, in particular lattice constants of two-dimensional periodic structures. In principle STM can be calibrated against the lattice-constant of the substrate under investigation; however, the imaging process can significantly distort the adsorbate overlayer. In the case of molecular overlayers on graphite systematic errors as large as 10% have been reported [93DAI]. Today STM is becoming a standard technique in the structural characterization of conducting surfaces (metals, semi-conductors). For insulators the situation is hampered by the lack of conductivity, but materials like TiO2 have successfully been imaged at higher temperatures [99BEN]. A major drawback of STM is the lack of chemical sensitivity. Despite significant effort and several promising developments a routine procedure is not yet in sight to reliably determine the type of atom imaged with the STM. The technique is not limited to ultrahigh vacuum and studies at ambient pressure and in the liquid phase are carried out routinely.
2.6.7 Atomic Force Microscopy (AFM)
Laser
Detector A B C
Height h ~ (A+B) - (C+D)
Lateral-Force F ~ (A+C) - (B+D)
Cantilever motion of sample
F
h
D x-, y-, zScanner
x
x
Fig. 13. In scanning force microscopy, SFM, or atomic force microscopy, AFM, the force between a sharp tip and a substrate is determined by measuring the deflection of a flexible cantilever. Scanning the tip across the substrates then yields the morphology of the substrate. Several imaging modes are possible with modern instruments, including the detection of the lateral force (on the right).
Lando lt -Bö rnst ein New Series III/42A2
Ref. p. 2-35]
2 Measuring techniques
2-25
In scanning force microscopy, or SFM (also known as atomic force microscopy, AFM), a sharp tip at the end of a cantilever is approached towards a substrate while monitoring the force between tip and substrate. Using specially designed cantilevers the sensitivity can be increased to a point where the attraction (originating from van der Waals forces) between tip and substrate can be detected. Depending on the particular requirements, the distance can be reduced further up to the point where the short-range repulsive (instead of the long range attractive) forces dominate. Using a feedback system in a similar fashion as in STM (see above) the tip is scanned across the surface while keeping the force between tip and surface constant by readjusting the distance between tip and surface. Compared to STM the technique has the advantage that electrical conductivity of the substrate is not required. With regard to the characterization of adsorbed layers, however, atomic force microscopy, is not quite as powerful as STM, since the resolution is somewhat limited. The resolution of single adsorbed molecules has been reported in few cases, e.g. for alkanethiolate adlayers adsorbed on Au-substrates [92ALV]. Very recently highresolution images have also been obtained for the case of Xe-adlayers grown on a graphite substrate [99ALL]. A striking advantage of AFM in comparison to STM and other surface science techniques is the fact that AFM can be used for virtually all types of solid materials (including insulators) under ambient conditions and for substrates immersed in liquids in a rather straightforward fashion. As a result, AFM is becoming a standard technique for the structural characterization of materials [92BRU]. Despite significant efforts in connection with a chemical functionalization of the scanning tip, a major limitation of AFM is the lack of chemical sensitivity.
2.7 Vibrational spectroscopy of adsorbed particles A11
A12
O
O
O
O
C
C
C
C
Ni
Ni
Ni
Ni
E 4
E 3
Fig. 14. An adsorbed molecule shows characteristic vibrational frequencies which provide important information on the adsorption site and on the chemical interaction with the substrate. Whereas the internal vibrations like the internal stretch ν1 of the CO-molecule shown in the top can be compared to the corresponding values in the gas-phase, the socalled external vibrations, ν2–ν4, exist only in for the adsorbate.
With regard to the identification of adsorbed molecular species, vibrational spectroscopy plays a key role. For determining the stoichiometry of a molecule other methods are better suited (e.g. XPS), but the chemical state of an adsorbed molecule can be best identified by vibrational spectroscopy. This is in part due to the fact that a vast amount of data exists for bulk compounds. For example the comparison of C–O stretch frequencies in metal-organic compounds like nickeltetracarbonyl, Ni(CO)4, with corresponding data for the surface species allows important conclusions to be drawn about the nature of the molecular adsorbate. In many cases the number of modes observed in vibrational spectroscopy provides direct information on the symmetry of the adsorption site. It has been found that in many cases the frequency of internal stretching modes shows a correlation with the adsorption site. For example the internal vibration Lando lt -Bö rnst ein New Series III/42A2
2-26
2 Measuring techniques
[Ref. p. 2-35
has been demonstrated to significantly vary between the gas phase, for an on-step species e.g. on a Pt(111)-surface and for a bridge-species on the same surface. However, this correlation should be applied with great care since recently a number of exceptions from a simple correlation between vibrational frequency and adsorption site has been reported (CO/Pd(110) [93WAN], CO/Ni(111) [93SCHb], NO/Pt(111)+NO/Ni(111) [93MAT], NO/Ni(111) [93MAP], N2/Ni(110) [96BER]).
2.7.1 Electron Energy Loss Spectroscopy (EELS) In connection with the determination of the vibrational excitations of clean and adsorbate-covered surfaces the technique which has had the greatest impact is electron energy loss spectroscopy (EELS). Electrons with energies of typically between 2 and 400 eV are first monochromatized, then scattered off a surface and finally detected using an energy analyzer. During the interaction with the sample, energy can be transferred to the sample in the form of elementary excitations (electronic transitions, substrate phonons, adsorbate vibrations). In addition to the energy of the respective excitation the polarization of the particular vibrational mode and the momentum (in case of ordered structures) can be determined by recording energy loss spectra at scattering angles different from the specular. With regard to vibrational spectroscopy the technique is mostly applied to the energy range between 10 and 400 meV, but studies at lower energies have also been reported. Measurements at larger energy transfers probe electronic excitations (intramolecular, inter- and intraband transitions), from which detailed information on the electronic structure of the surface can be derived. For electron energy loss spectroscopy, two scattering regimes with different scattering geometries can be identified. If electrons are detected in the specular or near specular direction (to within a few degrees), the so-called dipole scattering regime, the excitation of vibrations is governed by a dipole mechanism. In close analogy to IR-spectroscopy (see below), in this regime only vibrations with transition dipole moments orientated perpendicular to the surface can be observed. For example in case of hydrogen adlayers adsorbed on W(001) only the totally symmetric modes, where the H-atom is displaced normal to the surface, can be observed [87WOO]. For scattering angles significantly away from the specular direction the intensity for the dipole mechanism typically drops by several orders of magnitude and excitations dominated by another mechanism, impulsive scattering [82IBA], can be detected. In this regime also vibrations with non-perpendicular orientations of the transition dipole moment to the surface become visible in the experimental spectra. An example is H/W(001), for which impulsive scattering reveals those modes where the H-atom vibrates parallel to the surface [87WOO]. Measurements in this impulsive regime are also very important for the detection of surface vibration (phonon) dispersion curves, which carry information on the interaction between adsorbed particles [91WOE]. The method can be directly applied to metal and semiconductor substrates; however, in the case of insulators charging problems can make measurements very difficult. Nevertheless, it has been possible to overcome this limitation in many cases and high-quality EEL-spectra have been obtained, e.g. for hydrogen adlayers on diamond C(111) [94AND].
2.7.2 Infrared Reflection-Absorption Spectroscopy (IRAS) The standard technique for probing the vibrational excitation spectrum of molecular materials in the bulk is infrared absorption spectroscopy. Photons in the infrared regime (400 – 4000 cm-1) can be absorbed by excitation of vibrations with appropriate frequencies. Since photons in the IR-regime are not intrinsically surface sensitive, the application of the technique for problems related to surface science is hampered by the small absorbance of an adsorbed monolayer. For a saturated monolayer of CO molecules, a rather favorable case, the extinction has been found to vary between 1.7 x 10-3 for CO on Pt(111) [92HOL] and 1.4 x 10-2 for CO on Cu(111)[88RAV]. In addition, on metal surfaces electric fields are rather effectively screened. At the surface of a metal, this screening is very strong parallel to, but less effective normal to the surface. This effect is the basis of the so-called IR surface selection rule, which states that in
Lando lt -Bö rnst ein New Series III/42A2
Ref. p. 2-35]
2 Measuring techniques
2-27
IR-spectroscopy only vibrations exhibiting transition dipole moments orientated normal to the surface can be detected. An important application of this technique is the determination of orientation (e.g. tilt-angle of molecular axis) in ultrathin organic layers on metal and semiconductor substrates, e.g. organothiols adsorbed on Au or organosilanes adsorbed on Si. This method works by comparing spectra recorded at grazing incidence for the monolayer (typically the spectra are recorded in ambient) to the corresponding bulk data [92PAR]. Compared to electron energy loss spectroscopy (EELS), the technique offers a significantly higher resolution (refined apparatuses can reach values of 0.005 cm-1 and better). Experimental halfwidths as low as 0.025 cm-1 have been reported for physisorbed monolayers, e.g. CO-adlayers on NaCl(001) [96HEI]. Since, however, the experimental setup for recording IR-spectra of adsorbed monolayers on substrates mounted in an UHV-apparatus is somewhat more complicated, EELS is the more versatile technique. On the other hand, IR-spectroscopy can be applied to insulators in a straightforward way and can be used outside vacuum if the problems related to the absorption by the ambient gas can be overcome. Very recently synchrotrons have been used as a source for infrared radiation. Despite the significant experimental effort, this approach extends investigations towards the far-infrared [90HIR]. A particular exciting result is the fact that by monitoring the reflectivity of an adsorbate covered metal surface vibrational modes can be seen which are invisible in conventional IR-spectroscopy due to the „surface selection rule“ (see above)[94HIR]. In addition the radiation coming from single electron bunches in the storage ring can be employed for time-resolved studies down to the nanosecond-regime [99LOB].
2.7.3 Surface Enhanced Raman Spectroscopy (SERS) In Raman spectroscopy an intense light beam (typically from a laser source) illuminates the sample, and the amount of inelastically scattered light is determined as a function of wavelength. From the resulting spectra the vibrational frequencies of adsorbed species can be determined and used to identify the adsorbates, similar to the case of IR-spectroscopy. Note, that the selection rules for Raman spectroscopy and IR-spectroscopy are different. For application to adsorbate adlayers normal Raman spectroscopy lacks sensitivity, although recently the method could be applied to detect vibrations on clean and adsorbate covered semiconductor surfaces (e.g. Sb and Bi adsorbed on GaAs(110) [98HAI]). For significantly curved („rough“) metal surfaces in certain cases a huge amplification of the signal is observed and forms the basis for a technique which has been dubbed surface enhanced Raman spectroscopy (SERS) [85MOS]. The strong amplification is assigned to a coupling between the light and surface plasmons of the curved metal surface and has made possible a number of studies in ultrahigh vacuum as well as on the liquid/solid interface [99HAI].
2.7.4 Inelastic scattering of He-atoms In addition to obtaining structural information about adsorbate overlayers on a surface, He-atom scattering is also suited to obtain information on adsorbate vibrations. By using a time-of-flight technique the amount of energy exchanged with the surface can be determined and used to infer on the vibrational excitation spectrum of a surface. The technique has mostly been applied to study thermal energy (< 25 meV) external vibrations. These are particular normal modes of the adsorbed particle, where the whole molecule performs periodic motions relative to the surface. These modes, which were first seen for CO adsorbed on Pt(111) [86LAH], carry important information on the potential energy surface, which governs the motion of a particle along a surface [96HOF]. For larger molecules, also internal vibrations like the so-called xylophone-mode in n-octane are located in the thermal energy regime and can be detected with He-atom scattering [97WIT]. The energy resolution of He-atom scattering is sufficiently high (< 0.1 meV or < 0.8 cm–1) to determine the vibrational lifetime via an analysis of the profile of the corresponding
Landolt -Börnst ein New Series III/42A2
2-28
2 Measuring techniques
[Ref. p. 2-35
loss-peaks and thus to draw important conclusions on the damping-mechanism of molecular motion relative to a surface [98WIT], an issue directly related to wearless sliding friction [99PER]. Important information on interaction of adsorbates with the substrate can also be obtained by comparing the surface phonon dispersion curves before and after the adsorption. In the case of hydrogen adsorption the effects are small for most cases (e.g. H on Pt(111)[89BOR]), in some cases rather striking differences are seen( H on W(110), [92HUL]). Although for an adsorbate the interaction between adsorbate and substrate is of primary interest, also the interaction between the adsorbates is of importance for a detailed understanding of e.g. two-dimensional phase transitions. Information on the interaction between adjacent adparticles can be derived from analyzing the corresponding phonon dispersions curves for the frustrated translations. For example in case of CO-adlayers for most metals only weak adparticle-adparticle interactions are found [97BRA]. The method is sufficiently sensitive to check whether e.g. Xe-Xe interactions in a physisorbed monolayer on Cu-surfaces differ from those seen in the gas-phase [97GRA]. The ultimate resolution available today with a state-of-the-art He-atom scattering apparatus is better than 100 µeV and allows to study diffusion of adsorbates on surfaces by analyzing the energetic width of the quasi-elastic scattering peak [88FRE]. The method has been applied to quite different systems, e.g. H/Pt(111) [99GRA] and Xe/Pt(111)[99ELL]. Since the probe particles used in He-atom scattering carry no charge, the method can be applied to all kinds of substrates. Limitations apply to the maximum energy which can be detected with this technique. So far the detection of vibrations above 30 meV has been limited to only very few cases.
2.8 Techniques probing the electronic structure To understand the nature of the interaction between an adsorbate and a substrate it is of paramount interest to gather precise information on the adsorption induced changes in electronic structure of both, the adparticle and the substrate. Since very often this type of information is also the key for understanding the theoretical aspects of adsorption phenomena a variety of techniques has been used, depending on the particular kind of information desired.
2.8.1 Ultraviolet Photoelectron Spectroscopy (UPS)
Continuum
eh fixed
Count rate
Electron energy
to electron energy analyzer
Fig. 15. In ultraviolet photoelectron spectroscopy, or UPS, photons in the UV-regime (10-100 eV) generate photoelectrons. From the electron kinetic energy as determined by an energy analyzer the positions of occupied electronic states can be determined.
In the case of ultraviolet photoelectron spectroscopy, photons in the energy range of up to 100 eV are used for the primary excitation process. As a result, information on core-level binding energies cannot be obtained and the type of elements present on a surface cannot easily be determined. The photoelectrons emitted from the sample upon absorption of an UV-photon originate from more weakly bound electronic
Lando lt -Bö rnst ein New Series III/42A2
Ref. p. 2-35]
2 Measuring techniques
2-29
states, and the photoelectron spectra thus provide direct information of the valence levels, see Fig. 15. In particular for adsorbates such data allow for important conclusions on the adparticle-substrate and the adparticle-adparticle interaction. The method also makes a more reliable identification of an adsorbed molecule possible. As an example the distinction of adsorbed C2H4 and C2H6 (which is very difficult with XPS, see above) causes no problem in this case, since the occupied π-orbital of C2H4 (which is absent in C2H6) can easily be seen with UPS. In many cases the comparison of UV-spectra of adsorbed molecular species with the corresponding data for the gas phase provides precise information about the changes of the molecular electronic structure upon adsorption of the molecule. Depending on the symmetry of the adsorbate, the technique can also be used to infer on the orientation of the adsorbed molecule by using polarized photons and by employing the dipole selection rules. As an example, the UPS-technique has been employed to decide whether a linear (unbrachned), saturated hydrocarbon (n-alkane) is adsorbed with its C-C-C-plane normal or parallel to the substrate [97WEC]. In the case of ordered adlayers, the dispersion of adsorbate-induced valence states can be determined with UPS by restricting the angular acceptance of the energy analyzer. From data obtained by this so-called angular resolved ultraviolet photoelectron spectroscopy (ARUPS) method the electronic bandstructure can be determined, from which in turn important information on the adsorbate-adsorbate interaction can be extracted [92WEI]. The technique can also be used to determine the work-function Φ and the adsorption-induced workfunction changes ∆Φ by analyzing the position of the secondary electron cut-off at low binding energies in the UPS data [94HOF]. The application of the technique and the interpretation of the experimental results is not as straightforward as in the case of XPS (see above). As in the other variants of photoelectron spectroscopy the application is difficult for insulating substrates. UPS is still the standard method for obtaining information on the electronic structure in the valence regime (binding energies < 30 eV), although – at least in cases of metal substrates – small changes in the molecular electronic structure are observed by the superimposed electronic structure of the substrate.
2.8.2 Inverse Photoemission (IPE)
Photon energy
e-
Fig. 16. In inverse photoemission, or IPE, an incident electron is temporarily trapped in an unoccupied molecular orbital typically several eV above the Fermi edge, from where it can decay to an low-lying empty orbital (at the Fermi edge) by photon emission.
Count rate
In principle this technique is a reversed version of ultraviolet photoelectron spectroscopy, or UPS. The Bremsstrahlung emitted when low energy electrons are decelerated and absorbed in a sample is analyzed using a monochromator. The resulting emission spectra (see Fig. 16) contain structures, from which the position and dispersion of the unoccupied electronic levels at a surface can be determined by computing the difference between the incident electron energy and the energy of the emitted photons. The technique thus provides information complementary to UPS, where the occupied states are probed. The application of the method to adsorbates is not straightforward since the resulting photon emission intensities are very low and the obtainable resolution is rather limited. Despite these experimental problems, it has been possible to determine the position and dispersion of unoccupied electronic states for a number of different
Landolt -Börnst ein New Series III/42A2
2-30
2 Measuring techniques
[Ref. p. 2-35
adsorbate systems, including molecular adlayers, e.g. carbon monoxide chemisorbed on Ni(110) [89MEM]. The method can in a straightforward fashion applied only to conducting (metal) substrates.
Continuum
h variable Absorption
Photon enenergy h
2.8.3 Near Edge X-ray Absorption Fine-Structure Spectroscopy (NEXAFS)
Fig. 17. In NEXAFS-spectroscopy a core electron is excited into an unoccupied molecular orbital by absorption of a X-ray photon. The absorption spectrum (right) shows sharp maxima when the photon energy matches the corresponding difference of the electronic orbitals.
One major problem concerning the evaluation of the electronic structure of an adsorbate is the fact that with the standard technique, ultraviolet photoelectron spectroscopy, or UPS, only the total sum of all electronic states is observed. There is no way, a priori, to determine whether the electronic states giving rise to a particular feature in the UP-spectra are localized mainly at the adsorbate (i.e. backdonation from a metallic substrate as in the case of CO adsorbed on transition metal surfaces), or in the substrate (e.g. donation from an adsorbed particle into the substrate) or whether it is due to states best described by a hybridisation between molecular and adsorbate states. In particular for transition metals with their d-bands located close to the Fermi edge the UPS-data are typically dominated by emission from these d-states, and subtle changes are virtually impossible to detect. A typical example for such an interaction is the case of saturated hydrocarbons, where the changes in electronic structure accompanying the so-called CH-stretch „soft modes“ seen in EELS [78DEM] and IR-spectroscopy [93RAV; 95HOS] could not be seen with UPS [98WIT]. Another technique, X-ray absorption spectroscopy, however, has been successfully employed to image these states. Here the application of X-ray absorption spectroscopy in the vicinity of the K-edges of low-Z elements (most important: C, N, O) offers significant advantages, since by the excitation process only elements of one type (e.g. the carbon atoms) are addressed. In X-ray photoelectron spectroscopy (XPS) (see above) the experimental information is obtained by analyzing the kinetic energy of the photoelectrons generated by the absorption of photons of fixed energy. In X-ray absorption spectroscopy the absorption of X-ray photons is measured as a function of photon energy. Accordingly, the technique requires a tunable X-ray source and can only be carried out at an electron synchrotron. The principle of this soft X-ray absorption spectroscopy (the commonly used acronym is NEXAFS, for near edge X-ray absorption fine structure spectroscopy) is schematically depicted in Fig. 17. For photon energies above the ionization threshold the core-electron is excited into a continuum state corresponding to a free electron with a positive kinetic energy. If the photon energy lies below the ionization threshold, absorption is only possible if the photon energy matches the difference in energy between the initial state (typically a core level, e.g. C1s, N1s, O1s) and an unoccupied molecular orbital. In that case the excitation process does not lead to an ionized, but rather to a quasibound state. In contrast to EXAFS (see above), here only the near edge regime (intervals of 50 eV) is investigated. The NEXAFS-technique is mainly used for deriving two different types of information. First, the spectroscopical data are useful in determining the electronic structure of an adsorbate. In the case of acetylene (C2H2), for example, adsorption on a Cu-surface leads to a splitting of the two π-levels, which are degenerated in the gas-phase. The technique can thus be used to obtain information about the electronic structure and is complementary to ultraviolet photoelectron spectroscopy (UPS) in the sense that unoccupied states are observed. The main advantage over UPS stems from the fact that in NEXAFS Lando lt -Bö rnst ein New Series III/42A2
Ref. p. 2-35]
2 Measuring techniques
2-31
the matrix elements governing the excitation process are large only for final states with significant contributions from atomic orbitals localized at the core-excited atom. As an example, in the case of hydrocarbons adsorbed on transition metal surfaces, pure metal states are not observed, which considerably simplifies the analysis of the experimental results [99WEI]. A second important application of this technique is the determination of molecular orientation within an adsorbed overlayer. Since the X-rays generated in the electron synchrotron by deflecting electrons with energies in the 1 GeV range are polarized with the E-vector orientated parallel to the plane of the synchrotron, the X-ray absorption dichroism can be conveniently measured by recording absorption spectra for normal and grazing incidence, respectively. From measurements at different angles of incidence one can thus obtain the orientation of the transition dipole moment with respect to the surface normal, from which in turn the orientation of the molecule can be derived. For many adsorbates the adsorption process is accompanied by molecular distortions, e.g. an aplanar, out-of-plane bend of the C-H-bonds in benzene adsorbed on transition metal surfaces [95MAI]. In the case of hydrocarbons, such distortions are difficult to detect with photoelectron diffraction or X-ray diffraction, because the scattering cross-section of the H-atoms for electrons and X-ray photons is very small. NEXAFS, on the other hand, is sensitive to the accompanying changes in symmetry of the molecular orbitals and can thus be used to determine these distortions in a semiquantitative fashion. Using this method it could also be demonstrated that ethylene, C2H4, adsorbs on a Cu(001)-surface in an essentially undistorted, planar adsorption geometry, whereas acetylene, C2H2, on the same surface shows a significant tilt of the C-H-bonds away from the C-C-bond [98FUH]. NEXAFS can be applied to a large number of adsorbate/substrate combinations. If the absorption is detected via the secondary electron yield, highly insulating substrates represent a problem. The situation is, however, considerably better than in conventional photoelectron spectroscopy, since small (several eV) shifts in the kinetic energy of the secondary electrons do not affect the positions of resonances in the spectra. Charging problems are eliminated by employing the X-ray fluorescence to monitor the absorption (Fluorescence Yield Near Edge Structure or FYNES) instead of the secondary electrons.
Kontinuum Continuum
h’
h fixed h fest Intensity Intensität
h’ Photonenenergie Fluorescent Photon enenergy h’
2.8.4 Resonant X-ray Emission Spectroscopy (XES)
Fig. 18. In X-ray emission spectroscopy, or XES, the energy distribution of the X-ray photons emitted after the primary absorption process is determined using a second monochromator.
Although NEXAFS-spectroscopy has obvious advantages over the standard technique to determine electronic structure, namely UPS, the interpretation and theoretical analysis of the data suffers to some extent from the fact that the final state of the excitation process is characterized by the presence of a corehole. The presence of such a core-hole can be described by increasing the atomic number Z by 1 (so called equivalent cores approximation), and as a result the binding energies of the electronic states are significantly lowered. Although the theoretical analysis of this situation can be handled by explicitly considering the presence of the core-hole, it is not the true ground state which this spectroscopy probes. Only recently has this problem been overcome by establishing a much more sophisticated variant of this technique, namely resonant X-ray emission spectroscopy, XES. Landolt -Börnst ein New Series III/42A2
2-32
2 Measuring techniques
[Ref. p. 2-35
In X-ray emission spectroscopy, it is the X-ray radiation emitted when a second electron undergoes a transition to the core-hole generated in the primary X-ray absorption process, that is detected with an energy dispersive analyzer, see Fig. 18. Principally, this process is the same as that used in electron microscopes for the EDX (energy dispersive X-ray detection) technique where core-holes excited by the high-energy (typ. 10 keV up to several 100 keV) electrons give rise to X-ray fluorescence, which is measured by energy-dispersive semiconductor detectors with a resolution of typically 100 eV. With this kind of resolution it is only possible to determine the different elements present in a sample. When the resolution is increased to beyond 1 eV by using a X-ray monochromator, additional information on the electronic structure of the sample can be obtained. If furthermore soft X-ray photons are used for the excitation process, the technique can be applied to investigate final states which are basically the same as probed with UP-spectroscopy. The striking advantage over UPS, however, is the fact that only final states with electron densities around a given element are imaged, e.g. in the case of saturated hydrocarbons on a transition metal surface pure metal states are invisible. Although this technique has so far been applied to a few systems only, it is expected that with the availability of third generation synchrotron sources the technique will find a more widespread application.
2.9 Nonlinear optical techniques 2.9.1 Second Harmonic Generation (SHG)
SHG
SFG
Fig. 19. The two nonlinear techniques SHG and SFG employ laser radiation which is so intense that interaction with matter leads to the combination of two photons of the same frequency (SHG, left) or of two photons of different energy (SFG, right).
When the intensity of electromagnetic radiation becomes very intense, in addition to linear effects (electronic and vibrational excitations, Raman scattering, etc.) nonlinear effects become important. This can be described formally by adding higher terms to the Taylor expansion of the polarizability tensor. Experimentally, the second quadratic polarizability term becoming nonzero results in the generation of photons with twice the incident energy, see Fig. 19. In bulk crystals exhibiting inversion symmetry, the second term has to be zero, but for non-centrosymmetric crystals like e.g. β-barium borate (β-BaB2O4) the effect becomes so strong that it can be used for frequency doubling. The relevance of second harmonic generation, or SHG, for the investigation of adsorbate layers becomes apparent when one considers that the mere presence of the surface considerably lowers the symmetry and, in particular, implies the loss of inversion symmetry, even if present in the bulk of the material. As a result, the surface of any substrate can in principle give rise to a SHG-signal. After the sensitivity of SHG to adsorbed layers in the monolayer and submonolayer regime had been demonstrated for a number of systems [89SHE; 94COR], this method has in recent years received considerable attention. Note, however, that this method is useful only for materials with bulk inversion symmetry, since the surface signal is otherwise dominated by that from the bulk. The striking advantage of this method as compared to other methods employed in surface science is the fact that it does not require ultrahigh vacuum. Basically, the only requirement is that there are no other Lando lt -Bö rnst ein New Series III/42A2
Ref. p. 2-35]
2 Measuring techniques
2-33
sources for the SHG-signal. Since this condition is generally fulfilled by solids with inversion symmetry, by normal liquids (but not by liquid crystals), and by gases, adsorption phenomena at surfaces can be studied for a large variety of systems. Although this spectroscopic technique is not inherently structure sensitive, the symmetry of both, solid substrate and adsorbate overlayer can be mapped by using polarized light. One of the first SHG-experiments carried out in connection with adsorbates on solid substrates in an ultrahigh-vacuum environment were measurements on the diffusion of CO-molecules adsorbed on a Ni(110)-surface [91XU]. In this experiment, first a pattern of regularly spaced stripes of adsorbed CO-molecules is generated using a laser beam. By detecting the SHG-signal diffracted from this grating the temporal decay of the pattern could be monitored and analyzed in terms of a diffusion constant. By orienting the diffraction pattern with regard to the substrate, anisotropies in the diffusion coefficient could also be studied [91XU]. In later work the technique has been used to follow adsorption/desorption phenomena at the solid-gas interface for pressures up to 1 atm. Investigations have also successfully been performed at the solid/liquid interface, e.g. the adsorption of organothiols from an ethanolic solution on a solid Au-substrate could be followed in real time [99DAN].
2.9.2 Sum Frequency Generation (SFG) The technique of sum frequency generation, or SFG, is related to the SHG technique discussed above. In contrast to SHG, where the incident laser beam consists of photons of one wavelength only, in SFG two different types of photons with frequencies ν1 and ν2 are used. At sufficiently high intensity this will not only generate photons with twice the energy of the incident photons, 2⋅ν1 and 2⋅ν2, but the nonlinear effects will in addition lead to the emission of photons with an frequency equal to the sum of the different frequencies, ν1 + ν2. By using one wavelength in the visible part of the spectrum and a second, tunable laser in the IRregime, the intensity of the SFG signal can be determined as a function of IR-wavelength. Also in this case the sensitivity to adlayers in the submonolayer coverage regime has been demonstrated [95BAI] [89SHE]. By a symmetry analysis it can be demonstrated that molecular vibrations which are both IR- and Ramanactive can be seen. The current large interest in this method results from the fact that vibrational spectra of adsorbed species which provide information complementary to IR can be recorded under non-vacuum conditions. As an example, very recently the technique has been used to investigate molecular orientations and conformations in confined systems in the context of tribological phenomena [00EIS]. In addition it should be noted that the method can be used to study very fast processes with a time resolution down to the pico/femto second regime. In the past the complexity of the equipment necessary to carry out SFG experiments has limited the number of studies but recent advances in laser technology have strongly reduced the effort (and the expenses) needed to set up an experiment.
2.10 Bulk techniques 2.10.1 Nuclear Magnetic Resonance (NMR) and Electron Spin Resonance (ESR) Today the characterization of bulk (solid and liquid) chemical compounds, in particular in the absence of crystalline order is dominated by nuclear magnetic resonance (NMR) spectroscopy. Sophisticated spectrometers operating at frequencies of 850 MHz and above can be used to determine the structure and to trace the dynamics of single atoms even in large biological molecules. The application to molecules adsorbed on surfaces, however, is limited by the rather low sensitivity of the technique. So Landolt -Börnst ein New Series III/42A2
2-34
2 Measuring techniques
[Ref. p. 2-35
far, studies on surface phenomena on single crystal surfaces with standard NMR (i.e. for nuclear spins in C or H atoms) have not been successfully carried out. It was possible, however, to apply standard NMR-techniques to investigate the dynamics of a lithium isotope, 8Li, adsorbed e.g. on a Ru(0001)surface [96EBI]. A different situation emerges if materials with a very high specific surface are used (compare to neutron spectroscopy). A particular important example are zeolithes [94BEL], where 1H and 13C NMR has been directly used to study the adsorption of CO [92BRU] and benzene [92LIU]. Also powders have been successfully investigated, e.g. reactions of different organic molecules on charcoal [95WAG]. Recently, experiments have been carried out by employing a novel scheme for detecting the NMR resonance. By using a highly sensitive cantilever from an atomic force microscope, it has been possible to increase the sensitivity of the method to a point where the detection of individual nuclear spins - and thus the application to surface phenomena - comes into sight [92RUG; 94RUG]. There is another technique based on the detection of spin resonance phenomena, where instead of the nuclear spin that of an unpaired electron is detected. Although this technique is much more limited than NMR since only molecules (and atoms) with unpaired electrons can be investigated, the technique is several orders of magnitude more sensitive than NMR and, at first sight, appears to be better suited for surface applications than NMR. Unfortunately, however, it has turned out that the application of electron spin resonance, or ESR, to surface problems is severely hampered by the fact that the unpaired electron couples strongly to metallic substrates. As a result, ESR-measurements on adsorbed molecules are virtually impossible [85FAR; 87ZOM]. Substrates with lower electron density and with a significant bandgap, however, provide a better basis and recently ESR has successfully been used to study the molecular motion of NO2 on sapphire (Al2O3)-substrates [95SCH].
Lando lt -Bö rnst ein New Series III/42A2
2 Measuring techniques
2-35
References for 2 27DAVa 27DAVb 30EST 50MUE 68MUE 72KIN 72WIS 74DAV 76FUG 76SCO 77TAU 77TOE 78DEM 78WAG 78WED 79JOI
80HOI 81HER 82FUG 82IBA 83YU
83RIE 84HEI 84UMB
Davisson, C. J., Germer, L. H.: The scattering of electrons by a single crystal of Nickel.: Nature (London) 119 (1927) 558. Davisson, C. J., Germer, L. H.: Diffraction of Electrons by a Crystal of Nickel: Phys. Rev. 30 (1927) 705. Estermann, I., Stern, O.: Beugung von Molekularstrahlen: Z. Phys. 61 (1930) 95. Müller, E. W.: Die Sichtbarmachung einzelner Atome und Moleküle im Feldelektronenmikroskop: Z. Naturforsch. 5a (1950) 473. Müller, E. W., Panitz, J. A., McLane, S. M.: The atom-probe field ion microscope: Rev. Sci. Instrum. 39 (1968) 83. King, D. A., Wells, M. G.: Molecular beam investigation of adsorption kinetics on bulk metal targets: nitrogen on tungsten: Surf. Sci. 29 (1972) 454. Wissmann, P.: The effect of gas adsorption on the conductivity of thin metal films: Thin Solid Films 13 (1972) 189. Davis, D. W., Shirley, D. A.: The prediction of core-level binding-energy shifts from CNDO molecular orbitals: J. Electron. Spectrosc. Relat. Phenom. 3 (1974) 137. Fuggle, J. C., Umbach, E., Menzel, D.: X-ray excited Auger spectra (XAES) from chemisorbed species: Solid State Commun. 20 (1976) 89. Scofield, J. H.: Hartree-Slater subshell photoionization cross-sections at 1254 and 1487 eV: J. Electron. Spectrosc. Relat. Phenom. 8 (1976) 129. Taub, H., Carneiro, K., Kjems, J. K., Pasell, L., McTague, J. P.: Neutron scattering study of 36Ar monolayer films adsorbed on graphite: Phys. Rev. B 16 (1977) 4551. Toennies, J. P., Winkelmann, K.: Theoretical studies of highly expanded free jets: Influence of quantum effects and a realistic intermolecular potential: J. Chem. Phys. 66 (1977) 3965. Demuth, J., Ibach, H., Lehwald, S.: CH vibration softening and the dehydrogenation of hydrocarbon molecules on Ni(111) and Pt (111).: Phys Rev Lett 40 (1978) 1044. Wagner, C., Riggs, W., Davis, L., Moulder, J., Muilenberg, G.: Handbook of X-Ray Photoelectron Spectroscopy: Perkin Elmer Corporation. Wedler, G.:(1978) The role of adsorption calorimetry in the study of surface phenomena: J. Thermal Analysis 14 (1978) 15. Joite, S., Hoinkes, H., Kaarmann, H., Wilsch, H.: SIMS on ZnO surfaces: the influence of space charge accumulation layers on secondary ion yields and measurement of true hydrogen concentration.: Surf. Sci. 84 (1979) 462. Hoinkes, H.: The physical interaction potential of gas atoms with single-crystal surfaces, determined from gas-surface diffraction experiments.: Rev. Mod. Phys. 52 (1980) 933. Hermann, K., Bagus, P. S.: Core level shake up structures of N2 adsorbed on nickel surfaces: cluster models: Solid State Communications 38 (1981) 1257. Fuggle, J. C., Umbach, E., Kakoschke, R., Menzel, D.: High-resolution Auger spectra of adsorbates: J. Electron. Spectrosc. Relat. Phenom. 26 (1982) 111. Ibach, H., Mills, D. L.: Electron energy loss spectroscopy and surface vibrations: New York: Academic Press. Yu, C., Whaley. K. B., Hogg, C.S.,, Sibener, S.J.,:(1983) Selective adsorption resonances in the scattering of n-H2, p-H2, n-D2, and o-D2 from Ag(111): Phys. Rev. Lett. 51 (1982) 2210. Rieder, K. H.: Low-coverage Ordered Phases of Hydrogen on Ni(110): Phys. Rev. B 27 (1983) 7799. Heilmann, P., Lang, E., Heinz, K., Müller, K.: Determination of Surface Structure by LEED: Marcus, P. M., Jona, F. (eds.), New York: Plenum, 1984. Umbach, E., Hussain, Z.:(1984) Angle-dependent changes of Auger line shapes from adsorbed molecules: Phys. Rev. Lett. 52 (1984) 457.
Lando lt -Bö rnst ein New Ser ies III/42 A2
2-36
85AND 85BEN 85FAR 85MOS 85PUS
86ABE
86LAH 86SCH 87JAC 87LAH
87WIS 87WOO
87ZOM 88FAD 88FRE 88HEI 88ILL
88RAV
88YIN
89BOR
89KRU 89LUN
2 Measuring techniques Andersson, D., Kasemo, B., Wallden, L.: Surface chemiluminescence in the Ksolid+Cl2 gas reaction: Surf. Sci. 152-153 (1985) 576. Benninghoven, A.: Static SIMS applications-from silicon single crystal oxidation to DNA sequencing.: J. Vac. Sci. Technol. A 3 (1985) 451. Farle, M., Zomack, M., Baberschke, K.: ESR of adsorbates on single crystal metal surfaces under UHV conditions: Surf. Sci. 160 (1985) 205. Moskovits, M.: Surface-enhanced spectroscopy: Rev. Mod. Phys. 57 (1985) 783. Puschmann, A., Haase, J., Crapper, M. D., Rieley, C. E., Woodruff, D. P.: Structure determination of the formate intermediate on Cu(110) by use of X-ray-absorption finestructure measurements: Phys. Rev. Lett. 54 (1985) 2250. Abermann, R., Koch, R.: In situ study of thin film growth by internal stress measurement under ultrahigh vacuum conditions: silver and copper under the influence of oxygen.: Thin Solid Films 142 (1986) 65. Lahee, A. M., Toennies, J. P., Wöll, C.: Low energy adsorbate vibrational modes observed with inelastic helium atom scattering: CO on Pt(111): Surf. Sci. 177 (1986) 371. Scheithauer, U., Meyer, G., Henzler, M.: A new LEED instrument for quantitative spot profile analysis: Surf. Sci. 178 (1986) 441. Jacobi, K.: Work-function changes and photoemission final-state relaxation of Ne, Ar, Kr, Xe, H2 and N2 on gallium.: Surf. Sci. 192 (1987) 499. Lahee, A. M., Manson, J. R., Toennies, J. P., Wöll, C.: Helium Atom Differential Cross Sections for Scattering from Single adsorbed CO Molecules on a Pt(111) Surface: J. Chem. Phys. 86 (1987) 7194. Wissmann, P. (ed.): Thin metal films and Gas Chemisorption: Amsterdam: Elsevier. Woods, J. P., Kulkarni, A. D., Erskine, J. L., Wette, F.:(1987) Vibrational properties of beta1-H and beta1-D on W(001): electron-energy-loss measurements and lattice-dynamic calculations: Phys. Rev. B 36 (1987) 5848. Zomack, M., Baberschke, K.: Submonolayers of paramagnetic NO2 adsorbed on argon and xenon films: Phys. Rev. Lett. 36 (1987) 5756. Fadley, C. S.: . Core-Level Spectroscopy in Condensed Systems: Kanamor, J., Kotani, A. (eds.), Berlin: Springer, 1988. Frenken, J. M. W., Toennies, J. P., Wöll, Ch.:(1988) Self-Diffusion at a Melting Surface Observed by He Scattering: Phys. Rev. Lett. 60 (1988) 1727. Heinz, K.: Diffuse low-energy electron diffraction: Prog. Surf. Sci. 27 (1988) 239. Illing, G., Heskett, D., Plummer, E. W., Freund, H.-J., Somers, J., Lindner, T., Bradshaw, A. M., Buskotte, U., Neumann, M., Starke, U., Heinz, K., Andres, P. L. d., Saldin, D., Pendry, J. B.: Adsorption and reaction of CO2 on Ni(110): X-ray photoemission, near-edge X-ray absorption fine-structure and diffuse LEED studies: Surf. Sci. 206 (1988) 1. Raval, R., Parker, S. F., Pemble, M. E., Hollins, P., Pritchard, J., Chesters, M. A.: ETRAIRS, EELS, and LEED studies of the adsorption of carbon monoxide on Cu(111): Surf. Sci. 203 (1988) 353. Yinnon, A. T., Kosloff, R., Gerber, R. B., Poelsema, B., Comsa, G.: Cross sections for He scattering from surface imperfections: vacancies and CO adsorbates on Pt (111): J. Chem. Phys. 88 (1988) 3722. Bortolani, V., Franchini, A., Santoro, G., Toennies, J. P., Wöll, C., Zhang, G.: Surface phonons on the Pt(111) surface: a comparison of He-scattering experiments with latticedynamical calculations: Phys. Rev. B 40 (1989) 3524. Kruse, N., Abend, G., Block, J. H.: Observation of Rh-subcarbonyls on stepped Rh surfaces during catalytic reactions: J. Chem. Phys. 91 (1) (1989) 577-83 Luntz, A. C., Grimblot, J., Fowler, D. E.: Sequential precursors in dissociative chemisorption: O2 on Pt(111): Phys. Rev. B 39 (1989) 12903.
Lando lt -Börnst ein New Ser ies III/42A2
2 Measuring techniques 89MEM
89SCH 89SHE 89WES
90BRA 90EIG 90GOM 90HIR
90KRI 90POR
91AMR
91BOR 91CAM
91HOM 91LAR 91NIL 91PER 91SAN 91WOE 91XU 92ALV
92BOE 92BRU
2-37
Memmel, N., Rangelov, G., Bertel, E., Dose, V., Kometer, K., Rosch, N.: Carbon monoxide chemisorption on a nickel surface: an investigation of unoccupied bands: Phys. Rev. Lett. 63 (1989) 1884. Schweizer, E. K., Rettner, C. T.: Quantum effects in the scattering of argon from 2HW(100): Phys. Rev. Lett. 62 (1989) 3085. Shen, Y. R.: Surface properties probed by second-harmonic and sum-frequency generation: Nature (London) 337 (1989) 519. Wesner, D. A., Coenen, F. P., Bonzel, H. P.: X-ray photoelectron diffraction study of perpendicular and tilted CO on clean and potassium-modified Ni(100): Phys. Rev. B 39 (1989) 10770. Brand, J. L., Arena, M. V., Deckert, A. A., George, S. M.: Surface diffusion of n-alkanes on Ru(001): J. Chem. Phys. 92 (1990) 5136. Eigler, D. M., Schweizer, E. K.: Positioning single atoms with a scanning tunnelling microscope: Nature (London) 344 (1990) 524. Gomer, R.: Diffusion of adsorbates on metal surfaces: Rep. Prog. Phys. 53 (1990) 917. Hirschmugl, C. J., Williams, G., Hoffmann, F., Chabal, Y.: Adsorbate-substrate resonant interactions observed for CO on Cu(100) in the far infrared.: Phys. Rev. Lett. 65 (1990) 480. Krim, J., Watts, E., Digel, J.: Slippage of simple liquid films adsorbed on silver and gold substrates: J. Vac. Sci. Technol. A 8 (1990) 3417. Porwol, T., Illing, G., Freund, H.-J., Kuhlenbeck, H., Neumann, M., Bernstorff, S., Braun, W., Niessen, W. v., Liegener, C. M.: Autoionization versus photoionization of molecular adsorbates: CO2 physisorbed on Ni(100): Phys. Rev. B 41 (1990) 10510. Amrein, M., Wang, Z., Guckenberger, R.: Comparative study of a regular protein layer by scanning tunneling microscopy and transmission electron microscopy: J Vac Sci Technol B 9 (1991) 1276. Borroni-Bird, C. E., Al-Sarraf, N., Andersson, S., King, D. A.: Single crystal adsorption microcalorimetry: Chem. Phys. Lett. 183 (1991) 516. Camillone, N., Chidsey, C. E. D., Liu, G., Putvinski, T. M., Scoles, G.: Surface structure and thermal motion of n-alkane thiols self-assembled on Au(111) studied by low energy helium diffraction: J. Chem. Phys. 94 (1991) 8493. Homma, I., Tanishiro, Y., Yagi, K.: REM and TEM studies of 2D Au-Cu alloy adsorbates on a Si(111) surface: Surf. Sci. 242 (1991) 81. Larese, J. Z., Hastings, J. M.: Rotational tunneling of methane on MgO surfaces: a neutron scattering study: J. Chem. Phys. 95 (1991) 6997. Nilsson, A., Martensson, N.: Core-level shake-up spectra from ordered C, N and O overlayers on Ni (100): Chem. Phys. Lett. 182 (1991) 147. Persson, B. N. J.: Surface resistivity and vibrational damping in adsorbed layers: Phys. Rev. B 44 (1991) 3277. Sander, D., Ibach, H.: Experimental determination of adsorbate-induced surface stress: oxygen on Si(111) and Si(100): Phys. Rev. B 43 (1991) 4263. Wöll, C.: Phonons on surfaces: The importance of structure and adsorbates: Appl. Phys. A 53 (1991) 377. Xu-Dong, X., Zhu, X., Daum, W., Shen, Y.: Anisotropic surface diffusion of CO on Ni(110): Phys. Rev. Lett. 66 (1991) 2352. Alves, C. A., Smith, E. L., Porter, M.D.: Atomic scale imaging of alkanethiolate monolayers at gold surfaces with atomic force microscopy: J. Am. Chem. Soc. 114 (1992) 1222. Böttcher, A., Grobecker, R., Gerber, T., Morgante, A., Ertl, G.: Exoelectron emission during the oxidation of Na films: Surf. Sci. 280 (1992) 170. Brundle, C. R., C.A. Evans, J., Wilson, S., Eds.: Encyclopedia of Materials Characterization: Boston: Butterworth-Heinemann, 1992.
Lando lt -Bö rnst ein New Ser ies III/42 A2
2-38 92BRU 92HAN 92HOL 92HUL 92LIU
92PAR
92RUG 92SCH 92WEI
92WOE
93CRO 93DAI
93DHA
93FEN 93HEI
93MAC
93MAP
93MAT
93NIE 93RAV
2 Measuring techniques Brunner, E., Pfeifer, H., Wutscherk, T., Zscherpel, D.: 13C NMR Investigation on the Adsorption of Carbon Monoxide in H-ZSM-5: Z. Phys. Chem. 178 (1992) 173. Hansen, F. Y., Taub, H.: Melting mechanism in monolayers of flexible rod-shaped molecules: Phys. Rev. Lett. 69 (1992) 652. Hollins, P.: The influence of surface defects on the infrared spectra of adsorbed species: Surf. Sci. Rep. 16 (1992) 51. Hulpke, E., Ludecke, J.: Hydrogen-induced phonon anomaly on the W(110) surface: Phys. Rev. Lett. 68 (1992) 2846. Liu, S.-B., Ma, L.-J., Lin, M. W., Wu, J.-F., Chen, T.-L.: NMR Investigation of the Distribution of Benzene in NaX adn NaY Zeolites: Influence of Cation Location and Adsorbate Concentration: J. Phys. Chem. 96 (1992) 8129. Parikh, A. N., Allara, D. L.: Quantitative determination of molecular structure im multilayered thin films of biaxial and lower symmetry from photon spectroscopies. I. Reflection infrared vibrational spectroscopy: J. Chem. Phys. 96 (1992) 927. Rugar, D., Yannoni, C. S., Sidles, J. A.: Mechanical detection of magnetic resonance: Nature (London) 360 (1992) 563. Schultz, K. A., Seebauer, E. G.: Surface diffusion of Sb on Ge(111) monitored quantitatively with optical second harmonic microscope: J. Chem. Phys. 97 (1992) 6958. Weinelt, M., Huber, W., Zebisch, P., Steinrück, H.-P., Reichert, B., Birkenheuer, U., Rosch, N.: Ethylene adsorbed on Ni(110): an experimental and theoretical determination of the two-dimensional band structure: Phys. Rev. B 46 (1992) 1675. Wöll, C., Lahee, A. M.: Investigation of surface imperfections by diffuse scattering of Heatoms. Helium Atom scattering from surfaces: Hulpke, E.:(ed.), Springer Series in Surf Sci, Heidelberg: Springer Verlag, 1992. Crommie, M. F., Lutz, C. P., Eigler, D. M.:(1993) Confinement of electrons to quantum corrals on a metal surface: Science 262 (1992) 218. Dai, P., Wang, S.-K., Taub, H., Buckley, J. E., Ehrlich, S. N., Larese, J. Z., Binnig, G., Smith, D. P. E.: X-ray-diffraction and scanning-tunneling-microscopy studies of a liquidcrystal film adsorbed on single-crystal graphite: Phys. Rev. B 47 (1993) 7401. Dhanak, V. R., Baraldi, A., Comelli, G., Paolucci, G., Kiskinova, M., Rosei, R.: CO adsorption on unreconstructed and reconstructed Rh(100) surfaces: LEED and XPS studies: Surf. Sci. 295 (1993) 287. Fenter, P., Eisenberger, P., Liang, K. S.: Chain-length dependence of the structures and phases of CH3CH2 n-1SH self-assembled on Au(111): Phys. Rev. Lett. 70 (1993) 2447. Heinzelmann, H., Watanabe, F., McClelland, G. M.: Observing the Motion of a Single Adsorbed Atom with Picosecond and Subnanometer Resolution: Phys. Rev. Lett. 70 (1993) 3611. Maciejewski, P., Hofer, U., Wurth, W., Umbach, E.: Determination of adsorbate orientation by means of angle-resolved Auger fine structure: CO on Ni(110): J. Electron. Spectrosc. Relat. Phenom. 62 (1993) 1. Mapledoram, L., Wander, A., King, D.: Breakdown of adsorbate site assignment from vibrational frequencies. NO on Ni(111) revisited by tensor LEED: Chem. Phys. Lett. 208 (1993) 409. Materer, N., Barbieri, N., Gardin, D., Starke, U., Batteas, J. K., Van Hove, M. A., Somorjai, G. A.: Dynamical LEED analyses of the Pt(111)-p(2x2)-NO and the Ni(111)-c(4x2)-2NO structures: substrate relaxation and unexpected hollow-site adsorption.: Phys. Rev. B 48 (1993) 2859. Niehus, H., Heiland, W., Taglauer, E.: Low-energy ion scattering at surfaces: Surf. Sci. Rep. 17 (1993) 213. Raval, R., Parker, S. F., Chester, M. A.: C-H...M interactions and orientational changes of cyclohexane on Cu(111): a RAIRS, EELS and LEED study: Surf. Sci. 289 (1993) 227.
Lando lt -Börnst ein New Ser ies III/42A2
2 Measuring techniques 93SCHb
93SCHb
93WAN
93WIE
93YOU 93ZEG 94AND
94BEL 94COR 94GIM 94GRO
94GRO 94HIR 94HOF 94PER 94POR
94RIE 94RUG 95ARV 95BAI 95HOS
95MAI
2-39
Schindler, K. M., Hofmann, P., Fritzsche, V., Bao, S., Kulkarni, S., Bradshaw, A. M.: Experimental demonstrations of direct adsorbate site identification using photoelectron diffraction: Phys. Rev. Lett. 71 (1993) 2054. Schindler, K.-M., Hofmann, P., Weiss, K.-U., Dippel, R., Gardner, P., Fritzsche, V., Bradshaw, A., Woodruff, D., Davila, M., Asensio, M., Conesa, J., Gonzalez-Elipe, A.: Is the frequency of the internal mode of an adsorbed diatomic molecule a reliable guide to its local adsorption site?: J. Electron. Spectrosc. Relat. Phenom. 64-65 (1993) 75. Wander, A., Hu, P., King, D.: Ambiguities in adsorbate site assignment from vibrational frequencies. A TLEED structural study of (2x1)CO-Pd(110): Chem. Phys. Lett. 201 (1993) 393. Wiesendanger, R., Guntherodt, H.-J. (eds.): Scanning Tunneling Microscopy I-III : Theory of STM and Related Scanning Probe Methods: Springer Series in Surface Science, Heidelberg: Springer, 1993. Young, H., Meng, X., Hess, G.:(1993) Multilayer adsorption of xenon, krypton, and argon on graphite: an ellipsometric study: Phys. Rev. B 48 (1993) 14556. Zegenhagen, J.: Surface structure determination with X-ray standing waves: Surf. Sci. Rep. 18 (1993) 199. Ando, T., Aizawa, T., Yamamoto, K., Kamo, M., Sato, Y.: The chemisorption of hydrogen on diamond surfaces studied by high resolution electron energy-loss spectroscopy: Diamond Relat. Mater. 3 (1994) 975. Bell, A. T., Pines, A., Eds.: NMR Techniques in Catalysis: New York, Marcel Dekker. Corn, R. M., Higgins, D. A.: Optical second harmonic generation as a probe of surface chemistry: Chem. Rev. 94 (1994) 107. Gimzewski, J. K., Gerber, C., Meyer, E., Schlittler, R. R.: Observation of a chemical reaction using a micromechanical sensor: Chem. Phys. Lett. 217 (1994) 589. Grobecker, R., Shi, H., Bludau, H., Hertel, T., Greber, T., Bottcher, A., Jacobi, K., Ertl, G.: Emission of exoelectrons during oxidation of Cs via thermal activation of a metastable O-2 surface species.: Phys. Rev. Lett. 72 (1994) 578. Grossmann, A., Erley, W., Ibach, H.: Adsorbate-induced surface stress: CO on Ni(100) and Ni(111): Surf. Sci. 313 (1994) 209. Hirschmugl, C. J., Williams, G. P., Persson, B. N. J., Volokitin, A. I.: Adsorbate vibrational dynamics in the anomalous skin effect frequency region.: Surf. Sci. 317 (1994) L1141. Hofmann, M., Wegner, H., Glenz, A., Wöll, C., Grunze, M.: The adsorption of the cyclic ether trioxane on Cu(111): J. Vac. Sci. Technol. A 12 (1994) 2063. Persson, B. N. J., Volokitin, A. I.: Infrared reflection-absorption spectroscopy of dipoleforbidden adsorbate vibrations: Surf. Sci. 310 (1994) 314. Porwol, T., Domotor, G., Hemmerich, I., Klinkmann, J., Freund, H.-J., Liegener, C. M.: Angular-resolved autoionization study of CO on Ni(110): experiment and theory: Phys. Rev. B 49 (1994) 10557. Rieder, K. H.: Surface structural research with atom beam diffraction: helium versus neon: Surf. Rev. Lett. 1 (1994) 51. Rugar, D., Zuger, O., Hoen, S., Yannoni, C. S., Vieth, H.-M., Kendrick, R. D.: Force detection of nuclear magnetic resonance: Science 264 (1994) 1560. Arvanitis, D., Baberschke, K.: Adsorbate-substrate bonding and dynamics as determined by SEXAFS: J. Electron. Spectrosc. Relat. Phenom. 75 (1995) 149. Bain, C. D.: Sum frequency vibrational spectrocopy at the solid/liquid interface: J. Chem. Soc. Faraday Trans. 91 (1995) 1281. Hostetler, M. J., Manner, W.L., Nuzzo, R. G., Girolami, G. S.: Two-dimensional melting transitions of rod-like molecules analyzed by reflection-absorption infrared spectroscopy: J. Phys. Chem. 99 (1995) 15269. Mainka, C., Bagus, P. S., Schertel, A., Strunskus, T., Grunze, M., Wöll, C.: Linear dichroism in X-ray absorption spectroscopy of strongly chemisorbed planar molecules: role of adsorption induced rehybridisations: Surf. Sci. 341 (1995) 1055.
Lando lt -Bö rnst ein New Ser ies III/42 A2
2-40 95ROT
95SCH
95STE 95WAG 95WIT 95WIT 96BAB 96BAR
96BER
96CRO 96DAL 96EBI
96HAA 96HEI
96HOF 96LEG 96STA 96WES
97ASA
97BAR 97BRA
97BRI
2 Measuring techniques Rotermund, H. H., Haas, G., Franz, R. U., Tromp, R. M., Ertl, G.: Imaging pattern: formation in surface reactions from ultrahigh vacuum up to atmospheric pressures: Science 270 (1995) 608. Schlienz, H., Beckendorf, M., Katter, U. J., Risse, T., Freund, H.-J.: Electron spin resonance investigations of the molecular motion of NO2 on Al2O3/(111) under ultrahigh vacuum conditions: Phys. Rev. Lett. 74 (1995) 761. Stellwag, C., Held, G., Menzel, D.: The geometry of ordered benzene layers on Ru(001): Surf. Sci. 325 (1995) L379. Wagner, G. W., MacIver, B. K., Yang, Y.-C.: Magic Angle Spinning NMR Study of Adsorbate Reactions on Activated Charcoal: Langmuir 11 (1995) 1439. Witte, G., Toennies, J. P., Wöll, C.: Comparison of surface phonon dispersion for the clean and hydrogen covered Rh(111) surface: Surf. Sci. 323 (1995) 228. Witte, G., Wöll, C.: External vibrations of hydrocarbons on Cu(100): J. Chem. Phys. 103 (1995) 5860. Baberschke, K., Wende, H., Srivastava, P., Chauvistre, R.: New opportunities in the soft Xray absorption to characterize the adsorbate bonding: J. Phys. IV France 7 (1996) 469. Baraldi, A., Comelli, G., Lizzit, S., Cocco, D., Paolucci, G., Rosei, R.: Temperature programmed X-ray photoelectron spectroscopy: a new technique for the study of surface kinetics: Surf. Sci. 367 (1996) L67. Bertino, M., Steinhögel, W., Range, H., Hofmann, F., Witte, G., Hulpke, E., Wöll, C.: The low energy thermal excitation spectrum of nitrogen molecules adsorbed on Ni(110): Implications for molecular adsorption sites: Appl. Phys. A 62 (1996) 95. Crommie, M. F., Lutz, C. P., Eigler, D. M., Heller, E. J.: Quantum interference in 2D atomic-scale structures: Surf. Sci. 361/362 (1996) 864. Daly, C., Krim, J.: Sliding friction of solid xenon monolayers and bilayers on Ag(111).: Phys. Rev. Lett. 76 (1996) 803. Ebinger, H. E., Jänsch, H. J., Polenz, C., Polivka, B., Preyss, W., Saier, V., Veith, R., Fick, D.: NMR observation of Diffusion Barriers for Lithium Adsorbed on Ru(0001): Phys. Rev. Lett. 76 (1996) 656. Haas, G., Franz, R., Rotermund, H., Tromp, R., Ertl, G.: Imaging surface reactions with light: Surf. Sci. 352-354 (1996) 1003. Heidberg, J., Grunwald, M., Hustedt, M., Traeger, F.: High-resolution PIRSS using a tunable diode laser: the multiplet of the collective Nu2 bending vibration of the p(2x1) monolayer CO2 adsorbed on NaCl(001): Surf. Sci. 368 (1996) 126. Hofmann, F., Toennies, J. P.: High-resolution helium atom time-of-flight spectroscopy of low-frequency vibrations of adsorbates: Chem. Rev. 96 (1996) 1307. LeGoues, F. K., Hammar, M., Reuter, M. C., Tromp, R. M.: In situ TEM study of the growth of Ge on Si(111): Surf. Sci. 349 (1996) 249. Starke, U., Pendry, J. B., Heinz, K.: Diffuse low-energy electron diffraction: Prog. Surf. Sci. 52 (1996) 53. Westre, E. D., Brown, D. E., Kutzner, J., George, S. M.: Surface diffusion of carbon monoxide and potassium coadsorbed on Ru(001): confirmation of a 1:1 CO:K trapping interaction.: J. Chem. Phys. 104 (1996) 7313. Asakura, K., Lauterbach, J., Rotermund, H., Ertl, G.: Spatio-temporal pattern formation during catalytic CO oxidation on a Pt(100) surface modified with submonolayers of Au: Surf. Sci. 374 (1997) 125. Bartels, L., Meyer, G., Rieder, K.-H.: Basic steps involved in the lateral manipulation of single CO molecules and rows of CO molecules: Chem. Phys. Lett. 273 (1997) 371. Braun, J., Kostov, K. L., Witte, G., Wöll, C.: CO overlayers on Ru(0001) studied by Helium Atom Scattering: Structure, dynamics, and the influence of coadsorbed H and O: J. Chem. Phys. 106 (1997) 8262. Briner, B. G., Doering, M., Rust, H.-P., Bradshaw, A. M.: Mobility and trapping of molecules during oxygen adsorption on Cu(110): Phys. Rev. Lett. 78 (1997) 1516. Lando lt -Börnst ein New Ser ies III/42A2
2 Measuring techniques 97COL 97DOL
97GRA
97KRE 97KRU 97SCH
97WEC
97WIT 98BAU 98BER
98FOE
98FUH
98HAI 98LAR 98SNA
98STI 98UMB 98WIC
98WIT
99ALL
2-41
Collazo-Davila, C., Marks, L. D., Nishii, K., Tanishiro, Y.: Atomic Structure of the In on Si(111)(4x1) surface: Surf. Rev. Lett. 4 (1997) 65. Doll, R., Gerken, C. A., Van Hove, M. A,, Somorjai, G. A.: Structure of disordered ethylene adsorbed on Pt(111) analyzed by diffuse LEED: asymmetrical di-sigma bonding favored.: Surf. Sci. 374 (1997) 151. Graham, A. P., Bertino, M. F., Hofmann, F., Toennies, J. P., Wöll, C.: Experimental determination of a longitudinal phonon dispersion curve in a quasi-two-dimensional system.: J. Chem. Phys. 106 (1997) 6194. Kreuzer, H. J., Payne, S. H., Grunze, M., Wöll, C.: Adsorption and Desorption of N2 on Ni(110): Entropy vs. Energy: Z. Phys. Chem. 202 (1997) 273. Kruse, N., Voss, C.: Surface Reactions and Adsorbate-Induced Reconstruction: CO and NO on Rh Crystals: Z. Phys. Chem. 202 (1997) 213. Schaich, T., Braun, J., Toennies, J. P., Buck, M., Wöll, C.: Structural changes accompanying the hydrogen desorption from the diamond C(111) H(1x1)-surface revisited by helium atom scattering: Surf. Sci. 385 (1997) L958. Weckesser, J., Fuhrmann, D., Weiss, K., Wöll, C., Richardson, N. V.: Photoemission from long chain alkanes adsorbed on a metal surface and the electronic structure of transpolyethylene CnHan: Surf. Rev. Lett. 4 (1997) 209. Witte, G., Fuhrmann, D., Wöll, C.: Low-Energy Molecular Vibrations investigated by Inelastic Scattering of He Atoms: Chem. Phys. Lett. 265 (1997) 347. Bauer, E.: LEEM basics: Surf. Rev. Lett. 5 (1998) 1275. Bertino, M. F., Glebov, A. L., Toennies, J. P., Träger, F., Pijper, E., Kroes, G. J., Mowrey, R. C.: Observation of large differences in the diffraction of normal- and para-H2 from LiF(001).: Phys. Rev. Lett. 81 (1998) 5608. Föhlisch, A., Wassdahl, N., Hasselstrom, J., Karis, O., Menzel, D., Martensson, N., Nilsson, A.: Beyond the chemical shift: vibrationally resolved core-level photoelectron spectra of adsorbed CO: Phys. Rev. Lett. 81 (1998) 1730. Fuhrmann, D., Wacker, D., Weiss, K., Hermann, K., Witko, M., Wöll, C.: The adsorption of small hydrocarbons on Cu(111): A combined He-atom scattering and x-ray absorption study for Ethane, Ethylene and Acetylene: J. Chem. Phys. 108 (1998) 2651. Haier, P., Santos, P., Esser, N., Richter, W.: Interaction between Sb and Bi adsorbates on the GaAs(110) surface.: Surf. Sci. 399 (1998) 264. Larese, J. Z.: Neutron scattering studies of the structure and dynamics of methane absorbed on MgO(100) surfaces: Physica B 248 (1998) 297. Snabl, M., Ondrejcek, M., Chab, V., Chvoj, Z., Stenzel, W., Conrad, H., Bradshaw, A. M.: Surface diffusion of K on Pd(111): coverage dependence of the diffusion coefficient determined with the Boltzmann-Matano method.: J. Chem. Phys. 108 (1998) 4212. Stipe, B. C., Rezaei, M. A., Ho, W.: Single-molecule vibrational spectroscopy and microscopy.: Science 280 (1998) 1732. Umbach, E., Glockler, K., Sokolowski, M.:(1998) Surface "architecture" with large organic molecules: interface order and epitaxy: Surf. Sci. 402-404 (1998) 20. Wichtendahl, R., Fink, R., Kuhlenbeck, H., Preikszas, D., Rose, H., Spehr, R., Hartel, P., Engel, W., Schlögl, R., Freund, H.-J., Bradshaw, A. M., Lilienkamp, G., Bauer, E., Schmidt, T., Benner, G., Umbach, E.: SMART: an aberration-corrected XPEEM/LEEM with energy filter: Surf. Rev. Lett. 5 (1998) 1249. Witte, G., Weiss, K., Jakob, P., Braun, J., Kostov, K. L., Wöll, C.: Damping of molecular motion on a solid substrate: evidence for electron-hole pair creation: Phys. Rev. Lett. 80 (1998) 121. Allers, W., Schwarz, A., Schwarz, U. D., Wiesendanger, R.: Dynamic scanning force microscopy at low temperatures on a noble-gas crystal: atomic resolution on the xenon (111) surface: Europhys. Lett. 48 (1999) 276.
Lando lt -Bö rnst ein New Ser ies III/42 A2
2-42 99BEN
99BRA
99DAN 99DOA
99ELL 99GRA
99HAI
99JAC
99KRE 99LOB
99MEYa 99MEYb
99LEEM 99PER 99SUC
99WEI 00BEC
00EIS
2 Measuring techniques Bennet, R. A., Stone, P., Price, N. J., Bowker, M.: Two (1x1) reconstructions of TiO2(110): surface rearrangement and reactivity studied using elevated temperature scanning tunneling microscopy: Phys. Rev. Lett. 82 (1999) 3831. Braun, J., Toennies, J. P., Wöll, C.: Local layer-by-layer growth of Ni on hydrogen terminated diamond C(111): A combined helium atom scattering and XPS study: Phys. Rev. B 60 (1999) 11707. Dannenberger, O., Buck, M., Grunze, M.: Self-Assembly of n-Alkanethiols: A Kinetic Study by Second Harmonic Generation: J. Phys. Chem. B 103 (1999) 2202. Doak, R. B., Grisenti, R. E., Rehbein, S., Schmahl, G., Toennies, J. P., Wöll, C.: Towards Realization of an Atomic deBroglie Microscope: Helium Atom Focusing using Fresnel Zone Plates: Phys. Rev. Lett. 83 (1999) 4229. Ellis, J., Graham, A. P., Toennies, J. P.: Quasielastic helium atom scattering from a twodimensional gas of Xe atoms on Pt(111): Phys. Rev. Lett. 82 (1999) 5072. Graham, A. P., Menzel, A., Toennies, J. P.: Quasielastic helium atom scattering measurements of microscopic diffusional dynamics of H and D on the Pt(111) surface: J. Chem. Phys. 111 (1999) 1676. Hai, L., Weaver, M. J.: Surface-enhanced Raman scattering as a versatile vibrational probe of transition-metal interfaces: thiocyanate coordination modes on platinum-group versus coinage-metal electrodes: Langmuir 15 (1999) 8743. Jackson, G. J., Ludecke, J., Woodruff, D. P., Chan, A. S. Y., Singh, N. K., McCombie, J., Jones, R. G., Cowie, B. C. C., Formoso, V.: Chemical-shift X-ray standing wave studies: coadsorption site determination of PFx fragments on Ni(111): Surf. Sci. 441 (1999) 515. Kreuzer, H. J., Payne, S. H., Drozdowski, A., Menzel, D.: Theory of dissociative and nondissociative adsorption and desorption: J. Chem. Phys. 110 (1999) 6982. Lobo, R., LaVeigne, J., Reitze, D. H., Tanner, D. B., Carr, G. L.: Performance of new infrared beamline U12IR at the National Synchrotron Light Source: Rev. Sci. Instrum. 70 (1999) 2899. Meyerheim, H. L., Gloege, T., Maltor, H.: Surface X-ray diffraction on large organic molecules: thiouracil on Ag(111): Surf. Sci. 442 (1999) L1029. Meyerheim, H. L., Gloege, T., Maltor, H., Sokolowski, M., Umbach, E., Bäuerle, P.: Bond stretching and distortion in large organic molecules on Ag(111) determined by surface xray diffraction: Surf. Rev. Lett. 6 (1999) 883. See papers in: Surf. Rev. Lett., Vol. 5, Nr. 6, (1999). Persson, B. N. J., Tosatti, E., Fuhrmann, D., Witte, G., Wöll, C.: Low-frequency adsorbate vibrational relaxation and sliding friction: Phys. Rev. B 59 (1999) 11777. Suchorski, Y., Beben, J., James, E. W., Evans, J. W., Imbihl, R.: Fluctuation-induced transitions in a bistable surface reaction : catalytic CO oxidation on a Pt field emitter tip: Phys. Rev. Lett. 82 (1999) 1907. Weiss, K., Weckesser, J., Wöll, C.: An X-ray absorption study of saturated hydrocarbons physisorbed on metal surfaces: Theochem. 458 (1999) 143. Becker, T., Boas, C., Burghaus, U., Wöll, C.: Adsorption probability of CO on a metaloxide: The case of oxygen-terminated ZnO and the influence of defects: Phys. Rev. B 61 (2000) 4538. Eisert, F., Gurka, M., Legant, A., Buck, M., Grunze, M.: Detection of molecular alignment in confined films: Science 287 (2000) 468.
Lando lt -Börnst ein New Ser ies III/42A2
4 Data: Adsorbate-induced changes of substrate properties
4.1 Surface structure on metals and semiconductors M. A. VAN HOVE, K. HERMANN, P. R. WATSON
4.1.1 Introduction The structure of surfaces at the atomic scale is basic to the understanding of many surface and interface properties. The effect of adsorbates on surface structure is particularly important because adsorbatecovered surfaces are technologically far more relevant than the clean substrate surfaces. Adsorbatecovered surfaces are also very relevant to the vast class of interfaces between two solids or between a solid and a fluid (liquid or gas). This chapter lists the experimentally determined effects of adsorption on the substrate surface structure, focusing on those cases where detailed and rather complete structures have been determined. This implies single-crystal surfaces with mostly well-ordered adsorbates. Much of the information is derived from the atomic coordinates and other information contained in the Surface Structure Database (SSD), Version 3 [99W], and is complemented with more recent results from the literature. The data were obtained with a variety of surface techniques, which are listed with their acronyms in Table 1. The emphasis is on the atomic-scale structure as defined by atomic positions, relaxations and reconstructions, structural models and bonding configurations. Included are both atomic and molecular adsorbates. The data for atomic adsorbates far outnumber those for molecular adsorbates, but the effects are rather similar, which is interesting in its own right; the tables in this chapter therefore show them side by side for direct comparison. Adatom positions are included in the tables so that the adsorbate-induced effects can be directly related to the adatom. However, for adsorbed molecules only the positions of the atoms that bond to the substrate are listed in the tables, since they have the most direct influence on the substrate. More complete structural details can be found in the Surface Structure Database [99W]. The tables in this chapter are limited to adsorption on metal and semiconductor substrates for the simple reason that virtually no detailed information is available from experiment about adsorbate-induced structural effects on other substrate materials, including ionic crystals and many other compounds.
4.1.2 Relaxation vs. reconstruction Central to adsorbate-induced changes in a substrate are the two concepts of relaxation and reconstruction, which collectively may be called restructuring. The terms relaxation and reconstruction need to be defined here, since various interpretations are used in the literature, especially for reconstruction. By relaxation of a substrate surface we mean small atomic displacements from ideal or clean-substrate positions. The displacements shall be small compared to near-neighbor distances, such that no rebonding (bond breaking or new bond formation) takes place within the substrate. Such relaxation may induce the formation of a two-dimensional superlattice if the displacements modify the initial substrate surface symmetry. This is especially common in adsorption, since the adsorbate itself often creates a superlattice,
Lando lt -Bö rnst ein New Ser ies III/42A2
4.1-2
4.1 Surface structure on metals and semiconductors
[Ref. p 4.1-109
particularly at fractional coverages less than one. For example, a ¼-monolayer of atomic adsorbate could be arranged in a (2x2) superlattice, doubling the substrate periodicity in two surface directions; each adatom can induce relatively small local relaxations in the substrate and within the superlattice unit cell: these relaxations, especially layer bucklings and lateral displacements, often break the clean-substrate periodicity while conforming to the superlattice periodicity. Relaxations must be referenced to another structure, for which the obvious choices are the ideal bulklike positions or the already relaxed clean-substrate positions. Since the clean-substrate positions are not uniquely known (each analysis gives somewhat different results), we use as an unambiguous reference for relaxations the ideal bulk-like positions obtained by a mathematical termination of the bulk lattice. However, we also include in this chapter, for direct comparison with the adsorbate-induced relaxations, tables of the published structural results determined for relaxed clean surfaces. Adsorbate-induced relaxations occur in many varieties. Of general interest are interlayer spacing changes: since clean surfaces exhibit spacing changes relative to the ideal bulk lattice, it is useful to consider the further changes due to adsorbates. For instance, on metals the clean-surface spacing relaxations are often reversed by adsorption: while the clean surface usually (but not always) exhibits a contraction of the topmost interlayer spacing, an expansion is often observed after adsorption. Also interesting is layer buckling (also called rumpling), whereby a coplanar atomic layer loses its coplanarity because an adsorbate pulls or pushes some substrate atoms out of the plane relative to other atoms. Another effect is lateral relaxation, in which adsorbates shift substrate atoms parallel to the surface; a frequent case is a radial relaxation of substrate atoms away from or toward the adsorbate site. Another case of lateral relaxation is the collective rotation of substrate atoms around the adsorbate site; this displacement is often called clock rotation. One could also look at all these relaxations in terms of adsorbate-induced changes in bond lengths, which are the chemically more important quantities; however, surface scientists have thought mostly in terms of displacement components perpendicular and parallel to the surface, and we shall do so here as well. By reconstruction of a substrate surface we mean large atomic displacements that cause rebonding (bond breaking and/or new bond formation) within the substrate. Frequently, but not always, such a reconstruction changes the two-dimensional lattice of the surface, creating or modifying or removing a superlattice. Reconstructions are of course usually accompanied by additional small relaxations. Reconstruction is a relative term: here reconstruction is understood with respect to the ideal bulklattice termination, rather than with respect to the actual clean surface. Of particular interest in adsorption are several cases: the induction of a new reconstruction, when none was present on the clean surface; the removal of a clean-surface reconstruction (sometimes inelegantly called un-reconstruction or de-reconstruction); and the change from one reconstruction to another (which could be called rereconstruction). Many types of reconstruction exist at surfaces. One class of reconstruction, common on certain clean metal surfaces, is that of missing or added atoms (e.g. missing or added rows); the remaining atoms still occupy bulk-like positions, usually with small local relaxations from those bulk-like positions. Microfacetting is a frequent outcome of this type of reconstruction. Adsorption often removes such reconstructions, but can also induce them, or stabilize them. Another class consists in forming or removing a more closely-packed surface layes, such as a quasi-hexagonally close-packed layer on top of square-lattice substrate, as happens with some metal surfaces. Dimerization and similar types of rebonding (e.g. π-chain formation) are commonly found on semiconductors, and these reconstructions are frequently removed by adsorption, but can also be stabilized by adsorption. Stacking faults occasionally are also seen on these materials. Absorption of adatoms into subsurface sites occurs for a variety of materials and can lead to interstitial or substitutional absorption within the substrate, in which case the remaining substrate atoms have near-bulk-like positions; absorption can also lead to other forms of compound formation, that may not respect the substrate lattice, but rather tend toward the lattice of the bulk compound. As with many definitions, there exist borderline cases where our definitions of relaxation vs. reconstruction are debatable. For example, large bond rotations with substantial atomic displacements but without rebonding occur in surfaces such as clean GaAs(110): we classify these as not reconstructed (relative to the ideal bulk termination, which is also nearly regenerated by certain adsorbates), although many authors prefer to call these reconstructed. In the case of clean W(100)-c(2x2), the displacements Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.1-109]
4.1 Surface structure on metals and semiconductors
4.1-3
from the ideal bulk positions are relatively small and could be called relaxations, but these may be sufficient to cause new bond formation between W atoms, and we label this situation therefore as reconstruction (this case has also been called displacive reconstruction in the literature). We treat relaxations and reconstructions very differently in the tables of this chapter. With relaxations, it is of primary interest to compare the quantitative magnitude and direction of the small displacements, including in particular changes in interlayer spacings, such as expansions and contractions. By contrast, with reconstructions it is of primary importance to know the qualitative type of reconstruction, rather than the detailed atomic positions; and the type of reconstruction is more easily understood when described in words than in numbers. Thus, our tables will in general list relaxations numerically, but reconstructions will be explained textually, although some important structural quantities will often be listed as well in the latter case. If more details are desired, it is suggested to consult the Surface Structure Database [99W].
4.1.3 Notations and conventions The individual structures listed in the tables are named using standard notations, particularly for superlattices: we use Wood, “rect” (rectangular) or occasionally matrix notations for the superlattices, which are defined in many books and reviews [86V, 99W]; they appear in the exact form used in the Surface Structure Database [99W]. Adsorption sites are also labeled in a conventional way, e.g. fcc-hollow site for adsorption at an fcclattice-continuation site above an fcc(111) surface. Figures are provided to clarify the more common adsorption sites and local adsorption geometries. For an adatom, the adsorption site coincides with the atomic position, or its projection into the substrate: we may call this the adsorption axis. But with an admolecule this needs clarification. For a molecule with a rotation axis perpendicular to the surface, the adsorption site coincides with the molecular rotation axis, which we may again call adsorption axis. Thus, for CO standing perpendicular to the surface at a high-symmetry position, the C-O axis uniquely defines the site, and the C atom (which normally bonds to the surface) is located at that site; for ring-like benzene lying flat on the surface with its main symmetry axis perpendicular to the surface, the empty center of the molecular ring typically lies at a high-symmetry location and thereby defines the adsorption site, while the 6 carbon and 6 hydrogen atoms are all removed from that site at lower-symmetry positions. For low-symmetry adsorption, ad hoc descriptions are given in each individual case, and in these situations the adsorbate-induced relaxations often become quite complicated (asymmetrical) and are not listed in detail: it is suggested to consult the Surface Structure Database [99W] for further information. Relaxations are labeled in the tables as illustrated schematically in Figs. 1 and 2, which define our generic labeling scheme applicable to all metallic substrates. The principle is to look from the adsorption site or axis outward, in any given layer. Consider the four coplanar and symmetrical light-grey substrate atoms depicted in Fig. 1, which looks down onto a particular atomic layer: these symmetry-equivalent atoms form a shell numbered s, at a radial distance rls from the (projected) adsorbate site (more precisely, this shell is cylindrical around the adsorbate site axis, which is very often an axis of rotational symmetry). If the local rotational symmetry is maintained, adsorption can cause these four atoms to be displaced radially by the common distance ∆rls from the (projected) adsorbate site and rotated tangentially by a common angle αls around that site. Figure 2 shows a side view of several substrate layers, each of which is shown as a gray slab of non-zero thickness, since it may be buckled: each possibly buckled layer originates in one non-buckled layer of the ideally-terminated bulk lattice. The dashed line is the adsorption axis, i.e. the projection of the adsorbate site down to each substrate layer. In a given layer, the first shell of atoms around that projected adsorbate site is numbered i = 1, with possible radial displacement by ∆r1 and possible tangential rotation by α1. The z-coordinate (perpendicular to the surface) of these nearest atoms numbered i = 1 defines the reference plane for this given layer (shown as a heavy line in Fig. 2): by definition, it thus has buckling amplitude b1 ≡ 0. The atoms of the second, third and farther shells have radial displacements ∆r2, ∆r3, etc., and tangential rotations α2, α3, etc. They also can have buckling amplitudes b2, b3, etc. relative to
Lando lt -Bö rnst ein New Ser ies III/42A2
4.1-4
4.1 Surface structure on metals and semiconductors
[Ref. p 4.1-109
the reference plane of that layer. The radial displacements and bucklings are expressed in percent relative to the values and interlayer spacings in the bulk.
4.1.4 Organization of the tables The tables are arranged so that similar structures are close together for easiest comparison. The coarsest subdivision is thus between metal substrates (see Sects. 4.1.6-4.1.14) and semiconductor substrates (see Sects. 4.1.15-4.1.18). Within the metals, the tables progress generally from the surfaces with highest symmetry and closest packing to those with lowest symmetry and least packing of the ideal termination. The order is thus: fcc(111), hcp(0001), bcc(110), fcc(100), bcc(100), fcc(110), hcp(10-10), bcc(211), bcc(111). Within the semiconductors, the same principles apply, starting with elemental substrates before turning to compound substrates: diamond(111), diamond(100), diamond(311), zincblende(110), zincblende(111), zincblende(1-1-1), zincblende(100), and 6H-SiC(0001). For a given crystal face, a first table gives the clean-surface relaxations of the interlayer spacings, or the type of clean-surface reconstruction (all relative to the ideally terminated bulk). Then, a table gives the adsorbate-induced relaxations or reconstruction type. Within this table, the structures are grouped by two-dimensional superlattice, starting with the smallest and highest-symmetry unit cells and progressing to the largest and lowest-symmetry unit cells (this includes disordered adlayers where available). For a given unit cell, the structures are listed alphabetically by substrate material and then by adsorbate element(s). A particular structure with several adsorbates per unit cell will appear several times in the table if the adsorbates occupy inequivalent sites. This is because the tables focus on one type of adsorption site at a time, for the most direct comparison, so that different adsorption sites coexisting in a single structure are found listed in different parts of the tables.
4.1.5 Organization of data for individual structures In the tables, when relaxations are listed, each (possibly buckled) layer is given one row, starting with the top substrate layer (numbered 1 in Fig. 2). The absence of structural data for deeper layers in second or subsequent rows means that they were not determined. All distances and angles are given in Ångström and degrees, respectively. Multiple data in a data field correspond to successive shells of atoms in a particular layer, as defined above and in Figs. 1 and 2. Let us explain this with two examples extracted from Tables 3 and 9, respectively (omitting a few obvious columns): surface
clean adsrec. ind rec. no Pd(111)+(3x3)- no C6H6+2CO: C6H6 site surface
Ni(100)+ p4g(2x2)-2C
clean adsrec. ind rec. no no
∆dl,l+1 [%]
bls [%]
∆rls [%]
2.6 ± 2.2
0.0 ± 2.2, 2.2 ± 2.2
0, 0.8 ± 7.0 0, 0
∆dl,l+1 [%]
bls [%]
∆rls [%]
3.9 ± 4.5 4.4 ± 4.0
0 3.2 ± 3.9 0, 8.5 ± 4.5 0, 0
αls [°]
αls [°]
d01 [Å]
∆r0 [Å]
2.16 ± 0.05 0
d01 [Å]
∆r0 [Å]
± 14.3 ± 2.6 0.12 ± 0.04 0, 0
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.1-109]
4.1 Surface structure on metals and semiconductors
4.1-5
The first of these two structures, Pd(111)+(3x3)-C6H6+2CO, contains 3 adsorbates in each unit cell, all of which are adsorbed at fcc-hollow sites. In the entry shown above only the structure around the benzene site is described (the structure around the CO adsorption sites is listed as a separate entry in the same Table 3). The center of the benzene molecule, which defines the adsorption site or axis, lies over an fcc-hollow site (indicated by the heading of Table 3). The height of the C atoms of the benzene, above the first ring of Pd atoms around the fcc-hollow site in the top metal layer, is given as d01 = 2.16 ± 0.05 Å. The second shell of Pd atoms around that site in the top metal layer is buckled into the substrate by b1b = 2.2 ± 2.2 %, relative to the first shell, for which (by definition) b1a = 0.0 (± 2.2) %, while its shell radius is (perhaps) expanded by ∆r1b = 0.8 ± 7.0 % relative to bulk positions. No rotations αls are noted, and no information about the second metal layer l = 2 is given, other than its spacing of ∆d12 = 2.6 ± 2.2 Å, measured relative to the first shell of Pd atoms in the first Pd layer; the second Pd layer is thus, in this example, assumed to be internally unrelaxed, i.e. not to be buckled, expanded laterally or rotated. The second structure, Ni(100)+p4g(2x2)-2C, contains two (equivalent) C adatoms in each (2x2) unit cell, related by p4g symmetry (i.e. glide-plane symmetry, as well as 4-fold rotation and mirror planes). The “no” entries indicate that neither the clean Ni(100)-(1x1) nor the C-covered substrate are reconstructed (in the sense that no Ni-Ni bonds are made or broken relative to the ideally-terminated substrate); admittedly, this is debatable for the C-covered surface, since the Ni-Ni distances within the first Ni layer do change appreciably. The heading of Table 9, from which this entry was extracted, specifies adsorption at a clock-rotated hollow site; the absence of a non-zero entry for lateral adsorbate shifts ∆r0 confirms that the C atoms are indeed at the high-symmetry hollow sites. The height of the C adatoms over the plane of the nearest Ni atoms is listed as d01 = 0.12 ± 0.04 Å, indicating nearly coplanar adsorption. If there were other Ni atoms in that first layer at a different height, i.e. buckled, the corresponding C-Ni spacing would be included in the same data field, e.g. as an additional 0.22 ± 0.04 Å to indicate that the next shell of Ni atoms would be deeper in the surface, buckled inward, by 0.22 - 0.12 = 0.10 Å; however, this particular structure has no buckling in the top Ni layer (it is not allowed by symmetry), as also indicated by the absence of an entry b1b in the buckling column. The data imply that the first shell of four Ni atoms is probably expanded radially by ∆r1a = 3.2 ± 3.9 % and most likely rotated by α1a = ± 14.3 ± 2.6 °, relative to the ideally-terminated Ni lattice; the initial ± before the rotation angle specifies that both clockwise and counter-clockwise rotations occur within the unit cell. The spacing change (relative to the bulk value) between the first and second Ni layers is given as ∆d1,2 = 3.9 ± 4.5 %, indicating a probable expansion; note that this spacing is measured between the planes of those Ni atoms which are closest to the (projected) adsorption site in each layer, i.e. between first Ni shells in each layer, as shown in the general case in Fig. 2. In the second row of data for this structure, which describes the second Ni layer, we find that a buckling by b2b = 8.5 ± 4.5 % occurs between the first shell of Ni atoms closest to the (projected) adsorption site (in this case the Ni atom directly below the adsorption site, for which by definition b2a = 0 %) and the next shell of second-nearest Ni atoms: the positive value indicates that the second Ni shell in this layer lies deeper below the surface than the first shell. Furthermore, the spacing between the second and third layers is shown to also probably be expanded, by ∆d2,3 = 4.4 ± 4.0 %. We illustrate next an entry for semiconductors, from Table 23, which contains some numerical data: surface Si(111)+ (√3x √3)R30°-In
clean rec. yes
ads-ind d01 [Å] ∆d12 [Å] ω [°] rec. no 1.85 ± 0.05 -15 ± 3
description [description]
This entry indicates that the adsorbate (In) has removed the clean-surface reconstruction. The adatom is located at a height d01 = 1.85 ± 0.05 Å above the first shell of outermost Si atoms. The adsorption occurs in a T4 site (as stated higher in the table and in the description included in this entry). And the spacing
Lando lt -Bö rnst ein New Ser ies III/42A2
4.1-6
4.1 Surface structure on metals and semiconductors
[Ref. p 4.1-109
between Si atoms in the outermost bilayer is contracted by ∆d12 = -15 ± 3 % relative to the bulk value. (The rotation angle ω is not relevant to this structure.)
4.1.6 Adsorption on fcc(111) The clean fcc(111) and hcp(0001) surfaces are the most compact and dense possible, with hexagonal atomic arrangements. They have the least tendency to reconstruct and relax interlayer spacings. Only Au(111) among them is known to reconstruct (to an even denser hexagonal outer layer with smaller lattice constant). Table 2 for the clean fcc(111) surfaces shows that the topmost interlayer spacing can be either expanded (Ag, Al, Pd, Pt), or undecided (Cu, Ni), or contracted (Rh), based on experiment. There does exist a general trend toward contraction of the topmost interlayer spacing in many metal surfaces, but it is only systematically verified for less-close-packed surfaces, such as fcc(110). The deeper interlayer spacings in clean fcc(111) surfaces are less well characterized at this time: their relaxations can be assumed to be smaller than the uncertainty of the analysis. Table 3 lists the adsorbate-induced changes on fcc(111). Reconstructions are relatively rare, and occur mostly with adsorbed metal atoms (especially alkali atoms) in the form of substitutional adsorption. Phosphorus and sulfur also can produce reconstructions in some cases, of a more complex type, but also tending toward compound formation; the structure of this ultra-thin compound layer need not be simply related to any known bulk compound structure. Considering the non-reconstructed cases, one finds a general trend toward expansion of the local topmost substrate interlayer spacing, relative to the clean surface. But there is one major exception to this trend: electropositive adsorbates (especially the alkali atoms) generally produce a contraction of this spacing. A similar contrasting trend is seen in the buckling induced within the top substrate layer: with electronegative adsorbates, the trend is toward positive buckling, i.e. substrate atoms farther from the adsorbate site tend to be deeper in the surface; the reverse is seen for electropositive adsorbates (again for alkali atoms especially). Radial relaxations around the adsorbate site are mostly within the error bars and probably small or negligible in most cases; the few more decisive results are insufficient in number to establish a clear trend. This applies even more so to the few tangential rotations that may have been observed. Buckling in the second substrate layer shows a tendency to be the reverse of that in the first substrate layer, particularly for the (2x2) structures with adsorption in fcc-hollow sites.
4.1.7 Adsorption on hcp(0001) The surface structure of ideal hcp(0001) is very similar to that of fcc(111), the difference occuring in the stacking sequence of the third and deeper metal layers. No hcp(0001) surface is known to reconstruct when clean. Table 4 shows clean-surface relaxations for hcp(0001). As with fcc(111), the topmost interlayer spacing can be expanded (Be, Mg), undecided (Co), or contracted (Gd, Ru, Sc). Compared to the fcc(111) surfaces, it seems at present that even fewer hcp(0001) surface reconstruct upon adsorption, cf. Table 5, at least among those studied. Trends in adsorbate-induced relaxations on hcp(0001) are less clear than on fcc(111), cf. Table 5. Perhaps the effects seen on fcc(111) do not carry over to hcp(0001), or the effects on hcp(0001) are more sensitive to details of the atomic arrangements within the various unit cells. A more exhaustive analysis and comparison of the results on a single metal, Ru(0001) [97M1], also suggests that structural trends may be difficult to extract for this one metal, and thus even more so for the class of hcp(0001) surfaces.
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.1-109]
4.1 Surface structure on metals and semiconductors
4.1-7
4.1.8 Adsorption on bcc(110) The ideal bcc(110) surface presents a distorted hexagonal lattice of slightly lower intrinsic atomic density than fcc(111) or hcp(0001). No clean reconstructions of these surfaces are reported, cf. Table 6. There is a tendency toward a contraction of the outermost interlayer spacing for K, Mo and W, without clear deviation from the bulk value for the other studied metals. Adsorption does not cause reconstruction on bcc(110), cf. Table 7. (There have been reports of a possible H-induced lateral shift of the top metal layer; but later studies could not confirm these results.) Adatoms appear to favor the "center" site (which is the continuation site of the bcc lattice), even though it is only two-fold coordinated. Adjacent to this site is a three-fold coordinated hollow site which is preferred by hydrogen, while in one structure, Mo(110)+(2x2)-S, the adatom appears to settle midway between those two sites. The adsorbate does not seem to induce a systematic expansion of the outermost metal-metal interlayer spacing on bcc(110); this is somewhat surprising in view of the results on other surfaces, but perhaps the statistics in this small group of results are not sufficient to reach a firm conclusion.
4.1.9 Adsorption on fcc (100) The ideal bulk-like fcc(100) surface, cf. Table 8, is atomically less dense and more "open" than the hexagonal fcc(111) and hcp(0001) surfaces, or the bcc(110) surface. Also it is more asymmetrical between vacuum and bulk than the hexagonal surfaces, in the sense that a surface atom has 0 nearest neighbors on the vacuum side and 4 on the bulk side, compared with 0 and 3 for the hexagonal surfaces; in addition the surface atoms in fcc(100) have only 4 nearest neighbors in the surface plane, as opposed to 6 in the hexagonal surfaces, so that the surface atoms in fcc(100) are relatively more affected by the outof-plane asymmetry. As a result one finds a slightly stronger tendency to both reconstruction and relaxation on the square-lattice fcc(100) surface. Reconstruction of the clean surface occurs for Ir, Pt and Au(100), as on fcc(111): in each case the top layer contracts and rearranges to form a quasi-hexagonal layer more similar to the fcc(111) surface (but with slightly different lattice constants, yielding different superlattices). The relaxations of interlayer spacings on fcc(100) surfaces are more biased toward a contraction of the top spacing. This spacing still appears to expand slightly for a few metals (Al, Pd), while no clear relaxation is seen on others (Ag, Ni, Rh); several metals now show a contraction (Al, Pb, Pd). There is also a tendency toward an oscillatory relaxation of the deeper interlayer spacings: alternating contractions and expansions with decaying amplitudes. Table 9 lists the adsorbate-induced changes on fcc(100). Adsorbates induce reconstructions of fcc(100) perhaps more frequently than for the hexagonal surfaces, but the statistics are poor, and the choice of metals studied probably not random. However, the adsorbates that cause reconstructions tend to be the same as on the hexagonal surfaces: primarily alkali adatoms, some other metal adatoms that form a one-layer alloy with the substrate, and oxygen. While sulfur induces reconstructions on fcc(111) and fcc(110), none is evident on fcc(100). On the other hand, adsorbates can also remove a clean-surface reconstruction (few such cases are listed in Table 9, but examples are known qualitatively by the change in their LEED patterns). Atomic adsorption occurs predominantly at or near four-fold coordinated hollow sites of fcc(100); the smaller adsorbates (H, C, N) penetrate relatively deeply into that hollow and partly bond to the second metal layer. Interlayer spacings are changed by adsorption in similar ways as on the hexagonal surfaces. Many adsorbates (primarily the electronegative ones) cause an expansion of the outermost interlayer spacing, while others (primarily the electropositive ones) yield contractions. The magnitude of the effect seems to be comparable to the case on the hexagonal surfaces. Also, there are similar examples of buckling, especially in the second metal layer. Notable is the very clear case of "clock reconstruction" observed for C and N adsorbed on Ni(100).
Lando lt -Bö rnst ein New Ser ies III/42A2
4.1-8
4.1 Surface structure on metals and semiconductors
[Ref. p 4.1-109
4.1.10 Adsorption on bcc (100), pure or alloyed The bcc(100) surface is in turn less dense and more open than the fcc(100) surface. In fact, the surface atoms do not bond together on bcc(100); instead, the 4 nearest neighbors of a surface atom are all in the second metal layer, causing very strong asymmetry between vacuum and bulk. One thus finds an even stronger tendency toward reconstruction and relaxation on this surface, especially when clean. Table 10 shows that 2 of the 5 bcc(100) metals listed reconstruct when clean (Mo, W). The non-reconstructed clean metal surfaces exhibit quite strong contractions of the outermost interlayer spacing, and a probable expansion of the next deeper spacing. Adsorbates, cf. Table 11, tend to compensate or even overcompensate for the missing half-crystal: this is already apparent on the closer-packed surfaces, but becomes much clearer with the more open surfaces like bcc(100) and fcc(110) (see Sect. 4.1.11 for the latter). The reconstructions tend to be removed or replaced by other reconstructions, while the relaxation of the outermost interlayer spacing often turns from a large contraction to a sizable expansion. Adsorption of adatoms occurs primarily within the large hollows of this surface, with frequent bonding to the second metal layer and a large induced buckling of that second metal layer. Alloys with a bcc(100)-like lattice include MoRe with variable composition, listed in Tables 12 and 13. The clean surfaces behave like clean, unreconstructed bcc(100) surfaces [note that clean Mo(100) reconstructs, while pure Re has an hcp lattice], as shown by the interlayer spacings listed in Table 12. Oxygen adsorption causes a missing-row reconstruction, while H and C induce spacing changes (and C can also penetrate interstitially).
4.1.11 Adsorption on fcc (110) The tendency noted above toward more reconstructions and relaxations on more "open" surfaces is again very evident for the fcc(110) surface. There is once more a large asymmetry for surface atoms between the vacuum side and the bulk: each surface atom has 0 nearest neighbors in the vacuum and 5 toward the bulk, one of which is directly below the surface atom, and the latter only has 2 nearest neighbors in the surface plane. Clean Ir, Pt and Au(110) all reconstruct, cf. Table 14, as for the (111) and (100) surfaces. But the (110) surface reconstructs into missing-row structures that expose narrow facets of hexagonal symmetry. While no other fcc(110) surfaces are known to spontaneously reconstruct when clean, the ease with which trace amounts of adsorbates can reconstruct several of these surfaces suggests that they are energetically close to reconstructing. Relaxations of interlayer spacings on the clean unreconstructed (and reconstructed) fcc(110) surfaces show a clear pattern of oscillatory contractions and expansions as one penetrates from one layer to the next. Adsorbates can induce the removal or change of a reconstruction on fcc(110) surfaces, cf. Table 15. The resulting reconstruction which has been studied most is that of oxygen on Cu, Ag and Ni(110), and N on Rh(110): it consists of one-dimensional chains like -Cu-O-Cu-O-, where the Cu atoms can be most easily viewed as adatoms on a bulk-like (but relaxed) Cu(110) surface. Another interesting type of induced reconstruction is a simple 1:1 metallic alloy in the top layer, obtained by substitution of half the surface atoms. A number of more complex reconstructions are also known, produced primarily with N, O, S and P, as well as some other metallic adatoms. Adsorbate-induced relaxation changes on unreconstructed fcc(110) surfaces are similar in magnitude to the bcc(100) case. The larger adsorbates, S and metals, tend to occupy the higher-symmetry hollow site at the center of the rectangle formed by 4 surface atoms, maximizing the number of nearest neighbors, and in particular bonding directly to the second metal layer, thereby inducing a large buckling there. Smaller adatoms, like H and O, favor 3-fold coordinated bonding sites on the flanks of those hollows (also bonding to atoms of both the first and second substrate layers); this lowers the symmetry and induces more complex relaxations in the substrate, such as asymmetrical lateral relaxations.
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.1-109]
4.1 Surface structure on metals and semiconductors
4.1-9
4.1.12 Adsorption on hcp (10 1 0 ) The ideal hcp ( 10 1 0 ) surface shows strong similarities with fcc (110): it also consists of ridges and troughs of close-packed atomic chains. However, the bulk structure allows two inequivalent terminations, with shallow and deep troughs, respectively. In all cases, it is the shallow-trough termination that is observed. The studied cases, cf. Table 16, exhibit no reconstructions when clean, but clear contractions and expansions of the top two interlayer spacings, respectively; the effect is largest in Be, for which an oscillatory trend in the spacing relaxations is apparent down to the 4th interlayer spacing. Rather few adsorbate-induced structures on hcp ( 10 1 0 ) have been studied in detail, cf. Table 17. They show no reconstructions, but a tendency to reduction or even reversal of the interlayer spacing changes. An exception appears to be presented by hydrogen on Re and Ru(10-10), where the outermost interlayer spacing remains close to the clean-surface value, while the next interlayer spacing is contracted.
4.1.13 Adsorption on bcc (211) The ideal bcc(211) surface shows strong similarities to the fcc(110) surface, with ridges and troughs of close-packed chains of atoms, but the troughs are wider and shallower; also the ridges are displaced longitudinally to give a lower symmetry than fcc(110) has. No reconstruction of the clean surface is evident, cf. Table 18, and relaxations of the interlayer spacings are similar to the case of fcc(110). The bcc(211) surfaces appear to be prone to reconstruction due to adsorption, cf. Table 19, with missing-row structures of different kinds being induced by H and O on Fe(211). Oxygen on W(211) seems to reduce the clean-surface spacing relaxations, although these were not optimized in the one study of this system.
4.1.14 Adsorption on bcc (111) Only one study is reported on the detailed adsorbate-induced structure of bcc (111). The clean surfaces of Fe and Mo(111) are not reconstructed. The ideal bcc (111) surface is very open, exposing 1st, 2nd and 3rd layer substrate atoms; it exhibits large interlayer spacing relaxations that are oscillatory, but the oscillation is not simply antiphase from layer to layer, cf. Table 20. Hydrogen on Mo(111) at a coverage of 3 monolayers, cf. Table 21, fills each of the large hollows with 3 adatoms that are located off-center on lateral, inclined bridge sites. The outermost Mo-Mo interlayer spacing is barely affected, while the second interlayer spacing is brought back toward the bulk value from a large contraction in the clean case.
4.1.15 Adsorption on Si, Ge and C(111) The clean surfaces of the diamond(111) type are well known to reconstruct in a variety of complex ways, cf. Table 22. For instance, for clean Si(111) the well-known (7x7) structure is the stable form, while the metastable (1x1), (2x1), (5x5) and (9x9) structures have also frequently been reported. However, only the (1x1), (7x7) and (2x1) structures have been determined in detail (but the other (nxn) structures are expected to be straightforward generalizations of the (7x7) structure). Such reconstructions of the clean surface strongly improve the bonding between surface atoms from a very unfavorable bulk-like arrangement. It is then not surprising that adatoms will as a rule perturb this situation fundamentally, and thus generate completely different surface structures. Table 23 lists adsorbate-induced structures on Si, Ge and C(111). Hydrogen affects C(111) and presumably Si and Ge(111) in the simplest manner: removal of the reconstruction by capping the dangling bonds of the ideal bulk-like termination, with some residual interlayer spacing relaxations that
Lando lt -Bö rnst ein New Ser ies III/42A2
4.1-10
4.1 Surface structure on metals and semiconductors
[Ref. p 4.1-109
reflect the difference between a monolayer of H and the missing half-crystal of the bulk. The same appears to happen with some other adatoms, in particular halide adatoms, and molecules. In these instances, the bulk is terminated in a complete bilayer, which offers bonds perpendicular to the surface that can be capped well by monovalent adsorbates. The bulk diamond lattice can also be terminated between the layers of this bilayer, leaving three times as many dangling bonds to satisfy: this can be accomplished by adding a trivalent adsorbate like As, Sb or Bi, which then forms a layer that substitutes for the outermost half of the more stable Si bilayer. A similar feature is part of the so-called honeycomb-chained-trimer (HCT) reconstruction due to several metal adsorbates. Here a lateral relaxation in the lower half of the bilayer leads to trimerization of those Si or Ge atoms. A related type of structure, called conjugate honeycomb-chained-trimer (CHCT) model, occurs for other metal adsorbates: here it is the metal adatoms that trimerize instead of the substrate atoms; we thus classify this as not reconstructed, since the Si-Si bonding topology is bulk-like. As Table 23 shows, a number of other reconstructions have been identified, many of which are quite complex.
4.1.16 Adsorption on Si and Ge(100) Compared to their (111) surface, the (100) surface of diamond lattices are simpler: the main clean form of these surfaces is the tilted-dimer (2x1) or c(4x2) reconstruction, determined on both Si and Ge, cf. Table 24. The c(4x2) phase is regarded as the more stable form, in which alternate dimers tilt in opposite directions. When heated, the tilting of the dimers becomes random and then on average forms a (2x1) lattice with disordered tilts. Several adsorbates, cf. Table 25, remove the tilted-dimer reconstruction, by simply capping dangling bonds of the ideal bulk-like termination. This can occur with H, Co and S. At lower coverages, adatoms (or larger molecular species) can maintain the dimer by capping its own dangling bonds, but the tilt is removed, resulting in a symmetric dimer. Metallic adsorbates generally also maintain the dimer, while symmetrizing it, after adsorption in a variety of configurations above and between the dimers: the adsorption occurs in so-called bridge, top, valley, cave or pedestal sites, depending on the metal. In yet other cases, as with Sb, the adsorbate itself forms dimers above the bulk-like substrate. Or the adsorbate forms dimers above substrate dimers, as with Al and Ga. And, not surprisingly, more complex reconstructions can occur on this type of surface as well.
4.1.17 Adsorption on diamond-like(311) The clean surface of Ge(311) has a complex reconstruction, cf. Table 26. While the corresponding structure of Si(311) is not well-established, adsorption of either H or Pb on Si(311) produces a very different reonstruction than seen on Ge(311), cf. Table 27.
4.1.18 Adsorption on zincblende(110) The clean (110) surfaces of zincblende compounds exhibit large relaxations (without superlattice), sometimes called reconstruction, cf. Table 28. There is no bond breaking or making relative to the ideal bulk termination, but mainly bond rotations with small bond length changes. In particular, the surface exposes zigzag rows of atoms, which are coplanar (untilted) in the ideal surface, and are tilted in the actual clean surface by angles around 25-30° from the surface plane. Most adsorbates which have been deposited on zincblende(110) surfaces largely remove the cleansurface relaxations, in particular canceling or even slightly reversing the clean-surface tilting, cf. Table 29. These atoms cap the dangling bonds of the ideal surface, in some cases (Sb, Bi) forming an additional layer of zigzag atoms, thus mimicking a continuation of the bulk lattice. Aluminum, on the other hand, substitutes for Ga in the outermost layers, penetrating to deeper substitutional sites in proportion to the amount of adsorbate present, while maintaining the clean-surface tilting.
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.1-109]
4.1 Surface structure on metals and semiconductors
4.1-11
4.1.19 Adsorption on zincblende(111) and (-1-1-1) The clean (111) and (-1-1-1) surfaces of zincblende reconstruct, cf. Tables 30 and 32: in the (111) case a missing-atom (2x2) structure appears for GaAs, with extensive relaxations around the empty site; the clean (-1-1-1) structure is rather more complex, with a large (3x3) supercell and additional disorder. Adsorbates, however, can totally remove these complex clean-surface reconstructions, and restore a bulk-like termination, cf. Tables 31 and 33. Sulfur and oxygen can bond at top sites on a full-bilayerterminated substrate, capping the dangling bonds, while the interlayer spacings in the substrate can relax. Or S can substitute for the outer half of the external bilayer.
4.1.20 Adsorption on zincblende(100) Clean zincblende(100) reconstructs in various arrangements of dimers, forming different superlattices like (2x1), (4x2) and c(8x2), cf. Table 34. The one documented case of adsorbate structure, cf. Table 35, has S adatoms removing the reconstruction of clean GaAs(100) and adsorbing at bridge sites.
4.1.21 Adsorption on 6H-SiC(0001) Clean 4H-SiC(0001) has a bulk-like surface termination with a (1x1) unit cell and small relaxations of the interlayer spacings, cf. Table 36. The adsorption of H, O and OH saturates the dangling bonds at top sites of the ideal termination in a full SiC bilayer and changes the interlayer spacings by amounts smaller than 0.1Å, cf. Table 37.
Acknowledgments This work was supported in part by the Director, Office of Science, Office of Basic Energy Sciences, Materials Sciences Division of the U.S. Department of Energy under Contract No. DE-AC03-76SF00098. It relied heavily on the Surface Structure Database supported by the Standard Reference Data Program of the National Institute of Standards and Technology of the U.S. Department of Commerce, with newer results supplied by individual authors.
Lando lt -Bö rnst ein New Ser ies III/42A2
Table 1. Techniques used for surface structure determination; listed by their acronyms
ALICISS ARAES
Alkali ICISS Angular Resolved Auger Electron Spectroscopy
ARPES ARUPS ARXPS ARXPD ARPEFS At. diffr. ATLEED At. scatt.
Angular Resolved Photoelectron Spectroscopy Angular Resolved Ultraviolet Photoelectron Spectroscopy Angular Resolved X-ray Photoelectron Spectroscopy Angular Resolved X-ray Photoelectron Diffraction Angular Resolved Photoelectron Fine Structure Atom Diffraction Automated Tensor LEED Atom Scattering
CAICISS CMTA
Coaxial Impact-Collision Ion Scattering Spectroscopy Constant-Momentum Transfer Averaging
DLEED
Diffuse LEED
EAPFS EELFS EELS ESDIAD EXAFS EXELFS EXFAS
Electron Appearance Potential Fine Structure Electron Energy Loss Fine Structure Electron Energy Loss Spectroscopy Electron Stimulated Desorption Ion Angular Distribution Extended X-ray Absorption Fine Structure Extended Electron Energy Loss Fine Structure Extended Fine Auger Structure
Fluorescence XRD FYNES
Fluorescence X-ray Diffraction Fluorescence-Yield Near-Edge Structure
GIXD GIXS
Grazing-Incidence X-ray Diffraction Grazing-Incidence X-ray Scattering
He diffr. HEIS HREELS
Helium Diffraction High-Energy Ion Spectroscopy High-Resolution Electron Energy Loss Spectroscopy
ICISS ISS
Impact Collision Ion Scattering Spectroscopy Ion Scattering Spectroscopy
KLEED
Kinematic Low-Energy Electron Diffraction
Lando lt -Börnst ein New Ser ies III/42A2
4.1 Surface structure on metals and semiconductors
LEIS LEED LEPD
Low-Energy Ion Spectroscopy Low-Energy Electron Diffraction Low-Energy Positron Diffraction
MEED MEIS MEIS-SB
Medium-Energy Electron Diffraction Medium-Energy Ion Spectroscopy MEIS with Shadowing and Blocking
Neutr. diffr. NEXAFS NPD
Neutron Diffraction Near-Edge X-ray Absorption Fine Structure Normal Photoelectron Diffraction
OPD
Off-normal Photoelectron Diffraction
PED PES PEXAFS PLEED
Photoelectron Diffraction Photoelectron Spectroscopy Photoemission Extended X-ray Absorption Fine Structure (Spin-) Polarized LEED
QDLEED QKLEED
Quasi-Dynamic Low-Energy Electron Diffraction Quasikinematical Low-Energy Electron Diffraction
RBS RHEED
Rutherford Backscattering Reflection High-Energy Electron Diffraction
SEELFS SEXAFS SIMS SPLEED
Surface Electron Energy Loss Fine Structure Surface Extended X-ray Absorption Fine Structure Secondary Ion Mass Spectroscopy Spin-Polarized LEED
TEAS TED TOF-SARS
Thermal Energy Atomic Scattering Transmission Electron Diffraction Time-of-Flight Scattering and Recoiling Spectroscopy
XAFS XANES XAS XPD XPS XRD XSW
X-ray Absorption Fine Structure X-ray Absorption Near-Edge Structure X-ray Absorption Spectroscopy X-ray Photoelectron Diffraction X-ray Photoelectron Spectroscopy X-ray Diffraction X-ray Standing Wave
Lando lt -Bö rnst ein New Ser ies III/42 A2
4.1-13
4.1-14 Table 2. Structures of clean fcc(111) surfaces. Surface
∆d12 [%] 10 ± 2
∆d23 [%] 5.5 ± 2
∆d34 [%] 0±6
∆d45 [%] 0
∆d56 [%] 0
Ref.
Description
94S6
unreconstructed surface; exhibiting strong temperaturedependent interlayer spacings above 600K: top spacing grows from contraction of -2.5±0.5% below 600K to +10±2% at 1150K (wrt to bulk value); 2nd spacing grows from +0.6% to +5.5%; 3rd spacing shows smaller effect bulk termination with expanded top spacing bulk termination with expanded top spacing multilayer relaxation: expansion of the 1st and 2nd interlayer spacings unreconstructed surface with expanded top interlayer spacing bulk termination with expanded top interlayer spacing unreconstructed relaxed surface relaxed bulk termination relaxed bulk termination: possible slight expansion of top interlayer spacing unreconstructed surface with possible slight contraction of top interlayer spacing unreconstructed clean surface with negligible contraction of top interlayer spacing unreconstructed surface with expanded top interlayer spacing unrelaxed bulk termination bulk termination with top spacing contraction unreconstructed surface with multilayer relaxations unrelaxed bulk termination slight relaxation of top two interlayer spacings slight relaxation of top two interlayer spacings bulk termination with expanded top spacing
Ag(111)
Tech- Clean dbulk nique rec. [Å] MEIS no 2.36
Al(111) Al(111) Al(111)
LEED no LEED no LEED no
2.338 2.22 ± 1.3 2.329 0.91 ± 0.5 2.338 1.7 ± 0.3
0 0 0.5 ± 0.7
0 0 0
0 0 0
0 0 0
80J 82N1 90N
Al(111)
LEED no
2.338 1.3 ± 0.9
0
0
0
0
94S5
Al(111) Al(111) Cu(111) Cu(111)
no no no no
2.338 2.329 2.09 2.09
3.08 ± 2.1 1.33 ± 0.4 -0.67 ± 1 0.75 ± 1
0 0.04 ± 0.4 0 0
0 0 0 0
0 0 0 0
0 0 0 0
83M1 94B8 84L 95B1
Cu(111)
LEED LEED LEED VLEED XPD
no
2.09
-1.44 ± 1
0
0
0
0
97H1
Ni(111)
LEED no
2.035 -0.25 ± 1
0
0
0
0
93K1
Ni(111)
XPD
no
2.03
2.96
0
0
0
0
97H1
Ni(111) Ni(111) Pd(111) Pd(111) Pd(111) Pd(111) Pt(111)
HEIS LEED LEED HEIS LEED LEED LEED
no no no no no no no
2.033 2.03 2.246 2.25 2.27 2.246 2.265
0±1 -1.23 ± 1.2 2.41 ± 0.9 0 ± 4.4 0.88 ± 1.3 1.34 ± 1.3 1.1 ± 4.4
0 0 0.63 ± 0.9 0 -1.76 ± 1.3 -1.34 ± 1.3 0
0 0 0.63 ± 1.8 0 -1.76 ± 1.8 2.23 ± 1.3 0
0 0 0 0 0 0 0
0 0 0 0 0 0 0
81N1 75D 94G4 83K 94B4 87O 79A
4.1-15 Surface
Clean dbulk ∆d12 [Å] rec. [%] no 2.265 0.49 ± 0.9
∆d23 [%] 0
∆d34 [%] 0
∆d45 [%] 0
∆d56 [%] 0
Ref.
Description
81F
bulk termination with expanded top spacing unreconstructed relaxed bulk termination unreconstructed clean surface with slight first layer expansion unreconstructed surface with relaxed top two interlayer spacings; 0.5±0.4% contracted in-plane lattice parameter for all layers (incl. bulk) bulk termination with top spacing expansion unrelaxed bulk termination unreconstructed termination with relaxation of top two interlayer spacings unreconstructed relaxed bulk termination unrelaxed bulk termination slightly relaxed bulk termination
Pt(111) Pt(111)
Technique SPLEED LEED LEED
no no
2.26 1.33 ± 0.4 2.265 1.1 ± 1.3
0.44 ± 1.3 0.22
-1.33 ± 1.8 0 0 0
0 0
94B5 95M1
Pt(111)
LEED no
2.254 1.38 ± 0.6
-0.4 ± 0.7
0.22 ± 0.9
0
0
97G1
Pt(111) Pt(111) Rh(111)
MEIS no LEED no LEED no
2.268 1.41 ± 0.9 0 2.265 0 ± 2.2 0 2.196 -2.86 ± 1.4 0.16 ± 1.4
0 0 0
0 0 0
0 0 0
79V1 85H1 93W1
Rh(111) Rh(111) Rh(111)
LEED no LEED no LEED no
2.188 -1.28 ± 0.9 -1.28 ± 1.8 0.09 ± 2.3 2.192 0 ± 4.6 0 0 2.19 -1.37 ± 0.9 0 0
0 0 0
0 0 0
94B5 84V 80H
Pt(111)
Table 3. Adsorbate-induced structures on fcc(111) surfaces. Surface
Tech- Clean Adsnique rec. ind rec.
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 [Å]
Ref.
Description
adsorption at fcc-hollow sites (see Fig. 3) Ni(111)+ (√3x√3) R30°-Cl Ni(111)+ (√3x√3) R30°-O
AR- no PEFS
no
4.7 ± 0.0003 0
0
0
1.837 ± 0.0008 0
91W3
atomic adsorption in fcc-hollow site with contraction between the 1st and 2nd Ni layers
HEIS no
no
-4.2 ± 1.5
0
0
1.2
81N2
atomic adsorption (in undetermined hollow sites; fcc assumed here); expanded top Ni-Ni interlayer spacing
0
0
4.1-16 Tech- Clean Adsnique rec. ind rec. LEED no no
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 [Å]
Ref.
Description
0 ± 1.0
0
0
0
1.08 ± 0.02
0
91M2
SEno XAFS
no
0
0
0
0
1.16 ± 0.10
0
92H1
O adsorbed in fcc-hollow site; substrate has expanded 1st interlayer spacing; no lateral shifts or buckling oxygen adsorbed in fcc-hollow sites; no buckling in 1st Ni layer
LEED no
no
0.8 ± 2.0
0
0
0
1.59 ± 0.05
0
96W
LEED no
no
-3.9 ± 3.0
0
0
0
2.22 ± 0.06
0
93B2
LEED no
no
1.5 ± 0.9
0
2.5 ± 3.0
0
2.70 ± 0.03
0
94G4
LEED no
no
6.2 ± 2.2
0
0
0
1.29 ± 0.05
0
87O
LEED no
no
0.7 ± 1.3
0
0.6 ± 2.5
0
1.55 ± 0.03
0
97Y
atomic adsorption in fcc-hollow site; buckling in top two layers of substrate
LEED no
no
-0.9 ± 0.8 1.2 ± 1.3
-3.8 ± 1.7 1.3 ± 0.8
0 0
0 0
3.01 ± 0.04
0
97K1
Ag(111)+ (2x2)-K
LEED no
no
-0.9 ± 0.8 -0.1 ± 0.8
-4.2 ± 1.3 1.3 ± 0.8
0 0
0 0
1.52 ± 0.02
0
96L1
Ag(111)+ (2x2)-Rb
LEED no
no
-0.9 ± 0.8 -0.5 ± 0.8
-4.2 ± 0.1 1.3 ± 0.1
0 0
0 0
2.84 ± 0.03
0
96L1
atomic overlayer in fcc-hollow sites on unreconstructed substrate; with buckling in the first 2 substrate layers atomic overlayer in fcc-hollow sites on unreconstructed substrate; with buckling in the first 2 substrate layers atomic overlayer in fcc-hollow sites on unreconstructed substrate; with buckling in the first 2 substrate layers
Surface
Ni(111)+ (√3x√3) R30°-O Ni(111)+ (√3x√3) R30°-O Rh(111)+ (√3x√3) R30°-S Rh(111)+ (√3x√3) R30°-I Pd(111)+ (√3x√3) R30°-S Pd(111)+ (√3x√3) R30°-CO Pt(111)+ (√3x√3) R30°-S Ag(111)+ (2x2)-Cs
atomic adsorption on unreconstructed substrate: S adsorbs on fcc-hollow site; substrate relaxations negligible atomic adsorption in three fold fcc-hollow site on unreconstructed; relaxed Rh substrate atomic S in fcc-hollow site on unreconstructed; relaxed substrate; oscillitory expansion of top 4 Pd-Pd interlayer spacings molecular upright adsorption (C down) in fcchollow sites
4.1-17 Surface
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 [Å]
Ref.
Description
-2.3 ± 1.9 -2.5 ± 2.5
0 0.2 ± 2.6
-0.2 ± 5.0 -0.1 ± 6.7
0 0
2.07 ± 0.06
0
95M4
no
0.3 ± 1.5
2.0 ± 3.9
0
0
0.97 ± 0.08
0
93H1
no
5.7 ± 4.9
-1.5 ± 5.0; 0.0 ± 5.0
0
0
1.28 ± 0.05
0
95D1
complex reconstruction with overlayer and substitution: two Li adatoms located on fcc and hcp-hollow sites and one Li atom substituting for a Cu atom in each cell atomic adsorption with equal occupation of fcc and hcp-hollow sites; forming honeycomb-like lattice; buckling in 1st Ni layer: expansion of 2nd Ni-Ni interlayer spacing K atoms occupy atop sites; CO molecules perpendicular to surface; occupying fcc and hcphollow sites
no
1.7 ± 1.5
5.9 ± 1.5
5.0 ± 4.0
2.35
1.09 ± 0.03
0
90V3
Tech- Clean Adsnique rec. ind rec. LEED no no
Cu(111)+ (2x2)-3Li: 1 Li fcchollow site Ni(111)+ LEED no (2x2)-2H: 1 H at fcchollow site PED no Ni(111)+ (2x2)K+2CO: 1 CO at fcchollow site Ni(111)+ LEED no (2x2)-O
Ni(111)+ (2x2)-O
SEno XAFS
no
4.4 ± 4.9
8.3 ± 4.9
0
0
1.16 ± 0.10
0
92H1
Ni(111)+ (2x2)-O
LEED no
no
5.7 ± 1.0 0.8 ± 1.0
4.5 ± 1.0 -2.0 ± 1.0
0 0
0 0
1.11 ± 0.02
0
94S2
Ni(111)+ (2x2)-O Ni(111)+ (2x2)-S
PED
no
no
8.5 ± 5.0
4.9 ± 10.0
0
0
1.08 ± 0.10
0
96D1
LEED no
no
2.7 ± 1.5 2.2 ± 1.5
0 0
2.0 ± 2.0 0
0 0
1.5 ± 0.03
0
89W
oxygen adsorbed in fcc-hollow sites; buckling and lateral shifts in 1st Ni layer: 3 Ni next to O are lifted and rotated/outwards shifted; 1st Ni-Ni interlayer spacing contracts; deeper layers are bulk like oxygen adsorbed in fcc-hollow sites; buckling in 1st Ni layer S in fcc-hollow site on unreconstructed relaxed substrate: buckling in the first and second Ni layers; no evidence for rotation of hollow site atomic O overlayer in fcc-hollow sites on unreconstructed; slightly buckled substrate overlayer in 3-fold-hollow fcc sites; expansions of top 2 Ni-Ni interlayer spacings; lateral radial expansion of 3-fold site
4.1-18 Surface
Pt(111)+ (2x2)-C2H3
Tech- Clean Adsnique rec. ind rec. LEED no no
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 [Å]
Ref.
Description
-1.6 ± 4.4 -1.1 ± 4.4
-4.9 ± 4.4 -3.5 ± 4.4
-7.0 ± 5.5 0.2 ± 5.5
0 0
1.19 ± 0.10; 1.30 ± 0.10
0
93S4
ethylidyne species (CCH3=C2H3) formed from ethylene (C2H4) with upright C-C axis: lower C in fcc-hollow site; upper C forms methyl group (LEED data not sensitive to H positions); buckling in top 2 Pt layers densely packed molecular adsorption with 1 CO on top site; 1 CO on hcp-hollow site and 1 CO on fcchollow site; forms a buckled hexagonal overlayer on a relaxed substrate; substrate is buckled at the first layer densely packed molecular adsorption with 1 NO on top site; 1 NO on hcp-hollow site and 1 NO on fcc-hollow site; forms a buckled hexagonal overlayer on a relaxed substrate; substrate is buckled at the first layer atomic adsorption on unreconstructed relaxed substrate; adatom at fcc-hollow site coadsorption of atomic oxygen and molecular CO on relaxed substrate O on fcc-hollow site; CO on top site
Rh(111)+ LEED no (2x2)-3CO: 1CO at fcchollow site
no
3.1 ± 1.8 -0.1 ± 2.7
0.0 ± 1.8 3.7 ± 1.8
0.0 ± 7.0 -0.4 ± 7.0
0 0
1.47 ± 0.04
0
97G3
Rh(111)+ LEED no (2x2)-3NO: 1NO at fcchollow site
no
4.0 ± 1.8 -1.4 ± 2.7
0.0 ± 1.8 2.6 ± 1.8
0.0 ± 7.0 0.0 ± 7.0
0 0
1.30 ± 0.04
0
98Z
Rh(111)+ (2x2)-O Rh(111)+ (2x2)(O+1CO): O site Rh(111)+ (2x2)(O+2CO): O site Pt(111)+ (2x2)-C2H3
LEED no
no
4.8 ± 2.0
2.3 ± 2.3
0
0
1.24 ± 0.06
0
97S2
LEED no
no
5.3 ± 1.4
-1.8 ± 1.4
3.9 ± 3.8
0
1.28 ± 0.04
0
97S2
LEED no
no
4.4 ± 1.8
0.0 ± 2.3
1.3 ± 3.8
0
1.31 ± 0.09
0
97S2
coadsorption of atomic oxygen and molecular CO on unreconstructed; relaxed substrate; oxygen in fcc-hollow site; CO in top site and hcp-hollow site
LEED no
no
3.3 ± 1.3 -1.0 ± 4.4
4.9 ± 2.2 -3.5 ± 4.0
-6.0 ± 5.0 0.0 ± 5.0
0 0
1.49 ± 0.10
0
93S4
ethylidyne species (CCH3=C2H3) formed from ethylene (C2H4) with upright C-C axis: lower C in fcc-hollow site; upper C forms methyl group (LEED data not sensitive to H positions); buckling in top 2 Pt layers
4.1-19 Surface
Pt(111)+ (2x2)-O
Pt(111)+ (2x2)-NO Pt(111)+ (2x2)-S Ag(111)+ (3x3)-Cs
Tech- Clean Adsnique rec. ind rec. LEED no no
LEED no
no
LEED no
no
LEED no
no
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 [Å]
Ref.
Description
2.4 ± 1.3 -1.1 ± 1.3
3.1 ± 0.9 -0.9 ± 0.9
1.7 ± 2.0 0.1 ± 3.0
0 0
1.19 ± 0.02
0
95M1
2.4 ± 0.9 0 0.3 ± 2.2 3.5 ± 1.8 2.1 ± 0.8
3.1 ± 2.6 -0.9 ± 0.9 3.5 ± 1.8 3.5 ± 1.8 -4.2 ± 1.3; -4.7 ± 1.3 -1.7 ± 1.3; -2.5 ± 1.3 0; -1.3 ± 2.0; -1.7 ± 2.0 -3.4 ± 1.3; -3.8 ± 1.3 -1.7 ± 1.3; -2.5 ± 1.3 0; -1.3 ± 2.0; -1.7 ± 2.0
2.4 ± 1.2 -5.7 ± 1.2 1.9 ± 2.5 0.0 ± 3.8 0; 0 0; 0 0; 0; 0 0; 0 0; 0 0; 0; 0
0 0 0 0 0; 0 0; 0 0; 0; 0 0; 0 0; 0 0; 0; 0
1.26 ± 0.06
0
94M2
1.54 ± 0.03
0
97Y
3.02 ± 0.03
0
97K1
atomic overlayer in fcc-hollow sites on unreconstructed substrate; with buckling and lateral relaxation in the first 2 Pt layers; slight expansion and contraction of first two Pt-Pt interlayer spacings; resp. molecular adsorption perpendicular to surface in fcc 3-fold hollow sites on relaxed substrate atomic S adsorption on fcc-hollow sites; buckling in first layer of substrate atomic overlayer in fcc-hollow sites on unreconstructed substrate; with buckling in the first 3 substrate layers
2.72 ± 0.03
0
97K1
1.2 ± 1.3 0.0 ± 1.7
Ag(111)+ (3x3)-K
LEED no
no
2.0 ± 1.3 1.6 ± 2.0 -0.5 ± 3.8
atomic overlayer in fcc-hollow sites on unreconstructed substrate; with buckling in the first 3 substrate layers
4.1-20 Surface
Ag(111)+ (3x3)-Rb
Tech- Clean Adsnique rec. ind rec. LEED no no
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 [Å]
Ref.
Description
2.4 ± 0.8
-3.8 ± 1.3; -4.2 ± 1.3 -1.7 ± 1.3; -2.5 ± 1.3 0; -1.7 ± 1.3; -0.8 ± 1.3
0; 0 0; 0 0; 0; 0
0; 0 0; 0 0; 0; 0
2.84 ± 0.03
0
97K1
atomic overlayer in fcc-hollow sites on unreconstructed substrate; with buckling in the first 3 substrate layers
molecular coadsorption of one flat-lying C6H6 (benzene) and 2 upright CO per cell; all centered over fcc-hollow sites; both with relaxed bonds (H ignored); 1st substrate layer relaxed; topmost PdPd interlayer spacing expanded to 2.32Å (average) from bulk value of 2.25Å molecular coadsorption of one flat-lying C6H6 (benzene) and 2 upright CO per cell; all centered over fcc-hollow sites; both with relaxed bonds (H ignored); 1st substrate layer relaxed; topmost PdPd interlayer spacing expanded to 2.32Å (average) from bulk value of 2.25Å atomic overlayer with O adsorbed in fcc-hollow sites; possibly off-center toward top sites; top 2 substrate layers relaxed; both buckled atomic adsorption on unreconstructed relaxed substrate; adatom at fcc-hollow site molecular adsorption; C-O axis perpendicular to surface; CO occupy equally (0.25 ML each) fcc and hcp-hollow sites O atom sites not determined explicitly molecular adsorption in mixed fcc/hcp sites; CO tilted and bent away from nearest CO; buckled first and second Ni layers
1.2 ± 1.3 -0.5 ± 1.7
Pd(111)+ LEED no (3x3)-C6H6+ 2CO: 2CO sites
no
0.4 ± 2.2
0.0 ± 2.2; -2.2 ± 2.2
0; 3.2 ± 7.0
0; 0
1.22 ± 0.05; 1.31 ± 0.05
0
94B4
Pd(111)+ LEED no (3x3)-C6H6+ 2CO: C6H6 site
no
2.6 ± 2.2
0.0 ± 2.2; 2.2 ± 2.2
0; 0.8 ± 7.0
0; 0
2.16 ± 0.05
0
94B4
Rh(111)+ (2x1)-O
LEED no
no
-0.8 ± 0.1
-3.2 ± 0.05
0
0
1.18 ± 0.05
0
96C1
Rh(111)+ LEED no (2x1)-O PED no Ni(111)+ c(4x2)-2CO: 1CO at fcchollow site Ni(111)+ LEED no c(4x2)-2CO: 1CO at fcchollow site
no
3.9 ± 2.0
1.8 ± 2.0
0
0
1.23 ± 0.04
0
97S2
no
3.2 ± 7.4
0
0
0
1.29 ± 0.07
0
94D1
no
6.1 ± 4.9
5.9 ± 4.9; 4.9 ± 4.9
complex
0; 0
1.25 ± 0.10; 1.37 ± 0.10
0
94M1
4.1-21 Surface
Tech- Clean Adsnique rec. ind rec. LEED no no
Ni(111)+ c(4x2)-2NO: 1NO at fcchollow site Rh(111)+ LEED no c(4x2)-2S: 1 S at fcchollow site Rh(111)+ (disordered)-I
LEED no
no
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 [Å]
Ref.
Description
4.6 ± 2.0
7.3 ± 2.0; 0.0 ± 2.0
complex
0; 0
1.17 ± 0.04; 1.32 ± 0.04
0
94M2
molecular NO perp. to surface; in both fcc and hcp 3-fold hollow sites; relaxations in first 2 substrate layers
-2
-10.0; 0.2 -1.0; 0.5
complex
0; 0 0; 0
1.72; 1.49; 1.72
0
96W
atomic adsorption on unreconstructed substrate: equal occupation of fcc-hollow and hcp-hollow sites; S lateral shifts in both sites towards one of the nearby Rh atoms; to make S-S distances more equal; 1st Rh layer buckled atomic adsorption in three fold fcc-hollow site on unreconstructed; relaxed Rh substrate
-0.1 no
-3.9 ± 3.0
complex
0
0
0
2.22 ± 0.06
0
93B2
0.0 ± 2.0 0; 0.0 ± 2.0 0.0 ± 2.0 0; 0.0 ± 2.0 0.0 ± 2.0 0; 0.0 ± 2.0 0.0 ± 2.0
0 0; 0 0 0; 0 0 0; 0 0
3.10 ± 0.03
0
97K1
2.84 ± 0.03
0
96L1
2.97 ± 0.03
0
96L1
2.90 ± 0.03
0
96S1
0.0 ± 2.0
0
2.80 ± 0.03
0
96S1
adsorption at hcp-hollow sites (see Fig. 4) Ag(111)+ (√3x√3) R30°-Cs Ag(111)+ (√3x√3) R30°-K Ag(111)+ (√3x√3) R30°-Rb Rh(111)+ (√3x√3) R30°-Cs Rh(111)+ (√3x√3) R30°-K
LEED no
no
-0.1 ± 1.4 -0.5 ± 1.4
LEED no
no
-0.5 ± 0.8 0.0 ± 0.8
LEED no
no
-0.5 ± 0.8 0.0 ± 0.8
LEED no
no
-0.2 ± 1.4
0 0; 0.4 ± 1.4 0 0; 0.9 ± 0.8 0 0; 0.9 ± 0.8 0
LEED no
no
-1.1 ± 1.4
0
atomic overlayer in hcp-hollow sites on unreconstructed substrate; with buckling in the second substrate layer atomic overlayer in hcp-hollow sites on unreconstructed substrate; with buckling in the second substrate layer atomic overlayer in hcp-hollow sites on unreconstructed substrate; with buckling in the second substrate layer atomic adsorption on unreconstructed relaxed substrate; adatom at hcp-hollow site atomic adsorption on unreconstructed relaxed substrate; adatom at hcp-hollow site
4.1-22 Tech- Clean Adsnique rec. ind rec. LEED no no
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 [Å]
Ref.
Description
-0.2 ± 1.4
0
0.0 ± 2.0
0
2.84 ± 0.03
0
96S1
atomic adsorption on unreconstructed relaxed substrate; adatom at hcp-hollow site
LEED no
no
1.0 ± 0.8
0
0
0
2.71 ± 0.02
0
98M4
atomic adsorption on unreconstructed relaxed substrate; adatom at hcp-hollow site
LEED no
no
-2.1 ± 1.9 -2.7 ± 2.5
0 0; -0.2 ± 2.6
0.2 ± 5.0 0; 0
0 0; 0
2.15 ± 0.06
0
95M4
LEED no
no
1.8 ± 1.5
2.0 ± 3.9
0
0
0.97 ± 0.08
0
93H1
PED
no
no
5.7 ± 4.9
-1.5 ± 5.0; 0.0 ± 5.0
0; 0
0; 0
1.28 ± 0.05
0
95D1
complex reconstruction with overlayer and substitution: two Li adatoms located on fcc and hcp-hollow sites and one Li atom substituting for a Cu atom in each cell atomic adsorption with equal occupation of fcc and hcp-hollow sites; forming honeycomb-like lattice; buckling in 1st Ni layer: H-coordinated Ni atoms raised; expansion of 2nd Ni-Ni interlayer spacing K atoms occupy atop sites; CO molecules perpendicular to surface; occupying fcc and hcphollow sites
LEED no
no
-0.3 ± 1.0
-3.1 ± 0.9
0
0
2.68 ± 0.03
0
98M4
LEED no
no
4.6 ± 4.6 1.0 ± 4.6
3.6 ± 4.6 0; 0.0 ± 4.6
0.4 ± 6.1 0; 0.0 ± 0.2
0 0; 0
1.20 ± 0.10; 1.28 ± 0.10
0
94B5
Rh(111)+ LEED no (2x2)-3CO: 1CO at hcphollow site
no
6.7 ± 1.8 -3.8 ± 2.7
0.0 ± 1.8 0; -3.6 ± 1.8
-0.4 ± 6.1 0; 0.0 ± 0.2
0 0; 0
1.47 ± 0.07; 1.47 ± 0.07
0
97G3
Rh(111)+ (2x2)-K
no
-1.6 ± 1.4
-1.8 ± 1.4
0.0 ± 2.0
0
2.78 ± 0.03
0
96S1
Surface
Rh(111)+ (√3x√3) R30°-Rb Pt(111)+ (√3x√3) R30°-K Cu(111)+ (2x2)-3Li: 1 Li at hcphollow site Ni(111)+ (2x2)-2H: 1 H at hcphollow site Ni(111)+ (2x2)K+2CO: 1 CO at hcphollow site Pt(111)+ (2x2)-K Rh(111)+ (2x2)-C2H3
LEED no
atomic adsorption on unreconstructed relaxed substrate; adatom at hcp-hollow site ethylidyne species (CCH3 = C2H3) formed from ethylene (C2H4) with upright C-C axis: lower C in hcp-hollow site; upper C forms methyl group; buckling in top 2 Rh layers densely packed molecular adsorption with 1 CO on top site; 1 CO on hcp-hollow site and 1 CO on fcchollow site; forms a buckled hexagonal overlayer on a relaxed substrate; substrate is buckled at the first layer atomic adsorption on unreconstructed relaxed substrate; adatom at hcp-hollow site
4.1-23 Surface
Rh(111)+ (2x2)-3NO: 1NO at hcphollow site Rh(111)+ (3x3)-C6H6+ 2CO: 2CO sites Rh(111)+ (3x3)-C6H6+ 2CO: C6H6 site Ni(111)+ c(4x2)-2CO: 1CO at hcphollow site Ni(111)+ c(4x2)-2CO: 1CO at hcphollow site
Tech- Clean Adsnique rec. ind rec. LEED no no
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 [Å]
Ref.
Description
7.2 ± 1.8 -1.5 ± 2.7
0.0 ± 1.8 0; -2.7 ± 1.8
0.0 ± 6.1 0; 0.0 ± 0.2
0 0; 0
1.29 ± 0.07
0
98Z
densely packed molecular adsorption with 1 NO on top site; 1 NO on hcp-hollow site and 1 NO on fcc-hollow site; forms a buckled hexagonal overlayer on a relaxed substrate; substrate is buckled at the first layer molecular coadsorption of one flat-lying C6H6 (benzene) and 2 upright CO per cell; all centered over hcp-hollow sites; both with relaxed C-C bonds (H ignored); 1st substrate layer relaxed molecular coadsorption of one flat-lying C6H6 (benzene) and 2 upright CO per cell; all centered over hcp-hollow sites; both with relaxed C-C bonds (H ignored); 1st substrate layer relaxed molecular adsorption; C-O axis perpendicular to surface; CO occupy equally (0.25 ML each) fcc and hcp-hollow sites O atom sites not determined explicitly molecular adsorption in mixed fcc/hcp sites; CO tilted and bent away from nearest CO; buckled first and second Ni layers
LEED no
no
-1.1 ± 3.2
-0.9 ± 3.2; -0.9 ± 3.2
-0.7 ± 6.1; -2.1 ± 6.1
0; 0
1.36 ± 0.10; 1.39 ± 0.10
0
94B4
LEED no
no
-1.1 ± 3.2
0.9 ± 2.2; 0.9 ± 3.2
0; -3.9 ± 6.1
0; 0
2.07 ± 0.04
0
94B4
PED
no
no
3.2 ± 7.4
0
0
0
1.30 ± 0.07
0
94D1
LEED no
no
6.1 ± 4.9
-4.9 ± 4.9; -5.9 ± 4.9 0; -3.9 ± 4.9; -1.5 ± 4.9
complex
0; 0 0; 0; 0
1.37 ± 0.10; 1.27 ± 0.10; 1.25 ± 0.10
0
94M1
-4.6 ± 4.9
complex
4.1-24 Surface
Ni(111)+ c(4x2)-2NO: 1NO at hcphollow site
Rh(111)+ c(4x2)-2S: 1 S at hcphollow site
Tech- Clean Adsnique rec. ind rec. LEED no no
LEED no
no
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 [Å]
Ref.
Description
-1.2 ± 2.0
-7.4 ± 2.0; 0.0 ± 2.0
complex
0; 0
1.32 ± 0.04; 1.17 ± 0.04; 1.32 ± 0.04
0
94M2
molecular NO perp. to surface; in both fcc and hcp 3-fold hollow sites; relaxations in first 2 substrate layers
-0.7 ± 2.0
0; -1.5 ± 2.0; -2.5 ± 2.0
complex
0; 0; 0
-1.9
-10.3; -0.2 0; -0.3; -1.5 -3.9 ± 3.4; -6.9 ± 3.4
complex
0; 0 0; 0; 0 0; ± 1.6; ± 2.5
1.72; 1.49; 1.72
0
96W
1.93 ± 0.05; 2.01 ± 0.05; 2.01 ± 0.05
0
96H2
atomic adsorption on unreconstructed substrate: equal occupation of fcc-hollow and hcp-hollow sites; S lateral shifts in both sites towards one of the nearby Rh atoms; to make S-S distances more equal; 1st Rh layer buckled molecular C6H6 centered on hcp sites on unreconstructed substrate; C-C bonds parallel to [110] direction; slight ring expansion; no significant buckling of benzene; strong buckling of top Ni layer molecular C6H6 centered on hcp sites on unreconstructed substrate; C-C bonds parallel to [110] direction; slight ring expansion; no significant buckling of benzene; strong buckling of top Ni layer
-0.4
complex
Ni(111)+ ( LEED no √7x√7) R19°-C6H6: high C
no
2.5 ± 3.0
0; 0.8 ± 5.8
Ni(111)+ LEED no (√7x√7) R19°-C6H6: low C
no
2.5 ± 3.0
-3.9 ± 3.4; -6.9 ± 3.4
0; 0.8 ± 5.8
0; 1.97 ± 0.05; ± 1.6; 2.05 ± 0.05; ± 2.5 2.05 ± 0.05
0
96H2
-5.5 ± 2.1
0; -10.7 ± 1.7
0; 0
0; 0
0
94S5
adsorption at top sites (see Fig. 5) Al(111)+ (√3x√3) R30°-K (90K)
LEED no
no
3.23 ± 0.05
atomic K in top site on unreconstructed but relaxed substrate: Al directly below K depressed into bulk; Al in next layer laterally displaced by small shift; perpendicular relaxation between top two Al layers
4.1-25 Tech- Clean Adsnique rec. ind rec. LEED no no
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 [Å]
Ref.
Description
-5.8 ± 0.9
0, -11.4 ± 0.9
0; 0
0; 0
3.36 ± 0.03
0
94N2
adatoms in top sites of unreconstructed relaxed substrate: downward buckling of Al directly below Rb in top Al layer
LEED no
no
8.1 ± 2.3
97G3
no
1.7 ± 4.6 -8.6 ± 2.9
0; 0 0 0; 0
0
no
0; 0 0.0 ± 7.3 0; 0
1.20 ± 0.05
PED
0; 3.6 ± 2.7 0 0; -0.5 ± 4.4
2.87 ± 0.04
0
94D2
Ni(111)+ (2x2)-K
AR- no PEFS
no
-6.4 ± 2.0
0
0
0
3.02 ± 0.01
0
93H5
Ni(111)+ (2x2)-K
LEED no
no
-4.2 ± 1.5
0; -5.9 ± 1.0
0; 0
0; 0
2.82 ± 0.04
0
93K1
PED no Ni(111)+ (2x2)K+2CO: 1 K at top site Rh(111)+ LEED no (2x2)-3CO: 1 CO at top site
no
6.2 ± 4.9
0; 0.5 ± 5.0
0; 0
0; 0
3.02 ± 0.05
0
95D1
molecular adsorption at top sites: CO upright; C down on relaxed substrate; top substrate layer slightly buckled K atoms occupy atop sites; outer Ni layer spacing contracted but no significant buckling; K has large vibrational amplitude parallel to surface atomic adsorption on top sites; with contraction of first Ni interlayer spacing; negligible lateral relaxations and buckling atomic adsorption on top sites; with buckling of the first two Ni layer and small horizontal relaxation of the top Ni layer (within error bars) K atoms occupy atop sites; CO molecules perpendicular to surface; occupying fcc and hcphollow sites
no
3.1 ± 1.8
0; 0.0 ± 1.8 3.6 ± 1.8
0; 0.0 ± 0.2 -0.6 ± 7.0
0; 0 0
1.83 ± 0.07
0
97G3
Rh(111)+ LEED no (2x2)-Cs Rh(111)+ LEED no (2x2)-3NO: 1 NO at top site
no
-1.6 ± 1.5
0; 0 0; 0 0
0
96S1
4.5 ± 1.8
0; 0 0; 0.0 ± 0.2 0.0 ± 6.1
2.96 ± 0.03
no
0; -1.8 ± 1.4 0; 0.0 ± 1.8 2.7 ± 1.8
1.76 ± 0.07
0
98Z
Surface
Al(111)+ (√3x√3) R30°-Rb (100K) Rh(111)+ (√3x√3) R30°-CO Ni(111)+ (2x2)-K
-0.2 ± 2.7
1.2 ± 2.7
densely packed molecular adsorption with 1 CO on top site; 1 CO on hcp-hollow site and 1 CO on fcc-hollow site; forms a buckled hexagonal overlayer on a relaxed substrate; substrate is buckled at the first layer atomic adsorption on unreconstructed unrelaxed substrate; adatom at top site densely packed molecular adsorption with 1 NO on top site; 1 NO on hcp-hollow site and 1 NO on fcc-hollow site; forms a buckled hexagonal overlayer on a relaxed substrate; substrate is buckled at the first layer
4.1-26 Surface
Tech- Clean Adsnique rec. ind rec. LEED no no
Rh(111)+ (2x2)(O+1CO): CO at top site Rh(111)+ LEED no (2x2)(O+2CO): 1 CO at top site
no
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 [Å]
Ref.
Description
5.3 ± 1.4
0; 1.8 ± 1.4
0; 0.0 ± 0.1
0; 0
1.83 ± 0.05; 1.87 ± 0.05
0
97S2
coadsorption of atomic oxygen and molecular CO on relaxed substrate O on fcc-hollow site; CO on top site
4.4 ± 2.3
0; 0.0 ± 2.2
0; 0.0 ± 0.1
0; 0
1.86 ± 0.05; 1.86 ± 0.05
0
97S2
coadsorption of atomic oxygen and molecular CO on unreconstructed; relaxed substrate; oxygen in fcc-hollow site; CO in top site and hcp-hollow site
distorted molecular adsorption on relaxed; unreconstructed substrate: C-N axis near parallel to surface with N near fcc 3-fold hollow site and N near bridge site; C-C-N bond angle is 123±15° (vs. 180° for free molecule; making methyl (CH3) group of acetonitrile points away from surface; molecular adsorption; C-C axis (almost) parallel to surface: molecule in aligned-bridge site with C atoms almost directly above top layer Ni atoms; C-C bond extended ~0.27Å relative to gas phase molecule
molecular adsorption with adatoms at low-symmetry sites Ni(111)+ (2x2)CH3CN
LEED no
no
94G1
Ni(111)+ (disordered)C2H4
PED
no
94B2
no
adsorption at substitutional site in top substrate layer (see Fig. 6) Ag(111)+ (√3x√3) R30°-Sb
CA- no ICISS
yes
0
0
0
0
0
0
97N2
atomic Sb adsorbate substitutional in outermost layer site
4.1-27 Surface
Al(111)+ (√3x√3) R30°-K (300K) Al(111)+ (√3x√3) R30°-Li Al(111)+ (√3x√3) R30°-Na Al(111)+ (√3x√3) R30°-Na Al(111)+ (√3x√3) R30°-Na Al(111)+ (√3x√3) R30°-Na+O Al(111)+ (√3x√3) R30°-Rb (300K) Al(111)+ (√3x√3) R30°-Rb (300K) Cu(111)+ (√3x√3) R30°-Sn
Tech- Clean Adsnique rec. ind rec. LEED no yes
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 [Å]
Ref.
Description
-1.9 ± 1.0
0
0
0
2.16 ± 0.03
0
94S5
LEED no
yes
-1.7 ± 0.9 -0.8 ± 0.9
0 0
0 0
0 0
0.41 ± 0.1
0
96N
atomic K in quasi-substitutional sites formed by ejection of 1/3 of top-layer Al; perpendicular relaxation between top two Al layers; no lateral relaxations adatoms in substitutional sites in top Al layer
SEno XAFS
yes
-0.0 ± 1.3
0
0
0
1.67 ± 0.03
0
91S1
Na in a sixfold substitutional site
XSW no
yes
0
0
0
0
1.20 ± 0.2
0
92K1
Na atom in substitutional sites in top Al layer
LEED no
yes
-2.5 ± 1.1
0
0
0
1.47 ± 0.02
0
94B8
atomic adsorption in substitutional sites; replacing one third of atoms in top Al layer
XSW no
yes
0
0
0
0
1.20 ± 0.08
0
95S2
LEED no
yes
-2.7 ± 0.9
0
0
0
2.41 ± 0.02
0
94N2
Na atom in substitutional sites of reconstructed substrate; O atop Na atoms; substrate atom positions assumed bulk-like adatoms in substitutional sites in top Al layer
XSW no
yes
0
0
0
0
2.39 ± 0.10
0
94S4
Rb adatoms in substitutional sites on reconstructed substrate; substrate atom positions assumed bulklike
LEIS no
yes
0
0
0
0
0.39 ± 0.10
0
92O3
substitutional adsorption within top substrate layer; forming single layer thick surface alloy; with Sn atoms buckled outwards
4.1-28 Surface
Pt(111)+ (√3x√3) R30°-Sn Pt(111)+ (√3x√3) R30°-Sn Pt(111)+ (√3x√3) R30°-Sn Rh(111)+ (√3x√3) R30°-Sn Cu(111)+ (2x2)-3Li: 1 Li in subst. site Pt(111)+ (2x2)-Sn Pt(111)+ (2x2)-Sn
Tech- Clean Adsnique rec. ind rec. AL- no yes ICISS
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 [Å]
Ref.
Description
0
0
0
0
0.22 ± 0.05
0
91O3
atomic substitutional adsorption in fcc-hollow site; approximating Pt3Sn(111) termination substitutional adsorption within top substrate layer; forming single layer thick surface alloy; with Sn atoms buckled outwards substitutional adsorption within top substrate layer; forming single layer thick surface alloy; with Sn atoms buckled outwards atomic substitutional adsorption in fcc-hollow site; approximating Rh3Sn (111) termination
LEIS no
yes
0
0
0
0
0.22 ± 0.10
0
92O3
LEED no
yes
-0.2 ± 2.2 2.9 ± 4.4
0 0
0 0
0
0.23 ± 0.05
0
93A
AL- no ICISS XPD
yes
0.0 ± 2.3
0
0.29 ± 0.05
0
97L1
LEED no
yes
-2.3 ± 1.9 -2.5 ± 2.5
0 0.2 ± 2.6
0 0
0 0
0.60 ± 0.06
0
95M4
AL- no ICISS LEED no
yes
0
0
0
0
0.22 ± 0.05
0
91O3
yes
-0.2 ± 2.2 2.0 ± 4.4
0 0
0 0
0 0
0.30 ± 0.05
0
93A
yes
0
0
0
0
1.20 ± 0.2
0
92K1
Na atom in substitutional sites in top Al layer
97N2
atomic 1/4 ML Sb (2x2) overlayer adsorbed in hcp-hollow sites on mixed (√3x√3)R30° Ag+Sb layer containing 1/3 ML Sb
Al(111)+ XSW no (disordered)-Na
complex reconstruction with overlayer and substitution: two Li adatoms located on fcc and hcp-hollow sites and one Li atom substituting for a Cu atom in each cell atomic substitutional adsorption in fcc-hollow site; approximating Pt3Sn(111) termination substitutional adsorption within top substrate layer; forming single layer thick surface alloy; with Sn atoms buckled outwards
adsorption at substitutional site in top substrate layer and as overlayer Ag(111)+ (2√3x2√3) R30° -7Sb
CA- no ICISS
yes
4.1-29 Surface
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 [Å]
Ref.
Description
yes
94B1
ordered mixed alloy in top two layers: relaxation of top two interlayer spacings
surface alloy structure: Na-Al-Na 'sandwich' on a reconstructed Al layer with a (2x2) vacancy structure; lower Na in substitutional site in Al vacancy; upper Na in fcc sites; sandwich Al in hcp sites surface alloy structure: Na-Al-Na 'sandwich' on a reconstructed Al layer with a (2x2) vacancy structure; lower Na in substitutional site in Al vacancy; upper Na in fcc sites; sandwich Al in hcp sites composite double-layer surface alloy: 1 Na atom substituting for a surface Al atom; 1 Na atom in a fcc-hollow adsorption site; 1 Al atom in a hcphollow adsorption site ternary surface alloy: K-Al-Na 'sandwich' on a reconstructed Al layer with a (2x2) vacancy structure; Na in substitutional site in Al vacancy; K in fcc sites above 2nd-layer Al; sandwich Al in hcp sites
Tech- Clean Adsnique rec. ind rec.
adsorption at substitutional site in top two substrate layers Au(111)+ (√3x√3) R30°-4Pd
LEED yes
complex reconstruction Al(111)+ (2x2)-2Na
LEED no
yes
95B5
Al(111)+ (2x2)-2Na
SEno XAFS
yes
95B5
Al(111)+ (2x2)-2Na
XPD
no
yes
95F1
Al(111)+ LEED no (2x2)-Na+K
yes
96C2
4.1-30 Surface
Rh(111)+ (√7x√7) R19°-3P
Tech- Clean Adsnique rec. ind rec. LEED no yes
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 [Å]
Ref.
Description
97L2
reconstruction with packed Rh pentagons and triangles; 3 symm.-equivalent P atoms per unit cell in 8-fold coordinated sites; these form a dense; relatively coplanar layer (buckled 0.17Å); 2nd and 3rd layers are pure Rh; buckled 0.06Å and 0.08Å resp.; vs bulk reconstructed mixed top layer of stoichiometry CuS commensurate with substrate; Cu atoms in this CuS layer are coplanar; 2/3 of S lie ~0.56Å below this Cu layer in hollow sites relative to bulklike substrate; other 1/3 S lie about coplanar with top Cu; over top site of substr. complex reconstruction forming Cu4S units (1 per unit cell); each having a S atom adsorbed in the fourfold site on top of a Cu tetramer; additional S atoms are present at a level just below the Cu4 plane; the positions of these atoms relative to the bulk are undetermined complex reconstruction forming Cu4S units (2 per unit cell); each having a S atom adsorbed in the fourfold site on top of a Cu tetramer; additional S atoms are present at a level just below the Cu4 plane; the positions of these atoms relative to the bulk are undetermined S overlayer on 'clock-reconstructed' pseudo-(100) Ni outer layer such that S atoms have two different layer spacings; one from a 'dropped' layer at regular fault-lines in the reconstruction; note: outer layer Ni x,y coordinates are indicative only; as is exact substrate registry
Cu(111)+ (√7x√7) R19°-3S
XSW no SEXAFS
yes
90P2
Cu(111)+ (√7x√7) R19°-3S
XRD no
yes
97F2
Cu(111)+ XRD no (4,1/-1,4)-6S
yes
97F2
Ni(111)+ (5√3x2) rect-8S
yes
96L4
XSW no
4.1-31 Table 4. Structures of clean hcp(0001) surfaces. ∆d12 [%] 5.1 ± 0.4
∆d23 [%] -0.2 ± 0.5
∆d34 [%] 0.2 ± 0.5
∆d45 [%] 0
∆d56 [%] 0
Ref.
Description
Be(0001)
Tech- Clean dbulk nique rec. [Å] LEED no 1.79
92D
Co(0001) Gd(0001) Gd(0001) Mg(0001) Ru(0001) Sc(0001)
LEED LEED LEED LEED LEED LEED
0.0 ± 2.4 -1.4 ± 1.0 -1.4 ± 0.5 2.7 ± 0.3 -1.8 ± 0.9 -1.9 ± 0.8
0 2.1 ± 1.0 1.0 ± 0.5 0.8 ± 4.0 0 0
0 0 0 -0.4 ± 0.5 0 0
0 0 0 0 0 0
0 0 0 0 0 0
78L 92Q2 95G3 93S3 83M3 82T2
Tb(0001) Ti(0001)
LEED no LEED no
2.847 -5.3 ± 1.1 2.34 -2.1 ± 2.1
1.4 ± 1.1 0
0 0
0 0
0 0
91Q 76S1
Zn(0001) Zr(0001)
LEED no LEED no
2.44 2.57
0 0
0 0
0 0
0 0
75U 79M
bulk termination with large expansion of top interlayer spacing bulk hcp termination multilayer relaxation unreconstructed with multilayer relaxation bulk termination with top spacing expansion bulk termination with top spacing contraction bulk-like termination with contraction of top interlayer spacing multilayer relaxation bulk-like termination with contraction of top interlayer spacing bulk termination with top spacing contraction bulk hcp termination with top spacing contraction
Surface
no no no no no no
2.05 2.89 2.89 2.592 2.14 2.64
-2.0 ± 2.0 -1.7 ± 1.9
Table 5. Adsorbate-induced structures on hcp(0001) surfaces. Surface
Tech- Clean Adsnique rec. ind rec.
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 Ref. [Å]
Description
atomic adsorption in fcc-hollow sites; with slight contraction of topmost Ru-Ru interlayer spacing two O layers are present in the structure; one forms an overlayer in which the O bonds to 3fold hollow sites on the Zr surface; the other layer has the O atoms in tetrahedral hole sites between the first two Zr layers
adsorption at fcc-hollow sites (see Fig. 7) Ru(0001)+ (1x1)-H Zr(0001)+ (1x1)-2O: 1 O at fcchollow sites
LEED no
no
-1.8 ± 1.4
0
0
0
1.10 ± 0.06
0
87L2
LEED no
yes
33.7 ± 1.9
0
0
0
0.89 ± 0.05
0
97W
4.1-32 Surface
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 Ref. [Å]
Description
1.4 ± 1.9
8.9 ± 1.9
0
0
1.52 ± 0.03; 1.71 ± 0.03
0
95O2
Cs adsorption in on-top site; pronounced buckling in top substrate layer; CO in threefold coordinated hcp and fcc sites
no
-1.0 ± 1.4
0
0
0
2.90 ± 0.04
0
92G
no
-1.4 ± 1.4
0
0
0
2.50 ± 0.04
0
94H3
no
-0.5 ± 0.7 -0.5 ± 1.0
-8.8 ± 0.7 2.3 ± 1.0
-0.7 ± 2.8 3.0 ± 2.3 0.6 ± 3.5 0.8 ± 3.0
1.42 ± 0.05; 1.23 ± 0.05
0
97S4
no
0.9 ± 2.3
-5.6 ± 1.4
-5.1 ± 4.5 0
1.39 ± 0.07; 1.27 ± 0.07
0
99S1
atomic adsorption in fcc-hollow site on nearly unrelaxed substrate atomic adsorption in fcc-hollow site on nearly unrelaxed substrate intact molecular adsorption in top; hcp and fcc sites; upright orientation with the N end down; significant different site-specific inner NO bondlengths: NO(top)=1.13; NO(hcp/fcc)=1.24/1.22Å; significant buckling in top metal layer O in hcp-hollow site; NO in top and fcc-hollow sites
no
-0.5 ± 1.4
-3.3 ± 1.4
0.0 ± 4.5
-6.1 ± 3.0 1.39 ± 0.07; 1.26 ± 0.07
0
99S1
O in fcc and hcp-hollow sites; NO in top site
no
9.3 ± 0.9
4.2 ± 0.9
-5.2 ± 5.0 0
0
94N1
O atoms adsorbed in hcp and fcc sites; forming honeycomb pattern; CO molecules adsorbed upright in top sites; relaxations in topmost Ru layer in both lateral and perpendicular directions
Tech- Clean Adsnique rec. ind rec. LEED no no
Ru(0001)+ (2x2)Cs+2CO: 1 CO at fcchollow site Ru(0001)+ LEED no (2x2)-K Ru(0001)+ LEED no (2x2)-Na Ru(0001)+ LEED no (2x2)-3NO: 1 NO at fcchollow site
Ru(0001)+ LEED no (2x2)O+2NO: 1 NO at fcchollow site Ru(0001)+ LEED no (2x2)2O+NO: 1 O at fcc-hollow site Ru(0001)+ LEED no (2x2)2O+CO: 1 O at fcc-hollow site
1.42 ± 0.08; 1.51 ± 0.08
4.1-33 Tech- Clean Adsnique rec. ind rec. LEED no no
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 Ref. [Å]
Description
-1.9 ± 2.3
-2.8 ± 1.9
0
0
3.04 ± 0.05; 2.98 ± 0.05
0
94H2
LEED no
no
1.8 ± 2.8
0.9 ± 2.8
complex
0
1.32 ± 0.2; 1.34 ± 0.2
0
92H2
Ru(0001)+ LEED no c(4x2)-2S: 1 S near fcchollow site
no
-4.7 ± 0.9
-7.9 ± 0.9; -0.9 ± 0.9 0.5 ± 0.9
complex
1.79 ± 0.02; 1.60 ± 0.02; 1.77 ± 0.02
0
94S3
complex
0; 0 0
atomic adsorption in 3-fold coordinated fcc site on unreconstructed substrate; anisotropic thermal distribution of Rb; large parallel root mean square displacement = 0.37Å adsorption roughly on threefold fcc sites; buckling and pairing reconstruction of the first metal layer; slight expansion of the first metal interlayer spacing S close to hcp and fcc-hollow sites shifted away from symmetric positions; buckling and lateral shifts of rows in the first substrate layer; buckling in the second substrate layer
Surface
Ru(0001)+ (2x2)-Rb
Ru(0001)+ (2x1)-H
-1.5 ± 0.9
adsorption at hcp-hollow sites (see Fig. 8) Ru(0001)+ (1x1)-O Ru(0001)+ (√3x√3) R30°-Cs
LEED no
no
3.7
0
0
0
1.25
0
96S2
LEED no
no
-1.9 ± 1.9 -0.9 ± 3.3
0
0
0
3.15 ± 0.03
0
92O1
Ru(0001)+ LEED no (√3x√3) R30°-Cs+O: Cs site Ru(0001)+ LEED no (√3x√3) R30°-Cs+O: O site
no
-2.8 ± 1.0
0
0
0
3.04 ± 0.03
0
92O2
no
-2.8 ± 1.0
0
0
0
1.52 ± 0.07
0
92O2
atomic adsorption on unreconstructed relaxed substrate; adatom at hcp-hollow site; atomic adsorption in hcp-hollow sites of unreconstructed substrate; relaxations in top 2 Ru-Ru interlayer spacings; no detectable lateral relaxations adsorption of Cs and O in hcp-hollow sites; change of O-Ru bond length due to coadsorption of Cs adsorption of Cs and O in hcp-hollow sites; change of O-Ru bond length due to coadsorption of Cs
4.1-34 Surface
Ru(0001)+ (√3x√3) R30°-K Ru(0001)+ (√3x√3) R30°-Li Ru(0001)+ (√3x√3) R30°-N Ru(0001)+ (√3x√3) R30°-Na Ru(0001)+ (√3x√3) R30°-Rb
Tech- Clean Adsnique rec. ind rec. LEED no no
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 Ref. [Å]
Description
-1.9 ± 2.3
0
0
0
2.94 ± 0.04
0
92G
atomic adsorption in hcp-hollow site on nearly unrelaxed substrate
0 0; 0 1.3 ± 2.8
0 0; 0 0
2.25 ± 0.05
0
95G2
1.10 ± 0.06
0
97S3
atomic adsorption in 3-fold hcp-hollow site on unreconstructed substrate; buckling in 2nd substrate layer atomic adsorption on unreconstructed relaxed substrate; adatom at hcp-hollow site
LEED no
no
-2.4 ± 2.3 1.3 ± 2.3
LEED no
no
-0.9 ± 2.3
0 0; 2.3 ± 1.9 0
LEED no
no
-0.9 ± 2.3
0
0
0
2.51 ± 0.05
0
94H3
atomic adsorption in hcp-hollow site on nearly unrelaxed substrate
LEED no
no
-0.9 ± 2.3
0
0
0
3.03 ± 0.05
0
94H2
LEED no
no
-1.0 ± 0.9
0
0
0
1.67 ± 0.02
0
94J2
LEED no
no
-4.5 ± 3.6 4.6 ± 3.1
2.2 ± 3.1 0; 2.8 ± 3.6
1.4 ± 4.4 0; 0
0 0; 0
1.68 ± 0.04; 1.73 ± 0.07
0
94B3
Ru(0001)+ LEED no (2x2)Cs+CO: CO at hcp-hollow site
no
1.4 ± 1.9
8.4 ± 1.9
0
0
1.47 ± 0.04; 1.65 ± 0.04
0
95O2
atomic adsorption in 3-fold coordinated hcphollow site on unreconstructed substrate; anisotropic thermal distribution of Rb; large parallel root mean square displacement = 0.37Å S in hcp-hollow sites on unreconstructed; relaxed substrate: no lateral shifts or buckling in the substrate adatoms in 3-fold hcp-hollow sites; contracted average first and second substrate interlayer spacings of 2.16 and 2.18Å; resp.; compared to 2.23Å for the bulk Cs adsorption in on-top site; pronounced buckling in top substrate layer; CO in threefold coordinated hcp sites between Cs atoms
Ru(0001)+ (√3x√3) R30°-S Re(0001)+ (2x2)-S
4.1-35 Surface
Ru(0001)+ (2x2)Cs+2CO: 1 CO at hcphollow site Ru(0001)+ LEED no (2x2)-N Ru(0001)+ LEED no (2x2)-3NO: 1NO at hcphollow site
Ru(0001)+ (2x2)-O
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 Ref. [Å]
Description
1.4 ± 1.9
8.9 ± 1.9
0
0
1.52 ± 0.03; 1.71 ± 0.03
0
95O2
Cs adsorption in on-top site; pronounced buckling in top substrate layer; CO in threefold coordinated hcp and fcc-sites
no
-1.0 ± 2.3
3.3 ± 2.3
0
0
0
97S3
no
1.8 ± 0.7
-8.8 ± 0.7
0
97S4
-2.8 ± 1.0
0; -2.3 ± 1.0
1.05 ± 0.05; 1.12 ± 0.05 1.0 ± 2.8 -3.0 ± 2.3 1.31 ± 0.05; 1.12 ± 0.05 0; 0; -0.8 ± 3.5 0.8 ± 3.0
-2.3 ± 1.4 3.7 ± 1.4
3.3 ± 1.4 0; 3.7 ± 1.4
5.4 ± 6.4 0; 0
0
89L5
atomic adsorption on unreconstructed relaxed substrate; adatom at hcp-hollow site intact molecular adsorption in top; hcp and fcc sites; upright orientation with the N end down; significant different site-specific inner NO bond lengths: NO(top)=1.13; NO(hcp/fcc)=1.24/1.22Å; significant buckling in top metal layer atomic adsorption in hcp-hollow sites; slight contraction of first Ru-Ru interlayer spacing while second spacing essentially bulk-like; buckling of first and second Ru layers O atoms adsorbed in hcp sites; CO molecules adsorbed in top sites; tilted by 12.6°; relaxations of topmost Ru layer in both lateral and vertical directions CO tilt could be either vibrational or static O atoms adsorbed in hcp and fcc sites; forming honeycomb pattern; CO molecules adsorbed upright in top sites; relaxations in topmost Ru layer in both lateral and perpendicular directions
Tech- Clean Adsnique rec. ind rec. LEED no no
LEED no
no
0 0; 0
1.18 ± 0.03; 1.25 ± 0.03
Ru(0001)+ LEED no (2x2)-O+CO: O at hcphollow site
no
Ru(0001)+ LEED no (2x2)2O+CO: 1 O at hcp-hollow site Ru(0001)+ LEED no (2x2)(O+N2): O at hcp-hollow site
no
-3.3 ± 0.9
4.2 ± 0.9
5.2 ± 5.0
0
1.23 ± 0.08; 1.32 ± 0.08
0
94N1
no
-2.8 ± 2.8
3.3 ± 2.8
6.4 ± 2.8
0
1.25 ± 0.06; 1.32 ± 0.06
0
95O1
95N
coadsorption of atomic oxygen and molecular dinitrogen on unreconstructed; relaxed substrate; oxygen in hcp-hollow site; N2 on top site; perpendicular to surface
4.1-36 ∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 Ref. [Å]
Description
0.9 ± 1.9
-6.5 ± 1.4
6.4 ± 4.3
0
1.19 ± 0.05; 1.05 ± 0.05
0
99S1
O and NO in hcp-hollow sites
3.4 ± 2.3
-5.6 ± 1.4
5.1 ± 4.5
0
1.21 ± 0.07; 1.09 ± 0.07
0
99S1
O in hcp-hollow site; NO in top and fcc-hollow sites
4.6 ± 1.4
-3.3 ± 1.4
0.0 ± 4.5
6.1 ± 3.0
1.20 ± 0.07; 1.07 ± 0.07
0
99S1
O in fcc and hcp-hollow sites; NO in top site
no
0.2 ± 0.9 -1.6 ± 0.9
94J2
2.4 ± 0.9 -0.5 ± 0.9
0 0; 0 0 0; 0
0
no
4.5 ± 3.7 0; 0.0 ± 0.4 complex complex
1.61 ± 0.02; 1.64 ± 0.02
LEED no
1.4 ± 0.9 0; -1.4 ± 0.9 3.3 ± 0.9 0; -1.4 ± 0.9
1.20 ± 0.02; 1.27 ± 0.02
0
89P2
Ru(0001)+ LEED no (2x1)-O+NO: O at hcphollow site Ru(0001)+ LEED no (2x1)-O+NO: NO at hcphollow site
no
3.7 ± 1.9 -2.8 ± 1.4
0.0 ± 0.9 0; 0.0 ± 0.9
0 0
0 0; 0
1.26 ± 0.05; 1.26 ± 0.05
0
99S1
S in hcp-hollow sites on unreconstructed; relaxed substrate: buckling in the first and second Ru layers; lateral shifts in the first Ru layer atomic adsorption in hcp-hollow sites; top 2 Ru layers buckled; bulk-like first and second Ru-Ru interlayer spacings (measured wrt center of mass of the layers) O and NO in hcp-hollow sites
no
3.7 ± 1.9 -2.8 ± 1.4
0.0 ± 0.9 0; 0.0 ± 0.9
0 0; 0
0 0; 0
1.32 ± 0.04; 1.32 ± 0.04
0
99S1
O and NO in hcp-hollow sites
Surface
Tech- Clean Adsnique rec. ind rec. LEED no no
Ru(0001)+ (2x2)-O+NO: O at hcphollow site Ru(0001)+ LEED no (2x2)O+2NO: O at hcp-hollow site Ru(0001)+ LEED (2x2)2O+NO: 1 O at hcp-hollow site Ru(0001)+ LEED no (2x2)-S Ru(0001)+ (2x1)-O
no
4.1-37 Surface
Tech- Clean Adsnique rec. ind rec. LEED no no
Ru(0001)+ c(4x2)-2S: 1 S near hcphollow site Ru(0001)+ LEED no (√7x√7) R19°-C6H6
Ru(0001)+ (3x3)C6H6+2NO: C6H6 at hcphollow site Ru(0001)+ (3x3)C6H6+2NO: 1 NO at one hcp-hollow site Ru(0001)+ (3x3)C6H6+2NO: 1 NO at other hcp-hollow site Ru(0001)+ (3x3)C6H6+2O: C6H6 at hcphollow site
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 Ref. [Å]
Description
-3.3 ± 0.9
-7.9 ± 0.9; 0.9 ± 0.9 0; -0.5 ± 0.9 0.5 ± 2.3; 1.4 ± 2.3
complex
1.73 ± 0.02; 1.56 ± 0.02; 1.75 ± 0.02
0
94S3
0; 4.5 ± 9.0
0; 0 0; 0 0; 0.0 ± 5.0
2.15 ± 0.04; 2.07 ± 0.04
0
95S4
S close to hcp and fcc-hollow sites shifted away from symmetric positions; buckling and lateral shifts of rows in the first substrate layer; buckling in the second substrate layer intact molecular adsorption in hcp sites; with C3v(σ_v) orientation; i.e. C atoms near top and bridge sites; no significant buckling in top metal layer; very strong contraction of first two metal interlayer spacings; H ignored intact molecular C6D6 and NO adsorption in hcp sites; benzene essentially in C3(σ_d) orientation; i.e. C atoms in equal positions; no significant buckling in top metal layer; H ignored;
-2.0 ± 0.9
complex
no
-4.2 ± 2.3
LEED no
no
-4.8 ± 2.3
-0.8 ± 2.3; 0.4 ± 2.3
0; 0.0 ± 3.3
0; 2.18 ± 0.05; -4.6 ± 3.6 2.20 ± 0.05
0
97S5
LEED no
no
-5.1 ± 2.3
0.0 ± 2.3; -0.9 ± 2.3
0; 0.0 ± 3.3
0; 0.0 ± 3.6
1.33 ± 0.05; 1.33 ± 0.05; 1.31 ± 0.05
0
97S5
intact molecular C6D6 and NO adsorption in hcp sites; benzene essentially in C3(σ_d) orientation; i.e. C atoms in equal positions; no significant buckling in top metal layer; H ignored;
LEED no
no
-4.0 ± 2.3
0.9 ± 2.3; 0.0 ± 2.3
0; 2.0 ± 3.3
0; 1.30 ± 0.05; -1.6 ± 3.6 1.32 ± 0.05; 1.32 ± 0.05
0
97S5
intact molecular C6D6 and NO adsorption in hcp sites; benzene essentially in C3(σ_d) orientation; i.e. C atoms in equal positions; no significant buckling in top metal layer; H ignored;
LEED no
no
-4.5 ± 1.4
-1.9 ± 1.4; -1.0 ± 1.4
0; 0.6 ± 3.3
0; 0.0 ± 2.6
0
97S5
intact molecular C6D6 and atomic O adsorption in hcp sites; benzene essentially in C3(σ_v) orientation; i.e. C atoms near top and bridge sites; no significant buckling in top metal layer; clock rot. possible in top Ru layer; H ignored;
2.21 ± 0.03; 2.17 ± 0.03
4.1-38 Surface
Ru(0001)+ (3x3)C6H6+2O: 1 O at one hcp-hollow site Ru(0001)+ (3x3)C6H6+2O: 1 O at other hcp-hollow site
αls [°]
Tech- Clean Adsnique rec. ind rec. LEED no no
∆dl,l+1 [%]
bls [%]
∆rls [%]
d01 [Å]
∆r0 Ref. [Å]
Description
-3.5 ± 1.4
0.9 ± 1.4; -0.9 ± 1.4
0; 0; -2.0 ± 4.4 3.2 ± 3.6
1.38 ± 0.03; 1.40 ± 0.03; 1.36 ± 0.03
0
97S5
intact molecular C6D6 and atomic O adsorption in hcp sites; benzene essentially in C3(σ_v) orientation; i.e. C atoms near top and bridge sites; no significant buckling in top metal layer; clock rot. possible in top Ru layer; H ignored;
LEED no
-2.6 ± 1.4
1.0 ± 1.4; 2.0 ± 1.4
0; 0; 1.33 ± 0.03; -1.1 ± 4.4 -2.6 ± 3.6 1.35 ± 0.03; 1.37 ± 0.03
0
97S5
intact molecular C6D6 and atomic O adsorption in hcp sites; benzene essentially in C3(σ_v) orientation; i.e. C atoms near top and bridge sites; no significant buckling in top metal layer; clock rot. possible in top Ru layer; H ignored;
no
0.4 ± 1.8
0; 1.6 ± 1.4
0; 0
0; 0
1.10 ± 0.05
0
93O2
no
-4.2 ± 0.9
0; 0.5 ± 0.9; -2.8 ± 0.9
0; 0; 0
0; 0; 0
2.23 ± 0.02
0
94H1
molecular adsorption in top site on unreconstructed substrate; with buckling in top substrate layer intact molecular adsorption in two different top sites (bilayer) on unreconstructed relaxed substrate: significant buckling in top metal layer; contraction of first two metal interlayer spacings
no
-1.4 ± 0.9
0; 3.2 ± 0.9; 2.8 ± 0.9
0; 0; 0
0; 0; 0
2.08 ± 0.02
0
94H1
intact molecular adsorption in two different top sites (bilayer) on unreconstructed relaxed substrate: significant buckling in top metal layer; contraction of first two metal interlayer spacings
0
0
0
0
2.00 ± 0.05
0
94B7
molecular adsorption in on-top site with molecular axis perpendicular to unreconstructed substrate
no
adsorption at top sites (see Fig. 9) Ru(0001)+ LEED no (√3x√3) R30°-CO Ru(0001)+ LEED no (√3x√3) R30°-2H2O: 1 H2O at high top site Ru(0001)+ LEED no (√3x√3) R30°-2H2O: 1 H2O at low top site Ru(0001)+ LEED (√3x√3) R30°-N2
4.1-39 Tech- Clean Adsnique rec. ind rec. LEED no no
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 Ref. [Å]
Description
-2.8
0
0
0
3.54 ± 0.06
0
97N1
LEED no
no
0.0 ± 2.3
0; -4.7 ± 1.9
0; 0
0; 0
3.25 ± 0.08; 3.15 ± 0.08
0
92O1
Ru(0001)+ LEED no (2x2)Cs+CO: Cs at top site Ru(0001)+ LEED no (2x2)Cs+2CO: Cs at top site Ru(0001)+ LEED no (2x2)-3NO: 1NO at top site
no
-7.0 ± 1.9
0; -8.4 ± 1.9
0; 0
0; 0
3.12 ± 0.04; 2.94 ± 0.04
0
95O2
atomic overlayer in on-top sites on unreconstructed substrate; with buckling and lateral relaxation in the first metal layers atomic adsorption in top sites of unreconstructed substrate; relaxations in top 2 Ru-Ru interlayer spacings; buckling in top Ru layer; no detectable lateral relaxations Cs adsorption in on-top site; pronounced buckling in top substrate layer; CO in threefold coordinated hcp sites between Cs atoms
no
-7.5 ± 1.9
0; -8.8 ± 1.9
0; 0
0; 0
3.13 ± 0.04; 2.94 ± 0.04
0
95O2
Cs adsorption in on-top site; pronounced buckling in top substrate layer; CO in threefold coordinated hcp and fcc sites
no
8.3 ± 0.7
0; 8.4 ± 0.7; 0
0
97S4
2.3 ± 1.0
2.3 ± 1.0
0; 0; 1.72 ± 0.05; -2.9 ± 2.8; ± 3.0 1.90 ± 0.05 3.4 ± 2.8 ± 2.3; 0 -0.6 ± 3.5 -0.8 ± 3.0
intact molecular adsorption in top; hcp and fcc sites; upright orientation with the N end down; significant different site-specific inner NO bondlengths: NO(top)=1.13; NO(hcp/fcc)=1.24/1.22Å; significant buckling in top metal layer O atoms adsorbed in hcp sites; CO molecules adsorbed in top sites; tilted by 12.6°; relaxations of topmost Ru layer in both lateral and vertical directions CO tilt could be either vibrational or static O atoms adsorbed in hcp and fcc sites; forming honeycomb pattern; CO molecules adsorbed upright in top sites; relaxations in topmost Ru layer in both lateral and perpendicular directions
Surface
Ru(0001)+ (√3x√3) R30°-Xe Ru(0001)+ (2x2)-Cs
Ru(0001)+ LEED no (2x2)-O+CO: CO at top site
no
Ru(0001)+ LEED no (2x2)2O+CO: CO at top site
no
95N
-3.3 ± 0.9
0; -4.2 ± 0.9
0; 0.5 ± 0.5
0; 0
1.98 ± 0.08; 1.89 ± 0.08
0
94N1
4.1-40 Surface
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 Ref. [Å]
Description
-6.1 ± 2.8
0; -3.3 ± 2.8
0; 0.1 ± 2.8
0; 0
1.93 ± 0.06; 1.86 ± 0.06
0
95O1
no
4.2 ± 1.9
0; 6.5 ± 1.4
0; 0.0 ± 0.4
0; 0
1.75 ± 0.04; 1.89 ± 0.04
0
99S1
coadsorption of atomic oxygen and molecular dinitrogen on unreconstructed; relaxed substrate; oxygen in hcp-hollow site; N2 on top site; perpendicular to surface O and NO in hcp-hollow sites
no
5.1 ± 1.4
0; 3.3 ± 1.4
complex
0; 0
1.76 ± 0.07; 1.89 ± 0.07
0
99S1
O in fcc and hcp-hollow sites; NO in top site
no
5.6 ± 2.3
0; 5.6 ± 1.4
0; ± 0.5 ± 0.5
complex
1.74 ± 0.06; 1.86 ± 0.06
0
99S1
O in hcp-hollow site; NO in top and fcc-hollow sites
95S3
1 S atom in fcc site; 3 S atoms close to hcp sites; shifted away from symmetric positions; buckling in the first substrate layer correlated with the number of coordinated S atoms; nearly identical bond lengths for all S-Ru bonds
76S2
atomic interstitial in octahedral sites between first and second Ti layers; slight expansion of Ti-Ti spacing; forms trilayer of TiN compound exposing (111) face
Tech- Clean Adsnique rec. ind rec. LEED no no
Ru(0001)+ (2x2)(O+N2): N2 at top site Ru(0001)+ LEED no (2x2)-O+NO: O at top site Ru(0001)+ LEED no (2x2)2O+NO: NO at top site Ru(0001)+ LEED no (2x2)O+2NO: 1 NO at top site
adsorption at both fcc-hollow and near-hcp sites Ru(0001)+ (√7x√7) R19°-4S
LEED no
no
adsorption at octahedral interstitial sites within 1st substrate spacing (see Fig. 10) Ti(0001)+ (1x1)-N
LEED no
no
4.3 ± 2.1
0
0
0
-1.22 ± 0.05; 1.22 ± 0.05
0
4.1-41 Surface
Zr(0001)+ (1x1)-C Zr(0001)+ (1x1)-N
Tech- Clean Adsnique rec. ind rec. LEED no no
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 Ref. [Å]
Description
0.4 ± 1.9
0
0
0
-1.33 ± 0.10; 1.33 ± 0.10
0
88W1
LEED no
-0.8 ± 0.9
0
0
0
-1.30 ± 0.05; 1.30 ± 0.05
0
87W4
atomic adsorption in octahedral interstitial sites between 1st and 2nd Zr layers; inducing slight expansion between these Zr layers atomic adsorption in octahedral interstitial sites between 1st and 2nd Zr layers; inducing slight contraction between these Zr layers
0
-1.22 ± 0.05; 2.22 ± 0.05
0
97W
two O layers are present in the structure; one forms an overlayer in which the O bonds to 3fold hollow sites on the Zr surface; the other layer has the O atoms in tetrahedral hole sites between the first two Zr layers
95W1
interstitial O in octahedral sites: 0.25ML O between 1st & 2nd Zr layers; 0.25ML between 2nd & 3rd Zr layers; these two (2x2) O arrays are displaced laterally from one another by a unit translational vector of the substrate; lowering the overall symmetry
94B3
sulfur adatoms; adsorbed near 3-fold hcp-hollow sites; form expanded hexamers crowning one 3Re-atom hump per unit cell; alternating S-S distances in the ring are 3.32Å and 2.95Å; average first substrate interlayer spacing is 2.21Å
no
adsorption at tetrahedral sites within 1st substrate spacing (see Fig. 11) Zr(0001)+ LEED no (1x1)-2O: 1 O interstitial
no
33.7 ± 1.9
0
0
adsorption at octahedral interstitial sites within 1st and 2nd substrate spacings Zr(0001)+ (2x2)-2O
LEED no
yes
adsorption at low-symmetry or mixed sites Re(0001)+ (2√3x2√3) R30°-6S
LEED no
no
4.1-42 Surface
Ru(0001)+ (3x3)-4Kr
Ru(0001)+ (2x2)-3O
Tech- Clean Adsnique rec. ind rec. LEED no no
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 Ref. [Å] 97N1
LEED no
no
98K
Ru(0001)+ LEED no (2x2)-3O Ru(0001)+ LEED no (2x2)-Cs+3O
no
98G2
no
98K
Description
multi-site atomic overlayer on unrecon-structed substrate; with buckling and lateral relaxation in the first metal layers: I Kr per cell in hcp or fcchollow site; 3 Kr per cell in lower-symmetry sites; see comments O atoms occupy 3/4 of hcp-hollow sites; sitting slightly off-hollow; 1st substrate layer is buckled: Ru atoms bonded to 3 O atoms are depressed inward relative to those bonded to 2 O atoms by 0.02 ± 0.03 Å; 2nd substrate layer is also buckled: Ru atoms below adatom vacancy are raised by 0.08 ± 0.03 Å over the others same as above; but buckling in 1st Ru layer is reversed to -0.03 ± 0.02 Å similar to Ru(0001)+(2x2)-3O: Cs occupies O vacancy sites; reversing the buckling in the 1st Ru layer; and reducing the average spacing between 1st and 2nd Ru layers 0.05 ± 0.03 Å compared to the O-only case
adsorption at interstitial sites near vacancy sites Be(0001)+ (√3x√3) R30°-3H
LEED no
yes
99P
1/3 of top-layer Be atoms are missing and each is replaced by 3 H atoms in bridge sites around the vacancy; 1st and 2nd Be-Be spacings are expanded by 0.6 ± 1.1 and 1.65 ± 1.3 %; resp.
4.1-43 Surface
Tech- Clean Adsnique rec. ind rec.
∆dl,l+1 [%]
αls [°]
∆rls [%]
bls [%]
d01 [Å]
∆r0 Ref. [Å]
Description
adsorption at interstitial sites in lattice reconstructed to fcc Zr(0001)+ (2x2)-O
LEED no
yes
85H2
O atoms in octahedral holes within fcc reconstructed Zr; with layer stacking AcBaCb... (O atoms in lower case); O atoms form (2x2) 0.25ML interstitial layers
Table 6. Structures of clean bcc(110) surfaces. ∆d23 [%] 0
∆d34 [%] 0
∆d45 [%] 0
∆d56 [%] 0
Ref.
Description
Fe(110)
Tech- Clean dbulk ∆d12 nique rec. [Å] [%] LEED no 2.029 0.5 ± 2.0
80S
K(110)
LEED no
3.72
0
0
0
0
92I
Mo(110) Mo(110)
LEED no LEED no
2.227 -1.7 ± 1.8 2.224 -4.0 ± 0.6
0 0.2 ± 0.8
0 0
0 0
0 0
81M 97A3
Nb(110)
HEIS no
2.338 0.0 ± 4.3
0
0
0
0
90W3
V(110) W(110) W(110) W(110)
LEED LEED HEIS ARXPD LEED
no no no no
2.141 2.23 2.23 2.238
-0.5 ± 0.5 0.0 ± 4.5 0.0 ± 1.8 1.0 ± 2.2
0 0 0.0 ± 1.8 0
0 0 0 0
0 0 0 0
0 0 0 0
81A 76V1 87S2 93K2
no
2.236 -3.1 ± 0.6
0.0 ± 0.9
0.0 ± 1.0
0
0
97A1
bulk termination with possible slight expansion of topmost interlayer spacing lateral shear displacement of 0.23Å between top 2 surface layers; preserving the 2-dimensional periodicity bulk termination with contracted top layer spacing bulk-like terminated surface with moderate inward relaxation of top layer bulk terminated structure with no detectable relaxations slightly contracted bulk termination unrelaxed bulk termination bulk-like termination unreconstructed surface with small expansion of top interlayer expansion possible bulk-like terminated surface with small inward relaxation of the top layer
Surface
W(110)
-0.7 ± 0.3
4.1-44 Table 7. Adsorbate-induced structures on bcc(110) surfaces. Surface
Tech- Clean adsnique rec. ind rec.
∆dl,l+1 [%]
bls [%]
∆rls αls [%] [°]
d01 [Å]
∆r0 [Å]
Ref.
Description
bcc Cr(110) film grown epitaxially on Cu(100); film is about 11Å thick; Cr(110) is overlain with 0.7±0.2 monolayer of pseudomorphic bcc Cu (with 0.3ML vacancies); in-plane lattice constant fit to 2.44±0.07Å atomic Fe adsorption in center sites (extending substrate lattice) on unreconstructed substrate atomic S at center site; top substrate layer laterally relaxed atomic overlayer near distorted center hollow site; i.e. bridging two nearest neighbors but shifted 0.04Å perp. to bridge toward 3-fold coordinated hollow site; substantial relaxations up to 0.3Å in top 2 substrate layers
adsorption at center sites (see Fig. 12) Cr(110)+ LEED no (1x1)-0.7MLCu
no
4.7 ± 0.0003
0
0
0
1.837 ± 0.0008
0
94J1
W(110)+ (1x1)-Fe Fe(110)+ (2x2)-S Mo(110)+ (2x2)-S
no
no
1.9 ± 2.2
0
0
0
2.07 ± 0.05 0
97T2
LEED no
no
81S1
LEED no
no
94T
XPD
adsorption at 3-fold coordinated sites (see Fig. 13) Mo(110)+ (1x1)-H
LEED no
no
-2.0 ± 0.4
0
0
0
1.10 ± 0.30
0.14 ± 0.48
97A3
W(110)+ (1x1)-H
LEED no
no
-1.7 ± 0.5
0
0
0
1.20 ± 0.30
0.19 ± 0.36
97A1
H adsorbed close to quasi threefold coordinated site; Mo surface exhibits moderate contraction of first interlayer distance; deeper layer distances are bulk-like H adsorbed in quasi-threefold coordinated site; W surface undergoes no reconstruction upon H adsorption; only small contraction of first interlayer spacing
4.1-45 Surface
Fe(110)+ (2x2)-2H
Mo(110)+ (2x2)-2H
Tech- Clean adsnique rec. ind rec. LEED no no
LEED no
no
∆dl,l+1 [%]
bls [%]
0.0 ± 2.0
-2.0 ± 1.2
1.0 ± 2.9
-1.0 ± 0.8
-3.5 ± 0.7 -0.2 ± 0.7
Fe(110)+ (2x1)-H Fe(110)+ (3x1)-2H
∆rls αls [%] [°]
d01 [Å]
∆r0 [Å]
Ref.
Description
atomic adsorption in threefold-coordinated sites with displacement towards twofoldcoordinated bridge sites; forming distorted honeycomb-like lattice; substrate relaxation of c(2x2) type: buckling in 1st and 2nd Fe layers H forms a honeycomb like adlayer occupying positions close to threefold coordinated hollow sites; adsorbate induces moderate buckling of two topmost Mo layers; contraction of first interlayer distance atomic adsorption in 3-fold coordinated hollow sites atomic adsorption in 3-fold coordinated hollow sites; two H per unit cell
0; 0 0; 0
0; 0 0; 0
1.09 ± 0.20
0.18 ± 0.33
93H1
0.9 ± 0.4; 2.7 ± 0.4 -1.4 ± 0.7; -1.4 ± 0.7
0; 0 0; 0
0; 0 0; 0
1.02 ± 0.20
0.23 ± 0.20
97A2
LEED
-1.0 ± 2.5
0
0
0
0.90 ± 0.10
0.25
85M2
LEED
-1.0 ± 2.5
0
0
0
1.00 ± 0.05
0.25
85M2
Table 8. Structures of clean fcc(100) surfaces. Surface
Tech- Clean nique rec. LEED no LEED no MEED no LEED no LEED no LEED no
Ag(100) Al(100) Al(100) Al(100) Au(100) Au(100)(1x1) Au(100)- XRD yes (incommen surate 'hex') Co(100)
LEED no
dbulk [Å] 2.043 2.025 2.022 2.025 2.04 2.04
∆d12 [%] 0.0 ± 4.9 0.0 ± 1.5 1.5 ± 4.9 2.6 ± 0.2 0.0 ± 4.9 -1.5 ± 2.0
∆d23 [%] 0.0 ± 1.5 0 0 0.0 ± 0.3 0 -2.0 ± 2.0
∆d34 [%] 0 0 0 -0.5 ± 0.4 0 0
∆d45 [%] 0 0 0 0 0 0
∆d56 [%] 0 0 0 0 0 0
2.04
1.77
Ref.
Description
91L 76V2 83M2 95B3 82L 94W5
no multilayer relaxation unrelaxed bulk termination bulk termination with possible slight top contraction unreconstructed surface with multilayer relaxations metastable unreconstructed surface impurity-stabilized unreconstructed surface; with possible contraction of top two interlayer spacings incommensurate hexagonal top layer; with 20% expanded spacing to 2nd layer (due to variable registries); top 4 layers are found corrugated by 14; 7; 3; 1 % (defined as maximum thickness of layer) bulk termination with top spacing contraction
91O1
-4.0 ± 2.8
0
0
0
0
78M
4.1-46 Surface Cu(100) Cu(100) Cu(100) Cu(100) Cu(100) Ir(100)(1x1) Ir(100)(5x1) Ir(100)(5x1) Ni(100) Ni(100) Ni(100) Ni(100) Ni(100) Ni(100) Pb(100) Pd(100) Pd(100) Pd(100) Pt(100)(1x1) Rh(100) Rh(100) Rh(100)
Technique LEED LEED SPLEED MEIS LEED LEED
Clean rec. no no no
dbulk [Å] 1.805 1.81 1.805
∆d12 [%] -1.1 ± 2.8 -1.7 ± 1.1 -1.2 ± 1.1
∆d23 [%] 1.7 ± 2.8 1.1 ± 1.1 0.9 ± 1.1
∆d34 [%] 1.5 ± 2.8 0 0
∆d45 [%] 0 0 0
∆d56 [%] 0 0 0
no no yes
1.807 -2.4 ± 0.8 1.807 -0.4 ± 5.5 1.92 -3.6 ± 0.5
1.0 ± 1.0 -0.4 ± 5.5 0
0 0 0
0 0 0
0 0
Ref.
Description
83D1 86A 87L1
bulk termination with multilayer relaxations bulk termination with multilayer relaxations bulk termination with multilayer relaxations
91J 93M3 83H
multilayer relaxation relaxed bulk termination unreconstructed metastable surface with top spacing contraction quasi-hexagonal commensurate buckled top-layer reconstruction with 'two-bridges' registry quasi-hexagonal commensurate buckled top-layer reconstruction with 'two-bridges' registry bulk termination with slight top spacing expansion bulk termination with top spacing contraction contraction of top interlayer spacing relaxed; unreconstructed surface relaxed; unreconstructed surface unreconstructed relaxed substrate multilayer relaxation essentially unrelaxed bulk termination multilayer relaxation multilayer relaxation unreconstructed metastable structure with slight top spacing expansion unrelaxed bulk termination bulk termination with possible slight top interlayer expansion bulk termination with slight top interlayer contraction
LEED yes
1.92
81V
LEED yes
1.92
83L
LEED MEIS LEED LEED SIMS LEED LEED LEED LEED LEED HEIS
1.76 1.76 1.762 1.762 1.762 1.762 2.463 1.945 1.945 1.945 1.96
no no no no no no no no no no no
1.1 ± 1.1 -8.9 ± 0.5 -1.1 ± 1.0 -1.3 ± 1.0 -4.7 ± 3.4 0.5 ± 0.6 -8.0 ± 1.2 0.3 ± 2.6 3.1 ± 1.5 4.9 ± 1.5 0.2 ± 2.6
0 0 0 0 -1.3 ± 9.1 -0.1 ± 0.6 3.1 ± 1.2 0 -1.0 ± 1.5 0.3 ± 0.5 0
0 0 0 0 0 0 -3.0 ± 1.2 0 0 -0.8 ± 1.0 0
0 0 0 0 0 0 -2.0 ± 4.0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0
75D 83F 89O 94L2 94X 94N3 90L1 80B 90Q 96B 81D
LEED no LEED no
1.9 0.5 ± 1.1 1.902 0.5 ± 1.0
0 0.0 ± 1.5
0 0
0 0
0 0
80H 88O
LEED no
1.902 -1.2 ± 1.6
0.0 ± 1.6
0
0
0
93B3
4.1-47 Table 9. Adsorbate-induced structures on fcc(100) surfaces. Surface
Technique
Clean Adsrec. ind rec.
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 [Å]
Ref.
Description
adsorption at hollow sites (see Fig. 14) Pd(100)+ Transm. no (1x1)-H (D) Channe ling Pt(100)+ LEED yes (1x1)-Cu
no
0
0
0
0
0.30 ± 0.05
0
88B
atomic adsorption in 4-fold hollow site
no
2.0 ± 5.1
0
0
0
1.79 ± 0.10
0
94A
Al(100)+ c(2x2)-Na (100K) Cu(100)+ c(2x2)-Bi Cu(100)+ c(2x2)-Cl Cu(100)+ c(2x2)-Cl
LEED no
no
0.35 ± 0.50
0
0
0
2.57 ± 0.01
0
95B3
GIXD no
no
-5.5
0
0
0
2.18 ± 0.08
0
97M2
XSW
no
no
3.9 ± 2.2
0
0
0
1.53 ± 0.04
0
89P1
ARPEFS
no
no
11.3 ± 1.2 0.5 ± 1.5
91W4
no
2.4 ± 1.7
0 0; 0 0
0
LEED no
0 0; 0 0
1.60 ± 0.005
Cu(100)+ c(2x2)-Cl Cu(100)+ c(2x2)-Li Cu(100)+ c(2x2)-N
0 0; 2.3 ± 0.7 0
1.60 ± 0.03
0
83J
LEED no
no
-0.4 ± 2.2
0
0
0
1.96 ± 0.08
0
93M3
partial pseudomorphic monolayer covering about 50% of unreconstructed substrate; probably in islands with 1ML; best fit with mix of 50% bare Pt(100)-(1x1) atomic Na in hollow site on unreconstructed and essentially unrelaxed substrate atomic adsorption on unreconstructed substrate; adatom at fcc-hollow site atomic adsorption in hollow site with expanded top Cu-Cu interlayer spacing atomic adsorption in hollow site; with multilayer relaxation and 2nd Cu layer buckling atomic adsorption in hollow site of unreconstructed substrate Li atoms in fourfold hollow sites
SEno XAFS
no
4.4 ± 2.8 0
93L2
7.9 ± 2.8
0 0; 0 0
0
no
0 0; 0 0
0.40 ± 0.05
LEED no
0 0; -5.5 ± 2.8 0
0.00 ± 0.05
0
87Z
Cu(100)+ c(2x2)-N
atomic overlayer in 4-fold hollow sites; outward expansion of first Cu layer; possible corrugation of second Cu layer atomic overlayer coplanar with top Cu layer in 4-fold hollow sites
4.1-48 Surface
Cu(100)+ c(2x2)-N
Technique
Clean Adsrec. ind rec. LEED no no
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 [Å]
Ref.
Description
7.4 0
0 0; 0 0
0 0; 0 0
0.06
0
89Z
1.60 ± 0.02
0
90Y
N almost coplanar with 1st Cu layer; buckling in 2nd Cu layer (Cu below N pushed down atomic adsorption at a 4-fold hollow site top Ni layer relaxes outward
SEno XAFS XSW SEno XAFS
no
11.3 ± 2.8
0 0; -5.0 0
no
2.3
0
0
0
1.55
0
97T1
Ni(100)+ c(2x2)-Li
LEED no
no
-0.3 0.4
97J1
no
no
-1.7 ± 1.7 1.7 ± 1.7
0.84 ± 0.70
0
98D2
LEED no
no
-0.7 ± 0.6 -0.1 ± 0.6
0 0; 0 0 0; 0 0 0; 0 0 0
0
XRD
0 0; 0 0 0; 0 0 0; 0 0 0
1.92
Ni(100)+ c(2x2)-N+ (disord.)-K Ni(100)+ c(2x2)-Na
0 0; 1.5 0 0; 3.4 ± 1.7 0 0; 0 0 0
2.38 ± 0.04
0
94N3
atomic adsorption in 4-fold hollow sites of unreconstructed relaxed substrate; negligible buckling in 2nd Ni layer
0.86 ± 0.10
0
83F
atomic adsorption in 4-fold hollow sites
0 0; -2.0 ± 1.1 0 0; -11.3 ± 5.7 0
0 0; 0 0 0; 0 0
0 0; 0 0 0; 0 0
0.77 ± 0.02
0
89O
0.85 ± 0.10
0
94X
1.31 ± 0.03
0
86B
oxygen adsorbed in hollow site; buckling in 2nd Ni layer; top Ni-Ni interlayer spacing expanded overlayer in hollow sites on relaxed; unreconstructed substrate; 2nd Ni layer buckled atomic adsorption in hollow sites
Ni(100)+ c(2x2)-Cl Ni(100)+ c(2x2)-Cl
-0.9 ± 1.1 5.1 ± 5.7
Ni(100)+ c(2x2)-O Ni(100)+ c(2x2)-O
MEIS no
no
LEED no
no
6.7 ± 1.1 -1.2 ± 1.1
Ni(100)+ c(2x2)-O
SIMS
no
no
12.3 ± 3.4 -14.3 ± 9.1
Ni(100)+ c(2x2)-S
ARPEFS
no
no
4.0 ± 1.7
atomic overlayer in 4-fold hollow sites on unreconstructed substrate; with lateral relaxations in the first 2 metal layers atomic adsorption on unreconstructed relaxed substrate; adatom at fourfold hollow site K removes clock-reconstruction of Ni(100)+pmg(2x2)-2N
4.1-49 Surface
Ni(100)+ c(2x2)-S
Technique
Clean Adsrec. ind rec. LEED no no
Ni(100)+ c(2x2)-S Pd(100)+ c(2x2)-K
XPD
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 [Å]
Ref.
Description
1.9 ± 1.7 -1.5 ± 1.7
0 0; -0.6 ± 1.7 0
0 0; 0 0
0 0; 0 0
1.30 ± 0.02
0
90S2
1.38 ± 0.10
0
92S1
0 0; 0 0
0 0; 0 0
2.54 ± 0.02
0
96B
sulfur in hollow site; expansion of top NiNi interlayer spacing; contraction of 2nd Ni-Ni spacing; second Ni layer buckled atomic atomic adsorption in 4-fold hollow sites; with expansion of top Ni-Ni spacing atomic adsorption in 4-fold hollow site; possible slight buckling in 2nd Pd layer
1.24 ± 0.02
0
96K1
adsorption of S on fourfold hollow sites; multilayer substrate relaxations 4-fold site; lateral expansion of top Cu layer S in 4-fold hollow; site laterally expanded; no vertical buckling in 2nd Cu layer 4-fold hollow site for S; lateral expansion of site; buckling in 2nd layer (atom below S pushed down)
no
no
5.7 ± 5.7
LEED no
no
0.2 ± 3.0 2.1 ± 1.0
Pd(100)+ c(2x2)-S
LEED no
no
2.6 ± 0.8
0 0; 2.1 ± 1.0 0
Cu(100)+ (2x2)-S Cu(100)+ (2x2)-S Cu(100)+ (2x2)-S
XRD
no
no
0
0
1.6 ± 0.7
0
1.19 ± 0.10
0
90V2
MEIS no
no
0
0
1.6 ± 0.7
0
1.30 ± 0.02
0
90J2
LEED no
no
2.7 ± 2.8 1.6 ± 2.8
90Z2
no
no
1.8 0
1.28 ± 0.03
0
92S2
Ni(100)+ (2x2)-O
LEED no
no
4.7 ± 1.1 -3.2 ± 1.1
0.80 ± 0.05
0
90O1
Ni(100)+ (2x2)-O
SIMS
no
8.4 ± 6.8 -3.2 ± 1.1
0 0; 0; 0 0 0; 0; 0 0 0; 0; 0 0 0; 0; 0
0
ARPEFS
0 0; 0; 0 2.2 0; 0; 0 0 0; 0; 0 0 0; 0; 0
1.28 ± 0.03
Cu(100)+ (2x2)-S
0 0; -4.0 ± 2.8; -4.0 ± 2.8 0 0; -0.6; -1.8 0 0; -2.3 ± 1.1; -5.7 ± 1.1 0 0; -14.8 ± 6.8; -14.8 ± 6.8
0.85 ± 0.10
0
94X
no
atomic adsorption in 4-fold hollow sites with lateral relaxation of the first Cu layer and vertical buckling of the second Cu layer oxygen in hollow site; expansion of top Ni-Ni interlayer spacing; second Ni layer buckling overlayer in hollow sites on relaxed; unreconstructed substrate; 2nd Ni layer buckled
4.1-50 Surface
Ni(100)+ (2x2)-S
Technique
Clean Adsrec. ind rec. LEED no no
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 [Å]
Ref.
Description
2.7 ± 2.8 -2.4 ± 2.8
0 0; -4.0 ± 2.8; -4.0 ± 2.8
0 0; 0; 0
0 0; 0; 0
1.25 ± 0.03
0
90O2
sulfur in hollow site; 1st Ni-Ni interlayer spacing expanded; second Ni layer buckling
Pd(100)+ (2x2)-O
LEED no
no
6.7 ± 1.0 -3.1 ± 0.8
0 0; -2.6 ± 0.8; -6.2 ± 0.8
0.0 ± 2.0 0; 0; 0
0 0; 0; 0
0.83 ± 0.02
0
96K1
adsorption of O on fourfold hollow sites; multilayer substrate relaxations; no lateral relaxations of substrate atoms; significant buckling allowed by symmetry
Pd(100)+ (2x2)-S
LEED no
no
6.3 ± 0.8 -1.6 ± 0.8
96K1
adsorption of S on fourfold hollow sites; multilayer substrate relaxations; no lateral relaxations of substrate atoms; significant buckling allowed by symmetry
no
-0.6 ± 2.1
0 0; 0; 0 0
0
LEED no
0.0 ± 2.0 0; 0; 0 0
1.13 ± 0.02
Rh(100)+ (2x2)-O Ni(100)+ c(4x2)-K
0 0; -3.1 ± 0.8; -4.2 ± 0.8 0
0.95 ± 0.04
0
88O
LEED no
no
-4.3 ± 2.3 4.3 ± 4.3
93F3
-0.6 ± 2.1
0 0; 0 0
0
no
0 0; 0 0
2.68 ± 0.05
Rh(100)+ LEED no c(4x2)-Cs XRD no Cu(100)+ (disordered)K 0.18ML
0 0; 4.3 ± 4.3 0
2.87 ± 0.06
0
89v2
hollow site adsorption with slight top RhRh interlayer contraction atomic adsorption in hollow sites; buckling of 2nd Ni layer; lateral shift in 1st Ni layer 4-fold symmetric hollow site adsorption
no
0.7 ± 1.0
0
0
0
2.10 ± 0.40
0
93M1
LEED no Ni(100)+ (disordered)K 1/4ML
no
-2.6 ± 2.3 2.6 ± 2.6
0 0; 2.6 ± 2.6
0 0; 0
0 0; 0
2.66 ± 0.03
0
93W5
disordered fourfold hollow adsorption of atomic K; with little vertical relaxation of top two interlayer spacings and no lateral displacements disordered atomic adsorption at K coverages of 0.04,0.08; 0.14,0.17,0.22 and 0.25: K in hollow sites; adsorption height: 2.72,2.735,2.675,2.675,2.675 and 2.66Å; resp.; buckling of 2nd Ni layer: Ni atom directly below K moves up by 0.075,0.06,0.075,0.060,0.060,0.045Å; resp.
4.1-51 Surface
Technique
Clean Adsrec. ind rec.
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 [Å]
Ref.
Description
0
0
0.80 ± 0.03
0.1
83D2
atomic adsorption 0.1Å laterally away from 4-fold hollow site towards bridge site atomic adsorption in quasi fourfold hollow sites; S atoms shifted towards bridge sites; relaxation of the first 2 Rh layers and slight buckling of 2nd Rh layer atomic adsorption in quasi fourfold hollow sites; S atoms shifted towards bridge sites; relaxation of the first 2 Rh layers and buckling of 2nd Rh layer; lateral shift of atoms in 1st Rh layer
adsorption at off-hollow sites Ni(100)+ c(2x2)-O Rh(100)+ c(2x2)-S
LEED no
no
2.3
LEED no
no
2.3
-0.5
0
0
1.3
0.27
93L4
Rh(100)+ (2x2)-S
LEED no
no
1.8 -0.7
0 0.0; 3.2
-3.6 0
0 0
1.35
0.27
93L4
LEED no Ni(100)+ (disordered)O
no
-5.2 ± 2.8 4.0 ± 2.8
0 4.0 ± 2.8
0 0
0 0
0.86 ± 0.03
0.45 ± 0.10 91S2
Ni(100)+ LEED no (disordered)-S
no
-1.3
0
0
0
1.2
0.6
2.7 ± 1.7
0
0
0
2.01 ± 0.03 93Z
91S2
disordered hollow site adsorption in off center position (pseudobridge); 2nd layer buckled; sideshift of Ni atoms close to O of up to 0.15Å possible; local minimum for 4-fold-site with 1st layer buckling disordered hollow site adsorption in off center position (pseudobridge); 2nd layer buckled; side shift of Ni atoms close to O of up to 0.15Å possible; local minimum for 4-fold-site with 1st layer buckling
admolecules at top sites (see Fig. 15) Ni(100)+ AR- no (disordered)- PEFS NH3
no
0
molecular NH3 adsorbed at top site on relaxed substrate; H ignored
4.1-52 Surface
Technique
Clean Adsrec. ind rec.
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 [Å]
Ref.
Description
atomic adsorption (3Pb per supercell) at and near hollow sites; forming 3-Pb-wide strips (domains) of c(2x2) structure with compressed domain boundaries; no buckling in Pb layer or relaxations in substrate detected atomic adsorption on unreconstructed substrate; antiphase boundary structure of c(2x2) domains; all Li atoms occupy hollow sites domain-wall overlayer structure; inducing relaxations in substrate
adsorption at hollow and other sites Cu(100)+ c(5√2x√2) R45°-3Pb
LEED no
no
86H
Ni(100)+ c(5√2x√2) R45°-3Li
LEED no
no
97J2
Cu(100)+ c(9√2x√2) R45°-5Bi Cu(100)+ c(8x2)-7Mn
XRD no
no
98M1
LEED no
no
94G2
commensurate quasi-hexagonal Mn overlayer: one Mn per cell over hollow site of unreconstructed substrate; Mn layer strongly buckled (0.53Å); and slightly relaxed laterally; top Cu layer slightly buckled (0.04Å)
91G
carbon adsorbed in fcc-hollow site; clockwise rotation of top Ni layer atoms around hollow (shift in <010> directions by 0.45Å); buckling of 2nd Ni layer (Ni directly below C moves up)
adsorption at clock-rotated hollow site Ni(100)+ LEED no p4g(2x2)-2C
no
3.9 ± 4.5
0
3.2 ± 3.9
4.4 ± 4.0
0; 8.5 ± 4.5
0; 0
± 14.3 0.12 ± 0.04 ± 2.6 0; 0
0
4.1-53 Clean Adsrec. ind rec. no no
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
-2.8 ± 5.7
0
4.8 ± 7.9
no
no
-2.8 ± 5.7
0
Ni(100)+ XRD no p4g(2x2)-2N
no
3.4 ± 4.0
0
Surface
Technique
Ni(100)+ PED p4g(2x2)-2C Ni(100)+ PED p4g(2x2)-2N
∆r0 [Å]
Ref.
Description
± 17.4 0.10 ± 0.10 ± 7.1
0
91K
4.8 ± 7.9
± 17.4 0.10 ± 0.10 ± 7.1
0
91K
2.9 ± 0.1
± 15.0 0.03 ± 0.13 ± 0.5
0
99D
carbon adsorbed in hollow site; clock rotation of 4 Ni neighbors by 0.55Å; expansion of top Ni-Ni interlayer spacing N adsorbed in hollow site; clock rotation of 4 Ni neighbors by 0.55Å; top Ni-Ni interlayer expansion N adsorbed in hollow site; clock rotation of 4 Ni neighbors by 0.30Å; top Ni-Ni interlayer expansion
d01 [Å]
adsorption at substitutional sites in top substrate layer (see Fig. 16) Cu(100)+ c(2x2)-Au Cu(100)+ c(2x2)-Mn Cu(100)+ c(2x2)-Mn
LEED no
yes
4.0 ± 2.8
0
0
0
0.10 ± 0.05
0
87W2
LEED no
yes
-0.9 ± 1.7
0
0
0
0.30 ± 0.02
0
93W7
PED
no
yes
-9.7 ± 4.4
0
0
0
0.40 ± 0.04
0
96T1
Cu(100)+ c(2x2)-Pd Ni(100)+ c(2x2)-Mn
LEED no
yes
0.0 ± 1.7
0
0
0
0.02 ± 0.03
0
88W2
LEED no
yes
0.0 ± 1.7
0
0
0
0.25 ± 0.02
0
93W7
Ni(100)+ c(2x2)-Sn Pd(100)+ c(2x2)-Mn Al(100)+ c(2x2)-Na (300K)
LEIS no
yes
0
0
0
0
0.44 ± 0.05
0
94L1
LEED no
yes
-15.4 ± 2.6
0
0
0
0.20 ± 0.05
0
90T2
SEno XAFS
yes
2.9 ± 5.5
0
0
0
0.61 ± 0.10
0
92A
substitutional adsorption; forming buckled monolayer of mixed alloy ordered mixed Mn-Cu top layer with Mn buckled outwards 2-dimensional surface alloy of Mn and Cu; Mn replaces every other Cu atom in outermost layer; Mn buckled outwards substitutional adsorption; forming buckled monolayer of mixed alloy ordered mixed Mn-Ni top layer with Mn buckled outwards by 0.25Å; small relaxations of top 3 interlayer spacings ordered surface alloy with Sn buckled above Ni mixed top layer; with Mn buckled outward mixed top Al/Na layer: Na on top sites of next Al layer; top-layer Al atoms between Na atoms; buckled outward
4.1-54 Surface
Cu(100)+ (disordered)Bi 0.3ML
Technique
Clean Adsrec. ind rec. GIXD no yes
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 [Å]
Ref.
Description
2.9 ± 5.5
0
0
0
0.61 ± 0.10
0
97M2
adatom at substitutional site; in random configuration
93B4
single (1x1) Fe layer under single Au layer; acting as surfactant
missing row reconstruction with O incorporated at kink sites at nearly same height as 1st Cu layer O in 4-fold coordinated site with 1 Cu neighbor missing; missing Cu row in (1,1) direction; lateral shift of top Cu atoms adjacent to rows (pairing; 0.3Å) and lifting up (0.01Å); buckling in 2nd Cu layer (0.1Å); Cu below O is lifted missing-row reconstruction; with O in 4fold coordinated sites with 1 Cu neighbor missing; SEXAFS results consistent with earlier LEED results on lateral and perpendicular relaxations in top Cu layer (Cu expands into missing rows)
adsorption at substitutional sites in 2nd substrate layer Au(100)+ (1x1)-Fe+ (1x1)-Au
LEED yes
yes
adsorption at hollow sites of missing-row substrate Cu(100)+ (2√2x√2) R45°-2O Cu(100)+ (2√2x√2) R45°-2O
PED
no
yes
90A
LEED no
yes
90Z1
Cu(100)+ (2√2x√2) R45°-2O
SEno XAFS
yes
93L1
4.1-55 Surface
Technique
Clean Adsrec. ind rec.
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 [Å]
Ref.
Description
92A
mixed top Al/Na layer: Na on top sites of next Al layer; top-layer Al atoms between Na atoms; buckled outward by 1.41Å
every other [110] row in top Ag layer missing; with 1st Ag-Ag interlayer spacing reduced by -3.6 ± 2.4 %; K substitute for missing Cu; but 1.17 ± 0.05 Å above remaining top-layer Cu atoms; in 2nd Ag layer a lateral displacement of Ag by 0.04 ± 0.003 Å toward K sites is seen missing row type reconstruction; Li positions unknown
adsorption at substitutional sites of laterally shifted top substrate layer Al(100)+ c(2x2)-Na (300K)
SEno XAFS
yes
adsorption in troughs of missing-row reconstruction Ag(100)XRD no (2x1)+ (disordered)K
yes
98M3
Cu(100)LEED no (2x1)+ (disordered)Li
yes
93M2
adsorption in substitutional and near-hollow overlayer sites Cu(100)+ (3x3)-5Li
LEED no
yes
95M3
complex reconstruction with overlayer and substitution: small pyramids of 4 Cu atoms capped by single Li atoms; the pyramids being separated and joined by pairs of substitutional Li atoms
4.1-56 Surface
Cu(100)+ (4x4)-10Li
Technique
Clean Adsrec. ind rec. LEED no yes
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 [Å]
Ref.
Description
95M5
complex reconstruction with overlayer and substitution: 4 Li adatoms forming a square cluster located on top of islands of 9 Cu atoms; which islands are separated and joined by rows of substituting Li atoms four Li adatoms forming a square cluster located on top of islands of nine Cu atoms; the islands are separated and joined by rows of substituting Li atoms 9 Li adatoms forming a square cluster located on top of islands of 16 Cu atoms; the islands are separated and joined by rows of substituting Li atoms
Ni(100)+ (4x4)-10Li
LEED no
yes
97J1
Ni(100)+ (5x5)-17Li
LEED no
yes
97J1
complex reconstruction Al(100)+ (√5x√5) R27°-Yb
XPD; no LEED
yes
97F1
Pd(100)+ (√5x√5) R27°-4O
LEED no
yes
94V2
formation of mixed Yb-Al top layer by substitutional adsorption of Yb; residual first-layer Al atoms are strongly displaced from equilibrium position; also expansion of first interlayer spacing atomic adsorption: PdO oxide monolayer with Pd atoms placed on 3 different adsorption sites: 1 Pd sits on top; 2 Pd on bridge; 1 Pd on hollow sites per unit cell; significant expansion in interlayer spacing and rumpling in the oxide layer
4.1-57 Surface
Cu(100)+ c(4x4)-3Pb
Technique
Clean Adsrec. ind rec. LEED no yes
Pd(100)+ LEED no p4g(2x2)-2Al
∆dl,l+1 [%]
αls [°]
∆rls [%]
bls [%]
d01 [Å]
∆r0 [Å]
yes
Ref.
Description
96G2
Pb chains in [1,-1,0] direction; replacing every other Cu row; 3 Pb per unit cell: 1 Pb substitutional in hollow site; 2 Pb in intermediate asymmetrical sites; remaining Cu between Pb chains relaxed; small corrugation in first pure substrate layer top layer is 100% Pd; 2nd layer is 50% Pd and 50% Al; 3rd layer and beneath is 100% Pd at ideal fcc positions; clockreconstruction in top layer; buckling in 2nd layer (Pd outward)
97O1
Table 10. Structures of clean bcc(100) surfaces. Surface Fe(100) Fe(100) Fe(100) Mo(100)(disordered) Mo(100)(disordered) Mo(100)(disordered) Ta(100) Ta(100)
Technique LEED LEED MEIS LEED
Clean rec. no no no yes
dbulk [Å] 1.433 1.433 1.433 1.574
∆d12 [%] -1.6 ± 2.8 -4.9 ± 2.1 -4.5 ± 2.8 -11.7 ± 6.4
∆d23 [%] 0 4.9 ± 2.1 3.5 ± 2.8 0
∆d34 [%] 0 0 0 0
∆d45 [%] 0 0 0 0
∆d56 [%] 0 0 0 0
Ref.
Description
77L1 87W1 89H2 75I2
bulk termination with contraction of top layer spacing bulk termination with multilayer relaxation bulk termination with multilayer relaxation bulk termination with contraction of top interlayer spacing
LEED yes
1.574 -9.5 ± 1.9
-1.0 ± 1.9
0
0
0
80C
bulk termination with multilayer relaxation
LEED yes
1.575 -5.4 ± 1.3
1.6 ± 1.3
0.3 ± 1.3
0
0
75I2
bulk termination with contraction of top interlayer spacing
LEED no PED no
1.65 -0.9 ± 1.8 1.2 ± 1.8 1.649 -10.0 ± 5.0 0
0 0
0 0
0 0
82T1 89B1
bulk termination with multilayer relaxation contraction of first interlayer spacing
4.1-58 Surface V(100) W(100)(disordered) W(100)(disordered) W(100)(disordered) W(100)(disordered) W(100)c(2x2) W(100)c(2x2) W(100)c(2x2) W(100)c(2x2)
dbulk [Å] 1.514 1.58
∆d12 [%] -6.9 ± 0.7 -6.3 ± 6.3
∆d23 [%] 1.1 ± 0.7 0
∆d34 [%] 0 0
∆d45 [%] 0 0
∆d56 [%] 0 0
Ref.
Description
82J 76V1
bulk termination with 2-layer relaxation bulk termination with top layer spacing contraction
LEED yes
1.58
-7.6 ± 1.9
0
0
0
0
80M1
bulk termination with top layer spacing contraction
LEED yes
1.58
-6.3
1.9
0
0
0
88P2
multilayer relaxation
LEED yes
1.58
-9.2 ± 6.3
0
0
0
0
88P1
LEED yes
1.58
-3.2 ± 3.2
0
0
0
0
78B
disordered version of W(100)-c(2x2) reconstruction; with top-layer W atoms randomly displaced laterally by 0.16Å in 4 equivalent [011] directions zig-zag displacive reconstruction of top layer
XRD yes
1.58
-3.8 ± 10.1 0
0
0
0
88A
LEED yes
1.58
-7.0 ± 1.9
1.3 ± 1.9
0
0
0
89L1
LEED yes
1.583 -6.2 ± 1.6
0
0
0
0
92S3
Technique LEED LEED
Clean rec. no yes
zig-zag chain reconstruction with lateral relaxations in 1st and 2nd layers reconstructed zigzag; reconstruction with lateral displacements zig-zag chain relaxation with lateral displacements in 1st layer
Table 11. Adsorbate-induced structures on bcc(100) surfaces. Surface
Tech- Clean Adsnique rec. ind rec.
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 [Å]
Ref.
Description
28 -3.0
0 0
0 0
0 0
0.16
0
92J
atomic adsorption in 4-fold hollow sites; with large expansion of top Cr-Cr spacing
adsorption at hollow sites (see Fig. 17) Cr(100)+ (1x1)-N
LEED no
no
4.1-59 Tech- Clean Adsnique rec. ind rec. MEIS no no
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 [Å]
Ref.
Description
11.2 ± 2.8 0.7 ± 2.8
0 0
0 0
0 0
0.38 ± 0.04
0
89H2
Fe(100)+ (1x1)-O Fe(100)+ (1x1)-O Mo(100)+ (1x1)-Si Cr(100)+ c(2x2)-N
LEED no
no
7.7 ± 7.0
0
0
0
0.48 ± 0.10
0
77L2
LEED no
no
0 0 0
0 0 0
0
87J
no
0 0 0
0.45 ± 0.04
LEED yes
8.2 ± 2.8 2.7 ± 2.8 0.0 ± 6.4
1.16 ± 0.10
0
75I1
LEED no
no
11.6 ± 2.8 -6.4 ± 2.8
0 0, -9.0 ± 2.8
0 0, 0
0 0, 0
0.36 ± 0.04
0
98S2
Cr(100)+ c(2x2)-S
AR- no PEFS
no
0 0 0 0 0
88T1
no
0 0 0 0 0
0
LEED no
0 0 0 0 0
1.17 ± 0.02
Fe(100)+ c(2x2)-C+O (chemically disordered) Fe(100)+ c(2x2)-N Fe(100)+ c(2x2)-P Fe(100)+ c(2x2)-S Fe(100)+ c(2x2)-S
-9.0 ± 1.4 2.1 ± 2.1 -1.4 ± 2.1 -2.1 ± 4.9 0.0 ± 7.0
atomic adsorption in 4-fold hollow sites (assumed); with expansion of top 2 Fe-Fe spacings\ atomic adsorption deep in 4-fold hollow sites atomic adsorption in 4-fold hollow sites; with expansion of top 2 Fe-Fe spacings\ atomic adsorption in 4-fold hollow sites on unrelaxed substrate atomic overlayer in bcc-hollow sites on unreconstructed substrate; expansion and (slight) contraction of top 2 substrate interlayer spacings; resp.; with buckling in the second metal layer atomic adsorption in hollow sites with top Cr-Cr spacing relaxation (no detectable layer buckling)
0.48 ± 0.10
0
78J
LEED no
no
7.7 ± 3.5
0
0
0
0.27 ± 0.05
0
82I
XPD
no
no
0
0
0
0
1.02
0
97H2
LEED no
no
0
0
0
0
1.05 ± 0.05
0
77L3
AR- no PEFS
no
-2.1 ± 1.4
0
0
0
1.10 ± 0.02
0
88Z
Surface
Fe(100)+ (1x1)-O
decomposed CO as atomic C and O randomly positioned in hollow sites of a c(2x2) lattice; LEED shows c(2x2) (C and O indistinguishable) atomic adsorption in 4-fold hollows atomic adsorption in hollow sites on unreconstructed unrelaxed substrate atomic adsorption in hollow sites atomic adsorption in hollow sites with multilayer relaxation (no detectable layer buckling)
4.1-60 Tech- Clean Adsnique rec. ind rec. LEED yes no
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 [Å]
Ref.
Description
-6.7 ± 3.2 7.9 ± 2.5
0 -9.5 ± 2.5
0 0
0 0
0.47 ± 0.03
0
95J
Mo(100)+ c(2x2)-S
LEED yes
no
-1.6 ± 3.8
0
0
0
1.03 ± 0.10
0
95J
atomic adsorption in hollow site; with buckling in 2nd Mo layer; with shortest CMo bond to 2nd Mo layer atomic adsorption in hollow site; with buckling in 2nd Mo layer
W(100)+ c(2x2)-N
LEED yes
no
-2.9 ± 3.8 8.7 ± 3.8 -9.0 ± 3.8
-3.1 ± 3.8 0 -17.1 ± 3.8
0 0 0
0 0 0
0.41 ± 0.05
0
95B4
W(100)+ c(2x2)-S
LEIS yes
no
-0.5 ± 2.5
0
0
0
1.02 ± 0.02
0
94O2
Mo(100)+ (3√2x√2) R45°-2S Mo(100)+ c(4x2)-3S
LEED yes
no
95J
LEED yes
no
95J
W(100)+ Dyes (disordered)- LEED O
no
Surface
Mo(100)+ c(2x2)-C
0.0 ± 6.3
0
-9.6 ± 5.0
0
0.59 ± 0.10
0
86R
-1.3 ± 12.7
0
0
0
1.17 ± 0.04
0
85P
atomic adsorption in four fold hollow sites; second W layer buckled (outward under adsorbate) atomic overlayer on undistorted four-fold hollow site; top W-W spacing relaxed to near bulk value atomic adsorption in quasi hollow site; with buckling and lateral relaxation in the first 2 Mo layers atomic adsorption: 1 S in hollow and 2 S in quasi hollow sites (at different heights) per unit cell; buckling in 2nd Mo layer; lateral relaxations in the first two Mo layers atomic adsorption in hollow sites with lateral W relaxations towards O position
adsorption at bridge sites (see Fig. 18) W(100)+ (1x1)-2H
LEED yes
no
atomic adsorption in bridge sites of both azimuthal orientations (2H per unit cell)
4.1-61 Surface
Tech- Clean Adsnique rec. ind rec.
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 [Å]
Ref.
Description
85T
atomic O adsorption under bridge in top Ta layer and above bridge in second Ta layer (4-fold coordinated interstitial site); top Ta layer buckled
89M3
missing-row reconstruction of substrate oxygen is disordered in 2nd layer top sites
92S3
adsorption site of H not determined; dimer reconstruction with lateral displacements in 1st layer; contraction of 1st interlayer spacing by 4.5%
interstitial adsorption between two topmost substrate layers (see Fig. 19) Ta(100)+ (3x1)-O
LEED yes
no
adsorption on missing-row reconstructed substrate W(100)LEIS yes (2x1)+ (disordered)O
yes
dimerization in top substrate layer W(100)+ c(2x2)-H
LEED yes
yes
4.1-62 Table 12. Structures of clean alloyed bcc(100) surfaces. Surface
Tech- Clean dbulk ∆d12 ∆d23 nique rec. [%] [%] [Å] LEED no 1.564 -11.9 ± 0.6 5.1 ± 0.9
∆d34 [%] -3.7 ± 0.8
∆d45 [%] 3.9 ± 1.1
∆d56 [%] -2.5 ± 1.3
Ref.
Description
96H1
unreconstructed; relaxed surface: strong oscillatory relaxation of interlayer spacings; top layer is pure Mo; oscillatory segregation in deeper layers
1.567 -11.5 ± 0.6 4.7 ± 0.7
-3.3 ± 0.8
3.2 ± 0.8
-2.1 ± 1.0
97K2
deep multilayer relaxation; layer dependent stoichiometry: c1(Mo)=100%±15%; c2(Mo)=72%±13%; c3(Mo)=90%±13%; c4(Mo)=88%±16%
1.57
-3.0 ± 1.0
2.3 ± 1.0
-1.8 ± 1.1
97K2
deep multilayer relaxation; layer dependent stoichiometry: c1(Mo)=91%±13%; c2(Mo)=85%±16%; c3(Mo)=89%±14%; c4(Mo)=98%±20%
Mo75Re25 (100)-(1x1) (chem. disordered alloy) Mo85Re15 LEED no (100)-(1x1) (chem. disordered alloy) Mo95Re05 LEED no (100)-(1x1) (chem. disordered alloy)
-11.1 ± 0.8 4.4 ± 0.9
4.1-63 Table 13. Adsorbate-induced structures on alloyed bcc(100) surfaces. Surface
Tech- Clean adsnique rec. ind rec.
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 [Å]
Ref.
Description
no
96H1
no
96K2
unreconstructed; relaxed substrate: H in all bridge sites; oscillating concentration profile of clean surface remains due to low adsorption temperature; cleansurface relaxation of first two interlayer spacings is lifted; relaxation of deeper interlayer spacing remains occupation of hollow sites by C atoms; 1st interlayer spacing similar to MoC(100); c1(Mo)=76%±23%; c2(Mo)=66%±22%; c3(Mo)=82%±20%
no
96H1
unreconstructed; relaxed substrate: C resides both deep in hollow sites of top layer and interstitially in octahedral sites below top layer atoms; C causes expansion of top two interlayer spacings; oscillatory layer relaxation below these layers; Mo segregation in top two layers
94O1
missing row reconstruction of substrate with O adsorbed on top of second layer substrate atoms; substrate: disordered alloy with surface segregation: 1st metal layer Mo concentration >= 0.96; Re depletion in 2nd and enrichment in 3rd metal layers; resp.
adsorption on unreconstructed bcc(100)-like substrate Mo75Re25(100) LEED no + (1x1)-2H (chem. disordered alloy) Mo75Re25(100) LEED no + (1x1)-C (chem. disordered alloy) Mo75Re25(100) LEED no + (1x1)-2C (chem. disordered alloy)
adsorption on reconstructed bcc(100)-like substrate Mo75Re25(100) LEIS no -(2x1)+ (2x1)2O (chem. disordered alloy)
yes
4.1-64 Surface
Tech- Clean adsnique rec. ind rec. yes Mo75Re25(100) LEED no -(2x1)+ (2x1)2O (chem. disordered alloy)
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
∆r0 [Å]
d01 [Å]
Ref.
Description
95H1
missing row reconstruction; 3-fold coordinated O on sides of remaining rows; Mo segregation toward Ocoordinated sites; expansion of first interlayer distance by 7.7%
Table 14. Structures of clean fcc(110) surfaces. Surface Ag(110) Ag(110) Ag(110) Ag(110) Ag(110) Al(110) Al(110) Al(110) Al(110) Au(110)(1x2) Au(110)(1x2) Au(110)(1x2) Au(110)(1x2) Cu(110) Cu(110)
∆d12 [%] -6.6 ± 1.5 -7.6 ± 2.8 -9.5 ± 2.1 -7.4 ± 2.0 1.0 ± 1.5 -10.0 ± 7.0
Technique LEED HEIS MEIS LEED ICISS LEED
Clean rec. no no no no no no
dbulk [Å] 1.445 1.44 1.446 1.445 1.445 1.428
LEED LEED LEED LEED
no no no yes
1.43 -9.1 ± 7.0 1.425 -8.5 ± 0.8 1.43 -8.4 ± 1.0 1.44
∆d23 [%] 0 4.2 ± 2.8 6.0 ± 2.8 0.6 ± 2.0 -4.0 ± 2.0 0
∆d34 [%] 0 0 0 -2.4 ± 2.0 0 0
∆d45 [%] 0 0 0 -0.4 ± 2.0 0 0
∆d56 [%] 0 0 0 0 0 0
0 5.2 ± 1.1 5.6 ± 1.1
0 0 2.3 ± 1.3
0 0 1.8 ± 1.5
0 0 0
Ref.
Description
82N2 84K 87H2 89L4 92B1 72L
bulk termination with top spacing contraction bulk termination with multilayer relaxation relaxations in top two interlayer spacings multilayer relaxations multilayer relaxations bulk termination; with suggested 10% relaxation of top interlayer spacing relaxed bulk termination bulk termination with multilayer relaxation bulk termination with multilayer relaxation missing-row reconstruction with multilayer relaxation; 2nd row pairing and 3rd row buckling missing-row reconstruction with relaxation of top layer spacing missing-row reconstruction with multilayer relaxation; including 3rd-layer buckling missing-row reconstruction; with multilayer relaxations down to 4th layer bulk termination with multilayer relaxations bulk termination with multilayer relaxations
77G 84A 84N 85M1
LEIS yes
1.44
86M
MEIS yes
1.44
86C2
XRD yes
1.443
90V1
HEIS no LEED no
1.278 -5.3 ± 1.6 1.278 -8.4 ± 0.6
3.3 ± 1.6 2.3 ± 0.8
0 0
0 0
0 0
83S 83A
4.1-65 Surface Cu(110) Cu(110) Cu(110) Cu(110) Cu(110) Cu(110)
Technique LEED MEIS ICISS LEED LEIS XRD
Clean rec. no no no no no no
dbulk [Å] 1.276 1.278 1.28 1.278 1.278 1.278
∆d12 [%] -9.2 ± 3.9 -7.5 ± 1.6 -10.2 ± 7.8 -9.4 ± 1.6 -3.1 ± 3.1 -7.8 ± 0.5
∆d23 [%] 2.3 ± 3.9 2.5 ± 1.6 0 4.9 ± 1.6 0 1.8 ± 0.5
∆d34 [%] 0 0 0 0 0 0
∆d45 [%] 0 0 0 0 0 0
∆d56 [%] 0 0 0 0 0 0
Ref.
Description
83D1 86C3 86Y2 87B 89V1 93H2
Ir(110)(1x2)
LEED yes
1.359
86C1
Ir(110)(1x3) Ir(110)(1x3) Ni(110) Ni(110) Ni(110) Ni(110) Ni(110) Ni(110) Ni(110) Pb(110) Pb(110) Pb(110) Pd(110) Pd(110)(1x2) Pd(110) Pd(110) Pt(110)(1x2)
TOF- yes SARS LEIS yes
1.358
90S1
1.357
92H3
bulk termination with multilayer relaxations bulk termination with multilayer relaxations bulk termination with top layer contractions bulk termination with multilayer relaxations contraction of the 1st interlayer spacing unreconstructed surface with relaxations of top 2 interlayer spacings missing-row reconstruction with multilayer relaxations; row-pairing in second layer and buckling in third layer missing-row reconstruction exposing (111) facets; with relaxations in first 2 layers missing-row reconstruction with multilayer relaxations
MEIS LEED HEIS LEED LEED MEIS LEED MEIS LEED LEED LEED LEED
1.245 1.245 1.245 1.245 1.245 1.246 1.245 1.75 1.74 1.75 1.37 1.37
no no no no no no no no no no no no
LEED no LEED no MEIS yes
-4.0 ± 0.8 -8.4 ± 0.8 -4.1 ± 0.8 -9.8 ± 1.6 -8.6 ± 0.5 -9.0 ± 1.0 -8.4 ± 1.6 -15.8 ± 2.3 -16.4 ± 1.7 -19.4 ± 2.9 -5.8 ± 2.9 -5.1 ± 2.2
1.37 -5.1 ± 1.5 1.376 -1.0 ± 1.5 1.39
0 3.1 ± 1.0 0 3.8 ± 1.6 3.1 ± 0.6 3.5 ± 1.4 3.6 ± 1.6 0 3.5 ± 5.7 4.6 ± 4.6 0.7 ± 2.2 0
0 0 0 0 -0.4 ± 0.7 0 1.2 ± 1.6 0 -4.4 ± 1.7 -6.9 ± 2.9 0 0
0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0
79V2 84G1 84T3 85X1 85A 86Y1 87R1 86F2 89L3 90B 85B1 85B1
bulk termination with top spacing contraction bulk termination with multilayer relaxations bulk termination with top spacing contraction bulk termination with multilayer relaxations bulk termination with multilayer relaxations bulk termination with multilayer relaxations bulk termination with multilayer relaxations bulk termination with top spacing contraction multilayer relaxation down to 3rd interlayer spacing multilayer relaxation down to 3rd interlayer spacing bulk termination with multilayer relaxation alkali-impurity stabilized missing-row reconstruction
2.9 ± 1.5 5.2 ± 1.5
0 0
0 0
0 0
87S1 93W3 88F1
relaxations in top two interlayer spacings unreconstructed surface with multilayer relaxations missing-row reconstruction with multilayer relaxation; including 3rd-layer buckling
4.1-66 Surface Pt(110)(1x2)
Tech- Clean dbulk nique rec. [Å] LEED yes 1.39
∆d12 [%]
∆d23 [%]
∆d34 [%]
∆d45 [%]
∆d56 [%]
Ref.
Description
88F2
missing-row reconstruction with multilayer relaxation; including 2nd- and 4th-layer pairing; and 3rd- and 5thlayer buckling missing-row reconstruction with multilayer relaxation; including 2nd- and 4th-layer pairing and 3rd-layer buckling missing-row reconstruction; with multilayer relaxations down to 4th layer missing-row reconstruction; with top spacing contraction missing-row reconstruction; with multilayer relaxations down to 3rd layer missing-row reconstruction; multilayer relaxation
Pt(110)(1x2)
LEED yes
1.387
88S
Pt(110)(1x2) Pt(110)(1x2) Pt(110)(1x2) Pt(110)(1x2) Pt(110)(1x3)
XRD yes
1.387
90V1
PED
yes
1.387
91H2
TOF- yes SARS RHEE yes D LEED yes
1.387
91M1
1.387
92K2
1.39
88F2
Pt(110)(1x3) Pt(110)(1x3)
XRD yes
1.387
93R
TOF- yes SARS
1.387
91M1
Rh(110) Rh(110)
LEED no LEED no
1.34 -0.8 ± 1.5 1.345 -6.9 ± 1.0
0 1.9 ± 1.0
0 0
0 0
0 0
80H 87N
Rh(110) Rh(110)(1x2)
LEED no LEED yes
1.345 -6.7 ± 1.5 1.345
2.2 ± 2.2
0
0
0
94B6 93C3
(1x3) reconstruction; probably impurity-stabilized; missing-row reconstruction with multilayer relaxation; including 2nd-layer pairing; and 3rd- and 4th-layer buckling missing-row reconstruction with multilayer relaxation 2-missing-rows reconstruction; leaving partial low 2nd-layer ridge within 3-wide trough; this structure is thought to be impurity-stabilized relaxed bulk termination unreconstructed surface with relaxations of top two interlayer spacings unreconstructed substrate with multilayer relaxation missing-row reconstruction with multilayer relaxation; metastable reconstruction after desorption of O from Rh(110)-p2mg(2x2)-2O
4.1-67 Table 15. Adsorbate-induced structures on fcc(110) surfaces. Surface
Tech- Clean Ads- ∆dl,l+1 nique rec. ind [%] rec.
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 [Å]
Ref.
Description
pseudomorphic Fe monolayer; Fe-Cu and Cu(1)-Cu(2) interlayer spacings are (within error bar) equal to Cu-Cu bulk interlayer spacing Pt filling troughs of unreconstructed; relaxed substrate; extending bulk Pd fcc structure atomic adsorption in hollow (center) site
adsorption at center sites of unreconstructed substrate (see Fig. 20) Cu(110)+ (1x1)-Fe
LEED no
no
-0.6 ± 2.0
0
0
0
1.25 ± 0.03
0
89M1
Pd(110)+ (1x1)-Pt Ni(110)+ c(2x2)-S Ni(110)+ c(2x2)-S Ni(110)+ c(2x2)-S
LEED no
no
6.1 ± 2.2
0
0
0
1.22 ± 0.03
0
93W4
LEED no
no
10.2 ± 1.6
0
0
0
0.84 ± 0.03
0
85B2
ICISS no
no
5.0 ± 3.2
0
0
0
0.89 ± 0.05
0
86F1
AR- no PEFS
no
10.4 ± 1.6 0
87R2
no
12.5 ± 3.2
0 0; 0 0
0
SEno XAFS MEIS no
0 0; 0 0
0.82 ± 0.02
Ni(110)+ c(2x2)-S Ni(110)+ c(2x2)-S Ni(110)+ c(2x2)-S
0 0; 10.4 ± 1.6 0
0.83 ± 0.04
0
87W3
no
5.2 ± 3.2
0
0
0
0.87 ± 0.03
0
79v2
SEno XAFS
no
14.0 ± 2.4
0
0
0
0.77 ± 0.02
0
94Y
Rh(110)+ c(2x2)-S
LEED no
no
7.5 -3.8
0 0; -8.3
0 0; 0
0 0; 0
0.82
0
94W4
atomic adsorption in bulk continuation site (center of rectangle) atomic adsorption in bulk continuation site (center of rectangle) with buckling in 2nd Ni layer atomic adsorption in bulk continuation site (center of rectangle) atomic adsorption in hollow (center) site atomic overlayer in hollow sites of unreconstructed substrate; with expansion of top Ni-Ni spacing atomic adsorption on relaxed; unreconstructed substrate: S on the center hollow site; 2nd layer Rh buckled
4.1-68 Surface
Tech- Clean Ads- ∆dl,l+1 nique rec. ind [%] rec.
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 [Å]
Ref.
Description
adsorption at 3-fold coordinated sites of unreconstructed substrate (see Fig. 21) Rh(110)+ (1x1)-2H
LEED no
no
-1.3 ± 3.7
0
0
0
0.78 ± 0.05
0.92 ± 0.05 91H1
atomic adsorption of hydrogen in 3-fold hollows on either side of Rh ridges; reducing clean-surface relaxation
Ni(110)+ (2x1)-2H
LEED no
no
-4.4 ± 1.6 5.2 ± 1.6
0 0
0 0
0 0
0.41 ± 0.10
0.66
Pd(110)+ (2x1)-2H
LEED no
no
-2.2 ± 1.5 2.9 ± 1.5
0 0
0 0
0 0
0.60 ± 0.10
0.46 ± 0.30 87S1
Rh(110)+ (2x1)-2O
LEED no
no
1.1 ± 4.5 2.6 ± 5.2
0 0
0 0
0 0
0.60 ± 0.05
0.58 ± 0.10 93G1
Rh(110)+ (2x1)-2O
LEED no
no
-1.1 ± 3.0 2.6 ± 5.2
0 0; 0
0 0; ± 0.05; ± 0.07
0 0; 0
0.60 ± 0.04
0.77 ± 0.10 95B2
atomic adsorption in fcc 3-fold hollows on (111) facets of unreconstructed substrate with multilayer relaxations perp. to surface atomic adsorption over outermost 3-fold coord. hollow sites over (111) facets of bulklike substrate with interlayer spacing relaxations atomic O (2 per (2x1) unit cell) in asymmetrical 3-fold coordinated sites; forming zigzag chains within troughs of slightly relaxed substrate O in fcc 3-fold hollow site on facets of unreconstructed substrate; with multilayer relaxation; incl. lateral relaxation in 2nd Rh layer
Rh(110)+ (1x2)-H
LEED no
no
-2.5 ± 2.0
3.0 ± 0.7
0.007 ± 0.03
0
0.80 ± 0.10
1.04 ± 0.10 89P3
87R1
atomic adsorption in nearly 3-fold sites on (111) facets on side of troughs (with long HRh distance to 2nd-Rh-layer atoms); top-Rhrows to which H is bonded are buckled out and laterally shifted towards H ('shiftbuckling')
4.1-69 Surface
Rh(110)+ (1x2)-3H
Rh(110)+ (1x3)-H
Tech- Clean Ads- ∆dl,l+1 nique rec. ind [%] rec. LEED no no -1.6 ± 1.0
LEED no
no
-4.1 ± 1.5 1.1 ± 1.5
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 [Å]
2.2 ± 1.5
0
0
0.71 ± 0.10; 1.00 ± 0.10; 1.15 ± 0.10
0.55 ± 0.20; 89M2 1.22 ± 0.20; 1.66 ± 0.20
2.2 ± 1.5 0
0.04 ± 0.03 0 0 0
0.51 ± 0.10
0.70 ± 0.20 89L2
Ref.
Description
atomic adsorption of hydrogen with top layer relaxation (slight buckling of doubly occupied Rh atoms); all H in 3 inequivalent quasi-3-fold sites in sides of troughs of unreconstructed substrate atomic adsorption of H in 3-fold sites on side of troughs; slight buckling of top layer
adsorption at outermost 3-fold sites and bottom long-bridge sites in trough (see Fig. 21 and 22) LEED no Rh(110)+ c(4x2)-N+2O: O at 3-fold sites
no
0.7 ± 3.7
0
0
0
0.57 ± 0.04
-0.57 ± 0.10 95G1
LEED no Rh(110)+ c(4x2)-N+2O: N at longbridge site
no
0.7 ± 3.7
0
0
0
-1.23 ± 0.05
0
95G1
0
1.37 ± 0.05
0
78C
substrate reconstruction with missing rows parallel to ridges; atomic adsorption in outermost 3-fold coordinated fcc-hollow sites on the flanks of the ridges; N in long-bridge sites at bottom of troughs; buckling in 3rd substrate layer substrate reconstruction with missing rows parallel to ridges; atomic adsorption in outermost 3-fold coordinated fcc-hollow sites on the flanks of the ridges; N in long-bridge sites at bottom of troughs; buckling in 3rd substrate layer
adsorption at short-bridge sites of unreconstructed substrate (see Fig. 23) Ir(110)+ c(2x2)-O
LEED yes
no
-2.2 ± 5.1
0
0
atomic adsorption in short-bridge site on unreconstructed substrate with top Ir-Ir layer spacing contraction
4.1-70 Surface
Tech- Clean Ads- ∆dl,l+1 nique rec. ind [%] rec.
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 [Å]
Ref.
Description
95W2
atomic adsorption on relaxed; unreconstructed substrate: 1 S at center,1 S at long-bridge; 2 S at off-center sites; off-center site S shift by 0.39Å from center; 1st-layer Rh atoms forming the long-bridge site are buckled outward by 0.20Å and laterally shift by 0.27Å to open up the site
CO occupies atop sites on unreconstructed substrate; small buckling of top Cu layer molecular CO adsorption near bridge site of unreconstructed; perhaps slightly relaxed; substrate; with C-O axis tilted 19° from surface normal CO molecules tilted in alternate directions along the short bridge rows; 20° tilt of whole molecule CO near bridge site adsorption on ridges of unreconstructed substrate; C-O axis tilted 24° from surface normal in zigzag fashion; multilayer relaxation in substrate CH3COO (acetate) adsorption; with both O down; O are approx. atop so molecule bridges 2 Cu atoms; C-C axis and molecular plane perp. to surface; H atom sites in methyl group not determined
adsorption at multiple sites Rh(110)+ (3x2)-4S
LEED no
no
admolecules near top or short-bridge sites over ridges of unreconstructed substrate (see Figs. 23 and 24) Cu(110)+ (2x1)-CO Ni(110)+ (2x1)-2CO
PED
no
no
-11.0 ± 4.7
AR- no PEFS
no
Ni(110)+ (2x1)-2CO
LEED no
Rh(110)+ (2x1)-2CO
LEED no
Cu(110)+ PED (disordered)CH3COO
no
0; 0 0
0; 0 0
1.87 ± 0.02
0
95H3
1.9 ± 1.6
0; -11.0 ± 4.7 0
1.43 ± 0.02
0
93H4
no
0.0 ± 4.0
0
0
0
1.29 ± 0.06
0
94Z
no
1.9 ± 3.7
0
0
0
1.41 ± 0.05
0
94B6
no
-2.3 ± 3.1
0
0
0
1.90 ± 0.04
0
92W2
4.1-71 Surface
Cu(110)+ (disordered)CF3COO
Tech- Clean Ads- ∆dl,l+1 nique rec. ind [%] rec. PED no no -2.3 ± 3.1
Cu(110)+ PED (disordered)NHx (x=2 or 1)
no
no
0.0 ± 5.5
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 [Å]
Ref.
Description
0
0
0
1.90 ± 0.04
0
92W2
0; -5.5 ± 5.5
0; 0
0; 0
1.33 ± 0.02
0
96H3
CF3COO (trifluoro-acetate) adsorption; both O down; O approx. atop so molecule bridges 2 Cu atoms; C-C axis and molecular plane perp. to surface; F atom sites in fluoro-methyl group not determined disordered overlayer of NH2 or NH in short bridge sites of unreconstructed relaxed substrate
admolecules at center sites (see Fig. 20) Ni(110)+ c(2x2)-CN
NE- no XAFS PD
no
98B1
unreconstructed; relaxed substrate with CN lying perpendicular to troughs across center site of rectangular hollow; N higher than C
added row reconstruction with multilayer relaxation; O in long bridge site atomic adsorption in long-bridge sites (O below top Cu layer); with missing Cu [001] rows atomic adsorption in long bridge sites with missing-row reconstruction and slight secondrow pairing away from O sites atomic adsorption in long bridge sites with missing-row reconstruction and slight secondrow pairing away from O sites
adsorption at long-bridge sites on cross-ridge missing/added-rows substrate Ag(110)+ (2x1)-O Cu(110)+ (2x1)-O
ICISS no
yes 14.9 ± 3.5
ICISS no
Cu(110)+ (2x1)-O Cu(110)+ (2x1)-O
0
0.08 ± 0.05 0
-0.03 ± 0.05
0
93C1
yes 25.2 ± 15.6 0
0
-0.60
0
86Y2
XRD no
yes 29.0 ± 3.9
0
0.03 ± 0.05 0
-0.34 ± 0.20
0
90F1
LEED no
yes 16.6 ± 3.9
0
0.03 ± 0.05 0
0.04 ± 0.05
0
90P1
0
4.1-72 ∆r0 [Å]
Ref.
Description
0.12 ± 0.07 0
-0.08 ± 0.20
0
91D2
0
0
0
-0.05 ± 0.06
0
93D2
yes 20.4
0
0
0
0.2
0.1 ± 0.1
90K
LEED no
yes -1.5 ± 5.9
0
0.0 ± 0.14
0
0.0 ± 0.08
0
95D2
LEED no
yes -3.7 ± 3.7
0
0.0 ± 0.05
0
0.09 ± 0.04
0
95G1
O in long bridge sites with missing row reconstruction; row pairing (away from O) of second Cu layer added-row reconstruction with O in long bridge site missing-row structure in which the O atoms are above long bridge sites in [001] direction with slight asymmetry; top 2 Ni layers have an expanded separation while the 2nd and 3rd have a contracted separation; the 3rd layer is slightly buckled missing/added row reconstruction; with N atoms in long bridge sites added-row reconstruction across ridges; N in long-bridge positions forming Rh-N-Rh chains; buckling in 3rd substrate layer
Cu(110)+ (2x1)-O Ni(110)+ (2x1)-O
LEIS no
yes 0
LEED no
Rh(110)+ (2x1)-N Rh(110)+ (2x1)-N
Cu(110)+ (2x1)-O
∆rls [%]
αls [°]
d01 [Å]
bls Tech- Clean Ads- ∆dl,l+1 [%] nique rec. ind [%] rec. ICISS no yes 18.2 ± 11.7 0
Surface
adsorption on missing-row/added-rows substrate along ridge; at outermost 3-fold sites Ir(110)-(1x2)+ LEED yes (2x2)-2S
yes -3.3 ± 7.4
0
0
0
0.94 ± 0.10
-0.20
87C1
missing-row structure of substrate; atomic S over outermost 3-fold fcc-hollow sites in zigzag arrangement (2 per cell); bonding to two top-layer Ir atoms and one second-layer Ir atom
-0.40 ± 0.12
92B2
atomic H resides at the pseudo-three-fold sites; Ni substrate is (1x2) missing-row reconstructed
adsorption on missing-row/added-rows substrate along ridge; at middle 3-fold sites Ni(110)+ (1x2)-2H
TOF- no SARS
yes 0
0
0
0
0.21
4.1-73 Surface
Tech- Clean Ads- ∆dl,l+1 nique rec. ind [%] rec.
bls [%]
αls [°]
d01 [Å]
0
0
1.02 ± 0.04
∆rls [%]
∆r0 [Å]
Ref.
Description
0
94H4
(1x2) missing row reconstruction induced by K adsorption; K coverage < 0.5; so not ordered overlayer; K atoms occupy 4-fold coordinated hollows at bottom of missing-row troughs
mixed Au/K top layer; inducing spacing relaxations and buckling in deeper Au layers almost perfectly ordered mixed Mn-Cu top layer: 87% Mn on site 1; 94% Cu on site 2; no Mn diffusion into 2nd and deeper layers; buckling in top layer; relaxation of top 3 layers
adsorption on missing-row/added-rows substrate at in-trough hollow site PED Cu(110)(1x2)+ (disordered)K
no
yes 2.4 ± 6.3
0
adsorption at substitutional sites in top layer (see Fig. 25) Au(110)+ c(2x2)-K Cu(110)+ c(2x2)-Mn
MEIS yes
yes -13.0 ± 3.0
0
0
0
1.05 ± 0.20
0
89H1
LEED no
yes -5.7 ± 1.6
0
0
0
0.22 ± 0.05
0
98R
± 0.20 ± 0.02
0
0
0
87K
H-induced row pairing reconstruction (H positions not determined)
93B1
N-induced reconstruction of top Cu layer to form nearly square buckled lattice of higher density; N deep in 4-fold hollow sites of this layer; forming 'c(2x2)' superlattice wrt it; 2nd through 4th Cu layers slightly buckled
row-pairing reconstruction in top substrate layer Pd(110)+ (1x2)-H
LEED no
yes -11.0 ± 2.2
0
complex reconstruction Cu(110)+ (2x3)-4N
XRD no
yes
4.1-74 Surface
Cu(110)+ (2x3)-4N
Tech- Clean Ads- ∆dl,l+1 nique rec. ind [%] rec. LEED no yes
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 [Å]
Ref.
Description
94V1
N-induced reconstruction of top Cu layer to form nearly square buckled lattice of higher density; N deep in 4-fold hollow sites of this layer; forming 'c(2x2)' superlattice wrt it; 2nd Cu layer slightly buckled buckled pseudo-(100) surface reconstruction of topmost layer; which has 3 N and 6 Cu atoms per (3x2) unit cell; N atoms occupy 4-fold coordinated hollows; outermost N site occupation only 30%; the following 4 substrate layers are also buckled reconstruction with inserted Ni row in [1-10] direction; forming buckled top Ni layer with quasi-square lattice; 1 N atom in hollow sites slightly above deepest buckled Ni atoms and 2 N atoms below hollow site of inclined Ni square (interstitial site between top 2 Ni layers) missing-row-pair reconstruction; S adsorbed at hollow sites on remaining-Ni-row pairs; and near hollow sites substituting for missing Ni rows; buckling of top Ni layers substrate reconstruction with missing rows and overlayer Ni atoms; O adatoms between overlayer-Ni and next-layer Ni; and within next inter-Ni spacing substrate reconstruction with missing rows and overlayer Cu atoms; O adatoms between overlayer-Cu and next-layer Cu; and within next inter-Cu spacing
Cu(110)+ (2x3)-3N
LEED no
yes
97M4
Ni(110)+ (2x3)-3N
SEno XAFS
yes
94W2
Ni(110)+ (4x1)-3S
XRD no
yes
93F2
Ag(110)+ c(6x2)-4O
LEIS no
yes
93D1
Cu(110)+ c(6x2)-4O
LEIS no
yes
93D2
4.1-75 Surface
Cu(110)+ c(6x2)-4O
Tech- Clean Ads- ∆dl,l+1 nique rec. ind [%] rec. LEED no yes
bls [%]
∆rls [%]
αls [°]
∆r0 [Å]
d01 [Å]
Ref.
Description
95L2
atomic adsorption on reconstructed substrate: two types of O; each bonded with 4 Cu; this structure is composed of double-stranded Cu-O chains and is similar to a modified (211) plane of bulk Cu2O; the basic building blocks are OCu-O 3-atom rods each P occupies an identical 6-coordinate site created by the reconstructed Cu(110); which itself corresponds to a quarter ML of added Cu atoms at hollow sites; each bonding to 2 P atoms and 5 other bulk-like Cu atoms combination of Bi overlayer in troughs and substitution of every fourth Cu row in the [001] direction of the topmost Cu layer by Bi atoms every 4th Cu row in the [001] direction (perp. to troughs) is substituted by Li atoms; remaining Cu rows are covered by 2 Li adatoms per unit cell
Cu(110)+ (2,2|-1,1)-2P
LEED no
yes
96L2
Cu(110)+ (4x1)-3Bi
GIXD no
yes
96L3
Cu(110)(4x1)-3Li
LEED no
yes
97M3
Table 16. Structures of clean hcp(10-10) surfaces. Surface
∆d12 [%] -25.0
∆d23 [%] 5.1
∆d34 [%] -11.0
∆d45 [%] 2.0
∆d56 [%] 0
Ref.
Description
96H4
-6.5 ± 2.0
1.0 ± 2.0
0.0 ± 4.0
0
0
90L2
relaxed bulk with lower-corrugation termination (of two possible terminations for a (10-10) hcp surface) relaxed bulk with lower-corrugation termination (of two possible terminations for a (10-10) hcp surface) and multilayer relaxations
1.436; -13.0 ± 0.4 3.0 ± 0.2 2.872
0.5 ± 0.6
0
0
91O2
Tech- Clean dbulk nique rec. [Å] Be(10-10) LEED no 1.319; 2.637 Co(10-10) LEED no 1.45; 2.9 Co(10-10) LEED no
relaxed bulk with lower-corrugation termination (of two possible terminations for a (10-10) hcp surface) and multilayer relaxations
4.1-76 Surface
Tech- Clean dbulk nique rec. [Å] Re(10-10) LEED no 2.4; 4.8
Ti(10-10)
LEED no
∆d23 ∆d12 [%] [%] -16.2 ± 12.6 2.0 ± 4.2
2.555; -4.3 ± 6.0 5.11
4.7 ± 3.0
∆d34 [%] 0
∆d45 [%] 0
∆d56 [%] 0
Ref.
Description
80D
bulk termination with top interlayer spacing contraction; second interlayer spacing may be expanded; termination between widely spaced layers
0
0
0
90W1
70% of surface bulk terminated with narrow top interlayer spacing (d12) contracted about 5%; second interlayer spacing (d23) expanded about 1-2%; 30% of surface bulk terminated with expanded (+6%) large (d23) interlayer spacing
Table 17. Adsorbate-induced structures on hcp(10-10) surfaces. Surface
Tech- Clean Adsnique rec. ind rec.
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
0
0
2.44 ± 0.10 0
∆r0 [Å]
Ref.
Description
91B
atomic adsorption at 4-fold hollow of bulk terminated structure of lower corrugation
adsorption at center site (see Fig. 26) Co(10-10)+ c(2x2)-K
LEED no
no
-5.3 ± 14.0 0
adsorption in 3-fold hollow sites on sides of troughs; relaxations given relative to center sites (see Fig. 27) Co(10-10)+ (2x1)-2O
LEED no
no
25.4 ± 4.2 0 -3.2 ± 3.5 0
0 0
0 0
0.74 ± 0.05 0.97 ± 0.41 97G4
Ru(10-10)+ (2x1)-2O
LEED no
no
3.7 ± 1.3 0 -2.1 ± 1.3 0
0 0
0 0
0.96 ± 0.02 1.13 ± 0.05 98S1
relaxed bulk with lower-corrugation termination (of two possible terminations for a (10-10) hcp surface); oxygen forms zigzag chains; in hcp-hollow sites on sides of Co ridges relaxed bulk with lower-corrugation termination (of two possible terminations for a (10-10) hcp surface); oxygen forms zigzag chains; in hcp-hollow sites on sides of Ru ridges
4.1-77 Surface
Ru(10-10)+ c(2x4)-2O
Tech- Clean Adsnique rec. ind rec. LEED no no
∆dl,l+1 [%]
bls [%]
-4.0 ± 5.0; 0; -7.8 ± 5.0; 0; -1.4 ± 5.0 0
∆rls [%]
αls [°]
∆r0 [Å]
d01 [Å]
Ref.
2.0 ± 3.0; complex 1.02 ± 0.03 0.95 ± 0.06 98S1 0; 0
-1.4 ± 1.3 -3.8 ± 5.0; 0; 2.6 ± 5.0 0
0.01 ± 0.03; 0
Description
relaxed bulk with lower-corrugation termination (of two possible terminations for a (10-10) hcp surface); oxygen forms zigzag chains; in hcp-hollow sites on sides of alternate Ru ridges
adsorption at short-bridge sites and 3-fold hollow sites in sides of troughs (see Fig.s 27 and 28) Re(10-10)+ c(2x2)-3H
LEED no
no
98D1
Ru(10-10)+ c(2x2)-3H
LEED no
no
98D1
little change in top two Ru-Ru interlayer spacings; but contraction by 0.09 Å of third spacing; Re atoms of short-bridge site are possibly displaced laterally toward site by 0.02 Å little change in top two Re-Re interlayer spacings; but contraction by 0.05 Å of third spacing; Re atoms of short-bridge site are possibly displaced laterally toward site by 0.02 Å
Table 18. Structures of clean bcc(211) surfaces. Surface Fe(211) W(211)
Tech- Clean dbulk nique rec. [Å] LEED no 1.17
∆d23 ∆d12 [%] [%] -10.4 ± 2.6 5.0 ± 2.6
∆d34 [%] -1.8 ± 3.4
∆d45 [%] 0
∆d56 [%] 0
Ref.
Description
84S
TOF- no SARS
-9.4 ± 5.4
0
0
0
89R
bulk termination with multilayer relaxation perpendicular and parallel to surface bulk termination with registry shift by 6.0%; relative to bulk
1.29
-0.2 ± 5.4
4.1-78 Table 19. Adsorbate-induced structures on bcc(211) surfaces. Surface
Tech- Clean Adsnique rec. ind rec.
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 [Å]
Ref.
Description
89B3
atomic O in three out of four 3-fold coordinated sites on an unrelaxed and unreconstructed W substrate; as found consistent with experimental data
95H3
hydrogen induced missing row reconstruction of Fe(211); removal of close-packed rows in top layer; row pairing in 2nd layer and buckling in 3rd layer; adsorption site of H not determined
86S1
atomic adsorption in long-bridge sites; forming -FeO-Fe-O- strings perpendicular to clean-surface ridges; in which half the Fe atoms are missing ('missing-row' model)
adsorption at 3-fold coordinated sites of unreconstructed substrate W(211)+ (1x2)-3O
TOF- no SARS
no
adsorption on close-packed missing-row reconstruction Fe(211)+ (1x2)-2H
LEED no
yes
adsorption on non-close-packed missing-row reconstruction Fe(211)+ (2x1)-O
LEED no
yes
4.1-79 Table 20. Structures of clean bcc(111) surfaces. Surface
Clean rec. no no
∆d12 [%] -15.4 ± 3.6 -16.6 ± 3.0
∆d23 [%] 0 -9.3 ± 3.0
∆d34 [%] 0 4.0 ± 3.6
∆d45 [%] 0 -2.1 ± 3.6
∆d56 [%] 0 0
Ref.
Description
81S2 86S2
bulk termination with top spacing contraction bulk termination with multilayer relaxation perpendicular to surface bulk termination with multilayer relaxation perpendicular. to surface bulk termination with multilayer relaxation perpendicular to surface
Fe(111) Fe(111)
Technique LEED LEED
Mo(111)
LEIS no
0.909 -18.0 ± 2.0 4.0 ± 4.0
0
0
0
86O
Mo(111)
LEED no
0.907 -18.8 ± 2.0 -18.9
6.4
2.2
0
99A
dbulk [Å] 0.827 0.827
Table 21. Adsorbate-induced structures on bcc(111) surfaces. Surface
Tech- Clean Adsnique rec. ind rec.
∆dl,l+1 [%]
bls [%]
∆rls [%]
αls [°]
d01 [Å]
∆r0 [Å]
Ref.
Description
-17.4 ± 1.5
0
0
0
0.03 ± 0.51
0
99A
H adsorbs in triplets around each deep hollow site; inducing little change in 1st Mo-Mo spacing; but large derelaxation of 2nd Mo-Mo spacing to near bulk value
adsorption at asymmetrical sites Mo(111)+ (1x1)-3H
LEED no
no
4.1-80 Table 22. Structures of clean Si; Ge and C(111) surfaces. Here; dbulk gives the spacing between the pairs of bilayers in the bulk. Surface
Tech- Clean dbulk nique rec. [Å] 2.35 Si(111)-(1x1) LEED no (laser annealed) Si(111)-(2x1) LEED yes 2.35 Si(111)-(2x1) MEIS yes 2.35 Si(111)-(2x1) LEED yes 2.35 Si(111)-(7x7) LEED yes 2.35 Ge(111)LEED yes 2.45 c(8x2)
d12 [%] -
ω (°) -
Ref.
description
86J
unreconstructed bulk termination with multilayer relaxations perpendicular to surface
-
-
84H1 85S 86S3 88T2 90T3
tilted π-bonded chain model with overall compression tilted π-bonded chain model; with tilt in lower chain in same direction as tilt in upper chain tilted π-bonded chain model with relaxations down to 4th bilayer optimized DAS (dimer-adatom-stacking fault) model 2 adatoms A and B in the top layer in T4 sites with identical local environments; relaxations found in the top 5 Ge layers (adatoms + 2 bilayers)
Table 23. Adsorbate-induced structures on Si; Ge and C (111) surfaces. Here; d01 is the local adsorbate height; while ∆d12 is the relative first bilayer spacing change. Surface
Tech- Clean Adsnique rec. ind rec.
d01 [Å]
∆d12 [%]
ω [°]
Ref.
Description
atomic adsorption stabilizing unreconstructed substrate with relaxed top two interlayer spacings (H position not determined) unreconstructed; nearly unrelaxed ideal bulk Si termination (H position not determined)
adsorption at unknown sites Ge(111)+ (1x1)-H Si(111)+ (1x1)-H
LEED yes
no
-
0
87I
MEIS yes
no
-
-2 ± 2
94N4
1.32
1
91W2 atomic adsorption of Bi in T4 site (3-fold hollow above 2nd Ge layer) on unreconstructed; relaxed substrate
adsorption at T4 sites (see Fig. 29) Ge(111)+ (√3x√3) R30°-Bi
LEED yes
no
4.1-81 Surface
Ge(111)+ (√3x√3) R30°-Pb (1/3ML) Si(111)+ (√3x√3) R30°-Al Si(111)+ (√3x√3) R30°-Al Si(111)+ (√3x√3) R30°-Al Si(111)+ (√3x√3) R30°-Al Si(111)+ (√3x√3) R30°-Bi Si(111)+ (√3x√3) R30°-Ga Si(111)+ (√3x√3) R30°-Ga Si(111)+ (√3x√3) R30°-Ga Si(111)+ (√3x√3) R30°-In
Tech- Clean Adsnique rec. ind rec. LEED yes no
d01 [Å]
∆d12 [%]
1.7
LEED yes
no
LEED yes
RHEED PD
ω [°]
Ref.
Description
1
89H3
α structure: atomic adsorption of Pb in T4 sites on unreconstructed; relaxed substrate: buckling of second and third Ge monolayers (first is planar)
1.39
-22
90H2
no
1.38
-22
92N
yes
no
1.42 ± 0.06
-15
95H2
Al adsorbed at T4 site; the three 1st-layer Si atoms are moved radially inwards and up; the Si below the T4 site is moved down; pushing the Si right below it downwards; other 2nd- and 3rd-layer Si atoms below them are moved upwards Al at T4 site on unreconstructed; relaxed substrate; 1st-layer Si atoms are moved radially inwards and up; the Si below the T4 site is moved down; pushing the Si right below it downwards; other 2nd- and 3rd-layer Si atoms below them are moved upwards atomic adsorption in 4-fold coordinated T4 site; large rumpling in 2nd and 3rd layers of substrate
yes
no
1.30 ± 0.20
-
99S2
LEED yes
no
1.11
-14
MEIS yes
no
1.45
-23
RHEED
yes
no
1.51 ± 0.06
3±2
92W1 Bi centered at T4 site; nearest Si neighbors squeezed together; Si atom directly below Bi and third layer Si atom directly below pushed downwards; second-layer Si atoms surrounding the hollow H3 site are moved upwards 92C Ga centered at T4 site on unreconstructed; relaxed substrate; nearest Si atoms squeezed together; two Si atoms directly below Ga pushed downwards; 2nd-layer Si atoms surrounding the hollow H3 site are moved upwards 95H2 atomic adsorption in 4-fold coordinated T4 site; large rumpling in 2nd and 3rd layers of substrate
LEED yes
no
1.35
-24
88K
atomic adsorption in 4-fold coordinated T4 'top' site over top bilayer; with relaxations down into 2nd bilayer
XRD yes
no
1.85 ± 0.05
-15 ± 3
93F1
Ga centered at T4 site on unreconstructed; relaxed substrate; nearest Si atoms squeezed together; two Si atoms directly below Ga pushed downwards; 2nd-layer Si atoms surrounding the hollow H3 site are moved upwards
Al at T4 site on unreconstructed; relaxed substrate; 1st-layer Si atoms are moved radially inwards
4.1-82 Surface
Si(111)+ (√3x√3) R30°-In Si(111)+ (√3x√3) R30°-In Si(111)+ (√3x√3) R30°-In Si(111)+ (√3x√3) R30°-Pb (β phase) Si(111)+ (√3x√3) R30°-Sn Ge(111)+ (2x1)-2Sb
Tech- Clean Adsnique rec. ind rec. yes no SEXAFS XSW RH- yes no EED
d01 [Å]
∆d12 [%]
2.10 ± 0.06
0±2
93W6 In at T4 site on unreconstructed substrate with no appreciable surface relaxations within about 0.25Å
1.83 ± 0.06
-13 ± 3
95H2
atomic adsorption in 4-fold coordinated T4 site; large rumpling in 2nd and 3rd layers of substrate
PD
ω [°]
Ref.
Description
yes
no
1.70 ± 0.10
-
99S2
In at T4 site on unreconstructed; relaxed substrate; 1st-layer Si atoms are moved radially inwards
LEED yes
no
1.43 ± 0.05
-6 ± 2
91D1
XRD yes
no
1.59 ± 0.3
-25
89C
XRD yes
no
2.62 ± 0.03
3±3
92V
atomic adsorption above T4 site; the three first-layer Si atoms are moved in as well as up; the Si right below Pb is moved down together with the Si atom below it; all the other Si's in the 2nd; 3rd; and 4th Si layers are moved upwards; the 5th Si layer and below are in bulk positions atomic adsorption at T4 site; the three first-layer Si's are moved radially inwards; the Si below the T4 site is moved down; pushing the Si right below it downwards; other second-layer Si's and third-layer Si's below them are moved upwards; layers 4; 5; and 6 are laterally moved Sb forms 6° tilted zig-zag chains; saturating the dangling bonds of the unreconstructed; relaxed; full-bilayer-terminated substrate by slightly off-top adsorption
adsorption at top sites (see Fig. 30) C(111)+ (1x1)-H (diamond) Ge(111)+ (1x1)-Cl Ge(111)+ (1x1)-I Ge(111)+ (1x1)-PHx
MEIS yes
no
-
0
86D
unreconstructed bulk diamond termination between bilayers; probably stabilized by H; with minor C-C spacing contraction in top bilayer (H positions not determined; but probably terminate dangling bonds) atomic adsorption in top sites on unrelaxed unreconstructed substrate
SEyes XAFS SEyes XAFS XSW AR- yes PEFS
no
2.07 ± 0.03
0
83C
no
2.50 ± 0.04
0
89B2
atomic adsorption of I in top sites on unreconstructed; relaxed substrate: first substrate interlayer spacing contracted by 10%
no
2.26 ± 0.04
8
90T1
adsorption of partially dissociated PH3 in tilted top sites on unreconstructed; relaxed substrate; first Ge-Ge interlayer spacing contracted by 16%
4.1-83 Surface
Si(111)+ (√3x√3) R30°-Pb
d01 [Å]
∆d12 [%]
2.56
ω [°]
Ref.
Description
0
87D2
atomic adsorption in 1-fold coordinated top sites over unreconstructed; unrelaxed substrate terminated between bilayers
1.03 ± 0.05
8±2
87R3 atomic adsorption in bridge sites with shorter bond to 3rd Ge atom; with unreconstructed substrate relaxed perpendicular to surface
no
2.21
-21
92W1 Bi trimers centered at T4 site; nearest Si neighbors squeezed together; Si atom directly below Bi and third layer Si atom directly below pushed downwards; second-layer Si atoms surrounding the hollow H3 site are moved upwards
LEED yes
yes
-2.32
-25
90H1 B atom replaces a second layer Si atom; which becomes an adatom at the T4 site over the B atom; this B position is the B5 site
PD
yes
-2.21
-20
99B1 B atom replaces a second layer Si atom; which becomes an adatom at the T4 site over the B atom; this B position is the B5 site
Tech- Clean Adsnique rec. ind rec. XSW yes no
adsorption at bridge sites (see Fig. 31) Ge(111)+ (2x2)-S
AR- yes PEFS
no
adclusters at T4 site (see Fig. 29) Si(111)+ (√3x√3) R30°-3Bi
LEED yes
substitution below T4 site Si(111)+ (√3x√3) R30°-B Si(111)+ (√3x√3) R30°-B
yes
substitution of top half of top bilayer (see Fig. 32) Ge(111)+ (1x1)-Sb Si(111)+ (1x1)-As
HEIS yes
no
1.19
0
94G3
MEIS yes
no
0.99
0
87C2
atomic substitutional replacement of top half of top Si bilayer: otherwise unreconstructed; but relaxed substrate atomic substitutional replacement of top half of top Si bilayer: otherwise unreconstructed; unrelaxed substrate
4.1-84 Surface
Si(111)+ (1x1)-As Si(111)+ (1x1)-As
Tech- Clean Adsnique rec. ind rec. XSW yes no
d01 [Å]
∆d12 [%]
0.99 ± 0.03
MEIS yes
1.02 ± 0.06
no
ω [°]
Ref.
Description
0
87P
0
87H1
atomic substitutional replacement of top half of top Si bilayer: otherwise unreconstructed; unrelaxed substrate atomic substitutional replacement of top half of top Si bilayer: otherwise unreconstructed; unrelaxed substrate
partial substitution of top half of top bilayer (see Fig. 32) Si(111)+ (√3x√3) R30°-3Bi Si(111)+ (√3x√3) R30°-3Bi
XRD yes
yes
-0.8
14 ± 1
87T
triangles of 3 Bi replace every third Si in top layer; which is lower half of a bilayer
LEED yes
yes
2.21
41
91W1 triangles of 3 Bi replace every third Si in top layer; which is lower half of a bilayer
honeycomb-chained-trimer (HCT) structure Ge(111)+ (√3x√3) R30°-3Ag Si(111)+ (√3x√3) R30°-3Li Si(111)+ (√3x√3) R30°-3Ag Si(111)+ (√3x√3) R30°-3Ag Si(111)+ (√3x√3) R30°-3Ag
LEED yes
yes
0.70 ± 0.03
-1
94H5
honey-comb chained trimer (HCT) model: top Ge half bilayer replaced by Ag; 2nd layer Ge atoms form trimers
LEED yes
yes
0.45
-2
93O1
top Si half-bilayer substituted by Li (missing top layer); 2nd half-bilayer Si atoms form trimers
XRD yes
yes
0.80 ± 0.02
-4
93T
top Si half-bilayer substituted by Ag (missing top layer); 2nd half-bilayer Si atoms form trimers; deep relaxations
LEED yes
yes
0.69
-2
93O1
top Si half-bilayer substituted by Ag (missing top layer); 2nd half-bilayer Si atoms form trimers
QK- yes LEED/ CMTA
yes
0.79
0
93J
top Si half-bilayer substituted by Ag (missing top layer); 2nd half-bilayer Si atoms form trimers; deep relaxations
4.1-85 Surface
Si(111)+ (√3x√3) R30°-3Ag
Tech- Clean Adsnique rec. ind rec. LEED yes yes
d01 [Å]
∆d12 [%]
0.78 ± 0.05
ω [°]
Ref.
Description
-2
95O3
top Si half-bilayer substituted by Ag (missing top layer); 2nd half-bilayer Si atoms form trimers
conjugate HCT structure Ge(111)+ (√3x√3) R30°-3Au Ge(111)+ (√3x√3) R30°-3Au Si(111)+ (√3x√3) R30°-3Au Si(111)+ (√3x√3) R30°-3Au Si(111)+ (√3x√3) R30°-3Au
XRD yes
no
0.42 ± 0.02
6
93H3 conjugate honeycomb-chained-trimer (CHCT) model: Au trimers centered at T4 sites; replacing top half of top Ge bilayer; nearest Ge neighbors squeezed apart
LEED yes
no
0.51
0
95O4 conjugate honeycomb-chained-trimer (CHCT) model: Au trimers centered at T4 sites; replacing top half of top Ge bilayer; nearest Ge neighbors squeezed apart
LEED yes
no
0.56
0
92Q1 conjugate honeycomb-chained-trimer (CHCT) model: Au trimers centered at T4 sites; nearest Si neighbors in the missing-top-layer are squeezed apart
LEED yes
no
0.56
0
93O1 top Si half-bilayer substituted by Au (missing top layer); Au atoms form trimers
XRD yes
no
0.93
-8
94K
94W3 reconstruction with zigzag Si chains separated by CaF2 chains filling missing Si rows; Si chains oriented along [1-10]; obtained by mainly lateral displacements by <1Å; Ca on top of Si near missing Si position; F bonding to two Ca and weakly to one Si of a Si chain 98G1 complex reconstruction; with 14 independent Au positions in a tiling of incomplete pentagonal and trimer units; coordinates normal to surface not determined
conjugate honeycomb-chained trimer (CHCT) model: Au trimers centered at T4 sites
complex reconstruction Si(111)+ (1x3)-CaF2
XRD yes
yes
1
-58
Si(111)+ (6x6)-14Au
XRD yes
yes
-
-
4.1-86 Surface
Ge(111)+ (4x4)-6Ag Si(111)+ (4x1)-4In Si(111)+ (3x1)-Li
Tech- Clean Adsnique rec. ind rec. XRD yes yes
d01 [Å]
∆d12 [%]
-
-
XRD yes
yes
-
XRD yes LEED
yes
0.10; 0.21 2.24 ± 0.04
ω [°]
Ref.
Description
98C
missing-top-layer reconstruction; with 6 Ag atoms placed on Ge substitutional sites in one triangular subunit of the 2D unit cell; and 9 Ge atoms forming a ring-like assembly in the other triangular subunit; coordinates normal to surface not determined 99B2 chains of Si atoms alternating with zig-zag chains of In atoms on an essentially unperturbed Si lattice 98L reconstruction into consecutive 5- and 6-fold Si rings separated by channels containing the Li atoms
-
Table 24. Structures of clean Si and Ge (100) surfaces. Here; dbulk is the bulk interlayer spacing; d12 is the spacing between the Group IV dimer atoms; and ω is the Group IV dimer rotation angle. Surface Ge(100)(2x1) Ge(100)(2x1) Ge(100)(2x1) Ge(100)(2x1) (disordered) Si(100)-(2x1) Si(100)-(2x1) Si(100)-(2x1) Si(100)-(2x1) Ge(100)c(4x2) Si(100)c(4x2)
Tech- Clean dbulk nique rec. [Å] XRD yes 1.41
d12 [Å] 1.28 ± 0.04
ω (°) 31
Ref.
Description
81E
tilted dimer reconstruction with lateral relaxation in 2nd layer
XRD yes
1.412
0
0
88G
symmetric dimer reconstruction
XRD yes
1.414
0.74
17
92R
XRD yes
1.415
0.69 ± 0.04
16
96T2
asymmetric dimer reconstruction with multilayer relaxations; lateral and perpendicular; in top 10 layers disordered reconstruction with asymmetric Ge dimers; 2 equivalent and random orientations
LEED GIXD LEED LEED XRD
yes yes yes yes yes
1.358 1.358 1.358 1.358 1.415
0.36 ± 0.2 0.31 0.14 0.73 ± 0.04 0.83
8 7 3 19 -
84H2 90J1 91Z 97O2 95F2
buckled dimer with multilayer relaxations clean surface with buckled dimers 2 coexisting phases: 75% (2x1) and 25% c(4x2); (2x1) has weakly buckled dimers asymmetrical buckled dimer structure; with multilayer relaxation to 5th layer ordered reconstruction based on dimers in 'antiferromagnetic' arrangement
LEED yes
1.358
0.56
14
91Z
2 coexisting phases; 75% (2x1) and 25% c(4x2); c(4x2) has strongly buckled dimers
4.1-87 Table 25. Adsorbate-induced structures on Si and Ge (100) surfaces. Here; d01 is the local adsorbate height; d12 is the spacing between the Group IV dimer atoms; and ω is the Group IV dimer rotation angle. Surface
Tech- Clean Adsnique rec. ind rec.
d01 [Å]
d12 [Å]
ω [°]
Ref.
Description
-
91M3
atomic adsorption in-plane with top layer of bulk-like Si(100); at center of square of top-layer Si atoms
adsorption at center sites of unreconstructed substrate (see Fig. 33) Si(100)+0.4 ML-Co
SEyes XAFS
no
0.00 ± 0.02
0.00 ± 0.02
adsorption at continuation bridge sites of unreconstructed substrate (see Fig. 34) Ge(100)+ (2x1)-S
AR- yes PEFS
no
1.08
-
-
88L
atomic adsorption in bridge (i.e. bulk continuation) sites of unreconstructed but relaxed substrate
-
-
93S2
atomic H saturates the Si dangling bonds; forming unreconstructed substrate
adsorption at dangling-bond sites of unreconstructed substrate Si(100)+ (1x1)-2H
TOF- yes SARS
no
0.81
adsorption at dangling bond sites of dimers Ge(100)+ (2x1)-H (D)
LEED yes
yes
1.35
0
0
96P
H (D) atoms cap non-tilted Ge dimer atoms; symmetric dimers; relaxations down to fifth layer
HEIS yes Si(100)+ (disordered)Ge+ (disordered)Sb Si(100)+ TOF- yes (2x1)-2H SARS
yes
1.017 (Ge) 1.428 (Ge) 2.847 (Sb) 3.183 (Sb)
0
-
94G3
Sb forms asymmetrical dimers on Ge monolayer on unrelaxed substrate; Ge resides near continuation sites of substrate; so that whole structure is similar to clean dimerized Si(100); but considerably disordered
yes
0.89
0.0
0.0
93S2
atomic H resides at the Si dangling bond position of symmetrical dimers
4.1-88 Surface
d01 [Å]
d12 [Å]
ω [°]
Ref.
Description
1.62 ± 0.4
0.3 ± 0.4
8±8
97F3
NH2 adsorbed on one end of Si dimers; buckling of dimers probably lifted
yes
-
-
-
98F
OH and H adsorbed at dangling-bond sites of relatively symmetric Si dimers
yes
3.06 ± 0.03
0.83 ± 0.03
20 ± 2
95C1
Rb adsorbed on top of the highest of the two Si atoms forming an asymmetric surface dimer
Tech- Clean Adsnique rec. ind rec. PED yes yes
Si(100)(2x1)+ (disordered)NH2 Si(100)PED yes (2x1)+ (disordered)OH+H XSW yes Si(100)+ (2x1)-Rb (top; disordered)
adsorption at pedestal sites on dimers Si(100)+ (2x1)-Na Si(100)+ (2x1)-Rb (pedestal; disordered)
LEED yes
yes
1.85
0
0
90W2
XSW yes
yes
1.44 ± 0.03
0.00 ± 0.02
0±2
95C1
2.40 ± 0.03
0.00 ± 0.02
0±2
95C1
atomic adsorption in 'pedestal site'; bridging pairs of adjacent Si dimers; which are stretched wrt clean Si(100)-(2x1) Rb adsorbed at pedestal site; at center between two adjacent symmetrical Si dimers
adsorption at bridge sites on dimers Si(100)+ (2x1)-Rb (bridge; disordered)
XSW yes
yes
Rb adsorbed at bridge site; over midpoint of symmetrical dimer
4.1-89 Surface
Tech- Clean Adsnique rec. ind rec.
d01 [Å]
d12 [Å]
ω [°]
Ref.
Description
1.38 ± 0.03
0.00 ± 0.02
0±2
95C1
Rb adsorbed at valley site; at center between 4 symmetrical dimers
atomic adsorption as 'double layer' model; with K at both the pedestal and cave sites on a dimerized Si(100)-(2x1) substrate atomic adsorption as 'double layer' model; with K at both the pedestal and cave sites on a dimerized Si(100)-(2x1) substrate atomic adsorption as 'double layer' model; with Cs at both the pedestal and cave sites on a dimerized Si(100)-(2x1) substrate
adsorption at valley sites on dimers Si(100)+ (2x1)-Rb (valley; disordered)
XSW yes
yes
adsorption at cave+pedestal sites on dimers Si(100)+ (2x1)-2K Si(100)+ (2x1)-2K Si(100)+ (2x1)-2Cs
LEED yes
yes
1.75
1.15 ± 0.1
29
91U
LEED yes
yes
0
0
93U
LEED yes
yes
1.03; 1.58 2.46
0
0
93U
2.95 adsorption at cave+bridge sites on dimer
0
0
Si(100)+ (2x1)-2K Si(100)+ (2x1)-2Cs
0
0
98M2
0
0
98M2
-
0
92L
XRD yes
yes
XRD yes
yes
2.72 2.17 2.66
partial lifting of clean-surface dimerization; with adsorption on both dimer-bridge site and valley-bridge site partial lifting of clean-surface dimerization; with adsorption on both dimer-bridge site and valley-bridge site
dimers on unreconstructed substrate Ge(100)+ (2x1)-2Sb
XRD yes
no
1.39 ± 0.06 1.43 ± 0.06
asymmetric Sb-Sb dimers replace Ge-Ge dimers of clean Ge(100); dimers are laterally shifted from symmetry axis by 0.16 Å; and perhaps slightly tilted; substrate relaxes to 4th Ge layer (laterally in 1st; 4th layers; buckling in 2nd; 3rd layers)
4.1-90 Surface
d12 [Å]
ω [°]
Ref.
Tech- Clean Adsnique rec. ind rec. XSW yes no
d01 [Å] 2.01 ± 0.07
-
0
95L1
Si(100)+ (2x1)-2Sb
XSW yes
no
1.64 ± 0.02
-
0
95L3
Si(100)+ (2x1)-2Sb
SEyes XAFS
no
1.74 ± 0.06
-
0
91R
LEED yes
yes
1.08 ± 0.05
0.00 ± 0.05 0 ± 1
93S1
LEED yes
yes
1.07 ± 0.05
0.00 ± 0.05 0 ± 1
94S1
XSW yes
yes
1.03 ± 0.02
-
95T
TOF- yes SARS XRD yes
yes
-
0
0
93W2
yes
0.057
0.792
19
94M3
XRD yes
yes
0.51 ± 0.2
0.57 ± 0.06
12 ± 2
95M2
XRD yes
yes
0.79 ± 0.2
0.57 ± 0.06
12 ± 2
95M2
Ge(100)+ (2x1)-2Sb
Description
symmetrical Sb dimer overlayer on unreconstructed; relaxed substrate: topmost Ge-Ge interlayer spacing contracted (this contraction could be spread more uniformly over more spacings) Sb dimer on unreconstructed substrate (dimer orientation perp. to that of the Si dimer formed after removal of the Sb layer; i.e. parallel to Si dimer formed by substitution of Si for Sb) Sb dimer on unreconstructed substrate (dimer orientation perp. to that of the Si dimer formed after removal of the Sb layer; i.e. parallel to Si dimer formed by substitution of Si for Sb)
dimers on dimers (parallel) Si(100)+ (2x2)-2Al Si(100)+ (2x2)-2Ga Si(100)+ (2x2)-2Ga
-
non-buckled Al dimer between and parallel to Si dimers (like clean-surface dimers but without buckling); with multilayer relaxations non-buckled Ga dimer between and parallel to Si dimers (like clean-surface dimers but without buckling); with multilayer relaxations non-buckled Ga dimers are centered at valley bridge sites with the Ga-dimer bond oriented parallel to the underlying Si-dimer bonds
complex reconstructions Si(100)+ c(4x4)-12H Ge(100)(2x1)+Cs (disordered) Ge(100)(2x1)+Na (disordered) Ge(100)(2x1)+K (disordered)
for Si substrate; the crosswise linked dimer (CLD) model is consistent with experimental data disordered overlayer on reconstructed relaxed substrate; adatoms occupy T3 site (on top of 3rd layer Ge); asymmetric Ge-dimer remain; with 2 equivalent random orientations disordered overlayer on reconstructed relaxed substrate; Na occupies two sites: near T3 (on top of 3rd layer Ge) and near T4 site; asymmetric Ge dimers remain; with 2 equivalent random orientations disordered overlayer on reconstructed relaxed substrate; adatoms occupy T3 site (on top of 3rd layer Ge); asymmetric Ge-dimers remain; with 2 equivalent random orientations
4.1-91 Surface
Si(100)+ (3x4)-6In
Tech- Clean Adsnique rec. ind rec. GIXD yes yes STM
d01 [Å]
d12 [Å]
ω [°]
Ref.
Description
0.866 (Si) 0.996(In) 2.396(In) 2.566 (Si)
0
0
98B2
dimer rows with a sequence of two In-Si dimers followed by a Si vacancy allowing stress relief; In-Si-In 'trimers' between the dimer rows saturating dangling bonds of Si atoms; relaxations down to the sixth layer
Table 26. Structures of clean Si(311) surfaces. Surface Ge(311)(3x1)
Tech- Clean dbulk nique rec. [Å] GIXD yes 1.706
d12 [Å]
ω (°)
Ref.
Description
98V3
reconstructed dimer-adatom-interstitial model (interstitial site half occupied); relaxation around the interstitial sites amounts up to about 1 Å
Table 27. Adsorbate-induced structures on Si(311) surfaces. Surface
Tech- Clean Adsnique rec. ind rec.
d01 [Å]
d12 [Å]
ω [°]
Ref.
Description
overlayer in 2-fold coordinated continuation site Si(311)+ (1x1)-Pb
QK- yes LEED
no
1.37
95Z
adatom on bridging continuation site on unreconstructed substrate relaxed down to 9th Si monolayer
yes
-
94H6
2 top layer (100)-like Si atoms form dimers; 3rd (100)-like Si atom absent; 2 Si atoms; previously bonded to it; form another dimer; surface relaxations extend down to six layers from the surface; H positions not determined
dimerization of substrate Si(311)+ (3x1)-H
LEED yes
4.1-92 Table 28. Structures of clean zincblende(110) surfaces. Here; dbulk is the bulk interlayer spacing; d12 is the outermost spacing (buckling) between the tilted Group III-V (or II-VI) atom chains; and ω is the tilt angle of these chains. Surface AlP(110)(1x1) CdTe(110)(1x1) CuBr(110)(1x1) CuCl(110)(1x1) GaAs(110)(1x1) GaAs(110)(1x1) GaAs(110)(1x1) GaP(110)(1x1) GaSb(110)(1x1) GaSb(110)(1x1) InP(110)(1x1) InP(110)(1x1) InP(110)(1x1) InP(110)(1x1) InSb(110)(1x1)
Tech- Clean dbulk nique rec. [Å] LEED no 1.925
d12 [Å] 0.63
ω (°) 25
Ref.
Description
83D3
top layer composed of tilted zigzag chain
LEED no
2.291
0.73
30
97D
top layer composed of tilted zigzag chain
LEED no
2.012
0.76
35
96D3
top layer composed of tilted zigzag chain
LEED no
1.911
0.78
53
96D3
top layer composed of tilted zigzag chain
LEED no
1.999
0.69
28
84T1
top layer composed of tilted zigzag chain
LEED no
1.999
0.40
16
84G2
top layer composed of tilted zigzag chain
LEED no
1.999
0.67
29
93C2
top layer composed of tilted zigzag chain
LEED no
1.927
0.61
28
93L3
top layer composed of tilted zigzag chain
LEED no
2.163
0.77
30
83D4
top layer composed of tilted zigzag chain
MEIS no
2.163
0.73
29
86S4
top layer composed of tilted zigzag chain
LEED no
2.075
0.64
26
80T
top layer composed of tilted zigzag chain
SEno XAFS LEPD no
2.074
0.66
27
92W3
top layer composed of tilted zigzag chain
2.075
0.61
25
93C2
top layer composed of tilted zigzag chain
PED
2.074
0.57
23
93G2
top layer composed of tilted zigzag chain
2.29
0.78
29
80M2
top layer composed of tilted zigzag chain
no
LEED no
4.1-93 Surface InSb(110)(1x1) ZnS(110)(1x1) ZnSe(110)(1x1) ZnTe(110)(1x1)
Tech- Clean dbulk [Å] nique rec. LEED no 2.29
d12 [Å] 0.81
ω (°) 41
Ref.
Description
87D1
top layer composed of tilted zigzag chain
LEED no
1.913
0.55
30
93L3
top layer composed of tilted zigzag chain
LEED no
2.004
0.68
29
84D
top layer composed of tilted zigzag chain
LEED no
2.153
0.71
28
83D5
top layer composed of tilted zigzag chain
Table 29. Adsorbate-induced structures on zincblende(110) surfaces. Here; d01 is the local adsorbate height; d12 is the outermost spacing (buckling) between the tilted Group IIIV atom chains; and ω is the tilt angle of these chains. Surface
Tech- Clean Adsnique rec. ind rec.
d01 [Å]
d12 [Å]
ω [°]
Ref.
Description
adsorption at dangling-bond sites GaAs(110)+ H (0.25 ML) GaAs(110)+ H (0.8 ML) GaAs(110)+ H (low coverage) GaAs(110)+ H (high coverage) GaAs(110)+ (1x1)-2Sb
PD
no
no
-
0.15
6 ±1.5
95R
surface derelaxes towards ideal termination; H atom positions unknown
GIXD no
no
-
-0.115
-5 ± 1
94R
small counter-relaxation; H atom positions unknown
TOF- no SARS
no
-
0.0 ± 0.08
0±3
97G2
surface derelaxes towards ideal termination; H atom positions unknown
TOF- no SARS
no
-
-0.08 ± 0.08
-3 ± 3
97G2
small counter-relaxation; H atom positions unknown
LEED no
no
2.39 2.29
-0.100
-4
82D
Sb forms zigzag chains continuing GaAs lattice outward; but with expanded Sb-Sb and Sb-substrate distances; and with slight tilting of topmost GaAs chains
4.1-94 Tech- Clean Adsnique rec. ind rec. GaAs(110)+ LEED no no (1x1)-2Sb
d01 [Å]
d12 [Å]
ω [°]
Ref.
Description
2.36 2.29
-0.111
-5
90F2
GaAs(110)+ LEED no (1x1)-2Bi
no
2.51 2.42
-0.106
-4
90F2
GaSb(110)+ XRD no (1x1)-2Bi
no
-
-
34 (Bi-Bi)
98V1
Sb forms slightly tilted zigzag chains continuing GaAs lattice outward but with expanded Sb-Sb and Sb-substrate distances and with slight tilting of topmost GaAs chains Bi forms slightly tilted zigzag chains continuing GaAs lattice outward but with expanded Bi-Bi and Bi-substrate distances and with slight tilting of topmost GaAs chains Bi forms almost untilted zigzag chains bonded alternately to Ga and Sb atoms of bulk-terminated unrelaxed surface
InP(110)+ LEED no (1x1)-2Sb InP(110)+ LEED no (1x1)-2Bi InP(110)+ XSW no (1x1)-SH+H
no
-1
92F
adatoms forming (slightly tilted) zigzag chains; continuing relaxed substrate lattice
1
92F
adatoms forming (slightly tilted) zigzag chains; continuing relaxed substrate lattice
no
2.39 -0.027 2.26 2.6 0.038 2.4 1.97 ± 0.06 0.0
0
96D2
S atoms bonded to surface In and occupying sites near P sites of continuation of bulk structure into vacuum; outer InP layer is 'unrelaxed' to bulk-terminated structure
yes
-
-
-
98V2
2 strongly tilted (34°) Bi-Bi zig-zag rows replace every other Ga-Sb zig-zag row of clean surface; inducing subsurface relaxations
yes
-
0.69
31
81K
substitution of Al in 2nd-layer Ga positions; otherwise same structure as GaAs(110) (class. no. 31.33.26); except for 0.1Å reduction of 1st-2nd layer spacing
Surface
no
substitution in 1st layer GaSb(110)+ XRD no (2x1)-4Bi substitution in 2nd layer GaAs(110)+ LEED no (1x1)-1Al (low coverage)
4.1-95 Surface
d01 [Å]
d12 [Å]
ω [°]
Ref.
Description
yes
-
0.69
31
81K
substitution of Al in 2nd- and 3rd-layer Ga positions; otherwise same structure as GaAs(110) (class. no. 31.33.26); except for 0.1Å reduction of 1st-2nd layer spacing
yes
-
0.69
31
81K
substitution of Al in 1st; 2nd- and 3rd-layer Ga positions; otherwise same structure as GaAs(110)-2Al; except for 0.1Å reduction of 1st-2nd layer spacing; higher coverages cause Al substitution in deeper layers; e.g. at 8.5ML substitution down to at least 6th layer
Tech- Clean Adsnique rec. ind rec.
substitution in deeper layer GaAs(110)+ LEED no (1x1)-2Al (medium coverage) GaAs(110)+ LEED no (1x1)-3Al (high coverage)
Table 30. Structures of clean zincblende(111) surfaces. Here; dbulk is the bulk interlayer spacing; d12 is the outermost spacing between Group III-V atoms; and ω is the tilt angle of these III-V bonds; relative to the surface plane. Surface
Tech- Clean dbulk [Å] nique rec.
d12 [Å]
ω (°)
Ref.
Description
GaAs(111)(2x2) GaP(111)(2x2) GaSb(111)(2x2)
LEED yes
0.2
5
84T2
one missing Ga per (2x2) unit cell in heavily relaxed top bilayer; top bilayer almost planar
0.1
2
85X2
one missing Ga per (2x2) unit cell in heavily relaxed top bilayer; top bilayer almost planar
0
0
87F
one missing Ga per (2x2) unit cell in heavily relaxed top bilayer; top bilayer almost planar
LEED yes XRD yes
0.816; 2.448 0.787; 2.360 0.88; 2.64
4.1-96 Table 31. Adsorbate-induced structures on zincblende(111) surfaces. Here; d01 is the local adsorbate height; d12 is the outermost spacing between Group III-V atoms; and ω is the tilt angle of these III-V bonds; relative to the surface plane. Surface
d01 [Å]
d12 [Å]
ω [°]
Ref.
Description
no
2.17 ± 0.04
-0.816
19
93S5
no
1.61
-0.63
19
97S1
S adatoms at top sites (bonding to Ga) on unreconstructed full-bilayer termination; substrate assumed unrelaxed adsorption at top sites; inducing multilayer subsurface relaxations
Tech- Clean Adsnique rec. ind rec.
adsorption at top sites (see Fig. 35) GaAs(111)+ XSW yes (1x1)-S 3CLEED no SiC(111)+ (disordered)-O
Table 32. Structures of clean zincblende(-1-1-1) surfaces. Here; dbulk is the bulk interlayer spacing; d12 is the outermost spacing between Group III-V atoms; and ω is the tilt angle of these III-V bonds; relative to the surface plane. Surface
Tech- Clean dbulk [Å] nique rec. InSb XRD yes 0.935; (-1-1-1)-(3x3) 2.806 (disordered)
d12 [Å]
ω (°)
Ref.
Description
94W1
complex reconstruction composed of two types of rings of 6 atoms each; partly disordered
Table 33. Adsorbate-induced structures on zincblende(-1-1-1) surfaces. Here; d01 is the local adsorbate height; d12 is the outermost spacing between Group III-V atoms; and ω is the tilt angle of these III-V bonds; relative to the surface plane. Surface
GaAs (-1-1-1)+ (1x1)-S
Tech- Clean Adsnique rec. ind rec. XSW yes no
d01 [Å]
d12 [Å]
ω [°]
Ref.
Description
0.69 ± 0.04
0.816
-
93S5
S adatoms substituting for top half of top bilayer; i.e. bonding to 3 Ga atoms; substrate assumed unrelaxed
4.1-97 Table 34. Structures of clean zincblende(100) surfaces. Here; dbulk is the bulk interlayer spacing; d12 is the outermost spacing between Group IV-IV or III-V atoms; and ω is the tilt angle of their bonds; relative to the surface plane. Surface SiC(100)(2x1) SiC(100)c(2x2) (C2H4 exposed) SiC(100)c(2x2) (Si sublimation) GaAs(100)(4x2) GaAs(100)(4x2) InP(100)(4x2) GaAs(100)c(8x2) (Gaterminated)
Tech- Clean dbulk nique rec. [Å] LEED yes 1.093 LEED yes
1.093
LEED yes
1.093
0.0 (Si-Si) 1.60 (Si-C)
RH- yes EED GIXD yes
1.413
1.52
1.413 1.47
TOF- yes SARS LEED yes
ω (°)
d12 [Å] 0.20 (Si-Si) 1.21 (Si-C) 0.0 (Si-Si) 1.62 (Si-C)
1.414
Ref.
Description
95S1
Si-rich Si-terminated reconstruction with asymmetric buckled Si dimers; small relaxations in deeper layers C-rich C-terminated reconstruction with symmetric C pairs bridging Si pairs; slight relaxations in second layer; this structure possibly contains hydrogen
91P
91P
C-rich C-terminated reconstruction with symmetric C pairs bridging Si pairs; marked relaxations in second layer; this structure is presumably hydrogen-free
35
90F2
1.77
41
96G1
0.15 (In-In) 1.32 (In-P) 0.86; 1.05
32 27
reconstruction with As termination as three As2 dimers; with substrate assumed unrelaxed reconstruction with As termination as two As dimers; missing Ga row in second layer; As dimers in third layer reconstruction with In termination as three In2 dimers; with a 2nd-layer P2 dimer exposed in the trough three Ga dimers and a dimer vacancy in top layer; the middle Ga dimer is fully dimerized; while dimerization of the other two dimers is subtle; second (As) layer and deeper layers have no vacancies; strong relaxations down to the third layer
96D2 95C2
Table 35. Adsorbate-induced structures on zincblende(100) surfaces. Here; d01 is the local adsorbate height; d12 is the outermost spacing between Group III-V atoms; and ω is the tilt angle of these III-V bonds; relative to the surface plane. Surface
Tech- Clean Adsnique rec. ind rec. GaAs(100)+ XSW yes no (1x1)-S
d01 [Å]
d12 [Å]
ω [°]
Ref.
Description
1.1
0
-
94S7
S atoms at bridge sites on Ga-terminated surface; which is assumed non-reconstructed
4.1-98 Table 36. Structures of clean 6H-SiC(0001) surfaces. Here; dbulk is the bulk interlayer spacing; d12 is the outermost spacing between Group IV-IV atoms; and ω is the tilt angle of their bonds; relative to the surface plane. Surface 6HSiC(0001)(1x1)
Tech- Clean dbulk nique rec. [Å] LEED no 1.9
d12 [Å] 0.64
ω (°) 20
Ref.
Description
97S1
small relaxations of interlayer spacings
Table 37. Adsorbate-induced structures on 6H-SiC(0001) surfaces. Here; d01 is the local adsorbate height; d12 is the outermost spacing between Group IV-IV atoms; and ω is the tilt angle of these IV-IV bonds; relative to the surface plane. Surface
d01 [Å]
d12 [Å]
ω [°]
Ref.
Description
1.02
0.60
18
97S1
adsorption at top sites; inducing multilayer subsurface relaxations
no
1.66
0.55
17
97S1
adsorption at top sites; inducing multilayer subsurface relaxations
no
1.65± 0.03
0.58 ± 0.02
18
95S1
unreconstructed relaxed substrate; with OH groups saturating the dangling bonds of top Si layer; adatom site: top position on Si (T1-site) (H ignored) O-Si bond length: 1.65Å; first bilayer spacing 7.5% contracted; interbilayer spacings are bulklike
Tech- Clean Adsnique rec. ind rec. LEED no no
6HSiC(0001)+H 6HLEED no SiC(0001)+O 6HLEED no SiC(0001)+ (1x1)-OH
Figures for 4.1
Fig. 1. Generic labeling scheme for relaxations in a surface - top view. This Fig. shows only one shell (labeled s) of symmetrically equivalent atoms in one particular layer (labeled l), surrounding the adsorbate site. The relaxed atomic positions are shown as black balls, displaced relative to the ideal bulk-like positions (gray balls). The relaxed radial position is labeled as rls(1+∆rls), with an in-plane rotation angle of αls.
Fig. 2. Generic labeling scheme for relaxations in a surface - side view. An adsorbate defines layer 0 and the adsorbate site (or adsorption axis, which is usually a symmetry axis); the adsorbate may be displaced away from the symmetry axis by an amount ∆r0, and it may contain more atoms (not shown here). Substrate layers are labeled l = 1, 2, 3, …, and shown here as gray bars, with a non-zero thickness due to buckling from a planar layer in the bulk. The spacings between layers are labeled dbulk(1+∆dl,l+1), where dbulk is given in the tables for clean surfaces; these spacings are measured between the thick lines defined as the height of those atoms which are nearest to the dashed adsorption axis (these atoms are labeled a). In a given layer l = 1, 2, 3, …, the radial distance of atoms in shells s = a, b, c, … (centered on the adsorption axis) is given by rls(1+∆rls), where rls is the ideal unrelaxed distance. Similarly, the buckling of an atom within layer l is given as bls/dbulk, relative to its ideal nonbuckled position on the thick line.
Lando lt -Bö rnst ein New Ser ies III/42A2
4.1-100
4.1 Surface structure on metals and semiconductors
(a)
3c 1c 2c 3c
2b 3b
1b 2c
1a
3b
1c
1c
2b
1b
2c
1c
3c 2b
1a
2b
1c 3b
2b 1b
3c
(b)
3a
3a
1c
2c
1b
2a
1a 3b
3c
3c
(b)
3c 2b
1a 3a
2b
1c
3b
2c
3c
3b
2a 3b
1b
2c
1a
1c 3b
2b
1b
3a
2b 3c
3c
3c
2a
1a
2c 1c
2c 3b
2a
1c
(a)
1c
[Ref. p 4.1-109
2c 1c
3c
1c 1b 1a 1a 1a 1b 1c
1c 1b 1a 1a 1a 1b 1c
2c 2b 2a 2a 2a 2b 2c
2c 2b 2b 2a 2b 2b 2c
3c 3b 3b 3a 3b 3b 3c
3c 3b 3a 3a 3a 3b 3c
Fig. 3. Sketch of fcc(111) fcc-hollow site.
Fig. 4. Sketch of fcc(111) hcp-hollow site.
Views are (a) along the surface normal and (b) parallel to surface. The dashed line in (a) denotes the cutting plane used for the view in (b). The digits 1, 2, 3, … label atomic layers of the substrate (index l), while the letters a, b, c, … label atomic shells around the adsorption site axis (index s). These views and conventions are used in Figs. 3 - 35. (a)
(a)
1c
1c 3c 2c 1c
2b 1b
3b 2c
2a 1a 2a
2c
2c
3a
3a 2a
1b 3c
1b
3c
3c
1c
1b
2c 2b 2a 2a 2a 2b 2c
1b 3b
2a
2c 1a
3a
3a 2a
1a 2c
1c 1b 1a 1a
1c 3c
2b 1a
3b
1c
(b) 1c 1b 1b 1a 1b 1b 1c
2a
3c
2c
2c 1a
3a
2b
3c
1c
(b)
2b
1a
2b
3b 2c
1c
1c 3c
1a 3b
1b
2b 1c
1b
1c 3b
1b 3c
2c
2c 1b
3a
1b 3c
3c
1b 3c
2c 1b
1c
1a 1a 1b 1c
2c 2b 2a 2a 2a 2b 2c 3c 3b 3a 3a 3a 3b 3c
3c 3b 3a 3a 3a 3b 3c
Fig. 5. Sketch of fcc(111) top site.
Fig. 6. Sketch of fcc(111) substitutional site.
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.1-109]
4.1 Surface structure on metals and semiconductors
(a)
1c 2c 1b 2c
1c 2b
1c
1b 2c
(b)
1c
1c
2c
2c
2c
2b 2b 2a 2b 2b
2c
3c
3c
3b 3a 3a 3a 3b
3c
3b 3a 3a 3a 3b
Fig. 7. Sketch of hcp(0001) fcc-hollow site.
(a)
Fig. 8. Sketch of hcp(0001) hcp-hollow site.
(a)
1c
1b
1c
2a 1a 2a
2c
2c 1b
2a
1b 2a
1a 2b
2c
1a
1c 2b
2a
1c 1c
2c
1b 2c
1c
(b) (b)
2c
1a 2a
1c
2b 1b
2c
1c 2b
2c 1b
1b
1c 2c
1b 1c
2c 1c
2c
3c
2b
2b 1b
1c
2b 2a 2a 2a 2b
2c
2b
1c
1b 1a 1a 1a 1b
2c
1b
2b 1a
1c
1c
2b
1b
2a
1a
1c
(b)
2b 1a
2b 1c
1b 1a 1a 1a 1b
1c
1b
2b
1c
2c
1c
2b 2c
1a 2a
1c
1c
1b 2a
1a 2b
2c
2c
1a 2a
(a)
4.1-101
1c 2c
1a 1c
1b
1a
2c
2b
2a
3c
3b
3a
1a
1b
1c
2a
2a
2b
2c
3a
3a
3b
3c
1c 1b 1b 1a 1b 1b 1c 2c 2b 2a 2a 2a 2b 2c 3c 3b 3b 3a 3b 3b 3c
Fig. 9. Sketch of hcp(0001) top site.
Lando lt -Bö rnst ein New Ser ies III/42A2
Fig. 10. Sketch of hcp(0001) octahedral interstitial site.
4.1-102
4.1 Surface structure on metals and semiconductors
(a)
2c
(a)
1c
1c
2b 1b
2b 1a
1a
2c
(b)
2b
2c
1a
1c
2b
1c
1b
2b
1c
1a
2c
1b
2b
1c
1a
1b
1a
1c
2c
2b
2a
2b
2c
3c
3a
3b
3a
3c
2a
2b 1a
2b 1c
1c 1b
2a
2b 1c
[Ref. p 4.1-109
1c
2b 1b
2c 1c
1a 1c
1b
1a
1a
1b
1c (b)
2c
2b
2b
2a
2b
2b
2c
3c
3b
3a
3a
3a
3b
3c
Fig. 11. Sketch of hcp(0001) tetrahedral interstitial site.
Fig. 12. Sketch of bcc(110) center site.
(a)
(a)
1c
1b 2c
1d
2b
1a
2b
1b 2b
1c 2c
1d 1b
1a
1a
1b
2a
2d
1b
1e
2c
2a
1b
2d
2c
1e
2b 1b
1c
2b 1a
2c
(b)
1d
1b
1a
1b
1d
2d
2b
2a
2b
2d
3d
3b
3a
3b
3d
Fig. 13. Sketch of bcc(110) 3-fold coordinated hollow site.
(b)
1a 2b
1b 2c
1c
1b
1b
1c
1b
1a
1a
1b
2b 3b
2a 3a
2b 3a
3b
Fig. 14. Sketch of fcc(100) hollow site.
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.1-109]
4.1 Surface structure on metals and semiconductors
(a)
(a) 2c
2b 1c
2b
2b 1b
2a
1a
1b 2b 1c 2c
2c
2b
2b
2a 1b
2b
2b 1a
2a
2c 1b
2a
2b
3a
1c
1a
2b
2b
2c
2c
1c 2b
2b 1b
1b 2a
1c 2c
1c 2a
4.1-103
1a 2a
1b
2a 1a
2b
1c 2b
1b 2b
2c
1c
(b) (b)
1b 2b
1a 2a
3b
1b 2a
3a
1c
1b 2c
1b
2b
3d
1a 2a
3b
2a 3a
1c 2b
3b
3d
3b
Fig. 16. Sketch of fcc(100) substitutional site.
1b 2b
1a
1a 2b
Fig. 15. Sketch of fcc(100) top site.
(a)
1c
1c
(a)
2c 1b
2c 1a
2b
1b
1b 2a
2b
2a
2b 1b
2b 1a
2c
(b)
1a 2b
1c 1b
1b
1c
1b
1a
1a
1b
2a 3a
Fig. 17. Sketch of bcc(100) hollow site.
Lando lt -Bö rnst ein New Ser ies III/42A2
2a
(b)
1c
2b 1b
1a 2b
3b
1c
2c
2b 3a
1a
1b
1b
3b
2b
2c
1c
2b
1a
3c
1a 2a
3a
1c 2b
3a
Fig. 18. Sketch of bcc(100) bridge site.
3c
4.1-104
4.1 Surface structure on metals and semiconductors
(a)
[Ref. p 4.1-109
2c (a) 1b 2b 1c
2a 1a
2b
1b
1b
2d 2b
1a 2a
1b
1c 1c
1b 2b
1a
2a
2d 1a
2c 1c
2b
2c 1a
2d
1b
1c
1a 2b
1c 2d
1b
1b
1a
1a
2c
(b)
1c
1a 2b
3c
1a 2a
3a
1c
(b)
1c
2b 3a
2c 3c
3c
Fig. 19. Sketch of bcc(100) 4-fold coordinated interstitial site.
(a)
(a)
1c 2d
2b
2a
2b 2c
1c
1a
1a
2d
1a 2a
3b
(b)
1c
2c
2c
3a
Fig. 21. Sketch of fcc(110) 3-fold coordinated hollow site.
3c
2d 1c
1a 2b
1a 2a
3a
1c 2b
1b
1c
1b
2b
2a 1b
1c
2d 1b
2a
2b
1a 2b
(b)
3c
1c 2c
1b 1a
1b
2c 3a
Fig. 20. Sketch of fcc(110) center site.
1c
1b
2a 3a
1c
1c 2b
3a
3c
Fig. 22. Sketch of fcc(110) long-bridge site.
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.1-109]
4.1 Surface structure on metals and semiconductors
(a)
(a)
2d 1c
1b
1b
2b
1c 1d
2c
2b 1b
2c
2a 1a
2b
2b 1a
2a
2c
2c
2a
1b 2b
1b
1b
2b 1b 1a
1d 2a
2c
1c 2c
2c
1c 2a
1d 1c
4.1-105
1c
2a
2c
1b 2b
1d 2b
2d
(b)
1b 2c
1a 2b
3b
1a 2a
3a
1b 2b
3a
2c
(b)
1c 2c
3b
1a 2a
3c
Fig. 23. Sketch of fcc(110) short-bridge site.
(a)
2c
2b
3a
1b
1b
1c 2a
3b 2b
4c
1a
3a
1a 2a
2a 1b
2c
(b)
1a 2b
4a
4c
2b
1a 3b
1c
1b
3b 1a
4c
3a 4a 2b 4b
1a
2c 4c
3b 1b
1a 2a
3a
2b 3b
(b)
1a 2c
1a 2a
3a 4c
Fig. 25. Sketch of fcc(110) upper substitutional site.
Lando lt -Bö rnst ein New Ser ies III/42A2
1b
2c
2a 3b
2b
3a
1b 2c
4b
2a
1a
1c
3c
2c
2a
2b
2c
Fig. 24. Sketch of fcc(110) upper top site.
(a) 1c
1c 2a
2c 3a
4a
Fig. 26. Sketch of hcp(10-10) center site.
4c
4.1-106
4.1 Surface structure on metals and semiconductors
(a) (a)
4c 2b 1b 3c
1c
1c
2a
2b
1a
4b
4b
3a
2c
2a 4a
1b
4a
1a
4c
4b
1a 3a
1b 3b
4b 2b
3b
2b
2b 4a
1a 3b
1b
1c 3c
3b
4a
[Ref. p 4.1-109
4b
2a 4a
2b 4a
4b
1c 1c
1c 3c
(b)
1b
1a 2a
2c
3c
(b)
3a 4a
1b
1a 2b
4b
3b 4b
Fig. 27. Sketch of hcp(10-10) 3-fold coordinated hollow site.
1b 1c
2b
2b 4a
4b 1a
1c
Fig. 28. Sketch of hcp(10-10) short-bridge site.
1c
1c
2c
2b 4a
4a 1b
2c 4b
1b
4c
1c
1a
1b
1c
2b 4c
2b 4b
2b
1a
1b
2b
3a 4a
4a
4c 1b
2c
1b
2a 4a
2a 4b
1b 2c
4b 1b
2c 4c
2b 4c
1c
1c
1b
2a
3b 4b
1c 2b
4a
2c
1c
1a
2b
4c
2a
1c
(b)
4b
1a
1a 2b
3b 4a
2a
4b
1b 2b
3a 4a
(a) (a)
1a 2a
(b)
1c
2b
1b
4c 2a
1a
2a
1b
2c
1c
3b 4a
Fig. 29. Sketch of diamond(111) T4 site.
3b
4a
3a
4a
3a
4b
3c
Fig. 30. Sketch of diamond(111) top site.
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.1-109]
4.1 Surface structure on metals and semiconductors
(a) (a)
1d
4c 2b
1b
2c 1a
4a 2b
1d
2c
4b 2a
1a 4c
1b
1e 4c 1c
2c
1a
4c
4b
1b
1a 2b
1c
(b)
2a
3b
3a 4a
1c
2c
1c
3d
4b
3c
4b
3d
1b
2b
1a
2a
1a
2b
1b
4c
3b
4a
4a
3b
1b
2b
1a
2a
1a
2b
3d
4b
3c
4b
3d
1c
2c
1c
3a
1b
1a
1a
(a)
2a
2b
3b
3a
3b
4c
4a
4a
4a
3a
1a
2c
4b
1b
3c
1b
4b
1b
4d
2b
3b
2a
3a
2a
3b
2b
4c
1c
4c
1a
1a
4c
1c
1b
2b
3b
2a
3a
2a
3b
2b
4d
1b
4b
1b
4d
4c
Fig. 33. Sketch of diamond(100) center site.
Lando lt -Bö rnst ein New Ser ies III/42A2
4c 1b
2a
2a
1b 2c
1a
4c
3a
4b
2b
1a
2c
4d
1b
2b
1a
4a
2c
4a
4c
Fig. 32. Sketch of diamond(111) substitutional top site.
(b) (b)
3b
2b
2a
4b
1a
1b
4a
2a
1a
2b
4c
4b
Fig. 31. Sketch of diamond(111) bridge site.
(a)
1b
1a 2a
1b
(b)
4c
4a
2c
1e
2c 4b
2b
1b
4.1-107
4a
1c
1a
1a
1c
2b
2a
2a
2b
3b
3a
3b
4c
4a
4c
Fig. 34. Sketch of diamond(100) continuation bridge site.
4.1-108
4.1 Surface structure on metals and semiconductors
(a)
1c 2c 4c
2c 1b
4b 1b
4c
2a
[Ref. p 4.1-109
1c 2b
4c 1b
4a
2c
1a
1c
4a
2b 4c
1b
1c
2b
4c
3b
1b
2a
4a
3a
1b 2b
1b 4c
2c
1c
(b)
4a
2a 4b
2c
4b
2a
1a
2c 4c
1c
2a
4a
1c
3a
1b
2c
4b
1c
3c Fig. 35. Sketch of zincblende(111) top site.
Lando lt -Börnst ein New Ser ies III/42 A2
References for 4.1 72L 75D 75I1 75I2 75U 76S1 76S2 76V1 76V2 77G 77L1 77L2 77L3 78B 78C 78J 78L 78M 79A 79M 79V1 79V2 80B 80C 80D 80H 80J 80M1 80M2 80S 80T 81A 81D 81E 81F 81K 81M 81N1 81N2 81S1 81S2 81V 82D 82I
Laramore, G.E., Duke, C.B.: Phys. Rev. B5 (1972) 267. Demuth, J.E., Marcus, P.M., Jepsen, D.W.: Phys. Rev. B11 (1975) 1460. Ignatiev, A., Jona, F., Jepsen, D.W., Marcus, P.M.: Phys. Rev. B11 (1975) 4780. Ignatiev, A., Jona, F., Shih, H.D., Jepsen, D.W., Marcus, P.M.: Phys. Rev. B11 (1975) 4787. Unertl, W.N., Thapliyal, H.V.: J. Vac. Sci. Technol. 12 (1975) 263. Shih, H.D., Jona, F., Jepsen, D.W., Marcus, P.M.: J. Phys. C9 (1976) 1405. Shih, H.D., Jona, F., Jepsen, D.W., Marcus, P.M.: Surf. Sci. 60 (1976) 445. Van Hove, M.A., Tong, S.Y.: Surf. Sci. 54 (1976) 91. Van Hove, M.A., Tong, S.Y., Stoner, N.: Surf. Sci. 54 (1976) 259. Groupe d'Etude des Surfaces (Grenoble), : Surf. Sci. 62 (1977) 567. Legg, K.O., Jona, F., Jepsen, D.W., Marcus, P.M.: J. Phys. C10 (1977) 937. Legg, K.O., Jona, F., Jepsen, D.W., Marcus, P.M.: Phys. Rev. B16 (1977) 5271. Legg, K.O., Jona, F., Jepsen, D.W., Marcus, P.M.: Surf. Sci. 66 (1977) 25. Barker, R.A., Estrup, P.J., Jona, F., Marcus, P.M.: Solid State Commun. 25 (1978) 375. Chan, C.-M., Luke, K.L., Van Hove, M.A., Weinberg, W.H., Withrow, S.P.: Surf. Sci. 78 (1978) 386. Jona, F., Legg, K.O., Shih, H.D., Jepsen, D.W., Marcus, P.M.: Phys. Rev. Lett. 40 (1978) 1466. Lee, B.W., Alsenz, R., Ignatiev, A., Van Hove, M.A.: Phys. Rev. B17 (1978) 1510. Maglietta, M., Zanazzi, E., Jona, F., Jepsen, D.W., Marcus, P.M.: Appl. Phys. 15 (1978) 409. Adams, D.L., Nielsen, H.B., Van Hove, M.A.: Phys. Rev. B20 (1979) 4789. Moore, W.T., Watson, P.R., Frost, D.C., Mitchell, K.A.R.: J. Phys. C12 (1979) L887. van der Veen, J.F., Smeenk, R.G., Tromp, R.M., Saris, F.W.: Surf. Sci. 79 (1979) 219. van der Veen, J.F., Tromp, R.M., Smeenk, R.G., Saris, F.W.: Surf. Sci. 82 (1979) 468. Behm, R.J., Christmann, K., Ertl, G., Van Hove, M.A.: J. Chem. Phys. 73 (1980) 2984. Clarke, L.J.: Surf. Sci. 91 (1980) 131. Davis, H.L., Zehner, D.M.: J. Vac. Sci. Technol. 17 (1980) 190. Hengrasmee, S., Mitchell, K.A.R., Watson, P.R., White, S.J.: Can. J. Phys. 58 (1980) 200. Jona, F., Sondericker, D., Marcus, P.M.: J. Phys. C13 (1980) L155. Marsh, F.S., Debe, M.K., King, D.A.: J. Phys. C13 (1980) 2799. Meyer, R.J., Duke, C.B., Paton, A., Yeh, J.L., Tsang, J.C., Kahn, A., Mark, P.: Phys. Rev. B21 (1980) 4740. Shih, H.D., Jona, F., Bardi, U., Marcus, P.M.: J. Phys. C13 (1980) 3801. Tear, S.P., Welton-Cook, M.R., Prutton, M., Walker, J.A.: Surf. Sci. 99 (1980) 598. Adams, D.L., Nielsen, H.B.: Surf. Sci. 107 (1981) 305. Davies, J.A., Jackman, T.E., Jackson, D.P., Norton, P.R.: Surf. Sci. 109 (1981) 20. Eisenberger, P., Marra, W.C.: Phys. Rev. Lett. 46 (1981) 1081. Feder, R., Pleyer, H., Bauer, P., Mueller, N.: Surf. Sci. 109 (1981) 419. Kahn, A., Carelli, J., Kanani, D., Duke, C.B., Paton, A., Brillson, L.: J. Vac. Sci. Technol. 19 (1981) 331. Morales de la Garza, L., Clarke, L.J.: J. Phys. C14 (1981) 5391. Narusawa, T., Gibson, W.M., Tornqvist, E.: Phys. Rev. Lett. 47 (1981) 417. Narusawa, T., Gibson, W.M., Tornqvist, E.: Surf. Sci. 114 (1981) 331. Shih, H.D., Jona, F., Jepsen, D.W., Marcus, P.M.: Phys. Rev. Lett. 46 (1981) 731. Shih, H.D., Jona, F., Jepsen, D.W., Marcus, P.M.: Surf. Sci. 104 (1981) 39. Van Hove, M.A., Koestner, R.J., Stair, P.C., Biberian, J.P., Kesmodel, L.L., Bartos, I., Somorjai, G.A.: Surf. Sci. 103 (1981) 218. Duke, C.B., Paton, A., Ford, W.K., Kahn, A., Carelli, J.: Phys. Rev. B26 (1982) 803. Imbihl, R., Behm, R.J., Ertl, G., Moritz, W.: Surf. Sci. 123 (1982) 129.
Lando lt -Bö rnst ein New Ser ies III/42 A2
4.1-110 82J 82L 82N1 82N2 82T1 82T2 83A 83C 83D1 83D2 83D3 83D4 83D5 83F 83H 83J 83K 83L 83M1 83M2 83M3 83S 84A 84D 84G1 84G2 84H1 84H2 84K 84L 84N 84S 84T1 84T2 84T3 84V 85A 85B1 85B2 85H1 85H2 85M1 85M2 85P 85S 85T 85X1
4.1 Surface structure on metals and semiconductors Jensen, V., Andersen, J.N., Nielsen, H.B., Adams, D.L.: Surf. Sci. 116 (1982) 66. Lang, E., Grimm, W., Heinz, K.: Surf. Sci. 117 (1982) 169. Nielsen, H.B., Adams, D.L.: J. Phys. C15 (1982) 615. Noonan, J.R., Davis, H.L.: Vacuum 32 (1982) 107. Titov, A., Moritz, W.: Surf. Sci. 123 (1982) L709. Tougaard, S., Ignatiev, A., Adams, D.L.: Surf. Sci. 115 (1982) 270. Adams, D.L., Nielsen, H.B., Andersen, J.N.: Surf. Sci. 128 (1983) 294. Citrin, P.H., Rowe, J.E., Eisenberger, P.: Phys. Rev. B28 (1983) 2299. Davis, H.L., Noonan, J.R.: Surf. Sci. 126 (1983) 245. Demuth, J.E., Dinardo, N.J., Cargill III, G.S.: Phys. Rev. Lett. 50 (1983) 1373. Duke, C.B., Paton, A., Kahn, A., Bonapace, C.R.: Phys. Rev. B28 (1983) 852. Duke, C.B., Paton, A., Kahn, A.: Phys. Rev. B27 (1983) 3436. Duke, C.B., Paton, A., Kahn, A.: J. Vac. Sci. Technol. A 1 (1983) 672. Frenken, J.W.M., van der Veen, J.F., Allan, G.: Phys. Rev. Lett. 51 (1983) 1876. Heinz, K., Besold, G.: Surf. Sci. 125 (1983) 515. Jona, F., Westphal, D., Goldman, A., Marcus, P.M.: J. Phys. C16 (1983) 3001. Kuk, Y., Feldman, L.C., Silverman, P.J.: Phys. Rev. Lett. 50 (1983) 511. Lang, E., Mueller, K., Heinz, K., Van Hove, M.A., Koestner, R.J., Somorjai, G.A.: Surf. Sci. 127 (1983) 347. Martinez, V., Soria, F., Munoz, M.C., Sacedon, J.L.: Surf. Sci. 128 (1983) 424. Masud, N., Baudoing, R., Aberdam, D., Gaubert, C.: Surf. Sci. 133 (1983) 580. Michalk, G., Moritz, W., Pfnur, H., Menzel, D.: Surf. Sci. 129 (1983) 92. Stensgaard, I., Feidenhans'l, R., Sorensen, J.E.: Surf. Sci. 128 (1983) 281. Andersen, J.N., Nielsen, H.B., Petersen, L., Adams, D.L.: J. Phys. C17 (1984) 173. Duke, C.B., Paton, A., Kahn, A., Tu, D.W.: J. Vac. Sci. Technol. B 2 (1984) 366. Gauthier, Y., Baudoing, R., Joly, Y., Gaubert, C., Rundgren, J.: J. Phys. C17 (1984) 4547. Grossman, H.J., Gibson, W.M.: J. Vac. Sci. Technol. B 2 (1984) 343. Himpsel, F.J., Marcus, P.M., Tromp, R., Batra, I.P., Cook, M.R., Jona, F., Liu, H.: Phys. Rev. B30 (1984) 2257. Holland, B.W., Duke, C.B., Paton, A.: Surf. Sci. 140 (1984) L269. Kuk, Y., Feldman, L.C.: Phys. Rev. B30 (1984) 5811. Lindgren, S.A., Wallden, L., Rundgren, J., Westrin, P.: Phys. Rev. B29 (1984) 576. Noonan, J.R., Davis, H.L.: Phys. Rev. B29 (1984) 4349. Sokolov, J., Shih, H.D., Bardi, U., Jona, F., Marcus, P.M.: J. Phys. C17 (1984) 371. Tong, S.Y., Mei, W.M., Xu, G.: J. Vac. Sci. Technol. B 2 (1984) 393. Tong. G. Xu, S.Y., Mei, W.M.: Phys. Rev. Lett. 52 (1984) 1693. Tornqvist, E., Adams, E.D., Copel, M., Gustafsson, T., Graham, W.R.: J. Vac. Sci. Technol. A 2 (1984) 939. Van Hove, M.A., Koestner, R.J.: Determination of Surface Structure by LEED, Marcus, P.M., Jona, F. (eds.), 1984, p. 357. Adams, D.L., Petersen, L.E., Sorensen, C.S.: J. Phys. C18 (1985) 1753. Barnes, C.J., Ding, M.Q., Lindroos, M., Diehl, R.D., King, D.A.: Surf. Sci. 162 (1985) 59. Baudoing, R., Gauthier, Y., Joly, Y.: J. Phys. C18 (1985) 4061. Hayek, K., Glassl, H., Gutmann, A., Leonhard, H., Prutton, M., Tear, S.P., Welton-Cook, M.R.: Surf. Sci. 152 (1985) 419. Hui, K.C., Milne, R.H., Mitchell, K.A.R., Moore, W.T., Zhou, M.Y.: Solid State Commun. 56 (1985) 83. Moritz, W., Wolf, D.: Surf. Sci. 163 (1985) L655. Moritz, W., Imbihl, R., Behm, R.J., Ertl, G., Matsushima, T.: J. Chem. Phys. 83 (1985) 1959. Passler, M.A., Lee, B.W., Ignatiev, A.: Surf. Sci. 150 (1985) 263. Smit, L., Tromp, R.M., van der Veen, J.F.: Surf. Sci. 163 (1985) 315. Titov, A., Jagodzinski, H.: Surf. Sci. 152/153 (1985) 409. Xu, M.L., Tong, S.Y.: Phys. Rev. B31 (1985) 6332. Lando lt -Börnst ein New Ser ies III/42A2
4.1 Surface structure on metals and semiconductors 85X2 86A 86B 86C1 86C2 86C3 86D 86F1 86F2 86H 86J 86M 86O 86R 86S1 86S2 86S3 86S4 86V 86Y1 86Y2 87B 87C1 87C2 87D1 87D2 87F 87H1 87H2 87I 87J 87K 87L1 87L2 87N 87O 87P 87R1 87R2
4.1-111
Xu, G., Hu, W.Y., Puga, M.W., Tong, S.Y., Yeh, J.L., Wang, S.R., Lee, B.W.: Phys. Rev. B32 (1985) 8473. Abu-Joudeh, M.A., Davies, B.M., Montano, P.A.: Surf. Sci. 171 (1986) 331. Barton, J.J., Bahr, C.C., Robey, S.W., Hussain, Z., Umbach, E., Shirley, D.A.: Phys. Rev. B34 (1986) 3807. Chan, C.-M., Van Hove, M.A.: Surf. Sci. 171 (1986) 226. Copel, M., Gustafsson, T.: Phys. Rev. Lett. 57 (1986) 723. Copel, M., Gustafsson, T., Graham, W.R., Yalisove, S.M.: Phys. Rev. B33 (1986) 8110. Derry, T.E., Smit, L., Van der Veen, J.F.: Surf. Sci. 167 (1986) 502. Fauster, Th., Durr, H., Hartwig, D.: Surf. Sci. 178 (1986) 657. Frenken, J.W.M., van der Veen, J.F., Barnett, R.N., Landman, U., Cleveland, C.L.: Surf. Sci. 172 (1986) 319. Hoesler, W., Moritz, W.: Surf. Sci. 175 (1986) 63. Jona, F., Marcus, P.M., Davis, H.L., Noonan, J.R.: Phys. Rev. B33 (1986) 4005. Moeller, J., Snowdon, K.J., Heiland, W.: Surf. Sci. 178 (1986) 475. Overbury, S.H.: Surf. Sci. 175 (1986) 123. Rous, P.J., Pendry, J.B., Saldin, D.K., Heinz, K., Mueller, K., Bickel, N.: Phys. Rev. Lett. 57 (1986) 2951. Sokolov, J., Jona, F., Marcus, P.M.: Europhys. Lett. 1 (1986) 401. Sokolov, J., Jona, F., Marcus, P.M.: Phys. Rev. B33 (1986) 1397. Sakama, H., Kawazu, A., Ueda, K.: Phys. Rev. B34 (1986) 1367. Smit, L., van der Veen, J.F.: Surf. Sci. 166 (1986) 183. Van Hove, M.A., Weinberg, W.H., Chan, C.-M,: LEED Experiment, Theory and Structural Determination, Heidelberg: Springer, 1986. Yalisove, S.M., Graham, W.R., Adams, E.D., Copel, M., T Gustafsson,: Surf. Sci. 171 (1986) 400. Yarmoff, J.A., Cyr, D.M., Huang, J.H., Kim, S., Williams, R.S.: Phys. Rev. B33 (1986) 3856. Baddorf, A.P., Lyo, I.-W., Plummer, E.W., Davis, H.L.: J. Vac. Sci. Technol. A 5 (1987) 782. Chan, C.-M., Van Hove, M.A.: Surf. Sci. 183 (1987) 303. Copel, M., Tromp, R.M.: Phys. Rev. B37 (1987) 2766. de Carvalho, V.E., Prutton, M., Tear, S.P.: Surf. Sci. 184 (1987) 198. Dev, B.N., Materlik, G., Grey, F., Johnson, R.L.: Springer Series in Surface Sciences 11 (1987) 340. Feidenhans'l, R., Nielsen, M., Grey, F., Johnson, R.L., Robinson, I.K.: Surf. Sci. 186 (1987) 499. Headrik, R.L., Graham, W.R.: J. Vac. Sci. Technol. A 6 (1987) 637. Holub-Krappe, E., Horn, K., Frenken, J.W.M., Krans, R.L., van der Veen, J.F.: Surf. Sci. 188 (1987) 335. Imbihl, R., Demuth, J.E., Himpsel, F.J., Marcus, P.M., Thompson, W.A., Jona, F.: Phys. Rev. B36 (1987) 5037. Jona, F., Marcus, P.M.: Solid State Commun. 64 (1987) 667. Kleinle, G., Skottke, M., Penka, V., Ertl, G., Behm, R.J., Moritz, W.: Surf. Sci. 189/190 (1987) 177. Lind, D.M., Dunning, F.B., Walters, G.K., Davis, H.L.: Phys. Rev. B35 (1987) 9037. Lindroos, M., Pfnur, H., Feulner, P., Menzel, D.: Surf. Sci. 180 (1987) 237. Nichtl, W., Bickel, N., Hammer, L., Heinz, K., Mueller, K.: Surf. Sci. 188 (1987) L729. Ohtani, H., Van Hove, M.A., Somorjai, G.A.: Surf. Sci. 187 (1987) 372. Patel, J.R., Golovchenko, J.A., Freeland, P.E., Grossman, H.J.: Phys. Rev. B36 (1987) 7715. Reimer, W., Penka, V., Skottke, M., Behm, R.J., Ertl, G., Moritz, W.: Surf. Sci. 186 (1987) 45. Robey, S.W., Barton, J.J., Bahr, C.C., Liu, G., Shirley, D.A.: Phys. Rev. B35 (1987) 1108.
Lando lt -Bö rnst ein New Ser ies III/42 A2
4.1-112 87R3 87S1 87S2 87T 87W1 87W2 87W3 87W4 87Z 88A 88B 88F1 88F2 88G 88K 88L 88O 88P1 88P2 88S 88T1 88T2 88W1 88W2 88Z 89B1 89B2 89B3 89C 89H1 89H2 89H3 89L1 89L2 89L3 89L4 89L5 89M1
4.1 Surface structure on metals and semiconductors Robey, S.W., Bahr, C.C., Hussain, Z., Barton, J.J., Leung, K.T., Lou, J., Schach von Wittenau, A.E., Shirley, D.A.: Phys. Rev. B35 (1987) 5657. Skottke, M., Behm, R.J., Ertl, G., Penka, V., Moritz, W.: J. Chem. Phys. 87 (1987) 6191. Smith, R.J., Hennessy, C., Kim, M.W., Whang, C.N., Worthington, M., Xu, M.: Phys. Rev. Lett. 58 (1987) 702. Takahashi, T., Nakatani, S., Ishikawa, T., Kikuta, S.: Surf. Sci. 191 (1987) L825. Wang, Z.Q., Li, Y.S., Jona, F., Marcus, P.M.: Solid State Commun. 61 (1987) 623. Wang, Z.Q., Li, Y.S., Lok, C.K.C., Quinn, J., Jona, F., Marcus, P.M.: Solid State Commun. 62 (1987) 181. Warburton, D.R., Thornton, G., Norman, D., Richardson, C.H., McGrath, R., Sette, F.: Surf. Sci. 189/190 (1987) 495. Wong, P.C., Mitchell, K.A.R.: Surf. Sci. 187 (1987) L599. Zheng, H.C., Sodhi, R.N.S., Mitchell, K.A.R.: Surf. Sci. 188 (1987) 599. Altman, M.S., Estrup, P.J., Robinson, I.K.: Phys. Rev. B38 (1988) 5211. Besenbacher, F., Stensgaard, I., Mortensen, K.: Springer Series in Surface Sciences 11 (1988) 195. Fenter, P., Gustafsson, T.: Phys. Rev. B38 (1988) 10197. Fery, P., Moritz, W., Wolf, D.: Phys. Rev. B38 (1988) 7275. Grey, F., Johnson, R.L., Pederson, J.S., Nielsen, M., R Feidenhans'l,: Springer Series in Surface Sciences 11 (1988) 292. Kawazu, A., Sakama, H.: Phys. Rev. B37 (1988) 2704. Leung, K.T., Terminello, L.J., Hussain, Z., Zhang, X.S., Hayashi, Y., Shirley, D.A.: Phys. Rev. B38 (1988) 8241. Oed, W., Doetsch, B., Hammer, L., Heinz, K., Mueller, K.: Surf. Sci. 207 (1988) 55. Pendry, J.B., Heinz, K., Oed, W., Landskron, H., Mueller, K., Schmidtlein, G.: Surf. Sci. 193 (1988) L1. Pendry, J.B., Heinz, K., Oed, W.: Phys. Rev. Lett. 61 (1988) 2953. Sowa, E.C., Van Hove, M.A., Adams, D.L.: Surf. Sci. 199 (1988) 174. Terminello, L.J., Zhang, X.S., Huang, Z.Q., Kim, S., Schach von Wittenau, A.E., Leung, K.T., Shirley, D.A.: Phys. Rev. B38 (1988) 3879. Tong, S.Y., Huang, H., Wei, C.M., Packard, W.E., Men, F.K., Glander, G., Webb, M.B.: J. Vac. Sci. Technol. A6 (1988) 615. Wong, P.C., Lou, J.R., Mitchell, K.A.R.: Surf. Sci. 206 (1988) L913. Wu, Z.Q., Lu, S.H., Wang, Z.Q., Lok, C.K.C., Quinn, J., Li, Y.S., Tian, D., Jona, F., Marcus, P.M.: Phys. Rev. B38 (1988) 5363. Zhang, X.S., Terminello, L.J., Kim, S., Huang, Z.Q., Schach von Wittenau, A.E., Shirley, D.A.: J. Chem. Phys. 89 (1988) 6538. Bartynski, R.A., Heskett, D., Garrison, K., Watson, G.M., Zehner, D.M., Mei, W.N., Tong, S.Y., Pan, X.: Phys. Rev. B40 (1989) 5340. Bedzyk, M.J., Shen, Q., Keeffe, M.E., Navrotski, G.: Surf. Sci. 220 (1989) 419. Bu, H., Grizzi, O., Shi, M., Rabalais, J.W.: Phys. Rev. B40 (1989) 10147. Conway, K.M., MacDonald, J.E., Norris, C., Vlieg, E., van der Veen, J.F.: Surf. Sci. 215 (1989) 555. Haberle, P., Gustafsson, T.: Phys. Rev. B40 (1989) 8218. Headrick, R.L., Konarski, P., Yalisove, S.M., Graham, W.R.: Phys. Rev. B39 (1989) 5713. Huang, H., Wei, C.M., Li, H., Tonner, B.P., Tong, S.Y.: Phys. Rev. Lett. 62 (1989) 559. Landskron, H., Bickel, N., Heinz, K., Schmidtlein, G., Mueller, K.: J. Phys. Condens. Matter 1 (1989) 1. Lehnberger, K., Nichtl-Pecher, W., Oed, W., Heinz, K., Mueller, K.: Surf. Sci. 217 (1989) 511. Li, Y.S., Quinn, J., Jona, F., Marcus, P.M.: Phys. Rev. B40 (1989) 8239. Lindroos, M., Barnes, C.J., Valden, M., King, D.A.: Surf. Sci. 218 (1989) 269. Lindroos, M., Pfnur, H., Held, G., Menzel, D.: Surf. Sci. 222 (1989) 451. Marcano, J., Darici, Y., Min, H., Yin, Y., Montano, P.A.: Surf. Sci. 217 (1989) 1. Lando lt -Börnst ein New Ser ies III/42A2
4.1 Surface structure on metals and semiconductors 89M2 89M3 89O 89P1 89P2 89P3 89R 89V1 89v2 89W 89Z 90A 90B 90F1 90F2 90H1 90H2 90J1 90J2 90K 90L1 90L2 90N 90O1 90O2 90P1 90P2 90Q 90S1 90S2 90T1 90T2 90T3 90V1 90V2 90V3 90W1 90W2 90W3
4.1-113
Michl, M., Oed, W, Nichtl-Pecher, W., Landskron, H., Heinz, K., Mueller, K.: Surf. Sci. 220 (1989) 59. Mullins, D.R., Overbury, S.H.: Surf. Sci. 210 (1989) 481. Oed, W., Lindner, H., Starke, U., Heinz, K., Mueller, K., Pendry, J.B.: Surf. Sci. 224 (1989) 179. Patel, J.R., Berreman, D.W., Sette, F., Citrin, P.H., Rowe, J.E., Cowan, P.L., Jach, T., Karlin, B.: Phys. Rev. B40 (1989) 1330. Pfnur, H., Held, G., Lindroos, M., Menzel, D.: Surf. Sci. 220 (1989) 43. Puchta, W., Nichtl, W., Oed, W., Bickel, N., Heinz, K., Mueller, K.: Phys. Rev. B39 (1989) 1020. Rabalais, J.W., Grizzi, O., Shi, M., Bu, H.: Phys. Rev. Lett. 63 (1989) 51. Van de Riet, E., Smeets, J.B.J., Fluit, J.M., Niehaus, A.: Surf. Sci. 214 (1989) 111. von Eggeling, C., Schmidt, G., Besold, G., Hammer, L., Heinz, K., Mueller, K.: Surf. Sci. 221 (1989) 11. Wu, Y.K., Mitchell, K.A.R.: Can. J. Chem. 67 (1989) 1975. Zeng, H.C., Mitchell, K.A.R.: Langmuir 5 (1989) 829. Asensio, M.C., Ashwin, M.J., Kilcoyne, A.L.D., Woodruff, D.P., Robinson, A.W., Lindner, Th., Somers, J.S., Ricken, D.E., Bradshaw, A.M.: Surf. Sci. 236 (1990) 1. Breuer, U., Prince, K.C., Bonzel, H.P., Oed, W., Heinz, K., Schmidt, G., Mueller, K.: Surf. Sci. 239 (1990) L493. Feidenhans'l, R., Grey, F., Johnson, R.L., Mochrie, S.G.J., Bohr, J., Nielsen, M.: Phys. Rev. B41 (1990) 5420. Ford, W.K., Guo, T., Lessor, D.L., Duke, C.B.: Phys. Rev. B42 (1990) 8952. Huang, H., Tong, S.Y., Quinn, J., Jona, F.: Phys. Rev. B41 (1990) 3276. Huang H., Tong S.Y., Yang W.S., Shih H.D., Jona, F.: Phys. Rev. B42 (1990) 7483. Jedrecy, N., Sauvage-Simkin, M., Pinchaux, R., Massies, J., Greiser, N., H. Etgens, V.: Surf. Sci. 230 (1990) 197. Jiang, Q.T., Fenter, P., Gustafsson, T.: Phys. Rev. B42 (1990) 9291. Kleinle, G., Wintterlin, J., Ertl, G., Behm, R.J., Jona, F., Moritz, W.: Surf. Sci. 225 (1990) 171. Lin, R.F., Li, Y.S., Jona, F., Marcus, P.M.: Phys. Rev. B42 (1990) 1150. Lindroos, M., Barnes, C.J., Hu, P., King, D.A.: Chem. Phys. Lett. 173 (1990) 92. Noonan, J.R., Davis, H.L.: J. Vac. Sci. Technol. A8 (1990) 2671. Oed, W., Lindner, H., Starke, U., Heinz, K., Mueller, K., Saldin, D.K., de Andres, P.L., Pendry, J.B.: Surf. Sci. 225 (1990) 242. Oed, W., Starke, U., Bothe, F., Heinz, K.: Surf. Sci. 234 (1990) 72. Parkin, S.R., Zeng, H.C., Zhou, M.Y., Mitchell, K.A.R.: Phys. Rev. B41 (1990) 5432. Prince, N.P., Seymour, D.L., Ashwin, M.J., McConville, C.F., Woodruff, D.P.: Surf. Sci. 230 (1990) 13. Quinn, J., Li, Y.S., Tian, D., Li, H., Jona, F., Marcus, P.M.: Phys. Rev. B42 (1990) 11348. Shi, M., Bu, H., Rabalais, J.W.: Phys. Rev. B42 (1990) 2852. Starke, U., Bothe, F., Oed, W., Heinz, K.: Surf. Sci. 232 (1990) 56. Terminello, L.J., Leung, K.T., Hussain, Z., Hayashi, Y., Zhang, X.S., Shirley, D.A.: Phys. Rev. B41 (1990) 12787. Tian, D., Lin, R.F., Jona, F., Marcus, P.M.: Solid State Commun. 74 (1990) 1017. Tong, S.Y., Huang, H., Wei, C.M.: Chem. Phys. Solid Surf. VIII 22 (1990) 395. Vlieg, E., Robinson, I.K., Kern, K.: Surf. Sci. 233 (1990) 248. Vlieg, E., Robinson, I.K., McGrath, R.: Phys. Rev. B41 (1990) 7896. Vu Grimsby, D.T., Wu, Y.K., Mitchell, K.A.R.: Surf. Sci. 232 (1990) 51. Watson, P.R., Mischenko III, J.M.: Phys. Rev. B42 (1990) 3415. Wei, C.M., Huang, H., Tong, S.Y., Glander, G.S., Webb, M.B.: Phys. Rev. B42 (1990) 11284. Whang, Xu Mingde, C.N., Smith, R.J.: J. Vac. Sci. Technol. A 8 (1990) 2501.
Lando lt -Bö rnst ein New Ser ies III/42 A2
4.1-114 90Y 90Z1 90Z2 91B 91D1 91D2 91G 91H1 91H2 91J 91K 91L 91M1 91M2 91M3 91O1 91O2 91O3 91P 91Q 91R 91S1 91S2 91U 91W1 91W2 91W3 91W4 91Z 92A 92B1 92B2 92C 92D 92F 92G
4.1 Surface structure on metals and semiconductors Yokoyama, T., Takata, Y., Ohta, T., Funabashi, M., Kitajima, Y., Kuroda, H.: Phys. Rev. B42 (1990) 7000. Zeng, H.C., Mitchell, K.A.R.: Surf. Sci. 239 (1990) L571. Zeng, H.C., McFarlane, R.A., Mitchell, K.A.R.: Can. J. of Phys. 68 (1990) 353. Barnes, C.J., Hu, P., Lindroos, M., King, D.A.: Surf. Sci. 251 (1991) 561. Doust, T.N., Tear, S.P.: Surf. Sci. 251/252 (1991) 568. Duerr, H., Fauster, Th., Schneider, R.: Surf. Sci. 244 (1991) 237. Gauthier, Y., Baudoing-Savois, R., Heinz, K., Landskron, H.: Surf. Sci. 251/252 (1991) 493. Heinz, K., Oed, W Nichtl-Pecher, W., Landskron, H., Michl, M., Mueller, K.: Springer Series in Surface Sciences 24 (1991) 401. Holmberg, S., Poon, H.C., Jugnet, Y., Grenet, G., Tran Minh Duc,: Surf. Sci. 254 (1991) L475. Jiang, Q.T., Fenter, P., Gustafsson, T.: Phys. Rev. B44 (1991) 5773. Kilcoyne, A.L.D., Woodruff, D.P., Robinson, A.W., Lindner, Th., Somers, J.S., Bradshaw, A.M.: Surf. Sci. 253 (1991) 107. Li, H., Quinn, J., Li, Y.S., Tian, D., Jona, F., Marcus, P.M.: Phys. Rev. B43 (1991) 7305. Masson, F., Rabalais, J.W.: Surf. Sci. 253 (1991) 258. Mendez, M.A., Oed, W., Fricke, A., Hammer, L., Heinz, K., Mueller, K.: Surf. Sci. 253 (1991) 99. Meyerheim, H.L., Dobler, U., Puschmann, A.: Phys. Rev. B44 (1991) 5738. Ocko, B.M., Gibbs, D., Huang, K.G., Zehner, D.M., Mochrie, S.G.J.: Phys. Rev. B44 (1991) 6429. Over, H., Kleinle, G., Ertl, G., Moritz, W., Ernst, K.H., Wohlgemuth, H., Christmann, K., Schwarz, E.: Surf. Sci. 254 (1991) L469. Overbury, S.H., Mullins, D.R., Paffett, M.F., Koel, B.E.: Surf. Sci. 254 (1991) 45. Powers, J.M., Wander, A., Rous, P.J., Van Hove, M.A., Somorjai, G.A.: Phys. Rev. B44 (1991) 11159. Quinn, J., Li, Y.S., Jona, F., Fort, D.: Surf. Sci. 257 (1991) L647. Richter, M., Woicik, J.C., Pianetta, P., Miyano, K.E., Kendelewicz, T., Bouldin, C.E., Spicer, W.E., Lindau, I.: J. Vac. Sci. Technol. A 9 (1991) 1951. Schmalz, A., Aminpirooz, S., Becker, L., Haase, J., Neugebauer, J., Scheffler, M., Batchelor, D.R., Adams, D.L., Bogh, E.: Phys. Rev. Lett. 67 (1991) 2163. Starke, U., Oed, W., Bayer, P., Bothe, F., Fuerst, G., de Andres, P.L., Heinz, K., Pendry, J.B.: Springer Series in Surface Sciences 24 (1991) 427. Urano, T., Uchida, Y., Hongo, S., Kanaji, T.: Surf. Sci. 242 (1991) 39. Wan, K.J., Guo, T., Ford, W.K., Hermanson, J.C.: Phys. Rev. B44 (1991) 3471. Wan, K.J., Ford, W.K., Lapeyre, G.J., Hermanson, J.C.: Phys. Rev. B44 (1991) 6500. Wang, L.-Q., Hussain, Z., Huang, Z.Q., Schach von Wittenau, A.E., Lindle, D.W., Shirley, D.A.: Phys. Rev. B44 (1991) 13711. Wang, L.-Q., Schach von Wittenau, A.E., Ji, Z.G., Wang, L.S., Huang, Z.Q., Shirley, D.A.: Phys. Rev. B44 (1991) 1292. Zhao, R.G., Jia, J.F., Li, Y.F., Yang, W.S.: Springer Series in Surface Sciences 24 (1991) 517. Aminpirooz, S., Schmalz, A., Becker, L., Pangher, N., Haase M.M. Nielsen, J., Batchelor, D.R., Bogh, E., Adams, D.L.: Phys. Rev. B46 (1992) 15594. Bracco, G., Canepa, M., Cantini, P., Fossa, F., Mattera, L., Terreni, S., Truffelli, D.: Surf. Sci. 269/270 (1992) 61. Bu, H., Roux, C., Rabalais, J.W.: Surf. Sci. 271 (1992) 253. Chester, M., Gustafsson, T.: Surf. Sci. 264 (1992) 33. Davis, H.L., Hannon, J.B., Ray, K.B., Plummer, E.W.: Phys. Rev. Lett. 68 (1992) 2632. Ford, W.K., Guo, T., Wan, K.-J., Duke, C.B.: Phys. Rev. B45 (1992) 11896. Gierer, M., Bludau, H., Hertel, T., Over, H., Moritz, W., Ertl, G.: Surf. Sci. 297 (1992) L170. Lando lt -Börnst ein New Ser ies III/42A2
4.1 Surface structure on metals and semiconductors 92H1 92H2 92H3 92I 92J 92K1 92K2 92L 92N 92O1 92O2 92O3 92Q1 92Q2 92R 92S1 92S2 92S3 92V 92W1 92W2 92W3 93A 93B1 93B2 93B3 93B4 93C1 93C2 93C3 93D1 93D2 93F1 93F2 93F3
4.1-115
Haase, J., Hillert, B., Becker, L., Pedio, M.: Surf. Sci. 262 (1992) 8. Held, G., Pfnuer, H., Menzel, D.: Surf. Sci. 271 (1992) 21. Hetterich, W., Niehus, H., Weiland, W.: Surf. Sci. 264 (1992) L177. Itchkawitz, B.S., Baddorf, A.P., Davis, H.L., Plummer, E.W.: Phys. Rev. Lett. 68 (1992) 2488. Joly, Y.: Phys. Rev. Lett. 68 (1992) 951. Kerkar, M., Fisher, D., Woodruff, D.P., Jones, R.G., Diehl, R.D., Cowie, B.: Phys. Rev. Lett. 68 (1992) 3204. Korte, U., Meyer-Ehmsen, G.: Surf. Sci. 271 (1992) 616. Lohmeier, M., van der Vegt, H.A., van Silfhout,E. Vlieg, R.G., Thornton, J.M.C., Macdonald, J.E., Scholte, P.M.L.O.: Surf. Sci. 275 (1992) 190. Nishikata, K., Murakami, K.-I., Yoshimura, M., Kawazu, A.: Surf. Sci. 269/270 (1992) 995. Over, H., Bludau, H., Skottke-Klein, M., Ertl, G., Moritz, W., Campbell, C.T.: Phys. Rev. B45 (1992) 8638. Over, H., Bludau, H., Skottke-Klein, M., Moritz, W., Ertl, G.: Phys. Rev. B46 (1992) 4360. Overbury, S.H., Ku, Y.-S.: Phys. Rev. B46 (1992) 7868. Quinn, J., Jona, F., Marcus, P.M.: Phys. Rev. B46 (1992) 7288. Quinn, J., Li, Y.S., Jona, F., Fort, D.: Phys. Rev. B46 (1992) 9694. Rossmann, R., Meyerheim, H.L., Jahns, V., Wever, J., Moritz, W., Wolf, D., Dornisch, D., Schulz, H.: Surf. Sci. 279 (1992) 199. Saiki, R.S., Kaduwela, A.P., Kim, Y.J., Friedman, D.J., Osterwalder, J., Thevuthasan, S., Fadley, C.S.: Surf. Sci. 279 (1992) 305. Schach von Wittenau, A.E., Hussain, Z., Wang, L.Q., Huang, Z.Q., Ji, Z.G., Shirley, D.A.: Phys. Rev. B45 (1992) 13614. Schmidt, G., Zagel, H., Landskron, H., Heinz, K., Mueller, K., Pendry, J.B.: Surf. Sci. 271 (1992) 416. van Silfhout, R.G., Lohmeier, M., Zaima, S., van der Veen, J.F., Howes, P.B., Norris, C., Thornton, J.M.C., Williams, A.A.: Surf. Sci. 271 (1992) 32. Wan, K.J., Guo, T., Ford, W.K., Hermanson, J.C.: Surf. Sci. 261 (1992) 69. Weiss, K-U., Dippel, R., Schindler, K-M., Gardner, P., Fritzsche, V., Bradshaw, A.M., Kilcoyne, A.L.D., Woodruff, D.P.: Phys. Rev. Lett. 69 (1992) 3196. Woicik, J., Kendelewicz, T., Miyano, K.E., Richter, M., Bouldin, C.E., Pianetta, P., Spicer, W.E.: Phys. Rev. B46 (1992) 9869. Atrei, A., Bardi, U., Wu, J.X., Zanazzi, E., Rovida, G.: Surf. Sci. 290 (1993) 286. Baddorf, A.P., Zehner, D.M., Helgesen, G., Gibbs, D., Sandy, A.R., Mochrie, S.G.J.: Phys. Rev. B48 (1993) 9013. Barnes, C.J., Wander, A., King, D.A.: Surf. Sci. 281 (1993) 33. Begley, A.M., Kim, S.K., Jona, F., Marcus, P.M.: Phys. Rev. B48 (1993) 12326. Begley, A.M., Kim, S.K., Quinn, J., Jona, F., Over, H., Marcus, P.M.: Phys. Rev. B48 (1993) 1779. Canepa, M., Cantini, P., Fossa, F., Mattera, L., Terreni, S.: Phys. Rev. B47 (1993) 15823. Chen, X.M., Canter, K.F., Duke, C.B., Paton, A., Lessor, D.L., Ford, W.K.: Phys. Rev. B48 (1993) 2400. Comicioli, C., Dhanak, V.R., Comelli, G., Astaldi, C., Prince, K.C., Rosei, R., Atrei, A., Zanazzi, E.: Chem. Phys. Lett. 214 (1993) 438. Dorenbos, G., Boerma, D.O.: Surf. Sci. 287/288 (1993) 443. Dorenbos, G., Breeman, M., Boerma, D.O.: Phys. Rev. B47 (1993) 1580. Finney, M.S., Norris, C., Howes, P.B., van Silfhout, R.G., Clark, G.F., Thornton, J.M.C.: Surf. Sci. 291 (1993) 99. Foss, M., Feidenhans'l, R., Nielsen, M., Findeisen, E., Buslaps, T., Johnson, R.L., Besenbacher, F., Stensgaard, I.: Surf. Sci. 296 (1993) 283. Fritzsche, V., Pendry, J.B., Loeffler, U., Wedler, H., Mendez, M.A., Heinz, K.: Surf. Sci. 289 (1993) 389.
Lando lt -Bö rnst ein New Ser ies III/42 A2
4.1-116 93G1 93G2 93H1 93H2 93H3 93H4 93H5 93J 93K1 93K2 93L1 93L2 93L3 93L4 93M1 93M2 93M3 93O1 93O2 93R 93S1 93S2 93S3 93S4 93S5 93T 93U 93W1 93W2 93W3 93W4 93W5 93W6 93W7 93Z 94A 94B1
4.1 Surface structure on metals and semiconductors Gierer, M., Over, H., Ertl, G., Wohlgemuth, H., Schwarz, E., Christmann, K.: Surf. Sci. 297 (1993) L73. Gota, S., Gunnella, R., Wu, Z-Y., Jezequel, G., Natoli, C.R., Sebilleau, D., Bullock, E.L., Proix, F., Guillot, C., Quemerais, A.: Phys. Rev. Lett. 71 (1993) 3387. Hammer, L., Landskron, H., Nichtl-Pecher, W., Fricke, A., Heinz, K., Mueller, K.: Phys. Rev. B47 (1993) 15969. Helgesen, G., Gibbs, D., Baddorf, A.P., Zehner, D.M., Mochrie, S.G.J.: Phys. Rev. B48 (1993) 15320. Howes, P.B., Norris, C., Finney, M.S., Vlieg, E., van Silfhout, R.G.: Phys. Rev. B48 (1993) 1632. Huang, Z.Q., Hussain, Z., Huff, W.T., Moler, E.J., Shirley, D.A.: Phys. Rev. B48 (1993) 1696. Huang, Z.Q., Wang, L.Q., Schach von Wittenau, A.E., Hussain, Z., Shirley, D.A.: Phys. Rev. B47 (1993) 13626. Jia, J.F., Zhao, R.G., Yang, W.S.: Phys. Rev. B48 (1993) 18109. Kaukasoina, P., Lindroos, M., Diehl, R.D., Fisher, D., Chandavarkar, S., R Collins, I.: J. Phys. Condens. Matter 5 (1993) 2875. Kim, B., Chen, J., Erskine, J.L., Mei, W.N., Wei, C.M.: Phys. Rev. B48 (1993) 4735. Lederer, T., Arvanitis, D., Comelli, G., Troeger, L., Baberschke, K.: Phys. Rev. B48 (1993) 15390. Lederer, T., Arvanitis, D., Tischer, M., Comelli, G., Troeger, L., Baberschke, K.: Phys. Rev. B48 (1993) 11277. Lessor, D.L., Duke, C.B., Kahn, A., Ford, W.K.: J. Vac. Sci. Technol. A 11 (1993) 2205. Liu, W., Lou, J.R., Mitchell, K.A.R.: Surf. Sci. 281 (1993) 21. Meyerheim, H.L., Robinson, I.K., Jahns, V., Eng, P.J., Moritz, W.: Z.. Kristallogr. 208 (1993) 73. Mizuno, S., Tochihara, H., Kawamura, T.: Surf. Sci. 292 (1993) L811. Mizuno, S., Tochihara, H., Kawamura, T.: Surf. Sci. 293 (1993) 239. Over, H., Huang, H., Tong, S.Y., Fan, W.C., Ignatiev, A.: Phys. Rev. B48 (1993) 15353. Over, H., Moritz, W., Ertl, G.: Phys. Rev. Lett. 70 (1993) 315. Robinson, I.K., Eng, P.J., Romainczyk, C., Kern, K.: Phys. Rev. B47 (1993) 10700. Sakama, H., Murakami, K., Nishikata, K., Kawazu, A.: Phys. Rev. B48 (1993) 5278. Shi, M., Wang, Y., Rabalais, J.W.: Phys. Rev. B48 (1993) 1689. Sprunger, P.T., Pohl, K., Davis, H.L., Plummer, E.W.: Surf. Sci. 297 (1993) L48. Starke, U., Barbieri, A., Materer, N., Van Hove, M.A., Somorjai, G.A.: Surf. Sci. 286 (1993) 1. Sugiyama, M., Maeyama, S., Oshima, M.: Phys. Rev. B48 (1993) 11037. Takahashi, T., Nakatani, S.: Surf. Sci. 282 (1993) 17. Urano, T., Hongo, S., Kanaji, T.: Surf. Sci. 287/288 (1993) 294. Wander, A., Barnes, C.J., Mapledoram, L.D., King, D.A.: Surf. Sci. 281 (1993) 42. Wang, Y., Shi, M., Rabalais, J.W.: Phys. Rev. B48 (1993) 1678. Warren, O.L., Thiel, P.A.: Phys. Rev. B47 (1993) 10848. Warren, O.L., Kang, H.-C., Schmitz, P.J., Thiel, P.A., Kaukasoina, P., Lindroos, M.: Phys. Rev. B47 (1993) 10839. Wedler, H., Mendez, M.A., Bayer, P., Loeffler, U., Heinz, K., Fritzsche, V., Pendry, J.B.: Surf. Sci. 293 (1993) 47. Woicik, J.C., Kendelewicz, T., Herrera-Gomez, A., Miyano, K.E., Cowan, P.L., Bouldin, C.E., Pianetta, P., Spicer, W.E.: Phys. Rev. Lett. 71 (1993) 204. Wuttig, M., Knight, C.C., Flores, T., Gauthier, Y.: Surf. Sci. 292 (1993) 189. Zheng, Y., Moler, E., Hudson, E., Hussain, Z., Shirley, D.A.: Phys. Rev. B48 (1993) 4760. Aberdam, D., Gauthier, Y., Durand, R., Faure, R.: Surf. Sci. 306 (1994) 114. Baddeley, C.J., Barnes, C.J., Wander, A., Ormerod, R.M., King, D.A., Lambert, R.M.: Surf. Sci. 314 (1994) 1.
Lando lt -Börnst ein New Ser ies III/42A2
4.1 Surface structure on metals and semiconductors 94B2 94B3 94B4 94B5 94B6 94B7 94B8 94D1
94D2 94G1 94G2 94G3 94G4 94H1 94H2 94H3 94H4 94H5 94H6 94J1 94J2 94K 94L1 94L2 94M1 94M2 94M3 94N1 94N2 94N3 94N4 94O1 94O2 94R 94S1 94S2 94S3 94S4
4.1-117
Bao, S., Hofmann, Ph., Schindler, K-M., Fritzsche, V., Bradshaw, A.M., Woodruff, D.P., Casado, C., Asensio, M.C.: J. Phys. Condens. Matter 6 (1994) L93. Barbieri, A., Jentz, D., Materer, N., Held, G., Dunphy, J., Ogletree, D.F., Sautet, P., Van Hove, M.A., Somorjai, G.A.: Surf. Sci. 312 (1994) 10. Barbieri, A., Van Hove, M.A., Somorjai, G.A.: Surf. Sci. 306 (1994) 261. Barbieri, A., Van Hove, M.A., Somorjai, G.A.: The Structure of Surfaces IV (1994) 201. Batteas, J.D., Barbieri, A., Starkey, E.K., Van Hove, M.A., Somorjai, G.A.: Surf. Sci. 313 (1994) 341. Bludau, H., Gierer, M., Over, H., Ertl, G.: Chem. Phys. Lett. 219 (1994) 452. Burchhardt, J., Nielsen, M.M., Adams, D.L., Lundgren, E., Andersen, J.N.: Phys. Rev. B50 (1994) 4718. Davila, M.E., Asensio, M.C., Woodruff, D.P., Schindler, K-M., Hofmann, Ph., Weiss, K.U., Dippel, R., Gardner, P., Fritzsche, V., Bradshaw, A.M., Conesa, J.C., Gonzalez-Elipe, A.R.: Surf. Sci. 311 (1994) 337. Davis, R., Hu, X-M., Woodruff, D.P., Weiss, K-U., Dippel, R., Schindler, K-M., Hofmann, Ph., Fritzsche, V., Bradshaw, A.M.: Surf. Sci. 307/309 (1994) 632. Gardin, D.E., Barbieri, A., Batteas, J.D., Van Hove, M.A., Somorjai, G.A.: Surf. Sci. 304 (1994) 316. Gauthier, Y., Poensgen, M., Wuttig, M.: Surf. Sci. 303 (1994) 36. Grant, M.W., Boshart, M.A., Dieleman, D.J., Seiberling, L.E.: Surf. Sci. 316 (1994) L1088. Grillo, M.E., Stampfl, C., Berndt, W.: Surf. Sci. 317 (1994) 84. Held, G., Menzel, D.: Surf. Sci. 316 (1994) 92. Hertel, T., Over, H., Bludau, H., Gierer, M., Ertl, G.: Phys. Rev. B50 (1994) 8126. Hertel, T., Over, H., Bludau, H., Gierer, M., Ertl, G.: Surf. Sci. 301 (1994) 1. Hofmann, Ph., Bao, S., Schindler, K.-M., Schaff, O., Polcik, M., Fritzsche, V., Bradshaw, A.M., Davis, R., Woodruff, D.P.: Surf. Sci. 319 (1994) L7. Huang, H., Over, H., Tong, S.Y., Quinn, J., Jona, F.: Phys. Rev. B49 (1994) 13483. Huang, H., Tong, S.Y., Myler, U., Jacobi, K.: Surf. Rev. Lett. 1 (1994) 221. Jandeleit, J., Gauthier, Y., Wuttig, M.: Surf. Sci. 319 (1994) 287. Juergens, D., Held, G., Pfnuer, H.: Surf. Sci. 303 (1994) 77. Kuwahara, Y., Nakatani, S., Takahasi, M., Aono, M., Takahashi, T.: Surf. Sci. 310 (1994) 226. Li, Y.D., Jiang, L.Q., Koel, B.E.: Phys. Rev. B49 (1994) 2813. Loeffler, U., Doell, R., Heinz, K., Pendry, J.B.: Surf. Sci. 301 (1994) 346. Mapledoram, L.D., Bessent, M.P., Wander, A., King, D.A.: Chem. Phys. Lett. 228 (1994) 527. Materer, N., Barbieri, A., Gardin, D., Starke, U., Batteas, J.D., Van Hove, M.A., Somorjai, G.A.: Surf. Sci. 303 (1994) 319. Meyerheim, H.L., Sawitzki, R.: Surf. Sci. 301 (1994) L203. Narloch, B., Held, G., Menzel, D.: Surf. Sci. 317 (1994) 131. Nielsen, M.M., Burchhardt, J., Adams, D.L., Lundgren, E., Andersen, J.N.: Phys. Rev. Lett. 72 (1994) 3370. Nielsen, M.M., Burchhardt, J., Adams, D.L.: Phys. Rev. B50 (1994) 7851. Nishiyama, A., ter Host, G., Lohmeier, M., Molenbroek, A.M., Frenken, J.W.M.: Surf. Sci. 321 (1994) 261. Overbury, S.H., van den Oetelaar, R.J.A.: Surf. Sci. 301 (1994) 313. Overbury, S.H., van den Oetelaar, R.J.A., Mullins, D.R.: Surf. Sci. 317 (1994) 341. Ruocco, R., Nannarone, S., Sauvage-Simkim, M., Jedrecy, N., Pinchaux, R., Waldhauer, A.: Surf. Sci. 307-309 (1994) 662. Sakama, H., Murakami, K., Nishikata, K., Kawazu, A.: Phys. Rev. B50 (1994) 14977. Schmidtke, E., Schwennicke, C., Pfnuer, H.: Surf. Sci. 312 (1994) 301. Schwennicke, C., Juergens, D., Held, G., Pfnuer, H.: Surf. Sci. 316 (1994) 81. Scragg, G., Cowie, B.C.C., Kerkar, M., Woodruff, D.P., Daimellah, A., Turton, S., Jones, R.G.: J. Phys. Condens. Matter 6 (1994) 1869.
Lando lt -Bö rnst ein New Ser ies III/42 A2
4.1-118 94S5 94S6 94S7 94T 94V1 94V2 94W1 94W2 94W3 94W4 94W5 94X 94Y 94Z 95B1 95B2 95B3 95B4 95B5 95C1 95C2 95D1 95D2 95F1 95F2 95G1 95G2 95G3 95H1 95H2 95H3 95H3 95J 95L1 95L2 95L3
4.1 Surface structure on metals and semiconductors Stampfl, C., Scheffler, M., Over, H., Buchhardt, J., Nielsen, M., Adams, D.L., Moritz, W.: Phys. Rev. B49 (1994) 4959. Statiris, P., Lu, H.C., Gustafsson, T.: Phys. Rev. Lett. 72 (1994) 3574. Sugiyama, M., Maeyama, S., Oshima, M.: Phys. Rev. B50 (1994) 4905. Toofan, J.,Tinseth, G.R., R. Watson, P.R.: J. Vac. Sci. Technol. A 12 (1994) 2246. Vu, D.T., Mitchell, K.A.R.: Phys. Rev. B49 (1994) 11515. Vu, D.T., Mitchell, K.A.R., Warren, O.L., Thiel, P.A.: Surf. Sci. 318 (1994) 129. Wever, J., Meyerheim, H.L., Moritz, W., Jahns, V., Wolf, D., Schulz, H., Seehofer, L., Johnson, R.L.: Surf. Sci. 321 (1994) L225. Wilde, L., Pangher, N., Haase, J.: Surf. Sci. 316 (1994) L1093. Wong, G.C.L., Lucas, C.A., Loretto, D., Payne, A.P., Fuoss, P.H.: Phys. Rev. Lett. 73 (1994) 991. Wong, K.C., Mitchell, K.A.R.: Surf. Sci. 304 (1994) L481. Wu, S.C., Li, H., Quinn, J., Tian, D., Li, Y.S., Begley, A.M., Kim, S.K., Jona, F., Marcus, P.M.: Phys. Rev. B49 (1994) 8353. Xu, C., Burnham, J.S., Goss, S.H., Caffey, K., Winograd, N.: Phys. Rev. B49 (1994) 4842. Yokoyama, T., Hamamatsu, H., Kitajima, Y., Takata, Y., Yagi, S., Ohta, T.: Surf. Sci. 313 (1994) 197. Zhao, C., Passler, M.A.: Surf. Sci. 320 (1994) 1. Bartos, I., Jaros, P., Barbieri,, A., Van Hove, M.A., Chun, W.F., Cai, Q., Altman, M.S.: Surf. Rev. Lett. 2 (1995) 477. Batteas, J.D., Barbieri, A., Starkey, E.K., Van Hove, M.A., Somorjai, G.A.: Surf. Sci. 339 (1995) 142. Berndt, W., Weick, D., Stampfl, C., Bradshaw, A.M., Scheffler, M.: Surf. Sci. 330 (1995) 182. Bessent, M.P., Hu, P., Wander, A., King, D.A.: Surf. Sci. 325 (1995) 272. Burchhardt, J., Nielsen,D.L. Adams,E. Lundgren,J.N. Andersen, .M., Stampfl,M. Scheffler,A. Schmalz,S. Aminpirooz, C., Haase, J.: Phys. Rev. Lett. 74 (1995) 1617. Castrucci, P., Lagomarsino, S., Scarinci, F., Franklin, G.E.: Phys. Rev. B51 (1995) 5043. Cerda, J., Palomares, F.J., Soria, F.: Phys. Rev. Lett. 75 (1995) 665. Davis, R., Woodruff, D.P., Schaff, O., Fernandez, V., Schindler, K.-M., Hofmann, Ph., Weiss, K.-U., Dippel, R., Fritzsche, V., Bradshaw, A.M.: Phys. Rev. Lett. 74 (1995) 1621. Dhanak, V.R., Baraldi, A., Comelli, G., Prince, K.C., Rosei, R., Atrei, A., Zanazzi, E.: Phys. Rev. B51 (1995) 1965. Fasel, R., Aebi, P., Schlapbach, L., Osterwalder, J.: Phys. Rev. B52 (1995) 2313. Ferrer, S., Torrelles, X., Etgens, V.H., van der Vegt, H.A., Fajardo, P.: Phys. Rev. Lett. 75 (1995) 1771. Gierer, M., Mertens, F., Over, H., Ertl, G., Imbihl, R.: Surf. Sci. 339 (1995) L903. Gierer, M., Over, H., Bludau, H., Ertl, G.: Surf. Sci. 337 (1995) 198. Giergiel, J., Pang, A.W., Hopster, H., Guo, X., Tong, S.Y., Weller, D.: Phys. Rev. B51 (1995) 10201. Hammer, L., Seiferlein, F., Dingfelder, U., Kottcke, M., Doell, R., Heinz, K., Mueller, K.: Surf. Sci. 337 (1995) 224. Hanada, T., Daimon, H., Ino, S.: Phys. Rev. B51 (1995) 13320. Hassold, E., Loeffler, U., Schmiedl, R., Grund, M., Hammer, L., Heinz, K., Mueller, K.: Surf. Sci. 326 (1995) 93. Hofmann, Ph., Schindler, K-M., Bao, S., Fritzsche, V., Bradshaw, A.M., Woodruff, D.P.: Surf. Sci. 337 (1995) 169. Jentz, D., Rizzi, S., Barbieri, A., Kelly, D., Van Hove, M.A., A Somorjai, G.: Surf. Sci. 329 (1995) 14. Lessmann, A., Drube, W., Materlik, G.: Surf. Sci. 323 (1995) 109. Liu, W., Wong, K.C., Mitchell, K.A.R.: Surf. Sci. 339 (1995) 151. Lyman, P.F., Qian, Y., Bedzyk, M.J.: Surf. Sci. 325 (1995) L385.
Lando lt -Börnst ein New Ser ies III/42A2
4.1 Surface structure on metals and semiconductors 95M1 95M2 95M3 95M4 95M5 95N 95O1 95O2 95O3 95O4 95R 95S1 95S2 95S3 95S4 95T 95W1 95W2 95Z 96B 96C1 96C2 96D1 96D2 96D3 96G1 96G2 96H1 96H2 96H3
96H4 96K1 96K2 96L1 96L2 96L3 96L4
4.1-119
Materer, N., Starke, U., Barbieri, A., Doell, R., Heinz, K., Van Hove, M.A., Somorjai, G.A.: Surf. Sci. 325 (1995) 207. Meyerheim, H.L., Sawitzki, R., Moritz, W.: Phys. Rev. B52 (1995) 16830. Mizuno, S., Tochihara, H., Barbieri, A., Van Hove, M.A.: Phys. Rev. B51 (1995) 1969. Mizuno, S., Tochihara, H., Barbieri, A., Van Hove, M.A.: Phys. Rev. B51 (1995) 7981. Mizuno, S., Tochihara, H., Barbieri, A., Van Hove, M.A.: Phys. Rev. B52 (1995) 11658. Narloch, B., Held, G., Menzel, D.: Surf. Sci. 340 (1995) 159. Over, H., Bludau, H., Kose, R., Ertl, G.: Chem. Phys. Lett. 243 (1995) 435. Over, H., Bludau, H., Kose, R., Ertl, G.: Phys. Rev. B51 (1995) 4661. Over, H., Tong, S.Y., Quinn, J., Jona, F.: Surf. Rev. Lett. 2 (1995) 451. Over, H., Wang, C.P., Jona, F.: Phys. Rev. B51 (1995) 4231. Ruocco, R., Biagini, M., di Bona, A., Gambacorto, N., Valeri, S., Nannarone, S.: Phys. Rev. B51 (1995) 2399. Schardt, J., Bram, Ch., Mueller, S., Starke, U., Heinz, K., Mueller, K.: Surf. Sci. 337 (1995) 232. Scragg, G., Kerkar, M., Ettema, A.R.H.F., Woodruff, D.P., Cowie, B.C.C., Daimellah, A., Turton, S., Jones, R.G.: Surf. Sci. 328 (1995) L533. Sklarek, W., Schwennicke, C., Juergens, D., Pfnuer, H.: Surf. Sci. 330 (1995) 11. Stellwag, C., Held, G., Menzel, D.: Surf. Sci. 325 (1995) L379. Tang, S., Freeman, A.J., Qian, Y., Franklin, G.E., Bedzyk, M.J.: Phys. Rev. B51 (1995) 1593. Wang, Y.M., Li, Y.S., Mitchell, K.A.R.: Surf. Sci. 342 (1995) 272. Wong, K.C., Liu, W., Mitchell, K.A.R.: Surf. Sci. 344 (1995) 258. Zhao, R.G., Hu, C., Yang, W.S.: Surf. Rev. Lett. 2 (1995) 245. Burchhardt, J., Lundgren, E., Nielsen, M.M., Andersen, J.N., Adams, D.L.: Surf. Rev. Lett. 3 (1996) 1339. C. Wong, K., Liu, W., A. R. Mitchell, K.: Surf. Sci. 360 (1996) 137. Christensen, S.V., Nerlov, J., Nielsen, K., Burchhardt, J., Nielsen, M.M., Adams, D.L.: Phys. Rev. Lett. 76 (1996) 1892. Davila, M.E., Asensio, M.C., Woodruff, D.P., Schindler, K-M., Hofmann, Ph., Bao, S., Fritzsche, V., Bradshaw, A.M.: Surf. Sci. 359 (1996) 185. Dudzik, E., Leslie, A., O'Toole, E., McGovern, I.T., Patchett, A., Zahn, D.R.T., Luedecke, J., Woodruff, D.P., Cowie, B.C.C.: J. Phys. Condens. Matter 8 (1996) 15. Duke, C.B., Paton, A., Lazarides, A., Kahn, A.: Phys. Rev. B54 (1996) 14692. Garreau, Y., Sauvage-Simkin, M., Jedrecy, N., Pinchaux, R., Veron, M.B.: Phys. Rev. B54 (1996) 17638. Gauthier, Y., Moritz, W., Hoesler, W.: Surf. Sci. 345 (1996) 53. Hammer, L., Kottcke, M., Heinz, K., Mueller, K., Zehner, D.M.: Surf. Rev. Lett. 5-6 (1996) 1701. Held, G., Bessent, M.P., Titmuss, S., King, D.A.: J. Chem. Phys. 105 (1996) 11305. Hirschmugl, C.J., Schindler, K-M., Schaff, O., Fernandez, V., Theobald, A., Hofmann, Ph., Bradshaw, A.M., Davis, R., Booth, N.A., Woodruff, D.P., Fritzsche, V.: Surf. Sci. 352-354 (1996) 232. Hofmann, Ph., Pohl, K., Stumpf, R., Plummer, E.W.: Phys. Rev. B53 (1996) 13715. Kolthoff, D., Juergens, D., Schwennicke, C., Pfnuer, H.: Surf. Sci. 365 (1996) 374. Kottcke, M., Doell, R., Weiss, W., Seiferlein, F., Arabczyk, W., Hammer, L., Heinz, K.: Surf. Sci. 352-354 (1996) 592. Leatherman, G.S., Diehl, R.D., Kaukasoina, P., Lindroos, M.: Phys. Rev. B53 (1996) 10254. Liu, W., A. R. Mitchell, K.: Surf. Rev. Lett. 3 (1996) 1247. Lottermoser, L., Buslaps, T., Johnson, R.L., Feidenhans'l, R., Nielsen, M., Smilgies, D., Landemark, E., Meyerheim, H.L.: Surf. Sci. 373 (1996) 11. Luedecke, J., Ettema, A.R.H.F., Driver, S.M., Scragg, G., Kerkar, M., Woodruff, D.P., Cowie, B.C.C., Jones, R.G., Bastow, S.: Surf. Sci. 366 (1996) 260.
Lando lt -Bö rnst ein New Ser ies III/42 A2
4.1-120 96N 96P 96S1 96S2 96T1 96T2 96W 97A1 97A2 97A3 97D 97F1 97F2 97F3 97G1 97G2 97G3 97G4 97H1 97H2
97J1 97J2 97K1 97K2 97L1 97L2 97M1 97M2 97M3 97M4 97N1 97N2 97O1 97O2 97S1 97S2 97S3
4.1 Surface structure on metals and semiconductors Nielsen, M.M., Christensen, S.V., Adams, D.L.: Phys. Rev. B54 (1996) 17902. Pflanz, S., Buchtler, R., Moritz, W., Over, H.: Phys. Rev. B54 (1996) 8313. Schwegmann, S., Over, H.: Surf. Sci. 360 (1996) 271. Stampfl, C., Schwegmann, S., Over, H., Scheffler, M., Ertl, G.: Phys. Rev. Lett. 77 (1996) 3371. Toomes, R., Theobald, A., Lindsay, R., Giessel, T., Schaff, O., Didszhun, R., Woodruff, D.P., Bradshaw, A.M., Fritzsche, V.: J. Phys. Condens. Matter 8 (1996) 10231. Torrelles, X., van der Vegt, H.A., Etgens, V.H., Fajardo, P., Alvarez, J., Ferrer, S.: Surf. Sci. 364 (1996) 242. Wong, K.C., Liu, W., Saidy, M., Mitchell, K.A.R.: Surf. Sci. 345 (1996) 101. Arnold, M., Hupfauer, G., Bayer, P., Hammer, L., Heinz, K., Kohler, B., Scheffler, M.: Surf. Sci. 382 (1997) 288. Arnold, M., Sologub, S., Frie, W., Hammer, L., Heinz, K.: J. Phys. Condens. Matter 9 (1997) 6481. Arnold, M., Sologub, S., Hupfauer, G., Bayer, P., Frie, W., Hammer, L., Heinz, K.: Surf. Rev. Lett. 4 (1997) 1291. Duke, C.B., Paton, A., Lazarides, A., Vasumathi, D., Canter, K.F.: Phys. Rev. B55 (1997) 7181. Fasel, R., Gierer, M., Bludau, H., Aebi, P., Osterwalder, J., Schlapbach, L.: Surf. Sci. 374 (1997) 104. Foss, M., Feidenhans'l, R., Nielsen, M., Findeisen, E., Buslaps, T., Johnson, R.L., Besenbacher, F.: Surf. Sci. 388 (1997) 5. Franco, N., Avila, J., Davila, M.E., Asensio, M.C., Woodruff, D.P., Schaff, O., Fernandez, V., Schindler, K-M., Fritzsche, V., Bradshaw, A.M.: J. Phys. Condens. Matter 9 (1997) 8419. Gallego, S., Ocal, C., Soria, F.: Surf. Sci. 377-379 (1997) 18. Gayone, J.E.,Pregliasco, R.G., Snachez, E.A., Grizzi, O.: Phys. Rev. B56 (1997) 4194. Gierer, M., Barbieri, A., A. Van Hove, M., A. Somorjai, G.: Surf. Sci. 391 (1997) 176. Gierer, M., Over, H., Rech, P., Schwarz, E., Christmann, K.: Surf. Sci. 370 (1997) L201. Huff, W.R.A., Chen, Y., Kellar, S.A., Moler, E.J., Hussain, Z., Huang, Z.Q., Zheng, Y., Shirley, D.A.: Phys. Rev. B56 (1997) 1540. Huff, W.R.A., Chen, Y., Zhang, X.S., Terminello, L.J., Tao, F.M., Pan, Y.K., Kellar, S.A., Moler, E.J., Hussain, Z., Wu, H., Zheng, Y., Zhou, X., Schach von Wittenau, A.E., Kim, S., Huang, Z.Q., Yang, Z.Z., Shirley, D.A.: Phys. Rev. B55 (1997) 10830. Jiang, H., Mizuno, S., Tochihara, H.: Surf. Sci. 380 (1997) L506. Jiang, H., Mizuno, S., Tochihara, H.: Surf. Sci. 385 (1997) L930. Kaukasoina, P., Lindroos, M., Leatherman, G.S., Diehl, R.D.: Surf. Rev. Lett. 4 (1997) 1215. Kottcke, M., Doetsch, B., Hammer, L., Heinz, K., Mueller, K., M Zehner, D.: Surf. Sci. 376 (1997) 319. Li, Y., Voss, M.R., Swami, N., Tsai, Y.-L., Koel, B.E.: Phys. Rev. B56 (1997) 15982. Liu, W., Wong, K.C., Mitchell, K.A.R.: Surf. Sci. 372 (1997) 312. Menzel, D.: Surf. Rev. Lett. 4 (1997) 1283. Meyerheim, H.L., Zajonz, H., Moritz, W., Robinson, I.K.: Surf. Sci. 381 (1997) L551. Mizuno, S., Jiang, H., Tochihara, H.: Surf. Rev. Lett. 4 (1997) 1221. More, S., Berndt, W., Stampfl, C., Bradshaw, A.M.: Surf. Sci. 381 (1997) L589. Narloch, B., Menzel, D.: Chem. Phys. Lett. 270 (1997) 163. Noakes, T.C.Q., Hutt, D.A., McConville, C.F., Woodruff, D.P.: Surf. Sci. 372 (1997) 117. Onishi, H., Sakama, H., Aruga, T., Kawazu, A., Iwasawa, Y.: Surf. Sci. 392 (1997) L51. Over, H., Wasserfall, J., Ranke C. Ambiatello, W., Sawitzki, R., Wolf, D., Moritz, W.: Phys. Rev. B55 (1997) 4731. Starke, U.: Phys. Status Solidi (b) 202 (1997) 475. Schwegmann, S., Over, H., De Renzi, V., Ertl, G.: Surf. Sci. 375 (1997) 91. Schwegmann, S., Seitsonen, A.P., Dietrich, H., Bludau, H., Over, H., Jacobi, K., Ertl, G.: Chem. Phys. Lett. 264 (1997) 680. Lando lt -Börnst ein New Ser ies III/42A2
4.1 Surface structure on metals and semiconductors 97S4 97S5 97T1 97T2 97W 97Y 98B1
98B2 98C
98D1 98D2 98F
98G1 98G2 98K 98L
98M1 98M2 98M3 98M4 98R 98S1 98S2 98V1 98V2
98V3 98Z 99A 99B1
4.1-121
Stichler, M., Menzel, D.: Surf. Sci. 391 (1997) 47. Stichler, M., Weimar, R., Menzel, D.: Surf. Sci. 384 (1997) 179. Tischer, M., Srivastava, P., Wende, H., Baberschke, K., Yokoyama, T., Terada, S., Sakano, M., Kitajima, Y., Ohta, T.: Surf. Sci. 371 (1997) 409. Tober, E.D., Ynzunza, R.X., Palomares, F.J., Wang, Z., Hussain, Z., Van Hove, M.A., Fadley, C.S.: Phys. Rev. Lett. 79 (1997) 2085. Wang, Y.M., Li, Y.S., Mitchell, K.A.R.: Surf. Sci. 380 (1997) 540. Yoon, H.A., Materer, N., Salmeron, M., Van Hove, M.A., Somorjai, G.A.: Surf. Sci. 376 (1997) 254. Booth, N.A., Davis, R., Woodruff, D.P., Chrysostomou, D., McCabe, T., Lloyd, D.R., Schaff, O., Fernandez, V., Bau, S., Schindler, K.-M., Lindsay, R., Hoeft, J.T., Terborg, R., Baumgärtel, P., Bradshaw, A.M.: Surf. Sci. 416 (1998) 448. Bunk, O., Falkenberg, G., Seehofer, L., Zeysing, J.H., Johnson, R.L., Nielsen, M., Feidenhans'l, R., Landemark, E.: Appl. Surf. Sci. 123 (1998) 104. Collazo-Davila, C., Grozea, D., Marks, L.D., Feidenhans'l, R., Nielsen, M., Seehofer, L., Lottermoser, L., Falkenberg, G., Johnson, R.L., Göthelid, M., Karlsson, U.: Surf. Sci. 418 (1998) 395. Döll, R., Hammer, L., Heinz, K., Bedürftig, K., Muschiol, U., Christmann, K., Seitsonen, A.P., Bludau, H., Over, H.: J. Chem. Phys. 108 (1998) 8671. Dudzik, E., Norris, A.G., McGrath, R., Charlton, G., Thornton, G., Murphy, B., Turner, T.S., Norman, D.: Phys. Rev. B58 (1998) 12659. Franco, N., Chrost, J., Avila, J., Asensio, M.C., Müller, C., Dudzik, E., Patchett, A.J., McGovern, I.T., Giebel, T., Lindsay, R., Fritzsche, V., Bradshaw, A.M., Woodruff, D.P.: Appl. Surf. Sci. 123/124 (1998) 219. Grozea, D., Landree, E., Marks, L.D., Feidenhans'l, R., Nielsen, M., Johnson, R.L.: Surf. Sci. 418 (1998) 32. Gsell, M., Stichler, M., Jakob, P., Menzel, D.: Isr. J. Chem. 38 (1998) 339. Kim, Y.D., Wendt, S., Schwegmann, S., Over, H., Ertl, G.: Surf. Sci. 418 (1998) 267. Lottermoser, L., Landemark, E., Smilgies, D.-M., Nielsen, M., Feidenhans'l, R., Falkenberg, G., Johnson, R.L., Gierer, M., Seitsonen, A.P., Kleine, H., Bludau, H., Over, H., Kim, S.K., Jona, F.: Phys. Rev. Lett. 80 (1998) 3980. Meyerheim, H.L., De Santis, M., Moritz, W., Robinson, I.K.: Surf. Sci. 418 (1998) 295. Meyerheim, H.L., Jedrecy, N., Sauvage-Simkin, M., Pinchaux, R.: Phys. Rev. B58 (1998) 2118. Meyerheim, H.L., Moritz, W.: Appl. Phys. A67 (1998) 645. Moré, S., Berndt, W., Bradshaw, A.M., Stumpf, R.: Phys. Rev. B57 (1998) 9246. Ross, C., Schirmer, B., Wuttig, M., Gauthier, Y., Bihlmayer, G., Bluegel, S.: Phys. Rev. B57 (1998) 2607. Schwegmann, S., Seitsonen, A.P., De Renzi, V., Dietrich, H., Bludau, H., Gierer, M., Over, H., Jacobi, K., Scheffler, M., Ertl, G.: Phys. Rev. B57 (1998) 15487. Sporn, M., Platzgummer, E., Pinczolits, M., Hebenstreit, W., Schmid, M., Hofer, W., Varga, P.: Surf. Sci. 396 (1998) 78. Van Gemmeren, T., Lottermoser, L., Falkenberg, G., Bunk, O., Johnson, R.L., Feidenhans'l, R., Nielsen, M.: Surf. Sci. 414 (1998) 254. Van Gemmeren, T., Lottermoser, L., Falkenberg, G., Seehofer, L., Johnson, R.L., Gavioli, L., Mariani, C., Feidenhans'l, R., Landemark, E., Smilgies, D., Nielsen, M.: Phys. Rev. B57 (1998) 3749. Vogler, H., Iglesias, A., Moritz, W., Over, H.: Phys. Rev. B57 (1998) 2315. Zasada, I., Van Hove, M.A., Somorjai, G.A.: Surf. Sci. 418 (1998) L89. Arnold, M., Fahmi, A., Frie, W., Hammer, L., Heinz, K., J. Phys. Condens. Matter 11 (1999) 1. Baumgärtel, P., Paggel, J.J., Hasselblatt, M., Horn, K., Fernandez, V., Schaff, O., Weaver, J.H., Bradshaw, A.M., Woodruff, D.P., Rotenberg, E., Denlinger, J.: Phys. Rev. B59 (1999) 13014.
Lando lt -Bö rnst ein New Ser ies III/42 A2
4.1-122 99B2 99D 99P 99S1 99S2 99W
4.1 Surface structure on metals and semiconductors Bunk, O., Falkenberg, G., Seehofer, L., Zeysing, J.H., Lottermoser, L., Johnson, R.L., Nielsen, M., Berg-Rasmussen, F., Feidenhans'l, R.: Phys. Rev. B59 (1999) 12228. Dudzik, E., Norris, A.G., McGrath, R., Charlton, G., Thornton, G., Murphy, B., Turner, T.S., Norman, D.: Surf. Sci. 424 (1999) 74. Pohl, K., Plummer, E.W.: Phys. Rev. B59 (1999) 5324. Stichler, M., Menzel, D.: Surf. Sci. 419 (1999) 272. Sumitani, S., Abukawa, T., Kosugi, R., Suzuki, S., Sato, S., Kono, S.: J. Electron. Spectrosc. Relat. Phenom. 103 (1999) 245. Watson, P.R., Van Hove, M.A., Hermann, K.: NIST Surface Structure Database - Ver. 3.0, National Institute of Standards and Technology, Gaithersburg, Maryland (1999). Contact: Standard Reference Data Program, National Institute of Standards and Technology, Building 820, Room 113, Gaithersburg, MD 20899; http://www.nist.gov/srd/nist42.htm; http://electron.lbl.gov/ssd/ssd.html.
Lando lt -Börnst ein New Ser ies III/42A2
4.2 Electron work function of metals and semiconductors K. JACOBI
4.2.1 Introduction 4.2.1.1 List of abbreviations AES ARUPS ∆Φ ELS FEM HAS HREELS INS IPES IRAS LEED MDS min ML NMR NRA PYS RBS SE TDS SIMS XPS
Auger Electron Spectroscopy Angle-Resolved UV Photoelectron Spectroscopy work-function change Energy Loss Spectroscopy Field Emission Microscopy He Atom Scattering High-Resolution Electron Energy Loss Spectroscopy Ion Neutralization Spectroscopy Inverse Photoelectron Spectroscopy IR Reflection Absorption Spectroscopy Low-Energy Electron Diffraction Metastable Deexcitation Spectroscopy minimum monolayer Nuclear Magnetic Resonance Nuclear Reaction Analysis Photoelectron Yield Spectroscopy Rutherford Backscattering Spectroscopy Secondary Electron Thermal Desorption Spectroscopy Secondary Ion Mass Spectroscopy X-ray Photoelectron Spectroscopy
4.2.1.2 Definition of work function At the solid-state vacuum interface, the electron density drops to zero within less than an atomic distance normal to the surface (z-direction). This drop in electron density is typically characterized by some spillout of the most weakly bound electrons, i.e., the electrons in the valence or conduction band, into the vacuum leaving behind some positively charged volume in the first atomic layer. Thus, at the surface a dipole is established with its negative end pointing out of the surface. If the electrostatic potentials energy of an electron is given by v(z), this surface dipole can be described by a potential step D = v() – v(- )
(1)
So, the potential of an electron at rest in a macroscopic distance away from the surface v() is larger than the average potential deep in the crystal v(- ). This potential step serves, in part, to keep the electrons within the crystal. v() often is called the “vacuum level”. The second part of the surface barrier keeping the electrons within the solid matter (at low temperature) is due to short range Coulomb interactions – exchange and correlation – which is a pure bulk effect. On this background the work function Φ is defined as the minimum energy needed to transfer an electron from the bulk to a point in a macroscopic distance outside the surface leaving it there a rest, i.e., at zero kinetic energy. With EN, the total energy of N electrons in the bulk, Φ is given by:
Lando lt -Bö rnst ein New Ser ies III/42A2
4.2-2
4.2 Electron work function of metals and semiconductors Φ = v() + EN–1 – EN = v() – µ ,
[Ref. p 4.2-118 (2)
where µ=
∂F = EN – EN–1 ∂N T, V
(3)
is the electrochemical potential of the electron as derived from the free Helmholtz energy F at constant temperature T and constant volume V of the system. By this equation the work function is defined as the energy difference of an electron at the Fermi level EF Łµ and at an infinite distance at rest v(). Choosing v(– ) as a reference level, Eq. (2) transforms into Φ=D– µ
(4)
where µ is the bulk chemical potential referred to the mean electrostatic potential in bulk v(- ). Formula (4) clearly separates the surface component D and the bulk component µ of the work function. At this point, it becomes also evident how adsorbates can influence Φ. Adsorbates at a condensed-matter surface do certainly not influence µ but may influence the dipole layer at the surface. As it was outlined already by Bonzel in the introduction, adsorbed species may develop a dipole moment during bond formation with the surface atoms or its permanent dipole may get oriented in the electric field at the surface. The work function change ∆Φ is given by the classic Helmholtz equation ∞
∆Φ = 4πe
∫ zδn (z)dz .
(5)
−∞
δn ( z ) denotes the redistribution of valence charge density that accompanies adsorption. A compilation of work function data for clean metal surfaces (mostly single cristalline) are published in [94J3]. 4.2.1.3 Work function versus local potential It is well known that the work function of a single-crystalline sample depends on the crystallographic surface plane for which it is measured. Generally, Φ increases with the surface atomic density. On the other hand, according to the definition given above Φ is a macroscopic thermodynamic quantity independent of surface crystallography. If the work function would simply depend on the path way normal to the surface, along which the electron is transferred into vacuum, the construction of a perpetuum mobile would be possible. Since the latter cannot be the case, a paradoxical situation arises. The answer to this paradoxon has been found in the consideration of the inhomogeneous field at the edges between the differently oriented surfaces. Moving the electron from in front of one surface to another the electron looses or gains energy in crossing the edge fields. At infinity there is only one value of Φ and the face-specific values have to be lowered or raised approaching the material-specific value at infinity. From this argument it is much more reasonable to talk about the local potential in front of a surface instead of the work function of this surface. This point was stressed by Wandelt who introduced photoemission from adsorbed Xe as a method to probe the local potential in front of a surface [87W]. The question remains how far the probe has to be above the surface to measure the local potential. From our remarks up to this point, an atomic distance would be enough as we have only considered the electrostatic potential of the surface dipole layer. Besides this there is a second contribution, the image potential which is of larger range. Outside a metal surface (which is the most obvious example) an electron repels electrons at the metal surface thus modifying its charge density. Between the positive charge density at the surface and the electron there is an attraction which is described by the well known image potential, e2/4z, where e denotes the electron charge and z the distance from the surface. The positive charge induced at the surface can be considered as the residue of the exchange and correlation hole the electron created around itself in the bulk.
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors
4.2-3
Therefore, a safe distance from the surface at which all distance-dependent changes of the local potential have vanished is z0 = 104 ǖ > +@ 7KLV GLVWDQFH LV PDFURVFRSLFDOO\ VWLOO D VKRUW GLVWDQFH ,Q RUGHU WR avoid any influence of the edge fields the lateral distance to such edges should be larger than z0. This is easily fulfilled for the case, where single crystalline surfaces of a diameter of several mm are studied. The above cited method of photoemission from adsorbed rare gases does not fulfill this criterion and has, therefore, to be used with care. The great advantage on the other hand is the small lateral extension of the rare gas atom probe which makes it possible to study surfaces of very small patches down to locally stoichiometric compound surfaces. Actually, the method was invented when it was found that photoemission from Xe physisorbed at steps gives rise to different binding energies compared to those from the terrace [79K3]. 4.2.1.4 Standardization of work-function change with coverage In Fig. 1 four different types of work-function changes with coverage are sketched. Types I and II are for electronegative adsorbates as, e.g., for oxygen or chlorine: the electronegative species attracts some negative charge which increases the barrier for the outgoing electron. Types III and IV are due to an inversion of the dipole moments of types I and II. Typical examples for electropositive species are the alkali metals. ∆Φ1
Type I
θ1
0
Work − function change ∆Φ
∆Φ1
Type II ∆Φ2
θ1
0
θ2
0
Type III ∆Φ1 θ1
0
θ2
∆Φ2 ∆Φ1 Coverage θ
Lando lt -Bö rnst ein New Ser ies III/42A2
Type IV
Fig. 1. Four different types of work-function changes ∆Φ as function of coverage θ. Characteristic maxima, minima, or saturation values are marked by (θi, Φi).
4.2-4
4.2 Electron work function of metals and semiconductors
[Ref. p 4.2-118
For all types in Fig. 1 is common that there is a more or less extended linear change with exposure θ for θ ĺ 0. This is quite easily understood assuming that each adsorbed species contributes by its own typical dipole moments p to the overall work-function change ∆Φ which is given by the Helmholtz equation ∆Φ = -4πepNa
(6)
where Na is the number of adsorbed atoms per unit area. Eq. (6) describes basically the types I and III. A linear change of Φ with Na is actually not observed, instead the change of Φ per adsorbed atom becomes smaller. This is formally explained by depolarisation due to lateral interaction between the dipoles. This has been modeled by Topping [27T] for mobile adsorption: ∆Φ = -4πeµ0Na(1 + 9αNa3/2)-1 = 3.77·10-15µθ(1 + 9αθ3/2)-1
(7) (7’)
where µ0 is the initial dipole moment (for Na ĺ 0) and α denotes an effective polarizability. In Eq. (7’) θ is the surface coverage in atoms cm-2, µ the dipole moment in D, and α the polarizability in cm3. This Topping formula is often used to extract p0 and α from the measured ∆Φ curves. It should be noted, however, that the depolarization may be a very involved process and may be differ among different systems. So, it was shown in calculations for Cs/W(100) that not only Cs 6s and W 5d contribute but also a significant counter-polarization of the Cs 5p shallow core level was found [83W2]. 4.2.1.5 Experimental methods This short paragraph is not intended to describe the experimental techniques to measure work function and work-function changes in detail. For this purpose one may look into chapter 2.4 or into older review articles [69R, 72H2, 79H3]. There are basically three absolute methods: Thermionic emission (Therm), field electron emission (FEM), and photoelectron emission (PYS, ARUPS). Besides this and even more important are relative methods which can be divided into three groups: secondary electron edge methods (SE edge), Kelvin methods (Kelvin) and the reflection of electron beams (diode). We have introduced here the acronyms used in the tables below. Before we start presenting the data collection we will briefly comment on the above listed methods: 4.2.1.5.1 Thermionic emission (Therm) According to the Dushman-Richardson equation, the electron current upon heating a substrate of work function Φ is given by I = A(1 – r) T2 exp(-Φ/kT)
(8)
where A is a known constant, T the temperature, k the Boltzmann constant and r the reflection coefficient of the outgoing electron at the surface potential barrier. The experiments to deduce Φ from Eq. (8) are very difficult; the current depends exponentially on Φ and space charge problems can introduce severe problems. Also the geometry of the emitting surface and fringe fields have to be controlled. Interestingly, it could be shown that the maximum of the energy distribution of thermoionic emitted electrons shifts with Φ [85E]. For many adsorbate-induced work-function changes this method is useless, since the adsorbate may desorb before the temperature is high enough to produce measurable current densities. 4.2.1.5.2 Field electron emission (FEM) If an electric field is applied to a metal surface the potential barrier at the surface may become narrower so that electrons may tunnel through the barrier. The field-emitted electron current I is given by the Fowler-Nordheim equation [28F] I = BE2 exp(-βE-1)
(9)
where B and β are constants containing Φ, and E is the electric field strength. A so-called FowlerLando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors
4.2-5
Nordheim plot of ln(IE-2) vs. E-1 yields a straight line from which Φ can be derived. Usually, field emission sets in at fields of the order of 106 Volt cm-1. Such fields can easily be obtained if the metal surface is formed as a tip. As such a tip is composed of different surfaces with different Φ, measuring the total current leads to only an average value of Φ, weighted towards the surfaces of low Φ. Much more sensible results are achieved with the probe hole technique by which the current from different areas of the tip is analyzed separately. It became possible to follow the arrival of single evaporated atoms in the current jumps from a W(110) surface [77K]. During the sixties FEM was the best-choice method. Later, some drawbacks were clearly recognized [71F, 81S]: (1) (2) (3)
(4)
The shape of the emitter influences the strength of the electric field. If a planar facet is too large, the field gets reduced in its center region. The state of the adsorbate may be influenced by the electric field. There is a large uncertainty about the actual coverage of an adsorbed metal at an individual facet. The adsorbate under investigation is usually deposited onto one side of the tip which is kept at low temperature (room temperature) or below. Later the adsorbate is spread over the whole tip at elevated temperatures. Assuming that an equilibrium between the different faces is achieved this way, the coverage at the faces with the higher binding energy may be larger. There may be also structural changes within the adsorbate layer occurring during the preparation at higher temperatures.
In spite of these difficulties, reasonable results have been collected using the FEM method [79S2, 81S]. 4.2.1.5.3 Photoemission (PYS, ARUPS) We call this method photoemission yield spectroscopy (PYS) if photons near to threshold are used and all photoelectrons are collected [77S]. If VUV photons are used and photoelectron spectra are measured, we call the method ARUPS from angle-resolved UV-light photoelectron spectroscopy. Energy conservation in photoemission is given by F
Ekin = hν – E B – Φ ,
(10)
where the kinetic energy Ekin of the outgoing photoelectron is given by the photonenergy hν, the binding F
energy of the electron E B (with reference to the Fermi edge) and the work function Φ. Eq. (10) indicates that there is threshold photonenergy (hν)t so that photoelectrons with Ekin 0 are emitted for hν (hν)t. For a metal the electronic levels are filled up to EF so that (hν)t = Φ .
(11)
So, the photoemission process establishes the possibility to determine an absolute value of Φ. In practice there are several ways to make use of Eqs. (10) and (11). The first way was to use UV light with hν (hν)t § 5 eV. It can be shown [31F] that there is a narrow photon energy range (§ 0.5 eV) above threshold in which the yield of photoelectrons Y(hν) increases proportional to (hν-Φ)2. If one plots Y(hν)1/2 as a function of hν (Fowler plot) and extrapolates for hν ĺ 0, one can obtain Φ. The second way could be realized after development of VUV-light sources and energy analyzers for the photoelectrons. If one collects all electrons without cutting off some at the low energy end of the spectrum, one measures the width W of the photoelectron energy distribution curve. For a metal this is quite easy, since both the secondary electron threshold as well as the Fermi edge exhibit a large enough intensity. Thus, the work function can be determined from Φ = hν - W.
(12)
By this method absolute work function values can be determined with an accuracy of ±10 meV under the following conditions:
Lando lt -Bö rnst ein New Ser ies III/42A2
4.2-6 (1)
(2)
4.2 Electron work function of metals and semiconductors
[Ref. p 4.2-118
The measurements have to be performed in an angle-resolved mode of photoelectron spectroscopy (ARUPS). Angle-integrated modes collect, with increasing kinetic energy, an increasing number of secondary electrons with kɊ 0. The threshold can therefore have a width of up to 1 eV and is not a sharp level. Therefore, an extrapolation procedure has to be used which always includes some degree or arbitrariness. The spectrometer sample configuration should be of such a geometry that a planar electric field is built in front of the sample, if one supplies the sample with a bias voltage of, e.g., -2 Volt. This voltage accelerates all photoelectrons by 2 eV and ensures that the full spectrum, including the electrons of the true secondary-electron threshold, enters the spectrometer.
Both conditions are fulfilled for the ARUP spectrometer (ADES 400, VG Scientific) which we use in our laboratory. For a Pt(111) surface and a pass energy of the spectrometer of 5 eV we have measured a linear increase of intensity from 10...90% within 120 meV at the secondary-electron threshold and a 10...90% drop of intensity within 140 meV at the Fermi edge. Under these conditions the secondary-electron threshold is as sharp as the Fermi edge. We have therefore included the energy resolution of our spectrometer at both edges. Furthermore, one can derive great benefit from the VUV-discharge lamps (e.g., the He-lamp) whose photon energy is precisely known. The energy of the HeIα line, e.g., is hν = 21.217 eV [70T]. Alternatively, one can perform two-photon photoelectron emission by using UV lasers. In this case one overcomes the surface barrier with the help of 2hν and hν is also known with high precision. 4.2.1.5.4 Secondary electron edge method (SE edge) If photons or charged particles, like electron or ions, interact with bulk material, inelastic processes occur and so-called secondary electrons (SE) are created. These electrons are in empty states above EF and even above the vacuum level. They can leave the bulk if their energy (with wave vector perpendicular to the surface) is larger than Φ (taking EF as the energy zero). The secondary-electron edge, i.e., the energy interval in which the current of secondary-electron drops to zero has a width of 0.05 to 1.0 eV depending on geometry and energy resolution of the electron energy spectrometer. Quite clearly, the SE edge shifts as Φ is changed. This shift can be used to determine a work-function change ∆Φ. The shift is measured very often at the half height of the SE edge where the SE current depends linearly from energy in most cases. In our tables, presented below, we have indicated this experimental method by SE edge (XPS) including in brackets the process which creates the SE edge, XPS given as an example here. Further probes to create SEs are electrons (E) or UV photons (UPS). 4.2.1.5.5 Diode method (Diode) If an electron beam is directed towards a surface, it gets reflected if its potential is equal to - (EP/e + ∆Φ), the negative value of the primary energy divided by e and corrected for ∆Φ between the surface and the electron emitter (in the widest sense: cathode, electron gun, etc.). Since the surface serves here as the anode in a diode configuration, the name diode method has been chosen. This method was introduced early by P.A. Anderson [35A]. Many details of different experimental set-ups are discussed in [73K2, 79H3]. It was pointed out [85K8] that for carefully chosen conditions and for a patchy surface, i.e., a surface consisting of a composite of smaller areas of different work function, the diode method measures the same arithmetical average of Φ as the Kelvin method (see below). How to use a HREEL spectrometer for the diode method is reported in Ref. [85S3]. 4.2.1.5.6 Vibrating capacitor method (Kelvin) The vibrating capacitor method is based on the work of Lord Kelvin [1898K] and of Zisman [32Z]. A condensor is formed of the surface to be studied and a reference electrode in front of it which are connected by a ammeter and a variable voltage source. If the capacitance between the plates (sample and reference electrode) is changed, e.g., by changing their distance, a current will flow. By compensating the
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors
4.2-7
contact potential difference through the voltage source, the current can be brought to zero. Since Φ of the surface is part of the contact potential, its changes relative to the reference electrode can be measured. A more extended description can be found in Ref. [79H3]. A very versatile instrument of this kind was developed by Besocke [76B]. 4.2.1.6 Data collection Data have been collected for metal as well as semiconductor substrates. In the case of metals only elemental, single-crystalline samples were considered. There are a few exceptions to this general rule. Some metallic alloys are listed in case of single-crystalline samples of well defined (stoichiometric) composition. Some data are also incorporated for evaporated, mostly polycrystalline films of materials for which no single-crystal data are available. For semiconductor substrates, adsorbate-induced workfunction changes consist of two contributions: band-bending and electron-affinity changes. Systems were discarded for which the overall change in work function was small (<0.2 eV) or for which the authors did not report a separation of the two contributions. With respect to the adsorbates, only single-component adsorption layers were considered, i.e., co-adsorbates were omitted. Furthermore, it should be noted that completeness – although intended – could not be achieved. It was learned that work-function data are very often not in the center of a publication. Work-function data even seemed to many authors too marginal to give explicitly reference to them in the title, abstract or key words. Therefore, also computer based research could not guarantee completeness. In the tables the following data are listed: 1. 2. 3. 4. 5. 6. 7.
8.
Reference (Ref.), Substrate, polycr. means evaporated film which is very likely polycrystalline., Sample temperature T [K] during measurements, Method of ∆Φ measurement, The type (Type) of ∆Φ variation with increasing coverage as described in section 4.2.1.5, The work-function change ∆Φ at θ1 (+∆Φ or ∆Φ means increase of Φ, –∆Φ decrease of Φ), Coverage θ1, for which ∆Φ is determined; sometimes θ1 marks a relative coverage for which extrema of the ∆Φ variation occur; ML stands for monolayer. A coverage notation θindex is defined as the number ratio of adsorbed index atoms and substrate surface atoms. Comments refer to additional methods applied to characterize the substrate surface and remarkable results. µ0 is the dipole moment of the adsorbate for coverage extrapolated to zero (in units of Debye (D)). α is the respective polarizability (in units of cm3).
If the method or substrate temperature are not mentioned in the reference these informations could not be included in the tables. A missing temperature mostly indicates room temperature measurements (300 K). If the method was not unambiguously identified it is set into parentheses in the table: (method). The electron work-function data are presented in tables. Figures are shown only for some remarkable results. Exception is made for H, CO and Cu for which more figures are shown. These systems may serve as examples for all the other adsorbates.
4.2.2 Rare gases In the late forties Mignolet discovered that adsorption of inert gases produces a large decrease in work function of transition metals [50M]. Although these data [53M] were collected still in the “glass age” of ultra-high vacuum, they are remarkably correct compared to what we know today. Therefore, we have added them to the collection. A decrease of Φ by 0.5 to 1 eV was a great surprise at that time since one did not expect any charge transfer resulting in a dipole formation for physisorbed gases. Only in the seventies this phenomenon could be explained as a valence charge fluctuation stabilized by the image force between the metal surface and the center of the rare gas atom. Lando lt -Bö rnst ein New Ser ies III/42A2
4.2-8
4.2 Electron work function of metals and semiconductors
[Ref. p 4.2-118
Table 1. Neon (Ne) Ref. 87J2
Ne/ T [K] Substrate Ga Polycr. 10
Method
Type
SE edge (UPS)
∆Φ [eV] at θ1 -0.15
Comments, interpretation
ML
Table 2. Argon (Ar) Ref.
82J 88J
Ar/ Substrate Ga (polycr.) Ni(110) Pb(111)
Method
10 20 20
SE edge (UPS) ARUPS ARUPS
W(100)
FEM
70E3
W(110)
FEM
70E3
W(111)
FEM
-0.6 -0.13 ML -0.145 2. layer -0.46... -0.6 -0.85... -1.05 -0.40
70E3
70E3
W(120)
FEM
-0.70
70E3
W(211)
FEM
-0.34
87J2
Type
∆Φ [eV] at θ1
T [K]
-0.1
Comments, interpretation
ML multilayer LEED, ARUPS µ0 = 0.31 D at monolayer density of Ar of 7.9·1014 atoms cm-2 µ0 = 0.29 D at monolayer density of Ar of 7.9·1014 atoms cm-2 µ0 = 0.16 D at monolayer density of Ar of 7.9·1014 atoms cm-2 µ0 = 0.4 D at monolayer density of Ar of 7.9·1014 atoms cm-2 µ0 = 0.29 D at monolayer density of Ar of 7.9·1014 atoms cm-2
Table 3. Krypton (Kr) Ref.
Kr/ Substrate 76R3 Ag(111) 76R3 Cu(211) 82J Ni(110) 88J Pb(111)
T [K]
Method
77 77 20 20
Kelvin Kelvin ARUPS ARUPS
84M
Pd(100)
70E3
W(100)
FEM
70E3
W(110)
FEM
70E3
W(111)
FEM
70E3
W(120)
FEM
70E3
W(211)
FEM
Type
∆Φ [eV] at θ1
Comments, interpretation
-0.29 LEED -0.35 LEED -0.6 multilayer -0.10 ML LEED, ARUPS -0.14 2. layer -0.36(5) µ0 = 0.17 (5) D α = 1.7 cm-24 cm3 -0.83 µ0 = 0.38 D at a monolayer atom density of Kr of 7.2·1014 atoms cm-2 -1.97 µ0 = 1.93 D at a monolayer atom density of Kr of 7.2·1014 atoms cm-2 -0.83 µ0 = 0.50 D at a monolayer atom density of Kr of 7.2·1014 atoms cm-2 -0.95 µ0 = 0.43 D at a monolayer atom density of Kr of 7.2·1014 atoms cm-2 -0.58 µ0 = 0.44 D at a monolayer atom density of Kr of 7.2·1014 atoms cm-2
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors
4.2-9
Table 4. Xenon (Xe) Fig. 2. Xe adsorption on Pd(110) Ref.
Comments, interpretation
-0.45 -0.44 -0.45
LEED LEED LEED
T [K]
Method
77 77 77
Kelvin Kelvin Kelvin
20
SE edge (UPS)
86J3
Ag(111)
58
73C2 Ag(211) 72K Ag (polycr.) 80C2 Al(111)
77 77
SE edge (UPS) Kelvin Diode
84C
15
SE edge (UPS) Kelvin
78
PYS
-0.52
77 20
Kelvin ARUPS
77
Kelvin
-0.45 -0.1 >-0.2 0.0
77
Kelvin
-0.9
77
Diode
0.0
10
ARUPS
0.0
15
Kelvin
-0.025
77 77 77 45 77
Kelvin Kelvin Kelvin ARUPS Kelvin SE edge (UPS) SE edge (UPS) Kelvin Kelvin
-0.47 45 L -0.47 -0.61(2) -0.61(2) -0.48 -0.58
LEED LEED LEED
-0.58
µ0 = 0.24 D
-0.53 -0.58
LEED LEED, AES
71C4 73C2 73C2 82M2 73C2 86J3
Al (polycr.) Au (polycr.) Au(100) Ba (polycr.) Ca (polycr.) Cr (polycr.) Cs (polycr.) Cs (polycr.) Cs (polycr.) Cu(100) Cu(100) Cu(110) Cu(110) Cu(111) Cu(111)
86E3
Cu(111)
74N 76M2 88A 53M 53M 74K 83R2 84C
76R3 Cu(211) 75P Cu(311)
Lando lt -Bö rnst ein New Ser ies III/42A2
40
77 77
Type
∆Φ [eV] at θ1
Xe/ Substrate 73C2 Ag(110) 73C2 Ag(111) 76M3 Ag(111) 76R3 86B5 Ag(111)
III
-0.48(1) monolayer TDS, XPS, UPS,LEED -0.6 multilayer UPS angle-integrated µ0 = 0.2 D -0.48 µ0 = 0.2 D
III
-0.45 -0.47
III
-0.29 -0.33 -0.25
III
III
LEED
1 ML multilayer 1 ML* *1 ML has been taken as 6·1014 atoms cm-2 ML AES, ELS, LEED ML 2. layer
ARUPS 1 ML
LEED µ0 = 0.24 D
4.2-10
4.2 Electron work function of metals and semiconductors
Ref.
Xe/ Substrate 75P3 Cu(100) Cu(111) Cu(110) Cu(211) Cu(311) Cu(755) 71K Cu (polycr.) 74N4 Cu (polycr.) 53M Fe (polycr.) 80P Fe(110) 74N Fe (polycr.) 87J2
T [K]
Method
Type
∆Φ [eV] at θ1
77
Kelvin
III
77
Diode
-0.47 -0.48 -0.61 -0.53 -0.55 -0.53 -0.57
78
PYS
-0.63
77
Kelvin
-0.66
78
PYS
-0.3 -0.5
∆Φ values for surfaces annealed at higher temperatures do not vary much
82L4 53M
77
SE edge (UPS) SE edge (E) SE edge (UPS) Kelvin
78 78 78 78 78 78
FEM FEM FEM FEM FEM FEM
-1.6 -0.8 -1.8 -1.3 -1.0 -1.05
Kelvin
0.0 -0.05
1 ML*
Hg (polycr.) 74N2 Ir(100) Ir(110) Ir(111) Ir(210) Ir(321) 74N Ir (polycr.)
-0.22(1) ML
-0.23
∆Φ values for surfaces annealed at higher temperatures do not vary much
K (polycr.) 77 K (polycr.) 15
84C
15
Kelvin
III
-0.1
1 ML*
15
Kelvin
III
-0.3
1 ML*
30...100 Kelvin
86M2 Ni(100)
20
µ0 = 0.14 D
-0.6
53M 84C
Li (polycr.) 84C Mg (polycr.) 74M6 Mo (polycr.) 71K Na (polycr.) 84C Na (polycr.) 82C Ni(100)
Comments, interpretation
ML
Ga 10 (polycr.) Ge(111)- 60 c(2 × 8) Gd(0001)
88P2
-0.25
[Ref. p 4.2-118
*1 ML has been taken as 6·1014 atoms cm-2 *1 ML has been taken as 6·1014 atoms cm-2 *1 ML has been taken as 6·1014 atoms cm-2
-0.70 77
Diode
15
Kelvin
SE edge (UPS)
0.0 III
-0.05
1 ML*
III*
-0.38
10 L
-0.3
ML
*1 ML has been taken as 6·1014 atoms cm-2 *very weak Type IV LEED, TDS, UPS µ0 = 0.29 D TDS, AES, influence of K
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118] Ref.
4.2 Electron work function of metals and semiconductors T [K]
Method
20
ARUPS ARUPS
53M
Ni (polycr.) 74N Ni (polycr.) 74N4 Ni (polycr.) 88J Ni(111)(7 × 7)Pb 85D2 NiO
77
Kelvin
78 590* 78
PYS PYS
-1.01 -0.6 -0.82
20
ARUPS
0.0 -0.4(2)
88J
Pb(111)
20
SE edge (UPS) ARUPS
71P
Pd(100)
77
Kelvin
80K
Pd(100)
40
84M
Pd(100)
SE edge (UPS) SE edge (E)
84W
Pd(100)
95
79K2 Pd(110)
100
84W
Pd(110)
95
84W
Pd(111)
95
ML 2. layer
ARUPS
*film annealed at 590 K ML Xe 5p and 4d levels
ML 2. layer at 6 L
-0.65
1 ML
III
-0.70(2)
SE edge (UPS)
III
-0.86(2)
SE edge (UPS) SE edge (UPS) SE edge (UPS)
III
-0.92(1)
III
-0.96(2)
III
-0.85(2)
LEED: no 2D island at 10 K µ0 = 0.45(3) D α = 3.6(8)·10-24 cm3 LEED, AES, UPS; hcp Xe layer µ0 = 0.61 D α = 8.4·10-24 cm3 LEED, TDS, UPS µ0 = 0.42 D LEED, TDS, UPS; hcp Xe layer µ0 = 0.44 D LEED, TDS, UPS; (¥î¥ 5ÛVWUXFWXUH µ0 = 0.70 D step edges µ0 = 1.12 D full layer µ0 = 0.49 D 2. layer µ0 = 0.11 D ∆Φ values for surfaces annealed at higher temperatures do not vary much *values taken from Fig. 3 of [74N3]
SE edge (UPS)
74N3 Pt(100) Pt(111) Pt(110) Pt(210) Pt(311) Pt(321) 86S2 Pt(111)
40
89A
95
FEM FEM FEM FEM FEM FEM SE edge (UPS) SE edge (UPS)
Lando lt -Bö rnst ein New Ser ies III/42A2
-0.75 -0.75 -0.90 -0.85
Comments, interpretation
-0.085 -0.135 -0.94
40 83M2 Pd(810) [8(100)î (110)] 74N Pd 78 (polycr.)
Pt(111)
Type
∆Φ [eV] at θ1
Xe/ Substrate 82J Ni(110) 83R2 Ni(110)
4.2-11
-0.27(2) -1.03(2) -1.26 -1.12
PYS
-1.0 -0.85* -0.95* -1.1 -0.9 -0.9 -0.6 III
-0.55
LEED, ARUPS LEED, AES, Fig. 2 µ0 = 0.95 D α = 8.2·10-24 cm3
AES, UPS θXe = 1
UPS
4.2-12
4.2 Electron work function of metals and semiconductors
[Ref. p 4.2-118
T [K]
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
< 50
Diode
IV
-0.58 -0.53
at 2θ1 at 3θ1
78 573* 78
PYS PYS
-0.90 -0.65 -0.95
ARUPS dips in ∆Φ var 3 different ordered structures µ0 = 0.3(1) D *film annealed at 573 K
ML
78
PYS
-1.09
74N4 Rh 78 (polycr.) 81W Ru(0001) stepped
PYS
-1.08
Ref.
Xe/ Substrate 96O3 Pt(111)
74N
Pt (polycr.) 74N4 Pt (polycr.) 74N Rh (polycr.)
86J3 86E3 87S5 74N
53M
Ru(0001)
SE edge (UPS) SE edge (UPS)
Ru(0001) Ru 78 (polycr.)
III
-0.50
-0.72
PYS
-0.65 -0.95
77
Kelvin
-0.1
77
Diode
0.0
77
Kelvin
-0.84
70E3
Se (polycr.) Sn (polycr.) Ti (polycr.) W(100)
FEM
-1.35
75W
W(100)
80
-0.99(5)
80W
W(100)
SE edge (UPS) Kelvin
70E3
W(110)
80C 80L 80W
W(110) W(110) W(110)
83O 70E3
W(110) W(111)
74K 53M
FEM
FEM FEM Kelvin
30
FEM FEM
∆Φ values for surfaces annealed at higher temperatures do not vary much
µ0 = 0.25 D µ0 = 1.0 D at step edges µ0 = 0.34 D at step edges µ0 = 0.3 D ∆Φ values for surfaces annealed at higher temperatures do not vary much
µ0 = 0.97 at a Xe atom monolayer density of 6·1014 atoms cm-2
-1.05(2) at 4·1014 also co-adsorption of oxygen atoms cm-2 µ0 = 0.98 D α = 6·10-24 cm3 -2.4 µ0 = 1.67 D at a Xe atom density of 6·1014 Xe atoms cm-2 later it was noted that Fowler Nordheim equation breaks down for Xe/W(110) [80W] -2.0 ML -2.0 1 ML -0.45(2) also co-adsorption of oxygen µ0 = 0.35 D α = 6.6·10-24 cm3 -2.1 -1.13 µ0 = 0.41 D at monolayer density of 6·1014 Xe atoms cm-2
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors
4.2-13
T [K]
Method
Type
∆Φ [eV] at θ1
74D
Xe/ Substrate W(111)
104
Diode
III*
70E3
W(120)
FEM
70E3
W(211)
FEM
53M
W (polycr.) Zn (polycr.)
77
-1.1 (1) at 1·1015 ∗shows a weak Type IV behavior, atoms cm-2 TDS µ0 = 0.66...0.75 D α = 3.5...4.9·10-24 cm3 -1.4 µ0 = 0.6 D at monolayer density of 6·1014 Xe atoms cm-2 -0.92 µ0 = 0.81 D at monolayer density of 6·1014 Xe atoms cm-2 -1.14
Ref.
53M
77
Kelvin
Comments, interpretation
-0.21
4.2.3 Atomically chemisorbed adsorbates 4.2.3.1 Atomic Hydrogen (H), Atomic Deuterium (D) Fig. 3...10 Table 5. Atomic Hydrogen (H), Atomic Deuterium (D) Ref.
T [K]
Method
89Z3
H, D/ Substrate Ag(111)
100
93S3 95G
Ag(110) Ag(111)
100 100
SE edge (UPS) Diode Diode
80K3 Al(100)
300
Kelvin
90R
Be(0001)
100
94E
Co(10 1 0) 85
94R
Cu(110)
Lando lt -Bö rnst ein New Ser ies III/42A2
Kelvin
90.... Kelvin 400
Typ
∆Φ [eV] at θ1
Comments, interpretation
-0.17
at saturation TDS, UPS
I I
0.22 0.32
1L 0.55
I
+0.24 +0.25 -0.55 -0.45 0.20 0.10
2L 200 L θ = 0.04 θ = 1.0 θH = 1 θH = 1.5
0.11 -0.5
20 L 500 L
II
IV
LEED, TDS, HREELS LEED, TDS, HREELS TDS: β2 (180 K), β1 (160 K) (shoulder) LEED: (2 × 2); 0.25 < θH < 0.5 (2 × 2) + (3 × 3); θH > 0.5 HREELS: threefold-hollow site; µ0 = 0.18 D
HREELS LEED, TDS, HREELS α and β states in TDS LEED: c(2 × 4), p2mg(2 × 1); p2mg(2 × 1) at θH = 1.5 used for calibration. (1 × 2) at θH = 1.5 assigned to a paired row structure. LEED, TDS The main effects in ∆Φ are due to changes in reconstruc-tion from (1 × 1) into (1 × 2).
4.2-14
4.2 Electron work function of metals and semiconductors
[Ref. p 4.2-118
T [K]
Method
Typ
∆Φ [eV] at θ1
Comments, interpretation
140 140 140 140 300
Kelvin Kelvin Kelvin
Ge(111)
300
Kelvin
IV
82D
Ir(100)
77
FEM
IV
80I
Ir(110) -(1 × 2)
140
Diode
-0.08 +0.07 +0.23 +0.22 +0.18 +0.05 +0.05 -0.05 +0.12 -0.22 -0.14 +0.3 -0.05
LEED, TDS, UPS
Kelvin
III I I I II
77D 73C
Ir(111) Ir(100) Mo(110)
89E
Mo(100) Mo(111) Mo(110)
Ref.
H, D/ Substrate 77B2 Fe(110) Fe(100) Fe(111) 81E Fe(111) 84S Ge(100)
FEM FEM
II
350
Diode
I I IV
74H2 Nb(100) 74D3 Ni(001) Ni(110) 83K Ni(100)
90 300 300 100
84P5
Ni(100)
95
74T
Ni(110)
85G
Ni(110)
170 300 175
Kelvin Kelvin Kelvin SE edge (UPS) SE edge (UPS, E) Diode?
87J Ni(110) 88H 86N3
175
II
I
? Kelvin
-0.8 -0.8 0.48 0.3 0.45 0.68 0.42 -0.015 +0.12 +0.52 +0.08 +0.40 +0.17 +0.11 +0.1 +0.05 0.58 0.50 +0.23 +0.50 0.25
0.5
98V
Ni(110)
(300)
Diode
I
0.35
500 L 500 L 500 L 20 L 0.05 ML 0.5 ML 1.0 ML 0.05 ML 0.6 ML 1L 100 L 0.25 L 25 L
5L 7L 16 L 40 L 50 L 0.2 L 3L at 10 L max 0.5 L 17 L (sat.) θD = 0.5 θD = 1.0 2L 9L
θH = 1 θH = 15
4L
TDS ELS surface conductivity
TDS β2 sites β1 sites
TDS, ESD
LEED LEED (1 × 2) UPS, TDS TDS, XPS co-adsorption with D LEED, AES (2 × 1) phase in LEED (1 × 2) phase in LEED (2 × 1) θH = 1.0 (β2 state) µ0 = 0.054 D (1 × 2)
µ0 = 0.1 D
θH = 1.5 (α state)
LEED, TDS, RBS, NRA See Figs. 3, 4. LEED, AES, TDS
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors
H, D/ Substrate 74C3 Ni(111) Ni(100) Ni(110)
T [K]
Method
Typ
∆Φ [eV] at θ1
Comments, interpretation
300 300 120
Kelvin, Diode
I I I
0.20 0.16 0.53
sat. sat. sat.
(1 × 1) (1 × 1) streaks, than 1 × 2 LEED, AES, TDS
77D4 Ni(111)
80
SE edge (E)
0.16
14 L
0.12 0.45 0.10 0.18 0.09 0.18 0.21 0.15
6L 6L 20 L 0.5 θmax 0.9 θmax θH = 1.0 θH = 1.25 θH = 2.0 θ = 1.35 1L
Ref.
300 86I
Ni(111)
79C2 Ni(111)
150
94W2 Pd(100)
SE edge (E) Kelvin
II II
Theory
Rh(100) 80B4 Pd(100) 83C Pd(110)
170 120
Theory Kelvin Kelvin
I I
+0.2 0.33
88H4 Pd(110)
140
Kelvin
I
0.30
89M
Pd(110)
130
Kelvin
I
0.30
90H2 Pd(110) 98M Pd(210) 77D4 Pd(111)
100 120 80
I I
0.30 0.17 0.14 0.18 0.18 0.32 0.20 +0.25 +0.07* -0.18*
99F 91P3
Pd(111) Pd(110) Pd(100) Pd(311) Pt(100)
120 100
Kelvin Kelvin SE edge (UPS) Theory Theory Theory Kelvin Kelvin
91P2
Pt(100)
35
Kelvin
98D
Lando lt -Bö rnst ein New Ser ies III/42A2
I IV
-0.37
4.2-15
LEED, AES, TDS, ESD LEED, TDS; see Fig. 5 Delocalisation of H discussed 4-fold hollow site for θH = 1.0 in addition subsurface sites up to θH = 2. See Fig. 6.
LEED, TDS. See Fig. 7. (2 × 1) at 0.3 L (1 × 2) > 0.5 L not observed as discontinuities in ∆Φ. LEED, TDS 4 L; θ = 1.5 LEED, TDS (2 × 1): θ = 1 (1 × 2): θ = 1.5 Authors discuss 2 surface phases and a subsurface hydrogen phase. LEED, TDS, NRA, RBS Authors discuss subsurface D! 1.5 ML TDS 5L LEED, TDS, HREELS 1L 2L good agreement with the given [74C] references [74C] [80B] LEED, TDS, HREELS θH = 1 LEED, TDS b state three (a1, a2, b) states; state b a1, a2, b states transfers the Pt(100) hex into the Pt(100) (1 × 1) surface at 330 K. *with respect to Pt(100) hex phase; see Fig. 8. at 100 L LEED, TDS 4 H-states: a1, a2, a3, b At 35 K (100)hex structure not lifted by H adsorption.
4.2-16 Ref. 76N
4.2 Electron work function of metals and semiconductors H, D/ Substrate Pt(111) Pt(100) ~Pt(110) Pt(210)
T [K]
Method
78
FEM probe-hole
Typ
[Ref. p 4.2-118
∆Φ [eV] at θ1
Comments, interpretation
-0.56 -0.37 +0.10 +0.14
p H 2 = 2·10-9 Torr p H 2 = 2·10-9 Torr p H 2 = 2·10-9 Torr p H 2 = 2·10-9 Torr
76C Pt(111) 76C2 Pt(997)
130
Kelvin, Diode
III II
76C2 Pt(111)
300
III
77D4 Pt(111)
80
79N2 Pt(111) 87E Pt(110) -(1 × 2)
95 120
Kelvin, Diode SE edge (E) Kelvin Diode
92S
Pt(110) -(1×2) Pt(110)
170
Pt0.5Ni0.5 (110) Re film
-0.35 +0.02 -0.35 -0.23
sat. 0.25θsat θsat ∆φ = -0.23 × θ1.33 eV LEED, TDS, ELS
-0.2 III II
-0.45 0.17 -0,5
θH = 0.3 θH = 1.0
Diode (LEEM) Diode
IV
120
Diode
I
0.15 -0.7 +0.14 0.0 -0.4 -0.65 +0.60
θrel = 0.05 θrel = 1 0.1 L 0.2 L 0.6 L 20 L θH = 0.9
300
Diode
I
0.2
300
FEM
II
95M2 Re(10 1 0) 120
Kelvin
II
0.52 0.35 0.37 0.15
84P
100?
SE edge (UPS)
I
0.2
84H2 Rh(100) 84P6 Rh(100)
100 100
I
0.2 +0.20
87K
Rh(100) Rh(111)
300 300
Diode SE edge (UPS, E) PYS PYS
1.5·1014 molecules cm-2 (sat.) Also results for O, CO, C2H4 50 L * The central plane of the tip is 1000 L (10 1 0). 2L LEED, TDS 40...2000 L TDS: α, β1, β2 states LEED: c(2 × 2)-2H, (1 × 1)-2H sat. UPS, XPS, ELS A weak max. in ∆Φ is observed with coverage. sat. LEED, TDS UPS, TDS θD = 0.9
I II
0.27 0.23 0.18
87C2 Rh(110) 88E
100
Kelvin
I
0.9
92S6
94F2 76E2
82D2 Re*
Rh(100)
7·104 L (sat). 6·103 L 7·104 L (sat.) sat.
β2 state β1 state; saturation LEED, TDS LEED, TDS two H states in TDS: β1, β2
LEED, TDS, NRA
AES
LEED, TDS There are several changes in slope in ∆Φ (exposure) and several LEED structures.
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors T [K]
Method
Typ
∆Φ [eV] at θ1
87K
H, D/ Substrate Rh(111)
300
PYS
IV
Rh(100) Rh(113)
300 90
PYS
III
91N
-0.23 -0.20 -0.28 0.97
min saturation saturation θH = 1
85F
Ru(0001) 95
0.025 -0.01 0.03
70 Ex
+0.030 +0.048 +0.030 +0.005 0.42 0.30 -0.25
0.5 L 0.8 L 1.1 L 2.5 L θ =1 θ =2
Ref.
Kelvin
86H3 Ru(0001) 80
Kelvin
91S2
Ru(0001) 45
Kelvin
89L2 96C 96B
Ru(10 1 0) 100
Kelvin
Si(100) -(2 × 1) W(100) (ribbon) W(100)
300
Diode
300
Diode
300
Thermoemission FEM FEM FEM
66E 69A 72P 73C
W(100) W(110) W(110)
74F2
W(100) W(112) W(100)
84H5 W(100) 86H2 W(100) W(110) 73R W(112)
Lando lt -Bö rnst ein New Ser ies III/42A2
300 300
II
II
II
I
0.2 I II II I I
300 300 450 300 300
SE edge (UPS) Diode Diode Diode Kelvin
0.9
I I I III II
0.9 -0.5 0.83 0.0 0.73 0.65 +0.9
Comments, interpretation
LEED, TDS Low-coverage structures (1×3)−Η, (1×2)−Η, (1×3)−2Η have no influence on Rh surface structure. High-coverage structure (1×2) opens diffusion channels to subsurface sites. There are two states. depending on temperature LEED, TDS some small changes of Φ as observed in [85F] LEED 3 phases in LEED
LEED, TDS, HREELS three structures in LEED TDS atomic H used 1×1015 mole LEED -cules cm-2 sat.
0.1 L 10 L 6L 1.2 L UPS
+0.55 +0.27 0.97 -0.46 0.61
θH = 0.45 θH = 0.45 3L 35 L 1/2θsat
0.27
θsat
4.2-17
step at 0.2 L; ∆Φ = 0.25 eV linear increase β2 state (TD = 675 K) filled linear decrease β1 state (TD = 330 K) filled
4.2-18 Ref. 74B
4.2 Electron work function of metals and semiconductors H, D/ Substrate W(110) W(111) W(112)
T [K]
Method
Typ
∆Φ [eV] at θ1
*
Kelvin
III I II
-0.5 +0.26 0.6 +0.32 0.9
W(100)
97N
W(110)
72M3 W(111)
I
90
Kelvin
III
300 125 (300) 77
Diode
I
70A 97C
W(112) W(310)
77M
ZnO (0001)Zn (000 1 )O
FEM FEM
Zr(10 1 0) 100
Kelvin
96Z 96C
Kelvin I FEM II probe hole
370
-0.3 -0.5 +0.07(2) +0.21(2) 0.7 0.56 0.43 0.43
0.5θsat θsat
8L 240 L
[Ref. p 4.2-118
Comments, interpretation
linear increase linear decrease linear increase See Fig. 9. TDS *dosed at 135 K LEED See Fig. 10. TDS LEED, TDS
0.5 L 4L 20 L
-0.2 -0.7 IV III
-0.01 +0.075 -0.06
0.25 L 3.0 L >0.7 L
AES, NRA, SIMS
Type
∆Φ [eV] at θ1
Comments, interpretation
~+0.5 -1.1
LEED p(2 × 2) LEED: ringlike diffraction features LEED: ringlike diffraction features *hydrocarbons at a hot (500 K) Pt(111) surface AES gives coverage
Results are discussed in terms of two H sites: one site above the surface (∆Φ > 0) and one subsurface site (∆Φ < 0).
4.2.3.2 Atomic Carbon (C, C60) Table 6. Atomic Carbon (C) Ref.
C/ Substrate 74D3 Ni(001) 74G Pt(111) -(1 × 1) Pt(100) -(5 × 1) 86A3 Pt(111)
T [K]
Method
300 1170
Kelvin
1170 *
-1.1 Kelvin
-0.5
θC = 0.75
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors
4.2-19
Table 7. C60 Ref.
C60/ Substrate 96M3 Al(111)
T [K]
Type
SE edge (UPS)
Al(110) 97K3 Cu(111)
SE edge (UPS) SE edge (UPS)
94G2 GeS(001)
94J
Method
Rh(111)
SE edge (UPS) SE edge (UPS)
93R3 Ta(110)
III
∆Φ [eV] at θ1
Comments, interpretation
+0.95
1 ML
XPS
+0.95 -0.08
1 ML 1 ML
0.1
1 ML
-0.5
1 ML
+0.6
1 ML
LEED, UPS, XAS See also Table 8. LEED, X-Diffraction, SEM, XPS, UPS C60(111)-lage UPS, EELS ARUPS first C60 molecules are decomposed
Table 8. Work functions of clean metal surfaces and after adsorption of a monolayer C60. From [97K3]. Conclusion: All C60 monolayers are metallic showing a work function of about 5 eV. The dipole layer at the substrate-C60 interface is screened out by the C60 film. Ref.
Surface
[97K3] [97K3] [96M3] [96M3]
Cu(111) Ni(111) Al(110) Al(111) Au(119)a Rh(111) Ta(110)
[94J] [93R3] a
Clean surface Φ [eV] 4.94 5.36 4.35 4.25 5.37 5.4 4.8
Φ [eV] of 1 ML C60 on surface 4.86 4.93 5.25 5.15 4.82 4.9 5.4f
∆Φ [eV] -0.08 -0.43 +0.95 +0.95 -0.45 -0.5 +0.6b
) P. Rudolf et al, unpublished, quoted in [96M3] ) for reference only, since C60 decomposes on this surface at RT
b
4.2.3.3 Atomic Nitrogen (N) Table 9. Atomic Nitrogen (N) Ref. 90S
98G
79G
N/ Substrate Cr(110)
Cu(100)/ Fe(100) fcc Ni(110)
Lando lt -Bö rnst ein New Ser ies III/42A2
Type
∆Φ [eV] at θ1
Comments, interpretation
-0.55
UPS adsorbed at 90 K and annealed stepwise to 300 K; transformation N2 ĺ1IROORZHG by UPS for epitaxial fcc-Fe films of thickness 1.2...8 ML Exposure 3000 L LEED, TDS p(2 × 3), authors discuss formation of surface nitride
T [K]
Method
300
SE edge (UPS)
75
Kelvin
I
0.8 ± 0.1
590
Kelvin
III
-0.5
4·105 L
4.2-20
4.2 Electron work function of metals and semiconductors
N/ Substrate 91B4 Rh(111)
T [K]
Method
Type
∆Φ [eV] at θ1
I
+0.45
θN = 0.4
69A 71A
W(100) W(100)
300 300
SE edge (UPS) Therm Kelvin
300 300 300 400
Kelvin Kelvin Kelvin Kelvin
saturation 2L 4L 4L 4L
74F2 93O
W(210) W(310) W(100) W(100)
89S2
W(110)
200
Kelvin?
-0.7 -0.55 -0.50 0.25 0.18 -0.3 -0.4 -0.35 0.2
Ref.
IV I I IV
5L 300 L
[Ref. p 4.2-118
Comments, interpretation microwave discharge to produce atomic N
UPS ELS Chemisorbed N2 at 90 K irra-diated with electrons and heated to 200 K
4.2.3.4 Atomic Oxygen (O) Fig. 11 and 12 Table 10. Atomic Oxygen (O) T [K]
Method
Type ∆Φ [eV] at θ1
Kelvin
I III I
Ag(111)
300 300 400 300
85S3
Ag(110)
300?
Kelvin Diode
I
73D
Ag(111)
300?
I
Ref. 76E
O/ Substrate Ag(110) Ag(100)
78M2 Ag(331)
300
photoelectric Diode
77B5 Al(111)
300
Kelvin
79H4 Al(111) Al(110) Al(100) 77G4 Al(111) Al(110) Al(100) 80M Al(111) Al(110)
300 300 300 300
Kelvin Kelvin Kelvin PYS
88M
300
Al(100)
116
0.85 -0.15 +0.3 0.04 0.625 0.32 0.5 0.72 0.4
sat. 1000 L 1000 L p=10-5 Torr O2 sat. 5000 L θ = 0.25 θ = 0.3 θ = 0.50 1400 L
+0.7(1)
Kelvin
III III III I III III III
Kelvin
III II
-0.17 -0.21 -0.2 -0.48 -1.08 +0.12 -0.05 -0.48 -0.2 -0.8 -1.25 -0.7 -0.8 +0.25 +0.05
50 L 300 L 500 L 500 L 500 L 100 L 200 L 300 L 350 L 350 L 350 L 3·103 L 8·103 L 400 L 1600 L
Comments, interpretation (n × 1) LEED structures
no Auger signal! i.e. sticking coefficient very small LEED, AES LEED: (4 × 1) LEED: (3 × 1) LEED: (2 × 1)
LEED, AES facetted (2 × 1) chemisorbed layer oxidation
AES
LEED, AES
depending on pressure At low temperatures oxygen stays first on top.
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118] Ref.
4.2 Electron work function of metals and semiconductors
O/ Substrate Au(111)
300
78G5 Be(0001) 83T Bi(0001)
300
98S3
T [K]
82C3 Co(0001) 300 93K3 Co(11 2 0) 100 300 95G2 Co(11 2 0) 100
Method
PYS SE edge (E) Kelvin?
Type ∆Φ [eV] at θ1
Comments, interpretation
I
0.85
1.3 ML
III III
-1.8 -1.1
3000 L sat.
I
0.55
5L
LEED, AES, TDS, HREELS, XPS oxidation through O3; see Fig. 11 LEED, AES LEED, AES, ELS presumably oxide formation LEED, AES, UPS
SE edge (UPS) SE edge (UPS)
320
1.1
I IV
79P
Cr(100)
300
78G
Cr(111)
300 300
SE edge (UPS) SE edge (UPS) SE edge (UPS)
300* 300
Diode
300 300
Diode Diode
I I I
300 300 300
I
I II
97K2 Co(11 2 0)
82S7
Cr(110)
85F2
72E 78H
Cr(100) Cr(110) Cr2O3 (0001) Cu(111) Cu(100) Cu(110) Cu(110) Cu(100)
350
Kelvin Kelvin Kelvin Kelvin Kelvin
79H 80H
Cu(110) Cu(100)
475 600
Kelvin Kelvin
83N2 Cu(110) Cu(111) 84B Cu(110)
300 300 300 110
Kelvin Kelvin Kelvin
86F4 71D
Lando lt -Bö rnst ein New Ser ies III/42A2
4.2-21
IV
II III II
I II
LEED, UPS, XPS
-1.0 1.0
3L
0.8 0 -0.1 -0.4
1L 5L 12 L at 1.5 L
-0.2 +1.7 0 0.9 0.4 -1.2 +0.2 0.0 -0.25 0.0 +0.3 +0.15 +2.4 +1.2 +2.0
2L 20 L <1 L 10 L 1000 L 2L 3L 6L 10 L 15 L 40 L 300 L 300 L 1.5 L
0.13 0.40 0.68 0.25 0.33
sat. sat. sat.
0.38 0.3 0.0 0.25 <0.02 0.36 0.43 0.37
12 L 80 L 500 L
100 L
10 L 0.8 L 10 L
oxide formation AES, UPS, XPS island growth of oxide
LEED CoO(100) formation LEED, AES at ∆Φ = 0.4 (5 L) oxidation starts XPS, UPS C2O3 formation C2O3 formation * plus annealing at 770 K LEED, AES, ELS
LEED: O(2 × 1) structure; AES LEED; at higher T decrease of Φ at higher exposures LEED LEED, AES, Ellipsometry LEED, AES, ISS oxygen on top, disordered layer LEED, UPS, TDS
4.2-22 Ref.
4.2 Electron work function of metals and semiconductors O/ Substrate
T [K]
Method
Cu(111)
300
SE edge (UPS)
Cu(111)
100 300
Type ∆Φ [eV] at θ1
82S3
82S4
SE edge (UPS)
100
0.0
1000 L
I
-0.4 0.0
III
-0.4
1000 L up to 1000 L 1000 L
+0.43
at 6 L O2 3L 20 L 45 L 6L 60 L 100 L
95S7
Cu17Al83 (100) 84S10 Fe(100)
300
Diode
II
86M3 Fe(110)
300
Diode
II
SE edge (UPS) Diode Kelvin
IV
0.25 0.02 0.20 0.58 0.0 -0.1 +0.4
I
1.2
6·105 L
-0.7 0.0
30 L O2 100 L O2
-0.52 +0.42
2·104 L O2 2·104 L O2
81S2
Ga polycr. 300
76D 85I
GaAs(110) 300 GaAs(110) cleaved p-type n-type GaAs(110) Kelvin cleaved p-type n-type GaAs(110) 60...300 Kelvin cleaved p-type
86I2
93N
n-type 87B3 GaSb(110) 300 cleaved p-type
Ge InAs(110) cleaved p-type n-type 86B2 InAs(110) 300 p-type n-type 76I Ir(111) 300
Comments, interpretation LEED, AES, UPS, ELS AES indicates θ0 = 0.32 ML; therefore the authors conclude surface penetration of O atoms. LEED, AES, UPS, ELS At 100 K: 2-peak spectrum in (UPS); chemisorbed O2. At 300 K: incorporation of atomic O into the Cu surface discussed. UPS LEED, AES, ELS
AES, LEED, ELS
10 L O2 condensed at 20 K and annealed to 300 K
oxygen induced surface acceptors 0.0 -0.3 +0.4
< 103 L O2 5·104 L O2 5·104 L O2
-0.05 -0.15 +0.5 +0.35 0.8
4·102 L O2 4·103 L O2 4·102 L O2 4·103 L O2
-0.7 0.0
30 L O2 100 L O2
Kelvin
n-type 72M 85I
[Ref. p 4.2-118
FEM Kelvin
Kelvin
Diode
-0.4 104 L O2 -0.15 104 L O2 +0.56(4) saturation
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118] Ref. 79T
O/ Substrate Ir(110)
82D3 Ir(100) Ir(111) 97L3 Ir(110)
4.2 Electron work function of metals and semiconductors T [K]
Method
Type ∆Φ [eV] at θ1
Comments, interpretation
90 300 725 77 77 300
Diode
I
LEED, AES, TDS
FEM FEM Kelvin
I
78G4 LaB6(100) 100 80N LaB6(100)
Kelvin
Mg(0001)
Kelvin
IV
Mg(10 1 0)
Kelvin
IV
Mg(0001) 300
Kelvin
IV
Mg(10 1 0) 300
Kelvin
IV
FEM
I
LaB6(110) LaB6(100) LaB6(111) 81N2 Mg(0001)
82L5
300 300 300 300
74M3 Mo(100) Mo(110) Mo(111) Mo(112) 75Z 75R
I I I I I IV
82N
81H
Diode SE edge (UPS) SE edge (UPS)
Mo(110) Mo(100)
I II II Diode Diode
I IV
79B3 Mo(100)
300 370... 500 300*
Diode
IV
75Z2
Nb(110)
300
Kelvin
IV
77P
Nb(100)
300
Diode
IV
Nb(110)
300
Diode
IV
Nb(111)
300
Diode
85K3 NbC(100) 300 NbC(111) 300 71S Ni(100) 300
INS*
72E
Kelvin
Ni(110)
Lando lt -Bö rnst ein New Ser ies III/42A2
I
4.2-23
+0.65 +0.45 +0.1 0.6 0.95 +0.7 +1.1 +1.3 +1.6
10 L 10 L 10 L 1L <0.1 L 1L 15 L 20 L
1.3 1.7 1.1 -0.8 -0.1 0 -1.3 -0.9 -1.4 -1.2 -1.2 -1.0 -1.4 -1.25 +0.9 +1.4 +0.8 +0.5 +0.55 +0.1 1.35 -0.4 1.3 -0.35 +1.4 -0.6 +1.0 -0.4 1.5 -0.45 +0.7 -0.16 +1.1 1.2 -0.2 +0.30(5) +0.37(5)
1.5 L 3L 1.5 L LEED, ELS 8L 100 L 150 L 12 L LEED, ELS, Ellipsometry 50 L 14 L 50 L min at 12 L 20 L min 15 L 22 L 1016 atoms cm-2 1018 atoms cm-2 2·1015 atoms cm-2 intermediate max. at 7·1014 atoms cm-2 2·1015 atoms cm-2 1018 atoms cm-2 LEED also at 900, 1100, 1300 K 1L LEED, AES 12 L 1L LEED, AES, TDS 12 L *also at 1100 K similar behavior LEED θ1 4 θ1 0.5 L LEED 5L 1L for Nb(110) see also [79J] 25 L 0.5 L 6L 8L LEED, AES, UPS 10 L LEED p(2 × 2) LEED c(2 × 2) *ion neutralization spectroscopy; assuming ΦNi(100) = 4.75 eV LEED, AES
0.60
XPS LEED, AES, TDS LEED, UPS µ0 = 0.54 D LEED, UPS, XPS
4.2-24
4.2 Electron work function of metals and semiconductors
Ref.
T [K]
74D3 Ni(100)
300
Kelvin
Ni(110)
300
Kelvin
NI(111) Ni(100)
300
Kelvin
300
Diode
II
SE edge (UPS)
II
SE edge (UPS) SE edge (E)
74H
76E3
Method
Type ∆Φ [eV] at θ1
O/ Substrate 73B2 Ni(111) Ni(110)
Diode* Diode*
+0.70 +0.33 +0.44 +0.22 +0.36 +0.26 +0.46 +0.42 ~+0.7 0.3 ~0 -0.65 +0.5 0.0 -0.5
θ = 0.25 θ ~ 0.5
I
0.6
at p(2 × 2)
II
5L 20 L 120 L at 1 L at 30 L at 50 L at 90 L 10 L 25 L 50 L
4L 20 L 100 L
76K
Ni(111)* Ni(110)* Ni(100)* Ni, polycr.* Ni(100)
79A
Ni(100)
300
91P7
Ni(100)
325
Kelvin
II
80B5 Ni(110)
300
Kelvin
II
81C
Ni(111)
82H
Ni(110)
610 370 20
Kelvin Kelvin SE edge (UPS)
I I I
+0.17 0.0 -0.15 +0.35 +0.35 0.0 -0.50 +0.5 0.0 -0.4 0.6 ± 0.1 1.05 0.95
84B3 Ni(111)
300
I
1.0
3L
84S5
77
SE edge (E) Diode
I
0.31
θ = 0.5
86N2 Ni(110)
420 300
Kelvin Kelvin
I II
0.3 0.55 0.0
1.5 L 1.5 L 30 L
87J
Ni(111)
300?
II
88B
Ni(111)
8 77
SE edge (E) Diode
0.85 -0.7 1.2 1.3
4L 15 L 3.5 L 1.5 L
Ni(111)
I I
[Ref. p 4.2-118
Comments, interpretation LEED (2 × 2), *using ions LEED (2 × 1), *using ions LEED (3× 1) LEED p(2 × 2) LEED c(2 × 2) LEED (3 × 1), θΟ = 0.33 LEED (2 × 1), θΟ = 0.50 LEED (3 × 1), θΟ = 0.60 LEED p(2 × 2) LEED, AES p(2 × 2) c(2 × 2) at max. intensity NiO formation UPS * ∆Φ curve is independent of surface orientation
LEED, UPS, XPS µ0 = 0.37 D p(2 × 2) in LEED c(2 × 2) NiO p(2 × 2), c(2 × 2) O phases then nucleation of NiO
AES, TDS, ELS
LEED, TDS 2L >2 L
chemisorbed atomic oxygen physisorbed O2 on top no additional change in Φ TDS, MDS ∆Φ = 0.31 eV = constant for 0.5 < θ < 1 LEED, XPS, TDS, NRA At 420 K three ordered phases are found. (3 × 1): θ = 0.33 (2 × 1): θ = 0.5 (3 × 1): θ = 0.66 LEED, AES
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118] Ref. 89P
O/ Substrate Ni(111)
4.2 Electron work function of metals and semiconductors T [K]
Method
100?
SE edge (E) Kelvin Kelvin
95K2 Ni(775) 96S3 Ni(311)
300 300
84S3 89H
Diode Kelvin
90H2 Pd(110) 88H5 Pd(110)
300 100... 900 475 300 200 100 100
96B2 Pd(110)
300
SE edge (UPS)
78N
300
SE edge (E) Kelvin
Pd(111) Pd(110)
Pt(111) stepped* 84G2 Pt(100) 84N
400... 700
Kelvin Kelvin
Type ∆Φ [eV] at θ1 0.6
θ = 0.25
I I
0.75 0.5
2L 0.3 L
I
0.8
2L
I I I I I
0.7 0.45 0.4 0.7 0.7
I
+0.55 +0.42 +0.42 0.35 0.55
θ = 0.9* 1.2...1.5 L θ0 = 0.50±0.05 at 1 L at 2.5 L at 10 L 1L 500 L
0 0.48 0.37 -1.2
θ= 0 θ = 0.63 θ = 0.44 sat.
4.2-25
Comments, interpretation p(2 × 2) LEED, ARUPS, XPS, TDS LEED, UPS, TDS HREELS At 0.3 L O2 ∆Φ for the fully oxided surface (40 L) is already reached. AES, ELS, TDS
c(2 × 4) + (2 × 3) – 1D c(2 × 4) pseudo (2 × 1) * from NRA LEED, TDS, NRA c(4 × 2) in LEED
LEED, AES, TDS * 9(111) + 1(111) LEED, RBS, NMA reversible structure and oxygen coverage changes with T at p = 5.3·10-3 Pa = const. structure: hex; T = 770 K structure: (3 × 1); T = 670 K structure: complex; T < 650 K due to subsurface oxygen PEEM UPS, XPS 570 K for coverages > 4·1014 atoms cm-2 570 K for coverages > 2.7·1014 atoms cm-2
93R2 Pt(100)
650
PYS
85D
Pt(111)
370 570
Kelvin
I
0.30
7·1014 atoms cm-2
Pt(100)
370 570 300 120 560 1100
Kelvin
I
0.75
Diode Diode Diode Diode
I I
I
0.3 0.75 +1.15 +1.65 +2.5 0.2
1.4·1015 atoms cm-2 θ = 0.4 θ = 1.3 θO = 0.33 θO = 0.07 θO = 0.5
I
0.75
3.5 L
UPS good agreement between the two methods and with Ref. [86F2]
I
0.55
0.8 ML
LEED, AES, TDS, UPS, HREELS (2 × 2)-O at θ0 = 0.25 Exposure to NO2; see Fig. 12
86F2 92S6
Pt(110) -(1 × 2) Pt(110)
89R
Pt(111)
89F
Pt(112) (1 × 2)
89P2
Pt(111)
Lando lt -Bö rnst ein New Ser ies III/42A2
90...300 SE edge (E) 100 Kelvin and SE edge (UPS) 400 SE edge (UPS)
UPS
4.2-26 Ref. 92S2
4.2 Electron work function of metals and semiconductors O/ Substrate Pt(210)
72Z
Re(0001) Re(10 1 0) 74F Re(0001) (ribbon) 82D2 Re*
Method
330 430 >480
Kelvin
0.65 0.75 0.77
300 300 300... 850 300?
Diode Diode Diode
82L3 Re(10 1 0) 300? 88R Re(0001) 80 97B2 Rh(111) 40 87K
99S3
Type ∆Φ [eV] at θ1
T [K]
FEM
I I I
0.5 1.2 0.9 1.2 0.94 1.15 1.33 1.3 0.45 0.75
I
0.38
I I I
Rh(100)
300
FEM? Diode SE edge (UPS) PYS
Rh(111)
300
PYS
I
0.28 +0.75 +0.95 0.2 0.8 1.0 +1.0 +0.2 +0.85 +1.15 1.1 0.7 0.5 0.3 0.92 0.3 1.12 +1.2 +0.4 +0.35 +0.35
Rh(111) 450 Rh(533) 340 Ru(0001) 300
Kelvin
I
Kelvin
I
100 77K5 Ru(10 1 0) 300 85S7 Ru(0001) 300
Kelvin Diode Diode
I I
86H3 Ru(0001) 80 300 87S Ru(0001) 300 93S2 Ru(0001) 400
Kelvin Kelvin Diode Kelvin
75M
I I I
640 99B
Ru(0001) 300
93S
300 500
Diode
20 300
Diode Kelvin
I II
SE edge (E) SE edge (UPS)
III
Si(100) -(2 × 1) + Ge 88S Si(111) 99P Si(111) -(7 × 7) 89B2 SiC(001) 92S3
SnO2(110) 150
II
+1.6 +0.95 +0.2 -0.25
500 L 500 L 500 L
[Ref. p 4.2-118
Comments, interpretation LEED, STM, TDS For T .D(5 × 2)-rect structure is observed which is found by STM as due to (110) and (310) microfacets LEED: (2 × 2) or (2 × 1) LEED: (1 × 3)
0.5 L * The central plane of the tip is 1L Re(10 1 0). 1L p = 10-5 Pa 2L SHG 2.3 L for exposures larger 2.3 L physisorbed O2 appears in UPS. 2·104 L AES (sat). 3·104 L (sat). LEED, TDS, PEEM θO = 0.2 θO = 0.25 1.6 L p(2 × 2) 2.5 L two states 2.5 L LEED, AES 3L FEM pictures θO = 0.25 AES, TDS θO = 0.50 θO = 0.70 2.5 L TDS 6L 4L AES, TDS, ELS 1L p(2 × 2) ĺS î 10 L 1L 10 L 1 ML TDS, UPS 6 ML 30 L 50 L 1L 2.5 L 70 L
0.25
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors T [K]
Method
Type ∆Φ [eV] at θ1
67F
O/ Substrate Ta(110)
300
Diode
IV
76T
Th(100)
300
Diode
IV
69A 72B 72M2 73P3 73B2 73D2 74F2
W(100) W(100) W(100) W(100) W(100) W(100) W(100)
300? 300 300 350 300 300
Ref.
76B2 W(100)
300 1050
84S7
W(100)
300
69T2
W(110)
300
Therm Kelvin Diode Diode Diode Kelvin SE edge (UPS) Diode Diode
I
I
I IV
SE edge (E) Kelvin
W(112)
69W
70E
W(110) W(111) W(211) W(100) W(100) W(211)
W(110) W(111) W(120) 74M3 W(100) W(110)
75E2
90 90 90 90 20 100 20 100 20 20, 100 20 20
FEM FEM FEM FEM FEM
I I I I
FEM
FEM FEM
I II
W(111)
FEM
II
W(112)
FEM
II
W(110)
300
Kelvin
IV
77B3 W(110)
700
Kelvin
I
Lando lt -Bö rnst ein New Ser ies III/42A2
-0.45 0 +0.2 -0.60min -0.46 0.94 1.45 1.6 1.4 1.75 +1.5 +1.5 1.4 -0.2 +0.8 1.2 +0.70 +0.75 +0.75 +0.92 +0.91 +1.05 1.3 1.4 1.6 1.7 1.2 1.4 1.4
0.6 1.4 1.3 +1.9 +0.9 +0.7 +1.3 +0.85 +0.4 +0.7 +2.1 +1.5 -0.05 +0.2 +0.1 +1.3
at θ1 at 2θ1 at 3θ1 8L 36 L sat. 50 L (sat.) 6L
Comments, interpretation
LEED, AES
µ0 = 2.2 D ESD LEED
saturation UPS LEED, AES 1L 3L
6L 8L 1.2 L 2L 3L 8L
0.1 ML 0.5 ML θO = 0.5 θO = 1.0
p(2 × 2), AES, LEED p(2 × 1) p(1 × 1)
1018 atoms cm-2 2·1015 atoms cm-2 1016 atoms cm-2 1018 atoms cm-2 7·1014 atoms cm-2 8·1015 atoms cm-2 2·1017 atoms cm-2 2·1015 atoms cm-2 1018 atoms cm-2 LEED
4.2-27
4.2-28
4.2 Electron work function of metals and semiconductors
Ref.
O/ Substrate 72M3 W(111)
72W
77E3
W(110) W(112) W(111) W(013) W(110) stepped 24(110)× (011) 10(110)× (011)
T [K]
Method
Type ∆Φ [eV] at θ1
Comments, interpretation
300 125 90 90 90 90 300
Diode Diode FEM FEM FEM FEM Kelvin
I I I I I I I
TDS
+1.2 +1.7 1.2 1.7 1.45 1.65
LEED, TDS 0.0 +0.25
300
Kelvin
I
78B4 W(110)
300
Kelvin
IV
300*
Kelvin
I
+0.1 +0.12 +0.48 -0.15 0.0 +0.8 +1.1
78W
W(110)
FEM
I
+0.9
80R
W(110)
50 100 300
Diode
IV
81M2 W(110)
300
Diode
I
83A3 W(110)
300
SE edge (E) Kelvin
-0.07 +0.3 0.0 0.4 1.0
88L
98W 80F
90 800 W(110) 90 W(100) 300 W(111) 300 W(110) 90 Zr polycr. 300
Kelvin FEM FEM Kelvin Diode
88G
Zr(0001)
Kelvin
IV
91Z4 94Z
Zr(0001) 475 Zr(10 1 0) 90
Kelvin Kelvin
IV
300
Kelvin
IV
470
Kelvin
IV
89S3 92Y
[Ref. p 4.2-118
W(110)
80
I I I
I IV
θO = 0.1 θO = 0.4 θO = 0.01 θO = 0.15 θO = 0.45 θO = 0.25 θO = 0.5 θO > 1 ML θO > 1 ML
LEED, TDS
LEED, TDS, AES oxygen dosing by adsorption of WO2 *plus annealing to 1300 K for 30 s
LEED, AES θ1 3 θ1 up to 0.8 L 10 L 11 L
1.0 1.5 0.95 1.6 1.1 1.0 -0.2 +0.55 -0.2 +0.9
LEED, AES, TDS, XPS
sat. sat. θ = 0.65 0.5 L 30 L 0.8 L 12 L
-0.32 -0.14 +0.55 -0.20 +0.25 -0.24 +0.06
θO = 0.5 0.8 L 5L 1L 5L 1.5 L 5L
LEED, AES, TDS
XPS, TDS
LEED, AES initial decrease of Φ is believed to be due to incorporation of oxygen into the bulk LEED, AES, NRA Although ordered surfaces are observed, the sticking coefficient of O2 is high. Only after a film thickness of 12.4 ǖSDVVLYDWLRQLV observed. It is concluded that atomic oxygen penetrates the bulk even at low temperatures.
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118] Ref. 98N
O/ Substrate ZrC(111)
4.2 Electron work function of metals and semiconductors T [K]
Method
Type ∆Φ [eV] at θ1
Comments, interpretation
300 1050 1170 1270
SE edge (E)
I IV
UPS
1.0 -0.2 +0.6 <0
1.5 L 0.2 L 4L 0...10 L
4.2-29
4.2.3.5 Sulfur (S) A summary of the results for S adsorbed on Ni and Cu surface has been given by Oudar [80O, 80O2]. Table 11. Atomic Sulfur (S) Type
∆Φ [eV] at θ1
saturation AES, LEED, TDS Single-crystalline Cu cylinders with [100] and [110] axes exposed a variety of different Cu faces.
I
+0.60 0.43 0.66 0.70 0.63 1.0
sat. at p(2 × 2)
prep. H2S LEED, AES
Kelvin 80-670 Kelvin
I
0.7
sat.
84M2 Mo(100)
300
Kelvin
I
+0.55
1.1 ML
85B4 Mo(110) Mo(100) Mo(211) Mo(111) 71S Ni(100)
~500
FEM
I I I I
sat. sat. sat. sat.
300
INS*
1.1 0.8 1.0 1.2 +0.63(5)
LEED, AES prep: S-beam LEED, AES For interpretation a variety of structures with bonding sites other than hollow sites have to be included. Preparation by S-beam
300
Diode* Diode* Kelvin
300 530
Kelvin FEM
86H6 Ni(100)
300 970 300*
88B2 Ni(111)
570
Ref.
93L
S/ Substrate Ag(111) Cu(111) Cu(110) Cu(100) Cu(311) Cu(001)
78P 88N
Cu Fe(001)
79S3 78P
73B2 Ni(111) Ni(110) 74D3 Ni(100) Ni(111) 83B3 Ni(110) (tip) 84G Ni(100)
Lando lt -Bö rnst ein New Ser ies III/42A2
T [K]
Method
300 300
Diode Kelvin
UPS
I
+0.35 +0.59 +0.24 +0.38 ~+1.0 +0.4
Diode similar SE edge (UPS) + Diode
I
+0.3
PYS
I
Comments, interpretation
LEED c(2 × 2) *ion neutralization spectroscopy; assuming ΦNi(100) = 4.75 eV LEED (2 × 2), *using ions LEED (2 × 2), *using ions LEED p(2 × 2) LEED c(2 × 2) LEED p(2 × 2)
+0.36
θS = 0.4
0.5
θ = 0.8
prep. S2-beam LEED, AES AES, TDS H2S-adsorption θS = 0.4 *plus heating to 600 K LEED, AES
4.2-30 Ref.
4.2 Electron work function of metals and semiconductors Method
Type
∆Φ [eV] at θ1
Comments, interpretation
Kelvin
I
0.18
p(2 × 2)
LEED, AES, TDS prep. H2S
Diode
III
0.25 -0.23
c(2 × 2)
100
300
UPS
III
-0.25
0.4 0.4 0.55 0.55 -0.38 -0.05
θS = 0.25 p(2 × 2) θS = 0.48 c(2 × 2) θ = 0.1 θ = 0.27 θ = 0.33 θ = 0.8 0.25 ML 0.33 ML
0.25 0.3 0.15
0.5 ML 1 ML 2 ML
+0.33 +0.42 +0.4
1 ML 2 ML
-0.12 +0.48 about the same -0.15 0 0.25 -0.4 0.0 +0.4
θ = 0.3 θ=1
T [K]
95P
S/ Substrate Ni(100)
87P3
Pd(111)
77F
Pt(100)
-0.7 83P
Pt(111)
300
Kelvin
I
Pt(110) 84B4 Pt(111)
350 900
Kelvin Diode + Kelvin
I IV
96P
300
Kelvin
II
Si(100) -(2×1)
97P 97P2 99L3 82P3
Si(100) -(2 × 1) Si(100) -(2 × 1) W(100)
Kelvin PYS
I
Diode
IV
300
Diode
IV
*
SE edge (UPS)
IV
300 900
82P3
W(110)
92M4 W(100)
[Ref. p 4.2-118
θ1 2θ1 4θ1 θS = 0.4 θS = 0.5 θS = 0.8
LEED, TDS complicated dependencies of ∆Φ from S2 doses at higher temperatures; at 550 K sulfide forma-tion H2S Langmuir kinetics LEED, UPS
LEED, µ0 = 0.8 D p(2 × 2) (¥î¥ 5Û p(2 × 2) ¥ LEED, AES, TDS prep. H2 + H2S flash to 900 K (2 × 1) (1 × 1) subsurface LEED, AES, TDS LEED, AES, TDS LEED, AES, dosing of S2 LEED, AES, TDS
LEED, AES, TDS S- sublimation for preparation. Similar results for T = 1000 K. *annealed at 900 K
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors
4.2-31
4.2.3.6 Atomic Selenium (Se) Table 12. Atomic Selenium (Se) Se/ Substrate 83N3 Fe(100)
T [K]
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
I
0.7
LEED c(2 × 2), AES
71S
300
SE edge (E) INS*
Ref.
Ni(100)
73B2 Ni(111) Ni(110) 74D3 Ni(001)
+0.25(5)
Diode*
300
76C3 W(100)
FEM IV probe hole
Mo(100)
IV
Mo(112)
IV
Mo(111) Mo(110)
I II
W(100)
300
Diode
82P5
W(110)
300
Diode
LEED c(2 × 2) *ion neutralization spectroscopy; assuming ΦNi(100) = 4.75 eV LEED (2 × 2) *using ions
+0.13
Kelvin
82P
0.5 ML
+0.40 +0.08 -0.07 -0.3 +1.1 -0.5 +0.85 -0.2 +1.1 +0.5 +1.2 +1.0
LEED p(2 × 2) LEED c(2 × 2) θ = 0.2 θ = 1.0 θ = 0.5 θ=2 θ = 0.5 θ=2 θ=2 θ = 1.5 θ=2 sat.
I
0.45
LEED, AES, TDS several structures during warming to 1800 K LEED, AES two phases 0.2 θSe 0.4
Type
∆Φ [eV] at θ1
Comments, interpretation
I
0.45
sat.
LEED, AES
-0.11 0.0 +0.4 -0.1 0.7 -0.3 0.4 -0.2 0.1 -0.4 0.3
θTe = 0.1 θTe = 0.3 θTe = 1.0 0.1 ML 1.2 ML 0.3 ML 1.0 ML 0.5 ML 1.2 ML 0.5 ML 1.2 ML
4.2.3.7 Tellurium (Te) Table 13. Atomic Tellurium (Te) Ref. 83N
Te/ Substrate Fe(100)
T [K]
Method
300 600
77C2 Mo(110)
FEEM
IV
78C
FEM
IV
Mo(110) Mo(111)
IV
Mo(100)
IV
Mo(211)
IV
Lando lt -Bö rnst ein New Ser ies III/42A2
4.2-32
4.2 Electron work function of metals and semiconductors
Ref.
Te/ Substrate 74D3 Ni(001)
T [K]
Method
300
Kelvin
Type
77C2 W(110)
FEEM
IV
78C
FEM
IV
W(110) W(111)
IV
W(100)
IV
W(112)
IV
[Ref. p 4.2-118
∆Φ [eV] at θ1
Comments, interpretation
-0.29 -0.43 -0.13 0.0 +0.12 -0.25 -0.1 -0.4 -0.2 -0.15 -0.1 ∆Φ >
LEED p(2 × 2) LEED c(2 × 2) θTe = 0.2 θTe = 0.4 θTe = 1 0.5 1.0 0.5 1.0 1.0 1.5 <2
- 0.1
82P2
W(100)
300 500
Diode
II
0.25 0.15
2θ1 3θ1
LEED, AES, TDS
4.2.3.8 Chlorine (Cl) Fig. 13 and 14 Table 14. Atomic Chlorine (Cl) Ref.
Cl/ Substrate 75R2 Ag(100) 80K2 Ag(100) 77G Ag(111) 92W
T [K]
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
300 300
Diode Diode? Diode
I I
+1.0 1.4 +1.8
I
+1.5
LEED LEED LEED, AES different ordered phases AES, UPS, HREELS
Ag(111)
78M2 Ag(331) 89B Al(111) 93K Au(111) 82C2 Bi(0001) cleaved 82F Cr(100)
87F
Cr(110)
77G
Cu(111)
300 300 120 500 300
SE edge (UPS) Diode Diode SE edge (UPS) ?
300
300
96W2 Co50Ni50 (111) 79D Fe(100)
300
88J3
300
n-MoSe2 (0001)
sat. sat.
I
+1.6 1.08 1.2 0.9 1.6
Diode
I
-1.1
?
IV
Diode
I
-0.25 0 +1.2
SE edge (UPS) Diode CMA SE edge (UPS)
I
+1.3
I
1.43
1.2·1015 LEED, AES, TDS, UPS atoms cm-2 several LEED structures, solidstate source for Cl LEED, AES, TDS θ1 solid-state source for Cl > 2θ1 sat. LEED, AES different ordered phases AES also studied at higher temperatures sat. c(2 × 4), LEED
1.8
sat.
I I
sat. sat. sat. sat.
LEED: (6 × 1) µ0 = 0.4 D at θ = 0.6
LEED, AES, TDS
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors
4.2-33
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
Diode
I
+0.47
0.5
300
Diode
II
1.1 0.9 1.1
1.3 L 1.7 L 3.5 L
Ni(110)
300
I
1.1
sat.
82E2 80E
Pd(110) Pd(111)
300 300
SE edge (UPS) Diode Diode
LEED, AES ¥DQGDPRUHFRPSOH[VWUXFWXUH c(2 × 2), LEED, AES, TDS diffuse p(10 × 1) for exposures > 1.5 L µ0 = 0.51 D A dip in ∆Φ occurs at θCl = 0.5. AES, UPS
I I
1.22 0.57
1.7 L 1.8 L
88T2
Pd(111)
300
I
0.7
sat.
82E2
Pt(110)
300
Diode
I
0.55
1.0 L
80E
Pt(111)
300
Diode
IV
-0.08 +0.34
1L 2.3 L
Kelvin
IV
sat.
Ref.
T [K]
77E
Cl/ Substrate Ni(111)
82E2
Ni(110)
91Z2
98H2 Pt(111)
diffuse c(16 × 2), µ0 = 0.63 D (¥î¥ 5Û/(('VWUXFWXUH at 1.2...1.6 L Cl2; see Fig. 13. 4·1014 molecules cm-2 (¥î¥ 5ÛDW 2.5...3.0·1014 molecules cm-2 LEED, AES, TDS solid-state source for Cl2 diffuse p(2 × 1) for exposures > 0.8 L, for 0.3 L Pt(110)- (21× 2) reconstruction spots appear LEED, AES, TDS (3 × 3) LEED structure at 1.6...1.9 L Cl2; see Fig. 14. 1.2·1014 atoms cm-2 7·1014 atoms cm-2 LEED, AES, TDS, UPS 4 ordered surface structures For (110): high electronegativity, so that differences to Cl smaller so that Smoluchowski smoothing and polarization effects take over. explains decrease of Φ
83G
Ru(10 1 0) 300
?
I
-0.04 +0.38 0.55
83S
Ta(100) Ta(110)
?
I II
1.0 -1.0
sat. sat.
97W
Ta(110)
Theory
+0.6 -0.4 -1.0 -1.2
top site bridge site hollow site threefold site ML average ∆Φ 2ML
71A2 Ti,
300
FEM
I
69F2 81K 70J
300 300 300
Diode Diode K
I I III I I
300
FEM
370
SE edge (UPS)
W(100) W(100) W(110) W(100) W(111) 72H W(211) W(110) 79B4 W(100)
Lando lt -Bö rnst ein New Ser ies III/42A2
0.8 1.4 +0.64(2) 0.75 -0.26 +0.58 +1.03
sat. sat. sat. sat.
AES, LEED, TDS
±∆Φ depending on pressure I
0.65
1.5 L
UPS
4.2-34 Ref. 80B
79C
4.2 Electron work function of metals and semiconductors Cl/ Substrate W(110) W(111)
T [K]
Type
∆Φ [eV] at θ1
Comments, interpretation
III I
-0.5 +0.7
Diode
I
Diode Diode
I I
0.64 0.73 0.81 1.0 0.85
LEED, TDS Prep.: surface ionization of KCl. W(111) facettes at higher coverages. * temperature before dosing Cl
Method
Diode
ZnO (000 1 )O
900* 1000* 1100* ZnO(0001) 300 300 ZnO (10 1 0)
[Ref. p 4.2-118
sat. sat.
4.2.3.9 Bromine (Br) Table 15. Atomic Bromine (Br) Br/ Substrate 78G2 Ag(111)
T [K] Method
Type
∆Φ [eV] at θ1
300
Diode?
I
1.4
85B
Ag(110)
120
Kelvin
I
1.4
80B3 Au(100)
320 300
Kelvin Kelvin
I
0.78
83R
300
(Diode)
I
1.1
Ref.
Cr(100)
1.10
3.5·1014 LEED, AES,TDS molecules cm-2 sat. LEED, AES, TDS p(2 × 1) at θBr = 0.5, fourfoldhollow site c(4 × 2) at θBr = 0.75, AgBr bilayer 16·1014 LEED, TDS molecules cm-2 0.4·1015 LEED, AES, TDS atoms cm-2 solid-state source for Br 3.3·1015 atoms cm-2 8·1014 LEED, AES, TDS atoms cm-2 solid-state source for Br; authors assume Br to metal charge transfer. 40·1014 atoms cm-2 sat. LEED, AES
1.8
sat.
+0.45 -0.28
sat. 0.7·1014 molecules cm-2 6·1014 molecules cm-2
1.6 84F
Cr(110)
300
(Diode)
IV
-0.45 -0.2
79D2 Fe(100)
300
88J3
300
82T2 79B
n-MoSe2 (0001) Pd(111) Pt(111)
300 300
SE edge (E)? SE edge (UPS) Diode Kelvin
I
I IV
520
70J
W(110) W(100) W(111)
300
+0.25
Kelvin
III I I
Comments, interpretation
-0.32 +0.80 +0.88
TDS LEED, AES, TDS little charge transfer (3 × 3) ordered overlayer at 300 K order-disorder transition at 520 K
sat. sat. sat.
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors
Ref.
Br/ Substrate 69F2 W(100) 79B4 W(100)
T [K] Method
Type
∆Φ [eV] at θ1
Comments, interpretation
300 370
4.2-35
Diode SE edge (UPS) Kelvin
I I
+0.41(2) 0.4 3L
UPS
I
+1.1
UPS
T [K]
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
300
Kelvin
IV
130 Fe(100) 300 GaAs(110) 300
Diode Kelvin
III I
-0.1 +0.08 +0.6 -0.55 +0.6
sat.
LEED, TDS Correlated with LEED structures I2 on top of chemisorbed layer LEED, AES, TDS Surface states of acceptor character within the bulk band gap, Fig.3
0.9
sat.
IV
-0.7
0.33 ML
I
-0.55 0.35
sat. sat.
+0.8 -0.9 -0.78 -0.18 -0.13 -0.4
sat. sat.
0.5 ML
-0.4 +0.08 -0.37 -0.1
min saturation 1L UPS /
96M2 WSe2(0001) n-type 4.2.3.10 Iodine (I) Table 16. Atomic Iodine (I) Ref.
I/ Substrate 93N2 Au(100)
79J2 93T 88J3 92J
93C
n-MoSe2 (0001) Pt(111)
300 300 1000 300
SE edge (UPS) SE edge (UPS)
300
SE edge (UPS) ? ? Kelvin
74A
Si(111) -(7 × 7) Ta(100) Ta(110) W(110) W(100) W(111) W(110)
300
Diode
I III III III III III
69F2
W(100)
300
Diode
IV
79B4 W(100)
370
SE edge (UPS)
IV
83S 70J
0.5 ML 1 ML
threefold-hollow site: ∆Φ < 0 on-top site: ∆Φ > 0
LEED, AES some different LEED patterns
4.2.4 Small molecules 4.2.4.1 Molecular Hydrogen (H2) Table 17. Molecular Hydrogen (H2) Ref. 83A
87J2
H2 / Substrate Cu(100)
Ga (polycr.)
Lando lt -Bö rnst ein New Ser ies III/42A2
T [K] 10 10 15 10
Method
SE edge (UPS)
Type
∆Φ [eV] at θ1
III
-0.18 -0.19 -0.23 -0.1
Comments, interpretation
normal H2 HREELS para- H2 D2 UPS
4.2-36
4.2 Electron work function of metals and semiconductors
[Ref. p 4.2-118
4.2.4.2 Molecular Nitrogen (N2) Table 18. Molecular Nitrogen (N2) T [K]
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
91H
N2 / Substrate Ag(111)
20
III
-0.45
1 ML
LEED, UPS, HREELS
89J2
Al(111)
20
SE edge (UPS) SE edge (UPS)
III
-0.15
1 ML
LEED, UPS, HREELS physisorbed N2
82E
Fe(111)
125
I
0.10*
180 L
85S2
Fe(111)
65
(Kelvin)
IV
θ1 3 θ1
87J2
Ga (polycr.) Ir(111) Ir(100) ~Ir(110) Ir(210) Ir(731) Ni(110) Ni(110)
10
SE edge (UPS) FEM probe hole
-0.27 -0.23 0.0
TDS desorption temperature 155 K * at 2·10-6 Torr max. coverage 1·1014 molecules cm-2 TDS, this is the γ-N2
Ref.
73N
79G 82H
86B4 Ni(111)
80 80 80
90 20
Kelvin SE edge (UPS) Kelvin
I
-0.2 -0.7 +0.1 -0.3 -0.1 0.1 0.0 -0.56 -0.08
92B3 Pd(111)
73N2 Pt(111) Pt(100) Pt(331) Pt(320) 81N3 Rh(111) Rh(100) Rh(110) Rh(210) 77K5 Ru(10 1 0) 87D Ru(0001) 86D 92S7 Ru(0001) 76Y 80F
W(110) Zr (polycr.)
20
SE edge (UPS)
UPS
III
-0.7
chemisorbed physisorbed 1 ML*
LEED, TDS LEED, ARUPS chemisorbed + physisorbed N2 XPS, UPS, TDS chemisorption saturates for coverages smaller than 1 ML leading to coadsorption of a physisorbed species * from UPS chemisorbed + physisorbed N2 only chemisorbed N2
60 80
FEM
120 85
Diode Kelvin
III III
-0.6 -0.34 -0.31 -0.76 -0.77 -0.15 -0.5 +0.2 +0.3 -0.04 -0.54
40
SE edge (UPS)
III
-0.67
1 ML
ARUPS, HREELS ML from UPS
Diode
III
-0.19 -0.15
100 L
Authors conclude on dissociative adsorption. No proof that N2 sticks!
120 300
0.8 L LEED, AES, TDS
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors
4.2-37
4.2.4.3 Molecular Oxygen (O2) Table 19. Molecurlar Oxygen (O2) Ref.
O2 / Substrate 79H2 Al(111)
T [K]
Method
20
82S4
Cu(111)
100
SE edge (UPS) SE edge (UPS)
81S2
Ga polycr. 20
Type
III
SE edge (UPS)
∆Φ [eV] at θ1
Comments, interpretation
+0.85
5 L O2
-0.4
1000 L
condensed O2 on Al(111) ΦAl(111) = 4.25 eV LEED, AES, UPS, ELS chemisorbed O2 2-peak spectrum in UPS condensed O2 layer (10 L) ΦGa = 4.0 eV physisorbed O2 monolayer after warming to 70 K unidentified O2 intermediate
+0.2 +0.5 +1.4
-
(presumably O ) 2
84S5
Ni(111)
5.5
Diode
I
0.07
89R
Pt(111)
20
SE edge (UPS)
I
-0.45
6 L O2
∆Φ = 0.07 eV = const. for exposures up to 12 L UPS, XPS
4.2.4.4 Carbonmonoxide (CO) Fig. 15...21 Table 20. Carbonmonoxide (CO) Ref.
CO/ Substrate 76M3 Ag(111) 82K Al(100)
83K2 Al(111)
T [K] Method 77 300
300
Type ∆Φ [eV] at θ1
Kelvin Kelvin
-0.2 0.0
<100 L
Kelvin
0.5 0.0
105 L <100L
1.35 -0.85 +1.0 +1.35 +0.85 +0.3 +1.2 +0.1 -0.22 -0.09 -0.24 -0.12 -0.45 -0.09
105 L
I 76M2 Au(100) 78P4 Co(10 1 2) 83P Co(0001) 98L
Co(0001)
77
Kelvin
100 300 180
Kelvin
I I I
82K2 Cr(110) 71C4 Cu(100)
300 77
SE edge (XPS) Diode Kelvin
75P3
Cu(100)
77
Kelvin
IV
Cu(111)
77
Kelvin
IV
Lando lt -Bö rnst ein New Ser ies III/42A2
I IV
1L 2.5 L
Comments, interpretation LEED LEED, AES, ELS no interaction for doses <100 L dissociation no interaction for exposures < 100 L dissociation for exposures >103 L AES, ELS LEED, AES, UPS
θCO = 0.3 LEED, AES, TDS, LEIS, XPS θCO = 0.65 1L 1.5 L 4L
4.2-38
4.2 Electron work function of metals and semiconductors CO/ Substrate Cu(110)
T [K] Method
Type ∆Φ [eV] at θ1
77
Kelvin
IV
Cu(211)
77
Kelvin
IV
Cu(311)
77
Kelvin
IV
Cu(755)
77
Kelvin
IV
77K3 Cu(111)
120
Diode
I
79H5 Cu(111)
82
Kelvin
IV
82L 86K
Cu(111) Cu(111)
300 100
(Diode) Kelvin
IV
75P
Cu(311)
77
Kelvin
IV
94B2 Cu(332)
180 107
Kelvin
III IV
96S4 96S5 98B
Cu(111)
90
Kelvin
Cu(332)
95
Kelvin
IV
84S2 88U 91B2 78T2 78T2
Fe(111) Fe(110) Fe(111) Ir(110) Ir(110)
220 300 80
I I I
97L3
Ir(110)
90 300 300
Kelvin Diode Kelvin ? Diode Diode Kelvin
73L
Mo(100)
300
Diode
IV
Ref.
78F
Mo(100)
73T
Ni(110)
300
74C4 Ni(111) 74D3 Ni(001) Ni(110) Ni(111) 79A2 Ni(100)
205 300 170 300 300 300 300 300
81C
300
Ni(111)
Kelvin Kelvin Kelvin Kelvin SE edge (E) Kelvin
Comments, interpretation
LEED: two structures AES, TDS IRAS
1L 2.5 L 1L 2L 4L 0.6 L 1.5 L 1L 1.5 L 3L 0.9 L 4L 1.7 L 3L 5L 7L 1L sat. 3L 3L 1L 15 L θCO = 0.3
I
-0.47 -0.05 -0.5 -0.4 -0.28 -0.32 -0.22 -0.27 -0.4 -0.33 -0.35 -0.08 -0.36 -0.17 1.6 0.43 1.0 0.23 0.29 0.21 +0.7 +1.1 -0.10 0.0 +0.07 +0.50 -0.2 0.0 +0.4 +1.1 1.3 1.6 1.3 +1.1 +0.95 ~+0.7 +1.0
1.8 L ~2 L 3L
LEED, AES, TDS LEED c(2 × 2) LEED LEED AES, ELS
I
1.1
0.5 L
LEED, µ0 = 0.28 D
I I I
IV
Diode
-0.31 -0.18 -0.33 -0.15 -0.32 -0.19 -0.42 -0.18 1.0
[Ref. p 4.2-118
I I I I
θCO = 0.5 0.6 L 0.8 L 1.5 L at 4 L θ = 0.66 θ = 1.0
UPS LEED, UPS, TDS
LEED, TDS
HREELS, TDS LEED, AES., TDS, UPS LEED, HREELS, TDS LEED, TDS UPS LEED, AES, TDS XPS 1L 1.2 L 5 L saturation AES, TDS
LEED, AES, TDS
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors
4.2-39
T [K] Method
Type ∆Φ [eV] at θ1
Comments, interpretation
81N
CO/ Substrate Ni(110)
300
I
1.1
82H
Ni(110)
20
I
1.55
LEED, AES θ high ĺ î VWUXFWXUH ARUPS see Fig. 15.
82M
Ni(100) Ni(510) Ni(310) Ni(110) Ni(100)
300 300 300 300 100
I I I I I
0.85 1.1 1.25 1.35 1.1
sat. sat. sat. sat. 1L
85B3 Ni(110)
130
SE edge (E) SE edge (UPS) FEM FEM FEM FEM SE edge (UPS) Kelvin
I
1.5
4L
LEED, TDS c(8 × 2) at θ = 0.62 c(4 × 2) at θ = 0.75 (2 × 1)p2mg at θ = 1.0 see Fig. 16.
I
0.16
8L
CO precursor + finite amount of chemisorbed CO chemisorbed CO molecular beam, HREELS, no evidence for physisorbed CO at 8 K contradicts [85S]. IRAS µ0 = 0.65 D for bridge CO µ0 = 0.17 D for on-top CO temperature-dependent site switching from bridge to on top with increasing temperature; see Fig. 17. AES, UPS
Ref.
83K
85D2 Ni(111)
1L
85S
Ni(111)
5.5
SE edge (UPS) Diode
88B
Ni(111)
80 8
Diode Diode
I I
0.9 1.3
6L 3L
88S2
Ni(111)
90... 300
SE edge (XPS)
I
1.4
θ = 0.5
95S2
Ni(110)
300
I
1.1
sat.
95K2 Ni(775)
300 145
SE edge (UPS) Kelvin
I I
0.5 1.1
1L 2L
70E2
Pd(111)
300
Diode + Kelvin
I
0.99
74C5 Pd(111) Pd(100) Pd(110) Pd(311) Pd(201) 79B4 Pd(100) 80B2 Pd(100) 88H5 Pd(110)
300 300 300 300 300
Kelvin Kelvin Kelvin Kelvin Kelvin
I I I I I
300 100 100 100
Kelvin Kelvin
I I I I
0.98 >0.75 1.26 1.27 1.06 0.94 0.9 1.06 1.09 0.980
sat. 3 L CO θCO = 0.5 θmax = 0.5 ~0.7 1.0
Lando lt -Bö rnst ein New Ser ies III/42A2
+0.7(2)
1.5 sat. θ* = 0.73(5) θ* = 1.00(5) θ** = 0.55
(775) = 6(111) + 1(11 1 ) = 5(111) + 2(110) LEED, UPS LEED, TDS At = 3.3 (¥î¥ 5ÛVWUXFWXUH in LEED. LEED,TDS at µ = 0.33D max. coverage: 0.29 D 0.35 D 0.33 D LEED, UPS, TDS LEED: (4 × 2), *from NRA LEED: (2 × 1), *from NRA LEED: c(2 × 2), **from [89H]
4.2-40
4.2 Electron work function of metals and semiconductors T [K] Method
Type ∆Φ [eV] at θ1
89O
CO/ Substrate Pd(111) Pd(111)/ Cu
300
Kelvin
I
77E2
Pt(111)
323
Kelvin
IV
79N
Pt(111)
95
Kelvin
IV
300
Kelvin
77
FEM
300
Kelvin
Ref.
81N3 Pt(111) Pt(100) Pt(210) 82P4 Pt(111)
IV
Cu = 0 Å Cu = 1 Å Cu = 2 Å Cu = 6 Å θ = 0.33 θ = 0.5
-0.25 0.05 -0.15 0.05 0.0 +0.1 +0.4 -0.24
θ = 0.33 θ = 0.4 θ = 0.33 θ = 0.4 sat. sat. sat. 1.5·1014 LEED, AES, HAS molecules cm-2 at θCO = 0.1 4·1014 molecules cm-2 LEED, ELS, TDS θ = 0.5 (1 × 1) prepared following [78B3] θ = 0.75 θ = 0.5 was calibrated from the maximum of the LEED c(2 × 2) intensity. LEED; RBS, NRA θ = 0.68 hex to (1 × 1) starts at θ = 0.08 (1 × 1) to hex starts at θ = 0.25 LEED, oscillations in ∆Φ, see Fig. 18. LEED, XPS θ = 0.5 θ=1 θ = 0.5 θ = 0.9 θ = 0.5 θ=1 1.5 L LEED, TDS, ESDIAD 6L Also co-adsorption of S. FEM Figs. 19 and 20 3L LEED, AES, TDS TDS
83B
Pt(100)(1 × 1)
310
Kelvin
I
0.18 0.4
83J
Pt(100)
300
SE edge (UPS)
I
0.3
86E
Pt(110)
86F
Pt(110)-(1 × 2) -(1 × 1)
460... Kelvin 620 140 SE edge (UPS) 140 SE edge (UPS) 300 SE edge (UPS)
IV
-0.17 -0.04 -0.23 -0.19 -0.11 +0.05
88K2 Pt(111)
90
90L
300
90E 93A
94A
Pt, Rh high index Pt(120) Pt50Ni50 (110) Pt50Ni50 (111) Pt80Fe20 (111)
300 300 120 300 120 120
IV IV
SE edge (E) FEM
IV
Kelvin Diode
I I III
Diode
IV
Comments, interpretation
0.68 0.1 0.04 0.00 -0.17 0.0
-0.1
-(1 × 2)
[Ref. p 4.2-118
-0.14 -0.05 see Fig. 19 0.12 +0.60 +0.90 -0.10 -0.23 -0.3 0.0 +0.12
LEED, TDS Assume two different adsorption sites. XPS, UPS, TDS
min, 0.8 L LEED, TDS, HREELS 2L 7L
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118] Ref.
CO/ Substrate Re film
4.2 Electron work function of metals and semiconductors T [K] Method
Type ∆Φ [eV] at θ1
300
I
4.2-41
Comments, interpretation
77M4 Rh(110) 84P Rh(100)
300 (Kelvin) (100) SE edge (UPS)
I I
84P6
Rh(100)
100
I
+1.3
2·1014 β state molecules cm-2 6·1014 β + α state molecules cm-2 LEED: (2 × 2) or (2 × 1) (1 × 1) 3L XPS, TDS 20 L 20 L θ = 0.5 θsat. SHG, TDS sat. 5L LEED, AES, TDS θ = 0.3; 1 UPS, XPS, ELS, TDS L θ = 0.6; 15 L θCO = 0.6 TDS, UPS
88M2 Rh(111)
170
I
89K
90
I
+0.3 +0.5 +1.1 0.5
θCO = 0.33 ¥VWUXFWXUH θCO = 0.55 θCO = 0.75 (2 × 2) saturation 1L UPS, XPS, TDS
I I
0.76 0.6
θ = 0.66 10 L
Fig. 21 MDS, IRAS, TDS
-0.8
10 L
1 ML Cu on Ru(0001)
-0.9
10 L
2.4 ML Cu on Ru(0001)
I I
1.1 1.15
θ = 0.7 θ = 1.2
LEED, AES, ELS LEED, HREELS, TDS
IV
-0.40 -0.28 +0.43
3L LEED, AES 15 L 10·1014 LEED atoms cm-2 θCO = 0.5 if irreversibly transferred into the β state by heating to 1000 K 7·1014 LEED, TDS molecules cm-2 6·1014 molecules cm-2 5.5·1014 molecules cm-2
76E2
0.47
0.72
72Z 85T
Re(0001) Re(10 1 0) Re(0001)
90R2 Re(0001)
Diode Diode Kelvin
II
300 80
Kelvin
I I
SE edge (UPS, E) Diode
SE edge (UPS) 83P2 Ru(0001) 200 Kelvin 88H2 Ru(0001) 85 SE edge (MDS) Ru(0001) 85 SE edge +1 ML Cu (MDS) Ru(0001) SE edge 85 +2.4 ML Cu (MDS) 88K Ru(10 1 0) 300 Diode 89L Ru(10 1 0) 120... Kelvin 650 76T Th(100) 300 Diode 67A
Rh(111)
300 300 100
W(100)
300
(Diode)
I
0.35 0.32 0.50 0.45 0.50 0.3 0.45 0.97 0.6 1.3
-0.16 79W2 W(100)
Lando lt -Bö rnst ein New Ser ies III/42A2
87
Kelvin
I
0.55
300
I
0.36
400
I
0.36
4.2-42
4.2 Electron work function of metals and semiconductors T [K] Method
Type ∆Φ [eV] at θ1
100
FEM
I
300 300
I
20 100
Kelvin SE edge (UPS) FEM FEM
W(110) + 1 ML Cu W(110) +4 ML Cu 91H3 W(110)
95 25
80F
300
Ref.
72A 74F2
CO/ Substrate W(110) W(111) W(120) W(100) W(210) W(100)
77L 78W
W(110) W(110)
69E
87C
Zr polycr.
[Ref. p 4.2-118
Comments, interpretation
1.2 1.0 0.85 0.65 0.7 +0.4
sat. sat. sat. sat. sat.
I I
0.6 +0.8
Kelvin
I
0.34
sat. 10·1014 “virgin CO” molecules cm-2 3L Cu layers on W(110)
Kelvin
IV
-0.1 +0.18 +0.08 +0.85
(Diode)
IV
-0.12 0.2
SE edge (UPS)
UPS
0.2 L 3L θCO = 0.33 TDS, HREELS θCO = 0.70 µ0 = 0.015 D µ0 = 0.12 D 1L dissociative adsorption; atoms 10 L penetrate the bulk
4.2.4.5 NO, N2O Table 21. NO T [K]
Method
Type ∆Φ [eV] at θ1
Comments, interpretation
84S6
NO/ Substrate Cu(110)
90
SE edge (UPS)
II
0.25 0.08
0.5 L 1L
81I
Ir(110)
100
(Diode)
IV
-0.08 -0.04 -0.11 -0.10
θ = 0.5 θ=1 θ = 0.75 θ=1
first dissociative adsorption For θO = 0.25 ML N2O stays undissociatively adsorbed. LEED, AES, TDS, UPS, XPS
Ref.
300 80S
Ni(100)
84B3 Ni(111)
300
90
84P5
Ni(100)
95
90B
Pd(111)
100
20
IV SE edge (E) SE edge (UPS)
SE edge (UPS, E) SE edge (UPS)
I III I
0.75 -0.25 0.9
+0.77 +0.75 §
LEED, AES, TDS dissociative adsorption 0.8 L 0.8...2.0 L NO coadsorbed MDS/TDS 3.2 L at least partial dissociation; If NO is adsorbed to a O precovered surface, Φ falls 0.2 eV below the value for the clean Ni(111) surface. 0.42 ML TDS, XPS 0.55 ML co-adsorption with D LEED, ARUPS, HREELS bridge sites γ state bridge sites β state bridge and on-top sites α state thick layer containing (NO)2 Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors
NO/ Substrate 84K5 Pt(111)
T [K]
Method
Type ∆Φ [eV] at θ1
120
II
86F
140
88I
Pt(110) -(1 × 2) Pt(110) -(1 × 2) Pt(110) -(1 × 2) Pt(110)
SE edge (UPS) SE edge (E)
315
Kelvin
89R
Pt(111)
20
Ref.
θNO = 0.17 θNO = 0.52 θNO = 0.8 ML θNO = 0.5 ML θNO = 0.6 ML 1L 3.5 L 6L
4.2-43
Comments, interpretation
III
+0.14 -0.16 -0.40
140
III
-0.34
300
III
-0.46
SE edge (UPS) SE edge (UPS) SE edge (UPS) SE edge (UPS) FEM
I
-0.045 0.0 +0.040 -0.85
I I
77K5 Ru(10 1 0) 295 80F2 Ru(0001) 86
SE edge (E) SE edge (E) Diode Kelvin
At 77 K molecularly adsorbed on all surfaces. At 300 K 30% at rough surfaces dissociate. ∆Φ: 0.9 eV = (100) < (111) < (511) < (410) < (331), (533) < (321) < (110) < (650) < (531), (210) = 1.4 eV 0.9 0.4...0.65 LEED, AES, TDS ML 0.9 0.5 ML LEED, TDS
I I
+0.4 0.9
6L 10 Ex
80F
300
(Diode)
I
0.9
30 L
T [K]
Method
Type ∆Φ [eV] at θ1
Comments, interpretation
90
SE edge (UPS)
II
first dissociative adsorption For θO = 0.25 ML N2O stays undissociatively adsorbed.
77B6 Pt(100)
500
85T3
120
Re(0001)
85H2 Rh(100)
300
86H
Rh several faces
77
84H
Rh(100)
100
84H2 Rh(100)
100
Zr (polycr.)
I
I
LEED, TDS pCO = 5·10-8 Torr UPS, XPS
+0.4 +0.8 +0.3 0.4
XPS, UPS µ0 = 0.42 D LEED, XPS
1.5 L >3L 2L
LEED, UPS, XPS NO dissociates. UPS, XPS
LEED, TDS, XPS 1 Ex = 1018 cm-2 At higher T different curves with some dips occur. Authors discuss the results in terms of two different NO species. dissociative adsorption Small (-0.15 eV) dip at the beginning due to subsurface species.
Table 22. N2O Ref. 84S6
N2O/ Substrate Cu(110)
Lando lt -Bö rnst ein New Ser ies III/42A2
0.25 0.08
0.5 L 1L
4.2-44
4.2 Electron work function of metals and semiconductors
[Ref. p 4.2-118
4.2.4.6 NH3, PH3, PF3, P(CH3)3, AsH3 Fig. 22 Table 23. NH3 NH3 / Substrate 78G3 Fe(111) Fe(100) 79W Fe(110)
T [K]
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
135 135 120
Kelvin Kelvin (Kelvin)
III III III
-2.0 -2.0 -2.3
sat. sat. 15 L
LEED, AES, TDS, UPS
80P
Ir(111)
190
III
-2.5
sat.
77A
Mo(110)
200 300
SE edge (UPS) FEM (probehole)
Mo(100)
Ref.
-2.25 -1.2
For all faces: NH3 decomposes at higher T N increases Φ
80S5
Ni(111)
200 300 200 300 200 300 200
81F
Pt(111)
100
95K4 97V3 96V2 88R 90R2 91A 96V
Pt(111)
100
Kelvin
Pt(111) Re(0001) Re(0001)
90 80 (80)
Kelvin Diode Kelvin
III III
-0.29 -2.1 -2.3
6L sat.
SE edge (E) SE edge (E)
III
-2.3
θ = 0.25
III
-2.4
θ = 0.73
(300)
PYS
III
-0.5
sat.
(300) 300
PYS PYS
III III
-0.59 -0.6
sat. sat.
III
-0.3
2L
Mo(211) MO(111)
Rh(111)
83B5 Ru(0001)
91C
Si(111) -(7 × 7) 91C2 Si(100) 92C Si(111) -(2 × 1) 92R TiO2(110)
300
SE edge (UPS) SE edge (UPS)
LEED, AES, UPS, TDS µ0 = 2.2 D ARUPS
III
-1.95 -1.1 -1.9 -1.0 -1.55 -0.9 -1.7(2)
sat.
ARUPS, TDS
III
-3.0
sat.
UPS, TDS ∆Φ corresponds to the sum of α state (TD = 350 K) and β state (TD = 150 K) LEED, AES, TDS, IRAS
-3.0
IRAS SHG SHG (2 × 1) in LEED, a1 + a2 state µ0 = 1.9 D LEED, TDS, ESDIAD three states from TDS α, β, γ α state: θ = 0.25, disordered β state: bilayer formed through hydrogen bonds γ state: multilayer µ0 = 1.9 D see Fig. 22
LEED, AES Authors conclude dissociation to happen. UPS
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors
4.2-45
Table 24. PH3 T [K]
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
89Z2
PH3/ Substrate Ag(111)
105
III
-1.4
TDS, UPS
98Y
Au film
100
SE edge (UPS) Kelvin
85H
Rh(100)
100
SE edge (E)
III
-0.24 -0.32 -0.45 -1.2
T [K]
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
105
SE edge (UPS)
III
-0.15
TDS, UPS
T [K]
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
105
SE edge (UPS)
III
-2.2
TDS, UPS
T [K]
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
100
Kelvin
-0.24 -0.32 -0.45
under ambient conditions; rise time of Kelvin probe signal was 10 s; same behavior for AsH3.
Ref.
20 ppb 50 ppb 80 ppb 3L
under ambient conditions; rise time of Kelvin probe signal was 10 s; same behavior for AsH3. LEED, AES, TDS Bonding to surface via P concluded.
Table 25. PF3 Ref. 89Z2
PF3/ Substrate Ag(111)
Table 26. P(CH3)3 Ref. 89Z2
P(CH3)3/ Substrate Ag(111)
Table 27. AsH3 Ref. 98Y
AsH3/ Substrate Au film
20 ppb 50 ppb 80 ppb
4.2.4.7 H2O, D2O Sass and Richardson [84S8] pointed out earlier that in studies of water adsorption on clean metal surfaces, thermal desorption spectra, characteristically, show a two-peak behavior in the temperature range 150...200 K, although in certain cases a considerably more complex pattern is observed. In the usual interpretation, the higher temperature peak (ca. 170...200 K) is attributed to molecular H2O in the first monolayer at the surface, whereas the lower temperature peak (ca. 150...160 K) accompanies the onset of multilayer ice formation. These temperatures can be correlated with binding energies of ca. 48...57 and 43...45 kJ mol-1, respectively. The latter corresponds, as expected, to the enthalpy of vaporization of ice whilst the former lies in the upper part of the range generally considered to characterize physisorption. With respect to the work-function changes induced by H2O adsorption there is always a decrease of 0.6 to 1.3 eV observed indicating that the lower half of the bilayer –pointing to the metal substrate – interacts with the oxygen part. For higher exposures multilayer ice is condensed which does not contribute very much to a further work-function decrease as the H2O dipoles are apparently randomly oriented. Figs. 23...25
Lando lt -Bö rnst ein New Ser ies III/42A2
4.2-46
4.2 Electron work function of metals and semiconductors
[Ref. p 4.2-118
Table 28. H2O, D2O H2O, D2O/ T [K] Substrate 87B2 Ag(110) 80
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
(Kelvin)
III
-0.65
2L
LEED, ESDIAD, TDS no long-range order at 80 K
89M2 Al(100) 93B3 Al(100)
100 100
Kelvin Kelvin
III IV
82H2 Co(0001) 100 Co(11 2 1) 100
Kelvin Kelvin
I I
-0.95 -1.2 -0.9 -1.1 -1.2
12 L 2.5 L 16 L 10 L 10 L
94G
Co(11 2 0)
III
-1.3
0.7 L
82S
Cu(110)
SE edge (UPS) SE edge (UPS)
FT IR-RAS, NRA at 100 K no dissociation of H2O UPS, TDS H2O adsorption reversible below 300 K; ∆Φ > 0 XPS, UPS
III
-0.9
1L
UPS, LEED, ELS
III III
-0.95 -0.85
Ref.
90
83B4 84B Cu(110) Cu(111)
110 110
Kelvin Kelvin
-0.09 -0.8
LEED, UPS, TDS µ0 = 0.85 D µ0 = 0.5 D see Fig. 23 *mirror electron microscopy saturation UPS
83P5 85S5
Cu(110) Cu(100)
350 80
93B2 Cu(100)
120
* SE edge (UPS) Kelvin
III
-0.9
10 L
Diode
III
-0.7
1L
HREELS, TDS defects stabilize H2O clusters TDS, XPS
81W2 Ir(110) -(1 × 2) 81B Ni(110) 84P4 Ni(100)
140 150 100
Kelvin SE edge (UPS) (Kelvin)
III
-0.7 -1.05
1.2 L sat.
UPS, TDS, ELS UPS, XPS, TDS
87N
Ni(111)
100
III
-0.65
2.5 L
III
-1.1
θ = 0.66
130
SE edge (UPS) Kelvin
III
-1.15
92B2 Ni(665)
150
Kelvin
III
-0.7
1.2 L θ § θ = 0.75
Ni(221)
150
Kelvin
III
-1.4
92C2 Ni(110)
180
Kelvin
III
-0.6
93M
140
Kelvin
III
-1.05
disordered layer LEED, UPS ARUPS, LEED, XPS, TDS Authors propose bilayer model. LEED, TDS, NRA c(2 × 2) structure LEED, TDS H2O decorates the steps (665): 11 (111) terraces + 1 (11 1 )step (221): 3 (111) terraces + 1 (11 1 )step LEED, ESDIAD, TDS, FTIR-RAS c(2 × 2), H2O plane highly inclined to surface normal LEED, TDS (11 11 9): 10.5 (111) terraces + 1 (11 1 )step µ0 = 1.2 D Steps are decorated by H2O:
89P
Ni(111)
(100)
90C
Ni(110)
Ni(11 11 9)
4L 4L
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors
Ref.
H2O, D2O/ T [K] Substrate 94M2 Ni(775) 150
98R 90H4 86F3 89R
NiO(100) 120 Pd(110) 100 Pt(110) 100 Pt(111) 90
97V3 Pt(111) 90 81T Ru(0001) 95
91P
Ru(0001) 120
95H
Ru(0001)
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
Kelvin
III
-0.75
1.5 L
LEED, AES also: co-adsorption with Na
III III III
-1.0 -0.73 -1.0 -1.15
1 ML θ = 0.5 5L
III III
-1.1 -0.6
5L 2L
III
-1.2
5L
III
-1.28
θ = 0.66 bilayer
? Kelvin Kelvin SE edge (UPS) Kelvin Diode
SE edge (UPS)
4.2-47
LEED, TDS ESDIAD, TDS UPS see Fig. 24 LEED, AES, IRAS LEED, HREELS, TDS hydrogen bonded bilayer (¥î¥ 5ÛVWUXFWXUHE\/((' LEED, UPS, XPS see Fig. 25 LEED, TDS, p(¥î¥ µ0 = 0.34 D
ȝ '0 = 0.65 D;
+0.20 +0.75
0.25 ML 0.5 ML
III
+0.20 +0.77 -1.3
Kelvin
III
-1.7 -1.34
1.6 L 6L bilayer at 1.3 L 3.5 L 2L
SE edge (XPS)
III
-1.1
100... ARUPS 140
III
-1.4
III
-0.7
III III
-0.9 -0.9
10 L
Kelvin
III
-0.2
3L
(Kelvin)
III
-1.1 -1.3
1. layer LEED, TDS, NRA, FTIR-RAS 2. layer (θ = 0.75)
96K2 Ru(0001) 400
96L3
97H
Ru(0001) 82
Ru(0001) 120
94H2 TiO2(110) 90
92M5 WSe2 (p-type) WSe2 (n-type) InSe GaSe (p-type) 96M2 WSe2 (0001) (p-type) 97B Zr(0001)
Lando lt -Bö rnst ein New Ser ies III/42A2
depolarization included with two A states for the H2O bilayer one A state for the D2O bilayer LEED, HREELS, TDS similar result for Ru(12(001) × (010)) similar result for Ru(12(001) × (010)) MDS, TDS
80
Kelvin
Kelvin
TDS: 2 states A1, A2 for the H2O bilayer only one A state for D2O θ* = 0.75 * θ = 1.0 refers to the saturation value for the 275 K TDS peak. Band bending only 0.1 eV. XPS, TDS 10 L UPS band bending also determined 6L
UPS
4.2-48
4.2 Electron work function of metals and semiconductors
[Ref. p 4.2-118
4.2.4.8 H2S Table 29. H2S Ref. 79F
H2S/ T [K] Substrate Ru(11 2 0) 80
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
SE edge (UPS)
II
0.16 -0.36
H2S dissociates molecular adsorption
0.8 L /
4.2.4.9 CO2, SO2, (CH3)2SO, (CH3)3PO3 Table 30. CO2 CO2/ Substrate 94B3 Cu(332) 96H2 Cu(111)
T [K]
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
95 100
Kelvin Kelvin
III
-0.4
200 L
86B3 Fe(111)
140
SE edge (UPS)
1.25
1.5 L
69O
Ni(100)
300
0.3
60 L
LEED, AES, UPS, TDS TDS, UPS, XPS also with co-adsorbed K UPS unclear which species this is LEED dissociative adsorption CO2 ĺ&22
87B
Ni(110)
80
W(100) W(100)
140 300 300
1L 2L 3L
69A 76H
Therm Diode
I
0.6 0.5 0.9 0.44 0.56
T [K]
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
Kelvin
I III
-0.22 0.24 0.3
LEED, AES, TDS
0.4 1.3
SO2 dissociates LEED, UPS, XPS dissociative adsorption leading to TiO2 and TiS2
Type
∆Φ [eV] at θ1
Comments, interpretation
III
-0.77
TDS, XPS
Ref.
SE edge (UPS)
II I
ARUPS, HREELS CO2 parallel to surface ±20° anionic bent species LEED, AES, TDS
Table 31. SO2 Ref. 92A 88O
85S4
SO2/ Substrate Cu(111)
80 200 TiO2(110) 300 TiO2(441) 300 Ti2O3 300 (1012)
SE edge (UPS) SE edge (UPS) SE edge (UPS)
SO2 dissociates
Table 32. (CH3)2SO Ref. 97S2
(CH3)2SO / T [K] Substrate Au(100) 100
Method
25 L
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors
4.2-49
Table 33. (CH3)3PO3 Ref.
(CH3)3PO3/ T [K] Substrate 85H3 Rh(100) 100
Method
Type
SE edge (UPS)
∆Φ [eV] at θ1 -2.25 -2.50
Comments, interpretation
ML TDS, XPS, UPS multilayer conclusion: PO points to the surface: µ0 = 2.5 D
4.2.4.10 C2N2, HCN Table 34. C2N2 Ref.
C2N2/ Substrate 89R2 Pd(110)
78N
Pt(111)
T [K]
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
300 80
SE edge (UPS)
I ?
1.0 1.8
sat. sat.
300
SE edge el.
I
0.5
sat.
LEED, ARUPS, TDS, several LEED structures; above 200 K C2N2 is believed to decompose into 2 CN. LEED, AES, TDS
I
+0.8
2.5 L
LEED, AES, TDS, UPS
83G3 Ru(10 1 0) 300 Table 35. HCN Ref.
HCN/ Substrate 88H6 Pt(111)
Lando lt -Bö rnst ein New Ser ies III/42A2
T [K]
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
90
Kelvin
III
-1.15
TDS, LEED
4L
4.2-50
4.2 Electron work function of metals and semiconductors
[Ref. p 4.2-118
4.2.4.11 CH3CN, HCOOH, HNCO Table 36. CH3CN (Acetonitrile) Ref. 83S2
CH3CN/ Substrate Pt(111)
T [K]
Method
100
SE edge (UPS)
92O2 Pt(111) 95K4 Pt(111) 97V3
100
Type
∆Φ [eV] at θ1 -1.5 -1.75
Comments, interpretation
ML XPS, TDS, HREELS multilayer conclusion: CŁ1UHK\EULGL]HVWR Cő1DQGFKHPLVRUEVQHDUO\ parallel to surface 2L LEED, AES, IRAS, TDS 4L (multilayer) LEED, AES, TDS, IRAS
III
-1.4 -1.5 -1.5
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
K
III
-0.5 -0.65 -0.9
sat. sat. sat.
n-type, see Figs. and p-type molecularly adsorbed
-0.7
sat.
molecularly adsorbed
Kelvin
Table 37. HCOOH (formic acid) Ref. HCOOH/ T [K] Substrate 83M GaAs(110) 300 88O TiO2(110)
300
TiO2(441)
300
SE edge (UPS) SE edge (UPS)
Table 38. HNCO Ref.
HNCO/ T [K] Substrate 83G3 Ru(10 1 0) 300
∆Φ [eV] at θ1
Comments, interpretation
I
+0.80
LEED, AES, UPS, TDS
Method Typ
2.5 L
4.2.4.12 KOH, KCl, HCl, HBr Table 39. KOH Ref. 95M
KOH/ Substrate Si(100)
T [K]
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
300
Diode
III
-3.0
assumed intact KOH to be adsorbed. µ0 = 1 D
T [K]
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
100 670 100 300 670
FEM
III III III
-1.1 -0.35 -1.0 -0.9 -0.35
quartz microbalance, AES
2 nm
Table 40. KCl Ref. 86S
KCl/ Substrate Ag(111)
89S
Ag(110)
FEM
sat. sat. sat. sat. sat.
completely reversible
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors
4.2-51
Table 41. HCl, HBr Ref. 78M
HCl, HBr/ T [K] Substrate Si(111) 300
Method
Type
SE edge
∆Φ [eV] at θ1
Comments, interpretation
0.2
both for HCl, HBr both adsorb as molecular entities
sat.
4.2.5 Nonpolar hydrocarbons Table 42. Methane (CH4) T [K] Method
Type
∆Φ [eV] at θ1
Comments, interpretation
96A
CH4/ Substrate Pt(111)
55
III
-0.42
96M
Pt(111)
40
TDS, UPS µ0 = 0.54 D XPS, TDS
Ref.
71Y W(100) 72M3 W(111) 78S W(100)
110 125 300
SE edge (UPS) SE edge (XPS) FEM Diode FEM
W(111)
300
FEM
III
-0.5
0.3 ML
I III IV
sat.
I
-0.34 -0.30(5) -0.3 0.2 0.35
θ1 3θ1 θ1
TDS adsorbed species is probably CH2 probably CH3 + H
Table 43. Propane (C3H8) Ref. 71L
C3H8/ Substrate Ni(111)
T [K]
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
300
Diode
III
-0.3
LEED
∆Φ [eV] at θ1
Comments, interpretation LEED, UPS, TDS max. coverage < 0.5 at 100 K C2H4 π-bonded to surface c(2 × 2) structure bonding via the O-atom LEED, TDS, HREELS conclusion: O interacts with Ag surface; µ0 = 0.4 D LEED, AES
Table 44. Ethylene (C2H4) Ref.
C2H4/ Substrate 86K3 Ag(110) 86B
T [K]
Method Type
100...300 K
III
-0.7 -1.45
2L sat
90...750 K
III
-0.35
1L
80K3 Al(100)
300
K
II
84R2 Cu(110)
90
θ1 θ2 sat.
97L2
90
SE edge III (UPS) K III
+0.24 -0.4 -1.1 -0.9
1.8 L
300
Diode
-0.3
sat.
96H
Ag(110)
Cu(111)
74D2 Ni(111)
Lando lt -Bö rnst ein New Ser ies III/42A2
III
UPS LEED, HREELS, TDS conclusion: π-bond to surface adsorption is reversible TDS
4.2-52 Ref. 75F
4.2 Electron work function of metals and semiconductors C2H4/ T [K] Substrate Ni(111)*+ 80
Method Type
∆Φ [eV] at θ1
FN
II
Pd(111)*+ 80
FN
II
Pt(111)*+ Cu(111)* Au(111)* Al(111)*
FN FN FN
III III III II
+0.13 -0.44 +0.08 -0.8 -1.45 +0.28 -0.46 +0.04 -0.06 -0.3
θ1 θ2 θ1 θ2 sat. sat. sat. θ1 θ2 sat.
80 80 80 80
79B2 Ni(111)
300
76G
300 525 300 525
Diode Diode Diode Diode
-1.5 -1.7 -1.2 -1.5
1·10-8 1·10-8 1·10-8 1·10-8
300
SE edge III (E)
-1.6
sat.
-1.4 -1.3 -0.7 -1.4 -1.2 -0.9 -1.1 -1.0 -0.9 -1.5 -1.2 -0.18 0.0 -0.35
sat. sat. sat. sat. sat. sat.
Pt(111) Pt(100) -(5 × 1)
78N 79V
Pt(111) stepped Pt(111)
Pt(533) Pt(110) Pt(210) 86A2 Pt(111) 88Z
Pt(111)
88M2 Rh(111) 76E2 Re film
84K 74B
Si(111) W(100) W(111) W(211) W(110)
90 210 325 210 210 210 300 120 100 320 300 300
III III III III III SE edge III (E) III Diode III Diode II
330 300 300 300 300
K K K K K
FEM FN FN FN FN Kelvin
III
III III III III III
-0.15 -0.5 -0.45 -0.45 -1.1
[Ref. p 4.2-118
Comments, interpretation *film + dissociation at the beginning
torr torr torr torr
LEED, TDS, HREELS conclusion: dehydrogenation to C2H2 LEED: diffuse (1/2 O) features disordered LEED: substrate: (1 × 1) adsorbate: (¥î¥ 5Û (1 × 1) disordered LEED, AES, TDS
TDS, SIMS also other temperatures 6L 1·1014 molecules cm-2 2.5·1014 molecules cm-2 5.5·1014 molecules cm-2 104 L sat. sat. sat. sat.
TDS
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors
4.2-53
Table 45. Acetylene (C2H2) C2H2/ Substrate 74D2 Ni(111)
T [K]
Method
Type
∆Φ [eV] at θ1
300
Diode
III
77D2 Ni(111)
180
at 4·10-9 mbar at 1·10-8 mbar saturation
Pd(111)
180
-1.4
saturation
Pt(111)
180
SE edge (UPS) SE edge (UPS) SE edge (UPS)
-0.6 -1.0 -1.2
-1.6
saturation
Ni(111) Pt(111)
300 300
-1.3 -1.5
6L
Diode
Diode
-1.65 -1.8 -1.65
LEED, TDS, HREELS LEED (2 × 2) p = 1·10-8 torr after 10 min, disordered, 1·10-8 torr, disordered LEED: substrate changes to (1 × 1) Adsorbate structure (¥î¥ 5Û 4·10-7 torr , no further change in structure.
0.2 L 0.7 L 5L
AES, ELS
Ref.
78B 76G
III
420 Pt(100) -(5 × 1)
300 420
86A2 Pt(111) 78R
W(100)
300 120 300
-1.7 Kelvin
Comments, interpretation TDS UPS
III III II
-1.3 -1.4 +0.3 0.0 -0.6
Type
∆Φ [eV] at θ1
Comments, interpretation
Diode
-1.3
LEED: (2 × 2)
Diode
-1.2
LEED: ½ order streaks
∆Φ [eV] at θ1
Comments, interpretation
Diode
Table 46. Propylene (CH3CH:CH2) Ref. 76G
CH3CH:CH2 T [K] /Substrate Pt(111) 300 -(1 × 1) Pt(100) 300 -(5 × 1)
Method
Table 47. Cyclopentane (C5H10) Ref. 76G
C5H10/ Substrate Pt(111) -(1 × 1) Pt(100) -(5 × 1)
T [K]
Method
Type
300
Diode
-1.0
300 300
Diode
-0.7 -0.4 -0.3
Lando lt -Bö rnst ein New Ser ies III/42A2
7·10-9 torr LEED: (1 × 1) low background 4·10-7 torr disordered 7·10-9 torr LEED: (5 × 1) low background 4·10-7 torr diffuse features at ½ order
4.2-54
4.2 Electron work function of metals and semiconductors
[Ref. p 4.2-118
Table 48. Pentadiene (C5H8) C5H8/ Substrate 84A2 Pt(111)
Ref.
T [K]
Method
90
Diode
Type
∆Φ [eV] at θ1
Comments, interpretation
-1.5
TDS, HREELS conclusion: tilted C5-ring
sat.
Table 49. n-hexane (C6H14) Ref. 76G
C6H14/ Substrate Pt(111) -(1 × 1) Pt(100) -(5 × 1)
∆Φ [eV] at θ1
Comments, interpretation
Diode
-1.1
LEED: disordered
Diode
-0.8
LEED: disordered
∆Φ [eV] at θ1
Comments, interpretation
T [K]
Method
300 300
Type
Table 50. Cyclohexane (C6H12) Ref. 76G
C6H12/ Substrate Pt(111)
Pt(100)(5 × 1)
T [K]
Method
300 300 420 573 300 300
Diode
Type
-1.2 -0.7 -1.1 -1.4 -0.75 -0.4
III
-1.5 -0.89
LEED: (1 × 1) very poorly ordered apparent (2 × 2) disordered LEED: (5 × 1) LEED: (1 × 1) and diffuse streaked (2 × 1) pattern 4·10-7 torr LEED: (1 × 1) and diffuse streaked (2 × 1) pattern 4·10-7 torr LEED: (1 × 1) disordered at 1.2 L
III
-0.6
sat.
Type
∆Φ [eV] at θ1
Diode
420
91E
Pt(111)
97S
Pt(111)
-1.2
573 130
SE edge (UPS) 160... SE edge 380 (UPS)
6·10-9 torr 4·10-7 torr 4·10-7 torr 4·10-7 torr 6·10-9 torr 4·10-7 torr
TDS, HREELS
Table 51. Cyclohexene () Ref. 76G
C6H10/ Substrate Pt(111) -(1 × 1)
T [K]
Method
300
Diode
425 Pt(100) -(5 × 1)
300
-1.7 -1.6
Diode
-1.6 -1.5
Comments, interpretation LEED:
2 4
2 − 2
LEED: apparent (2 × 2) LEED: (1 × 1) diffuse (½ O) features LEED: (1 × 1) streaked (2 × 1)
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors
4.2-55
Table 52. 1,3 Cyclohexadiene (C6H8) Ref. 76G
C6H8/ Substrate Pt(111) -(1 × 1)
Pt(100) -(5 × 1)
Type
∆Φ [eV] at θ1
T [K]
Method
300
Diode
-1.8 -1.3 -0.8
300
Diode
-1.7 -1.6 -1.4
Comments, interpretation
2·10-8 torr LEED: poorly ordered 1h 4 − 2 2·10-8 torr LEED: 0 4 5h -8 4 − 2 2·10 torr LEED: 0 5 2·10-8 torr LEED: diffuse, ½ order streaks LEED: diffuse, ½ order streaks 1h 2·10-8 torr 5h LEED: diffuse, ½ order streaks 2·10-8 torr
Table 53. Benzene (C6H6, C6D6) Ref. 90Z2
C6H6, C6D6/ T [K] Substrate Ag(111) 100
Method
Type
∆Φ [eV] at θ1
I III
-0.7 -0.9 -0.9
98V2 Cu(111)
85
SE edge (UPS) 2PPE
74D2 Ni(111)
300
Diode
III
88N3 Pd(110)
80
SE edge (UPS)
III
73G
Pt(111)
300
ret. field
IV
Pt(100)(5 × 1)
300
ret. field
IV
Pt(111)
300 300 300
Diode
76G
-1.2 -0.8 -1.1
-1.4 -0.7 -1.6 -1.1 -1.8 -1.4 -0.7
Pt(100)(5 × 1)
300
Diode
-1.6
85A Pt(111) 95K4 Pt(111) 82R Pt(100)(5 × 20) 88M2 Rh(111)
300 100 300
Kelvin Kelvin SE edge (UPS) Diode
III
-1.5 -1.3 -1.5
III
-1.4
Lando lt -Bö rnst ein New Ser ies III/42A2
300
Comments, interpretation
1 ML TDS, XPS, UPS multilayer sat. LEED, 2PPE Fig. 3 TDS 3.5 L after pumping ARUPS, LEED, c(4 × 2), AES 3L linear decrease of Φ azimuthally oriented, tilted by 10 - 20º with respect to the surface LEED, ordered structures θ1 θ2 LEED, ordered structures θ1 θ2 4·10-7 torr, poorly ordered 4 − 2 5 min at 4·10-7 LEED: 0 4 4 − 2 40 min at 4·10-7 LEED: 0 5 LEED: substrate changes into (1 × 1) adsorbate: diffuse mig-like ½ order streakes saturation AES, HREELS, TDS LEED, AES, TDS, IRAS 10 L ARUPS C6D6
4.2-56 Ref. 88J2
99W
4.2 Electron work function of metals and semiconductors
[Ref. p 4.2-118
C6H6, C6D6/ T [K] Method Substrate Ru(0001) 120...25 K 0
Type
∆Φ [eV] at θ1
Comments, interpretation
III
-1.8
sat.
W(110)
III
-1.5
2.5·1014 atoms cm-2
LEED, HREELS C6H6-mig parallel to surface max. coverage: 0.14 molecule/Ru atom; µ0 = 2.2 D TDS, XPS
Type
∆Φ [eV] at θ1
Comments, interpretation
Diode
-1.7
LEED: streaks at 1/3 order
Diode
-1.5
Kelvin
-1.6
Kelvin
Table 54. Toluene (C6H5CH3) Ref. 74G
85A
C6H5CH3/ T [K] Substrate Pt(111) 300 -(1 × 1) 425 Pt(100) 300 -(5 × 1) 425 300 Pt(111)
Method
(4 × 2) LEED: (5 × 1), streaks at 1/3 order (1 × 1) high background saturation AES, HREELS, TDS
Table 55. Ethylbenzene (C6H5C2H5) C6H5C2H5/ Substrate 98R2 Pt(111) Ref.
T [K] Method
Type
∆Φ [eV] at θ1
Comments, interpretation
135
III
-1.8
0.5 ML
UPS, TDS
III
-1.2
1 ML
III
-0.2 -0.5
1 ML 2 ML
Type
∆Φ [eV] at θ1
Comments, interpretation
-1.5
LEED: disordered
-1.5
LEED: (1 × 1) disordered
∆Φ [eV] at θ1
Comments, interpretation
Diode
-1.7
LEED: disordered
Diode
-1.8
LEED: (1 × 1) disordered
Fe3O4(111) 135
FeO(111)
135
SE edge (UPS) SE edge (UPS) SE edge (UPS)
Table 56. N-butylbenzene (C6H5C4H9) Ref. 74G
C6H5C4H9/ T [K] Substrate Pt(111) 300 -(1 × 1) Pt(100) 300 -(5 × 1)
Method Diode Diode
-
Table 57. T-butylbenzene (C6H5C(CH3)3) Ref. 74G
C6H5C(CH3)3 T [K] /Substrate Pt(111) 300 -(1 × 1) Pt(100) 300 -(5 × 1)
Method
Type
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors
4.2-57
Table 58. M-xylene (C6H4(CH3)2) Ref. 74G
C6H4(CH3)2/ T [K] Substrate Pt(111) 325 -(1 × 1) Pt(100) 325 -(5 × 1)
∆Φ [eV] at θ1
Comments, interpretation
Diode
-1.8
LEED: streaks at 1/2.6 order
Diode
-1.7
LEED: (5 × 1) streaks at 1/3 order
∆Φ [eV] at θ1
Comments, interpretation
Diode
-1.9
LEED: very poorly ordered
Diode
-1.8
LEED: (1 × 1) disordered
Method
Type
Table 59. Biphenyle (C6H5C6H5) Ref. 74G
C6H5C6H5/ T [K] Substrate Pt(111) 300 -(1 × 1) Pt(100) 300 -(5 × 1)
Method
Type
Table 60. Naphtalene (C10H8) Ref. 73G 76G
C10H8/ Substrate Pt(100) -(5 × 1) Pt(111) Pt(100) -(5 × 1)
T [K]
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
300
Diode
III
-1.7
sat.
LEED
300 425 300
Diode Diode Diode
-1.95 -2.0 -1.7
9·10-9 torr LEED: apparent (3 × 1) 9·10-9 torr LEED: (6 × 6) 9·10-9 torr LEED: substrate: (1 × 1) adsorbate: disordered 9·10-9 torr LEED: substrate: (1 × 1) adsorbate: disordered
-1.65
Table 61. 2-Methylnaphtalene (C10H7CH3) Ref. 74G
C10H7CH3/ T [K] Substrate Pt(111) 300 -(1 × 1) Pt(100) 300 -(5 × 1)
Lando lt -Bö rnst ein New Ser ies III/42A2
∆Φ [eV] at θ1
Comments, interpretation
Diode
-2.0
LEED: very poorly ordered
Diode
-1.6
LEED: disordered
Method
Type
4.2-58
4.2 Electron work function of metals and semiconductors
[Ref. p 4.2-118
4.2.6 Polar hydrocarbons Table 62. Methanol (CH3OH) Ref. 92S8
CH3OH / Substrate Cr(110)
T [K]
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
90
III
-2.2
UPS
III
-1.6
at 6 L
TDS, UPS
-1.2
at 80 L
TDS, HREELS
III
-1.1 -1.8
at 3 L
TDS, UPS LEED, AES, TDS, IRAS
77R2 Ni(111)
80
85S6
80
SE edge (UPS) SE edge (UPS) Diode
77 100
Kelvin Kelvin
Si(111) -(7 × 7) 82C2 Pd(100) 95K4, Pt(111) 97V3
Table 63. Ethyleneoxide (C2H4O) C2H4O / Substrate 86K3, Ag(110) 86B Ref.
87B4 Fe(100) 87B4 Ni(111) 90N
Ni(111)
93W
Ni(110)
93W2 Pt(110) -(1 × 2)
T [K]
Method Type
100...300 Kelvin
III
100...300 SE edge IV (UPS) 100...300 SE edge III (UPS) 100 Kelvin III
140
SE edge III (UPS) SE edge III (UPS)
∆Φ [eV] at θ1
Comments, interpretation
-1.45
sat.
-2.2 -1.9 -1.3
0.5 ML 0.75 ML sat.
LEED, UPS, TDS c(2 × 2) structure bonding via the O-atom ARUPS
-1.6
2L
-2.9
0.5 ML
-2.1
0.5 ML
ARUPS TDS co-adsorption with K LEED, TDS, ARUPS c(2 × 2) structure LEED, TDS, ARUPS two differently oriented species
Table 64. Ethylenedioxide ((CH2)4O2) Ref. 96H
(CH2)4O2/ T [K] Method Substrate Ag(110) 90...750 Kelvin
Type
∆Φ [eV] at θ1
Comments, interpretation
III
-0.35
LEED, TDS, HREELS conclusion: O interacts with Ag surface; µ0 = 0.4 D
Type
∆Φ [eV] at θ1
Comments, interpretation
-1.6
LEED, AES, TDS, IRAS
1L
Table 65. Acetone (C3H6O) Ref.
C3H6O / Substrate 95K4, Pt(111) 97V3
T [K]
Method
100
Kelvin
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors
4.2-59
Table 66. Furan (C4H4O) C4H4O / Substrate 96O2 Pd(111) Ref.
T [K]
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
175
SE edge (UPS)
III
-1.5
XPS, UPS
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
ARUPS
III
-0.6
Table 67. Benzenethiol (C6H5SH) Ref.
C6H5SH / T [K] Substrate 99W2 Au(111) 300 82A
Cu(111)
300
SE edge (UPS)
-1.0
at 10 L
LEED, HREELS, ARUPS, XPS µ0 = 1.6·1030 Cm saturation ARUPS at 10 L
Table 68. Pyridine (C6H5N) Ref.
C6H5N / Substrate 88N2 Pd(110)
73G
76G
Pt(111) Pt(100) -(5 × 1) Pt(111) -(1 × 1)
Pt(100) -(5 × 1)
T [K]
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
300
SE edge (UPS)
III
-1.07
sat. (5 L)
300 300
Diode Diode
III III
-2.4 -2.4
sat. sat.
LEED, ARUPS c(4 × 2) structure orientation parallel to surface LEED LEED
300
Diode
-2.7
1·10-8 torr LEED: diffuse (1/2 O) features
525
Diode
-1.7
300
Diode
-2.4
1·10-8 torr LEED: well defined streaks at 1/3, 2/3, 3/3 order 1·10-8 torr LEED: (1 × 1) and disordered
525
Diode
1·10-8 torr LEED: (1 × 1) plus (¥ × ¥ 5Û
Table 69. Aniline (C6H5NH2) Ref. 74G
C6H5NH2/ T [K] Substrate Pt(111) 300 -(1 × 1) Pt(100) 300 -(5 × 1)
∆Φ [eV] at θ1
Comments, interpretation
Diode
-1.8
LEED: streaks at 1/3 order
Diode
-1.8
LEED: (1 × 1) disordered
∆Φ [eV] at θ1
Comments, interpretation
Diode
-1.5
LEED: 1/3 order features
Diode
-1.4
LEED: (1 × 1) disordered
Method
Type
Table 70. Nitrobenzene (C6H5NO2) Ref. 74G
C6H5NO2/ T [K] Substrate Pt(111) 300 -(1 × 1) Pt(100) 300 -(5 × 1)
Lando lt -Bö rnst ein New Ser ies III/42A2
Method
Type
4.2-60
4.2 Electron work function of metals and semiconductors
[Ref. p 4.2-118
Table 71. Cyanobenzene (C6H5CN) Ref. 74G
C6H5CN / T [K] Substrate Pt(111) 300 -(1 × 1) Pt(100) 300 -(5 × 1)
∆Φ [eV] at θ1
Comments, interpretation
Diode
-1.6
LEED: 1/3 order features
Diode
-1.5
LEED: (1 × 1) disordered
Method
Type
4.2.7 Halohydrocarbons Table 72. Chloro-methane (ClCH3) Ref.
ClCH3/ Substrate
89Z
Ag(111) 100
97Y2 Al(111)
T [K]
90
90S2
Pd(100)
99L
Ru(0001) 100
97K4 Si(111)
100
100
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
SE edge (UPS)
IV
-0.8 -0.6
0.9 ML 1.3 ML
XPS, UPS, TDS 1 ML = 4.6(3)·1014 molecules cm-
SE edge (UPS) SE edge (UPS) Kelvin
III
-0.55
at 7 L
IV IV
K
I
-0.9 -0.75 -1.9 -1.5 -1.7 0.4
3L UPS, TDS 12 L min, 1.8 L 3.5 L 6L 4L CH3Cl weakly bound at 100 K does not react
2
UPS
Table 73. Chloro-ethane (ClC2H5) Ref. 91Z3
ClC2H5/ Substrate Ag(111)
T [K]
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
100
SE edge (UPS)
III
-1.0
TDS, UPS, XPS
Type
∆Φ [eV] at θ1
Comments, interpretation
-0.6
LEED, AES, TDS, IRAS
Method Typ
∆Φ [eV] at θ1
Comments, interpretation
SE edge (UPS)
+1.0
LEED, UPS
1 ML
Table 74. Di-chloro-methane (Cl2CH2) Ref.
Cl2CH2/ Substrate 95K4 Pt(111)
T [K]
Method
100
Kelvin
Table 75. Tri-chloro-methane (Cl3CH) Ref.
Cl3CH / T [K] Substrate 84G1 Ag(111) 300
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors
4.2-61
Table 76. Tetra-chloro-methane (Cl4C) Ref.
Cl4C / Substrate
T [K]
Method
79J3
Fe(100)
300
Diode
Type
∆Φ [eV] at θ1
Comments, interpretation
1.30
mobile precursor
sat.
Table 77. Bromo-methane (BrCH3) T [K]
Method
Type
∆Φ [eV] at θ1
100
SE edge (UPS) Kelvin
IV
-1.0 -0.7 -2.2 -1.85
89Z
BrCH3/ Substrate Ag(111)
99L2
Ru(0001) 82
Ref.
IV
Comments, interpretation
0.9 ML XPS, UPS, TDS 1.4 ML 1 ML = 4.6(3)·1014 molecules cm-2 min, 3.5 L TDS, also with a ML of Cu 6.5 L
Table 78. Di-bromo-methane (Br2CH2) Br2CH2/ Substrate 84G2 Ag(111) Ref.
T [K]
Method
300
SE edge (UPS)
Type
∆Φ [eV] at θ1
Comments, interpretation
+0.7
LEED, UPS
Table 79. Tetra-bromo-methane (Br4C) Ref.
Br4C / Substrate
79D3 Fe(100)
T [K]
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
300
Diode
I
0.95
LEED, AES CBr4 dissociates
Type
∆Φ [eV] at θ1
Comments, interpretation
+0.3
LEED, UPS
sat.
Table 80. Iodo-methane (ICH3) ICH3/ Substrate 80G2 Ag(111)
T [K]
Method
300
95Y
Au(100)
105
SE edge (UPS) Diode
93S8
Pd(100)
85
Ref.
SE edge (UPS)
III
-1.0 min at 5...15 L TDS, IRAS, HREELS -0.8 30 L -1.5 1.5 L UPS
Type
∆Φ [eV] at θ1
Comments, interpretation
-0.85 min 7 L +0.1 25 L
TDS, IRAS, HREELS
Table 81. Iodo-ethane (IC2H5) Ref. 95Y
IC2H5/ Substrate Au(100)
T [K]
Method
105
Diode
Table 82. Chloro-tri-fluoro-methane (ClCF3) Ref.
ClCF3/ Substrate
T [K]
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
92K
Pt(111)
50
SE edge (UPS)
III
-0.15
XPS, UPS, TDS CF3Cl does not react at 50 K
Lando lt -Bö rnst ein New Ser ies III/42A2
2.5 ML
4.2-62
4.2 Electron work function of metals and semiconductors
[Ref. p 4.2-118
Table 83. 1,2-di-chloro-ethane (ClCH2CH2Cl) ClCH2CH2Cl T [K] /Substrate 92W2 Cu(111) 110
Ref.
Method
Type
SE edge (UPS)
∆Φ [eV] at θ1 -0.55 -0.45
Comments, interpretation
at 1 ML UPS multilayer
Table 84. 1,2-di-chloro-ethene (ClCH:CHCl) Ref. 97Y
ClCH:CHCl / T [K] Substrate Cu(100) 120
Method
Type
SE edge (E)
∆Φ [eV] at θ1
Comments, interpretation
-0.25* -0.45**
NEXAFS * CHClő&&O2 ** cis-CHClő&+&O
Table 85. 1,2-chloro-bromo-ethane (ClCH2CH2Br) ClCH2CH2Br T [K] /Substrate 93K2 Cu(111) 111
Ref.
99T
Cu(111)
100
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
SE edge (E) SE edge (UPS)
I
0.8
sat.
-0.55 -0.4 +0.75
12 L 30 L 10 L
at 300 K Br/Cl adsorbate is formed and C2H4 desorbed LEED, AES, UPS
300
Table 86. Iodo-benzene (IC6H5) Ref. 92X
Substrate Cu(111)
T [K] 110
Method SE edge (E)
Type
∆Φ [eV] at θ1 0.6 2L
Comments, interpretation AES, TDS, HREELS
Table 87. Chloro-benzene (ClC6H5) Ref.
ClC6H5/ Substrate
T [K]
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
82R
Pt(100)(5 × 20)
300
SE edge (UPS)
III
-0.85
ARUPS
Method
Type
∆Φ [eV] at θ1
SE edge (UPS) SE edge (E)
IV
-1.1 -0.6 -1.3
10 L
4.2.8 Other hydrocarbons Table 88. Di-ethyl-zink ((C2H5)2Zn) Ref.
(C2H5)2Zn / T [K] Substrate 94K2 Pd(100) 90 99K4 Rh(111)
90
III
θ1 4θ1 2L
Comments, interpretation XPS, TDS XPS, TDS, HREELS
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors
Table 89. glycine (α-amino acetic acid) (H2NCH2CO2H) Ref.
89E3
H2NCH2 – T [K] CO2H / Substrate Pt(111) 120
Method
Type
∆Φ [eV] at θ1
SE edge (UPS)
III
-1.7
Comments, interpretation
10·1014 LEED, TDS, UPS atoms cm-2
Table 90. Closo-1,2-di-carbado-decaborane (C2B10H12) Ref. 94Z2
C2B10H12/ T [K] Method Substrate Cu(100) 150... SE edge 400 (UPS)
Type
∆Φ [eV] at θ1
I
2.0
Comments, interpretation
sat.
Table 91. TCNQ (Tetra-cyano-quino-dimethane) (C12N4H4) T [K]
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
86E2
C12N4H4/ Substrate Cu(111)
100
Diode
I
86E4
Cu(111)
100
Diode
I
0.8 1.36 0.78 1.28 1.36
HREELS supports negatively charged layer HREELS
Ref.
at 1 ML at 2 ML 1. layer 2. layer 3. layer
4.2.9. Alkali metals Table 92. Lithium (Li) Ref. 86P2
Li/ Substrate Ag(111)
86P3 Ag(111) 85P4 89H2 Al(111)
T [K]
Method Type
∆Φ [eV] at θ1
Comments, interpretation
300
Kelvin
IV
300
Kelvin
IV
AES
140
Kelvin
III
-1.86 -1.76 -1.9 min -1.8 ML -1.20
Diode
III
-1.8
95G3 CdTe(100) 94M3 Cu(100)
180
96L
160
Cu(111)
87A4 GaAs(100) (IBA) 79G2 Mo(211) 77 84K4 Mo(110) 5, 77, 300
Lando lt -Bö rnst ein New Ser ies III/42A2
SE edge IV (E) Diode IV Kelvin Diode Diode
III IV
min ML θLi = 0.5 θLi = 1.0
1 1015 atoms cm-2 LEED, AES, TDS µ0 = 2.1 D ML LEED, AES, ELS µ0 = 3.2 D LEED, AES θLi = 0.55 θLi = 0.8 min ELS ML
-2.0 -1.7 -2.4 -1.85 -1.8 min -1.6 ML -1.5 ML -2.6 min θLi = 0.35 -1.7 ML θLi = 1
4.2-63
4.2-64
4.2 Electron work function of metals and semiconductors
Ref.
Li/ Substrate 88G3 Ni(100)
T [K]
Method Type
∆Φ [eV] at θ1
Comments, interpretation
310
Diode
-2.8 -2.5 -2.4 -2.1 -3.5 -2.8 -3.6 min -2.5
min ML
RP
-2.4 -1.8 -1.9 -2.2 -2.4
min
NMR, TDS
1 ML 3 ML
AES, LEED
98M3 Ni(775)
IV IV
94J2
Ru(0001)
96E
Ru(0001) 200
SE edge IV (MDS) Kelvin IV
98E
Ru(0001)
Kelvin
88N4 Si(111)(7 × 7) 91C3 Si(111) 93F
300
66G
77
73M
IV
SE edge III (UPS) IV
Si(111)(7× 7) 94E2 Si(100) 95K3 n-type p-type 95K6 Si(100)(2× 1) 95K7 Si(100)(2× 1) W(211)
360 360
SE edge III (E) Diode III Diode Diode
300
III III III
FEM
III
W(110)
FEM
FEM
W(111) W(211)
FEM Diode
III III III
300
Diode
IV
W(110)
77
Diode
IV
W(110)
77
FEM
IV
W(211)
300
Diode
IV
W(100) W(111)
300 300
Diode Diode
III III
74M5 W(110)
[Ref. p 4.2-118
77 300
µ0 = 1.5 D
TDS, MDS 3 θLi = 0.46 α = 12.8 Å θLi = 0.45 NMR θLi = 1.0 µ changes from 4 to 0.5 D with coverage -3.5 min θLi = 0.5 µ0 = 4.9 D -2.5 -2.3 AES, MDS
-2.2 -1.8 -2.4 -2.3
-1.5 -1.8 -3.0 -2.4 -1.7 -1.5 -1.8 -1.5 -1.8 -2.9 -1.9 -2.3 -2.8 -2.2 -3.0 -2.4 -1.5 -2.0 -1.9 -1.4 -1.4
AES, TDS
1 ML 2 ML AES, LEED, UPS different Li induced superstructures ML 2. layer
ML 2. layer ML 2. layer min ML 2. layer min ML min ML 1 min 2 min ML ML
5 1014 atoms cm-2 12 1014 atoms cm-2 5 1014 atoms cm-2 LEED
5 1014 cm-2 12 1014 cm-2 20 1014 cm-2
5 1014 12 1014 16 1014 12 1014 12 1014
cm-2 cm-2 cm-2 cm-2 cm-2
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118] Ref.
Li/ Substrate 84K4 W(110)
4.2 Electron work function of metals and semiconductors T [K]
Method Type
∆Φ [eV] at θ1
5, 77, 300
Diode
IV
Diode
IV
-2.9 min -2.0 ML -2.6 min -1.7 ML
Mo(110) 5, 77, 300
4.2-65
Comments, interpretation
θLi = 0.35 LEED θLi = 1 θLi = 0.35 θLi = 1
Table 93. Sodium (Na) Figs. 26 and 27 Ref.
Na / Substrate 77B4 Ag(110)
T [K]
74P
Al(111)
300
87P2
Al(100) Al(100)
300 100 350
Method
Type
∆Φ [eV] at θ1
SE edge (UPS) SE edge (E)
III
-2.0
θNa = 0.45
UPS, XPS
III
-1.6
ML
µ0 = 3.4 D
III IV
-1.6 -2.0 -1.6 -1.6
ML min ML ML
-1.5 -1.4 -1.7 -1.4 -2.7 -2.5 -2.5
θNa = 0.3
-2.0 -2.0 -2.3 -2.7 -2.3
at θNa =0.1 θNa = 0.25 θNa = 0.55 min ML
-2.1 -1.8 -2.2 -2.0
min ML min ML
-2.8 -2.3
min ML
SE edge (E) SE edge (E)
III
89H2 Al(111)
140
Kelvin
IV
Al(111)
300
Kelvin
IV
95N2 Au(100)
130
Kelvin
IV
300
III
95S5
Au(100)
80L
Cu(111)
300
Diode
IV
83W
Cu(100)
100
Diode
IV
91T
Cu(111)
300
Diode
IV
93S4 93S5
Cu(111)
Diode
IV
Lando lt -Bö rnst ein New Ser ies III/42A2
Kelvin
θNa = 0.3 min ML ML
Comments, interpretation
µ0 = 3.2 D µ0 = 3.2 D linear decrease for 0.08 < θNa < 0.5 explained by 2D clustering. See Fig. 26. LEED, UPS, ELS µ0 = 1.8 D µ0 = 2.1 D θNa = 0.22 θNa = 0.45 θNa = 0.45, no minimum observed LEED, XPS, AES lifting of (5 × 20) reconstruction XPS
θNa = 0.13, µ0 = 11.3 D θNa = 0.5, close-packed layer LEED, AES, ELS, ARUPS
θNa = 0.2 θNa = 0.4 LEED, TDS θNa = 0.2, µ0 = 4.3 D, UPS θNa = 0.4
4.2-66 Ref. 93S6 93T2
4.2 Electron work function of metals and semiconductors Na / Substrate Cu(110)
94F
Cu(111)
96L2
Cu(110)
67P
Ge(111)
69W2 Ge(111) 81B2 Ge(100)
T [K]
Method
Type
∆Φ [eV] at θ1
Diode SE edge (UPS)
IV
θNa = 0.5 θNa = 1.0, µ0 = 2.7 D UPS -2.0 > θNa = 0.5 LEED, IPES -2.75 min, θNa =0.33 2PPE -2.3 ML, θNa = 1 -2.4 2 ML AES, ARUPS -2.2 min θNa = 0.3 -1.8 ∆Φ is different after heating to θNa = 0.7 370 K -2.5 LEED
ARUPS (2PPE) 100 (370)
300
Ge(111) 40
III IV
SE edge (E) Diode FEM
III III IV
FEM
IV
SE edge (UPS) Diode
III
-2.5 -2.5 -2.3 -2.4 -2.3 -2.5
III
-2.6
1 ML
LEED, AES, ELS, TDS
-1.9 -1.8 -3.1 -2.2 -3.1 -2.5 -2.1 -2.0 -3.3 -2.6 -3.2 -2.4 -2.9 -2.3 -3.2 -2.6
min ML min ML min ML min ML min ML min ML
LEED
-2.2 -1.5 -2.8 -2.3 -3.6 -2.8 -3.0 -2.8 -3.6 -2.9
min thick layer min, θNa = 0.25 ML, θNa = 0.55 min ML min, θNa = 0.5 ML, θNa = 1.0 min ML
Diode
IV
70G
Ni(111)
300
Kelvin
IV
Ni(100)
300
Kelvin
IV
Ni(110)
300
74A2 Ni(100)
300
Diode
IV
88G3 Ni(100)
325
Diode
IV
IV
98M3 Ni(775)
IV Diode
IV
SE edge (UPS) Diode
IV IV
85K7 Ru(0001) 300
Diode
IV
87K2 Ru(10 1 0) 300
Diode
IV
87R
Diode
IV
94B4 NiO
180
88M2 Rh(111)
310
Ru(0001) 300
min ML
IV
77
Ni(111)
-2.1 -1.9
Comments, interpretation
ARUPS
96K3 Ge(111) (2 × 8) 97N4 Ge(100)(2 × 1) 80G Mo(211)
93S5
[Ref. p 4.2-118
7·1014 atoms cm-2 10·1014 atoms cm-2 7.5·1014 atoms cm-2 10·1014 atoms cm-2 UPS
θNa = 0.21, µ0 = 3.7 D θNa = 0.45 θNa = 0.26, µ0 = 3.6 D θNa = 0.5 See Fig. 27 θNa = 0.23, µ0 = 3.4 D θNa = 0.45 µ0 = 4.3 D
min ML
θNa = 0.18 θNa = 0.40 UPS UPS, XPS
µ0 = 3.4 D TDS co-adsorption with CO θNa = 0.3 θNa = 0.6, µ0 = 4.3 D TDS, ELS
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors Method
Type
∆Φ [eV] at θ1
IV
94H3 Ru(0001) 50
SE edge (UPS) Kelvin
-3.5 -3.0 -3.7 -2.9
69W2 89G2 89G3 91T2
Diode SE edge (E) Diode
Ref. 91P6
Na / T [K] Substrate Ru(0001) 120
Si(111) Si(001)(2 × 1) Si(001)(2 × 1) 92R2 Si(111)(2 × 1) 93H Si(100)(2 × 1) 93J Si(001)(2 × 1) 94O Si(111)
300 430 300
100
300
SE edge (UPS) ARUPS
97C2 Si(100)- 300 (2 × 1) 67O W(100) W(110) W(111) W(112) Re(10 1 1) Re(1120) Re(10 2 2) 68K W(110)
SE edge (UPS) SE edge (UPS) FEM FEM FEM FEM FEM FEM FEM FEM
68K
W(112)
FEM
W(100)
FEM
IV
-2.5 -2.9
III
-3.0
at θNa = 1 min
IV III
-2.7 -2.4 -2.7 -2.2 -3.0
min ML
III
-2.5 -2.3 -3.0 -2.45 -3.90 -2.0 -2.35 -3.6 -2.6 -2.9 -3.6 -2.9 -2.6 -2.4 -2.5 -2.2 -2.1 -2.0 -3.4 -2.5 -2.8 -3.5 -2.5 -2.0 -2.3 -2.1
min min min min min min min min
-2.0
at 0.5 ML at θNa = 0.75 ML
IV IV IV IV IV IV IV
W(111) 70M
W(110)
77
Diode
IV
W(110)
300
Diode
IV
71C5 W(112) 73M3 W(112)
300 77
Diode Diode
III IV
300 W(112) W(112) + 1 ML oxygen
Diode
70C
Lando lt -Bö rnst ein New Ser ies III/42A2
Comments, interpretation
min, θNa = 0.30 ML, θNa = 0.44 min θNa = 0.2, µ0 = 5.0(5) D ML θNa = 0.55 LEED, TDS
III III
LEED, AES
min ML
LEED, AES, ELS clustering for θNa > 0.5 IPES UPS LEED, IPES UPS ARUPS
min min
4.2-67
5·1014 atoms cm-2 10·1014 atoms cm-2 8·1014 atoms cm-2 15·1014 atoms cm-2 7·1014 atoms cm-2 10·1014 atoms cm-2 7·1014 atoms cm-2 10·1014 atoms cm-2
min ML 2. layer
7·1014 atoms cm-2 10·1014 atoms cm-2 200 K and 400 K similar LEED
4.2-68 Ref.
4.2 Electron work function of metals and semiconductors
85C
Na / Substrate W(100)
97O
ZrC(100)
[Ref. p 4.2-118
T [K]
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
300
SE edge (UPS) SE edge (UPS)
IV
-3.0 -2.7 -0.6 -0.1
LEED, AES, ARUPS
IV
min
θNa = 0.25, AES, UPS θNa = 0.8
Table 94. Potassium (K) Ref.
K/ Substrate 82F2 Ag(111)
T [K] Method
88A2 Ag(111) 89B4 Ag(111)
100
91O
Ag(100)
325 140
86P2 Al(111)
300
87P2 Al(100)
100 350
Type ∆Φ [eV] at θ1
Diode
IV
Kelvin
IV
SE edge IV (UPS) SE edge III (E) IV SE edge III (E) or Diode SE edge IV (E) SE edge III (E)
89H2 Al(111)
140
Kelvin
IV
95N2 Au(100)
130
Kelvin
IV
95S4 Au(100)
300 130
Kelvin Kelvin
III IV
90
87D2 Cu(100)
120
85W
Cu(110)
300
86A4 Cu(100)
330
92A2 Cu(100) 95H3 Cu(111)
90
min, θΚ = 0.15 ML, θΚ = 0.33 θΚ = 0.55 θΚ = 1.5 min, θΚ = 0.5 ML, θΚ = 1.2 θΚ = 1.2 min, θΚ = 0.2 ML, θΚ = 0.4
-2.8 -2.3 -2.3
min ML
-2.2 -1.7 -3.3 -3.0 -3.0 -3.3 -3.1 -2.7 -2.7 -3.1
SE edge (XPS) SE edge IV (E) SE edge IV (UPS) SE edge IV (E)
-3.0 -2.9 -3.6 -2.3 -3.1 -2.3 -3.0 -2.5
Kelvin
IV
Kelvin
IV
-2.87 -1.9 -2.9 -2.4
min, at θ1 at 5θ1 min, θΚ = 0.25 θΚ = 0.6
III
LEED, AES UPS, XPS, ELS
AES
min ML min, θΚ = 0.15 ML, θΚ = 0.4 ML θΚ = 0.15 θΚ = 0.45 θΚ = 0.1 θΚ = 0.2 θΚ = 0.45 θΚ = 0.5 θΚ = 1.0 min ML min ML min, θΚ = 0.17 θΚ = 0.3
300
99W3 Cr2O3(0001)
-2.9 -2.4 -2.8 -2.1 -3.5 -2.8 -2.2 -2.4 -2.1 -2.2
Comments, interpretation
LEED, AES, TDS µ0 = 4.6 linear decrease for 0.05 < θΚ < 0.4 explained by 2D clustering µ0 = 4.1 D LEED, AES, XPS
LEED, XPS K-induced (5 × 20) ĺ (1 × 1) “deconstruction”
LEED, XPS, Laser induced desorption AES, TDS, ELS MDS LEED, AES, ELS µ = 16 D, goes to 3 D with coverage
TDS CO-adsorption of CO Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors
4.2-69
T [K] Method
Type ∆Φ [eV] at θ1
Comments, interpretation
90
Kelvin
IV
LEED, AES, TDS, UPS
79B5 Fe(110)
300
81L
Fe(100)
300
SE edge IV (UPS) Kelvin IV
Fe(110)
300
Kelvin
IV
Fe(111)
300
Kelvin
IV
GaAs(110)*
300
Kelvin
300 300 300 300
Ref. 98B
92O
K/ Substrate Cu(332)
min, 0.8 ML 2 ML min, θΚ = 0.18 ML, θΚ = 0.31 min ML min ML min ML
III
-2.7 -2.3 -3.7 -2.8 -2.4 -2.1 -3.5 -3.0 -2.5 -2.4 -2.8
Kelvin
III
-3.5
1 ML
LEED, AES *prepared by ion bombardment and annealing **cleaved
Kelvin Diode Diode FEM
III III III IV
1 ML
**cleaved
at
Ge(111)
FEM
IV
4.5·1014 atoms cm-2 7.5·1014 atoms cm-2 4.5·1014 atoms cm-2 7.5·1014 atoms cm-2
Graphite(0001) 160 85
-2.4 -3.0 -3.4 -2.9 -2.65 -2.8 -2.65 -2.2(1)
GaAs(110)** p-type n-type 69W2 Ge(111) Ge(100) 81B2 Ge(100)
at
76B4 Mo(100)
77
Mo(110)
77
FEM
IV
-3.1 -2.3
Mo(211)
77
FEM
IV
-2.5 -2.1
Mo(111)
77
FEM
IV
-2.1 -1.7
300
Diode
III
-1.1
min, 5·1014 atoms cm-2 ML, 9·1014 atoms cm-2 min, 3·1014 atoms cm-2 ML, 6·1014 atoms cm-2 min, 4·1014 atoms cm-2 ML, 8·1014 atoms cm-2 min, 2.5·1014 atoms cm-2 ML, 7.5·1014 atoms cm-2 0.2 ML
SE edge III (UPS) SE edge IV (UPS) Diode
-2.0
θΚ = 0.5
-3.2 -2.8 -3.5 -2.9
θΚ = 0.3 θΚ = 1.0 min, θΚ = 0.2 ML, θΚ = 0.33
91P5 MoS2 (basal) 96O
NbC(100) NbC(111)
73A
Ni(100)
Lando lt -Bö rnst ein New Ser ies III/42A2
-2.4 -2.1
µ0 =4.4 D µ0 = 3.8 D
θK = 0.35
SE edge III (UPS) Diode FEM IV
99O
LEED, AES, UPS µ0 = 6.0 D µ0 = 7.0 D
LEED, AES, TDS 2 D and 3 D clusters for coverages θΚ > 0.2
LEED, UPS LEED µ0 = 6.3 D
4.2-70
4.2 Electron work function of metals and semiconductors
K/ Substrate 74A2 Ni(100)
T [K] Method
Type ∆Φ [eV] at θ1
300
Diode
IV
84S11 Ni(100)
120
88G3 Ni(100)
325
SE edge IV (UPS) Diode IV
70G
300
Kelvin
Ref.
Ni(110)
85L2 Ni(111)
IV
86U
Ni(111)
90
90N
Ni(111)
100
SE edge III (UPS) SE edge IV (E) Kelvin IV
40
Kelvin
91H2 Ni(100) 98M3 Ni(775)
IV IV
87B6 Pd(100)
300
83K3 Pt(111)
300
85L
Pt(111)
300
88W
Pt(111)
IV
96L2 Pt(111)
140
SE edge (UPS) SE edge (UPS) SE edge (E, UPS) ARUPS
78L3 Re(10 1 0)
245
Diode
IV
97V2 Re(0001)
105
Kelvin
IV
92J2
45
Rh(111)
IV IV IV
IV
85D3 Ru(0001)
80
Kelvin
85M
60
Ru(0001)
IV
IV
86H4 Ru(10 1 0)
430
SE edge IV (UPS) Diode IV
87R
Ru(0001)
300
Diode
IV
88D
Ru(0001)
450
Diode
IV
91P6 Ru(0001)
120
SE edge IV (UPS)
-3.5 -2.8 -3.6 -2.9 -3.7 -3.3 -2.7 -2.5 -4.1
min, θΚ = 0.2 ML, θΚ = 0.40 min, θΚ = 0.15 ML, θΚ = 0.33 min ML min, θΚ = 0.38 ML, θΚ = 0.5
-4.0 -3.5 -3.8 -3.1 -3.3 -2.5 -3.5 -2.8 -4.15 -3.2 -4.6 -3.9 -4.6 -4.0 -4.8 -3.2 -4.3 -3.7 -3.0 -2.6 -4.3 -3.0 -3.8 -3.4 -4.3 -2.4 -4.0 -3.3 -2.6 -2.4 -3.9 -3.2 -3.7 -3.2 -3.8 -3.0
min ML min, θΚ = 0.2 θΚ = 0.7 min ML
[Ref. p 4.2-118
Comments, interpretation µ0 = 6.7 D
µ0 = 5.3 D; see Fig. 27 MDS LEED, IRAS, TDS µ0 = 3.7 D TDS
µ0 = 6.3 D
min, θΚ = 0.17 ML, θΚ = 0.33 min, θΚ = 0.5 ML, θΚ = 1.0 min, θΚ = 0.3 ML, θΚ = 0.5 min ML min, θΚ = 0.45 ML, θΚ = 1.0 min, θΚ = 0.35 ML, θΚ = 1.0
min ML min ML min, θΚ = 0.17 ML, θΚ = 0.35 min min, θΚ = 0.2 ML, θΚ = 0.4
LEED, AES, TDS µ0 = 6.4 D XPS, UPS µ0 = 9.4 D AES, TDS, UPS, HREELS AES, TDS, UPS incorporation of K 4.5·1014 atoms cm-2 7·1014 atoms cm-2 TDS, SHG UPS
LEED, AES, UPS, TDS µ0 = 3.6 D µ0 = 3.9 D TDS, ELS µ0 = 7.8 D LEED, AES, TDS XPS, UPS
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors T [K] Method
Type ∆Φ [eV] at θ1
300 300
Diode Diode
III IV
83T2 Si(100)-(2 × 1) 86O Si(100)
200
Diode Kelvin
III IV
Si(111)
300
Kelvin
Ref.
K/ Substrate 69W2 Si(111) Si(100)
89E2 Si(100)-(2 × 1) 90M Si(111)-(7 × 7)
300
90N2 Si(100)-(2 × 1) 90R3 Si(100)-(2 × 1)
300
92B4 Si(111)
300
92M3 Si(100)-(2 × 1)
300
ARUPS SE edge (UPS) SE edge (UPS) SE edge (UPS) Diode
III IV IV IV IV
55 93F
Si(111)-(7 × 7)
300
-3.0 -3.4 -3.1 -2.1 -2.9 -2.6 -3.1 -2.9 -3.3 -3.2 -3.1 -3.3 -3.0 -3.45 -3.0 -3.1 -3.0 -3.3 -2.5 -3.3 -2.5 -3.4 -3.2 -3.0
94W
SE edge IV (E) Diode III
97N5 Si(111) cleaved 76B4 Ta(100)
77
Diode SE edge (UPS) SE edge (UPS) FEM
IV
Ta(110)
77
FEM
IV
-3.1 -2.2
Ta(111)
77
FEM
IV
-1.6 -1.3
Ta(211)
77
FEM
IV
-2.0 -1.8
95H2 TiO2(110)
ARUPS
IV
65S
FEM
-3.8 -3.4 -2.6 -2.2
Si(111)-(7 × 7) 300 Si(111) (¥î¥ 5Û% 300 97C3 Si(100)-(2 × 1) 300
W (averaged)
Lando lt -Bö rnst ein New Ser ies III/42A2
300
III III
-3.0 -3.5
III
-3.20 (-3.56) -2.3 -2.1
4.2-71
Comments, interpretation
min θΚ = 0.5 min
LEED, AES, ELS AES
min
min min, θΚ = 0.5 θΚ = 0.75 min ML min ML min ML min ML min, θΚ = 0.5 ML, θΚ
LEED, IPES, UPS
LEED, IPES, UPS TDS, LEED, AES LEED, AES, UPS, TDS includes band bending of 0.3 eV at 300 K. LEED, AES LEED, AES, ARUPS
min
LEED, AES, ARUPS ARUPS UPS second experiment
min, 2.2·1014 atoms cm-2 ML, 4·1014 atoms cm-2 min, 2.3·1014 atoms cm-2 ML, 4·1014 atoms cm-2 min, 2.2·1014 atoms cm-2 ML, 3.5·1014 atoms cm-2 min, 3·1014 atoms cm-2 ML, 4·1014 atoms cm-2 min, θΚ = 0.4 ML, θΚ = 0.7 min
LEED, ARUPS
4.2-72 Ref. 66S
4.2 Electron work function of metals and semiconductors K/ Substrate W(100)
T [K] Method
Type ∆Φ [eV] at θ1
300
FEM
IV
W(110)
300
FEM
IV
W(111)
300
FEM
IV
W(211)
300
FEM
IV
FEM
IV
67O2 W(100) W(110)
IV
W(111)
IV
W(112)
IV
min, θΚ = 0.8 ML, θΚ = 1.2 min, θΚ = 0.85 ML, θΚ = 1.1 min, θΚ = 0.85 ML, θΚ = 1.1 min, θΚ = 0.85 ML, θΚ = 1.1
min, 3.6·1014 atoms cm-2 ML, 6.2·1014 atoms cm-2 min, 2.8·1014 atoms cm-2 ML, 4.6·1014 atoms cm-2 min, 4·1014 atoms cm-2 ML, 7·1014 atoms cm-2 min, 3.5·1014 atoms cm-2 ML, 6·1014 atoms cm-2
74M5 W(211)
245
74M7 W(112)
245
Diode
75B
W(100)
77
FEM
IV
-3.0 -2.6
W(110)
77
FEM
IV
-4.1 -3.2
W(111)
77
FEM
IV
-2.5 -2.3
W(211)
77
FEM
IV
-2.9 -2.7
76B4 W(110) 85C W(100)
77 300
91D
78
FEM SE edge (UPS) FEM IV
W(112)
IV
-2.8 -2.4 -2.8 -2.4 -2.7 -2.4 -2.8 -2.4 -3.0 -2.6 -4.3 -3.4 -2.5 -2.3 -3.2 -2.8 -2.9 -2.7 -2.9 -2.2
-3.1 -2.7 -3.0 -2.7
min, ML min 2. layer
min ML, θΚ = 0.6 min ML
[Ref. p 4.2-118
Comments, interpretation µ0 = 4.7 D µ0 = 7.8 D µ0 = 5.7 D µ0 = 6.8 D
4·1014 atoms cm2 12·1014 atoms cm2 LEED µ0 = 4.8 D
µ0 = 4.1 D
µ0 = 4.1 D
µ0 = 8.6 D LEED, AES, ARUPS
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors
4.2-73
Table 95. Rubidium (Rb) Fig. 28 Ref.
Rb / Substrate 89H2 Al(111) 99S2
T [K]
Method
Type
∆Φ [eV] at θ1
140
Kelvin
IV
-2.3 -1.8 -2.8 -2.5
min ML min, θRb = 0.15 θRb = 0.3
-3.5
min
Cu(100)
97C3 Si(100) -(2 × 1)
IV
300
SE edge (UPS)
III
Comments, interpretation LEED, AES, UPS µ0 = 4.1 D; see Fig. 28 data of H. Schief, Diploma Thesis, University Göttingen, 1990 ARUPS
Table 96. Cesium (Cs) Fig. 29 T [K]
Method Type
∆Φ [eV] at θ1
Comments, interpretation
83H
Cs / Substrate Ag(110)
300
SE edge IV (UPS)
-2.5 -2.4
min ML
86D
Ag(110)
300
Kelvin IV
100
Kelvin Kelvin IV
-2.4 -2.2 -2.6 -3.1 -2.7 -2.9 -2.3 -2.6 -2.3 -2.4 -1.8 -2.4 -1.8 -2.57 -2.0 -2.4 -1.6 -1.7
min ML min θCs = 0.6 θCs = 1.3 min, θCs = 0.4 ML,θCs> 0.9 min ML min ML min ML min, θCs = 0.22 ML, θCs= 0.4 2·1014 atoms cm2
LEED, AES small amounts of alkali drive a (1 × 2) reconstruction θCs = 0.26 θCs = 0.4
Ref.
88A2 Ag(111) 93S7
Ag(100)
80
Kelvin IV
86P2
Al(111)
300
87H
Al(111)
140
SE edge IV (E) Kelvin IV
89H2 Al(111)
140
Kelvin IV
94K3 Al(111)
85
Diode
87T
Be (polycr.)
IV
94G3 CdTe(100)
Diode
III
78L2 80L
Cu(111)
300
Diode
IV
-3.4 -3.0
min ML
82P7
Cu(100)
300
Diode
IV
-3.0 -2.5
min ML
Lando lt -Bö rnst ein New Ser ies III/42A2
LEED, AES LEED, TDS AES UPS, µ0 = 4.1 D LEED, AES, UPS µ0 = 4.1 D TDS, HREELS AES θCs = 0.33 ML LEED, AES θCs = 0.16, µ0 = 9.6 D θCs = 0.26, p(2 × 2) closepacked layer LEED, AES, ELS, ARUPS θCs = 0.14 θCs = 0.27
4.2-74 Ref. 91S
4.2 Electron work function of metals and semiconductors Cs / Substrate Cu(110)
[Ref. p 4.2-118
T [K]
Method Type
∆Φ [eV] at θ1
Comments, interpretation
100
Kelvin IV
260
IV
-2.8 -2.4 -2.6 -2.4
min ML min ML min ML
θCs = 0.16 θCs = 0.28 θCs = 0.22 θCs = 0.33 θCs = 0.45, IPE θCs = 1.0
LEED, AES
97A
Cu(100)
300
Diode
IV
71M
GaAs(110) (cleaved) p-type GaAs(110) cleaved in air GaAs(110) 300 (cleaved) n-type Ge(111) 300 p-type GaAS(111) B GaAs(100) GaAs(110)* 300
Diode
III
-3.1 -2.6 -4.0
Diode
III
-3.4
saturation
Kelvin III
-3.3
θCs = 0.6
Kelvin III
-3.3
θCs = 0.8
Diode
III
-3.2
saturation
SE edge III (UPS) Diode III
-3.7
*prepared by IBA
-1.8(2)
LEED: (1 × 1)
77D3
78C2
84R3
89M3 75D
GaP(111) 80 or 300 GaP( 1 1 1 ) 69W2 Ge(111) 300 Ge(100)
300
86H5 Graphite (0001) 81G
Mo(211)
77
82S5
Mo(100)
?
92E2
Mo(110)
94G4 Mo(110)
77
300 MoS2 cleaved in 200 air 85K9 MoS2(0001) 300 85K10 170 78P2 NbSe2 200 NbSe2 300 70G Ni(110) 300 78P3
Diode
IV
Diode
IV
Diode
IV
IV
?
IV
Diode
IV
Diode
Diode
-3.2 -3.0 -3.4 -3.1 -2.4
-2.8 -2.7 -2.3 -3.6 -3.4 -3.6 -2.9 -2.5 -1.9
III III
-1.8 -2.8
III III Diode III Diode III Kelvin IV
-2.3 -3.0 -3.0 -0.6 -3.1
Diode
min min min 5·1014 atoms cm2 min ML 2. layer min ML min ML
LEED: (¥î¥ 5ÛSDWWHUQ LEED
ELS
3 1014 atoms cm−2 15·1014 atoms cm-2 LEED, ELS
AES, TDS LEED min
θCs = 0.33; see Fig. 27 Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors
4.2-75
T [K]
Method Type
∆Φ [eV] at θ1
Comments, interpretation
300
Diode
LEED
77K4 Ni(100) 88G3 Ni(100)
325
ARUPS III Diode IV
89D
100
-3.4 -2.9 -3.0 -3.8 -3.3 -3.8 -3.2 -3.0 -4.5 -4.0 -4.1 -3.8 -4.2 -3.5
Ref. 75P2
Cs / Substrate Ni(100)
Ni(111)
IV
SE edge IV (UPS) Diode III ARUPS IV
91K4 NiO(100) 89C Pt(111)
300
85H4 Ru(0001)
80
87R
Ru(0001)
300
SE edge IV (E) Diode IV
90D2 Ru(0001)
300
Diode
91P6
120
Ru(0001)
IV
Diode
III
-3.0
Diode
IV
-3.1 -3.0 -2.2
min ML 1 ML
-3.9 -3.2 -3.0 -2.8 -3.1 -2.3
min ML min ML min, (2 × 2) ML
300
Diode
82T
IV
SE edge IV (UPS) IV 200
Kelvin IV ARUPS IV
300
W(110)
SE edge III (XPS) FEM IV
W(100)
IV
Lando lt -Bö rnst ein New Ser ies III/42A2
130
300
SE edge IV (E)
TDS, also oxidation of Cs LEED, ARUPS
µ0 = 10.5 D see Fig. 29 θCs = 0.14 θCs = 0.3 TDS, ELS; µ0 = 11 D min LEED, TDS ML µ0 = 16.4 D min, θCs = 0.19 XPS, UPS ML,θCs= 0.40 min
300
Si(100)
69M2 W(100)
min, θCs = 0.25 ML, θCs= 0.4 min ML min ML
300
300
67S
min, θCs = 0.5 θCs= 1.0
SE edge IV (UPS) Diode III
69W2 Si(111)
97G2 TiO2(110)
XPS
-3.8 -3.6 -4.0 -3.7 -3.2 -2.9 -3.6 -3.2 -3.7 -3.3 -3.7 -3.2 -3.4 -2.8 -3.6 -3.1 -3.25 -3.0 -3.0
SE edge IV (UPS) Diode IV
Si(100) -(2 × 1) 85I2 Si(100) -(2 × 1) 87O2 Si(100) -(2 × 1) 89E2 Si(100) -(2 × 1) 90M Si(111) -(7 × 7) 94W3 Si(111) -(7 × 7) Si(111) -(¥î¥ R30Û% 67F Ta(110)
min ML
min min θCs = 0.7 θCs = 1.0 min ML min ML min ML
LEED, AES, ELS, UPS
AES
LEED, IPES, UPS LEED, AES, ARUPS
µ0 = 6 Band bending 0.3 eV D
LEED
4.2-76 Ref. 69S
4.2 Electron work function of metals and semiconductors Cs / Substrate W(110)
T [K]
Method Type
∆Φ [eV] at θ1
FEM
-3.6 -3.4 -3.0 -2.8 -3.2 -2.0 -2.6 -2.8 -3.7 -3.2 -3.1 -2.6 -3.0 -2.8 -3.1 -2.4 -3.8 -3.2
IV
W(100)
IV
70F
W(211) W(111) W(115) W(103) W(110)
77
72V
W(100)
300
III III III III SE edge IV (E) Diode IV
71P2
W(211)
300
Diode
IV
73P2
W(100)
300
Diode
IV
80D2 W(110)
250
Kelvin IV
87L
WSe2*
97K5 WSe2
Diode 85
III
-3.1
IV
-4.1 -3.9
[Ref. p 4.2-118
Comments, interpretation
min ML
1.8·1014 atoms cm-2 2.5·1014 atoms cm-2
min ML min ML min ML min ML min ML
θCs = 0.25, (2 × 2) LEED θCs = 0.43, close-packed layer
6·1014 atoms cm-2 min
3.5·1014 atoms cm-2 5.5·1014 atoms cm-2 LEED, AES AES, LEED, TDS *cleaved in air θCs = 0.4 θCs = 0.8 AES, TDS
4.2.10 Noble metals Besides the alkali metals, the noble metals (Cu, Ag, Au) are most thoroughly studied. The work-function changes reflect a larger number of effects which may occur during adsorption. The most sensitive coverage range is the monolayer, but some changes are also observed up to 10 ML. The work-function changes are mainly affected by the growth mode: pseudomorphic or not in registry, distributed single atoms or islands, cluster growth in three dimensions, layer-by-layer growth or clusters on a wetting layer (the so-called Stranski-Krastanov growth mode). These different modes depend on atomic fluxes and substrate temperature. Superimposed to these different growth modes, a change of the substrate reconstruction may occur which also may influence Φ. Obviously, work-function measurements alone can not discriminate all those different processes. The high melting metal surfaces (W, Mo, Ta) have been preferred substrates from the beginning of UHV technology in surface science, since they can easily be cleaned by high-temperature flashes. There are some interesting reviews on this topic (e.g. [85K6]). Also Figs. 30 and 31 show the richness of the observed Φ variations. As mentioned already in the introduction, Cu was selected to represent this class of adsorbates and some more figures are added to the Cu table.
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors
4.2-77
Table 97. Copper (Cu) Figs. 32...41 Ref.
Cu / Substrate 87B7 Al(111)
94H
T [K]
Method
Type
∆Φ [eV] at θ1
300
ARUPS
I
0.0 +0.4 0.0 +0.2 -1.1+ -1.4
Al(100)
300
Ir(100)
380
I FEM
III
Comments, interpretation
1 ML LEED, AES, ARUPS 4 ML 1 ML 4 ML 4...8 ML + average value 1.5...4.5 ML Cu grows as Cu(100) φ sat = 4.55 ± 0.02 eV 100
80S3
Mo(100)
300
Diode
90T
Mo(110)
300
Diode
87B5 Pd(111)* 88V 85P Pt(111)
95N
<475
450 350 84B2 Ru(0001) 540 1080 86H4 Ru(0001) 100
87P
Pt(111)
Ru(0001)* 300
88H2 Ru(0001) 85 93W3 Ru(0001) 640 93S2 94S2 94S3
Ru(0001) 640
Lando lt -Bö rnst ein New Ser ies III/42A2
II
Kelvin
III
+0.44 -0.23 -0.52 -0.2 -0.70
?
IV
-0.80
1 ML
?
I
SE edge (E)
III
-0.95 -1.0 0.75 0.60 -0.8
1 ML 1 ML θ ≥ 1*
Kelvin
Diode
IV
-1.0 -1.1 -0.9 -1.15
IV
-0.37
θ=1 θ = 1.5 θ = 2.3 θ=9 2 ML
III
-0.7 -0.75 -0.72 -0.64 -0.7
1 ML Cu 2.4 ML Cu 1 ML > 3 ML 1 ML
SE edge (E) Kelvin Kelvin
min, θCu = 1 θCu = 3.5 2 ML
quartz crystal microbalance; θ [ML] is given in relation to the number of substrate atoms, which is taken as 1.0×1015 Ir atoms cm-2. AES see Fig. 32 AES, LEED, TDS * film on mica LEED, AES T>475 K: alloy formation θ = 1: p(1×1), pseudomorphic Figs. 33 and 34
LEED, AES, TDS *from AES, annealed to 900 K following to deposition without annealing
* thick Ru(0001) film on Mo(110) LEED, AES growth mode: 2 D layer-bylayer; see Fig. 35 MDS, IRAS, TDS ∆Φ measured during Cu deposition: ∆Φ-oscillations Cu compresses oxygen on the surface.
4.2-78 Ref.
4.2 Electron work function of metals and semiconductors
85T2
Cu / Substrate Si(111)
T [K]
97V
V(100)
65M
W(110)
<670
69M
W(110)
300
73P
W(110)
300*
300
W(100)
Method ?
SE edge (UPS)
II
FEM
II
Kelvin
IV
FEM
IV
FEM
W(111)
Type
IV
∆Φ [eV] at θ1
Comments, interpretation
-0.15
0.3 ML
+0.44 +0.14 +0.54 0.25 -0.32 -0.75 -0.33 -0.85 -0.7
1 ML 2 ML 10 ML 2 ML >6 ML
LEED, AES, first 2D alloy formation then epitaxial growth of Cu LEED, AES, UPS, TDS
-0.65 -0.5
FEM
II
300
FEM
II
SE edge (E) SE edge (E)
IV
W(100)
300 (800) 300
75C
W(100)
77
FEM
II
+0.42 -0.20
76M
W(211)
300
Diode
II
0.35 0.0 -0.42 -0.28
77J2
W(100)
77J3
W(111)
400... FEM 700 500 FEM
II
W(112)
600
II
W(211)
74B3 W(110)
W(110) 77M3 W(112) 77R W(100) 79R
FEM
600 80...200 Diode 20 FEM
II
0.25 -0.3 -0.1 0.2 -0.7 -0.5 -0.80 -0.52 0.15 -0.75
II
III II II
[Ref. p 4.2-118
sat. Φ Cu(111)
strained Cu(111) film Cu(111) film * plus annealing (T not given) to spread the Cu over the tip face.
sat. Φ Cu(100)
2.0·1015 cm-2 LEED, AES, TDS 4.8·1015 cm-2 0.8·1015 cm-2 LEED, AES, TDS 1.8·1015 cm-2 0.5·1015 cm-2* µ0 = 0.5 D 1.2·1015 cm-2* * assignment of coverage by [77 R] θ1 2 θ1 3.5 θ1 8 θ1 Fig. 36
+0.4 -0.3 +0.2 +0.3 -0.9 -0.5 -0.7
θ1 4θ1 7θ1 1.5θ1 3.5θ1 5 θ1
+0.42 -0.32
0.5·1015 cm-2 1.2·1015 cm-2
W(310) similar to (112)
25·1014 atoms/cm2 Fig. 37 Fig. 38
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118] Ref.
Cu / Substrate 78B2 W(100)
81S
4.2 Electron work function of metals and semiconductors T [K]
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
78
FEM
II
Fig. 39
300... FEM 930
II
+0.16 -0.24 +0.20 f(θ1,T)
W(100) W(110) W(211) W(111) 85K6 W(110) 86C2 W(110)
800 300*
Diode Kelvin
III
87C
W(110)
300
Kelvin
III
87A2 W(100)
300
SE edge (E)
II
800 98Y2 ZnO(0001) Zn
IV SE edge (UPS)
IV
T [K]
Method
Type
300
SE edge (E)
-0.65 -0.72 -0.67 -0.72 -0.35 0.25 -0.89 -0.45 0 -0.15 +0.42
4.2-79
discussion of existing data Figs. 40 and 41
1 ML saturation θ = 1* θ=4 θ = 4** 0.5 2.0 0.5 1.0 θCu = 0.05 θCu = 1.3
µ0 = 0.7 D at 800 K LEED *annealed to 850 K LEED, AES, TDS *from AES **annealed to 850 K LEED, AES, TDS surface alloy formation reinterpretation of Bauer XPS, ISS
Table 98. Silver (Ag) Figs. 42...47 Ref. 91T3
Ag / Substrate Cu(110)
-0.1 -0.05 -0.40 -0.35 -0.22 -0.53
120
92M2 Cu(111)
300
94N
Cu(111)
95W 94H
Cu(111) Ir(100)
∆Φ [eV] at θ1
300
SE edge (E) Diode
IV III
78*
ARUPS FEM
III III
-0.35 -0.33 -0.45 -0.3 -1.05+ -1.20¹
θAg = 0.5 θAg = 1.0 θAg = 10 θAg = 0.3 θAg = 1.0 θAg = 10 min saturation 1 ML 1 ML 3...4 ML
Comments, interpretation AES, LEED
ML determination: Auger and ∆ĭ * spreaded at 442 K
2 ML φ sat = 4.63 ± 0.02 eV 100
76J
Mo(100)
300
Kelvin
IV
80S3
Mo(100)
300
Diode
II
90K
Mo(110)
370 550 850
Diode
III
Lando lt -Bö rnst ein New Ser ies III/42A2
-0.12 -0.08 +0.08 -0.10 -0.05 -0.07 -0.14
1 ML >7 ML 0.7 ML 3 ML 0.1 ML 0.1 ML 0.1 ML
AES AES also measured at 573, 863 K only low coverages; diluted disordered layer see Fig. 42
4.2-80
4.2 Electron work function of metals and semiconductors
[Ref. p 4.2-118
Type
∆Φ [eV] at θ1
Comments, interpretation
SE edge (UPS) SE edge (UPS) 310... SE edge 600 (E)
III
-0.50
1 ML
AES, UPS
III
-0.54
1 ML
III
-1.2 -1.5
1 ML 2.5 ML
82D2 Re*
300?
FEM
III
-0.55
83A2 Re-tip
350... FEM 600
IV
-0.72
— — — — — —
AES, LEED, TDS ML from TDS Stranski-Krastanov-growth: φ of the rough surface at θAg = 2 smaller than for the epitaxial ML. * The central plane of the tip is Re( 10 1 0 ). The final work function is 4.32 eV. average ∆Φ µ0 = (1.5±0.5) D *jump of Φ during spreading of Ag onto the indicated area
1 ML 2 ML 4 ML at 5 ML
TDS, XPS
θAg = 0.6
Ref. 83S3
Ag / Substrate Pt(100) Pt(997)
85P3
Pt(111)
T [K]
Method
98S4
Re(0001)
300
Kelvin
III
88P
Ru(0001) 300
Diode
ΙΙΙ
-0.80* -1.00* -0.48* -0.78* -0.70* -0.55* -1.00* -0.90* -0.60 -0.75 -0.70 −0.16
95N3 Ru(0001) 350
Kelvin
ΙΙΙ
−0.33
—
0.0±0.15 2 ML
Re( 10 1 0 ) Re( 10 1 1 ) Re( 10 2 0 )
Re( 11 2 2 )
95V
V(100)
70S
W(100)
250... SE edge 900 920 FEM
72J
W(100)
?
FEM
II
77K2 W(100) W(110)
300 300
Diode Diode
III IV
W(111)
300
Diode
IV
W(110)
300 500 300 600 800
Diode Diode Diode Diode Diode
IV
77B
W(100)
IV
-0.55 -0.35 +0.15 -0.35 -0.35 -0.87 -0.72 -0.45 -0.35 -0.75 -0.62 -0.30 -0.30 -0.25
AES; layer by layer growth; Ag(111); change in slope = transition to next layer ∆Φ measurements during Ag evaporation. At higher T change in slope of ∆Φ. AES, UPS layer growth for 2 ML
0.7 ML 1.5 ML
— — — — — 2 ML >3 ML 2.5 ML 2.5 ML >4 ML
1×1015 Ag atoms cm-2 5×1015 Ag atoms cm-2 Fig. 43
LEED, AES, TDS Fig. 44
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors
4.2-81
Ag / Substrate W(110) W(100) W(211) W(111)
T [K]
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
300 300 300 300
FEM
III III III II
various changes at annealing temperatures up to 900 K
W(110)
var.
Diode
IV
-0.8 -0.15 -0.7 +0.1 -0.3 see Fig. 45
84K2 W(211)
300 900 800 800 90 300 700 300
Diode
IV
Diode Diode Kelvin
— — III
Ref. 79S2
79K
85K6 W(110) W(211) 93Z W(110)
95D
W(110)
FEM
-0.65 -0.35 — — -0.80
— — 1 ML
see Fig. 47
µ0 = 1 D for surface gas µ0 = 0.1 D for strained Ag(111) µ0 = 0.05 D for unstrained Ag(111) 1.2×1015 atoms cm-2, AES 3 ×1015 atoms cm-2 µ0 = 0.6 D at 800 K µ0 = 0.2 D at 800 K Fig. 46
quartz crystal microbalance at Φsat: 5.25±0.25×1015 Ag atoms cm-2 θ [ML] is given relative to the number of substrate atoms which is taken as 1.0×1015 Ir atoms cm-2
Table 99. Gold (Au) Figs. 48...52 Ref. 95W 94H
Au / Substrate Cu(111) Ir(100)
83S3
Pt(100) Pt(111) Pt(997)
Lando lt -Bö rnst ein New Ser ies III/42A2
T [K]
Method
Type
∆Φ [eV] at θ1
78*
ARUPS FEM
I —
+0.6 0.10+ -0.20+ ±0.1
4 ML 1 ML 2 ML 1...5 ML
SE edge (UPS) SE edge (UPS) SE edge (UPS)
IV III
-0.45 -0.4 -0.3
1 ML 3 ML 1 ML
III
-0.25
1 ML
Comments, interpretation
quartz crystal microbalance DWĭsat: 2.25±0.18î1015 Au atoms cm-2 ɴ (ML) is given relative to the number of substrate atoms, which is taken as 1.0î1015 Ir atoms cm-2 * spreading temperature 445...520K + average value depending on spreading temperature AES, UPS
4.2-82 Ref. 77C
77C
4.2 Electron work function of metals and semiconductors Au / T [K] Substrate Re tip with 600* [11 2 0] orientation
Method
Type
∆Φ [eV] at θ1
FEM
II
0.35 0.20
θ = 1+
—
0.20
θ<1
—
-0.40
θ = 2...4
state 1, pseudomorphic film
—
-0.10
θ>4
state 2, Au(111)
—
0
θ < 2.5
—
0.20
3<θ <8
adsorbate structure incorporating Re Au(110)
—
0.40
θ>8
Re(10 1 1 ) 550*... FEM 850
Re( 10 1 0 ) 380*... FEM 940
θ = 2.5
Re(11 2 2 ) 420*... FEM 850
—
Re(11 2 0) 350*... FEM 250
—
—
θ<1
II
0.40
θ=1
0.25
θ=2
0.60 88P
Ru(0001) 300
Diode
II
0.01 -0.06
θ>4 0.7 ML 1.5ML
74Y 76J2
W(111) W(100) W(211) W(310) W(100)
FEM FEM
I I I I I
0.7 0.8 1.1 1.2 0.50
at: at: at: 0.3 ML*
I I I
0.55 0.40 0.12
— — 1 ML
I
0.40
1 ML
76R
76R2 W(110) W(211) 77B W(110) W(100)
? 77
[Ref. p 4.2-118
20...330 FEM
20 FEM 20 FEM 300... Diode 900 300... Diode 900
Comments, interpretation * temperature of spreading the evaporated Au + θ =1 is the amount of Au required to reach maximum coverage average for the whole tip see Fig. 48 Topping model can be applied: AuRe dipole, α = 10 Å3
Au(111), Φ is too high due to field reduction by the extension of the flat plane most open surface studied here, complicated behavior, surface alloy formation concluded α = 22 Å3
Au(111) AES, kinks 2D pseudomorphic island layer-by-layer growth 30·1014 atoms/cm2, µ0 = 0.6 D 25·1014 atoms/cm2, µ0 = 1.6 D 40·1014 atoms/cm2, µ0 = 3 D Au-Au interaction starts at θAu §0.25 *By comparing emission from W(111) facet with literature data µ0 = 0.7 D µ0 = 0.3 D AES, (see Fig. 49) AES, (see Fig. 50) superimposed are changes of ∆Φ due to coverage and structure
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
T [K]
Method
Type
∆Φ [eV] at θ1
78 78*
FEM FEM
I II
0.70 0.40 0.25 0.50
W(211) W(110)
78* 78*
FEM FEM
IV
-0.40 -0.17
W(110) W(100) W(211)
300 300 300
Diode Diode Diode
I I I
+0.28 +0.65 +0.25 +0.15 +0.43 0.50 0.15 0.63 —
Ref.
Au / Substrate 78B2 W(100) 78J W(100)
83P3
4.2 Electron work function of metals and semiconductors
84K2 W(211)
300... Diode 930
II
85K6 W(110) W(211) 86M W Zylinder
800 800 300
—
Diode Diode Diode
Comments, interpretation
θ = 1 ML see Fig. 51 ș=1 ș = (6.7 ± 2.5)1014 atoms cm-2 ș = 2.2 ș = 2.7 θ(Au(100)) ș>3 qualitatively similar to W(100) *measurements are performed also ș = 0.6 at higher temperatures ș=2 AES, ELS θ1 2θ1 6θ1 0.7 ML 2 ML 4 ML —
AES nearly no difference between 300 and 930 K µ0 = 0.7 D at 800 K µ0 = -0.3 D at 800 K
see Fig. 52
4.2.11 3d transition metals Table 100. Titanium (Ti) Ref.
Ti / Substrate 74B2 W
T [K]
Method
Type
FEM
∆Φ [eV] at θ1
Comments, interpretation
-0.6
Table 101. Vanadium (V) Ref. 92Z3
V/ T [K] Substrate TiO2(110)
Lando lt -Bö rnst ein New Ser ies III/42A2
4.2-83
Method
Type
∆Φ [eV] at θ1
SE edge (UPS)
IV
-0.3 +0.25 +0.5
Comments, interpretation
LEED, UPS, XPS min ML thicker layer
4.2-84
4.2 Electron work function of metals and semiconductors
[Ref. p 4.2-118
Table 102. Chromium (Cr) Ref. 93P
Cr / T [K] Substrate TiO2(110)
89B3 W(110) W(100)
100 1100
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
SE edge (He+) SE edge (SE)
IV
-1.5 min 1.8 Å -0.9 >6Å -1.3 ~0.5 ML -0.5 1 ML
LEED, XPS, LEIS
III
Fig. 53 pseudomorphic ML on both substrates at 100 K
Table 103. Iron (Fe) T [K]
Method
Type
∆Φ [eV] at θ1
82S6
Fe / Substrate Ag(100)
300
ARUPS
II
90T
Mo(110)
300
Diode
IV
85K4 MoS2
300
Diode
III
0.0 +0.75 +0.2 -0.55 -0.17 -0.45 -1.0
0.5 ML 1.0 ML 3 ML min,θFe = 2 θFe > 4 θ1 2θ1
88H3 Re(0001)
980
Diode
III
Diode SE edge (He+) FEM
III IV
-0.21 -0.26 -0.58 -1.3 -1.0 -0.6 -0.4
1 ML 2 ML 5 ML min, 1 Å >4Å
Kelvin
III (IV)
see Fig. 54
see Fig. 55 see Fig. 56.
Ref.
99K3 Ru(0001) 300 93P TiO2(110) 78J2
W(001)
97N2 W(110)
97N3 W(110) 83G2 W(110) W(112) W(111) W(001) 99K W(111)
300 600 1000
IV
90 300 300 + 600 90 ≥ 300 300
Kelvin
IV
Diode
IV
300
Diode
II
+0.03 -0.22 -0.1
Comments, interpretation UPS Stranski-Krastanov growth mode AES, LEED, TDS Phase I: island formation Phase II: reaction with substrate LEED, AES
LEED, AES LEED, XPS, LEIS at 12×1014 atoms cm-2 at 24×1014 atoms cm-2 also deposited at 600 and 1000 K without larger changes extension of Ref. [97N3]
AES kinks 1 ML = 1.4×1015 atoms cm-2 µ0 = 1.3 D (W(110)) LEED, AES, TDS 1 ML 28 ML
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors
4.2-85
Table 104. Cobalt (Co) Ref. 95W 90T
91F 96S
Co / Substrate Cu(111) Mo(110)
Pt(110) -(1 × 2) W(110) W(100) W(111)
89J
W(110) W(100)
T [K]
Method
Type
∆Φ [eV] at θ1
300
ARUPS Diode
I IV
+0.15 -0.35 0.0 +0.1 +0.2
SE edge (UPS)
III
-0.8
IV IV III II IV IV IV IV
-1.5 -0.45 -1.2 -0.55 -0.55 -0.55 see Fig. 57
µ0 = 4.6 D
Comments, interpretation
300 580 300 580 300 580 1100
SE edge (E)
Comments, interpretation
7 ML min, θCo = 0.8 AES, LEED, TDS θCo = 1.3 θCo = 1.5 θCo = 3 1 ML LEED, AES
µ0 = 3.3 D µ0 = 1.3 D strained pseudomorphic ML
Table 105. Nickel (Ni) Ref. 90T
Ni / Substrate Mo(110)
85P2
MoS2
T [K]
Method
Type
∆Φ [eV] at θ1
300
Diode
IV
-0.35 0.0 +0.23 +0.20
IV
-0.25 -0.05 -0.16 >0 -0.4 -0.3 -0.24 -0.12 -0.75
80
300 450 88B3 Ru(0001) 100* 99K3 Ru(0001) 300
SE edge (UPS) Diode
IV
84K3 W(110)
300 1100
Diode
IV
85K6 W(110) W(211) 94B W(110) W(100)
800 800
Diode Diode
W(111) W(112) 94W4 W(110)
Lando lt -Bö rnst ein New Ser ies III/42A2
IV
IV II
Kelvin
— — IV
-1.05 +0.35 -0.4 <±0.2 <±0.2 -0.75 -0.15
min, θNi = 0.8 AES, LEED, TDS θNi = 1.5 θNi = 3.5 θNi = 5
θNi = 1.0 θNi = 1.6 1 ML 2 ML
interpretation: 2D islands TDS *annealed to 700 K LEED, AES reaction occurs for W(112) at cleaved temperatures transition from pseudomorphic to coincidence lattice below 1 ML µ0 = 0.8 D at 800 K µ0 = -0.02 D
θNi = 0.45 3 ML
LEED
4.2-86 Ref. 99K
4.2 Electron work function of metals and semiconductors Ni / Substrate W(111)
[Ref. p 4.2-118
T [K]
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
300
Diode
II
+0.20 +0.05 +0.55 +0.3
LEED, AES, TDS
∆Φ [eV] at θ1
0.5 ML 1 ML 5 ML 10 ML
4.2.12 4d transition metals Table 106. Zirconium (Zr) Ref.
Zr / Substrate 71C2 (110) (112) (100) (111) (310) 80D W(100)
T [K]
Method
Type
295 295
FEM FEM
IV IV
300
Diode
1400
IV III
-1.1 -0.6 -0.5
θ1 5θ1 θZr= 0.5
Comments, interpretation φsat = 4.45 φsat = 3.92 φsat = 3.87 φsat = 3.88 φsat = 3.65 LEED, AES, TDS pseudomorphic monolayer c(2 × 2) structure
Table 107. Niobium (Nb) Ref. 79R 90A
Nb / Substrate W(100) Si(111) -(7 × 7)
T [K]
Method
Type
∆Φ [eV] at θ1
77
FEM
IV
300
SE edge (UPS)
-0.55 -0.4 +0.2 +0.2 -0.3
Type
∆Φ [eV] at θ1
Comments, interpretation
0.5 1.0 at 0.3 ML silicide at 8 ML silicide at 20 ML Nb value LEED, UPS
Table 108. Molybdenum (Mo) Ref. 95B 90A 79R
Mo/ Substrate Pt(111) Si(111) -(7 × 7) W(100)
T [K]
Method
300
Diode
300
SE edge (UPS) FEM
77
III
-0.5 -0.7 +0.15
1 ML >1 ML at 1 ML
-0.6
at 0.5 ML
Comments, interpretation
LEED, UPS reaches W value abrupt interface
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors
4.2-87
Table 109. Rhodium (Rh) Rh / T [K] Substrate 99K3 Ru(0001) 200 300 91K2 W(110) var.
Method
Type
∆Φ [eV] at θ1
Diode
III III
-0.07 ~-0.01
94K
350
Diode
IV
830
Diode
IV
1280
Diode
IV
800...12 Diode 00 200 Diode
III
500
IV
Ref.
W(110)
96K
W(110)
98F
W(011)
99K
W(111)
300
1 ML
Diode
IV
Diode
II
-0.7 +0.12 -0.55 -0.12 -0.55 -0.44 -0.4
0.6 ML 2 ML 0.8 ML 3 ML 0.8 ML 3 ML at 0.4 ML
-0.90 -0.25 -0.50 -0.25
min, θ = 0.35 θ = 1.1 θ = 0.9 θ = 1.1 1 ML 2 ML 10 ML
+0.32 +0.28 +0.9
Comments, interpretation
with LEED and ∆Φ transition 1 D – 2 D islands quasi Frank von der Moewe growth at low temperatures Stranski-Krastonov or alloying at higher temperatures
LEED metastable metal clusters
LEED, AES, TDS
Table 110. Palladium (Pd) Figs. 58 and 59 Pd / Substrate Ag(100)
T [K]
Method
Type ∆Φ [eV] at θ1
Comments, interpretation
300
IV
Ag(111)
300
SE edge (UPS) SE edge (UPS)
Al(111)
300
ARUPS
87B5 Cu(111) film on mica
420
88V2 Cu(111) 88V 300 nm film on mica 85P5 Mo(110)
Φ increases up to 8 ML Φ increases with coverage and reaches a saturation value of 5.6 eV at 8 ML which is equal to the bulk value very likely Pd diffusion into Al for the first 2 – 3 ML as con-cluded later from ARUPS data coverage by quartz oszillator Φsaturation = bulk Pd(111) Author: Similar curves found for (100)Pd/(100)Ag; (111)Pd/(110)W; (111)Pd/(110)Nb. comparison with other substrates see Fig. 9
Ref. 82S2
88F2
Lando lt -Bö rnst ein New Ser ies III/42A2
-0.3 ±0 +0.4
0.5 ML 1 ML 1 ML
IV
-0.1 +1.8
1 ML > 10 ML
Kelvin
IV
-0.25 +0.65
0.3 ML 3.5 ML
300
Kelvin
IV
-0.25 +0.65
0.2 ML > 3 ML
300
Kelvin
-0.18 0.0 +0.55 +0.60
θ1 1.5 θ1 2.5 θ1 3 θ1
I
LEED, AES, XPS
4.2-88 Ref. 98S2
4.2 Electron work function of metals and semiconductors Pd / Substrate Mo(211)
T [K]
Method
Type ∆Φ [eV] at θ1
Comments, interpretation
Diode
I
LEED, AES
100
I
300
I
800
I
80W2 Nb(110) (foil)
IV
0.2 0.52 0.07 0.7 0.08 0.48 -0.2 +0.65
1 ML* *from kinks in AES sat. at 3 ML µ0 = 0.3 D 1 ML* sat. >4 ML 1 ML* sat. >4 ML 1 ML UPS
0/
Ru(0001) 300 film on Mo(110) 99K3 Ru(0001) 300
SE edge (UPS) Diode
IV
-0.03 +0.12
~0.5 ML ~3 ML
Diode
I
86N
Si(111)(7 × 7)
SE edge
(I)
+0.04 +0.15 +0.12 +0.32
1 ML 3 ML 1 ML 2.5 ML
89R
Ta(110)
80S4
W(110)
300 830
Diode
IV IV
-0.35 0.0 +0.70 -0.45 -0.60
θPd = 0.75 θPd = 1.1 θPd = 0.5 1 ML 1 ML
81P
W(100)
300
Diode
II
0.3 0.17 0.5
85K6 W(110)
800
90Z
W(110)
900*
Kelvin
IV
-0.54 -0.38
98F
W(011)
110
Diode
IV
99K
W(111)
800 300
Diode
III II
-0.85 -0.40 -0.55 +0.25 +0.17 +0.7
88P
300
[Ref. p 4.2-118
IV
Fig. 3 2-dim. pseudomorphic islands later pseudomorphic Pd(111) LEED, AES θ = 1: 7.8·1014 atoms cm-2 (quartz oscillator) UPS
second layer metastable T > 700 K 3-dim. cluster see Fig. 58 1 ML AES, ML from kinks in AES 2 ML Also annealed to 460, 510, 620, 4 ML and 1020 K resulting in gradual changes. Behavior similar to other fcc metals on W(100); see Fig. 59 value from θ ĺ µ0 = 0.74 D 1 ML** *annealed to 900 K 1.8 ML*** **from TDS ***presumably cluster formation min,θ=0.35 LEED, metastable metal clusters θ = 1.2 1 ML LEED, AES, TDS 1 ML 2 ML 8 ML
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors
4.2-89
4.2.13 5d transition metals Table 111. Lanthanum (La) Ref. 82L2
La / Substrate Mo(112)
T [K]
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
Diode
IV
discussion of structures by LEED
77G2 W(100)
300
Diode
IV
77V
W(110)
300
Diode
IV
Mo(110)
300
Diode
IV
FN (FEM)
III
-1.8 -1.4 -1.8 -1.5 -2.5 -1.8 -1.8 -1.5 -2.8
Type
∆Φ [eV] at θ1
IV
-1.3** -0.5**
91B
W(110)*
at 0.6 ML at 1.2 ML at 0.5 ML at 0.8 ML 4·1014 cm-2 8·1014 cm-2 6·1014 cm-2 8·1014 cm-2 at 1 ML
at higher T up to 1350 K the minimum is more shallow on 0.3 eV LEED, AES; µ0 = 4.5 D LEED, AES; µ0 = 3.9 D also for (111) and (112) plans
Table 112. Hafnium (Hf) Ref. 94S
Hf / T [K] Method Substrate W tip with 300* FEM (111) center
θ1 6θ1
Comments, interpretation *measured at 300 K after spreading of Hf at 1300 K **average value
Table 113. Tantalum (Ta) Ref. 79R 90A
77K
Ta / Substrate W(100) Si(111) -(7 × 7)
T [K]
Method
Type
∆Φ [eV] at θ1
77 300
FEM SE edge (UPS)
III
-0.65 +0.22 +0.2 -0.45
W(110)
0.5 ML at 5 ML at 3 ML at 30 ML
FEM
Comments, interpretation
silicide silicide Nb value LEED, UPS µ0 = 0.5 D
Table 114. Tungsten (W) Ref.
W/ Substrate 86A Si(111) -(7 × 7) 90A Si(111) -(7 × 7) 75B2 W(110) 76B 77K
Lando lt -Bö rnst ein New Ser ies III/42A2
T [K]
Method
300
SE edge (UPS) SE edge (UPS) Kelvin
300
FEM
Type
∆Φ [eV] at θ1
Comments, interpretation
+0.28
UPS, LEED sharp interface at 300 K LEED, UPS reaches W value abrupt interface This change of Φ decreases with decreasing terrace width. µ0 = 0.2 D
+0.36
at 3 Å thickness at 2 ML
-0.6
θW = 0.5
4.2-90
4.2 Electron work function of metals and semiconductors
[Ref. p 4.2-118
Table 115. Rhenium (Re) Ref. 96S6 77K
Re / Substrate Si(111)(7 × 7) W(110)
T [K]
Method
400
Type
∆Φ [eV] at θ1
Comments, interpretation
I
+0.6
UPS, XPS sharp interface, µ0 = 0.11(5) D µ0 = 0.1 D
Comments, interpretation
FEM
Table 116. Iridium (Ir) Ref.
Ir / Substrate 79R W(100) 77K W(110) 91K2 W(110)
T [K]
Method
Type
∆Φ [eV] at θ1
77
I
0.8
var.
FEM FEM Diode
350*
Diode
IV
450* 77K 96K
W(110) W(110)
FEM 1100... Diode 1500
-0.55 -0.2** -0.3 -0.15**
0.5 ML
0.25 ML 0.75 ML 0.35 ML 1 ML
µ0 = 0.0 D with LEED and ∆Φ transition 1 D – 2 D islands *also annealed at 1250 K and 1650 K **no saturation
>-0.1
µ0 = 0.0 D LEED
Table 117. Platinum (Pt) T [K]
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
300, 1300 350
Diode
I
0.78
LEED, AES
PE-Kante IV
77K W(110) 91K2 W(110)
var.
FEM Diode
94 K
W(110)
400
Diode
IV
96K
W(110)
880... 1240
Diode
III
Ref. 98S2
Pt / Substrate Mo(211)
87A
Re(0001)
-0.1 +0.6
ML 1 ML
Pt grows epitaxially µ0 = 0.0 D LEED and ∆Φ indicate transition from 1D to 2D islands
-0.4 +0.5 >-0.1
ML 2 ML up to 1.5 ML
LEED
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors
4.2-91
4.2.14 Rare-earth metals Table 118. Neodymium (Nd) Ref.
Nd / Substrate 87N2 Cu(100)
88N5 Cu(111)
92S2
Mo(112)
92S5
87G
T [K]
Method
Type
∆Φ [eV] at θ1
300
?
III
-2.0
1.3 ML
III III III
-1.7 -1.4 -2.0 -1.7 -1.7 -1.6 -1.2 -1.3 -1.4 -1.9 -1.25 -1.45
1.3 ML 1.3 ML at 2.5 θ1 at θ1 at 2.5 θ1 0.5 ML 1.2 ML 1.2 ML 1.2 ML 4·1014 cm-2 7.5·1014 cm-2 12·1014 cm-2 0.5 LEED 1.0
550 800 300 900*
SE edge (UPS) Diode
IV
Mo(110)
300 300 600 900 300
(Diode)
IV
W(112)
300
Diode
IV
-1.8 -1.5
Comments, interpretation θ by kinks in Auger different sub ML phases Frank von der Marwe growth alloy formation alloy formation LEED, AES, ARUPS *annealed to
Table 119. Samarium (Sm) T [K]
Method
Type
∆Φ [eV] at θ1
89J3
Sm / Substrate Cu(111)
300
Diode
III
87S2
Mo(110)
300
Diode
IV*
88F 95R
Pd(100) Ru(0001) 500
Diode SE edge (UPS)
III IV
-1.9 -1.9 -2.2 -2.4 -1.5 -2.4 -2.2 -2.4 -2.2 -2.4
Ref.
θSm = 0.4 θSm = 1.0 θSm = 2.0 0.2 ML 1.0 ML 3 ML ? 0.3 ML 0.8 ML 3.0 ML
Comments, interpretation AES, LEED
*special: local maximum at 1 ML
valence charge = 2.75 at surfaces UPS
Table 120. Gadolinium (Gd) Ref. 97L
Gd / Substrate Mo(112)
T [K]
Method
Type
∆Φ [eV] at θ1
300
SE edge (E)
IV
-1.4 -0.8 -1.5 -1.2 -2.6
1100 76B5 W tip
Lando lt -Bö rnst ein New Ser ies III/42A2
FEM
1 ML 2 ML 1 ML 2 ML ?
Comments, interpretation LEED
specific discussion for W(111), (110), (121)
4.2-92
4.2 Electron work function of metals and semiconductors
Ref.
Gd / Substrate 86K2 W(110)
87G
W(112)
T [K]
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
300
Diode
IV
0.33 ML 0.66 ML
Auger, LEED, TDS
1200 300
Diode
IV
-2.5 -1.8 § -1.6 -1.4
0.5 ML 1.0 ML
linear chains of adatom for θ < 1 LEED, ordered structure
-2.1 -1.5 -1.3 -0.8 -1.7 -1.5 -1.7
5·1014 cm-2 7·1014 cm-2 5·1014 cm-2 Typ IV ĺ,,,DWKLJK7 8·1014 cm-2 4.5·1014 atoms cm-2 7.5·1014 atoms cm-2 9 ·1014 atoms cm-2
88G2 W(111) 91M2 W(100) 99S
[Ref. p 4.2-118
Diode 300 1200
Diode
IV
FEM
IV
T [K]
Method
Type
∆Φ [eV] at θ1
300
CPD
IV
300 up to 1050 300
Diode
IV
-1.9 -1.45 -1.55 -2.9 -2.7
4·1014 cm-3 8·1014 cm-3 13·1014 cm-3 0.5 ML 0.7 ML
Diode
IV
-2.8 -2.0 -1.7 -1.5
0.6 ML LEED, AES, TDS 1.0 ML 5·1014 cm-3 Typ IV ĺ,,,DW. 7·1014 cm-3
IV
-1.4 -0.9
5·1014 cm-3 Typ IV ĺ,,,DWKLJK7 8·1014 cm-3
Type
∆Φ [eV] at θ1
W(111)
Table 121. Terbium () Ref. 92S5
Tb / Substrate Mo(110)
85K
W(211)
86K2 W(110) 88G2 W(111)
91M2 W(100)
300 Ļ 1200 300 Ļ 1200
Diode
Diode
Comments, interpretation AES, LEED quartz microbalance Fig. 4 Auger, LEED, TDS electropositive material
Table 122. Dysprosium (Dy) Ref. 91P4
Dy / Substrate Mo(110)
T [K]
Method
300
Kelvin
-1.9 -1.2 -1.4
4·1014 atoms cm-2 7·1014 atoms cm-2 >12·1014 atoms cm-2
Comments, interpretation LEED, AES also at 850 K
Table 123. Holmium (Ho) Ref. 89G
Ho / Substrate W(112)
T [K]
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
300
Diode?
IV
-1.9 -1.3
LEED
0.5 ML 1.1 ML
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors
4.2-93
Table 124. Erbium (Er) Ref. 92S5
95K 95S6
Er / Substrate Mo(110)
T [K]
Method
Type
∆Φ [eV] at θ1
300
CPD
IV
III
4·1014 cm-2 7·1014 cm-2 12·1014 cm-2 5 Å Er
µ0 = 1.9 D
Kelvin
-1.85 -1.35 -1.45 -1.6
Kelvin
III
-1.1 -1.7
1 ML 9 ML
XPS µ0 = 1.1(5) D intermixing at higher T
T [K]
Method
Type
∆Φ [eV] at θ1
300
Diode
IV
-1.7 -1.55 -2.0
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
Diode
IV
-2.4 -1.8
0.5 ML 1 ML
AES, LEED (1 ML: 0.55 substrate units)
Diode
IV
0.6 ML 1 ML 0.6
AES, LEED
III
-1.75 -1.65 -0.6
300 αSiC(0001) Si(100) 230
Comments, interpretation
Table 125. Thulium (Tm) Ref. 92N
Tm / Substrate Mo(110)
Comments, interpretation
0.8 ML ML 2.5 ML
Table 126. Yterbium (Yb) Ref.
Yb / Substrate Mo(110)
87S4 also in 87S3 97K2 Si(111)
T [K]
300 800
Si forms a step layer
4.2.15 Group IIa metals Table 127. Beryllium (Be) T [K]
Method
Type
∆Φ [eV] at θ1
79Z
Be / Substrate W(110)
300*
Diode
IV
91D
W(100) W(112)
300* 300
FEM
I II
-0.75 -0.50 +0.28 +0.4 -0.6 0.0
Ref.
Lando lt -Bö rnst ein New Ser ies III/42A2
at θ1 at 2 θ1 saturation 1 ML saturation
Comments, interpretation *measured also at higher T
4.2-94
4.2 Electron work function of metals and semiconductors
[Ref. p 4.2-118
Table 128. Strontium (Sr) Ref. 77V
Sr / Substrate Mo(110)
T [K]
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
300
Diode
IV
W(110)
300
Diode
IV
-2.6 -2.0 -3.3
0.25 ML 1.0 ML 0.3 ML
-2.1
1.0 ML
IV
-2.1 -1.8
IV
-2.9 -1.9
4·1014 cm-2 7·1014 cm-2 = ML 0.3 1.0
LEED, AES µ0 = 5.1 D LEED, AES µ0 = 5.1 D several ordered structures µ0 = 6.6 D LEED, structures in sub-ML regime discussed
79M
Mo(112)
73K
W(110)
Diode
77, 300 FEM
Table 129. Barium (Ba) Ref.
T [K]
Method
Type
∆Φ [eV] at θ1
300
Kelvin
IV
-2.3 <2.15 -3.0 -2.4
93V
Ba / Substrate Ag(111)
91L
Cu(111)
70B
Mo(110)
81M
Mo(112) Diode Re(10 1 0) W(112)
IV 300
4.5·1014 cm-2 12·1014 cm-2 min at θ1 ML at 3θ1
IV
θmin = 2.3 eV θsat = 2.9 eV
IV
Comments, interpretation
UPS Φmin = 2.3 eV Φsat = 2.7 eV in russian language coverages from LEED and structures; same result for all three substrates 3·1014 atoms cm-2 6·1014 atoms cm-2 LEED, ELS AES, LEED, TDS
98G2 Mo(110)
Diode
IV
-3.0 -2.3
min
95V2 Ni(110)
Diode
IV
-3.2 -2.7
82L3 Re(10 1 0) FEM? 90H3 Si(100) 300
SE at XPS IV
94V
Diode
-2.8 -2.6 -2.5 -2.2 -2.9 -2.6 -2.3
at θ1 at 2θ1 θmin = 2.0 eV 2 ML 4 ML 1 ML 2 ML 2 ML 3 ML 0.6 ML
III
-1.9
θBa = 0.6
Dimers remain in sub ML become symmetric at 1 ML and silicides start to form. LEED, UPS
IV
-2.6
5·1014 cm-2 = 1 ML > ML
(θmin = 2.3 eV) (θsat = 2.7 eV) in Russian language
96W 98C
Si(100) -(2 × 1) Si(111)(7 × 7) Si(100) -(2 × 1)
99K2 Si(100) -(2 × 1) 69F W(100)
IV
SE edge IV (E) (SE edge)
1140 300
SE edge (UPS) ?
-2.1
ML: 6.8·1014 atoms cm-2
LEED
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118] Ref.
Ba / Substrate 74G2 W(110)
4.2 Electron work function of metals and semiconductors T [K]
Method
300
?
Type
∆Φ [eV] at θ1
Comments, interpretation
IV
-3.5 -2.6
2.35·1014 cm-2 5.5·1014 cm-2
FEM
IV
-3.6 -2.7
2.4·1014 cm-2 5.5·1014 cm-2
77G3 W(110)
Diode
IV
92L
Diode
-3.1 min -2.5 ML -2.1 -1.7 -2.7 -2.4
2.2·1014 cm-2 5.5·1014 cm-2 1 ML >2 ML 4·1014 cm-2 6·1014 cm-2
75G
W(110)
300
W(100)
73M2 W(112)
77
Diode
IV
4.2-95
LEED, linear branches in the ij FXUYH Φmin = 2.0 eV Φsat = 2.5 eV Φmin = 2.0 eV Φmax = 2.9 eV interaction with co-adsorbed Si µ0 = 13.5 D, LEED LEED, IPES LEED
4.2.16 Group IIIa metals Table 130. Aluminum (Al) Method
Type
∆Φ [eV] at θ1
SE edge (E)
III
91K3 Mo(110)
Diode
IV
90D
1 ML 2 ML 4 ML θ1 >θ1 2 ML
Ref. 92P
Al / Substrate Ag(111)
T [K]
Kelvin
III
98S
Pd(111) on mica Pd(100) 325
-0.2 -0.3 -0.38 -0.47 -0.44 -1.3
Kelvin
III
-1.3
2 ML
96P2
Re(10 1 0) 300
Kelvin
III
-1.2
1.3 ML
96K4 Ru(0001) 300
Kelvin
III
84P3
PYS
III
-0.8 -1.2 -0.45
1 ML 2.5 ML 1 ML
74M2 W
FEM
IV
-0.4* -0.3*
θ1 θ2
74M8 W tip
FEM
IV
-0.2 -0.15
at 2 θ1 at 3 θ1
Si(111) -(2 × 1)
Lando lt -Bö rnst ein New Ser ies III/42A2
300
Comments, interpretation LEED, AES
Stranski-Krastanov growth mode for θ > 2 ML; µ0 = 0.29 D At low θAl surface disordered. Alloying for T at 750...950 K. AES, LEED, TDS dips in ∆Φ at specific LEED structures STM LEED: (2 × 1) ĺ ¥3 × ¥ ĺ × 1) AES Problem: 0xygen growth with time and number of Al-doses. *average W(001) and W(111) show complicated dependencies
4.2-96
4.2 Electron work function of metals and semiconductors
[Ref. p 4.2-118
Table 131. Gallium (Ga) Ref.
Ga / Substrate 85K5 W(100)
T [K]
Method Type
∆Φ [eV] at θ1
700...1600 FEM
Comments, interpretation nearly constant at 4.5 eV (?)
Table 132. Indium (In) Ref. 96R
In / T [K] Substrate Au(111) 300
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
SE edge (E)
III*
-0.7
LEED, AES A disordered AuIn2 compound is formed. *from Ref. [ ]
Comments, interpretation
4.2.17 Group IVa elements For Carbon (C) see Table 6 and 7. Table 133. Silicon (Si) Si / Substrate 71C3 W(100)
T [K]
Method
Type
∆Φ [eV] at θ1
295
FEM
II
+0.55 +0.2
73B3 W(110)
300
Diode
III
Ref.
θ1 5θ1 LEED
Table 134. Germanium (Ge) T [K] Method
Type
∆Φ [eV] at θ1
Comments, interpretation
300
IV
n- and p-type
III I
-1.1 -1.0 -0.5 -0.45 -0.10 -0.08 -0.3 +0.65
Mo average 900* FEM
I
+0.85
W
I
+0.28
Ref.
Ge / Substrate 85K2 InP(110) 92B
Nb tip 300 (110) center 92S4 Si(100) -(2 × 1) 73B3 W(110) 300 73Z W average 900*
83Z
500
Kelvin
FEM IV probe hole Diode IV Diode FEM
FEM
0.4 ML >2 ML θGe = 1 θGe = 2 1 ML 3 ML >2 ML
LEED, AES LEED *spreading temperature final value: Φ = 5.2 ± 0.1 *spreading temperature final value: Φ = 5.2 ± 0.1
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors
4.2-97
Table 135. Tin (Sn) T [K]
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
91Z
Sn / Substrate Au(111)
300
SE edge
III
-0.9
1 ML
88T
Mo(110)
350
Diode
IV
-0.2 -0.9
0.2ML 0/ Fig. 7
300
PYS
+0.5
1 ML
AES AuSn forms which grows laterally as a double layer AES, LEED, TDS Stranski-Krastanov growth after 2 ML alloying at 600 K, repulsive interaction in ML. AES, LEED
300
PYS
III
-0.25
2 ML
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
SE edge (E)
III
-0.48
2 ML
LEED
III
-0.6 -0.45 -0.4 -0.36 -0.78 -1.5
1 ML 1 ML 0.7 1.0 2.5 1 ML
LEED, AES
+0.15 -0.3 -0.13 0 -0.2 -0.1 -0.45 -0.40 -0.15 0.0 -0.17 -0.13
3·1014 atoms cm-2 22·1014 atoms cm-2 3·1014 atoms cm-2 Â14 atoms cm-2 3·1014 atoms cm-2 10·1014 atoms cm-2 5·1014 atoms cm-2 8·1014 atoms cm-2 6·1014 atoms cm-2 surface reconstruction at Â14 atoms cm-2 800 K 3·1014 atoms cm-2 *deposition temperature 10·1014 atoms cm-2
Ref.
85T4
Si(111) -(2 × 1) 87A3 Si(100) -(2 × 1)
LEED, AES, PYS layer growth till 2 ML, then Stranski-Krastanov growth. Between θGe = 0.5...1.0 ML a (2 × 1) ĺ × 1) structure transition occurs.
Table 136. Lead (Pb) Ref.
Pb / Substrate Ag(111)
T [K]
300
88T
Cu(111) Cu(100) Mo(110)
300
Diode
IV
92M
Pt(111)
300
Kelvin
I
77J
W(211)
526
FEM
II
W(100)
463
FEM
IV
843
FEM
IV
W(110)
290
FEM
IV
W(100)
300*
FEM
IV
80T 84A
78J2
800*
Lando lt -Bö rnst ein New Ser ies III/42A2
IV
LEED, AES
After ML formation intermixed region occurs at the Pb/Pt interface
4.2-98
4.2 Electron work function of metals and semiconductors
[Ref. p 4.2-118
4.2.18 Group Va elements Table 137. Antimon (Sb) Ref.
Sb / Substrate 93M2 Au(111) 92E
T [K]
Method
300
GaAs(110) cleaved
Type
∆Φ [eV] at θ1
IV
-0.8 -0.7
Comments, interpretation
θ1 >2θ1
Kelvin
p-type
300
I
+0.5
1 ML
n-type
300
I
+0.6
0.4 ML
p-type
90
I
n-type
90
I
+0.75 +0.5 +0.66 +0.6 +0.7
5 ML 1 ML 10ML 1 ML 4 ML
control by electric field induced Raman spectroscopy from which band bending is derived no dipole contribution, only band bending no dipole contribution , only band bending 0.55 dipole contribution 0.25 dipole contribution 0.3 dipole contribution 0.3 dipole contribution 0.45 dipole contribution
Table 138. Bismuth (Bi) Ref. 90P
Bi / Substrate Au(111)
T [K]
82C4 Bi(0001)
Method
Type
∆Φ [eV] at θ1
SE edge (E)
III
-1.5
SE edge (E)
-1.0
86P
Pt(111)
640
IV
93G
Pt(110) (1 × 2)
150
III
-2.05 -1.98 -1.2
Comments, interpretation
1 ML
LEED, AES Bi forms monolayer followed of Bi-Au compound at the interface 3 ML AES linear decrease of ∆Φ ĺ subsurface O 0.75 ML* *adsorbate 1 ML* LEED, AES, TDS
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors
4.2.19 Other elements Table 139. Mercury (Hg) Ref. 68S
Hg / T [K] Method Substrate Mo tip with FEM (110) center
90S3
Ni(111)
68S 78J3
W tip with (110) center W(100) 295
92Z4
W(110)
Type
∆Φ [eV] at θ1
II
+0.4 +0.4 +0.1 -0.37
θHg = 0.2 θHg = 0.6 θHg = 1.8 12 L
+0.4 +0.3 +0.12(2) 0.0 -0.75 -0.65
θHg = 0.3 θHg = 0.75 θHg = 0.75 LEED, AES θHg = 1.0 4 ML LEED, TDS > 5 ML
SE edge (UPS) FEM
III II
Diode
II
Kelvin
IV
Comments, interpretation
LEED, UPS
Table 140. Uranium (U) T [K]
Method
Type
∆Φ [eV] at θ1
Comments, interpretation
68C
U/ Substrate W
300*
FEM
IV
*annealed to T > 1040 K
71C
W(100)
300*
W(110)
FEM IV probe hole IV
W(111)
IV
W(112)
IV
W(113)
IV
W(116)
IV
-1.3 -1.1 -1.0 -0.75 -1.20 -1.15 -1.25 -0.77 -1.75 -1.15 -1.1 -0.9 -0.95 -0.7
Ref.
Lando lt -Bö rnst ein New Ser ies III/42A2
min ML θ1 6θ1 θ1 2θ1 θ1 6θ1 θ1 3θ1 θ1 3θ1 θ1 2θ1
*deposition temperature
4.2-99
Figures for 4.2 0.5
Pd(110)Xe
Ni(110)D 2 Work − function change ∆Φ [eV]
Work − function change ∆Φ [eV]
0 − 0.2
a
b
− 0.4 c − 0.6
0.4
0.3
0.2
0.1
−0.8 2
1
3 5 4 Xe exposure L [Langmuir]
6
Fig. 2. Xe adsorption on Pd(110) at 77 K. (a) work-function change, (b) Xe Auger peak-to-peak amplitude, (c) Xe overlayer LEED beam intensity vs. Xe exposure. From [71P]. 0.8
4
0.4 β2 β1
D2 pressure p [arb.units]
Work − function change ∆Φ [eV]
0.5
α
0.6 0.8 1.0 1.2 D2 coverage θ [ML]
1.4
1.6
0.20
6
0.2
0.4
Ni(111)H
0.6
0.3
0.2
Fig. 3. Work-function change ∆Φ vs. coverage θ for D2 adsorption on Ni(110). T = 175 K, θ = 1 ML Ł·1015 atoms cm-2. From [87J]
8
Ni(110)D 2
0.7
0
7
2
Work − function change ∆Φ [eV]
0
0.15
0.10
0.05
0.1 0 190
230
270 310 Temperature T [K]
350
0 390
Fig. 4. Thermal desorption spectrum and work-function change for desorption of D2 from Ni(110). Initial coverage = 1.5 monolayer; adsorption temperature = 175 K; heating rate 0.5 K s-1.From [87J].
0
0.2
0.4 0.6 H coverage θ [ML]
0.8
1.0
Fig. 5. Work-function change caused by H2 adsorption at 150 K on Ni(111) as a function of the absolute coverage θ. From [79C2].
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors 0.24
0.25
Pd(100)H
0.20
Work − function change ∆Φ [eV]
Work − function change ∆Φ [eV]
Pd(100)H
0.15
0.10
0.05
0.5
1.0 H coverage θ [ML]
2.0
1.5
Fig. 6. Hydrogen adsorption on Pd(100). Calculated coverage dependence of work-function change (filled circles) and experimental results (crosses) from Ref. [80B4]. The work functions were calculated for ordered structures where the hydrogen occupies surface hollow sites up to θ = 1 followed by an occupation of subsurface (Oh) sites by the additional hydrogen atoms. From [94W], [94W2].
0.12 0.08
0.2
0.4
1.2
1.0 0.6 0.8 H coverage θ [ML]
1.4
Fig. 7: Work-function change for H on Pd(100) with coverage θ. From [80B4].
1.0
Pt(100)H2 Tad = 100K
a1
a2
b
0
− 0.1
Work − function change ∆Φ [eV]
0.2 0.1
W :H 2
0.8
H 2 desorption rate
Work − function change ∆Φ [eV]
0.16
0
0.4
− 0.2
0.20
0.04
0
0.3
4.2-101
W(100)
0.6 W(211) 0.4 0.2 W(111)
0 − 0.2
W(110)
− 0.4 − 0.6
100
300 200 Temperature T [K]
400
500
Fig. 8. Thermal desorption spectra (upper curve) and work-function change (lower curve) for 5 L H2 adsorbed on the (1 × 1)-like structure of Pt(100) at 100 K. The most prominent peaks are labeled a1, a2, and b, respectively. No hydrogen desorption below 100 K could be detected. A work-function change of 0 eV corresponds to the work function of the clean hexrot surface (Φ = 5.75 eV). From [91P3].
Lando lt -Bö rnst ein New Ser ies III/42A2
0
0.2
0.4 0.6 H 2 coverage θ [ML]
0.8
1.0
Fig. 9. Work-function change vs. coverage for H2 on W(110), W(100), W(211), and W(111). From [74B].
4.2-102
4.2 Electron work function of metals and semiconductors
[Ref. p 4.2-118
5.3
0
5.3
−0.1
5.2
−0.1
5.2
− 0.2
5.1
− 0.2
5.1
− 0.3
5.0
− 0.3
5.0
− 0.4
4.9
− 0.4
4.9
0
− 0.5
0
5
10
a
15 20 25 H 2 exposure L [L]
30
35
40
− 0.5 0
4.8
40
b
80 120 H 2 exposure L [L]
Work function [eV]
Work − function change ∆Φ [eV]
Work function [eV]
Work − function change ∆Φ [eV]
W(110)H 2
4.8 200
160
Fig. 10. Work function and work-function change vs. exposure in Langmuir of H2 for hydrogen adsorption on clean W(110) at 90 K. (a) shows the region from 0 to 40 L and (b) the entire curve. From [97N].
1.0
0.6
Pt(111)0 0.5
0.8
Work − function change ∆Φ [eV]
Work − function change ∆Φ [eV]
Au(111)0
0.6
0.4
0.2
0
0.4 0.3 0.2 0.1
0.2
0.4
1.0 0.6 0.8 O coverage θ [ML]
1.2
1.4
Fig. 11. Work-function change measured as a function of oxygen coverage. The solid curve is a fit for the data using equation (7’). The authors consider that the first steep increase in Φ could be due to lifting of the clean Au(111) surface reconstruction. The remainder range 0.1<θ0<1 ML is than nearly linear with a dipole moment of 0.12 D similar to the value for Pt(111) of µ = 0.115 D [89P2]. From [98S3]. Equation (7’):
∆Φ =
0
0.2
0.4 0.6 O coverage θ [ML]
0.8
1.0
Fig. 12. Work-function change of Pt(111) plotted as a function of oxygen coverage. The plot exhibits no change in slope for the entire range of oxygen coverage studied. The surface is exposed to NO2 at 400 K. From [89P2].
3.77 ⋅ 10−15θµ 1 + 9αθ 3 / 2
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors
100
70
Pt(111)Cl 60
0.5
50
0.4 0.3
40 0.2 (√3×√3)R30°
20
0.1
AUGER signal I [arb.units]
60
Work − function change ∆Φ [eV]
AUGER signal I [arb.units]
80
0.4
(3×3)
0.3 40 0.2
30 20
0.1 10 0
0
0
0 1 2 Cl exposure L [L]
0
3
0
Fig. 13. Work-function change (solid line) and chlorine AES signal at 181 eV (dashed line) as a function of Cl exposure in L units of the Pd(111) surface at 300 K. LEED structure indicated. From [80E].
Ni(110) 6.25
CO
6.00 5.75
O
5.50
2 Cl exposure L [L]
5.25 Coverage θ [ML]
4.75 4.50 0
N2 1.0
3.0 2.0 Exposure L [L]
4.0
d
c 1000
500
0 1.0
1.0 b
0.5
0.5
5.0 0
0 0
Fig. 15. Work function vs. exposure for CO, O2, and
N2 on Ni(110) at 20 K. The values are taken from the secondary electron threshold of the UP spectra. The arrows indicate first appearance of physisorbed species in the UP spectra. From [82H].
Lando lt -Bö rnst ein New Ser ies III/42A2
− 0.1
Ni(110)CO
1500
a
5.00
3
Fig. 14. Work-function change (solid line) and chlorine AES signal at 181 eV (dashed line) as a function of Cl exposure in L units of the Pd(111) surface at 300 K. LEED structure indicated. From [80E]. Work − function change ∆Φ [eV]
6.50
1
Work − function change ∆Φ [eV]
0.6
1
2 3 4 5 CO exposure L [L]
0
Relative sticking coefficient s/s0
Pd(111)Cl
Work − function Φ[eV]
4.2-103
0.5 1.0 CO coverage θ [ML]
Fig. 16. CO adsorption on Ni(110) at 130 K. (a) Exposure-coverage calibration; (b) relative sticking coefficient s/s0 as f(coverage); (c) ∆Φ as f(exposure); (d) ∆Φ as f(coverage). From [85B3].
4.2-104
4.2 Electron work function of metals and semiconductors
1.5
90 K
Ni(111) CO Work − function change ∆Φ [eV]
[Ref. p 4.2-118
1.0 288 K cooling experiments at θCO = constant 0.5
Fig. 17. Work-function changes obtained following CO adsorption on Ni(111) at 90 K and 288 K, respectively. The open circles show the initial and final ∆Φ value obtained upon cooling the CO overlayer from 288 to 90 K at constant coverage. From [88S2].
0 0.2 0.4 CO coverage θ [ML]
0
Pt(110)CO
580
Tem p
erat
ure
T [K
]
620
0.6
540
620
0
540 520
− 0.4
500 480
− 0.6 1 2 3 CO pressure p [10 −4 Torr]
erat
− 0.2
ure T [K ]
600 580 560 Tem p
Work − function change ∆Φ [eV]
500
Fig. 18. Work-function change of the Pt(110) surface vs. CO pressure and T at constant oxygen pressure of 5.2·10-4 Torr. Vertical bars indicate the maximum amplitude of oscillations obtained at the respective temperature. Temporal oscillations in the catalytic CO oxidation on Pt(110) under isothermal conditions in a flow reactor were detected and recorded by means of work function measurements between 440 and 590 K and in a pressure range between about 10-5 and 10-3 Torr. A large variety of oscillation forms, including well-defined transitions from periodic to irregular oscillations, was found, depending on the choice of partial pressures and temperature. LEED studies demonstrated that the oscillations occur near the completion of the CO induced 1×2 and 1×1 structural transformation of the surface. Slight variation of the parameters led to period doubling and transition to irregular behavior. From [86E].
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors
0.6
1.4
0.5 (741) (430) 0.4
(321) (320) (520)
0.3
a
(310)
5.15 5.30 5.20 5.25 5.35 Work function of clean surface Φ [eV]
(430)
Rh :CO
Pt :CO Work − function change ∆Φ [eV]
Work − function change ∆Φ [eV]
(210)
0.2 5.10
4.2-105
1.3 (321) (210)
1.2
(320)
1.1
(520) (310)
1.0
0.9 4.60
5.40
(531)
b
4.65 4.70 4.75 Work function of clean surface Φ [eV]
4.80
Fig. 19. Work-function change ∆ΦCO after saturated CO adsorption at 300 K. ∆ΦCO vs. work function of corresponding clean surface area {hkl}. Symbols indicate terrace structure. Dashed line represents linear regression line. (a) Platinum. Intercept, A0 = 5.2 ± 0.2 eV; slope, A1= -0.92 ± 0.04; r = 0.997, without {210} and {320}. (b) Rhodium. Intercept, A0 = 6.9 ± 0.9 eV; slope, A1= -1.2 ± 0.2; r = 0.97, without {430} and {321}. From [90L].
1.6
0.8
X :CO
Ru(0001) CO
FEM tip average
X = Rh
0.6
1.2 Pd
CO coverage θ [ML]
Work − function change ∆Φ [eV]
Rh
0.8 Ir
Pt Pt
0.4
0.4
Pt 0.2
0 4.60
5.00 5.20 4.80 Work function of clean surface Φ [eV]
5.40
Fig. 20. Work-function change after saturated CO adsorption at 300 K for different fcc metals vs. work function of corresponding clean surface. The plotted values represent measurements in which the {210} ([90L] and [81N3]) directions dominate (only for clean Pd was a general average value used). Dashed line represents linear regression line: intercept, A0 = 8 ± 1 eV; slope, A1= -1.4 ± 0.2; r = 0.97. From [90L].
Lando lt -Bö rnst ein New Ser ies III/42A2
0
0.6 0.2 0.4 Work − function change ∆Φ [eV]
0.8
Fig. 21. Calibration of the work-function change induced by CO adsorption of Ru(0001) vs. coverage at 200 K; relative coverage taken from integration of TPD traces; absolute calibration at θ = 0.33 by comparison with LEED. From [83P2].
4.2-106
4.2 Electron work function of metals and semiconductors
0
[Ref. p 4.2-118
0
− 0.5
Work − function change ∆Φ [eV]
Work − function change ∆Φ [eV]
Ru(0001) NH 3
−1.0 −1.5
−2.0 −2.5 0
0.2
0.6 0.4 NH3 coverage θ [ML]
2− O2 T = (90 K)
2 H2O exposure L [L]
3
4
Fig. 23. Work-function decrease due to water adsorption on Cu(110) and Cu(111). The initial dipole moments are 0.85 and 0.5 Debye, respectively. From [83B4].
Ru(0001) H2O
15
0.5 Work − function change ∆Φ [eV]
1
0
Pt(110)X
O (90→300 K) 0 NO (90 K)
0
Work − function change ∆Φ [eV]
0
Exposure L [1015 impacts cm−2] 9 3 12 6
Cu(110) H2 O
−1.0
0.8
Fig. 22. Work-function change for NH3 on Ru(0001) at 80 K as function of NH3 coverage. From [83B5].
Cu(111) H2 O
− 0.5
O2 (20 K)
− 0.4
− 0.8
− 0.5 NO (20 K) −1.0
−1.2 0
3 1 2 H2O exposure L [10− 6 mbar s]
4
5
H2O (90 K) 0
5 Exposure L [MLE]
10
Fig. 25. Work-function change upon H2O adsorption on Ru(0001) at 120 K. From [91P].
Fig. 24. Work-function change upon exposure for O2, H2O, and NO on Pt(111) at low temperature. The single points O 22 - (90 K) and O (90ĺ K) are for a saturated O 22 - layer at 90 K, and after annealing it to 300 K. An exposure of 1 MLE corresponds to 1.5·1015 impacts per cm2. From [89R].
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors
0
0
Ni(110) Na, K, Cs T = 300K Work − function change ∆Φ [eV]
Work − function change ∆Φ [eV]
Al(100) Na
−1 3.2D −2
−3
ionic
0
0.1
“ML”
0.2
0.4 0.5 0.3 Na coverage θ [ML]
1
−1
Cs
−2
Na K
−3
−4
2
Fig. 26. Sodium induced work-function changes. Circles represent data points for an unannealed overlayer and triangles values after annealing or high temperature adsorption. Porteus data (diamonds) were obtained at room temperature [74P]. 3.2 D is calculated from a least square fit in the ionic regime. θNa = 0.50, c(2 × 2), is defined as monolayer coverage “ML”. The sodium coverage is calculated from the integrated thermal desorption spectra. From [87P2].
0
0.2
Work − function change ∆Φ [eV]
T = 140 K
−1.0 (√3 × √3) R30° −1.5
(2 × 2)
Φ max
−2.0
1.4
ring
0
Al(111) Rb − 0.5
1.2 0.4 0.6 0.8 1.0 Coverage θ [1015 atoms cm−2 ]
Fig. 27. Work-function change vs. coverage for Na (open circles), K (open triangles), and Cs (open squares) on Ni(110) at 300 K. From [70G].
0
Work − function change ∆Φ [eV]
4.2-107
p(2 × 2) compressed and mixed
−1
(√3 × √3) R30° −2
Ru(0001) Cs −3
T = 80 K
−4
Φ min
−2.5 0
2 6 8 4 Rb coverage θ [1014 atoms cm−2 ]
10
Fig. 28. Work-function change for different amounts of Rb adsorbed on Al(111) at 140 K. From [89H2].
Lando lt -Bö rnst ein New Ser ies III/42A2
−5 0
1
3 6 7 multilayer 5 4 2 Cs coverage θ [1014 atoms cm−2 ]
Fig. 29. Work-function change for Cs on Ru(0001) at 80 K with increasing Cs coverage. The observed LEED structures are indicated. From [85H4].
4.2-108 0.2
4.2 Electron work function of metals and semiconductors 0.6
X = Au
W(110) X
W(100) X
X = Au
0.4
Work − function change ∆Φ [eV]
Work − function change ∆Φ [eV]
0 Ni
[Ref. p 4.2-118
Pd
− 0.2 −0.4 −0.6
Ag
−0.8
Cu
0.2 Pd 0 Co
− 0.2 −0.4 Cu
−1.0
0
5
10 15 20 25 30 Atomic density N [1014 atoms cm−2 ]
−0.6
35
Fig. 30. Work-function change of a W(110) surface as a function of coverage (in 1014 atoms cm-2) induced by various metals deposited at 300 K. The atomic density of the W(110) surface is 14.12·1014 atoms cm-2.From [85K6].
Work − function change ∆Φ [eV]
Work − function change ∆Φ [eV]
573 K 0.2 965 K 0.1 0 − 0.1
− 0.2
4
Pt(111) Cu
− 0.4 − 0.6
4
Fig. 32. Work-function change of Mo(100) with Cu coverage for depositions at 300 K (full dots), at 573 K (open triangles) and 965 K (open circles). From [80S3].
1 ML Cu (111)
− 0.8
T = 350 K
T = 450 K
− 1.0 − 1.2
3 2 Cu coverage θ [monolayers]
3
− 0.2
T = 300 K
1
2 Coverage θ [ML]
Start Cu deposition
0.4
0
1
0
Mo(100) Cu
−0.3
0
Fig. 31. Relative work function of annealed surfaces of Au (900 K), Pd (1020 K), Co (1100 K), Cu(800 K), and Fe (1000 K) on W(100) as a function of coverage. The Au, Pd, Cu, and Fe curves were reproduced from Refs. [77B], [81P], [74B3], and [78J2], respectively. From [89J].
0.5
0.3
Fe
0
200
600 400 Deposition time t [s]
800
Fig. 33. Work-function change measured in situ during Cu deposition on Pt(111) at two different temperatures T. Cu deposition starts at 0 s. At 145 s one monolayer of Cu is accumulated. The curve for T = 450 K shows a characteristic minimum-to-maximum structure at a coverage near 1 ML (1 ML defined as one Cu(111) layer). The slope of the curve for T = 350 K is more rounded, according to a less ideal layer growth. From [95N].
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118] 0
4.2 Electron work function of metals and semiconductors
Pt(110) Cu
Cu
− 0.02
Work − function change ∆Φ [eV]
T = 420 K R = 0.66 ML/min
a T = 400 K R = 0.7 ML/min
0 − 0.02
b
0
T = 370 K R = 0.66 ML/min
Fig. 34. Work-function change during deposition of Cu onto Cu (the substrate of the Cu layers is Pt(111)). Temperature dependence of the observed oscillations at almost identical deposition rates: (a) 420 K; (b) 400 K; (c) 370 K; (d) 340 K. Upon lowering the deposition temperature from 420 K, where besides an initial decrease no periodic variation is found, to 340 K an oscillatory behavior sets in and the amplitude of the work-function-change oscillations increases. This experiment nicely demonstrates the influence of surface roughness on work function (Smoluchowski effect). From [95N].
− 0.02 − 0.04 0
c T = 340 K R = 0.66 ML/min
− 0.02 − 0.04
d 0
300
200 100 Deposition time t [s]
5.0
0
Ru(0001) Cu
W(100) Cu
− 0.1
T = 78 K
Work − function Φ [eV]
Work − function change ∆Φ [eV]
4.2-109
− 0.2
600 K
4.5
− 0.3
− 0.4
4.0
0
1
2 Cu coverage θ [ML]
3
4
Fig. 35. Work-function change of Ru(0001) at 300 K with Cu coverage. From [87P].
Lando lt -Bö rnst ein New Ser ies III/42A2
0
15 10 5 Copper atom density N [1014 atoms cm−2 ]
20
Fig. 36. Work function vs. coverage produced by incremental doses of Cu condensed onto W(100) at 78 K and after spreading each dose at 600 K. From [77J2].
4.2-110
4.2 Electron work function of metals and semiconductors
[Ref. p 4.2-118
0.1
Work − function change ∆Φ [eV]
Work − function change ∆Φ [eV]
∆Φ max
0 − 0.1
∆Φsat
− 0.2
W(112)Cu
− 0.3 −0.4
∆Φmin
∆Φ max ∆Φsat ∆Φmin
− 0.5 −0.6 100
0 a
200 Temperature T [K]
300
400
Cu coverage θ
b
Fig. 37. Work-function changes induced by Cu adsorption on the W(112) face as a function of the substrate temperature. Open circles: ∆ϕmax, full circles: ∆ϕsat, crosses: ∆ϕmin. From [77M3].
0.6
4.8
W(100) Cu
0.4
[78B2] ,T = 78 K
4.6 Work − function Φ [eV]
Work − function change ∆Φ [eV]
W(100) Cu
0.2 0 − 0.2
[77R] ,T = 20 K [75R] 77 K [74B3] 300 K
− 0.4
4.4
4.2 [74B3] ,T = 800 K 4.0 [74B3] ,T = 300 K
− 0.6
0
2
10 12 4 6 8 14 −2 Cu coverage θ [10 atoms cm ]
14
Fig. 38. Work-function change vs. coverage of Cu adsorbed on W(100). [77R] adsorption at 20 K (open squares); [75C] adsorption at 77 K (open circles); [74B3] adsorption at 300 K, Cu axis rescaled (open triangles). From [77R].
3.8 0
1 2 Number of monolayers
3
Fig. 39. Work function of W(100) with Cu coverage: full circles at 78 K from [78B2]; open circles at 800 K from [74B3]; crosses at 300 K from [74B3]. From [78B2].
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors
4.2-111
5.3
5.3
W(100) Cu 5.1
Work − function Φ [eV]
Work − function Φ [eV]
5.1
4.9
4.7 1
2
4
4.9
4.7
3
1 4.5
4.5
2
4.3
4.3 0
5
a
20 10 15 Deposition time t [min]
25
0
30
5
b
20 10 15 Deposition time t [min]
25
3 4 30
Fig. 40. Average work function vs. deposition-time plots for Cu on W(100) at various substrate temperatures: (a) Curve 1, 400 K; curve 2, 450 K; curve 3, 500 K; curve 4, 550 K; (b) curve 1, 600 K; curve 2, 650 K; curve 3, 680 K, curve 4, 800 K. From [ 81S].
For Fig. 41, see next page 5.3
0
5.1 a − 0.05
Work − function Φ [eV]
Work − function change ∆Φ [eV]
Mo(110)Ag
b
−0.10 c
4.9 4.7 W(110)Ag 4.5 4.3 W(100)Ag 4.1
− 0.15
0
0.025
0.050 0.075 Ag coverage θ [ML]
0.100
Fig. 42. Work-function change as a function of silver coverage θ on the Mo(110) face (a) at 370 K, (b) at 550 K, and (c) at 850 K. In (a) the Ag atoms form 2D islands with a constant dipole moment per atom in the island. In (b) and (c) the adsorbed Ag atoms form a 2D gas. Obviously, the dipole moment per atom depends somewhat on temperature. From [90K].
Lando lt -Bö rnst ein New Ser ies III/42A2
4.0 0
W(111)Ag 1
3 2 Deposition time t [min]
4
Fig. 43. Work function caused by silver adsorption on low index tungsten planes by constant deposition rate. From [77K2].
4.2-112
4.2 Electron work function of metals and semiconductors
4.7
[Ref. p 4.2-118
5.3
W(111) Cu
W(211) Cu 5.1
4.5
Work − function Φ [eV]
Work − function Φ [eV]
4.6
1
4.4
2
4.3
2 1
4.7
3
3 4.2
4.9
4
4.5
5
4 5
4.0
4.3 0
5
a
10 15 25 20 Deposition time t [min]
30
35
0 b
5
10 15 25 20 Deposition time t [min]
30
35
6.2
W(110) Cu
Work − function Φ [eV]
6.0 5.8 5.6 3 5.4 2 5.2
4 5
5.0 1
4.8 0 c
1
5 2 3 4 Deposition time t [min]
6
7
Fig. 41. Average work function vs. Cu deposition-time plots for (a) the W(111) plane, (b) the W(211) plane and (c) the W(110) plane at various substrate temperatures: curves 1, 300 K; curves 2, 500 K; curves 3, 680 K; curves 4, 800 K; curves 5, 930 K. From [ 81S].
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors
4.2-113
0
0
W(110)Ag Work − function change ∆Φ [eV]
Work − function change ∆Φ [eV]
W(110)Ag − 0.2 T = 300 K T = 500 K − 0.4
− 0.6
− 0.2 d − 0.4 c
− 0.6
b b
− 0.8
− 0.8
−1.0
1
0
2 3 4 Ag coverage θ [units of Na ]
5
Fig. 44. Work-function change of a W{110} surface with Ag coverage. Coverage in units of Na = 12.89·1014 atoms cm-2. The maximum drift during the experiment is the difference between the work function after flashing off the Ag at the end of the experiment and the work function before the experiment. From [77B].
1
2
3 6 5 4 Deposition time t [min]
7
9
8
5.6
W(110)Ag
unannealed,T = 90 K unannealed,T = 300 K annealed at 700 K
W(110)Ag 5.2
0
Work − function Φ [eV]
Work − function change ∆Φ [eV]
0
Fig. 45. Work-function changes vs. time of Ag deposition at (a) 78 K, (b) 300 K, (c) 770 K, (d) 1000 K. Flux density is 5.27·1012 atoms/s cm2 (determined by the quartz oscillator). From [79K].
0.4
− 0.4
− 0.8
− 1.0
c
a
maximum drift
4.8
4.4
4.0 0
1
2 Ag coverage θ [ML]
3
4
Fig. 46. Work-function changes vs. coverage in monolayers for Ag deposition on W(110) at 90 and 300 K, and 300 K annealed for 120 s at 700 K. All measurements were carried out at 90 K. From [93Z].
Lando lt -Bö rnst ein New Ser ies III/42A2
0
1 2 Ag exposure L [ML]
3
Fig. 47. Work function of the (110) facet of a tungsten field emitter at 300 K as a function of silver exposure. The authors interpret this data as follows: Below an exposure treshold of about one ML, Ag adatoms migrate to the high-index facets that surround the W(110) plane, and the emission properties are indistinguishable from those of the bare substrate. At 1 ML the adatoms invade the (110) plane, modifying the surface density of electron states and bringing about an abrupt increase in electron emission. Above 2 ML the additionally evaporated Ag atoms migrate again to the surrounding facets. From [95D].
4.2-114
4.2 Electron work function of metals and semiconductors
5.4
0.25 Re:Au
W(110)Au
5.0
Work − function change ∆Φ [eV]
Work − function Φ [eV]
T = 900 K
0.20
5.2
W:Au
4.8
4.6
300 K 0.15 0.10 0.05 0
4.4 0
1
2
4 5 3 Au coverage θ [ML]
6
7
Fig. 48. Comparison of changes in average work function with average coverage for gold spread at 600 K on tungsten and rhenium. From [77C].
−0.05
maximum drift
0
1
2 3 Au coverage θ [ML]
5
4
Fig. 49. Work-function change of a W(110) surface with Au coverage at 300 and 900 K deposition temperature. From [77B].
0.6
5.4
W(100)Au
W(100)Au
T = 900 K 300 K 5.2
0.4 Work − function Φ [eV]
Work − function change ∆Φ [eV]
[Ref. p 4.2-118
0.2
5.0
4.8
0
[78B2],T = 78 K [76R],T = 20 K
maximum drift −0.2
4.6
0
1 2 Au coverage θ [ML]
3
Fig. 50. Work-function change of a W(100) surface with Au coverage at 300 and 900 K. From [77B].
0
1 2 Au coverage θ [ML]
3
Fig. 51. Work-function changes with Au coverage on W(100). Filled dots 78 K [78B2], open dots 20 K [76R]. From [78B2].
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors 0
1.0
W:Au
W(110)Cr Work − function change ∆Φ [eV]
W(110)
0.8 Work − function change ∆Φ [eV]
4.2-115
W(001) 0.6 W(112) W(115) 0.4
0.2
after T = 1100 K annealed − 0.50
−1.00 deposited at 1000 K
−1.50
W(111)
0
0.5
1.0 1.5 Cr coverage θ [ML]
2.0
2.5
0
− 0.2 0
1
2
4
3
Au coverage θ [1015 atoms cm−2 ]
Fig. 52. Work-function changes as a function of Au coverage of selected low-index faces of a W cylindrical crystal surface. The work function of the clean W(001) surface was taken as zero. Au coverage scale was calibrated by assuming that the first maximum for W(112) appears at 6.3·1014 atoms cm-2 as reported in Ref. [84K2]. From [86M].
0.2 T = 90 K 150 K 175 K 200 K 250 K 300 K 600 K
0 − 0.2
5.3 5.1
−0.4
4.9
− 0.6
4.7
− 0.8
4.5
−1.0
4.3 0
0.2
Lando lt -Bö rnst ein New Ser ies III/42A2
0.4 0.8 0.6 Fe coverage θ [ML]
1.0
1.2
Work − function Φ [eV]
Work − function change ∆Φ [eV]
Fig. 54. Work-function change and work function vs.
5.5
W(110)Fe
Fig. 53. Work-function change for Cr overlayers on W(110) at 100 K (open circles) and after a brief 1100 K anneal (solid circles). Chromium coverage is determined by TPD peak area. No change was observed for the AES and LEED data. Therefore, the ∆Φ difference is assigned to a difference in adatom mobility and two-dimensional ordering during the formation of a pseudomorphic monolayer for 0 < θCr < 1. From [89B3].
Fe coverage on W(110) for deposition at various temperatures, as indicated on the figure. Deposition was carried out at a rate of 0.1 monolayers per 90 s. After each dose the crystal was cooled to 90 K for work-function measurements and then reheated for the next dose, and so on. Conversion of Fe from the low to the high temperature form is governed by diffusion and aggregation into islands at T ≥ 160 K, with an activation energy of diffusion ~ 10 kcal mol-1. Direct conversion of isolated Fe atoms does not occur below 220 K and may not in fact play a significant role in the conversion of Fe(I) to Fe(II), which may exist only in close-packed patches. For high coverages conversion occurs already at 300 K. These findings suggest that Fe-Fe interactions contribute to conversion and that the rate limiting step for conversion may mainly be diffusion except at very high coverages. From [97N2].
4.2-116
4.2 Electron work function of metals and semiconductors
0.2
5.3
5.2
− 0.2
5.1 Fe(110)
−0.4
4.9 Fe(111)
− 0.6
4.7
Fe(100) − 0.8
4.5 Fe(poly film)
−1.0
0
0.5
2.0 2.5 1.0 1.5 Fe coverage θ [ML]
3.0
5.0
Work − function Φ [eV]
0
W:Fe
T = 90 K 300 K 300K /600 K
Work − function Φ [eV]
Work − function change ∆Φ [eV]
5.4
5.5
W(110)Fe
[Ref. p 4.2-118
4.3
W(110) 4.8
W(112)
W(111)
4.6
3.5
4.4
Fig. 55. Work function and work-function change vs. Fe coverage in monolayers on clean W(110) for various deposition temperatures. The curve marked 300 K/600 K refers to deposition at 300 K with 60 s anneal at 600 K after each dose. From [97N3].
W(001) 4.2 0
1
3 4 5 2 Fe coverage θ [1015 atoms cm−2 ]
6
Fig. 56. Work function during continuous room temperature deposition as a function of the iron coverage for the W(110), W(112), W(111), and W(001) surfaces. From [83G2].
0.2
0.4
0
W(100)Co
unannealed annealed
− 0.2 − 0.4 − 0.6 − 0.8 −1.0
a
unannealed annealed
0.3 Work − function change ∆Φ [eV]
Work − function change ∆Φ [eV]
W(110)Co
0.2 0.1 0
− 0.1
0
1
− 0.2 2 Co coverage θ [ML]
0
3 b
1
2 Co coverage θ [ML]
3
Fig. 57. Work-function change of the unannealed (100 K) and annealed (1100 K) surfaces of (a) Co/W(110); and (b) Co/W(100) as a function of Co coverage. From [89J].
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.2-118]
4.2 Electron work function of metals and semiconductors
0.4
0.6 T = 300 K
W(100)Pd
0.2
0
Work − function change ∆Φ [eV]
Work − function change ∆Φ [eV]
W(110)Pd
1 2 3
− 0.2 − 0.4
− 0.6
4.2-117
0.5 0.4 T = 460 K 0.3 0.2 0.1
0
0.5
1.0
1.5 2.0 2.5 Pd coverage θ [ML]
3.0
3.5
4.0
Fig. 58. Work-function change of a W(110) surface vs. Pd coverage at various deposition rates and substrate temperatures. Open circles: 17·1012 cm-2 s-1, 300 K, 2 min anneals at 830 K for θ < 1; filled circles: 28·1012 cm-2 s-1, 300 K, 2 min anneals at 830 K for all θ; open triangles: 17·1012 cm-2 s-1, 300 K. From [80S4].
Lando lt -Bö rnst ein New Ser ies III/42A2
0
1
2 3 Pd coverage θ [ML]
4
5
Fig. 59. Work-function change of a W(100) surface vs. Pd coverage evaporated and measured at 300 K. Filled circles as deposited at 300 K; crosses after anneal at 460 K. From [81P].
References for 4.2 1898K 27T 28F 31F 32Z 35A 50M 53M 65M 65S 66E 66G 66S 67A 67F 67O 67O2 67P 67S 68C 68K 68S 69A 69E 69F 69F2 69M 69M2 69O 69O2 69R 69S 69T2 69W 69W2 70A 70B 70C 70E 70E2 70E3 70F
Kelvin, Lord: Philos. Mag. 46 (1898) 82. Topping, J.: Proc. Roy. Soc. (London) A114 (1927) 67. Fowler, R.H., Nordheim, L.W.: Proc. Roy. Soc. (London) A119 (1928) 173. Fowler, R.H.: Phys. Rev. 38 (1931) 45. Zisman, W.A.: Rev. Sci. Instrum. 3 (1932) 367. Anderson, P.A.: Phys. Rev. 47 (1935) 958. Mignotlet, J.P.C.: Discuss. Faraday Soc. 8 (1959) 105. Mignolet, J.C.P.: J. Chem. Phys. 21 (1953) 1298. Melmed, A.J.: J. Chem. Phys. 43 (1965) 3057. Schmidt, L., Gomer, R.: J. Chem. Phys. 42 (1965) 3573. Estrup, P.J., Anderson, J.: J. Chem. Phys. 45 (1966) 2254. Gavrilyuk, V.M., Medvedev, V.K.: Fiz. Tverd. Tela 8 (1966) 1811; Sov. Phys. Solid State (English Transl.) 8 (1966) 1439. Schmidt, L.D., Gomer, R.: J. Chem. Phys. 45 (1966) 1605. Anderson, J., Estrup, P.J.: J. Chem. Phys. 46 (1967) 563. Fehrs, D.L., Stickney, R.E.: Surf. Sci. 8 (1967) 267. Ovchinnikov, A.P., Tsarev, B.M.: Fiz. Tverd. Tela 9 (1967) 1927; Sov. Phys. Solid State (English Transl.) 9 (1967) 1519. Ovchinikov, A.P.: Fiz. Tverd. Tela 9 (1967) 628; Sov. Phys. Solid State (English Transl.) 9 (1967) 483. Palmberg, P.W., Peria, W.T.: Surf. Sci. 6 (1967) 57. Swanson, L.W., Strayer, R.W.: J. Chem. Phys. 48 (1968) 2421. Collins, R.A., Blott, B.H.: Surf. Sci. 9 (1968) 1. Klimenko, E.W., Medvedev, V.K.: Fiz. Tverd. Tela 10 (1968) 1986; Sov. Phys. Solid State (English Transl.) 10 (1968) 1562. Swanson, L.W., Strayer, R.W., Davis, L.E.: Surf. Sci. 9 (1968) 165. Abey, A.E.: J. Appl. Phys. 40 (1969) 284. Engel, T., Gomer, R.: J. Chem. Phys. 50 (1969) 2428. Fedorus. G., Konoplev, Yu.M., Naumovets, A.G.: Fiz. Tverd. Tela 11 (1969) 207; Sov. Phys. Solid State (English Transl.) 11 (1969) 160. Fehrs, D.L., Stickney, R.E.: Surf. Sci. 17 (1969) 298. Moss, A.R.L., Blott, B.H.: Surf. Sci. 17 (1969) 240. MacRae, A.U., Müller, K., Lander, J.J., Morrison, J., Phillips, J.C.: Phys. Rev. Lett. 22 (1969) 1048. Onchi, M., Farnsworth, H.E.: Surf. Sci. 13 (1969) 425. Ovchinikov, A.P.: Fiz. Tverd. Tela 9 (1967) 628; Sov. Phys. Solid State (English Transl.) 9 (1967) 483. Rivière, J.C.: in: Solid State Surf. Sci., Vol. 1, Green, M. (ed.), New York: Dekker, 1969, p. 179. Sidorski, Z., Pelly, I., Gomer, R.: J. Chem. Phys. 50 (1969) 2382. Tracy, J.C., Blakely, J.M.: Surf. Sci. 15 (1969) 257. Workowski, C., Czyzewski, J.: Acta Phys. Pol. A 36 (1969) 1095. Weber, R.E., Peria, W.T.: Surf. Sci. 14 (1969) 13. Adams, D.L., Germer, L.H., May, J.W.: Surf. Sci. 22 (1970) 45. Bondarenko, B.V., Makhov, V.I.: Fiz. Tverd. Tela 12 (1970) 1912; Sov. Phys. Solid State (English Transl.) 12 (1970) 1522. Chen, J.M.: J. Appl. Phys. 41 (1970) 5008. Engel, T., Gomer, R.: J. Chem. Phys. 52 (1970) 1832. Ertl, G., Koch, J.: Z. Naturforsch. 24a (1970) 1906. Engel, T., Gomer, R.: J. Chem. Phys. 52 (1970) 5572. Fedorus, A.G., Naumovets, A.G.: Surf. Sci. 21 (1970) 426. Lando lt -Börnst ein New Ser ies III/42A2
4.2 Electron work function of metals and semiconductors 70G 70J 70M 70S 70T 71A 71A2 71C 71C2 71C3 71C4 71C5 71D 71F 71K 71L 71M 71P 71P2 71S 71Y 72A 72B 72B2 72E 72F 72H 72H2 72J 72K 72M 72M2 72M3 72P 72V 72W 72Z 73A 73B 73B2 73B3 73C 73C2 73D 73D2 73G 73K 73K2 73L
4.2-119
Gerlach, R.L., Rhodin, T.N.: Surf. Sci. 19 (1970) 403. Jowett, C.W., Hopkins, B.J.: Surf. Sci. 22 (1970) 392. Medvedev, V.K., Naumovets, A.G., Fedorus, A.G.: Fiz. Tverd. Tela 12 (1979) 375; Sov. Phys. Solid. State (English Transl.) 12 (1970) 301. Sugata, E., Takeda, K.: Phys. Status Solidi 38 (1970) 549. Turner, D.W., Baker, C., Baker, A.D., Brundle, C.R.: Molecular Photoelectron Spectroscopy, New York: Wiley Interscience, 1970. Adams, D.L., Germer, L.H.: Surf. Sci. 27 (1971) 21. Anderson, J.R., Thompson, N.: Surf. Sci. 28 (1971) 84. Collins, R.A., Blott, B.H.: J. Phys. D - Appl. Phys. 4 (1971) 102. Collins, R.A., Blott, B.H.: J. Phys. D - Appl. Phys. 4 (1971) 114. Collins, R.A.: Surf. Sci. 26 (1971) 624. Chesters, M.A., Pritchard, J.: Surf. Sci. 28 (1971) 460. Chen, J.M., Papageorgopoulos, C.A.: Surf. Sci. 26 (1971) 499. Delchar, T.A.: Surf. Sci. 27 (1971) 11. Fehrs, D.L., Stickney, R.E.: Surf. Sci. 24 (1971) 309. Klemperer, D.F., Snaith, J.C.: Surf. Sci. 28 (1971) 209. Legare, P., Maire, G.: J. Chim. Phys. Phys. Chim. Biol. 68 (1971) 1206. Madey, T.E., Yates, J.T.: J. Vac. Sci. Technol. 8 (1971) 39. Palmberg, P.W.: Surf. Sci. 25 (1971) 598. Papageorgopoulos, C.A., Chen, J.M.: J. Vac. Sci. Technol. 9 (1971) 570. Hagstrum, H.D., Becker, G.E.: J. Chem. Phys. 54 (1971) 1015. Yates, J.T.Jr., Madey, T.E.: Surf. Sci. 28 (1971) 437. Adams, D.L., Germer, L.H.: Surf. Sci. 32 (1972) 205. Bacal, M., Desplat, J.L., Alleau, T.: J. Vac. Sci. Technol. 9 (1972) 851. Becker, G.E., Hagstrum, H.D.: Surf. Sci. 30 (1972 ) 505. Ertl, G., Küppers, J.: J. Vac. Sci. Technol. 9 (1972) 829. Fort, T.Jr., Wells, R.L.: Surf. Sci. 32 (1972) 543. Hilaire, L., Whalley, L.: Surf. Sci. 32 (1972) 253. Haas, G.A., Thomas, R.E.: in Techniques of Metal Research, Vol. 4, I, Pasgalia, E. (ed.), New York: Interscience,1972, p. 91. Jones, J.P.: Surf. Sci. 32 (1972) 29. Knapp, A.G., Stiddard, M.H.B.: J. Chem. Soc. Faraday Trans. I 68 (1972) 2139. Mileshkina, N.V., Bakhtizin, R.Z.: Surf. Sci. 29 (1972) 644. Madey, T.E.: Surf. Sci. 33 (1972) 355. Madey, T.E.: Surf. Sci. 29 (1972) 571. Plummer, E.W., Bell, A.E.: J. Vac. Sci. Technol. 9 (1972) 583. Voronin, V.B., Naumovets, A.G., Fedorus, A.G.: JEPT Lett. 15 (1972) 370. Workowski, C.J.: Acta Phys. Pol. A 42 (1972) 9. Zehner, D.M., Farnsworth, H.E.: Surf. Sci. 30 (1972) 335. Andersson, S., Jostell, U.: Solid State Commun. 13 (1973) 829. Besocke, K., Wagner, H.: Phys. Rev. B 8 (1973) 4597. Berndt, H., Volter, J.: Z. Phys. Chem. 254 (1973) 178. Boiko, B.A., Gorodetskii, D.A., Yas'ko, A.A.: Fiz. Tverd. Tela 15 (1973) 3145; Sov. Phys. Solid State (English Transl.) 15 (1973) 2101. Chrzanowski, E.: Acta Phys. Pol. A 44 (1973) 711. Chesters, M.A., Hussain, M., Pritchard, J.: Surf. Sci. 35 (1973) 161. Dweydari, A.W., Mee, C.H.B.: Phys. Status Solidi A 17 (1973) 247. Desplat, J.L.: Surf. Sci. 34 (1973) 588. Gland, J.L., Somorjai, G.A.: Surf. Sci. 38 (1973) 157. Klimenko, E.V., Naumovets, A.G.: Fiz. Tverd. Tela 15 (1973) 3273 (Sov. Phys. Solid State 15 (1973) 2181). Knapp, A.G.: Surf. Sci. 34 (1973) 289. Lecante, J., Riwan, R., Guillot, C.: Surf. Sci. 35 (1973) 271.
Lando lt -Bö rnst ein New Ser ies III/42 A2
4.2-120 73M 73M2 73M3 73N 73N2 73P 73P2 73P3 73R 73T 73Z 74A 74A2 74B 74B2 74B3 74C 74C3 74C4 74C5 74D 74D2 74D3 74F 74F2 74G 74G2 74H 74H2 74K 74M2 74M3 74M5 74M6 74M7 74M8 74N 74N2 74N3 74N4 74P 74T 74Y 75B 75B2 75C 75D 75E2 75F
4.2 Electron work function of metals and semiconductors Medvedev, V.K., Naumovets, A.G., Smereka, T.P.: Surf. Sci. 34 (1973) 368. Medvedev, V.K., Smereka, T.P.: Fiz. Tverd. Tela 15 (1973) 724; Sov. Phys. Solid State (English Transl.) 15 (1973) 507. Medvedev, V.K., Smereka, T.P.: Fiz. Tverd. Tela 15 (1973) 1641; Sov. Phys. Solid State (English Transl.) 15 (1973) 1106. Nieuwenhuys, B.E., Meijer, D.Th., Sachtler, W.M.H.: Surf. Sci. 40 (1973) 125. Nieuwenhuys, B.E., Sachtler, W.M.H.: Surf. Sci. 34 (1973) 317. Polanski, J., Sidorski, Z.: Surf. Sci. 40 (1973) 282. Papageorgopoulos, C.A., Chen, J.M.: Surf. Sci. 39 (1973) 283. Papageorgopoulos, C.A., Chen, J.M.: Surf. Sci. 39 (1973) 313. Rye, R.R., Barford, B.D., Cartier, P.G.: J. Chem. Phys. 59 (1973) 1693. Taylor, T.N., Estrup, P.J.: J. Vac. Sci. Technol. 10 (1973) 26. Zebrowski, J.: Acta Phys. Pol. A 44 (1973) 201. Avery, N.R.: Surf. Sci. 43 (1974) 101. Andersson, S., Jostell, U.: Surf. Sci. 46 (1974) 625. Barford, B.D., Rye, R.R.: J. Chem. Phys. 60 (1974) 1046. Bhatia, C.S., Sinha, M.K.: Surf. Sci. 43 (1974) 369. Bauer, E., Poppa, H., Todd, G., Bonczek, F.: J. Appl. Phys. 45 (1974) 5164. Conrad, H., Ertl, G., Latta, E.E.: Surf. Sci. 41 (1974) 435. Christmann, K., Schober, O., Ertl, G., Neumann, M.: J. Chem. Phys. 60 (1974) 4528. Christmann, K., Schober, O., Ertl, G.: J. Chem. Phys. 60 (1974) 4719. Conrad, H., Ertl, G., Koch, J., Latta, E.E.: Surf. Sci. 43 (1974) 462. Dresser, M.J., Madey, T.E., Yates, J.T.Jr.: Surf. Sci. 42 (1974) 533. Dalmai-Imelik, G., Bertolini, J.C.: Jpn. J. Appl. Phys. 2 (1974) 205. Demuth, J.E., Rhodin, T.N.: Surf. Sci. 45 (1974) 249. Fusy, J., Bigeard, B., Cassuto, A.: Surf. Sci. 46 (1974) 177. Feuerbacher, B., Adriaens, M.R.: Surf. Sci. 45 (1974) 553. Gland, J.L., Somorjai, G.A.: Surf. Sci. 41 (1974) 387. Gorodetskii, D.A., Mel'nik, Yu.P.: Fiz. Tverd. Tela 16 (1974) 2781; Sov. Phys. Solid State (English Transl.) 16 (1974) 1805. Holloway, P.H., Hudson, J.B.: Surf. Sci. 43 (1974) 123. Hagen, D.I., Donaldson, E.E.: Surf. Sci. 45 (1974) 61. Klemperer, D.F., Snaith, J.C.: Surf. Sci. 45 (1974) 318. Melmed, A.J., Carroll, J.J., Meclewski, R.: Surf. Sci. 45 (1974) 649. Maly, R.R.: Jpn. J. Appl. Phys. 2 (1974) 293. Medvedev, V.K., Smereka, T.P.: Fiz. Tverd. Tela 16 (1974) 1599; Sov. Phys. Solid State (English Transl.) 16 (1974) 1046. Müller, J.: Surf. Sci. 45 (1974) 314. Medvedev, V.K., Yakivchuk, A.I.: Fiz. Tverd. Tela 16 (1974) 981; Sov. Phys. Solid State (English Transl.) 16 (1974) 634. Melmed, A.J., Carroll, J.J., Meclewski, R.: Surf. Sci. 45 (1974) 649. Nieuwenhuys, B.E., Bouwman, R., Sachtler, W.M.H.: Thin Solid Films 21 (1974) 51. Nieuwenhuys, B.E., Sachtler, W.M.H.: Surf. Sci. 45 (1974) 513. Nieuwenhuys, B.E., Meijer, D.Th., Sachtler, W.M.H.: Phys. Status Solidi A 24 (1974) 115. Nieuwenhuys, B.E., Aardenne, O.G., Sachtler, W.M.H.: Chem. Phys. 5 (1974) 418. Porteus, J.O.: Surf. Sci. 41 (1974) 515. Taylor, T.N., Estrup, P.J.: J. Vac. Sci. Technol. 11 (1974) 244. Young, P.L., Gomer, R.: Surf. Sci. 44 (1974) 268. Blaszczyszyn, R., Blaszczyszyn, M., Meclewski, R.: Surf. Sci. 51 (1975) 396. Besocke, K., Wagner, H.: Surf. Sci. 53 (1975) 351. Cetronio, A., Jones, J.P., Roberts, E.W.: Surf. Sci. 52 (1975) 473. Derrien, J., Arnand d’Achitaya, F., Glachant, A.: Surf. Sci. 47 (1975) 162. Engel, T., Niehus, H., Bauer, E.: Surf. Sci. 52 (1975) 237. Franken, P.E.C., Ponec, V.: Surf. Sci. 53 (1975) 341. Lando lt -Börnst ein New Ser ies III/42A2
4.2 Electron work function of metals and semiconductors 75G 75M 75P 75P2 75P3 75R 75R2 75W 75Z 75Z2 76B 76B2 76B4 76B5 76C 76C2 76C3 76D 76E 76E2 76E3 76G 76H 76I 76J 76J2 76K 76M 76M2 76M3 76N 76P 76R 76R2 76R3 76T 76Y 77A 77B 77B2 77B3 77B4 77B5 77B6 77C 77C2 77D 77D2 77D3 77D4
4.2-121
Garifullin, N.M., Zubenko Yu.V.: Fiz. Tverd. Tela 17 (1975) 3645; Sov. Phys. Solid State (English Transl.) 17 (1975) 2370. Madey, T.E., Engelhardt, H.A., Menzel, D.: Surf. Sci. 48 (1975) 304. Papp, H., Pritchard, J.: Surf. Sci. 53 (1975) 371. Papageorgopoulos, C.A., Chen, J.M.: Surf. Sci. 52 (1975) 40. Pritchard, J., Catterick, T., Gupta, R.K.: Surf. Sci. 53 (1975) 1. Riwan, R., Guillot, C., Paigne, J.: Surf. Sci. 47 (1975) 183. Rovida, G., Pratesi, F.: Surf. Sci. 51 (1975) 270. Waclawski, B.J., Herbst, J.F.: Phys. Rev. Lett. 35 (1975) 1594. Zykov, B.M., Ikonnikov, D.S., Tskhakaya, V.K.: Fiz. Tverd. Tela 17 (1975) 274; Sov. Phys. Solid State (English Transl.) 17 (1975) 163. Zykov, B.M., Ikonnikov, D.S., Tskhakaya, V.K.: Fiz. Tverd. Tela 17 (1975) 3562; Sov. Phys. Solid State (English Transl.) 17 (1975) 2322. Besocke, K., Berger, S.: Rev. Sci. Instr. 47 (1976) 840. Bauer, E., Poppa, H., Viswanath, Y.: Surf. Sci. 58 (1976) 517. Blaszozyszyn, M.: Surf. Sci. 59 (1976) 533. Bliznakov, G.M., Marinova, Ts.S., Popov, A.D.: Izv. Khim. 9 (1976) 203. Christmann, K., Ertl, G.: Surf. Sci. 60 (1976) 365. Christmann, K., Ertl, G., Pignet, T.: Surf. Sci. 54 (1976) 365. Collins, R.A., Kiwanga, C.A.: Surf. Sci. 61 (1976) 491. Dahlberg, S.C.: Surf. Sci. 59 (1976) 83. Engelhardt, H.A., Menzel, D.: Surf. Sci. 57 (1976) 591. Ehrhardt, J.-J., Fusy, J., Cassuto, A.: J. Microsc. Spectrosc. Electron. 1 (1976) 415. Evans, St., Pielaszek, J., Thomas, J.M.: Surf. Sci. 56 (1976 ) 644. Gland, J.L., Somorja, G.A.: Adv. Colloid Interface Sci. 5 (1976) 205. Hopkins, B.J., Jones, A.R., Winton, R.I.: Surf. Sci. 57 (1976) 266. Ivanov, V.P., Boreskov, G.K., Savchenko. V.I.. Egelhoff, W.F., Weinberg, W.H.: Surf. Sci. 61 (1976) 207. Jaschinski, W., Niedermayer, R.: Thin Solid Films 32 (1976) 181. Jones, J.P., Jones, N.T.: Thin Solid Films 35 (1976) 83. Krishnan, N.G., Delgass, W.N., Robertson, W.D.: Surf. Sci. 57 (1976) 1. Mroz, A., Sidorski, Z.: Acta Phys. Pol. A 49 (1976) 437. McElhiney, G., Pritchard, J.: Surf. Sci. 60 (1976) 397. McElhiney, G., Papp, H., Pritchard, J.: Surf. Sci. 54 (1976) 617. Nieuwenhuys, B.E.: Surf. Sci.59 (1976) 430. Polanski, J., Sidorski, Z., Zuber, S.: Acta Phys. Pol. A 49 (1976) 299. Richter, L., Gomer, R.: Phys. Rev. Lett. 37 (1976) 763. Richter, L., Gomer, R.: Surf. Sci. 59 (1976) 575. Roberts, R.H., Pritchard, J.: Surf. Sci. 54 (1976) 687. Taylor, T.N., Colmenares, C.A., Smith, R.L., Somorjai, G.A.: Surf. Sci. 54 (1976) 317. Yates, J.T.Jr., Klein, R., Madey, T.E.: Surf. Sci. 58 (1976) 469. Abon, M., Bergeret, G., Tardy, B.: Surf. Sci. 68 (1977) 305. Bauer, E., Poppa, H., Todd, G., Davis, P.R.: J. Appl. Phys. 48 (1977) 3773. Bozso, F., Ertl, G., Grunze, M., Weiss, M.: Appl. Surf. Sci. 1 (1977) 103. Butz, R., Wagner, H.: Surf. Sci. 63 (1977) 448. Briggs, D., Marbrow, R.A., Lambert, R.M.: Surf. Sci. 65 (1977) 314. Bradshaw, A.M., Hofmann, P., Wyrobisch, W.: Surf. Sci. 68 (1977) 269. Bonzel, H.P., Pirug, G.: Surf. Sci. 62 (1977) 45. Coles, S.J.T., Jones, J.P.: Surf. Sci. 68 (1977) 312. Collins, R.A., Kiwanga, C.A.: Surf. Sci. 64 (1977) 778. Derochette, J.-M., Marien, J.: Phys. Status Solidi A 39 (1977) 281. Demuth, J.E.: Chem. Phys. Lett. 45 (1977) 12. Derrien, J., Arnaud d’avitaya, F.: Surf. Sci. 65 (1977) 668. Demuth, J.E.: Surf. Sci. 65 (1977) 369.
Lando lt -Bö rnst ein New Ser ies III/42 A2
4.2-122 77E 77E2 77E3 77F 77G 77G2 77G3 77G4 77J 77J2 77J3 77K 77K2 77K3 77K4 77K5 77L 77M 77M3 77M4 77P 77R 77R2 77S 77V 78B 78B2 78B3 78B4 78C 78C2 78F 78G 78G2 78G3 78G4 78G5 78H 78J 78J2 78J3 78L2 78L3 78M 78M2 78N 78P 78P2 78P3
4.2 Electron work function of metals and semiconductors Erley, W., Wagner, H.: Surf. Sci. 66 (1977) 371. Ertl, G., Neumann, M., Streit, K.M.: Surf. Sci. 64 (1977) 393. Engel, T., Von dem Hagen, T., Bauer, E.: Surf. Sci. 62 (1977) 361. Fischer, T.E., Kelemen, S.R.: Surf. Sci. 69 (1977) 1. Goddard, P.J., Lambert, R.M.: Surf. Sci. 67 (1977) 180. Gupalo, M.S., Medvedev, V.K., Smereka, T.P., Babkin, G.V., Palyukh, B.M.: Fiz. Tverd. Tela 19 (1977) 2955; Sov. Phys. Solid State (English Transl.) 19 (1977) 1731. Gorodetsky, D.A., Melnik, Yu.P.: Surf. Sci. 62 (1977) 647. Gartland, P.O.: Surf. Sci. 62 (1977) 183. Jones, J.P., Roberts, E.W.: Surf. Sci. 62 (1977) 415. Jones, J.P., Roberts, E.W.: Surf. Sci. 64 (1977) 355. Jones, J.P., Roberts, E.W.: Surf. Sci. 69 (1977) 185. Kellog, G.L., Tsong, T.T.: Surf. Sci. 62 (1977) 343. Kolaczkiewicz, J., Sidorski, Z.: Surf. Sci. 63 (1977) 501. Kessler, J., Thieme, F.: Surf. Sci. 67 (1977) 405. Krishnan, N.G., Delgass, W.N., Robertson, W.D.: J. Phys. F 7 (1977) 2623. Klein, R., Shik, A.: Surf. Sci. 69 (1977) 403. Leung, C., Vass, M., Gomer, R.: Surf. Sci. 66 (1977) 67. Marien, J.: Phys. Status Solidi A 38 (1977) 513. Mróz, S., Mróz, A., Sidorski, Z., in: Proc. 7th Intern. Vacuum Congr. and 3rd Intern. Conf. on Solid Surfaces, Vienna, 1977, p. 1125. Marbrow, R.A., Lambert, R.M.: Surf. Sci. 67 (1977) 489. Pantel, R., Bujor, M., Bardolle, J.: Surf. Sci. 62 (1977) 589. Richter, L., Gomer, R.: Appl. Phys. 13 (1977) 303. Rubloff, G.W., Demuth, J.E.: J. Vac. Sci. Technol. 14 (1977) 419. Sébenne, C.A.: Nuovo Cimento 39B (1977) 768. Vedula, Yu.S., Gonchar, V.V., Naumovets, A.G., Fedorus, A.G.: Fiz. Tverd. Tela 19 (1977) 1569; Sov. Phys. Solid State (English Transl.) 19 (1977) 1505. Bertolini, J.-C., Massardier, J., Dalmai-Imelik, G.: J. Chem. Soc. Faraday Trans. 74 (1978) 1720. Billington, R.L., Rhodin, T.N.: Phys. Rev. Lett. 41 (1978) 1602. Brodén, G., Pirug, G., Bonzel, H.P.: Surf. Sci. 72 (1978) 45. Bauer, E., Engel, T.: Surf. Sci. 71 (1978) 695. Collins, R.A., Kiwanga, C.A., Surf. Sci. 71 (1978) 185. Clemens, H.J., Wienskowski, J., Mönch, W.: Surf. Sci. 78 (1978) 648. Felter, T.E., Estrup, P.J.: Surf. Sci. 76 (1978) 464. Gewinner, G., Peruchetti, J.C., Jaegle, A., Kalt, A.: Surf. Sci. 78 (1978) 439. Goddard, P.J., Schwaha, K., Lambert, R.M.: Surf. Sci. 71 (1978) 351. Grunze, M., Boszo, F., Ertl, G., Weiss, M.: Appl. Surf. Sci. 1 (1978) 241. Goldstein, B., Szostak, D.J.: Surf. Sci. 74 (1978) 461. Green, A.K., Bauer, E.: Surf. Sci. 74 (1978) 676. Hofmann, P., Unwin, R., Wyrobisch, W., Bradshaw, A.M.: Surf. Sci. 72 (1978) 635. Jones, J.P., Roberts, E.W.: Thin Solid Films 48 (1978) 215. Jones, J.P., Roberts, E.W.: Surf. Sci. 78 (1978) 37. Jones, R.G., Perry, D.L.: Surf. Sci. 71 (1978) 59. Lindgren, S.A., Walldén, L.: Solid State Commun. 25 (1978) 13. Lakh, Kh.I., Stasyuk, Z.V.: Fiz. Tverd. Tela 20 (1978) 1989; Sov. Phys. Solid State (English Transl.) 20 (1981) 1149. Miyamura, M., Sakisaka, Y., Nishijima, M., Onchi, M.: Surf. Sci. 72 (1978) 243. Marbrow, R.A., Lambert, R.M.: Surf. Sci. 71 (1978) 107. Netzer, F.P., Wille, R.A: Surf. Sci. 74 (1978) 547. Peralta, L., Margot, E., Berthier, Y., Oudar, J.: J. Microsc. Spectrosc. Electron. 3 (1978) 151. Papageorgopoulos, C.A.: J. Phys. C 11 (1978) L15. Papageorgopoulos, C.A.: Surf. Sci. 75 (1978) 17. Lando lt -Börnst ein New Ser ies III/42A2
4.2 Electron work function of metals and semiconductors 78P4 78R 78S 78T 78T2 78W 79A 79A2 79B 79B2 79B3 79B4 79B5 79C 79C2 79D 79D2 79D3 79F 79G 79G2 79H 79H2 79H3 79H4 79H5 79J 79J2 79J3 79K 79K2 79K3 79M 79N 79N2 79P 79R 79S 79S2 79S3 79T 79V 79W 79W2 79Z 80B 80B2 80B3
4.2-123
Prior, K.A., Schwaha, K., Lambert, R.M.: Surf. Sci 77 (1978) 193. Rawlings, K.J., Hopkins, B.J., Foulias, S.D.: Surf. Sci. 77 (1978) 561. Shigeishi, R.A.: Surf. Sci. 72 (1978) 61. Taylor, J.L., Weinberg, W.H.: J. Vac. Sci. Technol. 15 (1978) 1811. Taylor, J.L., Ibbotson, D.E., Weinberg, W.H.: J. Chem. Phys. 69 (1978) 4298. Wang, C., Gomer, R.: Surf. Sci. 74 (1978) 389. Akimoto, K., Sakisaka, Y., Nishijima, M., Onchi, M.: Surf. Sci. 82 (1979) 349. Akimoto, K., Sakisaka, Y., Nishijima, M., Onchi, M.: Surf. Sci. 88 (1979) 109. Bertel, E., Schwaha, K., Netzer, F.P.: Surf. Sci. 83 (1979) 439. Bertolini, J.C., Rousseau, J.: Surf. Sci. 83 (1979) 531. Bauer, E., Poppa, H.: Surf. Sci. 88 (1979) 31. Bhattacharya, A.K., Broughton, J.Q., Perry, D.L.: Faraday Trans. I 75 (1979) 850. Brodén, G., Bonzel, H.P.: Surf. Sci. 84 (1979) 106. Chandler, P.E., Taylor, P.A., Hopkins, B.J.: Surf. Sci. 82 (1979) 500. Christmann, K., Behm, R.J., Ertl, G., Van Hove, M.A., Weinberg, W.H.: J. Chem. Phys. 70 (1979) 4168. Dowben, P.A., Jones, R.G.: Surf. Sci. 84 (1979) 449. Dowben, P.A., Jones, R.G.: Surf. Sci. 88 (1979) 348. Dowben, P.A., Jones, R.G.: Surf. Sci. 89 (1979) 114. Fisher, G.B.: Surf. Sci. 87 (1979) 215. Grunze, M., Driscoll, R.K., Burland, G.N., Cornish, J.C.L., Pritchard, J.: Surf. Sci. 89 (1979) 381. Gupalo, M.S., Medvedev, V.K., Palyukh, B.M., Smereka, T.P.: Fiz. Tverd. Tela 21 (1979) 973; Sov. Phys. Solid State (English Transl.) 21 (1979) 568. Habraken, F.H.P.M., Bootsma, G.A., Hofmann, P., Hachicha, S., Bradshaw, A.M.: Surf. Sci. 88 (1979) 285. Hofmann, P., Horn, K., Bradshaw, A.M., Jacobi, K.: Surf. Sci. 82 (1979) L610. Hölzl, J., Schulte, F.K.: Work function of metals, Springer Tracts of Modern Physics, Vol. 85, Höhler, G., Niekisch, E.A. (eds.), Berlin: Springer, 1979, p. 1. Hofmann, P., Wyrobisch, W., Bradshaw, A.M.: Surf. Sci. 80 (1979) 344. Hollins, P., Pritchard, J.: Surf. Sci. 89 (1979) 486. Jupille, J., Bigeard, B., Fusy, J., Cassuto, A.: Surf. Sci. 84 (1979) 190. Jones, R.G., Perry, D.L.: Surf. Sci. 88 (1979) 331. Jones, R.G.: Surf. Sci. 88 (1979) 367. Kolaczkiewicz, J.: Surf. Sci. 84 (1979) 475. Küppers, J., Nitschke, F., Wandelt, K., Ertl, G.: Surf. Sci. 87 (1979) 295. Küpers, J., Wandelt, K., Ertl, G.: Phys. Rev. Lett. 43 (1979) 928. Medvedev, V.K., Yakovkin, I.N.: Fiz. Tverd. Tela 21 (1979) 313; Sov. Phys. Solid State (English Transl.) 21 (1979) 187. Norton, P.R., Goodale, J.W., Selkirk, E.B.: Surf. Sci. 83 (1979) 189. Norton, P.R., Goodale, J.W.: Solid State Commun. 31 (1979) 223. Peruchetti, J.C., Gewinner, G., Jaegle, A.: Surf. Sci. 88 (1979) 479. Richter, L., Gomer, R.: Surf. Sci. 83 (1979) 93. Sidorski, Z., Zuber, S., Polanski, J.: Surf. Sci. 80 (1979) 626. Sidorski, Z., Szelwicki, T., Dworecki, Z.: Thin Solid Films 61 (1979) 203. Schwaha, K., Spencer, N.D., Lambert, R.M.: Surf. Sci. 81 (1979) 273. Taylor, J.L., Ibbotson, D.E., Weinberg, W.H.: Surf. Sci. 79 (1979) 349. Van Strien, A.J., Nieuwenhuys, B.E.: Surf. Sci. 80 (1979) 226. Weiss, M., Ertl, G., Nitschke, F.: Appl. Surf. Sci. 2 (1979) 614. Wang, C., Gomer, R.: Surf. Sci. 90 (1979) 10. Zuber, S., Sidorski, Z., Polanski, J.: Surf. Sci. 87 (1979) 375. Bonczek, F., Engel, T., Bauer, E.: Surf. Sci. 97 (1980) 595. Behm, R.J., Christmann, K., Ertl, G.: J. Chem. Phys. 73 (1980) 2984. Bertel, E., Netzer, F.P.: Surf. Sci. 97 (1980) 409.
Lando lt -Bö rnst ein New Ser ies III/42 A2
4.2-124 80B4 80B5 80C 80C2 80D 80D2 80E 80F 80F2 80G 80G2 80H 80H2 80I 80K 80K2 80K3 80L 80M 80N 80O 80O2 80P 80R 80S 80S2 80S3 80S4 80S5 80T 80W 80W2 81B 81B2 81C 81E 81F 81G 81H 81I 81K 81L 81M 81M2 81N 81N2 81N3 81P
4.2 Electron work function of metals and semiconductors Behm, R.J., Christmann, K., Ertl, G.: Surf. Sci. 99 (1980) 320. Benndorf, C., Egert, B., Nöbl, C., Seidel, H., Thieme, F.: Surf. Sci. 92 (1980) 636. Chen, J.-R., Gomer, R.: Surf. Sci. 94 (1980) 456. Chiang, T.-C., Kaindl, G., Eastman, D.E.: Solid State Commun. 36 (1980) 25. Davis, P.R.: Surf. Sci. 91 (1980) 385. Desplat, J.-L., Papageorgopoulos, C.A.: Surf. Sci. 92 (1980) 97. Erley, W.: Surf. Sci. 94 (1980) 281. Foord, J.S., Goddard, P.J., Lambert, R.M.: Surf. Sci. 94 (1980) 339. Feulner, P., Kulkarni, S., Umbach, E., Menzel, D.: Surf. Sci. 99 (1980) 489. Gupalo, M.S., Medvedev, V.K., Palyukh, B.M., Smereka, T.P.: Fiz. Tverd. Tela 22 (1980) 3201; Sov. Phys. Solid State (English Transl.) 22 (1980) 1873. Gerenser, L.J., Baetzold, R.C.: Surf. Sci. 99 (1980) 259. Habraken, F.H.P.M., Mesters, C.M.A.M., Bootsma, G.A.: Surf. Sci. 97 (1980) 264. Hölzl, J., Porsch, G., Schrammen, P.: Surf. Sci. 97 (1980) 529. Ibbotson, D.E., Wittrig, T.S., Weinberg, W.H.: Surf. Sci. 97 (1980) 297. Kaindl, G., Chiang, T.-C., Eastman, D.E., Himpsel, F.J.: Phys. Rev. Lett. 45 (1980) 1808. Kitson, M., Lambert, R.M.: Surf. Sci. 100 (1980) 368. Khonde, K., Darville, J., Donnelly, S.E.: Appl. Surf. Sci. 6 (1980) 297. Lindgren, S.ǖ:DOOGpQ/ 3K\V5HY%22 (1980) 5967. Michel, R., Gastaldi, J., Allaria, C., Jourdan, C., Derrien, J.: Surf. Sci. 95 (19080) 297. Nishitani, R., Kawai, S., Iwasaki, H., Nakamura, S., Aono, M., Tanaka, T.: Surf. Sci. 92 (1980) 191. Oudar, J.: Catal. Rev. Sci. Eng. 22 (1980) 171. Oudar, J.: Proc. ICOSS-4 and ECOSS-3, Cannes (1980) 645. Purtell, R.J., Merrill, R.P., Seabury, C.W., Rhodin, T.N.: Phys. Rev. Lett. 44 (1980) 1279. Rawlings, K.J.: Surf. Sci. 99 (1980) 507. Sakisaka, Y., Miyamura, M., Tamaki, J., Nishijima, M., Onchi, M.: Surf. Sci. 93 (1980) 327. Schlenk, W., Bauer, E.: Surf. Sci. 94 (1980) 528. Soria, F., Hoppa, H.: J. Vac. Sci. Technol. 17 (1980) 449. Schlenk, W., Bauer, E.: Surf. Sci. 93 (1980) 9. Seabury, C.W., Rhodin, T.N., Purtell, R.J., Merrill, R.P.: Surf. Sci. 93 (1980) 117. Takayanagi, K., Kolb, D.M., Kambe, K., Lehmpfuhl, G.: Surf. Sci. 100 (1980) 407. Wang, C., Gomer, R.: Surf. Sci. 91 (1980) 533. Weng, S.L., El-Batanouny, M.: Phys. Rev. Lett. 44 (1980) 612. Benndorf, C., Nobl, C., Rusenberg, M., Thieme, F.: Surf. Sci. 111 (1981) 87. Bigun, G.I., Nabitovich, I. D., Sukhorskii, Yu.S.: Fiz. Tverd. Tela 23 (1981) 2128; Sov. Phys. Solid State (English Transl.) 23 (1981) 1241. Campuzano, J.C., Dus, R., Greenler, R.G.: Surf. Sci. 102 (1981)172. Ertl, G., Lee, S.B., Weiss, M.: Surf. Sci. 111 (1981) L711. Fisher, G.B.: Chem. Phys. Lett. 79 (1981) 452. Gupalo, M.S., Medvedev, V.K., Palyukh, B.M., Smereka, T.P.: Fiz. Tverd. Tela 23 (1981) 2076; Sov. Phys. Solid State (English Transl.) 23 (1981) 1211. Hayden, B.E., Schweizer, E., Kotz, R., Bradshaw, A.M.: Surf. Sci. 111 (1981) 26. Ibbotson, D.E., Wittrig, T.S., Weinberg, W.H.: Surf. Sci. 110 (1981) 294. Kramer, H.M., Bauer, E.: Surf. Sci. 107 (1981) 1. Lee, S.B., Weiss, M., Ertl, G.: Surf. Sci. 108 (1981) 357. Medvedev, V.K., Yakovkin, I.N.: Fiz. Tverd. Tela 23 (1981) 669; Sov. Phys. Solid State (English Transl.) 23 (1981) 379. Melamed B.Ya., Silant'ev, V.I., Shevchenko, N.A.: Fiz. Tverd. Tela 23 (1981) 2424; Sov. Phys. Solid State (English Transl.) 23 (1981) 1416. Nishijima, M., Masuda, S., Sakisaka, Y., Onchi, M.: Surf. Sci. 107 (1981) 31. Namba, H., Darville, J., Gilles, J.M.: Surf. Sci. 108 (1981) 446. Nieuwenhuys, B.E: Surf. Sci. 105 (1981) 505. Prigge, S., Roux, H., Bauer, E.: Surf. Sci. 107 (1981) 101. Lando lt -Börnst ein New Ser ies III/42A2
4.2 Electron work function of metals and semiconductors 81S 81S2 81T 81W 81W2 82A 82C 82C2 82C2 82C3 82C4 82D 82D2 82D3 82E 82E2 82F 82F2 82H 82H2 82J 82K 82K2 82L 82L2 82L3 82L4 82L5 82M 82M2 82N 82N2 82P 82P2 82P3 82P4 82P5 82P6 82P7 82R 82S 82S2 82S3 82S4 82S5 82S6 82S7 82T 82T2
4.2-125
Sidorski, Z., Szelwicki, T., Dworecki, Z.: Thin Solid Films 75 (1981) 87. Schmeisser, D., Jacobi, K.: Surf. Sci. 108 (1981) 421. Thiel, P.A., Hoffmann, F.M., Weinberg, W.H.: J. Chem. Phys. 75 (1981) 5556. Wandelt, K., Hulse, J., Küppers, J.: Surf. Sci. 104 (1981) 212. Wittrig, T.S., Ibbotson, D.E., Weinberg, W.H.: Surf. Sci. 102 (1981) 506. Agron, P.A., Carlson, T.A.: J. Vac. Sci. Technol. 20 (1982) 815. Christmann, K., Demuth, J.E.: Surf. Sci. 120 (1982) 291. Campbell, C.T., Taylor, T.N.: Surf. Sci. 122 (1982) 119. Christmann, K., Demuth, J.E.: J. Chem. Phys. 76 (1982) 6308. Castro, G.R., Küppers, J.: Surf. Sci. 123 (1982) 456. Campbell, C.T., Taylor, T.N.: Surf. Sci. 118 (1982) 401. Derochette, J.-M.: Phys. Status Solidi A 71 (1982) K99. Derochette, J.-M.: Bull. Soc. R. Sci. Liege 51 (1982) 136. Derochette, J.-M.: Bull. Soc. R. Sci. Liege 51 (1982) 147. Ertl, G., Lee, S.B., Weiss, M.: Surf. Sci. 114 (1982) 515. Erley, W.: Surf. Sci. 114 (1982) 47. Foord, J.S., Lambert, R.M.: Surf. Sci. 115 (1982) 141. Faldt, A.: Surf. Sci. 114 (1982) 311. Hsu, Y., Jacobi, K., Rotermund., H.H.: Surf. Sci. 117 (1982) 581. Heras, J.M., Papp, H., Spiess, W.: Surf. Sci. 117 (1982) 590. Jacobi, K., Rotermund H.H.: Surf. Sci. 116 (1982) 435. Khonde, K., Darville, J., Gilles, J.M.: J. Vac. Sci. Technol. 20 (1982) 834. Kato, H., Sakisaka, Y., Miyano, T., Kamel, K., Nishijima, M., Onchi, M.: Surf. Sci. 144 (1982) 96. Lindgren, S.A., Paul, J., Wallden, L.: Surf. Sci. 117 (1982) 426. Lozovyi, Ya., B., Medvedev, V.K., Smereka, T.P., Palyukh, B.M., Babkin, G.V.: Fiz. Tverd. Tela 24 (1982) 2130; Sov. Phys. Solid State (English Transl.) 24 (1982) 1213. Lakh, Kh.I., Stasyuk, Z.V.: Zh. Tekh. Fiz. 52 (1982) 1397. Lang, N.D., Williams, A.R., Himpsel, F.J., Reihl, B., Eastman, D.E.: Phys. Rev. B 26 (1982) 1728. Lange, P., Grider, D., Neff, H., Sass, J.K., Unwin, R.: Surf. Sci. 118 (1982) L257. Murayama, Z., Kojima, I., Miyazaki, E., Yasumori, I.: Surf. Sci. 118 (1982) L281. Mariani, C., Horn, K., Bradshaw, A.M.: Phys. Rev. B 25 (1982) 7798. Nishitani, R., Oshima, C., Aono, M., Tanaka, T., Kawai, S., Iwasaki, H., Nakamura S.: Surf. Sci. 115 (1982) 48. Nakanishi, S., Kanno, M., Horiguchi, T.: Jpn. J. Appl. Phys. Part 2 - Letters 21 (1982) L419. Park, C., Kramer, H.M., Bauer, E.: Surf. Sci. 115 (1982) 1. Park, C., Kramer, H.M., Bauer, E.: Surf. Sci. 116 (1982) 456. Park, C., Cramer, H.M., Bauer, E.: Surf. Sci. 116 (1982) 467. Popov, G. Bauer, E.: Surf. Sci. 122 (1982) 433. Poelsema, B., Palmer, R.L., Comsa, G.: Surf. Sci. 123 (1982) 152. Popov, G. Bauer, E: Surf. Sci. 123 (1982) 165. Papageorgopoulos, C.A.: Phys. Rev. B 25 (1982) 3740. Richardson, N.V., Palmer, N.R.: Surf. Sci. 114 (1982) L1. Spitzer, A., Lüth, H.: Surf. Sci. 120 (1982) 376. Smith, G.C., Norris, C., Binns, C., Padmore, H.A.: J. Phys. C: Solid State Phys. 15 (1982) 6481. Spitzer, A., Lüth, H.: Surf. Sci. 118 (1982) 121. Spitzer, A., Lüth, H.: Surf. Sci. 118 (1982) 136. Soukiassian, P., Riwan, R., Borenzstein, Y.: Solid State Commun. 44 (1982) 1375. Smith, G.C., Padmore, H.A., Norris, C.: Surf. Sci. 119 (1982) L287. Sakisaka, Y., Kato, H., Onchi, M.: Surf. Sci. 120 (1982) 150. Tochihara, H., Murata, Y.: J. Phys. Soc. Jpn. 51 (1982) 2920. Tysoe, W.T., Lambert, R.M.: Surf. Sci. 115 (1982) 37.
Lando lt -Bö rnst ein New Ser ies III/42 A2
4.2-126 83A 83A2 83A3 83B 83B3 83B4 83B5 83C 83G 83G2 83G3 83H 83J 83K 83K2 83K3 83M 83M2 83N 83N2 83N3 83O 83P 83P2 83P3 83P4 83P5 83R 83R2 83S 83S2 83S3 83T 83T2 83W 83W2 83Z 84A 84A2 84B 84B2 84B3 84B4 84C 84F 84G 84G2 84H
4.2 Electron work function of metals and semiconductors Andersson, S., Harris, J.: Phys. Rev. B 27 (1983) 9. Al-Rawi, O.Z., Jones, J.P.: Surf. Sci. 124 (1983) 220. Artamonov, O.M., Smirnov, O.M., Terekhov, A.N.: Poverkhnost Fizika Khimiya Mekhanika (1983); Phys. Chem. Mech. Surfaces (English Transl.) 2 (1985) 2281. Behm, R.J., Thiel, P.A., Norton, P.R., Ertl., G.: J. Chem. Phys. 78 (1983) 7437. Blaszczyszyn, M., Blaszczyszyn, R., Meclewski, R., Melmed, A.J., Madey, T.E.: Surf. Sci. 131 (1983) 433. Bange, K., Döhl, R., Grider, D.E., Sass, J.K.: Vacuum 33 (1983) 757. Benndorf, C., Madey, T.E.: Surf. Sci. 135 (1983) 164. Cattania, M.G., Penka, V., Behm, R.J., Christmann, K., Ertl, G.: Surf. Sci. 126 (1983) 382. Gudde, N.J., Lambert, R.M.: Surf. Sci. 134 (1983) 703. Gardiner, T.M.: Thin Solid Films 105 (1983) 213. Gudde, N.J., Lambert, R.M.: Surf. Sci. 124 (1983) 372. Hayden, B.E., Prince, K.C., Davie, P.J., Paolucci, G., Bradshaw, A.M.: Solid State Commun. 48 (1983) 325. Jackman, T.E., Griffiths, K., Davies, J.A., Norton, P.R.: J. Chem. Phys. 79 (1983) 3529. Koel, B.E., Peebles, D.E., White, J.M.: Surf. Sci. 125 (1983) 709. Khonde, K., Darville, J., Gilles, J.M.: Surf. Sci. 126 (1983) 414. Kiskinova, M., Pirug, G., Bonzel, H.P.: Surf. Sci. 133 (1983) 321. Mattern-Klosson, M., Ding, X.M., Lüth, H., Spitzer, A.: Surf. Sci. 129 (1983) 1. Miranda, R., Daiser, S., Wandelt, K., Ertl, G.: Surf. Sci. 131 (1983) 61. Nakanishi, S., Horiguchi, T.: Surf. Sci. 125 (1983) 605. Niehus, H.: Surf. Sci. 130 (1983) 41. Nakanishi, S., Horiguchi, T.: Surf. Sci. 133 (1983) 605. Okano, T.: Jpn. J. Appl. Phys. 22 (1983) 1496. Pradier, C.M., Berthier, Y., Margot, E., Oudar, J.: J. Microsc. Spectrosc. Electron. 8 (1983) 269. Pfnür, H., Menzel, D.: J. Chem. Phys. 79 (1983) 2400. Polanski, J., Sidorski, Z., Zuber, S.: Acta Phys. Pol. A 64 (1983) 377. Papp, H.: Surf. Sci. 129 (1983) 205. Phu, S.U., Bardolle, J., Bujor, M.: Surf. Sci. 129 (1983) 219. Reed, A.P.C., Lambert, R.M., Foord, J.S.: Surf. Sci. 134 (1983) 689. Rotermund, H.H., Jacobi, K.: Surf. Sci. 126 (1983) 32. Stott, Z.T., Hughes, H.P.: Surf. Sci. 126 (1983) 455. Sexton, B.A., Avery, N.R.: Surf. Sci. 129 (1983) 21. Salmerón, M., Ferrer, S., Jazzar, M., Somorjai, G.A.: Phys. Rev. B 28 (1983) 6758. Taylor, T.N., Campbell, C.T., Rogers, J.W.Jr., Ellis, W.P., White, J.M.: Surf. Sci. 134 (1983) 529. Tochihara, H.: Surf. Sci. 126 (1983) 523. Walldén, L.: Surf. Sci. 134 (1983) L513. Wimmer, E., Freeman, A.J., Hiskes, J.R., Karo, A.M.: Phys. Rev. B 28 (1983) 3074. Zubenko, Yu.V., Ishmukhametov, M.B.: Fiz. Tverd. Tela 25 (1983) 1239 (Sov. Phys. Solid State 25 (1983) 98). Argile, C., Barthes-Labrousse, M.-G., Rhead, G.E.: Surf. Sci. 138 (1984) 181. Avery, N.R.: Surf. Sci. 146 (1984) 363. Bange, K., Grider, D.E., Madey, T.E., Sass, J.K.: Surf. Sci. 137 (1984) 38. Brown, A., Vickerman, J.C.: Surf. Sci. 140 (1984) 261. Bozso, F., Arias, J., Hanrahan, C.P., Yates, J.T. Jr., Martin, R.M., Metiu, H.: Surf. Sci. 141 (1984) 591. Billy, J., Abon, M.: Surf. Sci. 146 (1984) L525. Chen, Y.C., Cunningham, J.E., Flynn, C.P.: Phys. Rev. B 30 (1984) 7317. Foord, J.S., Lambert, R.M.: Surf. Sci. 138 (1984) 258. Godowski, P., Mroz, S.: Thin Solid Films 111 (1984) 129. Griffiths, K., Jackman, T.E., Davies, J.A., Norton, P.R.: Surf. Sci. 138 (1984) 113. Ho, P., White, J.M.: Surf. Sci. 137 (1984) 103. Lando lt -Börnst ein New Ser ies III/42A2
4.2 Electron work function of metals and semiconductors 84H2 84H3 84H5 84K 84K2 84K3 84K4 84K5 84M 84M2 84N 84P 84P3 84P4 84P5 84P6 84R 84R2 84R3 84S 84S2 84S3 84S4 84S5 84S6 84S7 84S8 84S9 84S10 84S11 84W 85A 85B 85B3 85B4 85C 85D 85D2 85D3 85E 85F 85F2 85G 85H 85H2 85H3 85H4 85I 85I2 85K 85K2
4.2-127
Ho, P., White, J.M.: Surf. Sci. 137 (1984) 117. Hrbek, J., dePaola, R.A., Hoffmann, F.M.: J. Chem. Phys. 81 (1984) 2818. Horlacher, A., Smith R.A., Barker, R.A., Estrup, P.J.: Surf. Sci. 136 (1984) 327. Klimesh, P., Meyer, G., Henzler, M.: Surf. Sci. 137 (1984) 79. Kolaczkiewicz, J., Bauer, E.: Surf. Sci. 144 (1984) 477. Kolaczkiewicz, J., Bauer, E.: Surf. Sci. 144 (1984) 495. Kanash, O.V., Fedorus, A.G.: Zh. Eksp. Teor. Fiz. 86 (1984) 223; Sov. Phys. JETP (English Transl.) 59 (1984) 126. Kiskinova, M., Pirug, G., Bonzel, H.P.: Surf. Sci. 136 (1984) 285. Moog, E.R., Webb, M.B.: Surf. Sci. 148 (1984) 338. Maurice, V., Peralta, L., Berthier, Y., Oudar, J.: Surf. Sci. 148 (1984) 623. Norton, P.R., Griffiths, K., Bindner, P.E.: Surf. Sci. 138 (1984) 125. Peebles, D.E., Peebles, H.C., White, J.M.: Surf. Sci. 136 (1984) 463. Ping, C., Bolmont, D., Sebenne, C.A.: J. Phys. C: Solid State Phys. 17 (1984) 4897. Peebles D.E., White, J.M.: Surf. Sci. 144 (1984) 512. Peebles, D.E., White, J.M.: Surf. Sci. 148 (1984) 656. Peebles, D.E., Peebles, H.C., White, J.M.: Surf. Sci. 136 (1984) 463. Ruette, F., Blyholder, G., Head, J.D.: Surf. Sci. 137 (1984) 491. Ritz, A., Spitzer, A., Lüth, H.: Appl. Phys. A 34 (1984) 31. Rodway, D.: Surf. Sci. 147 (1984) 103. Surnev, L., Tikhov, M.: Surf. Sci. 138 (1984) 40. Seip, U., Tsai, M.-C., Christmann, K., Küppers, J., Ertl, G.: Surf. Sci. 139 (1984) 29. Surnev, L., Bliznakov, G., Kiskinova, M.: Surf. Sci. 140 (1984) 249. Sass, J.K., Bange, K., Dohl, R., Piltz, E., Unwin, R.: Ber. Bunsen-Ges. Phys. Chem. 88 (1984) 354. Shayegan, M., Cavallo, J.M., Glover, R.E., Park, R.L.: Phys. Rev. Lett. 53 (1984) 1578. Spitzer, A., Lüth, H.: Phys. Rev. B 30 (1984) 3098. Schaefer, J.E.: Surf. Sci. 148 (1984) 581. Sass, J.K., Richardson, N.V.: Surf. Sci. 139 (1984) L204. Sidorski, Z.: Appl. Phys. A 33 (1984) 213. Sakisaka, Y., Miyano, T., Onchi, M.: Phys. Rev. B 30 (1984) 6849. Sun, Y.-M., Luftman, H.S., White, J.M.: Surf. Sci. 139 (1984) 379. Wandelt, K., Hulse, J.E.: J. Chem. Phys. 80 (1984) 1340. Abon, M., Bertolini, J.C., Billy, J., Massardier, J., Tardy, B.: Surf. Sci. 162 (1985) 395. Benndorf, C., Krüger, B.: Surf. Sci. 151 (1985) 271. Behm, R.J., Ertl, G., Penka, V.: Surf. Sci. 160 (1985) 387. Baldinger, T., Bechtold, E.: Surf. Sci. 159 (1985) 406. Cousty, J., Riwan, R., Soukiassian, P.: J. Phys. (Paris) 46 (1985) 1693. Derry, G.N., Ross, P.N.: J. Chem. Phys. 82 (1985) 2772. Dolle, P., Alnot, M., Ehrhardt, J.J., Thomy, A., Cassuto, A.: Surf. Sci. 152-153 (1985) 620. de Paola, R.A., Hrbek, J., Hoffmann, F.M.: J. Chem. Phys. 82 (1985) 2484. Eyink, K.G., Lamartine, B.C., Haas, T.W.: Appl. Surf. Sci. 21 (1985) 29. Feulner, P., Menzel, D.: Surf. Sci. 154 (1985) 465. Foord, J.S., Lambert, R.M.: Surf. Sci. 161 (1985) 513. Griffiths, K., Norton, P.R., Davies, J.A., Unertl, W.N., Jackman, T.E.: Surf. Sci. 152/153 (1985) 374. Hegde, R.I., Tobin, J., White, J.M.: J. Vac. Sci. Technol. A 3 (1985) 339. Hochst, H., Colavita E., Fisher, G.B.: J. Vac. Sci. Technol. A 3 (1985) 1554. Hegde, R.I., Greenlief, C.M., White, J.M.: J. Phys. Chem. 89 (1985) 2886. Hrbek, J.: Surf. Sci. 164 (1985) 139. Ismail, A., Ben Brahim, A., Palau, J.M., Lassabatere, L.: Surf. Sci. 162 (1985) 195. Ishida, H., Shima, N., Tsukada, M.: Surf. Sci. 158 (1985) 438. Kolaczkiewicz, J., Bauer, E.: Surf. Sci. 154 (1985) 357. Koenders, L., Bartels, F., Ullrich, H., Mönch, W.: J. Vac. Sci. Technol. B 3 (1985) 1107.
Lando lt -Bö rnst ein New Ser ies III/42 A2
4.2-128 85K3 85K4 85K5 85K6 85K7 85K8 85K9 85K10 85L 85L2 85M 85P 85P2 85P3 85P4 85P5 85S 85S2 85S3 85S4 85S5 85S6 85S7 85T 85T2 85T3 85T4 85W 86A 86A2 86A3 86A4 86B 86B2 86B3 86B4 86B5 86C 86C2 86D 86E 86E2 86E3 86E4 86F 86F2 86F3 86F4 86H 86H2 86H3 86H4
4.2 Electron work function of metals and semiconductors Kojima, I., Orita, M., Miyazaki, E., Otani, S.: Surf. Sci. 160 (1985) 153. Kamaratos, M., Papageorgopoulos, C.A.: Surf. Sci. 160 (1985) 451. Kim, H., Okuno, K.: J. Vac. Sci. Technol. A 3 (1985) 2215. Kolaczkiewicz, J., Bauer, E.: Surf. Sci. 160 (1985) 1. Kiskinova, M., Rangelov, G., Surnev, L.: Surf. Sci. 150 (1985) 339. Kolaczkiewicz, J., Bauer, E.: Surf. Sci. 151 (1985) 347. Kennou, S., Ladas, S., Papageorgopoulos, C.: Surf. Sci. 164 (1985) 290. Kennou, S., Ladas, S., Papageorgopoulos, C.: Surf. Sci. 152/153 (1985) 1213. Lackey, D., Surman, M., Jacobs, S., Grider, D., King, D.A.: Surf. Sci. 152/153 (1985) 513. Lee, J., Hanrahan, C.P., Arias, J., Martin, R.M., Metiu, H.: Surf. Sci. 161 (1985) L543. Markert, K., Wandelt, K.: Surf. Sci. 159 (1985) 24. Paffett, M.T., Campbell, C.T., Taylor, T.N., Srinivasan, S.: Surf. Sci. 154 (1985) 284. Papageorgopoulos, C., Kamaratos, M.: Surf. Sci. 164 (1985) 353. Paffett, M.T., Campbell, C.T., Taylor, T.N.: Langmuir 1 (1985) 741. Parker, S.D.: Surf. Sci. 157 (1985) 261. Park, Ch., Bauer, E., Poppa, H.: Surf. Sci. 154 (1985) 371. Shayegan, M., Williams, E.D., Glover, R.E.III, Park, R.L.: Surf. Sci. 154 (1985) L239. Strasser, G., Grunze, M., Golze, M.: J. Vac. Sci. Technol. A 3 (1985) 1562. Sporken, R., Thiry, P.A., Pireaux, J.J., Caudano, R., Adnot, A.: Surf. Sci. 160 (1985) 443. Smith, K.E., Henrich, V.E.: Phys. Rev. B 32 (1985) 5384. Spitzer, A., Ritz, A., Lüth, H.: Surf. Sci. 152/153 (1985) 543. Stroscio, J.A., Bare, S.R., Ho, W.: Surf. Sci. 154 (1985) 35. Surnev, L., Rangelov, G., Bliznakov, G.: Surf. Sci. 159 (1985) 299. Tatarenko, S., Alnot, M., Ehrhardt, J.J., Ducros, R.: Surf. Sci. 152-153 (1985) 471. Taleb-Ibrahimi, A., Mercier, V., Sebenne, C.A., Bolmont, D., Chen, P.: Surf. Sci. 152-153 (1985) 1228. Tatarenko, S., Alnot, M., Ducros, R.: Surf. Sci. 163 (1985) 249. Taleb-Ibrahimi, A., Sebenne, C.A., Proix, F., Maigne, P.: Surf. Sci. 163 (1985) 478. Woratschek, B., Sesselmann, W., Küppers, J., Ertl, G., Haberland, H.: Phys. Rev. Lett. 55 (1985) 1231. Azizan, M., Nguyen Tan, T.A., Ciut, R., Baptist, R., Chauvet, G.: Surf. Sci. 178 (1986) 17. Abon, M., Billy, J., Bertolini, J.C.: Surf. Sci. 171 (1986) L387. Abon, M., Billy, J., Bertolini, J.C., Tardy, B.: Surf. Sci. 167 (1986) 1. Aruge, T., Tochihara, H., Murata, Y.: Phys. Rev. B 34 (1986) 8237. Benndorf, C., Nieber, B.: J. Vac. Sci. Technol. A 4 (1986) 1355. Baier H.-U., Koenders, L., Mönch, W.: J. Vac. Sci. Technol. B 4 (1986) 1095. Behner, H., Spiess, W., Wedler, G., Borgmann, D.: Surf. Sci. 175 (1986) 276. Breitschafter, M.J., Umbach, E., Menzel, D.: Surf. Sci. 178 (1986) 725. Behm, R.J., Brundle, C.R., Wandelt, K.: J. Chem. Phys. 85 (1986) 1061. Chrzanowski, E., Bauer, E.: Surf. Sci. 173 (1986) 106. Chelvayohan, M., Gomer, R.: Surf. Sci. 172 (1986) 337. Döhl-Oelze, R., Stuve, E.M., Sass, J.K.: Solid State Commun. 57 (1986) 323. Eiswirth, M., Ertl., G.: Surf. Sci. 177 (1986) 90. Erley, W., Ibach, H.: Surf. Sci. 178 (1986) 565. Eder, S., Markert, Jablonski, A., Wandelt, K.: Ber. Bunsenges. Phys. Chem. 90 (1986) 225. Erley, W., Ibach, H.: Surf. Sci. 178 (1986) 565. Feyer, N., Kiskinova, M., Pirug, G., Bonzel, H.P.: Appl. Phys. A 39 (1986) 209. Freyer, N., Kiskinova, M., Pirug, G., Bonzel, H.P.: Surf. Sci. 166 (1986) 206. Fusy, J., Ducros, R.: Surf. Sci. 176 (1986) 157. Foord, J.S., Lambert, R.M.: Surf. Sci. 169 (1986) 327. Hendrickx, H.A.C.M., Nieuwenhuys, B.E.: Surf. Sci. 175 (1986) 185. Herlt, H.-J., Bauer, E.: Surf. Sci. 175 (1986) 336. Hrbek, J.: J. Phys. Chem. 90 (1986) 6217. Harrison, K., Lambert, R.M., Prince, R.H.: Surf. Sci. 176 (1986) 530. Lando lt -Börnst ein New Ser ies III/42A2
4.2 Electron work function of metals and semiconductors 86H5 86H6 86I 86I2 86J3 86K 86K2 86K3 86M 86M2 86M3 86N 86N2 86N3 86O 86P 86P2 86P3 86S 86S2 86U 86V 87A 87A2 87A3 87A4 87B 87B2 87B3 87B4 87B5 87B6 87B7 87C 87C2 87D 87D2 87E 87F 87G 87H 87I 87J 87J2 87K 87K2 87L 87N 87N2
4.2-129
Hu, Z.P., Wu, N.J., Ignatiev, A.: Surf. Sci. 177 (1986) L956. Hardegree, E.L., Ho, P., White, J.M.: Surf. Sci. 165 (1986) 488. Inoue, M., Ueda, K.: Jpn. J. Appl. Phys. Part 1, 25 (1986) 802. Ismail, A., Palau, J.M., Lassabatere L.: J. Appl. Phys. 60 (1986) 1730. Jablonski, A., Eder, S., Markert, K., Wandelt, K.: J. Vac. Sci. Technol. A 4 (1986) 1510. Kirstein, W., Kruger, B., Thieme, F.: Surf. Sci. 176 (1986) 505. Kolaczkiewicz, J.. Bauer, E.: Surf. Sci. 175 (1986) 487. Krüger, B., Benndorf, C.: Surf. Sci. 178 (1986) 704. Mroz, S., Bauer, E.: Surf. Sci. 169 (1986) 394. Mullins, D.R., White, J.M., Luftman, H.S.: Surf. Sci. 167 (1986) 39. Miyano, T., Sakisaka, Y., Komeda, T., Onchi, M.: Surf. Sci. 169 (1986) 197. Nishigaki, S., Komatsu, T., Arimoto, M., Sugihara, M.: Surf. Sci. 167 (1986) 27. Norton, P.R., Bindner, P.E., Jackman, T.E.: Surf. Sci. 175 (1986) 313. Norton, P.R., Bindner, P.E.: Surf. Sci. 169 (1986) L259. Oellig, E.M., Miranda, R.: Surf. Sci. 177 (1986) L947. Paffett, M.T., Campbell, C.T., Taylor, T.N.: J. Chem. Phys. 85 (1986) 6176. Parker, S.D., Dobson, P.J.: Surf. Sci. 171 (1986) 267. Parker, S.D., Rhead, G.E.: Surf. Sci. 167 (1986) 271. Sendecki, S.: Surf. Sci. 165 (1986) 402. Schönhense, G.: Appl. Phys. A 41 (1986) 39. Uram, K.J., Ng, L., Yates Jr., J.T.: Surf. Sci. 177 (1986) 253. Vladimirov, G.G., Rump, G.A.: Poverkhnost N10 (1986) 61. Alnot, M., Gorodetskii, V., Cassuto, A., Ehrhardt, J.J.: Thin Solid Films 151 (1987) 251. Attard, G.A., King, D.A.: Surf. Sci. 188 (1987) 589. Andriamanantenaosa, I., Lacharme, J.P., Sebenne, C.A.: Surf. Sci. 189-190 (1987) 563. Argile, C., Rhead, G.E.: Thin Solid Films 152 (1987) 546. Bartos, B., Freund, H.-J., Kuhlenbeck, H., Neumann, M., Lindner, H., Müller, K.: Surf. Sci. 179 (1987) 59. Bange, K., Madey, T.E., Sass, J.K., Stuve, E.M.: Surf. Sci. 183 (1987) 334. Bonnet, J., Soonckindt, L., Ismail, A., Lassabatere, L.: Thin Solid Films 151 (1987) 103. Benndorf, C., Nieber, B., Krüger, B.: Surf. Sci. 189-190 (1987) 511. Bucci, J.V., Swirbel, T.J., Vook, R.W., Schwarz, J.A.: Scanning Microscopy 1 (1987) 1001. Berkó, A., Solymosi, F.: Surf. Sci. 187 (1987) 359. Barnes, C.J., Asonen, H., Salokatve, A., Pessa, M.: Surf. Sci. 184 (1987) 163. Chelvayohan, M., Gomer, R.: Surf. Sci. 186 (1987) 412. Christmann, K., Ehsasi, M.: Appl. Phys. A 44 (1987) 87. de Paola, R.A., Hoffmann, F.M., Heskett, D., Plummer, E.W.: Phys. Rev. B 35 (1987) 4236. Dubois, L.H., Zegarski, B.R., Luftman, H.S.: J. Chem. Phys. 87 (1987) 1367. Engstrom, J.R., Tsai, W., Weinberg, W.H.: J. Chem. Phys. 87 (1987) 3104. Foord, J.S., Lambert, R.M.: Surf. Sci. 185 (1987) L483. Gonchar, F.M., Medvedev, V.K., Smereka, T.P., Lozovyi, Ya.B., Babkin, G.V.: Fiz. Tverd. Tela 29 (1987) 2833; Sov. Phys. Solid State (English Transl.) 29 (1987) 1629. Hohlfeld, A., Sunjic, M., Horn, K.: J. Vac. Sci. Technol. A 5 (1987) 679. Inoue, M.: Jpn. J. Appl. Phys. Part 1, 26 (1987) 300. Jackman, T.E., Griffiths, K., Unertl, W.N., Davies, J.A., Gürtler K.H., Harrington, D.A., Norton P.R.: Surf. Sci. 179 (1987) 297. Jacobi, K.: Surf. Sci. 192 (1987) 499. Kalis, T., Belyaeva, M.E., Sergeev, S.I.: Elektrokhimiya 23 (1987) 126. (Sov. Electrochemistry (English Transl.)). Kiskinova, M.: Surf. Sci. 182 (1987) 150. Ladas, S., Kennou, S., Kamaratos, M., Foulias, S.D., Papageorgopoulos, C.: Surf. Sci. 189/190 (1987) 261. Nöbl, C., Benndorf, C.: Surf. Sci. 182 (1987) 499. Nix, R.M., Lambert, R.M.: Surf. Sci. 186 (1987) 163.
Lando lt -Bö rnst ein New Ser ies III/42 A2
4.2-130 87O 87O2 87P 87P2 87P3 87R 87S 87S2 87S3 87S4 87S5 87T 87W 88A 88A2 88B 88B2 88B3 88D 88E 88F 88F2 88G 88G2 88G3 88H 88H2 88H3 88H4 88H5 88H6 88I 88J 88J2 88J3 88J4 88K 88K2 88L 88M 88M2 88N 88N2 88N3 88N4 88N5 88O 88P
4.2 Electron work function of metals and semiconductors Onellion, M., Eskine, J.L.: Phys. Rev. B 36 (1987) 4495. Ortega, J.E., Oellig, E.M., Ferron, J., Miranda, R.: Phys. Rev. B 36 (1987) 6213. Park, C., Bauer, E., Poppa, H.: Surf. Sci. 187 (1987) 86. Paul, J.: J. Vac. Sci. Technol. A 5 (1987) 664. Patterson, C.H., Lambert, R.M.: Surf. Sci. 187 (1987) 339. Rangelov, G., Surnev, L.: Surf. Sci. 185 (1987) 457. Surnev, L.,Rangelov, G., Kiskinova, M.: Surf. Sci. 179 (1987) 283. Stenborg, A., Bauer, E.: Surf. Sci. 185 (1987) 394. Stenborg, A., Bauer, E.: Surf. Sci. 189-190 (1987) 570. Stenborg, A., Bauer, E.: Phys. Rev. B 36 (1987) 5840. Steinberger, I.T., Wandelt, K.: Phys. Rev. Lett. 58 (1987) 2494. Tompa, G.S., Seidl, M., Ermler, W.C., Carr, W.E.: Surf. Sci. 185 (1987) L453. Wandelt, K., in: Wißmann, P. (ed.), “Chemisorption on metal films”, Elsevier, 1990, p. 280. Astaldi, C., Jacobi, K.: Surf. Sci. 200 (1988) 15. Argile, C., Rhead, G.E.: Surf. Sci. 203 (1988) 175. Beckerle, J.D., Yang, Q.Y., Johnson A.D., Ceyer, S.T.: Surf. Sci. 195 (1988) 77. Bourgeois, S., Poirault, R., Plociennik J.-M., Randriamanivo, A.: J. Microsc. Spectrosc. Electron 13 (1988) 89. Berlowitz, P.J., Houston, J.E., White, J.M., Goodman, D.W.: Surf. Sci. 205 (1988) 1. Duszak, R., Prince, R.H.: Surf. Sci. 205 (1988) 143. Ehsasi, M., Christmann. K.: Surf. Sci. 194 (1988) 172. Faldt, A., Kristensson, D.K., Myers, H.P.: Phys. Rev. B 37 (1988) 2682. Frick, B., Jacobi, K.: Phys. Rev. B 37 (1988) 4408. Griffiths, K.: J. Vac. Sci. Technol. A 6 (1988) 210. Gonchar, F.M., Smereka, T.P., Stepanovskii, S.I., Babkin, G.V.: Fiz. Tverd. Tela 30 (1988) 3541; Sov. Phys. Solid State (English Transl.) 30 (1988) 2035. Gidley, D.W., Koymen, A.R., Capehart, T.W.: Phys. Rev. B 37 (1988) 2465. Harrington, D.A., Norton, P.R.: Surf. Sci. 195 (1988) L135. Hoffmann, F.M., Rocker, G., Tochihara, H., Martin, R.M., Metiu, H.: Surf. Sci. 205 (1988) 397. Haase, G., Asscher, M., Linke, U.: Appl. Surf. Sci. 35 (1988) 1. He, J.-W., Harrington, D.A., Griffiths K., Norton, P.R.: Surf. Sci. 198 (1988) 413. He, J.-W., Memmert, U., Griffiths, K., Lennard, W.N., Norton, P.R.: Surf. Sci. 202 (1988) L555. Hagaus, P.L., Guo, X., Chorkendorff, I., Winkler, A., Siddiqui, H., Yates, J.T.: Surf. Sci. 203 (1988) 1. Imbihl R., Ladas, S., Ertl, G.: Surf. Sci. 206 (1988) L903. Jacobi, K.: Phys. Rev. B 38 (1988) 5869. Jakob, P., Menzel, D.: Surf. Sci. 201 (1988) 503. Jaegermann, W.: Ber. Bunsen-Ges. Phys. Chem. 92 (1988) 537. Jacobi, K.: Phys. Rev. B 38 (1988) 6291. Kiskinova, M., Tikhov, M., Bliznakov, G.: Surf. Sci. 204 (1988) 35. Kiskinova, M., Szabo, A., Yates Jr., J.T.: J. Chem. Phys. 89 (1988) 7599. Lin, J.C., Shamir, N., Gomer, R.: Surf. Sci. 206 (1988) 61. Memmert, U., Norton, P.R.: Surf. Sci. 203 (1988) L689. Mate, C.M., Kao, Ch.-T., Somorjai, G.A.: Surf. Sci. 206 (1988) 145. Nakanishi, S., Sasaki, K.: Surf. Sci. 194 (1988) 245. Netzer, F.P., Rangelov, G., Rosina, G., Saalfeld, H.B.: J. Chem. Phys. 89 (1988) 3331. Netzer, F.P., Rangelov, G., Rosina, G., Saalfeld, H.B., Neumann, M., Lloyd, D.R.: Phys. Rev. B 37 (1988) 10399. Nishigaki, S., Ohara, M., Murakami, A., Fukui, S., Matsuda, S.: Appl. Surf. Sci. 35 (1988) 121. Nix, R.M., Judd, R.W., Lambert, R.M.: Surf. Sci. 203 (1988)307. Onishi, H., Aruga, T., Egawa, C., Iwasawa, Y.: Surf. Sci. 193 (1988) 33. Park, C.: Surf. Sci. 203 (1988) 395. Lando lt -Börnst ein New Ser ies III/42A2
4.2 Electron work function of metals and semiconductors 88P2 88R 88R2 88S 88S2 88T 88T2 88U 88V 88V2 88W 88X 88Z 89A 89B 89B2 89B3 89B4 89C 89D 89E 89E2 89E3 89F 89G 89G2 89G3 89H 89H2 89J 89J2 89J3 89K 89L 89L2 89M 89M2 89M3 89O 89P 89P2 89R 89R2 89S 89S2 89S3 89Y 89Z 89Z2
4.2-131
Packard, W.E., Webb, M.B.: Surf. Sci. 195 (1988) 371. Rosenzweig, Z., Asscher, M.: Surf. Sci. 204 (1988) L732. Rump, G.A., Vladimirov, G.G., Magkoev, T.T.: Poverkhnost N3 (1988) 54. Silvestre, C., Shayegan, M.: Phys. Rev. B 37 (1988) 10432. Surnev, L., Xu, Z., Yates Jr., J.T.: Surf. Sci. 201 (1988) 14. Tikhov, M., Bauer, E.: Surf. Sci. 203 (1988) 423. Tysoe, W.T., Lambert, R.M.: Surf. Sci. 199 (1988) 1. Ueda, K., Mega, T.: Jpn. J. Appl. Phys. Part 1, 27 (1988) 2227. Vook, R.W., Swirbel, T.J., Bucci, J.V.: J. Vac. Sci. Technol. A 6 (1988) 1710. Vook, R.W., Swirbel, T.J., Chao, S.S.: Appl. Surf. Sci. 33-34 (1988) 220. Windham, R.G., Bartram, M.E., Koel, B.E.: J. Chem. Phys. 92 (1988) 2862. Xu, Y. : Proceedings of the Chinese-Japanese Joint Seminar on Vacuum and Surface Analysis (VASA-85). Vacuum and Surface Analysis. Vol. 1. World Scientific. (1988) 192. Zhou, X.-L., Zhu, X.-Y., White, J.M.: Surf. Sci. 193 (1988) 387. Alnot, M., Ehrhardt, J.J., Barnard J.A.: Surf. Sci. 208 (1989) 285. Bermudez, V.M., Glass, A.S.: J. Vac. Sci. Technol. A 7 (1989) 1961. Bermudez, V.M.: J. Appl. Phys. 66 (1989) 6084. Berlowitz, P.J., Shinn, N.D.: Surf. Sci. 209 (1989) 345. Blass, P.M., Zhou, X.-L., White, J.M.: Surf. Sci. 215 (1989) 74. Cousty, J., Papageorgopoulos, C.A., Riwan, R.: Surf. Sci. 223 (1989) 479. Dolle, P., Tommasini, M., Jupille, J.: Surf. Sci. 211/212 (1989) 904. Ernst-Vidalis, M.-L., Bauer, E.: Surf. Sci. 215 (1989) 378. Enta, Y., Kinoshita, T., Suzuki, S., Kono, S.: Phys. Rev. B 39 (1989) 1125. Ernst, K.H., Christmann, K.: Surf. Sci. 224 (1989) 277. Fusy, J., Ducros, R.: Surf. Sci. 214 (1989) 337. Gonchar, F.M., Medvedev, V.K., Smereka, T.P., Savichev, V.V.: Fiz. Tverd. Tela 31 (1989) 249; Sov. Phys. Solid State (English Transl.) 31 (1989) 1056. Glander, G.S., Webb, M.B.: Surf. Sci. 222 (1989) 64. Glander, G.S., Webb, M.B.: Surf. Sci. 224 (1989) 60. He, J.-W., Memmert, U., Norton, P.R.: J. Chem. Phys. 90 (1989) 5088. Hohlfeld, A., Horn, K.: Surf. Sci. 211/212 (1989) 844. Johnson, B.G., Berlowitz, P.J., Goodman, W.D., Bartholomew, C.H.: Surf. Sci. 217 (1989) 13. Jacobi, K., Astaldi, C., Geng, P., Bertolo, M.: Surf. Sci. 223 (1989) 569. Jaffey, D.M., Gellman, A.J., Lambert, R.M.: Surf. Sci. 214 (1989) 407. Kiss, J., Klivenyi, G., Revesz, K., Solymosi, F.: Surf. Sci. 223 (1989) 551. Lauth, G., Solomun, T., Hirschwald, W., Christmann, K.: Surf. Sci. 210 (1989) 201. Lauth, G., Schwarz, E., Christmann, K.: J. Chem. Phys. 91 (1989) 3729. Memmert, U., He, J.-W., Griffiths, K., Lennard, W.N., Norton, P.R., Richardson N.V., Jackman, T.E., Unertl, W.N.: J. Vac. Sci. Technol. A 7 (1989) 2152. Memmert, U., Bushby, S.J., Norton, P.R.: Surf. Sci. 219 (1989) 327. Maeda Wong, T., Heskett, D., Dinardo, N.J., Plummer, E.W.: Surf. Sci. 208 (1989) L1. Oral, B., Kothari, R., Vook, R.W.: J. Vac. Sci. Technol. A 7 (1989) 2020. Pache, T., Steinruck, H.-P., Huber, W., Menzel, D.: Surf. Sci. 224 (1989) 195. Parker, D.H., Bartram, M.E., Koel, B.E.: Surf. Sci. 217 (1989) 489. Ruckman, M.W., Jiang, L.Q., Strongin, M.: Surf. Sci. 221 (1989) 144. Ramsey, M.G., Rosina, G., Netzer, F.P., Saalfeld, H.B., Lloyd, D.R.: Surf. Sci. 217 (1989) 140. Sendecki, S.: Surf. Sci. 213 (1989) 430. Shamir, N., Lin, J.C., Gomer, R.: Surf. Sci. 214 (1989) 74. Shamir, N., Gomer, R.: Surf. Sci. 216 (1989) 49. Ying, Z.C., Ho, W.: J. Chem. Phys. 91 (1989) 5050. Zhou, X.-L., Solymosi, F., Blass, P.M., Cannon, K.C., White, J.M.: Surf. Sci. 219 (1989) 294. Zhou, X.-L., White, J.M.: Surf. Sci. 221 (1989) 534.
Lando lt -Bö rnst ein New Ser ies III/42 A2
4.2-132 89Z3 90A 90B 90C 90D 90D2 90E 90H 90H2 90H3 90H4 90K 90K2 90L 90M 90N 90N2 90P 90R 90R2 90R3 90S 90S2 90S3 90T 90Z 90Z2 91A 91B 91B2 91B4 91C 91C2 91C3 91D 91E 91F 91H 91H2 91H3 91K 91K2 91K3 91K4 91L 91M2 91N 91O 91P 91P2
4.2 Electron work function of metals and semiconductors Zhou, X.-L., White, J.M., Koel, B.E.: Surf. Sci. 218 (1989) 201. Azizan, M., Nguyen Tan, T.A., Veuillen, J.Y.: Vacuum 41 (1990) 1132. Bertolo, M., Jacobi, K.: Surf. Sci. 226 (1990) 207. Callen, B.W., Griffiths, K., Memmert, U., Harrington, D.A., Bushby, S.J., Norton P.R.: Surf. Sci. 230 (1990) 159. Domenicucci, A., Vook, R.W.: Thin Solid Films 193-194 (1990) 227. Duszak, R., Prince, R.H.: Surf. Sci. 226 (1990) 33. Ehsasi, M., Rezaie-Serej, S., Block, J.H., Christmann, K.: J. Chem. Phys. 92 (1990) 7596. Höchst, H., Engelhardt, M.A.: Proc. SPIE Int. Soc. Opt. Eng. 1190 (1990) 17. He, J.-W., Norton, P.R.: Surf. Sci. 230 (1990) 150. Hollering, R.W.J., Dijkamp, D., Lindelauf, H.W.L., van der Heide, P.A.M., Krijn, M.P.C.M.: J. Vac. Sci. Technol. A 8 (1990) 3997. He, J.-W., Norton, P.R.: Surf. Sci. 238 (1990) 95. Kolaczkiewicz, J.: Surf. Sci. 231 (1990) 103. Kolaczkiewicz, J., Hochól, M., Zuber, S.: Surf. Sci. 247 (1991) 284. Li, X.Q.D., Vanselow, R.: Surf. Sci. 236 (1990) L369. Magnusson, K.O., Reihl, B.: Phys. Rev. B 41 (1990) 12071. Nieber, B., Benndorf, C.: Surf. Sci. 235 (1990) 129. Nishigaki, S., Matsuda, S., Sasaki, T., Kawanishi, N., Ikeda, Y., Takeda, H.: Surf. Sci. 231 (1990) 271. Puckrin, E., Slavin, A.J.: Phys. Rev. B 41 (1990) 4970. Ray, K.B., Hannon, J.B., Plummer, E.W.: Chem. Phys. Lett. 171 (1990) 469. Rosenzweig, Z., Asscher, M., Wittenzellner, C.: Surf. Sci. 240 (1990) L583. Reihl, B., Magnusson, K.O.: Phys. Rev. B 42 (1990) 11839. Shinn, N.D.: Phys. Rev. B 41 (1990) 9771. Solymosi, F., Berko, A., Revesz, K.: Surf. Sci. 240 (1990) 50. Singh, N.K., Jones, R.G.: Surf. Sci. 232 (1990) 229. Tikhov, M., Bauer, E.: Surf. Sci. 232 (1990) 73. Zhao, Y.B., Gomer, R.: Surf. Sci. 239 (1990) 189. Zhou, X.-L., Castro, M.E., White, J.M.: Surf. Sci. 238 (1990) 215. Asscher, M., Rosenzweig, Z.: J. Vac. Sci. Technol. A 9 (1991) 1913. Bhave, A.S., Kanitkar, P.L.: J. Phys. D - Appl. Phys. 24 (1991) 454. Borgmann, D., Kiessling, W., Stadelmann, M., Wedler, G.: Surf. Sci. 251-252 (1991) 831. Bugyi, L., Solymosi, F.: Surf. Sci. 258 (1991) 55. Cherif, S.M., Lacharme, J.-P., Sebenne, C.A.: Surf. Sci. 243 (1991) 113. Cherif, S.M., Lacharme, J.-P., Sebenne, C.A.: Surf. Sci. 251-252 (1991) 737. Chrost, J., Fick, D.: Surf. Sci. 251-252 (1991) 78. Dworecki, Z.: Surf. Sci. 247 (1991) 279. Ernst, K.H., Campbell, C.T.: Surf. Sci. 259 (1991) L736. Fusy, J., Alnot, M., Abouelaziz, H., Ehrhardt, J.J.: Surf. Sci. 252/252 (1991) 573. Hansen, W.: Thesis, TU Berlin, Germany (1991). Hölzl, J., Fritsche, L.: Surf. Sci. 247 (1991) 226. Houston, J.E.: Surf. Sci. 255 (1991) 303. Kleint, C., Halim, S.M.A.E.: Surf. Sci. 247 (1991) 375. Kolaczkiewicz, J., Bauer, E.: Phys. Rev. B 44 (1991) 5779. Kolaczkiewicz, J., Hochól, M., Zuber, S.: Surf. Sci. 247 (1991) 284. Kennou, S., Kamaratos M., Papageorgopoulos, C.A.: Surf. Sci. 256 (1991) 312. Lindgren, S.A., Walldén, L.: Surf. Sci. 257 (1991) L619. Medvedev, V.K., Smereka, T.P., Stepanovskii, S.I., Gonchar, F.M., Kamenetskii, R.R.: Fiz. Tverd. Tela 33 (1991) 3603; Sov. Phys. Solid State (English Transl.) 33 (1991) 2028. Nichtl-Pecher, W., Stammler, W., Heinz, K., Müller, K.: Phys. Rev. B 43 (1991) 6946. Okada, M., Tochihara, H., Murata, Y.: Surf. Sci. 245 (1991) 380. Pirug, G., Ritke, C., Bonzel, H.P.: Surf. Sci. 241 (1991) 289. Pennemann, B., Oster, K., Wandelt, K.: Surf. Sci. 249 (1991) 35. Lando lt -Börnst ein New Ser ies III/42A2
4.2 Electron work function of metals and semiconductors 91P3 91P4 91P5 91P6 91P7 91S 91S2 91T 91T2 91T3 91Z 91Z2 91Z3 91Z4 92A 92A2 92B 92B2 92B3 92B4 92C 92C2 92E 92E2 92J 92J2 92K 92L 92M 92M2 92M3 92M4 92M5 92N 92O 92O2 92P 92R 92R2 92S 92S2 92S3 92S4 92S5 92S6
4.2-133
Pennemann, B., Oster, K., Wandelt, K.: Surf. Sci. 251-252 (1991) 877. Pleshkov, V.A., Shakirova, S.A., Rump, G.A.: Poverkhnost Fizika Khimiya Mekhanika (Phys. Chem. Mech. Surfaces (English Transl.) 6 (1991) 2384). Papageorgopoulos, C.A., Kamaratos, M., Kennou, S., Vlachos, D.: Surf. Sci. 251-252 (1991) 1057. Pirug, G., Ritke, C., Bonzel, H.P.: Surf. Sci. 257 (1991) 50. Pope, T.D., Bushby, S.J., Griffiths, K., Norton, P.R.: Surf. Sci. 258 (1991) 101. Sass, J.K., Lackey, D., Schott, J., Straehler, B.: Surf. Sci. 247 (1991) 239. Sokolowski, M., Koch, T., Pfnür, H.: Surf. Sci. 243 (1991) 261. Tang, D., McIlroy, D., Shi, X., Su, C., Heskett, D.: Surf. Sci. 255 (1991) L497. Tikhov, M., Boishin, G., Surnev, L.: Surf. Sci. 241 (1991) 103. Taylor, T.N., Muenchhausen, R.E., Hoffbauer, M.A.: Surf. Sci. 243 (1991) 65. Zhang, Y., Slavin, A.J.: J. Vac. Sci. Technol. A 9 (1991) 1784. Zhuang Sh., Ji, M., Wu, J., Wandelt, K.: Surf. Sci. 251-252 (1991) 759. Zhou, X.-L., White, J.M.: Surf. Sci. 241 (1991) 244. Zhang, C.-S., Flinn, B.J., Mitchell, I.V., Norton, P.R.: Surf. Sci. 245 (1991) 373. Ahner, J., Effendy, A., Wassmuth, H.-W.: Surf. Sci. 269-270 (1992) 372. Argile, C., Rhead, G.E.: Surf. Sci. 279 (1992) 244. Bakhtizin, R.Z., Suvorov, A.L., Zaripov, R.F.: Acta Phys. Pol. A 81 (1992) 247. Benndorf, C., Mundt, C.: J. Vac. Sci. Technol. A 10 (1992) 3026. Bertolo, M., Jacobi, K.: Surf. Sci. 265 (1992) 1. Boishin, G., Surnev, L.: Surf. Sci. 273 (1992) 301. Cherif, S.M., Lacharme, J.-P., Sebenne, C.A.: Surf. Sci. 274 (1992) 257. Callen, B.W., Griffiths, K., Kasza, R.V., Jensen, M.B., Thiel, P.A., Norton, P.R.: J. Chem. Phys. 97 (1992) 3760. Esser, N., Benne, I., Srama, R., Richter, W.: Surf. Sci. 269-270 (1992) 1037. Ernst-Vidalis, M.-L., Papageorgopoulos, C., Stawinski, U., Bauer, E.: Phys. Rev. B 45 (1992) 1793. Jo, S.K., White, J.M.: Surf. Sci. 261 (1992) 111. Janssens, T., Castro, G.R., Busse, H., Schneider, U., Wandelt, K.: Surf. Sci. 269/270 (1992) 664. Kiss, J., Alberas, D.J., White, J.M.: Surf. Sci. 275 (1992) 82. Lamouri, A., Krainsky, I.L.: Surf. Sci. 278 (1992) 286. Mazina-Ngokoudi, M., Argile, C.: Surf. Sci. 262 (1992) 307. Mroz, S., Stachnik, B.: Acta Phys. Pol. A 81 (1992) 233. Michel, E.G., Pervan, P., Castro, G.R., Miranda, R., Wandelt, K.: Phys. Rev. B 45 (1992) 11811. Mullins, D.R., Lyman, P.F., Overbury, S.H.: Surf. Sci. 277 (1992) 64. Mayer, T., Klein, A., Lang, O., Pettenkofer, C., Jaegermann, W.: Surf. Sci. 269/270 (1992) 909. Nicklin, C.L., Binns, C., Norris, C., McCluskey, P., Barthes-Labrousse, M.-G.: Surf. Sci. 269-270 (1992) 700. Ortega, J.E., Miranda, R.: Appl. Surf. Sci. 56-58 (1992) 211. Ou, E.C., Young, P.A., Norton, P.R.: Surf. Sci. 277 (1992) 123. Polanski, G., Toennies, J.P.: Surf. Sci. 260 (1992) 250. Roman, E.L., de Segovia, J.L., Kurtz, R.L., Stockbauer, R., Madey, T.E.: Surf. Sci. 273 (1992) 40. Reihl, B., Sorensen, S.L., Dudde, R., Magnusson, K.O.: Surf. Sci. 269/270 (1992) 1005. Shern, C.S.: Surf. Sci. 264 (1992) 171. Sander, M., Imbihl, R., Schuster, R., Barth, J.V., Ertl, G.: Surf. Sci. 271 (1992) 159. Shen, G.L., Casanova, R., Thornton, G.: Vacuum 43 (1992) 1129. Surnev, S.: Surf. Sci. 278 (1992) 375. Shakirova, S.A., Pleshkov, V.A., Rump, G.A.: Surf. Sci. 279 (1992) 113. Shern, C.S.: Chinese J. Phys. 30 (1992) 841.
Lando lt -Bö rnst ein New Ser ies III/42 A2
4.2-134 92S7 92S8 92W 92W2 92X 92Y 92Z 92Z2 92Z3 92Z4 93A 93B2 93B3 93C 93F 93G 93H 93J 93K 93K2 93K3 93L 93M 93M2 93N 93N2 93O 93O2 93P 93R 93R2 93R3 93S 93S2 93S3 93S4 93S5 93S6 93S7 93S8 93T 93T2 93V 93W 93W2 93W3 93Z
4.2 Electron work function of metals and semiconductors Shi, H., Jacobi, K.: Surf. Sci. 278 (1992) 281. Shinn, N.D.: Surf. Sci. 278 (1992) 157. Wu, K. et al.: Surf. Sci. 264 (1992) 249. Walter, W.K., Jones, R.G.: Surf. Sci. 264 (1992) 391. Xi, M., Bent, B.E.: Surf. Sci. 278 (1992) 19. Gong, Y.-M., Leng, R.-H.: Solid State Commun. 84 (1992) 1085. Zhao, Y.B., Gomer, R.: Surf. Sci. 260 (1992) 129. Zadorozhnyl, L.P., Medvedev, V.K., Smereka, T.P., Gonchar, F.M.: Fiz. Tverd. Tela 34 (1992) 1051; Sov. Phys. Solid State (English Transl.) 34 (1992) 561. Zhang, Z., Henrich, V.E.: Surf. Sci. 277 (1992) 263. Zhao, Y.B., Gomer, R.: Surf. Sci. 271 (1992) 85. Atli, A., Abon, M., Bertolini, J.C.: Surf. Sci. 287/288 (1993) 110. Brosseau, R., Brustein, M.R., Ellis, T.H.: Surf. Sci. 294 (1993) 243. Bushby, S.J., Callen, B.W., Griffiths, K., Esposto, F.J., Timsit, R.S., Norton, P.R.: Surf. Sci. 298 (1993) L181. Chakarian, V., Shuh, D.K., Yarmoff, J.A., Hakansson, M.C., Karlsson, U.O.: Surf. Sci. 296 (1993) 383. Fan, W.C., Ignatiev, A.: Surf. Sci. 296 (1993) 352. Godfrey, D.C., Hayden, B.E., Murray, A.J., Parsons, R., Pegg, D.J.: Surf. Sci. 294 (1993) 33. Hamawi, A., Walldén, L.: Surf. Sci. 285 (1993) 93. Johansson, L.S.O., Reihl, B.: Phys. Rev. B 47 (1993) 1401. Kastanas, G.N., Koel, B.E.: Appl. Surf. Sci. 64 (1993) 235. Kadodwala, M., Jones, R.G.: J. Vac. Sci. Technol. A 11 (1993) 2019. Klingenberg, B., Grellner, F., Borgmann, D., Wedler, G.: Surf. Sci. 296 (1993) 374. Leschik, G., Courths, R., Wern, H.: Surf. Sci. 294 (1993) 355. Mundt, C., Benndorf, C.: Surf. Sci. 287-288 (1993) 119. Ma, P., Slavin, A.J.: J. Vac. Sci. Technol. A 11 (1993) 2003. Nienhaus, H., Mönch, W.: Appl. Surf. Sci. 66 (1993) 632. Neumann, A., Christmann, K., Solomun, T.: Surf. Sci. 287-288 (1993) 593. Ota, K., Usami, S.: Surf. Sci. 287-288 (1993) 99. Over, H., Hertel, T., Bludau, H., Pflanz, S., Ertl, G.: Phys. Rev. B 48 (1993) 5572. Pan, J.-M., Diebold, U., Zhang, L., Madey, T.E.: Surf. Sci. 295 (1993) 411. Radnik, J., Gitmans, F., Pennemann, B., Oster, K., Wandelt, K.: Surf. Sci. 287-288 (1993) 330. Rotermund, H.H., Lauterbach, J., Haas, G.: Appl. Phys. A 57 (1993) 507. Ruckman, M.W., Xia, B., Qiu, S.L.: Phys. Rev. B 48 (1993) 15457. Surnev, S.: Surf. Sci. 282 (1993) 10. Schmidt, M., Wolter, H., Schick, M., Kalki, K., Wandelt, K.: Surf. Sci. 287-288 (1993) 983. Sprunger, P.T., Plummer, E.W.: Phys. Rev. B 48 (1993) 14436. Shi, X., Tang, D., Heskett, D., Tsuei, K.-D., Ishida, H., Morikawa, Y., Terakura, K.: Phys. Rev. B 47 (1993) 4014. Shi, X., Tang, D., Heskett, D., Tsuei, K.-D., Ishida, H., Morikawa, Y.: Surf. Sci. 290 (1993) 69. Su, C., Shi, X., Tang, D., Heskett, D., Tsuei, K.-D.: Phys. Rev. B 48 (1993) 12146. Stolz, H., Höfer, M., Wassmuth, H.-W.: Surf. Sci. 287/288 (1993) 564. Solymosi, F., Révész, K.: Surf. Sci. 280 (1993) 38. Troost, D., Koenders, L., Mönch, W.: Appl. Surf. Sci. 66 (1993) 619. Tang, D., Su, C., Heskett, D.: Surf. Sci. 295 (1993) 427. van Slooten, U., Koppers, W.R., Bot, A., van Pinxteren, H.M., Moutinho, A.M.C., Frenken, J.W.M., Kleyn, A.W.: J. Phys. Condens. Matter 5 (1993) 5411. Weinelt, M., Zebisch, P., Steinruck, H.-P.: Surf. Sci. 287-288 (1993) 471. Weinelt, M., Zebisch, P., Steinrück, H.-P.: Chem. Phys. 177 (1993) 321. Wolter, H., Schmidt, M., Wandelt, K.: Surf. Sci. 298 (1993) 173. Zhao, Y.B., Gomer, R.: Surf. Sci. 280 (1993) 138. Lando lt -Börnst ein New Ser ies III/42A2
4.2 Electron work function of metals and semiconductors 94A 94B 94B2 94B3 94B4 94E 94E2 94F 94F2 94G 94G2
94G3 94G4 94H 94H2 94H3 94J 94J2 94J3 94K 94K2 94K3 94M2 94M3 94N 94O 94R 94S 94S2 94S3 94S4 94V 94W 94W2 94W3 94W4 94Z 94Z2 95B 95D 95G 95G2 95G3 95H 95H2 95H3 95K 95K2
4.2-135
Atli, A., Abon, M., Beccat, P., Bertolini, J.C., Tardy, B.: Surf. Sci. 302 (1994) 121. Blaszczyszynowa, M., Blaszczyszyn, R., Ciszewski, A.: Surf. Sci. 304 (1994) 325. Bönicke, I., Kirstein, W., Spinzig, S., Thieme, F.: Surf. Sci. 313 (1994) 231. Bönicke, I. A., Kirstein, W., Thieme, F.: Surf. Sci. 307-309 (1994) 177. Bender, M., Al-Shamery, K., Freund, H.-J.: Langmuir 10 (1994) 3081. Ernst, K.-H., Schwarz, E., Christmann, K.: J. Chem. Phys. 101 (1994) 5388. Eckhardt, M., Kleine, H., Fick, D.: Surf. Sci. 319 (1994) 219. Fischer, N., Schuppler, S., Fauster, Th., Steinmann, W.: Surf. Sci. 314 (1994) 89. Fallavier, M., et al.: Surf. Sci. 311 (1994) 24. Grellner, F., Klingenberg, B., Borgmann, D., Wedler, G.: Surf. Sci. 312 (1994) 143. Gensterblum, B., Hevesi, K., Han, B.-Y., Yu, L.-M., Pireaux, J.-J., Thiry, P.A., Caudano, R., Lucas, A.-A., Bernaerts, D., Amelinckx, S., Van Tendeloo, G., Bendele, G., Buslaps, T., Johnson, R.L., Foss, M., Feidenhans’l, R., Le Lay, G.: Phys. Rev. B 50 (1994) 11981. Gordon, J., Shechter, H., Folman, M.: Phys. Rev. B 49 (1994) 4898. Gorodetsky, D.A., Melnik, Yu.P., Usenko, V.A., Yas’ko, A.A., Yarigin, V.I.: Surf. Sci. 315 (1994) 51. Hashim, K.I., Jones, J.P.: Thin Solid Films 245 (1994) 64. Hugenschmidt, M.B., Gamble, L., Campbell, C.T.: Surf. Sci. 302 (1994) 329. Hertel, T., Over, H., Bludau, H., Gierer, M., Ertl, G.: Surf. Sci. 301 (1994) 1. Jiang, L.Q., Koel, B.E.: Phys. Rev. Lett. 72 (1994) 140. Jänsch, H.J., Huang, C., Ludviksson, A., Martin, R.M.: Surf. Sci. 315 (1994) 9. Jacobi, K.: in Landolt-Börnstein Vol. III/24B "Physics of Solid Surfaces", Section 3.1.2.4, p. 56, Chiarotti, G. (ed.), Berlin: Springer-Verlag, 1994. Kolaczkiewicz, J., Bauer, E.: Surf. Sci. 314 (1994) 221. Kovacs, I., Iost, N., Solymosi, F.: J. Chem. Phys. 101 (1994) 4236. Kondoh, H., Nozoye, H.: Surf. Sci. 318 (1994) 158. Mundt, C., Benndorf, C.: Surf. Sci. 307-309 (1994) 28. Mizuno, S., Tochihara, H., Kawamura, T.: Phys. Rev. B 50 (1994) 17540. Naparty, M.K., Skonieczny J.: Vacuum 45 (1994) 361. Okuda, T., et al.: Surf. Sci. 321 (1994) 105. Rohwerder, M., Benndorf, C.: Surf. Sci. 307-309 (1994) 789. Szczudlo, Z., Sendecka, K., Gubernator, W., Ciszewski, A.: Vacuum 45 (1994) 263. Schmidt, M., Wolter, H., Wandelt, K.: Surf. Sci. 307-309 (1994) 507. Schmidt, M., Wolter, H., Nohlen, M., Wandelt, K.: J. Vac. Sci. Technol. 12 (1994) 1818. Sato, M.: Appl. Surf. Sci. 82-83 (1994) 532. Vlachos, D., Kamaratos, M., Papageorgopoulos, C.: Solid State Commun. 90 (1994) 175. Wilke, S., Hennig, D., Lober, R., Methfessel, M., Scheffler, M.: Surf. Sci. 307-309 (1994) 76. Wilke, S., Hennig, D., Lober, R.: Phys. Rev. B 50 (1994) 2548. Weitering, H.H., Chen, J., Pérez-Sandoz, R., Di Nardo, N.J.: Surf. Sci. 307-309 (1994) 978. Whitten, J.E., Gomer, R.: Surf. Sci. 316 (1994) 1. Zhang, C.-S., Bing Li, Norton, P.R.: Surf. Sci. 313 (1994) 308. Hong Zeng, Dongjin Byun, Jiandi Zhang, Vidali, G., Onellion, M., Dowben, P.A.: Surf. Sci. 313 (1994) 239. Basset, D.W.: Surf. Sci. 325 (1995) 121. Derraa, A., Lee, M.J.G.: Surf. Sci. 329 (1995) 1. Geunseop Lee, Plummer, E.W.: Phys. Rev. B 51 (1995) 7250. Grellner, F., Klingenberg, B., Borgmann, D., Wedler, G.: J. Electron Spectrosc. Relat. Phenom. 71 (1995) 107. Gordon, J., Morgen, P., Shechter, H., Folman, M.: Phys. Rev. B 52 (1995) 1852. Held, G., Menzel, D.: Surf. Sci. 327 (1995) 301. Heise, R., Courths, R.: Surf. Rev. Lett. 2 (1995) 147. Hadenfeldt, S., Benndorf, C.: Surf. Sci. 331-333 (1995) 110. Kennou, S.: J. Appl. Phys. 78 (1995) 587. Kirstein, W., Petraki, I., Thieme, F.: Surf. Sci. 331-333 (1995) 162.
Lando lt -Bö rnst ein New Ser ies III/42 A2
4.2-136 95K3 95K4 95K6 95K7 95L 95M 95M2 95N 95N2 95N3 95P 95R 95S 95S2 95S3 95S4 95S5 95S6 95S7 95V 95V2 95W 95Y 96A 96B 96B2 96C 96D 96E 96H 96H2 96K 96K2 96K3 96K4 96L 96L2 96L3 96M 96M2 96M3 96O 96O2 96O3 96P 96P2
4.2 Electron work function of metals and semiconductors Kleine, H., Eckhardt, M., Fick, D.: Surf. Sci. 329 (1995) 71. Kizhakevariam, N., Villegas, J., Weaver, M.J.: Surf. Sci. 336 (1995) 37. Kleine, H., Ehrhardt, M., Jänsch, H.J., Fick, D.: Surf. Sci. 323 (1995) 51. Kim, C.Y., Shin, K.S., Lee, K.D., Chung, J.W.: Surf. Sci. 324 (1995) 8. Lee, S.C., Irokawa, Y., Inoue, M., Shimizu, R.: Surf. Sci. 330 (1995) 289. Mazur, P., Lewowski, T.: Vacuum 46 (1995) 417. Muschiol, U., Lenz, J., Schwarz, E., Christmann, K.: Surf. Sci. 331-333 (1995) 127. Nohlen, M., Schmidt, M., Wandelt, K.: Surf. Sci. 331-333 (1995) 902. Neumann, A., Schroeder, S.L.M., Christmann, K.: Phys. Rev. B 51 (1995) 17007. Nohlen, M., Schmidt, M., Wolter, H., Wandelt, K.: Surf. Sci. 337 (1995) 294. Papageorgopoulos, C.A., Kamaratos, M.: Surf. Sci. 338 (1995) 77. Ranga Rao, G., Kadowaki, Y., Kondoh, H., Nozoye, H.: Surf. Sci. 327 (1995) 293. Smereka, T.P., Stepanovskii, S.I., Kamenetskii, R.R.: Vacuum 46 (1995) 425. Shuxian Zhuang, Jianxin Wu, Xianming Liu, Jin Tu, Mingrong Ji, Wandelt, K.: Surf. Sci. 331-333 (1995) 42. Slavin, A.J.: Progr. Surf. Sci. 50 (1995) 1591. Schröder, S.L.M., Neumann, A., Solomun, T., Lenz-Solomun, P., Christmann, K.: Surf. Sci. 337 (1995) 285. Solomun, T.: Surf. Sci. 331-333 (1995) 52. Siokou, A., Kennou, S., Ladas, S.: Surf. Sci. 331-333 (1995) 580. Shen, W., Nyberg, G.L., Hoffmann, A.: Surf. Sci. 334 (1995) 209. Valla, T., Pervan, P., Milun, M.: Vacuum 46 (1995) 1223. Vlachos, D., Foulias, S.D., Kennou, S., Pappas, C., Papageorgopoulos, C.: Surf. Sci. 331-333 (1995) 673. Wallauer, W., Fauster, Th.: Surf. Sci. 331-333 (1995) 731. Yang, M.X., Jo, S.K., Paul, A., Avila, L., Bent, B.E., Nishikida, K.: Surf. Sci. 325 (1995) 102. Alberas-Sloan, D.J., White, J.M.: Surf. Sci. 365 (1996) 212. Boishin, G., Surnev, L.: Surf. Sci. 345 (1996) 64. Bondzie, V.A., Kleban, P., Dwyer, D.J.: Surf. Sci. 347 (1996) 319. Christmann, K., Muschiol, U.: Zeitschr. Phys. Chemie 197 (1996) 155. de Paola, R. A., Hoffmann, F.M.: Chem. Phys. Lett. 128 (1996) 343. Ebinger, H.D., et al.: Phys. Rev. Lett. 76 (1996) 656. Heiland, A., Christmann, K.: Surf. Sci. 355 (1996) 31. Hadenfeldt, S., Benndorf, C., Stricker, A., Töwe, M.: Surf. Sci. 352-354 (1996) 295. Kolaczkiewicz, J., Bauer, E.: Surf. Sci. 366 (1996) 71. Koch, M.H., Jakob, P., Menzel, D.: Surf. Sci. 367 (1996) 293. Kim, J.W., Seo, J.M., Kim, S.: Surf. Sci. 351 (1996) L239. Kopatzki, E., Keck, H.-G., Baikie, I.D., Meyer, J.A., Behm, R. J.: Surf. Sci. 345 (1996) L11. Lindgren, S.-A., Svensson, C., Walldén, L., Carlsson, A., Wahlström, E.: Phys. Rev. B 54 (1996) 10912. Lehmann, J., Roos, P., Bertel, E.: Phys. Rev. B 54 (1996) 2347. Livneh, T., Romm, L., Asscher, M.: Surf. Sci. 351 (1996) 250. Matsumoto, Y., Gruzdkov, Y.A., Watanabe, K., Sawabe, K.: J. Chem. Phys. 105 (1996) 4775. Mayer, T., Pettenkofer, C., Jaegermann, W.: J. Phys. Chem. 100 (1996) 16966. Maxwell, A.J., Bühwiler, P.A., Arvanitis, D., Hasselström, J., Mårtensson, N.: Chem. Phys. Lett. 260 (1996) 71. Ozawa, K., Tokumitsu, S., Sekine, R., Miyazaki, E., Edamoto, K., Kato, H., Otani, S.: Surf. Sci. 357-358 (1996) 350. Ormerod, R.M., Baddeley, C.J., Hardacre, C., Lambert, R.M.: Surf. Sci. 360 (1996) 1. Ostertag, Ch., Oelsner, A., Schicketanz, M., Schmidt, O., Fecher, G.H., Schönhense, G.: Surf. Sci. 352-354 (1996) 179. Papageorgopoulos, A., Kamaratos, M.: Surf. Sci. 352-354 (1996) 364. Parschau, M., Christmann, K.: Surf. Sci. 347 (1996) 63. Lando lt -Börnst ein New Ser ies III/42A2
4.2 Electron work function of metals and semiconductors 96R 96S 96S3 96S4 96S5 96S6 96V 96V2 96W 96W2 96Y 96Z 97A 97B 97B2 97C 97C2 97C3 97G2 97H 97K 97K2 97K3 97K4 97K5 97L 97L2 97L3 97N 97N2 97N3 97N4 97N5 97O 97P 97P2 97S 97S2 97V 97V2 97V3 97W 97Y 97Y2 98B 98C
4.2-137
Robinson, M.C., Slavin, A.J.: Phys. Rev. B 54 (1996) 14087. Sharma, R.B., Adsool, A.D., Pradeep, N., Joag, D.S.: Appl. Surf. Sci. 94-95 (1996) 177. Schilbe, P., Siebentritt, S., Pues, R., Rieder, K.-H.: Surf. Sci. 360 (1996) 157. Schröder, U., Linke, R., Boo, J.-H., Wandelt, K.: Surf. Sci. 357 (1996) 873. Schröder, U., Linke, R., Boo, J.-H., Wandelt, K.: Surf. Sci. 352-354 (1996) 211. Siokou, A., Kennou, S., Ladas, S., Nguyen Tan, T.A., Venillen, J.-Y.: Surf. Sci. 352-354 (1996) 628. van Hardeveld, R.M., van Santen, R.A., Niemantsverdriet, J.W.: Surf. Sci. 369 (1996) 23. Villegas, J., Weaver, M.J.: Surf. Sci. 367 (1996) 162. Weitering, H.H.: Surf. Sci. 355 (1996) L271. Wu, J., Zhang, Sh., Ji, M., Ma, M., Fang, W., Wandelt, K.: Surf. Sci. 352-354 (1996) 218. Yamamoto, M., Chan, C.T., Ho, K.M., Naito, S.: Phys. Rev. B 54 (1996) 14111. Zhang, C.-S., Li, B., Norton, P.R.: Surf. Sci. 346 (1996) 206. Arena, D.A., Curti, F.G., Bartynski, R.A.: Phys. Rev. B 56 (1997) 15404. Bing Li, Griffiths, K., Zhang, C.-S., Norton, P.R.: Surf. Sci. 370 (1997) 97. Brault, P., Range, H., Toennies, J.P., Woell, Ch.: Z. Phys. Chem. 198 (1997) 1. Choi, D.S., Paik, S.M., Han, J.H., Park, N.G., Kim, K.S., Whang, C.N.: Mod. Phys. Lett. B 11 (1997) 63. Chao, Y.-C., Johansson, L.S.O. Uhrberg, R.I.G.: Phys. Rev. B 55 (1997) 7178. Chao, Y.-C., Johansson, L.S.O. Uhrberg, R.I.G.: Phys. Rev. B 55 (1997) 7667. Grant, A.W., Campbell, C.T.: Phys. Rev. B 55 (1997) 1844. Hoffmann, W., Benndorf, C.: Surf. Sci. 377-379 (1997) 681. Krachino, T.V., Kuzmin, M.V., Loginov, M.V., Mittsev, M.A.: Fiz. Tverd. Tela 39 (1997) 1672; Sov. Phys. Solid State (English Transl.) 39 (1997) 224. Klingenberg, B., Grellner, F., Bergmann, D., Wedler, G.: Surf. Sci. 383 (1997) 13. Ku-Ding Tsuei, Jih-Young Yuh, Chyuan-Tsyr Tzeng, Ren-Yu Chu, Shih-Chun Chung, KingLung Tsang: Phys. Rev. B 56 (1997) 15412. Küster, R., Christmann, K.: Ber. Bunsen-Ges. Phys. Chem. 101 (1997) 1799. Kamaratos, M.: Solid State Commun. 103 (1997) 189. Losovyj Yab: Vacuum 48 (1997) 195. Linke, R., Becker, C., Pelster, T., Tanemura, M., Wandelt, K.: Surf. Sci. 377-379 (1997) 655. Ladas, S., Kennou, S., Hartmann, N., Imbihl, R.: Surf. Sci. 382 (1997) 49. Nahm, T.-U., Gomer, R.: Surf. Sci. 375 (1997) 281. Nahm, T.-U., Gomer, R.: Surf. Sci. 380 (1997) 52. Nahm, T.-U., Gomer, R.: Surf. Sci. 373 (1997) 237. Naydenov, B., Surnev, L.: Surf. Sci. 370 (1997) 155. Nelson, E.J., Kendelewicz, T., Liu, P., Pianetta, P.: Surf. Sci. 380 (1997) 365. Ozawa, K., Iwasaki, T., Edamoto, K., Tanaka, S., Otani, S.: Appl. Surf. Sci. 121/122 (1997) 142. Papageorgopoulos, A.: Solid State Commun. 101 (1997) 383. Papageorgopoulos, A., Corner, A., Kamaratos, M., Papageorgopoulos, C.A.: Phys. Rev. B 55 (1997) 4435. Shuxian Zhuang, Xianfeng Wang, Xuming Wei, Yinsheng Wang, Suzheng Ren, Runsheng Zhai: Surf. Sci. 376 (1997) L429. Schröter, C., Roelfs, B., Solomun, T.: Surf. Sci. 380 (1997) L441. Valla, T., Pervan, P., Milun, M., Wandelt, K.: Surf. Sci. 374 (1997) 51. Verhoef, R.W., Zhao, W., Asscher, M.: J. Chem. Phys. 106 (1997) 9353. Villegas, I., Weaver, M.J.: J. Phys. Chem. B 101 (1997) 5842. Wu, C.J., Klepeis, J.E.: Phys. Rev. B 55 (1997) 10848. Yang, M.X., et al.: Surf. Sci. 380 (1997) 151. Yang, S.C., Chen, J.M., Wen, C.R., Hsu, Y.J., Lee, Y.P., Chuang, T.J., Liu, Y.C.: Surf. Sci. 385 (1997) L1010. Bönicke, I.A., Thieme, F., Kirstein, W.: Surf. Sci. 395 (1998) 138. Chiu-Ping Cheng, Ie-Hong Hong, Tun-Wen, Pi: Phys. Rev. B 58 (1998) 4066.
Lando lt -Bö rnst ein New Ser ies III/42 A2
4.2-138 98D 98E 98F 98G 98G2 98H2 98L 98M 98M3 98N 98R 98R2 98S 98S2 98S3 98S4 98V 98V2 98W 98Y 98Y2 99B 99F 99K 99K2 99K3 99K4 99L 99L2 99L3 99O 99P 99S 99S2 99S3 99T 99W 99W2 99W3
4.2 Electron work function of metals and semiconductors Dong, W., Ledentu, V., Sautet, Ph., Eichler, A., Hafner, J.: Surf. Sci. 411 (1998) 123. Ebinger, H.D., Arnolds, H., Polenz, C., Polivka, B., Preyß, W., Veith, R., Fick, D., Jänsch, H.J.: Surf. Sci. 412/413 (1998) 586. Fedorus, A., Bauer, E.: Surf. Sci. 418 (1998) 420. Grüne, M., Radnik, J., Wandelt, K.: Surf. Sci. 402-404 (1998) 236. Gorodetsky, D.A., Melnik, Yu.P., Proskurin, D.P., Sklyar, V.K., Usenko, V.A., Yas’ko, A.A.: Surf. Sci. 416 (1998) 255. Hohenegger, M., Bechtold, E., Schennach, R.: Surf. Sci. 412-413 (1998) 184. Lahtinen, J., Vaari, J., Kauraala, K.: Surf. Sci. 418 (1998) 502. Muschiol, U., Schmidt, P.K., Christmann, K.: Surf. Sci. 395 (1998) 182. Mundt, C., Benndorf, C.: Surf. Sci. 405 (1998) 121. Noda, T., Nakane, T., Ozawa, K., Edamoto, K., Tanaka, S., Otani, S.: Solid State Commun. 107 (1998) 145. Reissner, R., Radke, U., Schulze, M., Umbach E.: Surf. Sci. 402-404 (1998) 71. Ranke, W., Weiss, W.: Surf. Sci. 414 (1998) 236. Shen, Y.G., O'Connor, D.J., Yao, J.: Appl. Surf. Sci. 125 (1998) 300. Stepanowskyi, S., Ubogyi, I., Kolaczkiewicz, J.: Surf. Sci. 411 (1998) 176. Saliba, N., Parker, D.H., Koel, B.E.: Surf. Sci. 410 (1998) 270. Schlatterbeck, D., Parschau, M., Christmann, K.: Surf. Sci. 418 (1998) 240. Vlachos, D.S., Papageorgopoulos, C.A.: Appl. Surf. Sci. 136 (1998) 230. Velic, D., Hotzel, A., Wolf, M., Ertl, G.: J. Chem. Phys. 109 (1998) 9155. Whitten, J.E., Gomer, R.: Surf. Sci. 409 (1998) 16. Young Sir Chung, Evans, K., Glaunsinger, W.: Appl. Surf. Sci. 125 (1998) 65. Yoshihara, J., Campbell, J.M., Campbell, C.T.: Surf. Sci. 406 (1998) 235. Böttcher, A., Niehus, H.: Phys. Rev. B 60 (1999) 14396. Farias, D., Schilbe, P., Patting, M., Rieder, K.H.: J. Chem. Phys. 111 (1999) 559. Kolaczkiewicz, J., Bauer, E.: Surf. Sci. 420 (1999) 157. Kim, J.-S., Ihm, K.-W., Hwang, Ch.-C., Kim, Y.-K., Lee, Ch., Park, Ch.Y.: Jpn. J. Appl. Phys. 38 (1999) 6479. Kolaczkiewicz, J., Bauer, E.: Surf. Sci. 423 (1999) 292. Klivényi, G., Kovács, I., Solymosi, F.: Surf. Sci. 442 (1999) 115. Livneh, T., Lilach, Y., Asscher, M.: J. Chem. Phys. 111 (1999) 11138. Livneh, T., Asscher, M.: J. Phys. Chem. B 103 (1999) 5665. Lacharme, J.P., Benazzi, N., Sebenne, C.A.: Surf. Sci. 435 (1999) 415. Osterlund, L., Chakarov, D.V., Kasemo, B.: Surf. Sci. 420 (1999) 174. Petermann, U., Baikie, I.D., Lägel, B.: Thin Solid Films 343-344 (1999) 492. Shakirova, S.A., Serova, E.V.: Surf. Sci. 422 (1999) 24. Senet, P., Toennies, J.P., Witte, G.: Chem. Phys. Lett. 299 (1999) 389. Schoak, A., Nieuwenhuys, B., Imbihl, R.: Surf. Sci. 441 (1999) 33. Turton, S., Kadodwala, M., Jones, R.G.: Surf. Sci. 442 (1999) 517 Whitten, J.E., Gomer, R.: Surf. Sci. 429 (1999) 14. Whelan, C.M., Barnes, C.J., Walker, C.G.H., Brown, N.M.D.: Surf. Sci. 425 (1994) 195. Wilde, M., Beauport, I., Stuhl, F., Al-Shamery, K., Freund, H.J.: Phys. Rev. B 59 (1999) 13401.
Lando lt -Börnst ein New Ser ies III/42A2
4.4 Surface free energy and surface stress D. SANDER , H. IBACH,
4.4.1 Introduction The surface free energy per area and the surface stress are macroscopic excess quantities, specific to surfaces of condensed matter. In short, the free energy is defined as the work per area necessary to create a surface. It is denoted as γ and called surface energy for simplicity in the following. The surface stress is the work per area necessary to strain an already existing surface. Both, surface energy and surface stress have the same dimension of an energy per area (J/m2). In order to emphasise the difference between the two we quote surface stresses in N/m. An alternative, sometimes useful definition of the surface stress follows directly from the definition as change in the surface energy per area with applied strain: The surface stress is the excess force per length which has to be applied to the surface in order to keep the surface undeformed when the material is cut perpendicular to the surface along a line, with the material on the right hand side of the cut removed in a Gedanken experiment. This definition leads to a qualitative useful insight into the connection between the local charge density distribution in the outermost atom layers near the surface and the sign and magnitude of the surface stress. The distinction between surface energy and surface stress was first pointed out by Gibbs [61Gib]. Excess free energies and stresses can also be defined for condensed matter interfaces, e. g. the solid-liquid interface. However, this section focuses entirely on surfaces, i. e. the solid-vacuum or the liquid-vacuum interface. The microscopic origin for the surface energy and the surface stress is that atoms or molecules at the surface of a solid or a liquid have a different local environment than the atoms in the bulk. This leads to a redistribution of the electronic charge compared to the bulk which affects both surface energy and surface stress. The strain of a surface is a second rank tensor ε ij with (i, j = 1,2) denoting the in-plane components. The energy associated with the strain, the surface stress, is therefore likewise a second rank tensor. Its components are denoted as τ (ijs) (i, j = 1,2). The work per area A associated with straining a surface is given by the derivative of the excess free energy of the surface Fs with respect to the strain ε ij at constant temperature τ
∂A ∂γ ∂γ (s) ∂Fs ∂ ( γA) = = =γ +A = γδ ij + ij ∂ε ij ε ij ∂ε ij ∂ε ij ∂ε ij
(1)
in which δij is the Kronecker symbol. This equation was first derived by Shuttleworth [50Shu, 53Her] and is named after him. The second term in the Shuttleworth equation makes for an important difference between the surface stress of liquids and solids. Isothermic stretching of the surface of a liquid results in a completely plastic deformation: The change of surface area leads to a flow of molecules from the interior to the surface, provided the liquid film is not too thin. The local environment of a surface molecule therefore does not change upon straining the surface, and consequently all area specific excess quantities such as the surface energy γ remain constant. Thus for liquids, the second term in eq. (1) is zero and the surface stress is equal to the surface energy in that case. For solids, on the other hand, no plastic flow of molecules or atoms to the surface occurs (unless the temperature is close to the melting point) and the strain derivative of γ does not vanish. The surface deforms elastically when the material is strained. The local environment of each surface atom therefore changes due to the strain in the surface layer and consequently the stress differs from the specific surface energy. For liquids, the term surface tension is frequently used for the specific surface energy γ. Since the word tension bears the connotation of "stress" the term surface "tension" should be avoided for solid surfaces where stress and specific energy are different. Calculations predict that the strain derivative of γ can be of the same magnitude as γ itself
Landolt -Börnst ein New Series III/42A2
4.4 -2
4.4 Surface free energy and surface stress
[Ref. p. 4.4 -44
[97Fei, 97Fill]. The sign of ∂γ / ∂ε
can be positive or negative. A positive value indicates that the ij surface energy is lowered by reducing the surface strain, i.e. by increasing the density of surface atoms, and vice versa. A different surface density compared to the underlying bulk layers is equivalent to a surface reconstruction and the sign and magnitude of ∂γ / ∂ε has therefore been associated with the ij propensity of the surface to reconstruct to a new structure with a higher or lower density of atoms in the surface layer [90Wol, 92Cam1, 92Cam2, 94Wol1, 93Cho, 93Nee, 97Bac, 97Iba1, 97Iba2]. Parameters β = ( τ − γ ) / ( Gb) [92Cam1, 94Cam], with the shear modulus G and the Burger’s vector b, and
α = ( τ − γ ) / ( E c a 0 ) [97Iba1], with the cohesion energy Ec and the lattice constant a0, have been introduced as an indicator for the propensity of a surface to reconstruct. Both parameters are proportional to the magnitude of the second term of equation (1). A large value of this term has been proposed as a driving force for reconstruction, both for the reconstruction of clean surfaces as well as for the adsorbate induced reconstructions. An example for a reconstruction of a clean surface driven by surface stress is presumably the reconstruction of the Au(111) surface [97Bac]; an example for a reconstruction driven by the adsorbate induced stress is the carbon induced p4g reconstruction of Ni(100) [86Mül, 92San, 97Iba1]. For data on surface reconstruction and relaxation see LANDOLT-BÖRNSTEIN New Series III/24a. The surface energy necessarily is a positive quantity. The material would desintegrate if it was not. The surface stress, on the other hand, can be positive or negative. For anisotropic surfaces the components of the stress tensor can be of opposite sign. A famous and frequently studied example is the reconstructed Si(100) surface [88Ale, 88Men, 94Web]. If the surface free energy increases upon an expansion of the surface area, i. e. the surface has the propensity to contract, the stress is called tensile. The sign of the stress τ(s) is defined as positive in that case (comp. eq. (1)). If the surface elastic energy would be lowered by an expansion, the surface stress is called compressive and the sign of the surface stress is negative. All calculations of the surface stress of clean metals indicate a positive surface stress. The stress may, however, become negative upon adsorption, in particular upon adsorption of electronegative atoms. On some clean semiconductor surfaces, the stress is negative, i. e. compressive. The absolute magnitude of the surface stress depends on the material and on the surface orientation. Large values are predicted for the 5d elements. For Pt(111), a surface stress as large as 6.27 N / m has been calculated [97Fei]. The surface stress of inert gas crystals, on the other hand, is slightly compressive, and amounts only to about 10-3 N / m [50Shu]. Due to the lack of methods, reliable experimental data for surface energy and surface stress are not available for clean solid surfaces at room temperature. Surface energy data are almost exclusively obtained near the melting point of the solids using the method of zero creep. So far, only cleavage experiments have shown the potential to determine absolute surface energy data at low temperatures. Recently, Bonzel has proposed a new method to determine the absolute value of the surface energy of singular surfaces from the temperature dependence of the size of a facet [2000Bon]. However, the new method has not been applied to an experimental system yet. The surface stress of clean surfaces is likewise difficult to measure directly. Several methods which have been proposed are discussed in 4.4.3. Changes of the surface stress due to adsorption, on the other hand, can be measured with sub-monolayer sensitivity and experimental data exist for a number of systems and are presented in section 4.4.9.
4.4.2 Experimental determination of surface free energy Despite the fundamental importance of the surface free energy γ in sintering, diffusion, nucleation and growth of inclusions, for the strength of materials, and for thin film growth, experimental data on γ are mostly from experiments performed at high temperatures near the melting point or for the liquid state. Early experimental data show a considerable scatter due to contamination and due to experimental difficulties inherent to the experimental methods [88Ida]. Nevertheless experimental data on the surface free energy of (bona fide) clean metals are compiled in this contribution as they serve as an important reference when the change of the surface free energy due to adsorption is discussed. References to
Lando lt -Bö rnst ein New Series III/42A2
Ref. p. 4.4 -44]
4.4 Surface free energy and surface stress
4.4 -3
empirical relations between surface free energy and other physical properties like the cohesion energy, the heat of sublimation, the work function and the compressibility are given in section 4.4.2.5. Experimental techniques to measure the surface free energy of liquids have been thoroughly discussed by Bakker [28Bak], Hondros [70Hon], and Adamson [90Ada]. The sessile drop method [59All], the pendant drop method [63All], the drop weight method [63All] and Lenard’s wire frame method have been applied [68Ger] to obtain the surface energy of liquid metals. Other experimental techniques like cleavage and zero creep experiments have been described by Bikerman [65Bik], Hondros [70Hon] and Blakely [73Bla]. 4.4.2.1 Cleavage experiments Cleavage experiments were introduced by Obreimoff who deduced the surface energy of mica from splitting thin mica sheets [30Obr]. He was the first to consider the influence of gas adsorption on the surface free energy in order to explain the vastly higher value of the surface free energy measured in vacuum as compared to data obtained from splitting in air. Gilman [60Gil] determined the surface energy of the ionic crystals LiF, MgO, CaF2, BaF2, CaCO3 and of Si and Zn by quantitative cleavage experiments. The method has been applied also to KCl [63Wes1], MgO [63Wes2], to Zn [69Mai], to W [65Hul] and to the fluorides CaF2, SrF2 and BaF2 [78Bec]. The elasto-mechanical aspects of the cleavage experiments have been critically analysed [64Gil, 65Gil, 68Wie]. The issue of plastic flow at the tip of the propagating crack [73Fre] and the influence of viscous fluids on crack propagation have been discussed [87Gen]. The application of cleavage experiments seems to be well suited to determine the surface free energy of brittle materials [73Kel, 93Law] and to investigate the fracture surface energy of bonded interfaces [36Ray, 98Krä, 99Plö]. For most metals however, plastic flow has to be anticipated near the front of the propagating crack, giving rise to irreversible processes which result in too high values of the surface energy [60Gil]. In how far this fundamental limitation of the technique to brittle materials can be circumvented to apply the technique to metals by working at low temperatures to hinder plastic flow has apparently not been investigated any further since the early experiments on Zn, Fe and W.
F w t L
F
Fig. 1. Double cantilever cleavage experiment. A tensile test machine is used to apply a force F to a presplit sample of width w and thickness t. For a given force F the equilibrium crack length L is measured to calculate the surface energy. For a discussion see [60Gil, 63Wes1, 64Gil].
Cleavage experiments can be performed by applying a force on a partially pre-split sample as indicated in Fig. 1. Equating the work done by advancing the crack incrementally by applying a force to the split sample with the increase of the elastic bending energy of the sample beams and with the increase of the surface energy due to the increased surface area, leads to the following expression for the determination of the surface free energy γ=
6F 2 L2 . Ew 2 t 3
(2)
The force applied to the bent beams is given by F, L denotes the length of the crack, E is Young’s modulus for the appropriate orientation, the beam width and thickness are given by w and t, respectively.
Landolt -Börnst ein New Series III/42A2
4.4 -4
4.4 Surface free energy and surface stress
[Ref. p. 4.4 -44
This equation is applicable for vanishing values of t/L, otherwise corrections of order t/L have to be considered [64Gil, 68Wie]. Surface energy data obtained by cleavage experiments are presented in section 4.4.7.1 in Table 2. These experiments were performed at room temperature or at low temperatures and represent the only measurements of γ which were not performed at high temperature. 4.4.2.2 Pendant drop and drop weight method Values of the surface free energy of metals in their liquid state have been obtained from the pendant drop method and from the drop weight method, as compiled by Allen [63All]. The end of a high purity rod is heated under vacuum to the melting temperature. In the former method, the profile of a pendant drop hanging from the supporting rod of the same material is analysed to extract the maximum diameter dm and the diameter ds at a distance dm from the end of the drop, as sketched in Fig. 2. A shape factor H has to be taken from tables for the given value of S=ds/dm to facilitate the calculation of ρgd 2 m γ= (3) H with the density of the liquid given by ρ and the gravitational acceleration g. Values of the correction factor H as a function of S = ds / dm have been tabulated [70Hon, 90Ada] with S ranging from 0.3 to 1, yielding values of 1/H from 7.1 to 0.31. In this range of S, 1/H can be approximated by the following relation 1/ H = 59.71 − 375.355 S + 991.543 S2 − 1331.321S3 + 899.366 S4 − 241.668 S5 .
2r ds dm dm
Fig. 2. The pendant drop method. A rod of diameter 2r is heated close to the melting temperature until a stable drop of maximum diameter dm is formed. One measures dm and in the distance dm from the bottom end of the drop the diameter ds. The surface energy of the liquid vapour interface is determined with equation (3) from the ratio of both diameters[63All, 88Ida, 90Ada].
The drop weight method relies on the measurement of the weight of a drop of material which drops off the end of a heated rod with radius r. It has been introduced as early as 1868 by Quincke [1868Qui]. The most basic evaluation is known as Tate’s law, stating that the weight of the drop, m g, is equilibrated by the surface free energy of the liquid metal acting along its circumference, γ 2 π r. A correction f depending on the ratio r / V1/3 has to be employed to account for the liquid which remains at the end of the rod after the drop has fallen. γ=
mg 2 πrf
(4)
The correction f approaches one for small rod diameters [70Hon, 90Ada]. Therefore, measurements performed on rods with different diameter can be extrapolated to zero diameter rods to obtain the correct value of γ [63All]. From a measurement of the mass of a drop, the volume of the drop V is calculated with the density of the liquid [88Ida]. Then the ratio between rod diameter r and V1/3 is calculated to determine f from a table [70Hon, 90Ada]. The following empirical relation gives the correction factor 1/3 f = 0.89 − 0.703 a + 0.413a 2 for a = r/V in the range 0.3 < a <1.0.
Lando lt -Bö rnst ein New Series III/42A2
Ref. p. 4.4 -44]
4.4 Surface free energy and surface stress
4.4 -5
It is claimed that the pendant drop technique and the drop weight technique give very accurate values which agree within 4 % [63All]. Surface energy data on the liquid vapour interface which were obtained by both techniques are given in section 4.4.7.2 in Table 3. Both techniques could be employed to determine the change of the surface free energy under partial pressures of various adsorbates. However, such measurements have not been performed yet. 4.4.2.3 Zero creep experiments The pendant drop and the drop weight method investigate the surface free energy of a metal in the liquid state with respect to its vapour pressure or with respect to vacuum. In a narrow temperature range, starting approximately at 70 % of the melting temperature Tm up to Tm, the surface free energy can be extracted from zero creep experiments [49Udi, 51Ale, 52But1, 63Inm, 64Pri, 70Hon]. (a)
(b)
10 8 6
2 cm
Strain X 103
4 2 0 -2
1
2
3
4 5
6
7
8 X 10
-4
Stress [Pa]
-4 -6 -8 -10
Fig. 3a, b. Schematic of a zero creep experiment. (a) Fine Cu wires (∅ ≈ 0.07 mm) are loaded with different weights of the same material of up to 100 mg and heated in a vacuum oven. (b) The strain of the wires after heating for 72 h 3 to 1000° C is measured. Depending on the load, positive and negative strains of the order 10- are observed. The load which gives zero strain ("zero creep") is inserted in equation (5) or (6) to determine the surface energy. Data points from [49Udi].
Thin wires with diameters of order several ten µm are suspended in a vacuum oven and loaded with different weights, as schematically indicated in Fig. 3. While the oven and the wire are heated, the heavily loaded wires will stretch, while the lightly loaded wires will shrink due to the contractile action of the surface energy. The mass m of the load which leads to zero strain rate of the wire with radius r at high temperature determines the surface free energy γ=
mg . πr
(5)
The surface free energy is calculated from the zero crossing of the strain vs. load curve [49Udi]. The Nabarro-Herring mechanism [50Her] describes this viscous flow from material from the sides of the wire to the end at low stress and high temperature [51Ale, 52Gre, 52But1, 63Inm, 64Pri, 76Bau]. Usually the wire undergoes structural changes in the process of thermal annealing which lead to the formation of grain boundaries, kinks, and bulges and waists [51Ale, 63Pri]. Grain boundaries are formed with a density of n per unit length, and they lie normal to the wire axis, extending over the wire cross
Landolt -Börnst ein New Series III/42A2
4.4 -6
4.4 Surface free energy and surface stress
[Ref. p. 4.4 -44
section. The data evaluation has to be modified to account for the surface energy of the grain boundaries γb [70Hon, 73Hod, 73McL] γ=
mg + nr γ b . πr
(6)
The energy of the grain boundary has to be determined independently. Relative values of γb / γ can be obtained from a measurement of the dihedral angle at a surface of a grain boundary groove, e.g. by electron microscopy [63Inm, 73Hod, 73McL]. An approximation is γb = γ/3 [52But2, 64Pri, 70Hon, 73Hod, 73McL, 76Bau]. The rather limited temperature range in which zero creep experiments are performed is typically less than 100 K. It has been extended to 330 K by replacing the wire sample with a thin foil of the material with a thickness of ≈10 µm. An advantage of using foils instead of wires was ascribed to the elimination of the contribution of grain boundary energies to the measurement by careful dimensioning of the foil [67Hon, 68Hon, 70Hon]. Surface free energies of metals measured by zero creep experiments are compiled in section 4.4.7.2 in Table 3. The zero creep method has been used to study the influence of gaseous adsorbates on the value of the surface free energy γ [52But2, 67Hon, 76Bau]. Starting from the Gibbs’ adsorption isotherm, a relation between the excess surface concentration Γ of an adsorbed species at constant temperature T and the dependence of the surface free energy on the partial pressure p of the adsorbate in the gas phase can be derived [73Hir] (see also H. P. Bonzel in this volume): Γ=−
1 ∂γ . kT ∂ ln p
(7)
Measurement of the change of the surface energy due to adsorption have been performed to obtain the adsorbate surface concentration. For the application of eq. (7) to an experimental situation it is necessary that the surface and the bulk of the material are in thermodynamic equilibrium, a condition which is not always fulfilled. Phase changes due to chemical reactions between substrate and adsorbate, or temperature driven phase transitions like the α-Fe, γ-Fe , δ-Fe transition [63Pri, 64Pri] might set in, e. g., and a straightforward interpretation of the change of the surface free energy as a function of the adsorbate partial pressure is not possible [68Hon, 73McL, 76Bau]. A new compound might form which has a different creep behaviour, or the new compound has a different surface free energy, and comparing to the surface free energy of the clean substrate is not meaningful. Experimental data on the change of the surface free energy with adsorption and adsorbate-driven compositional changes of the surface are given in section 4.4.8. Due to the problems noted above and also because numerous other methods to obtain the surface concentration are available for the solid gas interface the use of eq. (7) is no longer pursued. It may be useful to comment, however, that an equivalent relation for the dependence of the interface energy as a function of the electrode potential is still the major source of quantitative data on adsorbate concentrations at the solid-liquid interface (“chronocoulometry” [66Ans, 86Ric]). 4.4.2.4 Orientation dependence of the surface free energy Experiments on the equilibrium shape of small crystallites and on the groove angle at grain boundaries indicate an orientation dependence of the surface free energy. The value the surface free energy varies by several percent for different surface orientations at high temperature. This anisotropy is e.g. responsible for the faceted shape of the crystallites shown in Fig. 4.
Lando lt -Bö rnst ein New Series III/42A2
Ref. p. 4.4 -44]
4.4 Surface free energy and surface stress
4.4 -7
Fig. 4. Scanning electron microscopy image of the anisotropic faceted morphology of a lead crystallite. This equilibrium shape has been analysed to derive the orientation dependence of the surface free energy at various temperatures, see chapter 4.4.7.3.1 [83Hey].
Most experiments on the surface free energy which have been discussed in the preceding sections have been performed on polycrystalline material. One exception is the zero creep technique when applied to foils which can be prepared as single crystal surfaces [67Hon]. Absolute values for the surface free energy of a specific orientation have also been obtained by the cleavage technique, see data in section 4.4.7.1. The free energy specific to a particular crystal face is denoted as γhkl with the Miller indices hkl as a subscript. While the absolute value of the surface free energy is difficult to determine experimentally and the results are not very accurate, the dependence of the surface free energy on the crystalline orientation of the surface can be obtained with very high accuracy from the equilibrium shape of the crystals using an inverse Wulff construction [01Wul, 51Her, 53Her, 67Win, 73Win, 88Wor]. Electron microscopy using a replica technique on small particles of µm size, which were prepared to mimic equilibrium equilibrium shapes, has been analysed to determine the ratio of surface free energies for different orientations [64Sun]. Typically, the variation of γ is plotted in a stereographic projection and reveals a variation with orientation of less than 10 %. Scanning electron microscopy, transmission electron microscopy and reflection electron microscopy has been used to image equilibrium shape crystallites of Au, In, Pb, and Si directly [80Hey, 83Hey, 86Hey, 98Ber, 99Hey]. Data on the temperature dependence of the surface free energy and its anisotropy are presented in section 4.4.7.3 and 4.4.7.3.1. (a)
(b)
Fig. 5. Pd induced faceting of W(111). (a) Large area scanning tunneling microscopy image (100 nm × 100 nm) of Pd-W(111), after deposition of 1.2 atomic layers of Pd and annealing at 1075 K for 3 minutes. Three sided pyramids form a faceted surface. (b) The small area image (11 nm ×11nm) identifies the atomic row and trough structure of the bcc(211) facets, which form the three sided pyramids of (a). Images from [99Mad].
The grooves at the boundaries of grains of different orientation have been studied by electron microscopy to derive relations between the grain boundary energy and orientation [57Myk, 58Moo, 61Myk, 64McL, Lando lt -Bö rnst ein New Series III/42A2
4.4 -8
4.4 Surface free energy and surface stress
[Ref. p. 4.4 -44
64Rhe]. These data are analysed to derive the orientation dependence of the ratio of the surface free energy of γhkl / γref , where γref is assigned to the (100) or the (111) orientation. The anisotropy of γ increases with decreasing temperature and is influenced by adsorption [62Rhe, 86Hey]. Both effects are important factors in the discussion of faceting of single crystal surfaces. Gas adsorbates [98Gra] and monolayer coverage of metallic films [97Che, 99Mad, 99Nie] have been identified as driving force for substrate faceting. An example for adsorbate driven faceting is presented in Fig. 5 for the Pd-W(111) system. A monolayer coverage of Pd induces a large area faceting of initially planar W(111), exposing {211} pyramidal facets after annealing. The faceting has been ascribed to an increased anisotropy of the surface free energy due to the Pd coverage [99Mad]. 4.4.2.5 Empirical relation between surface free energy and other quantities There are several empirical relations in the literature which favour the physically appealing conclusion that a high bond strength leads to high values of the surface free energy [63All, 76Lan, 88Ida]. A very small scatter of the experimental data points for γ around the linear plot of γ vs. Tm / (Vm)2/3, with the melting temperature Tm and the molar volume at the melting point Vm , supports this view [63All, 88Ida]. A plot of the surface free energy vs. the heat of vaporisation reveals that high surface energies are correlated with high energies of vaporisation, as originally proposed by Skapski [48Ska, 56Ska, 63All, 76Lan, 78Mie1, 88Ida]. A linear relation between the surface free energy and the bulk modulus B has been suggested from a plot of γ vs. B [72Waw, 73Waw]. This finding has been exploited to calculate the alleged temperature dependence of γ from ultrasonic measurements of the elastic constants as a function of temperature [72Waw, 73Waw, 75Waw1, 75Waw2]. However, this procedure should be viewed with caution as there seems to be no physical justification for the assumed similar temperature dependence of both surface energy and compressibility [78Mie2]. Qualitative aggreement between an estimate of the surface free energy from phonon frequencies has been reported [76Tys]. This approach exploits the Orowan-Polanyi estimate [76Tys] between the ideal tensile strength and the surface energy. A proportionality between the electron work function and the surface energy has been proposed and verified empirically. This relation is based on the correlation between the electron work function and the heat of sublimation [73Mis, 78Mie2].
4.4.3 Experimental determination of the absolute value of the surface stress 4.4.3.1 Lattice parameter of small particles The stress at the surfaces of a solid body leads to a compression (or expansion) of the material. While the deformation is small it becomes measurable for small particles. The measurement of the lattice parameter of small particles may therefore be used to determine the surface stress. For simplicity we consider a sphere of a radius R of an elastically isotropic solid with a compressibility K subject to an isotropic surface stress τ(s). The incremental work against the surface stress and the bulk elasticity by expanding the body is δW = τ (s ) δA +
1 ∆V δV K V
(8)
In equilibrium the variation of the work δW is zero. By expressing δA and δV in terms of the radius δR one obtains τ (s ) = −
1 ∆V 3 ∆a =− 2K V 2K a
(9)
where ∆a/a represents the relative change of the lattice constant. A positive surface stress will lead to a compression of the lattice parameter, ∆a < 0 .
Lando lt -Bö rnst ein New Series III/42A2
Ref. p. 4.4 -44]
4.4 Surface free energy and surface stress
4.4 -9
Using electron diffraction the lattice parameters of small Au [68May], Ag [52Ber, 70Was], Pt and Cu [72Was] particles with diameters between 30 Å and 200 Å have been determined. The lattice parameter of the smallest particles was found to be smaller than that of a continuous film by 0.1 % (Cu) up to 0.6 % (Ag). A plot of the relative strain of the lattice parameter against the inverse of the particle dimension, ∆a / a vs. 1 / R, displayed a linear behaviour, and the surface stress was calculated from the slope of the curve. The method has also been recently applied to determine the interface stress of an oxide film on a nanosized Si particle, and a compressive interface stress, leading to a larger lattice constant of the smaller particles has been reported [99Hof]. Inherent deficiencies of the method are due to the dependence of the positions, intensities and breadths of the electron diffraction lines on the particle size, shape and structure, which complicates the determination of the lattice parameter from a diffraction image [52Ber, 70Was, 84Mon]. In addition, neither the anisotropy of the elastic constant nor the anisotropy of the surface stress is considered in eq. (9). Depending on the orientation of the surfaces of the particle the actual mean compression of the lattice constant is a result of a rather complex interplay between the stress on the various surfaces of the particle and the anisotropic elastic behaviour of the material. So far neither the elastic anisotropy nor the actual, irregular shape of the small crystallites has been taken into account. Furthermore, the values of the elastic constants and equilibrium lattice spacings of the nanosized materials are unknown. In conclusion, the quantitative determination of surface stress from an apparent lattice strain of small crystallites remains a challenge for the future. 4.4.3.2 Surface phonons as indicator of surface stress The dispersion relation of elastic surface waves of a solid, so-called Rayleigh waves, has been investigated to study the elastic interactions near the surface layer [71All1, 71All2, 71All3, 84Iba, 87Leh, 92Iba]. It has been proposed that the dispersion relation of Rayleigh waves should be an indicator of the surface stress [86Mül, 87Leh, 88Dau, 92Iba, 97Iba1]. The idea is based on the following consideration: the excitation of surface wave involves an enlargement of the surface area. In a simple picture [97Iba1], a positive (tensile) surface stress opposes the increase of the surface area, and is expected to provide an additional restoring force, leading to an upward shift of the frequency of the surface wave. A negative (compressive) surface stress should soften the vibrational mode. While this concept appears appealing and may be qualitatively sound it falls short of producing quantitative data. Firstly, because a quantitative evaluation of the surface stress using this concept would require the knowledge of the dispersion as it would be without a surface stress. Secondly, the most significant changes in the dispersion occur at the zone boundary where short range interactions between the atoms determine the frequency, rather than the macroscopic quantity surface stress. A general correlation between surface stress and the frequency of the Rayleigh wave can therefore rightfully be questioned [89Gas]. The situation differs from the case of capillary waves of liquids [66Lan, 78Som], also called ripples or ripplons. In the latter case, the surface stress (tension) is the only restoring force providing for a nonzero frequency of the ripplons, and interfacial energies as well as other visco-elastic properties of liquid surfaces or interfaces can be obtained from the study of ripplons [86San, 90Ada]. 4.4.3.3 Absolute surface stress from the bending of thin crystal plates The physical concept of surface stress as a force per length which acts in the surface layer of a solid leads to the idea, that the effective elasticity of small particles should be altered by the combined action of bulk elasticity and surface stress. A tensile surface stress would induce an apparent increase of the elastic stiffness whereas a compressive surface stress would soften the elastic behaviour. Müller and Kern suggested to measure the deflection of a thin circularly shaped crystalline sample in the gravitational field [94Mül]. According to their calculation, the deflection of the thin sample depends on the magnitude of the surface stresses acting on both crystal faces. A tensile surface stress leads to a smaller deflection as compared to a surface stress free situation, a compressive surface stress leads to a larger deflection [94Mül]. However, the magnitude of the effect of surface stress on the deflection depends, among other variables, on the diameter-to-thickness-ratio of the sample, and for a 1 cm diameter Si plate it is suggested that the thickness should be of the order 20 µm. Although such thin crystalline plates with well defined Landolt -Börnst ein New Series III/42A2
4.4 -10
4.4 Surface free energy and surface stress
[Ref. p. 4.4 -44
surfaces are available for semiconductors, other experimental difficulties are anticipated, and no experiments along these lines have been performed yet.
4.4.4 Experimental determination of changes of surface stress due to adsorption The most powerful technique to determine changes in the surface stress exploits the bending moment of a surface stress acting on thin samples. The idea of this measurement is that any difference of the surface stress between the front and the back surface will lead to a bending of the sample. The difference of surface stress between the two crystal faces can be determined in absolute numbers from a measurement of the bending. Continuum elasticity theory is applied to consider the elastic properties and the elastic anisotropy of the substrate properly [96Mar1, 96Mar2, 97Iba1, 99San1, 2000Dah]. Then the relation between the bending of the substrate, often expressed as radius of curvature R and the stress difference between front and back side ∆τ ( s) is derived. The basic idea of the technique is sketched in Fig. 6.
Fig. 6a, b. Cantilever bending technique. (a) A rectangular sample is clamped along its width to a sample manipulator. The free sample length l is of the order 10 mm, the sample width w is 2 mm. (b) Side view. Any difference of stress between the front and back side of the sample with thickness t induces a sample deflection ζ, which corresponds to a change of slope of the surface ζ ′ or a curvature ζ ′′ . The curvature κ is the inverse of the radius of curvature R [97Iba1, 99San1].
From a measurement of the deflection ζ, the slope ζ ′ , or the curvature κ = 1 / R = (ζ′(l1) − ζ′(l2 )) /(l1 − l2 ) , the radius of curvature is determined. The Stoney relation is employed to calculate the stress difference ∆τ ( s) = Yt 2 / (6(1 − ν) R ) [97Iba1]. Only the elastic properties of the substrate enter via the Young modulus Y and the Poisson ratio ν. The sample thickness is given by t. This analysis of the bending beam or cantilever bending technique has a long tradition in film stress measurements [09Sto], where the film stress τ(f) is calculated from a measurement of the sample curvature [66Hof, 88Doe, 89Nix, 90Abe] for a given film thickness tf, with ∆τ ( s) replaced with τ(f)tf . In general, the possible anisotropy of both stress and elastic properties require a refined analysis, as described below. The first measurements of surface stress induced bending were performed on III-V semiconductor compounds [64Cah, 64Fin, 66Dru], where the (111)- or (0001)-surface are formed by either the group III or the group V element [60Gat]. The bending of ultrathin crystals was investigated, e.g., in an electron microscope to determine the difference of the surface stress between crystal faces formed by the two constituents Al and N on AlN crystals in the thickness range 380 Å to 3500 Å [66Dru]. For InSb a surface stress difference between the two (111) faces of 1.15 ± 0.23 N / m [62Han], and for AlN a stress difference of 3.63 ± 0.15 N / m [66Dru] was reported. The influence of H2S and NH3 atmosphere on the radius of curvature of GaAs and InSb crystals has been investigated [64Fin]. NH3 exposure was found to increase the radius of curvature, whereas H2S induced a decrease of the radius of curvature. The high sensitivity of optical [90Sch, 90Mar, 95San1, 97Deg], capacitive [91San, 94Web] and tunnel current [97Bac, 97Iba1] deflection measurements allows to measure stress effects with sub-monolayer sensitivity [97Iba1, 99San1]. The change of surface stress on one crystal face due to adsorption [91San, 92San, 94Iba, 99San2], surface reconstruction [92San], film growth [90Sch, 90Mar, 96Gro, 97Koc, 98San, 99San2], film magnetisation [94Web, 99San1, 2001Dah] and surface reactions [95Gro] has been measured under ultra-high vacuum and in electrochemical cells [97Bac, 97Hai, 97Iba2].
Lando lt -Bö rnst ein New Series III/42A2
4.4 -10
4.4 Surface free energy and surface stress
[Ref. p. 4.4 -44
surfaces are available for semiconductors, other experimental difficulties are anticipated, and no experiments along these lines have been performed yet.
4.4.4 Experimental determination of changes of surface stress due to adsorption The most powerful technique to determine changes in the surface stress exploits the bending moment of a surface stress acting on thin samples. The idea of this measurement is that any difference of the surface stress between the front and the back surface will lead to a bending of the sample. The difference of surface stress between the two crystal faces can be determined in absolute numbers from a measurement of the bending. Continuum elasticity theory is applied to consider the elastic properties and the elastic anisotropy of the substrate properly [96Mar1, 96Mar2, 97Iba1, 99San1, 2000Dah]. Then the relation between the bending of the substrate, often expressed as radius of curvature R and the stress difference between front and back side ∆τ ( s) is derived. The basic idea of the technique is sketched in Fig. 6.
Fig. 6a, b. Cantilever bending technique. (a) A rectangular sample is clamped along its width to a sample manipulator. The free sample length l is of the order 10 mm, the sample width w is 2 mm. (b) Side view. Any difference of stress between the front and back side of the sample with thickness t induces a sample deflection ζ, which corresponds to a change of slope of the surface ζ ′ or a curvature ζ ′′ . The curvature κ is the inverse of the radius of curvature R [97Iba1, 99San1].
From a measurement of the deflection ζ, the slope ζ ′ , or the curvature κ = 1 / R = (ζ′(l1) − ζ′(l2 )) /(l1 − l2 ) , the radius of curvature is determined. The Stoney relation is employed to calculate the stress difference ∆τ ( s) = Yt 2 / (6(1 − ν) R ) [97Iba1]. Only the elastic properties of the substrate enter via the Young modulus Y and the Poisson ratio ν. The sample thickness is given by t. This analysis of the bending beam or cantilever bending technique has a long tradition in film stress measurements [09Sto], where the film stress τ(f) is calculated from a measurement of the sample curvature [66Hof, 88Doe, 89Nix, 90Abe] for a given film thickness tf, with ∆τ ( s) replaced with τ(f)tf . In general, the possible anisotropy of both stress and elastic properties require a refined analysis, as described below. The first measurements of surface stress induced bending were performed on III-V semiconductor compounds [64Cah, 64Fin, 66Dru], where the (111)- or (0001)-surface are formed by either the group III or the group V element [60Gat]. The bending of ultrathin crystals was investigated, e.g., in an electron microscope to determine the difference of the surface stress between crystal faces formed by the two constituents Al and N on AlN crystals in the thickness range 380 Å to 3500 Å [66Dru]. For InSb a surface stress difference between the two (111) faces of 1.15 ± 0.23 N / m [62Han], and for AlN a stress difference of 3.63 ± 0.15 N / m [66Dru] was reported. The influence of H2S and NH3 atmosphere on the radius of curvature of GaAs and InSb crystals has been investigated [64Fin]. NH3 exposure was found to increase the radius of curvature, whereas H2S induced a decrease of the radius of curvature. The high sensitivity of optical [90Sch, 90Mar, 95San1, 97Deg], capacitive [91San, 94Web] and tunnel current [97Bac, 97Iba1] deflection measurements allows to measure stress effects with sub-monolayer sensitivity [97Iba1, 99San1]. The change of surface stress on one crystal face due to adsorption [91San, 92San, 94Iba, 99San2], surface reconstruction [92San], film growth [90Sch, 90Mar, 96Gro, 97Koc, 98San, 99San2], film magnetisation [94Web, 99San1, 2001Dah] and surface reactions [95Gro] has been measured under ultra-high vacuum and in electrochemical cells [97Bac, 97Hai, 97Iba2].
Lando lt -Bö rnst ein New Series III/42A2
Ref. p. 4.4 -44]
4.4 Surface free energy and surface stress
4.4 -11
An analytical solution of the bending problem cannot be given for anisotropic surface stress acting on an elastically anisotropic substrate of arbitrary surface orientation with the substrate being clamped to a sample holder or otherwise hindered to deform freely [2000Dah]. However, the experiments can be performed such that a straightforward evaluation of the curvature data is feasible and even the influence of the clamping can be considered. The anisotropy of the elastic properties is taken into account by performing the appropriate transformation of the elastic compliances sij′ for the surface orientation of the substrate. The prime indicates properties in the coordinate system of the substrate. In general, two curvatures κ1 and κ2 have to be measured along the surface directions 1 and 2 to determine the components of the surface stress tensor [99San2, 2001He] τ 1( s) = τ (2s)
s′ t 2 s ′22 κ 1 − 12 κ 2 s 6 s
t2 = 6
(10)
′ s′ s11 κ 2 − 12 κ 1 , s = s11 ′ s ′22 − s12 ′ 2. s s
Stoney’s relation follows from this general expression for elastic isotropy in the surface plane with Y = 1 / s11, ν = -s12 / s11 for cubic (100) surfaces. The result of the appropriate tensor transformations for some surface orientations is given in Table 1, examples of how tensor transformations are performed for arbitrary surface orientations are given in the literature [85Nye, 97Iba1, 99San1]. Table 1. Young’s modulus Y and Poisson’s ratio ν for selected surface orientations. Y and ν are isotropic in the (111) plane, but anisotropic in the (100) plane. The values refer to directions along the crystal axes. The anisotropy parameter A = 2 (s11 − s12 ) / s 44 is included, A=1 indicates elastic isotropic behaviour of the bulk material. Elastic compliances were taken from [69Hea, 84Hea]. Material Cu Ni Si Pt W
Y(100) GPa 67 133 129 136 408
ν[010] 0.42 0.38 0.28 0.42 0.28
Y(111) GPa 131 224 168 185 410
ν(111)
A
0.50 0.41 0.26 0.45 0.28
3.23 2.45 1.56 1.59 1.01
A necessary condition for the presented discussion of substrate bending is that the concept of small bending of thin plates applies [59Tim, 84Sza]. Small bending means, that the resulting deflection of the substrate due to the stress imbalance between the two surfaces should be much smaller than the substrate thickness, which is of the order 100 µm. In most experimental situations R is of the order 100 m, and a minute deflection of 500 nm at the end of a 10 mm long sample results, in agreement with the assumption of small bending. If the deflection is of the order of the sample thickness or larger, the hindered Poisson contraction in plates [84Sza] as opposed to the behaviour of beams has to be considered, and the two dimensional bending can no longer be expressed by two radii of curvature [23Tim, 50Ash]. A substrate is considered thin, if its lateral dimensions are much larger than its thickness. This condition is usually met by typical substrates with a length of the order l = 10 mm, a width of w = 3 mm, and a thickness t = 100 µm. In conclusion, the condition of small bending of thin substrates can be experimentally fulfilled and eq. (10) describes the two dimensional bending due to anisotropic surface stress properly. The influence of the clamping of the substrate, usually performed along the top end of a rectangular substrate, on the bending behaviour is much more demanding to describe. Now, the lateral dimensions as well as the anisotropy of the elastic properties of the substrate enter. Only the limiting case of pure one dimensional bending can be solved analytically. Here, the sample curves only along one direction, usually along the sample length, and remains flat along the width. This situation is approximately realised in
Landolt -Börnst ein New Series III/42A2
4.4 -12
4.4 Surface free energy and surface stress
[Ref. p. 4.4 -44
experiments in which a sample with a length-to-width-ratio of the order of one or less is clamped along the width at the top and at the bottom end. Then, the curvature along the width vanishes and eq. (10) can be used with κ2 = 0 without significant errors. A finite element analysis of the bending of thin plates reveals that for a sample clamped along its width at only one end the case of one dimensional bending is realised for a length-to-width ratio of 0.1 [97Wat, 2000Dah]. The influence of clamping of the substrate can be described by introducing a dimensionality D of the bending problem [97Iba1, 2000Dah]. If one considers isotropic surface stress, τ1( s) = τ (2s) = τ ( s) , and a surface symmetry which warrants s11 ′ = s′22 , eq. (10) can be modified to introduce the dimensionality D τ( s ) =
t 2Y κ, 6(1 − ν)(1 + (2 − D)ν)
′ , Y = 1 / s11
′ / s11 ′ . ν = −s12
(11)
The dimensionality is two for a free substrate, and the clamping leads to a reduction of the dimensionality from D = 2 to D = 1, depending on the length-to-width ratio a and the Poisson ratio ν. No analytical relation is available for the dependence of the substrate deflection ζ, the change of slope ζ′, or the curvature ζ′′ on the various parameters. Instead, the results of numerical calculations using the finiteelement-method are presented in [2000Dah]. The results of these calculations apply to homogenous, isotropic surface stress on substrates with s11 ′ = s ′22 [2000Dah]. This symmetry is always given on elastically isotropic substrates with A = 1, or on (100)-, and (111)-surfaces of cubic materials, and for (0001)-orientations of hcp materials [99San1]. Amorphous substrates can be considered elastically isotropic, but most elements show a pronounced elastic anisotropy as indicated from the range of values of A for various elements given in Table 1. The dimensionality D is taken from the plots of Fig. 7 for different experimental situations, and eq. (11) should be used to take the effect of clamping into consideration. Fig. 7(c) indicates that the direct measurement of the curvature is beneficial, as already for a length-to-width ratio of 2 a dimensionality of D = 1.99 is calculated, whereas the measurement of the deflection, Fig. 7(a), leads to D ≈ 1.8, with a pronounced dependence on ν. The inclusion of an elastic anisotropy ( A ≠ 1 ) leads to a wider range of dimensionality values for a given length-to-width ratio, which depends drastically on the Poisson ratio [2000Dah]. Again the conclusion of these calculations is that one should measure the curvature directly to minimize the influence of the clamping. Reference [2000Dah] should be consulted to obtain the appropriate dimensionality for a given experimental situation. In conclusion, the finite-element analysis supports the intuitively appealing finding that the larger the length-to-width ratio, the smaller the effect of clamping on the bending of the substrate. A direct measurement of the curvature near the free end of the substrate yields results which are closer to the D = 2 situation, as compared to measurements of the slope or of the deflection. The use of the latter most indispensably requires a consideration of the clamping effect. Neglecting the effect on clamping on the curvature and using eq. (11) with D = 2 in a situation where D is different due to the clamping leads to an error. The magnitude of the error can be seen immediately from eq. (11) in connection with Fig. 7. Recent molecular dynamics calculations with many-body potentials consider the curvature of a slab of material as an additional degree of freedom to deduce the surface stress difference due to different adsorbate coverages or reconstructions on the two surfaces of the slab from its curvature [99Pas]. These calculations promise in principle a self-contained description of both the curvature analysis and the physical origin of surface stress. In section 4.4.9 experimental data changes of surface stress induced by the adsorption of gases, alkali metals, semiconductors and metals on single crystal surfaces are compiled from cantilever bending experiments.
Lando lt -Bö rnst ein New Series III/42A2
Ref. p. 4.4 -44]
4.4 Surface free energy and surface stress
4.4 -13
Fig. 7a-c. Finite element analysis of the effect of clamping on the curvature of a cantilevered substrate. (a) Deflection ζ, (b) slope ζ′, and (c) curvature ζ′′ as a function of the length-towidth ratio for A=1 and with the Poisson ratio ν as a parameter. From [2000Dah].
4.4.5 Calculations of surface free energy and surface stress The surface free energy of a solid at T = 0 K can be calculated in a two-step process from an integration of the interaction energy of a single atom in the interior of a solid with atoms situated in the half space above it. This energy value U′ is equal to the energy cost per atom when the atoms of the upper half space are removed, i.e. when the atom is moved to the surface layer. However, the surrounding atoms in the surface layer and underneath the surface layer will relax to minimise the total energy of the remaining half space of material. By this relaxation the energy cost U′ to create the surface will be lowered by U′′, and finally the surface free energy is given by γ = U ′ − U ′′ . The effect of relaxation on the lowering of the surface free energy can be small, as in the case of inert gas crystals [49Shu, 64Ben, 67Ben] or substantial, as for ionic crystals [49Shu, 50Shu, 65Ben, 67Ben, 79Tas] and metals [86Ack, 91Man, 94Sto]. Surface stress can then be calculated from the strain dependence of γ, as described by eq. (1). Surface stress is also
Landolt -Börnst ein New Series III/42A2
4.4 -14
4.4 Surface free energy and surface stress
[Ref. p. 4.4 -44
accessible in slab calculations without knowledge of the surface free energy by an evaluation of the work which is necessary to strain a slab infinitesimally to increase its surface area. Work has to be performed against bulk and surface stress, and calculating this work as a function of slab thickness allows to discriminate between the constant contribution of surface stress and the contribution of bulk stress, which grows in proportion to the thickness of the slab [97Iba1]. The calculation of surface free energy and surface stress data depends critically on the model used for the interatomic interactions. Therefore, calculations for inert gas crystals, ionic crystals, covalent crystals and metals are treated separately as each crystal class is described best by different models of the interactions. 4.4.5.1 Inert gas crystals The interatomic potential of inert gas crystals can be described by a Lennard-Jones potential [50Shu, 64Ben, 67Ben] with a repulsive interaction term which is proportional to r-12 and an attractive van der Waals term proportional to r-6, where r is the distance between the atom and its surrounding neighbours. Buckingham potentials, where the repulsive interaction is described by an exponential expression give similar results [64Ben, 67Ben]. A face-centered-cubic arrangements of atoms is considered. The calculations of the surface free energy by Shuttleworth [50Shu] with a Lennard-Jones potential and by Benson and Yun [67Ben] with a Buckingham potential agree within a few percent and are presented in section 4.4.7.4 in Table 4. The calculations indicate a slight outward relaxation by 2.5 % of the outermost (100)-layer, which leads to a negligible correction of the surface free energy by less than 1 %, and relaxation processes are not considered in the calculation. The surface free energy of inert gas crystals with (100) faces is of order several ten mJ / m2. Surface stress was calculated by Shuttleworth [50Shu], his results are given in Table 4. A slight compressive surface stress of the order of 10-3 N / m is calculated for inert gas crystals. It appears that these surface properties of inert gas crystals have not been studied experimentally, and a critical assessment of the validity of the calculated data cannot be given. 4.4.5.2 Ionic crystals The ionic interaction of alkali halides has been described by a Born-Mayer-Huggins potential which considers Coulomb interactions ∼ r-1, van der Waals dipole-dipole interactions ∼ r-6 and dipole-quadrupole interactions ∼ r-8, and exponential repulsive interactions [49Shu, 50Shu, 67Ben]. Composite potentials, which have been spline-fitted to produce a continuous potential have been employed also [79Tas]. The calculations indicate that the consideration of relaxation is essential. Early calculations of Shuttleworth [50Shu] seem to have overestimated the effect of relaxation, leading to negative surface stress for all alkali halides, except for NaF. More recent calculations by Benson and Yun [67Ben] and by Tasker [79Tas] still support the importance of relaxation effects on both, surface free energy and surface stress, but give positive surface stress values for the alkali halides. The parameters of the potential function are adjusted to give the best description of bulk properties of the ionic crystal. However, different parameters contribute differently to the surface properties as compared to the bulk properties and the choice of one parameter set might be good for bulk, but questionable for surface properties. Therefore, the results of the calculations of the surface free energies and of the surface stresses in section 4.4.7.5 in Table 5 should be understood merely as estimates, although the agreement with the scarce experimental data on surface free energy of liquid salts is within 10 %. The tables show that the surface energy of most (100) alkali halide surfaces lies in the range 0.1 J / m2 to 0.4 J / m2, the surface stress varies from 0.1 N / m to 1 N / m.
Lando lt -Bö rnst ein New Series III/42A2
Ref. p. 4.4 -44]
4.4 Surface free energy and surface stress
4.4 -15
4.4.5.3 III-V compounds The zinc-blende structure of III-V compounds is of special interest since this structure leads to the peculiarity that opposite (111) surface orientations are populated solely either by group III or by group V elements [60Gat, 62Han]. This leads to an inherent asymmetry of both surfaces due to the different bonding situations on the two surfaces. Group III elements are bonded triply to the neighbouring group V partners. However, group III elements are often bonded in planar sp2-hybrids to three partners, whereas they are forced into a sp3-like tetrahedral bonding environment at the surface. It was argued [64Cah], that a compressive stress should result on the group III surface, as the atoms would show the propensity to retain a planar bonding geometry. On the surface terminated by group V elements, the bonding geometry is very similar to a sp3-hybridization, which is known as a stable configuration of triply bonded group V elements with dangling bonds, like NH3. Due to the slight bond angle deviation of the triply bonded group V element from the tetrahedral configuration, a slight tensile stress was proposed for the group V terminated surface [64Cah]. This simple electronic picture was put forward to explain the spontaneous curvature of thin III-V compounds with (111) surface orientations [64Cah], see section 4.4.4. Cahn and Hanneman introduced a non-central force model which considers bond-stretching and bondbending contributions to the interaction energy explicitly to calculate the surface stress difference between group III and group V terminated surfaces [64Cah]. A compressive stress of order –1 N / m was calculated for the group III terminated surface and a smaller tensile stress of order 0.5 N / m was derived for the group V terminated surface, leading a surface stress difference of order 1.5 N / m. The calculations are in rough qualitative agreement with experimental results on InSb [64Cah]. The surface energy of covalent III-V compounds was claimed to be in good approximation the energy associated with the broken nearest neighbour bonds on the surface. The energy per bond was approximated from the sublimation energy and lies in the range of 0.6 J / m2 to 2 J / m2. The surface stress differences of (111) surfaces and the surface free energies for different orientations of various III-V compounds are tabulated in section 4.4.7.6 in Table 6. 4.4.5.4 Group IV materials Non-central force models have been applied to investigate the surface reconstruction and subsurface relaxation of Si(100) [78App] and Si(111) [85Tro]. The interatomic potential was described by a model due to Keating [66Kea], which takes central bond straining energy, and non-central bond bending energy into account by two parameters which can be expressed as function of the cubic bulk elastic constants c11, c12, and c44. The relation 2c 44 ( c11 + c 12 ) / ((c11 − c12 )(c11 + 3c12 )) = 1 has to be fulfilled in order to express the atomic interaction with just two parameters. This condition is valid for the semiconductors of the diamond structure diamond, Si and Ge [66Kea]. Pseudopotential methods have been employed to calculate surface free energy and surface stress of Si and Ge slabs with (100) and (111) surface orientations [87Van, 89Mea1, 89Mea2, 89Pay]. The surface energy Es is related to the energy per slab unit cell Eslab by E s = E slab − NE bulk , where N is the number of atoms in the slab unit cell, and E bulk is the energy per atom of the bulk [89Mea1]. The surface stress is 1 dE s calculated from the strain dependence of the surface energy τ (ijs) = , where A is the unit cell area A dε ij [89Mea1, 89Mea2]. The surface free energy follows as γ = E s / A . The effect of surface reconstruction and of adsorption on the surface energy and the surface stress has been calculated [89Mea1, 89Mea2, 89Pay]. Adsorption is found to modify the surface free energy and the surface stress. The adsorbate induced surface stress is mainly ascribed to the unnatural bonding topology of the adsorbate-substrate complex [89Mea2]. The results of these calculation are presented together with the other calculated properties in section 4.4.7.7 in Table 7 and in section 4.4.7.8 in Table 8. The calculations indicate surface free energies of Si and Ge of order 1.7 J / m2 (1.4 eV / 1x1 cell), and report a compressive surface stress of the clean and unreconstructed surfaces of the order – 0.7 N / m (– 0.5 eV / 1x1 cell).
Landolt -Börnst ein New Series III/42A2
4.4 -16
4.4 Surface free energy and surface stress
[Ref. p. 4.4 -44
4.4.5.5 Metals Pair potentials [90Wol, 91Wol] and many body potentials, corresponding to an effective medium theory or embedded atom method, have been employed to calculate surface energy and surface stress for various metals [86Ack, 87Ack1, 87Ack2, 88Dod, 91Gum, 90Wol, 91Wol, 94Wol1, 94Sto]. Many-body potentials have been employed to study surface reconstruction in the glue model [86Erc, 87Erc], and the concept of surface strain was introduced as a driving force for reconstruction [88Dod]. The role of surface stress for reconstruction has been elucidated [92Cam1, 92Cam2, 94Wol1, 94Wol2, 93Nee, 93Cho]. The effect of surface and interface stress on the elastic properties of metallic films and multilayers has been investigated by the embedded atom method [91Gum, 94Str1, 94Str2]. Pseudopotential total energy calculations in the local density approximation have been applied to calculate the surface energy and surface stress using a slab of material and a vacuum region which are repeated throughout space [87Nee, 89Pay, 90Nee, 91Nee, 91Man]. Surface energy and surface stress are calculated as the difference between surface and bulk properties. Pseudopotentials which use the linear combination of atomic orbitals (LCAO) in the local density approximation have been employed to calculate surface energy, surface stress and adsorbate induced changes of surface stress [95Fei1, 97Fei]. Unfortunately, an often cited paper which gives calculated values of surface stress and discusses the role of surface stress for reconstruction remained ambiguous as to whether the stress or the difference between the stress and the energy was tabulated [93Fio] (stress was tabulated). Furthermore, the stress was apparently calculated for unrelaxed surfaces. Later calculations for the same system lead to lower surface stresses [99Iba, 97Fill]. Calculated values of surface free energy and surface stress are presented in sections 4.4.7.9 and 4.4.7.10 in Table 9 and Table 10, respectively. Structural relaxations of the surface layer are considered to influence both properties considerably, and calculations which consider these relaxations should be regarded as providing more reliable results. 4.4.5.6 Calculated adsorbate-induced surface stress First principles calculations of the effect of gas adsorption on the surface stress of Pt(111) have been performed [97Fei]. The adsorption of hydrogen and oxygen was found to relief the tensile stress of the clean Pt(111) surface partially. The results of this study are presented in section 4.4.7.11 in Table 11 and in Fig. 11 and Fig. 12. These calculations suggest that the modification, i.e. weakening, of the surface bonds of the substrate in the vicinity of the adsorbate is an important issue in the discussion of adsorbateinduced stress. Recent ab-initio cluster calculations using the local density approximation provide a qualitative understanding of adsorbate-induced stress in terms of the charge transfer involved in the surface bond [99Mül]. It was found that tensile (compressive) stress correlates with increase (decrease) of charge in the metal-metal-bonds of the surface plane. Fig. 8 shows the change in the charge density induced by the adsorption of oxygen and potassium on the surface plane of a Pt(111) surface, which was represented in the calculation by a two-layer Pt25 cluster. The continuous (dashed) contour lines represent increase (decrease) of charge and show the regions of the surface plane where the bonding is strenghtened (weakened) by the adsorption. For O-adsorption the calculation shows that the induced compressive stress is due to a charge transfer from Pt-Pt bonds to the adsorbate. Fig. 8(a) shows a depletion of charge away from the three Pt-Pt bonds closest to the adsorbate, which is transferred to the O-atom. This charge transfer is due the interaction of empty O–2p states with Pt–5d orbitals, which is so strong that the 5d orbitals rotate in space to optimize the orbital overlap with the O-atom, leading to the weakening of the nearest-neighbour Pt–Pt bonds and to the observed compressive stress. For K-adsorption on the other hand, the calculation shows that the induced tensile stress is due to a charge transfer from the K-atom to surface Pt–Pt bonds, which are strengthened by the adsorption. Fig. 8(b) shows that the transferred charge goes into the region between the three Pt-atoms closest to the adsorbate. The K-surface bond is due to the interaction of the K–4s state with Pt–6s states. In the clean surface the Pt–6s states lie above the Fermi level, but due to the interaction with the K–4s state they move down and become locally occupied leading to the increased Pt–Pt bonding. It is worth noticing that the Pt–5d states do not interact with the K–4s Lando lt -Bö rnst ein New Series III/42A2
Ref. p. 4.4 -44]
4.4 Surface free energy and surface stress
4.4 -17
state. The latter state is so extended that it is essentially constant over the volume of the 5d states, such that the positive and negative parts of the 5d function cancel out in the overlap integral. This issue was raised by Feibelman, who pointed out that the unoccupied states at the Fermi level of Pt are antibonding, which means that a direct K→Pt charge transfer would actually lead to weakening of the Pt–Pt bonds, in contradiction with the experimental results for K [97Fei]. The point here is that the transferred charge remains constrained within the range of the 4s state of the K-atom. Because of the large extension of the 4s state this may not immediately apparent in some calculations.
Fig. 8a, b. (a) Difference charge density ∆ρ = ρ(Pt25O)-ρ(Pt25)-ρ(O) induced on the surface plane by the adsorption of a O-atom on a Pt25 cluster representing a Pt(111) surface. The adatom is out of the plane. The continuous (∆ρ > 0) and dashed (∆ρ < 0) contour lines represent density contours n310-5 eÅ-3, for n = −15,...,+15. (b) Id. for the adsorption of a K-atom. For a discussion see [99Mül].
Lando lt -Bö rnst ein New Series III/42A2
4.4 -18
4.4 Surface free energy and surface stress
[Ref. p. 4.4 -44
4.4.6 Data In the following section 4.4.7 experimental data and calculated values of surface free energy and surface stress of clean solid surfaces are compiled. The data are organised as follows: Table 2. Surface free energy from cleavage experiments Table 3. Surface free energy measured at high temperature with an estimate of the temperature dependence Fig. 9. Measured temperature dependence of the surface free energy of Cu Fig. 10. Measured temperature dependence of the anisotropy of the surface free energy of Pb Table 4. Calculated surface free energy and surface stress for inert gas crystals Table 5. Calculated surface free energies and surface stress for alkali halides Table 6. Calculated surface free energy and surface stress of III-V compounds Table 7. Calculated surface free energy and surface stress for Si and Ge for different surface reconstruction Table 8. Calculated adsorbate-induced changes of stress on semiconductor surfaces Table 9. Calculated surface free energies of metals Table 10. Calculated surface stress of metals Table 11. Calculated adsorbate induced surface stress on Pt(111). First principles calculations of adsorbate-induced surface stress for H and O on Pt(111) are quoted in section 4.4.7.11 in Fig. 11 and Fig. 12. Experimental results on adsorbate-induced changes of surface free energy are listed in section 4.4.8. The following data are presented: O / Ag Fig. 13 O / Fe Fig. 15 O / Fe-3% Si Fig. 14 O / Cu Fig. 16 Adsorbate-induced changes of surface stress are compiled in section 4.4.9 for the following systems. O / Si(100) O / Si(111) S / Ni(100) O / Ni(100) C / Ni(100) S / Ni(111) O / Ni(111) C / Ni(111) CO / Ni(100) CO / Ni(111) CO / Pt(111) O / Pt(111) O / CO / Pt(111) O / W(110) Cs / Ni(111)
Fig. 17 Fig. 17 Fig. 18 Fig. 19 Fig. 20 Fig. 21 Fig. 23 Fig. 25 Fig. 27 Fig. 28 Fig. 29 Fig. 29 Fig. 30 Fig. 31 Fig. 32
K / Pt(111) Ge / Si(100) As / Si(100) Ge / As / Si(100) Fe / Si(111) Ag / Pt(111) Fe / Cu(100) Co / Cu(100) Ni / Cu(100) Fe / W(100) Co / W(100) Ni / W(100) Pd / W(100) Fe / W(110)
Ga / Si(111): Only the stress difference τ Si ,7 × 7 − τ Ga ,
3× 3
Fig. 33 Fig. 34 Fig. 35 Fig. 36 Fig. 37 Fig. 38 Fig. 39 Fig. 40 Fig. 41 Fig. 42 Fig. 43 Fig. 44 Fig. 45 Fig. 46 = 1.28 N / m has been measured [90Mar].
Ag / Si(100): Only the Ag induced reduction of the surface stress of Si(100) has been reported for a coverage of 0.25 ML Ag: τSi – τ0.25 ML Ag/Si = 0.45 N/m [97Deg]
Lando lt -Bö rnst ein New Series III/42A2
Ref. p. 4.4 -44]
4.4 Surface free energy and surface stress
4.4 -19
4.4.7 Clean surfaces 4.4.7.1 Surface free energy from cleavage experiments Table 2. Surface free energy from cleavage experiments. Material
Cleavage plane
T [K]
Ambient atmosphere G [J/m2]
Reference
LiF MgO CaF2 CaCO3 Si Zn Zn W Fe-Si3% MgO KBr KCl NaCl LiF BaF2 SrF2 CaF2
(100) (100) (111) (100) (111) (0001) (0001) (001) (100) (100) (100) (100) (100) (100) (111) (111) (111)
77 77 77 77 77 77 300 77 20? 298 295 295 295 295 295 295 295
liq. N2 liq. N2 liq. N2 liq. N2 liq. N2 liq. N2 air liq. N2 liq. H2 air air air air air air air air
60Gil 60Gil 60Gil 60Gil 60Gil 60Gil 69Mai 65Hul 60Gil 63Wes2 78Bec 78Bec 78Bec 78Bec 78Bec 78Bec 78Bec
0.34 1.2 0.45 0.23 1.24 0.105 0.575 6.3 1.36 1.15 +/- 0.08 0.23 0.24 0.34 0.64 0.35+/-0.12 0.42+/-0.08 0.51+/-0.14
4.4.7.2 Surface free energy of metals near the melting point Most experimental values of the surface free energy are obtained at temperatures near the melting point of the material to ensure plastic flow for zero creep experiments performed on the solid state or to apply the pendant drop or drop weight methods to the liquid state. Both experiment and theoretical considerations suggest that the temperature dependence of the surface free energy is rather small, see section 4.4.7.3. An upper limit is of the order of -0.0002 J / (m2 K), and this temperature dependence does not vary by more than a factor of two for the different materials. Thus, in the following compilation, only the melting point is given to indicate the temperature range at which the experiments have been performed. This simplification seems tolerable in view of the rather large experimental deficiencies of the methods employed. When comparing surface free energy data obtained for the liquid state with data of the solid state, an approximately 13 % larger value for the solid state should be accounted for due to the energy contribution from the heat of fusion [78Mie2]. All data have been extracted from the following review articles [63All, 71Jon, 72All, 75Tys, 76Lan, 77Lan, 78Mie1, 78Mie2, 83Kum ].
Landolt -Börnst ein New Series III/42A2
4.4 -20
4.4 Surface free energy and surface stress
[Ref. p. 4.4 -44
Table 3. Surface free energy γ from drop-weight and pendant-drop methods, measured at the respective melting point under high vacuum. The free energy data are understood as describing the liquid-vapour interface energy. The data of the drop weight method have been extrapolated to zero rod diameter. Only zero creep experiments are considered for surface free energy data of the solid state. These data describe the solid-vapour interface energy. Where available, zero creep data measured under vacuum are listed. For measurements performed under a gas atmosphere, only data obtained for an inert gas atmosphere are considered. If several values have been obtained, the average and its standard deviation are listed. The calculated value of the temperature coefficient of γ for the solid state is taken from [78Mie2]. The melting point temperatures are taken from [88Ida]. Material Ag
Melting point [K] 1234
Au
1336
Bi Cd β-Co Co Cr Cu
544 594 1765 1765 2178 1356
δ-Fe γ-Fe Fe Ga Hf In Ir Mo
1356 1808 1808 1808 303 2480 430 2727 2895
Nb
2895 2740
Ni
2740 1728
Os Pb Pd Pt Re Rh Ru Sn Ta
1728 2973? 601 1828 2047 2047 3440 2239 2723? 505 3123 3123
drop weight pendant drop zero creep method [J / m2] method [J / m2] method [J / m2] 1.205 ± 0.026 1.005 ± 0.009 1.410 ± 0.037 1.350 ± 0.100 0.501 ± 0.004 0.675 ± 0.010 2.424 ± 0.023 1.9 1.855 ± 0.015 2.090 ± 0.020 1.520 ± 0.014 1.750 ± 0.089 1.31 1.295 ± 0.008 1.910 ± 0.19 2.170 ± 0.330 1.87 1.902 ± 0.007 0.767 ± 0.006 1.6 1.628 ± 0.008 0.633 ± 0.004 2.18 2.278 ± 0.013 2.630 ± 0.050 1.920 ± 0.200 2.246 ± 0.013 2.239 ± 0.01 2.210 ± 0.054 2.100 ± 0.100 1.924 ± 0.003 1.888 ± 0.005 1.940 ± 0.046 1.820 ± 0.180 1.77 1.728 ± 0.01 2.4 2.511 ± 0.009 0.560 ± 0.004 1.44 1.501 ± 0.007 1.950 ± 0.015 1.83 1.773 ± 0.005 2.7 2.638 ± 0.017 1.9 2.013 ± 0.015 2.23 2.223 ± 0.016 0.673 ± 0.007 0.685 ± N.A. 2.480 ± 0.070 2.15 ± 0.015 2.086 ± 0.009
Ref. dγ / dT [J /(m2K)] −0.00015 76Dig 51Fun –0.00014 76Dig 66Mul –0.00009 72She –0.00014 72Kho 76Dig –0.00020 63All –0.00017 76Dig –0.00019 76Dig 63Hoa 63All 64Pri 64Pri –0.00019 63All –0.00012 72Kok –0.00011 63All –0.00012 72Kho –0.00016 63All –0.00014 76Dig 71Jon 63All –0.00014 76Dig 61Rad 63All –0.00020 76Dig 59Hey 63All –0.00015 63All –0.00011 72Kho –0.00016 63All –0.00016 76Dig 63All –0.00016 63All –0.00016 63All –0.00017 63All –0.00011 72Kho 53Gre –0.00014 76Dig 63All Lando lt -Bö rnst ein New Series III/42A2
Ref. p. 4.4 -44] Material Ti
Tl V W Zn Zr
Melting point [K] 1998 1998 576 1973? 3655 3655 693 2130 2130
4.4 Surface free energy and surface stress drop weight pendant drop zero creep method [J / m2] method [J / m2] method [J / m2] 1.938 ± 0.042 1.700 ± N.A. 1.6 1.656 ± 0.004 0.562 ± 0.006 1.9 1.948 ± 0.007 2.690 ± 0.022 2.471 ± 0.038 2.545 ± 0.012 0.868 ± 0.014 0.830 ± N.A. 1.85 1.48 1.469 ± 0.004
4.4 -21 Ref. dγ / dT [J /(m2K)] –0.00013 69Lik 68Kos 63All –0.00011 72She –0.00016 63All –0.00015 76Dig 63All –0.00018 72Kok 65Bry –0.00011 73Kos 63All
4.4.7.3 Temperature dependence of the surface free energy
Fig. 9. The surface free energy of Cu vs. temperature. The melting temperature Tm is indicated by the dashed vertical line, data in the solid state have been obtained by the zero creep technique [49Udi], data of the liquid by the sessile drop technique [59All]. The jump of γ at the melting temperature is ascribed to the heat of fusion. The slope of the solid line in the liquid range is -0.00031 Nm-1K-1 (data from [59All]).
The limited temperature range of experiments which exploit viscous flow for T < Tm in connection with the scatter of the data on γ does not warrant to determine experimental data on the temperature coefficient in the solid state. The scatter of surface free energy data for the solid state can be appreciated from Fig. 9. The experimental determination of the temperature dependence of γ seems to be tractable only in the liquid state. A jump of ∆γ in passing through the melting temperature is ascribed to the heat of fusion Hf , scaled to the area per atom A: ∆γ = H f / A , in agreement with the experimental values of Fig. 9 [59All]. According to the Gibbs-Duhem relation the temperature dependence of the surface free energy is given by the surface entropy S(s), ∂γ / ∂T = −S ( s) [69Eri, 73Cou, 85Spa, 90Ada]. Configurational and vibrational contributions to the surface entropy have been estimated [75Tys, 77Tys, 78Mie2] and an estimate of the temperature coefficient dγ / dT is given for high temperature values of γ in section 4.4.7.2.
Landolt -Börnst ein New Series III/42A2
4.4 -22
4.4 Surface free energy and surface stress
[Ref. p. 4.4 -44
4.4.7.3.1 Temperature dependence of the anisotropy of the surface free energy The equilibrium shape of Pb crystallites of micrometer size on a graphite substrate has been analyzed by scanning electron microscopy to derive the polar diagram of the surface free energy. From shape analyses performed at different temperatures, the temperature dependence of the surface free energy anisotropy, expressed as ratio γ {hkl} / γ {111} has been determined. The result is presented in Fig. 10. The surface free energy anisotropy decreases non-linearly with increasing temperature.
1.06 1.05
#{ hkl} #{111}
1.04
{110} {113}
Pb X
{115} {331} {112}
X
X
{221} X
1.03 {100} 1.02 1.01 1.00 400
500 T [K]
600
Fig. 10. Temperature dependence of the surface free energy anisotropy of Pb. Equilibrium shapes of Pb crystallites on graphite have been analysed at 473 K, 523 K, 548 K and 573 K. A decrease of the anisotropy with increasing temperature is apparent from the negative slopes of the curves [83Hey].
4.4.7.4 Calculated surface free energy and surface stress for inert gas crystals Surface free energies of fcc inert gas crystals have been calculated with a Lennard-Jones Potential for {100}, {111}, and {110} surface orientations [49Shu, 64Ben, 67Ben]. The calculated values of the different authors agree on average within 5 %, and the more recent calculations are quoted. Surface stress has been calculated for the {100} surface [50Shu]. Structural relaxations have been considered in all calculations. Table 4. Calculated surface free energy γ of inert gas crystals for {111}, {100} and {110} orientations and of the surface stress τ of the {100} surface in a [100] direction. Calculations were performed for T = 0 K. Material Ne, fcc Ar, fcc Kr, fcc Xe, fcc
γ{111} [J / m2] [64Ben] 0.0197 0.0432 0.0528 0.0621
γ{100} [J / m2] [64Ben] 0.0203 0.0446 0.0545 0.0641
γ{110} [J / m2] [64Ben] 0.0213 0.0468 0.0572 0.0673
τ[100] [N / m] [50Shu] -0.0019 -0.0046 -0.0059 -0.0067
Lando lt -Bö rnst ein New Series III/42A2
Ref. p. 4.4 -44]
4.4 Surface free energy and surface stress
4.4 -23
4.4.7.5 Calculated surface free energies and surface stress for alkali halides The calculated values of surface free energy and surface stress depend strongly on the details of the potential which is used in the calculation. Although bulk properties are well reproduced by different potentials, the calculation of surface properties seems to be much more demanding. As experimental values for both properties are scarce and exhibit wide scatter, a comparison to experimental data does not help and no preference for one calculation can be given. Therefore calculations by Benson and Yun [67Ben] and by Tasker [79Tas] are presented in the following table. Table 5. Calculated surface free energy γ of alkali halide crystals for {100} and {110} surface orientation. Surface stress τ is calculated for the {100} surface in a [100] direction. Values by two groups [67Ben, 79Tas] are given for comparison. Calculations were performed for T = 0 K. Material LiF LiCl LiBr LiI NaF NaCl NaBr NaI KF KCl KBr KI RbF RbCl RbBr RbI CsF CsCl CsBr CsI
γ{100} [J / m2]
γ{100} [J / m2] γ{110} [J / m2] γ{110} [J / m2]
τ[100] [N / m]
τ[100] [N / m]
[67Ben]
[79Tas]
[67Ben]
[79Tas]
[67Ben]
[79Tas]
0.142 0.107 0.086 0.073 0.216 0.158 0.138 0.118 0.184 0.141 0.123 0.113 0.171 0.138 0.122 0.104 0.148
0.480 0.294 0.252 0.216 0.338 0.212 0.187 0.165 0.239 0.170 0.154 0.139 0.228 0.150 0.136 0.118
0.568 0.340 0.280 0.226 0.555 0.354 0.304 0.252 0.423 0.298 0.262 0.222 0.380 0.277 0.246 0.210 0.341 0.219 0.200 0.175
1.047 0.542 0.444 0.356 0.741 0.425 0.362 0.294 0.516 0.350 0.311 0.268 0.439 0.295 0.264 0.222
0.494 0.624 0.591 0.546 0.741 0.438 0.386 0.341 0.495 0.264 0.229 0.191 0.427 0.222 0.192 0.176 0.371
0.407 0.252 0.213 0.224 0.442 0.256 0.221 0.182 0.655 0.401 0.320 0.237 0.474 0.309 0.264 0.222
4.4.7.6 Calculated surface free energy and surface stress of III-V compounds A simple bond-straining bond-bending potential has been used to calculate surface stress on group III and group V surfaces due to the non-ideal bonding geometry of the surface atoms [64Cah]. The surface energy has been calculated from the number of broken bonds per surface area and using the sublimation energy as an estimate for the bond energy [64Cah].
Landolt -Börnst ein New Series III/42A2
4.4 -24
4.4 Surface free energy and surface stress
[Ref. p. 4.4 -44
Table 6. Calculated mean surface free energy γ for various orientations, and surface stress on the group III (A) and on the group V (B) terminated surface of (111) oriented III-V compounds A B γ 111 = 1 / 2( γ 111 + γ 111 ) . Calculations were performed for T = 0 K. Material
γ{110}
γ{100} 2
InSb GaAs InAs GaSb InP AlSb AlAs GaP AlP
γ{111} 2
τA, 2
{111}
τB,
{111}
[J / m ]
[J / m ]
[J / m ]
[N / m] [N / m]
1.1 2.2 1.4 1.6 1.9 1.9 2.6 2.9 3.4
0.75 1.5 1.0 1.1 1.3 1.3 1.8 2.0 2.4
0.6 1.3 0.84 0.91 1.1 1.1 1.5 1.7 2.0
-0.6 -1.0 -0.7 -0.8
0..3 0.5 0.3 0.4
-0.8
0.4
Reference 64Cah 64Cah 64Cah 64Cah 64Cah 64Cah 64Cah 64Cah 64Cah
4.4.7.7 Calculated surface free energy and surface stress for Si and Ge Structural relaxations have been considered in the calculations of the following data. Table 7. Calculated surface free energy γ and surface stress τ on various surface structures of Si and Ge. τx represents the surface stress along a dimer bond on the (100) surface, τy represents the stress perpendicular to the dimer bond. *Data for the Ge(100) dimer reconstruction represent the energy in eV per dimer. Calculations were performed for T = 0 K. Material
γ [J / m2]
Reference
Si(100), 1 × 1 2 × 1 , symmetric dimer reconstruction 2 × 1 , asymmetric dimer Si(111), 1 × 1 1 × 1 , faulted
1.82 1.89 1.59 3× 3 1.55 2 × 2 , adatom on top 2 × 2 , adatom on top, faulted 1.59 2 × 2 , adatom on hollow site 1.64
89Mea1 89Mea1 89Mea1 89Mea1 89Mea1 89Mea1
Ge(100), dimers buckled, 2 × 1 buckled, 4 × 1 buckled, c 4 × 2 buckled, 2 × 2
0*
89Pay
0.036* -0.066* -0.070*
89Pay 89Pay 89Pay
1.61 Ge(111), 1 × 1 1.67 1 × 1 , faulted 1.38 2 × 2 , adatom on top 2 × 2 , adatom on top, faulted 1.41
89Mea1 89Mea1 89Mea1 89Mea1
τx [N / m]
τy [N / m]
Reference
2.75 0.75
0.93 -2.11
89Pay 89Pay
0.56
-0.56
88Ale
-0.68 0.14 2.13 2.08 2.37 1.48
-0.68 0.14 2.13 2.08 2.37 1.48
89Mea1 89Mea1 89Mea1 89Mea1 89Mea1 89Mea1
-0.84 -0.3 1.65 1.93
89Mea1 89Mea1 89Mea1 89Mea1
Lando lt -Bö rnst ein New Series III/42A2
Ref. p. 4.4 -44]
4.4 Surface free energy and surface stress
Material
γ [J / m2]
Reference
Ge(111), 1 × 1 , unrelaxed 1 × 1 , relaxed 2 × 2 , adatom on top 2 × 2 , adatom on hollow site 3 × 3 , without adatoms 3 × 3 , with adatoms
1.41 1.15 1.20 1.30 1.29 1.01
89Pay 89Pay 89Pay 89Pay 89Pay 89Pay
τx [N / m]
τy [N / m]
4.4.7.8 Calculated adsorbate-induced changes of stress on semiconductor surfaces Structural relaxations have been considered in the calculation of the following data. Table 8. Calculated surface stress on substitutional and adsorbate covered Si and Ge surfaces. Calculations were performed for T = 0 K. Material
τ [N / m]
Reference
Si(111), 1 × 1 Al:Si(111), substitutional As:Si(111), substitutional B:Si(111), substitutional Ga:Si(111), substitutional Ge:Si(111), substitutional
-0.68 -8.08 2.84 6.1 -5.58 -1.4
89Mea2 89Mea2 89Mea2 89Mea2 89Mea2 89Mea2
3 × 3 Si / Si(111) 2 × 2 Si / Si(111) 3 × 3 As / Si(111)
2.13
89Mea2
2.08 2.93
89Mea2 89Mea2
3 × 3 Ga / Si(111)
1.69
89Mea2
-0.84 3.04
89Mea2 89Mea2
Ge(111), 1 × 1 As:Ge(111), subsitutional
Landolt -Börnst ein New Series III/42A2
4.4 -25
Reference
4.4 -26
4.4 Surface free energy and surface stress
[Ref. p. 4.4 -44
4.4.7.9 Calculated surface free energies of metals No structural relaxation has been considered in [98Vit], and consequently these values are expected to be significantly changed if relaxations are included. All other sources considered structural relaxations. Table 9. Calculated surface free energy γ of metals for various orientations. The subscripts A and B refer to the two possible surface terminations of (10 1 0) surfaces of hcp crystals [91Ove], where the termination with the smaller lattice spacing is denoted A [98Vit]. Calculations were performed for T = 0 K. The method of calculation is indicated: FS: empirical n-body Finnis-Sinclair potential, PSP: total energy pseudopotential, EAM: embedded atom method, DFT: density functional theory, FPLAPW: full potential linear combination of augmented waves, FPLMTO: full potential linear combination of muffin tin orbitals. Material
γ [eV / atom] γ [J / m2] method
Reference
Ac(100), fcc Ac(110), fcc Ac(111), fcc Ag(100)
0.764 1.006 0.786 0.59
98Vit 98Vit 98Vit 93Fio 89Wei 91Gum 91Ers 92Met 98Vit 87Ack2 98Vit 89Wei 92Met 87Ack2 91Gum 92Met 98Vit 99Rub 87Ack2 98Vit 95Sch 87Nee 95Sch 98Vit 70Lan 89Pay,90Nee, 91Nee 87Nee 70Lan 95Sch 98Vit 93Fio 91Gum 98Vit 87Ack2 98Vit 87Ack2
0.653 Ag(110), fcc
0.953
Ag(111) 0.553 0.576 Al(100), fcc
0.689
Al(110), fcc 0.919 Al(110), bcc Al(111)
Au(100)
0.531 0.75 0.895
Au(110), fcc
1.321
0.732 0.681 0.868 1.3 0.70 1.27 1.21 1.2 0.759 1.238 1.4 1.26 0.808 0.62 1.21 1.172 0.620 1.347 1.081 0.912 1.090 1.271 1.03 0.96 0.704 0.73 0.939 1.199 0.92 1.627 0.770 1.700 0.816
DFT DFT DFT DFT FPLAPW EAM FPLAPW FPLMTO DFT FS DFT FPLAPW FPLMTO FS EAM FPLMTO DFT FPLMTO FS DFT PSP DFT PSP DFT PSP DFT DFT PSP PSP DFT DFT EAM DFT FS DFT FS
Lando lt -Bö rnst ein New Series III/42A2
Ref. p. 4.4 -44]
Material
4.4 Surface free energy and surface stress γ [eV / atom] γ [J / m2] method
Au(111)
0.611
1.248 0.79 1.04 1.283 0.624 0.353 0.376 0.397 1.834 1.924 2.1 2.126
DFT EAM PSP DFT FS DFT DFT DFT DFT FPLAPW PSP DFT
Reference 89Pay, 91Nee 91Gum 91Tak 98Vit 87Ack2 98Vit 98Vit 98Vit 98Vit 92Fei 89Yu 98Vit
Ba(100), bcc Ba(110), bcc Ba(111), bcc Be(0001), hcp
0.616 0.464 1.199 0.495
Be (10 1 0) A, hcp
1.083
Be (10 1 0) B, hcp Bi(100), sc Bi(110), sc Ca(100), fcc Ca(110), fcc Ca(111), fcc Cd(0001), hcp Co(0001), hcp Co (10 1 0) A, hcp
1.626
3.192
DFT
98Vit
0.356 0.507 0.535 0.811 0.484 0.300 0.961 1.982
0.537 0.541 0.542 0.582 0.567 0.593 2.775 3.035
DFT DFT DFT DFT DFT DFT DFT DFT
98Vit 98Vit 98Vit 98Vit 98Vit 98Vit 98Vit 98Vit
2.476
3.791
DFT
98Vit
2.020 1.258 3.626 2.420 3.030 0.228
3.979 3.505 4.123 3.892 3.775 0.093 0.10 0.082 0.092 0.10 1.29 1.802 2.166 1.144 2.237 1.233 1.18 1.94 1.952 0.947 0.463 0.485 0.524 2.222 2.430 2.733 2.589 2.393
DFT DFT DFT DFT DFT DFT PSP DFT DFT PSP EAM FPLAPW DFT FS DFT FS EAM FPLMTO DFT FS DFT DFT DFT DFT DFT DFT DFT DFT
98Vit 98Vit 98Vit 98Vit 98Vit 98Vit 70Lan 98Vit 98Vit 70Lan 91Gum 95Bro 98Vit 87Ack2 98Vit 87Ack2 91Gum 94Pol 98Vit 87Ack2 98Vit 98Vit 98Vit 98Vit 98Vit 98Vit 98Vit 98Vit
Co (10 1 0) B, hcp Cr(100), bcc Cr(110), bcc Cr(111), bcc Cr(211), bcc Cr(310), bcc Cs(100), bcc Cs(110), bcc Cs(111), bcc Cs(111), fcc Cu(100)
0.142 0.390
0.906 Cu(110), fcc
1.323
Cu(111) 0.707 Eu(100), bcc Eu(110), bcc Eu(111), bcc Fe(100), bcc Fe(110), bcc Fe(111), bcc Fe(211), bcc Fe(310), bcc Landolt -Börnst ein New Series III/42A2
0.653 0.484 1.282 1.265 0.978 2.694 1.804 2.153
4.4 -27
4.4 -28
4.4 Surface free energy and surface stress
Material
γ [eV / atom] γ [J / m2] method
Reference
Fr(100), bcc Fr(110), bcc Fr(111), bcc Ga(001), bct Ga(110), bct Ga(100), bct Hf(0001), hcp Hf (10 1 0) A, hcp
0.2021 0.122 0.346 0.376 0.507 0.695 1.400 2.471
0.081 0.069 0.080 0.661 0.797 0.773 2.472 2.314
DFT DFT DFT DFT DFT DFT DFT DFT
98Vit 98Vit 98Vit 98Vit 98Vit 98Vit 98Vit 98Vit
Hf (10 1 0) B, hcp Hg(0001), hcp In(001), bct In(110), bct In(100), bct Ir(100)
2.892
2.709
DFT
98Vit
0.111 0.342 0.422 0.632 1.85 1.73 1.772 2.59 2.428 1.31
0.165 0.488 0.560 0.592
0.909 1.398
3.264 2.971 0.142 0.140 0.135 0.152 0.140 1.121 0.915
DFT DFT DFT DFT DFT DFT DFT DFT DFT DFT DFT DFT DFT PSP DFT DFT PSP DFT DFT
98Vit 98Vit 98Vit 98Vit 97Fill 93Fio 98Vit 97Fill 98Vit 97Fill 89Pay, 91Nee 98Vit 98Vit 70Lan 98Vit 98Vit 70Lan 98Vit 98Vit
1.690
1.106
DFT
98Vit
0.383
DFT PSP PSP DFT PSP DFT PSP PSP DFT DFT
98Vit 96Kok 70Lan 98Vit 96Kok 98Vit 96Kok 70Lan 98Vit 98Vit
Ir(110) Ir(111)
K(100), bcc K(110), bcc K(111), bcc K(111), fcc La(0001), hcp La (10 1 0) A, hcp La (10 1 0) B, hcp Li(100), bcc
1.225 0.249 0.167 0.462
3.722 3.606
Li(111), bcc
0.750
Li(111), fcc Lu(0001), hcp Lu (10 1 0) A, hcp
1.102 1.845
0.522 0.506 0.230 0.556 0.545 0.590 0.623 0.360 1.604 1.424
Li(110), bcc 0.289
Lu (10 1 0) B, hcp Mg(0001), hcp
2.093
1.616
DFT
98Vit
0.437
Mg (10 1 0) A, hcp
0.814
0.792 0.641 0.694 0.782
DFT PS FPLAPW DFT
98Vit 94Wri 92Fei 98Vit
Mg (10 1 0) B, hcp Mg(110), bcc Mg(111), fcc Mn(111), fcc
1.072
1.030
DFT
98Vit
1.043
0.640 0.540 3.100
PSP PSP DFT
70Lan 70Lan 98Vit
[Ref. p. 4.4 -44
Lando lt -Bö rnst ein New Series III/42A2
Ref. p. 4.4 -44]
4.4 Surface free energy and surface stress
Material
γ [eV / atom] γ [J / m2] method
Reference
Mo(100), bcc
2.410
98Vit 92Met 99Rub 99Mar 86Ack 98Vit 92Met 99Rub 86Ack 98Vit 98Vit 98Vit 86Ack 98Vit 70Lan 98Vit 98Vit 70Lan 98Vit 89Wei 92Met 99Rub 86Ack 98Vit 89Wei 92Met 99Rub 86Ack 98Vit 98Vit 98Vit 86Ack 91Gum 98Vit 87Ack2 98Vit 87Ack2 91Gum 98Vit 87Ack2 98Vit 98Vit 98Vit 98Vit 98Vit 98Vit 98Vit 98Vit 98Vit 91Man 98Vit 91Man 98Vit
2.09 Mo(110), bcc
1.534 1.6
Mo(111), bcc Mo(211), bcc Mo(310), bcc
4.068 2.738 3.601
Na(100), bcc Na(110), bcc
0.290
Na(111), bcc Na(111), fcc Nb(100), bcc
Nb(100), fcc Nb(110), bcc
0.197 0.546 1.987
1.320 1.2
Nb(111), bcc Nb(211), bcc Nb(310), bcc
3.668 2.410 3.145
Ni(100) 0.969 Ni(110), fcc
1.337
Ni(111) 0.695 Np(111), fcc Os(0001), hcp Os (10 1 0) A, hcp Os (10 1 0) B, hcp Pa(100), bct Pa(110), bct Pa(001), bct Pa(111), fcc Pb(100), fcc Pb(110)
1.252 1.869 3.874 4.595 2.075 1.648 2.638 1.424 0.307 0.513
Pb(111) 0.226
Landolt -Börnst ein New Series III/42A2
3.837 3.52 3.97 3.32 2.1 3.454 3.14 3.6 1.829 3.740 3.600 3.626 2.07 0.264 0.230 0.253 0.287 0.210 2.858 3.1 2.86 2.88 1.956 2.685 2.9 2.36 2.53 1.669 3.045 2.829 2.861 2.014 1.57 2.426 1.444 2.368 1.548 1.44 2.011 1.153 2.208 4.566 5.021 5.955 2.548 2.902 2.661 2.302 0.377 0.56 0.445 0.496 0.321
DFT FPLMTO FPLMTO DFT FS DFT FPLMTO FPLMTO FS DFT DFT DFT FS DFT PSP DFT DFT PSP DFT FPLAPW FPLMTO FPLMTO FS DFT FPLAPW FPLMTO FPLMTO FS DFT DFT DFT FS EAM DFT FS DFT FS EAM DFT FS DFT DFT DFT DFT DFT DFT DFT DFT DFT PS DFT PS DFT
4.4 -29
4.4 -30
4.4 Surface free energy and surface stress
Material
γ [eV / atom] γ [J / m2] method
Reference
Pd(100)
0.91
1.781 3.689
1.64 2.734 2.819 2.067 2.192 1.44 2.299 2.007 0.286 0.296 0.324 0.112 0.120 0.104 0.118 0.110 4.214 4.628
DFT FPLMTO FPLAPW DFT PS FPLAPW FPLMTO DFT FPLMTO DFT FPLMTO DFT DFT DFT EAM DFT DFT PS DFT EAM DFT DFT DFT DFT DFT DFT PSP DFT DFT PSP DFT DFT
93Fio 92Met 89Wei 98Vit 96Wac 89Wei 92Met 98Vit 92Met 98Vit 99Rub 98Vit 98Vit 93Fio 91Gum 98Vit 98Vit 95Fei2 89Pay, 91Nee 91Gum 98Vit 98Vit 98Vit 98Vit 98Vit 98Vit 70Lan 98Vit 98Vit 70Lan 98Vit 98Vit
4.770
5.985
DFT
98Vit
3.201
3.0 4.3 4.236
DFT FPLMTO PS FPLAPW DFT DFT FPLMTO DFT FPLMTO FPLMTO DFT FPLMTO PS PS DFT
93Fio 92Met 93Mor 90Fei 98Vit 98Vit 92Met 98Vit 92Met 99Rub 98Vit 99Rub 87Cho 87Cho 98Vit
3.669
4.856
DFT
98Vit
0.365
0.608
DFT
98Vit
1.152 Pd(110) 1.559 Pd(111)
Po(100), sc Po(110), sc Pt(100)
Pt(110) Pt(111)
Pu(111), fcc Ra(100), bcc Ra(110), bcc Ra(111), bcc Rb(100), bcc Rb(110), bcc Rb(111), bcc Rb(111), fcc Re(0001), hcp Re (10 1 0) A, hcp Re (10 1 0) B, hcp Rh(100)
1.559 0.848 0.306 0.370 1.21 1.378 2.009
1.004 1.104 0.515 0.377 1.010 0.229 0.150 0.417
0.437 0.373
1.26
Rh(110), fcc
1.310 1.919
Rh(111), fcc
1.002
Ru(0001), hcp
1.136 1.574 1.472
Ru (10 1 0) A, hcp Ru (10 1 0) B, hcp Sb(100), sc
1.86 2.3 2.326 2.130 2.5 1.97 2.225 1.64 2.225
2.81 2.65 2.592 2.799 2.899 2.88 2.472 2.53 3.928
[Ref. p. 4.4 -44
Lando lt -Bö rnst ein New Series III/42A2
Ref. p. 4.4 -44]
4.4 Surface free energy and surface stress
Material
γ [eV / atom] γ [J / m2] method
Reference
Sb(110), sc Sc(0001), hcp Sc (10 1 0) A, hcp
0.560 1.080 1.694
0.659 1.834 1.526
DFT DFT DFT
98Vit 98Vit 98Vit
Sc (10 1 0) B, hcp Sn(001), bct Sn(110), bct Sn(100), bct Sr(100), fcc Sr(110), fcc Sr(111), fcc Ta(100), bcc
2.011
1.812
DFT
98Vit
0.387 0.509 0.716 0.484 0.725 0.440 2.174
Ta(110), bcc
1.531
Ta(111), bcc Ta(211), bcc Ta(310), bcc
4.201 2.799 3.485
Tc(0001), hcp
1.527 1.472 3.040
0.611 0.620 0.616 0.408 0.432 0.428 3.097 2.328 3.084 1.980 3.455 3.256 3.139 2.512 3.691 3.897
DFT DFT DFT DFT DFT DFT DFT FS DFT FS DFT DFT DFT FS DFT FPLMTO DFT
98Vit 98Vit 98Vit 98Vit 98Vit 98Vit 98Vit 86Ack 98Vit 86Ack 98Vit 98Vit 98Vit 86Ack 98Vit 99Rub 98Vit
4.989
DFT
98Vit
3.83 3.61 3.19 1.468 1.450 1.476 2.632 2.194 2.516
FPLMTO FPLMTO FPLMTO DFT DFT DFT DFT FPLAPW DFT
99Rub 99Rub 99Rub 98Vit 98Vit 98Vit 98Vit 96Fei 98Vit
Tc (10 1 0) A, hcp Tc (10 1 0) B, hcp Tc(100), fcc Tc(110), fcc Tc(111), fcc Th(100), fcc Th(110), fcc Th(111), fcc Ti(0001), hcp Ti (10 1 0) A, hcp Ti (10 1 0) B, hcp Tl(0001), hcp Tl (10 1 0) A, hcp
3.893
1.233 1.722 1.073 1.234 2.224 2.435
2.754
DFT
98Vit
0.221 0.494
0.297 0.352
DFT DFT
98Vit 98Vit
Tl (10 1 0) B, hcp U(111), fcc V(100), bcc
0.529
0.377
DFT
98Vit
1.367 1.725
V(110), bcc
1.312
V(111), bcc V(211), bcc V(310), bcc
3.494 2.402 2.921
W(100), bcc
2.955
2.356 3.028 3.18 1.733 3.258 1.473 3.541 3.443 3.244 1.745 4.635 4.78 2.924
DFT DFT FPLAPW FS DFT FS DFT DFT DFT FS DFT FPLAPW FS
98Vit 98Vit 98Vit 86Ack 98Vit 86Ack 98Vit 98Vit 98Vit 86Ack 98Vit 98Vit 86Ack
Landolt -Börnst ein New Series III/42A2
4.4 -31
4.4 -32
4.4 Surface free energy and surface stress
Material
γ [eV / atom] γ [J / m2] method
Reference
W(110), bcc
1.806
W(111), bcc W(211), bcc W(310), bcc
4.916 3.261 4.338
Y(0001), hcp Y (10 1 0) A, hcp Y (10 1 0) B, hcp Yb(100), fcc Yb(110), fcc Yb(111), fcc Zn(0001), hcp Zn(110), bcc Zn(111), fcc Zr(0001), hcp
Zr (10 1 0) A, hcp Zr (10 1 0) B, hcp
1.077 1.676
4.005 2.575 4.452 4.177 4.303 3.036 1.506 1.243
DFT FS DFT DFT DFT FS DFT DFT
98Vit 86Ack 98Vit 98Vit 98Vit 86Ack 98Vit 98Vit
2.059
1.527
DFT
98Vit
0.484 0.721 0.423 0.385
0.478 0.503 0.482 0.989 0.580 0.440 2.260 2.044 1.729
98Vit 98Vit 98Vit 98Vit 70Lan 70Lan 98Vit 94Yam 96Fei 99Rub 98Vit 98Vit
1.216 2.269
2.111
DFT DFT DFT DFT PSP PSP DFT PS FPLAPW FPLMTO DFT
2.592
2.411
DFT
1.288
[Ref. p. 4.4 -44
4.4.7.10 Calculated surface stress Table 10. Calculated surface stress τ for metals for various orientations. The surface stress τaver is the average value τ = 0.5( τ x + τ y ) for the (110) and (310) surfaces, where x: [ 1 10] and y: [001] for the (110) plane and x: [ 1 30] and y: [001] for the (310) plane. Calculations were performed for T = 0 K. Ref. [97Fill] did not clearly identify the two in-plane directions for Ir(110). Material
τ [001]
Ag(100)
[eV / atom] [eV / atom] [ N / m] 0.88
τ [ 1 10]
τaver
τ [001]
τ [ 1 10] or τ [ 1 30]
[N / m]
[N / m]
0.82 1.172 Ag(110), fcc Ag(111)
0.738 0.64 0.620
Al(110), fcc Al(111) Au(100)
1.84
1.984 1.248 2.32
1.62 1.79 1.822
Au(110), fcc Au(111)
1.107 2.768 1.51 1.056
Reference 93Fio 91Gum 87Ack2 87Ack2 91Gum 87Ack2 87Nee 89Pay, 90Nee, 91Nee 87Nee 93Fio 91Gum 87Ack2 87Ack2 89Pay, 91Nee 91Gum 87Ack2
Lando lt -Bö rnst ein New Series III/42A2
Ref. p. 4.4 -44] Material
4.4 Surface free energy and surface stress τ [001]
τ [ 1 10]
τaver
[eV / atom] [eV / atom] [ N / m] Cu(100) Cu(110), fcc Cu(111)
τ [001]
τ [ 1 10] or τ [ 1 30]
[N / m] 1.38 1.696
[N / m]
0.957 0.86 0.626
Ir(100) Ir(110) Ir(111)
1.86 2.94 1.70 ?
3.21 ? 1.96 5.296 2.241 2.4 0.775 1.184 2.532 0.301 1.267 1.27 0.977
Mo(100), bcc Mo(110), bcc Mo(310), bcc Nb(100), bcc Nb(110), bcc Nb(310), bcc Ni(100) Ni(110), fcc Ni(111) Pb(110) Pb(111) Pd(100) Pd(110) Pd(111) Pt(100)
2.168 2.405
0.707 0.882
1.05 1.22
1.79 1.48
1.28
1.17 0.816
1.86
2.74 3.68
2.69
Pt(110) Pt(111)
1.21
Rh(100) Ta(100), bcc Ta(110), bcc Ta(310), bcc V(100), bcc V(110), bcc V(310), bcc W(100), bcc W(110), bcc W(310), bcc
1.94
Landolt -Börnst ein New Series III/42A2
2.019 2.247
3.40 2.77
2.69 1.81
3.249 0.392 1.647 2.424 0.263 1.255 3.032 0.271 1.450
5.07 6.75 5.60 2.86
2.535 3.085 1.939 2.335 2.385 2.833
4.4 -33 Reference 91Gum 87Ack2 87Ack2 91Gum 87Ack2 97Fill 93Fio 97Fill 97Fill 89Pay, 91Nee 86Ack 2000Mar 86Ack 86Ack 86Ack 86Ack 86Ack 91Gum 87Ack2 87Ack2 87Ack2 91Man 91Man 93Fio 95Fei1 95Fei1 93Fio 91Gum 95Fei1 95Fei1 89Pay, 91Nee 91Gum 93Fio 86Ack 86Ack 86Ack 86Ack 86Ack 86Ack 86Ack 86Ack 86Ack
4.4 -34
4.4 Surface free energy and surface stress
[Ref. p. 4.4 -44
4.4.7.11 Calculated adsorbate induced surface stress on Pt(111) Structural relaxations are considered in the following calculations. Table 11. Calculated surface stress of clean and adsorbate covered Pt(111). Coverage 1.0 equals one adsorbate atom per Pt surface atom. Calculations were performed for T = 0 K. Material
Coverage
τ [N / m]
Reference
Pt(111) 2 × 2 H / Pt(111) 2 × 2 H / Pt(111) 1 × 1 H / Pt(111) 2 × 2 O / Pt(111)
clean 0.25 0.75 1 0.25
6.27 5.18 2.78 1.7 3.07
97Fei 97Fei 97Fei 97Fei 97Fei
8.0 N/m 6.4
Surface stress of Pt(111) calculated for T = 0 K
surface stress
4.8 3.2 1.6 0
Fig. 11. Calculated energy per surface Pt(111) atom vs. surface strain. The curves for the (1x1)-H and p(2x2)-O covered surface are vertically displaced for clarity. The slope of the energy curves at strain 0 give the surface stress . Note, that this slope is largest for the clean surface, bottom curve, and smallest for the H coverage, middle curve (data from [97Fei]).
0
0.2
0.4 0.6 H coverage
0.8
1.0
Fig. 12. Calculated surface stress vs. H coverage on 15 2 Pt(111) (coverage 1.0: 1.50×10 atoms / cm ). Data from [97Fei].
4.4.8 Adsorbate-induced changes of surface free energy The zero creep technique described in section 4.4.2.3 has been employed to measure the influence of gas adsorbates on the surface free energy for oxygen on silver [52But2], oxygen on Fe-3 % Si [67Hon], oxygen on Fe [68Hon] and for oxygen on copper [73McL, 76Bau].
Lando lt -Bö rnst ein New Series III/42A2
Ref. p. 4.4 -44]
4.4 Surface free energy and surface stress
Fig. 13. Surface free energy of Ag as measured by the zero creep technique in dependence of the oxygen partial pressure. The slope of the solid curve indicates an oxygen surface concentration of 198 . × 1015 cm [52But2].
-2
Fig. 15. The surface free energy of iron as a function of the oxygen partial pressure. An oxygen surface concen14 -2 tration of 4.08x10 cm is calculated from the slope of the linear section. At higher partial pressures oxidation sets in and the zero creep technique measures the surface energy of two interfaces, iron-iron oxide and iron oxide-oxygen gas. Data from [68Hon].
Landolt -Börnst ein New Series III/42A2
4.4 -35
Fig. 14. The variation of the surface free energy of the (100) plane of silicon iron for different partial pressures of oxygen. An oxygen surface concentration of
5.6 × 10 −14 cm is deduced from the slope of the curve at 1330 °C, at 1410 °C the slope indicates 4.9 × 10 −14 -2
-2
cm . Data from [67Hon].
Fig. 16. Variation of the surface free energy of copper with oxygen pressure. Filled circles represent data measured by the zero creep technique at 927 °C [73McL], open squares are from measurements at 1027 °C [76Bau]. In the intermediate pressure range an 14 -2 oxygen surface concentration of 4.27x10 cm is calculated from the slope of the curve. At higher oxygen pressure, oxidation sets in that leads to an increase of the surface energy [76Bau].
4.4 -36
4.4 Surface free energy and surface stress
[Ref. p. 4.4 -44
4.4.9 Adsorbate-induced changes of surface stress The data of section 4.4.9 are all from cantilever bending experiments. The influence of sample clamping on the reduced dimensionality of the sample curvature, see section 4.4.4, has been considered where required. 4.4.9.1 Gas adsorption
Fig. 18. S-induced surface stress on Ni(100) vs. S coverage. Data from [92San], rescaled to account for the one dimensional bending. 15 2 (coverage 1.0: 1.61×10 atoms / cm ).
Fig. 17. O-induced surface stress on Si(111) vs. O coverage. The slope of the solid line indicates an oxygen induced compressive surface stress of -5.7 N / m per monolayer O. The inset shows the result for adsorption on Si(100). A slight tensile stress of order 0.2 N / m is induced per monolayer O. Data from [91San], rescaled to account for one dimensional bending [97Iba1] (Si(100): coverage 1.0: 6.78×1014 atoms / cm2, Si(111): coverage 1.0: 7.83×1014 atoms / cm2 ).
Fig. 19. O-induced surface stress on Ni(100). Data from [92San], rescaled to account for the one dimensional bending. (coverage 1.0: 1.61×1015 atoms / cm2).
Fig. 20. C-induced surface stress on Ni(100). The plateau in the stress curve starting at a coverage of 0.3 indicates the formation of the p4g reconstruction. Data from [92San], rescaled to account for the one dimensional bending. (coverage 1.0: 1.61×1015 atoms / cm2).
Lando lt -Bö rnst ein New Series III/42A2
Ref. p. 4.4 -44]
4.4 Surface free energy and surface stress
Fig. 21. S-induced surface stress on Ni(111). Data from [97Iba1]. The leveling off of the stress curve at a coverage of 0.3 indicates a restructuring of the Ni(111) surface, which is schematically shown in Fig. 22. Deposition at higher T leads to a complete restructuring of the surface with a small residual stress [97Iba1]. (coverage 1.0: 1.86×1015 atoms / cm2).
4.4 -37
Fig. 22. Schematic of the S-induced reconstruction of Ni(111). The black S atoms reside in four-fold coordinated sites on the reconstructed surfaces, which exhibits a structure similar to the p4g reconstruction of Ni(100). From [97Iba1].
Fig. 23. O-induced surface stress on Ni(111). The kink in the curve at a coverage of 0.3 is ascribed to a repulsive interaction of O in hcp and p(2x2) sites, schematically shown in Fig. 24. Data from [97Iba1]. (coverage 1.0: 1.86×1015 atoms / cm2).
Landolt -Börnst ein New Series III/42A2
4.4 -38
4.4 Surface free energy and surface stress
[Ref. p. 4.4 -44
Fig. 24. Schematic of the O adsorption sites, shown in lighter grey, at a coverage of 0.3. From [97Iba1].
Fig. 25. C-induced surface stress on Ni(111). The leveling off of the stress curve at a coverage of 0.4 is ascribed to a restructuring of the Ni(111) surface to a (100)-like structure, shown in Fig. 26. Data from [97Iba1]. (coverage 1.0: 1.86×1015 atoms / cm2).
Fig. 26. Model of the C-induced reconstruction of Ni(111). C, shown in black, resides in fourfold coordinated sites on a (100)-like surface. From [97Iba1].
Fig. 27. CO-induced surface stress on Ni(100). The solid line is calculated in a model, which uses a tensile stress for CO molecules without nearest and next-nearest neighbours and a compressive stress due to such neighbours. Data from [97Iba1]. (coverage 1.0: 1.61×1015 atoms / cm2).
Lando lt -Bö rnst ein New Series III/42A2
Ref. p. 4.4 -44]
4.4 Surface free energy and surface stress
4.4 -39
Fig. 28. CO-induced surface stress on Ni(111). The adsorption in bridge and three-fold coordinated hollow sites induces compressive stress for all coverages. Data from [94Gro]. (coverage 1.0: 1.86×1015 atoms / cm2).
Fig. 29. CO- and O-induced surface stress on Pt(111). Both adsorbates induce compressive stress. Data from [97Iba1]. Considerably larger surface stress is induced as compared to adsorption on Ni(111), see Fig. 28 and Fig. 23. This is ascribed to the much higher tensile surface stress of Pt(111) as compared to Ni(111), see Table 10. (coverage 1.0: 1.50×1015 atoms / cm2).
Fig. 30. Change of the surface stress of CO precovered Pt(111) at a coverage of 0.45 after exposure to O2. The solid line is a simulation of the CO2 production which leaves a O covered surface behind. Data from [97Iba1]. (coverage 1.0: 1.50×1015 atoms / cm2).
Fig. 31. O-induced anisotropic surface stress on W(110). At 800 s the sample has been exposed to O2 with a doser which has been closed at 1000 s. A 2x1-O structure with a coverage of 0.5 is formed which induces a compressive stress of -1.1 N / m along [ 1 10], upper curve, and no measurable stress along [001], lower curve. (coverage 1.0: 1.42×1015 atoms / cm2). After an initial O-uptake of the frontside the further oxidation slows down and the slower oxidation of the backside brings the stress difference between front and backside close to zero. The begin of the arrow indicates the formation of the (2x1)-O structure. The stress asymmetry is ascribed to the anisotropic tensile surface stress of W(110), see Table 10. Data from [99San2].
Landolt -Börnst ein New Series III/42A2
4.4 -40
4.4 Surface free energy and surface stress
[Ref. p. 4.4 -44
4.4.9.2 Alkali metal deposition
Fig. 32. Cs-induced surface stress on Ni(111). The solid curve is a guide to the eye. The first monolayer of Cs is completed at a coverage of 0.26 (coverage 1.0: 1.86×1015 atoms / cm2). The tensile stress is ascribed to a charge transfer from Cs to Ni (data from [97Iba1]).
Fig. 33. K-induced surface stress on Pt(111). Deposition at lower T, upper curve, induces tensile stress which is ascribed to adsorbed K. Deposition at higher T, lower curve, favours incorporation of K, which induces compressive stress. Data from [97Iba1] (coverage 1.0: 1.50×1015 atoms / cm2). Semiconductor and metal deposition
4.4.9.3 Semiconductor and metal deposition
Fig. 34. Ge-induced surface stress on Si(100) during deposition at 500 °C. Ge induces compressive surface stress which levels off after a deposition of 6 ML, a total of 7 ML has been deposited. Data from [94Sch] (1 ML: 6.78×1014 atoms / cm2).
Fig. 35. As-induced surface stress on Si(100) during deposition at 500 °C. The stress curve levels off after 160 s when an As coverage of 1 is reached. A monolayer As induces a tensile stress of 1.4 N / m. Data from [94Sch] (1 ML: 6.78×1014 atoms / cm2).
Lando lt -Bö rnst ein New Series III/42A2
Ref. p. 4.4 -44]
4.4 Surface free energy and surface stress 0 N/m -5
4.4 -41
Ag / Pt(111) T = 300 K
-10
)
-15 -20 0
Fig. 36. Surface stress on As-precovered Si(100) during the co-deposition of Ge and As at 500 °C. At 9 ML Ge coverage a slight kink in the stress curve indicates the end of pseudomorphic layer-by-layer growth and defects are formed for higher coverages. Data from [94Sch].
4 6 Ag coverage
8 ML 10
Fig. 37. Ag-induced surface stress on Pt(111). The Aginduced compressive stress is larger than the calculated misfit stress. Data from [97Iba1] (coverage 1.0: 1.50×1015 atoms / cm2).
Fig. 38. Fe-induced surface stress on Si(111) during deposition at 600 K and 300 K (inset). At higher temperature a silicide formation sets in which leads to high tensile stress. The stress continues to increase even after termination at the deposition of 1.2 nm Fe. Deposition of 1.5 nm at 300 K leads only to a minute stress which is ascribed to the growth of Fe islands on the intermixed Fe-Si interface. Data from [95San2].
Landolt -Börnst ein New Series III/42A2
2
4.4 -42
4.4 Surface free energy and surface stress
[Ref. p. 4.4 -44
Fig. 39. Fe-induced surface stress on Cu(100) at 300 K. Deposition proceeds beyond 15 ML. The kinks of the stress curve at 3 ML and at 11 ML indicate structural transitions in the Fe film from fct to fcc and from fcc to bcc, respectively. Data from [99Gut] (1 ML: 1.53×1015 atoms / cm2).
Fig. 40. Co-induced surface stress on Cu(100). Deposition proceeds beyond 15 ML. The slope corresponds to a tensile film stress of 2.5 GPa. The lattice mismatch of 2 % is expected to induce a tensile film stress of 2.9 GPa as calculated from 3rd order continuum elasticity. Data from [99Gut] (1 ML: 1.53×1015 atoms / cm2).
Fig. 41. Ni-induced surface stress on Cu(100). Deposition proceeds beyond 15 ML. The slope corresponds to a tensile film stress of 4.3 GPa. The lattice mismatch of 2.5 % is expected to induce a tensile stress of 4.2 GPa as calculated from 3rd order continuum elasticity. Data from [99Gut] (1 ML: 1.53×1015 atoms / cm2).
Fig. 42. Fe-induced surface stress on W(100). The kink in the stress curve around 3 ML indicates the end of pseudomorphic growth. The initial compressive stress is of opposite sign than the calculated misfit stress. The slope of the data points from 1 to 3 ML corresponds to a tensile film stress of 9.7 GPa. Data from [99Gut] (1 ML: 1.00×1015 atoms / cm2).
Lando lt -Bö rnst ein New Series III/42A2
Ref. p. 4.4 -44]
4.4 Surface free energy and surface stress 4 N/m 3
3
N/m 2
Co / W(100) T = 300 K
2 1
1
open
4.4 -43
Ni / W(100) T = 300 K
closed
open
0
0
)
)
-1 -1 -2
-2 0
2
4
6
8 ML 10
Co coverage
Fig. 43. Co-induced surface stress on W(100). Deposition proceeds beyond 10 ML. The kink in the data points at 2.5 ML indicates a structural transition in the film from pseudomorphic to hcp growth. The initial compressive stress is of opposite sign than the calculated misfit stress. Data from [99Gut] (1 ML: 1.00×1015 atoms / cm2).
Fig. 45. Pd-induced surface stress on W(100). The kink in the stress curve at 2 ML indicates the end of pseudomorphic growth and the onset of hcp growth. Data from [99Gut] (1 ML: 1.00×1015 atoms / cm2).
Landolt -Börnst ein New Series III/42A2
0
2
4
6 8 10 12 14 16 18 ML Ni coverage
Fig. 44. Ni-induced surface stress on W(100). The kink in the stress curve at 2 ML indicates the end of pseudomorphic growth. The initial compressive stress is of opposite sign than the calculated misfit stress. Data from [99Gut] (1 ML: 1.00×1015 atoms / cm2).
Fig. 46. Anisotropic Fe-induced surface stress on W(110). Stress components along [ 1 10], upper curve, and along [001], lower curve have been measured. The kink at 1.2 ML is ascribed to the formation of misfit distortions and indicates the end of pseudomorphic growth. The inset shows a blow-up of the small coverage range. Data from [99San2] (1 ML: 1.42×1015 atoms / cm2).
References for 4.4 1868Qui 01Wul 09Sto 23Tim 28Bak 30Obr 36Ray 48Ska 49Shu 49Udi 50Ash 50Her 50Shu 51Ale 51Fun 51Her 52Ber 52But1 52But2 52Gre 53Gre 53Her 56Ska 57Myk 58Moo 59All 59Hey 59Tim 60Gil 60Gat 61Gib 61Myk 61Rad 62Han 62Rhe 63All 63Hoa 63Inm 63Pri 63Wes1 63Wes2 64Ben 64Cah 64Fin 64Gil 64McL
Quincke, G.: Pogg. Ann. 134 (1868) 356. Wulff, G.: Z. Kristallogr. 34 (1901) 449. Stoney, G.G.: Proc. R. Soc. London A 82 (1909) 172. Timoshenko, S.: Mech. Eng. 45 (1923) 259. Bakker, G.: Kapillarität und Oberflächenspannung, Handbuch der Experimentalphysik, Leipzig: Akademie Verlag 1928, Band 6. Obreimoff, J.W.: Proc. R. Soc. London 127 (1930) 290. Rayleigh, L.: Proc. Phys. Soc. A 156 (1936) 326. Skapski, A.S.: J. Chem. Phys. 16 (1948) 389. Shuttleworth, R.: Proc. Roy. Soc. London A 62 (1949) 167. Udin, H., Shaler, A.J., Wulff, J.: Trans. AIME 185 (1949) 186. Ashwell, D. G.: J. R. Aeron. Soc. 54 (1950) 708. Herring, C.: J. Appl. Phys. 21 (1950) 437. Shuttleworth, R.: Proc. Roy. Soc. London A 63 (1950) 444. Alexander, B.H., Dawson, M.H., Kling, H.P.: J. Appl. Phys. 22 (1951) 439. Funk, E.R., Udin, H., Wulff, J.: J. Metals 3 (1951) 1206. Herring, C.: Phys. Rev. 82 (1951) 87. Berry, C.R.: Phys. Rev. 88 (1952) 596. Buttner, F.H., Funk, E.R., Udin, H.: J. Metals 4 (1952) 401. Buttner, F.H., Funk, E.R., Udin, H.: J. Phys. Chem. 56 (1952) 657. Greenough, A.P.: Philos. Mag. 43 (1952) 1075. Greenhill, E.B., McDonoald, S.R.: Nature (London ) 171 (1953) 37. Herring, C., in: Structure and properties of solid surfaces, Gomer, R., Smith, C.S. (eds.), Chicago: University Press, 1953, p. 5. Skapski, A.S.: Acta Metal. 4 (1956) 576. Mykura, H.: Acta Metal. 9 (1961) 570. Moore, A.J.W.: Acta Metal. 6 (1958) 293. Allen, B.C., Kingery, W.D.: Trans. Metal. Soc. AIME 215 (1959) 30. Hayward, E.R., Greenough, A.P.: J. Inst. Metals 88 (1959-60) 217. Timoshenko, S., Woinowsky-Krieger, S.: Theory of Plates and Shells. Singapore: McGraw-Hill, 1959. Gilman, J.J.: J. Appl. Phys. 31 (1960) 2208. Gatos, H.C., Lavine, M.C.: J. Electrochem. Soc. 107 (1960) 427. Gibbs, J.W.: The scientific papers of J. Willard Gibbs. New York: Dover, 1961. Mykura, H.: Acta Metal. 9 (1961) 570. Radcliffe, S.V.: J. Less-Common Met. 3 (1961) 360. Hanneman, R.E., Finn, M.C., Gatos, H.C.: J. Phys. Chem. Solids 23 (1962) 1553. Rhead, G.E., Mykura, H.: Acta Metal. 10 (1962) 843. Allen, B.C.: Trans. Metal. Soc. AIME 227 (1963) 1175. Hoage, J.J.: U.S. Atomic Energy Comm. Rep. (HW-78132), 1963. Inman, M.C., McLean, M., Tipler, H.R.: Proc. R. Soc. London A 273 (1963) 538. Price, A.T.: Acta Metal. 11 (1963) 634. Westwood, A.R.C., Hitch, T.T.: J. Appl. Phys. 34 (1963) 3085. Westwood, A.R.C., Goldheim, D.L.: J. Appl. Phys. 34 (1963) 3335. Benson, G.C., Claxton, T.A.: J. Phys. Chem. Solids 25 (1964) 367. Cahn, J.W., Hanneman, R.E.: Surf. Sci. 1 (1964) 387. Finn, M.C., Gatos, H.C.: Surf. Sci. 1 (1964) 361. Gillis, P.P., Gilman, J.J.: J. Appl. Phys. 35 (1964) 647. McLean, M., Mykura, H.: Acta Metal. 12 (1964) 326. Lando lt -Bö rnst ein New Series III/42A2
4.4 Surface free energy and surface stress 64Pri 64Rhe 64Sun 65Bik 65Ben 65Bry 65Gil 65Hul 66Ans 66Dru 66Hof 66Kea 66Lan 66Mul 67Ben 67Hon 67Win 68Ger 68Hon 68Kos 68May 68Wie 69Eri 69Hea
69Lik 69Mai 70Hon 70Lan 70Was 71All1 71All2 71All3 71Jon 72All 72Kho 72Kok 72Kho 72She 72Was 72Waw 73Bla
4.4 -45
Price, A.T., Holl, H.A., Greenough, A.P.: Acta Metal. 12 (1964) 49. Rhead, G.E., McLean, M.: Acta Metal. 12 (1964) 401. Sundquist, B.E.: Acta Metal. 12 (1964) 67. Bikerman, J.J.: Phys. Status Solidi 10 (1965) 3. Benson, G.C., Claxton, T.A.: J. Phys. Chem. Solids 25 (1964) 367. Bryukhanova, L.S., Andreeva, J.A., Likhtman, V.I.: Sov. Mater. Sci. 1 (1965) 82. Gillis, P.P.: J. Appl. Phys. 36 (1965) 1374. Hull, D., Beardmore, P., Valentine, A.P.: Philos. Mag. 12 (1965) 1021. Anson, F.C.: Anal. Chem. 38 (1966) 54. Drum, C.M.: Philos. Mag. 13 (1966) 1239. Hoffman, R.W.: Phys. Thin Films 3 (1966) 211. Keating, P.N.: Phys. Rev. 145 (1966) 637. Landau, L.D., Lifshitz, E.M.: Hydrodynamik. Berlin: Akademie Verlag 1966. Mullick, P.C., Craig, G.B.: C. Metall. Q. 5 (1966) 129. Benson, G.C., Yun, K.S., in: The solid-gas interface, Flood, E.A. (ed.), New York: Marcel Dekker, 1967, Vol. I, p. 203. Hondros, E.D., Stuart, L.E.H.: Philos. Mag. 17 (1967) 711. Winterbottom, W.L.: Acta Met. 15 (1967) 303. Germer, D., Mayer, H.: Z. Phys. 210 (1968) 391. Hondros, E.D.: Acta Metal. 16 (1968) 1377. Kostikov, V.I., Kharitonov, A.V., Savenko, V.Z.: Phys. Met. Metallogr. (English Transl.) 26 (1968) 181. Mays, C.W., Vermaak, J.S., Kuhlmann-Wilsdorf, D.: Surf. Sci. 12 (1968) 134. Wiederhorn, S.M., Shorb, A.M., Moses, R.L.: J. Appl. Phys. 39 (1968) 1569. Eriksson, J.C.: Surf. Sci. 14 (1969) 221. Hearmon, R.F.S., in: Landolt-Börnstein Numerical Data and Functional Relationships in Science and Technology, Group III, Hellwege, K.-H., Hellwege, A.M. (eds.), Berlin: SpringerVerlag, 1969, Vol. 2. Likhtman, V.I., Brukhanova, L.S. , Andreeva, I.A., Shukin, E.D.: Sov. Mater. Sci. (English Transl.) 4 (1969) 183. Maitland, H., Chadwick, G.A.: Philos. Mag. 19 (1969) 645. Hondros, E.D., in: Physicochemical measurements in metals research, Rapp, R. A. (ed.), New York: Interscience, 1970, p. 293. Lang, N.D., Kohn, W.: Phys. Rev. B 1 (1970) 4555. Wasserman, H.J., Vermaak, J. S.: Surf. Sci. 22 (1970) 164. Allen, R.E., Alldredge, G.P., Wette, F. d.: Phys. Rev. B. 4 (1971) 1648. Allen, R.E., Alldredge, G.P., Wette, F. d.: Phys. Rev. B. 4 (1971) 1661. Alldredge, G.P., Allen, R.E., Wette, F. d.: Phys. Rev. B. 4 (1971) 1682. Jones, H.: Met. Sci. J. 5 (1971) 15. Allen, B.C., in: Liquid metals. Chemistry and physics, Beer, S.Z. (ed.), New York: Marcel Dekker, 1972, p. 161. Khokonov, K.B., Shebzukhova, I.G., Kokov, Kh.N., in: Smachivaemost i Poverkhnostnie Svoistva Rasplavov i Tverdikh tel, Kiev, USSR: Naukova dumka 1972, p. 156. Kokova, A.Kh., Khokonov, K.B.: Mezhvuzovkaya Nauchnaya Konferentsia po Fizike Mezhfaznikh Yavleniy. Nalchik, USSR: KBGU, 1972. Khokonov, K.B., Kokova, A.Kh., in: Ucheniye Zapisky, Nalchik, USSR: KBGU 1972, p. 36. Shebzukhova, J.G., Khokonov, K.B., Zadumkin, S.N.: Phys. Met. Metallogr. (English Transl.) 33 (1972) 1112. Wasserman, H.J., Vermaak, J.S.: Surf. Sci. 32 (1972) 168. Wawra, H.H.: Materialprüfung 14 (1972) 413. Blakely, J.M., Introduction to the properties of crystal surfaces. Oxford: Pergamon Press, 1973, p. 53.
Landolt -Börnst ein New Series III/42A2
4.4 -46 73Cou 73Fre 73Hod 73Hir 73Kel 73Kos 73McL 73Mis 73Waw 73Win 75Tys 75Waw1 75Waw2 76Bau 76Dig 76Lan 76Tys 77Lan 77Tys 78App 78Bec 78Mie1 78Mie2 78Som 79Tas 80Hey 83Hey 83Kum 84Hea
84Iba 84Mon
84Sza 85Nye 85Spa 85Tro 86Ack 86Erc 86Hey 86Mül 86Ric 86San 87Ack1 87Ack2
4.4 Surface free energy and surface stress Couchman, P.R., Jesser, W.A.: Surf. Sci. 34 (1973) 212. Freiman, S.W., Mulville, D.R., Mast, P.W.: J. Mater. Sci. 8 (1973) 1527. Hodgson, B.K., Mykura, H.: J. Mater. Sci. 8 (1973) 565. Hirth, J.P., in: Structure and properties of metal surfaces, Shimodaira, L.S. (eds.), Tokyo: Maruzen, 1973, p.10. Kelly, A.: Strong Solids. Oxford: Clarendon Press, 1973. Kostikov, V.F., Kharitonov, A.V.: Phys. Met. Metallogr. (English Transl.) 35 (1973) 170. McLean, M., Hondros, E.D.: J. Mater. Sci. 8 (1973) 349. Missol, W.: Phys. Status Solidi (b) 58 (1973) 767. Wawra, U., Wawra, H.H.: Acta Phys. Chem. 19 (1973) 41. Winterbottom, W.L., in: Structure and properties of metal surfaces, Shimodaira, L. S. (eds.), Tokyo: Maruzen, 1973, p. 37. Tyson, W.R.: C. Metall. Q. 14 (1975) 307. Wawra, H.: Z. Metallkde. 66 (1975) 395. Wawra, H.: Z. Metallkde. 66 (1975) 492. Bauer, C.E., Speiser, R., Hirth, J.P.: Metal. Trans. A 7 (1976) 75. Digilov, R.M., Zadumkin, S.N., Kumikov, V.K., Khokonov, K.B.: Phys. Met. Metallogr. (English Transl.) 41 (1976) 979. Lang, G.: Z. Metallkde. 67 (1976) 549. Tyson, W.R.: J. Appl. Phys. 47 (1976) 459. Lang, G.: Z. Metallkde. 68 (1977) 213. Tyson, W.R., Miller, W.A.: Surf. Sci. 62 (1977) 267. Appelbaum, J.A., Hamann, D.R.: Surf. Sci. 74 (1978) 21. Becher, P.F., Freiman, S.W.: J. Appl. Phys. 49 (1978) 3779. Miedema, A.R., Boom, R.: Z. Metallkde. 69 (1978) 183. Miedema, A.R.: Z. Metallkde. 69 (1978) 287. Sommerfeld, A.: Mechanik der deformierbaren Medien. Thun: Harri Deutsch, 1978. Tasker, P.W.: Philos. Mag. A 39 (1979) 119. Heyraud, J.C., Métois, J.J.: Acta Metall. 28 (1980) 1789. Heyraud, J.C., Métois, J.J.: Surf. Sci. 128 (1983) 334. Kumikov, V.K., Khokonov, K.B.: J. Appl. Phys. 54 (1983) 1346. Hearmon, R.F.S., in: Landolt-Börnstein Numerical Data and Functional Relationships in Science and Technology Group III, Hellwege, K.-H., Hellwege, A.M. (eds.), Berlin: SpringerVerlag 1984, Vol. 18. Ibach, H., Rahman, T.S., in: Chemistry and physics of solid surfaces, Vanselow, R., Howe, R. (eds.), Berlin: Springer-Verlag 1984, Vol. V, p. 455. Monot, R., in: Physics of latent image formation in silver halides. Proceedings of an international symposium, Baldereschi, A., Czaja, W., Tosatti, E., Tosi, M. (eds.), Singapore: World Scientific 1984, p. 175. Szabó, I.: Einführung in die Technische Mechanik. Berlin: Springer-Verlag, 1984. Nye, J.F.: Physical Properties of Crystals. Oxford: Oxford University Press, 1985. Sparnaay, M.J.: Surf. Sci. Rep. 4 (1985) 101. Tromp, R.M.: Surf. Sci. 155 (1985) 432. Ackland, G.J., Finnis, M.W.: Philos. Mag. A 54 (1986) 301. Ercolessi, F., Parrinello, M., Tosatti, E.: Surf. Sci. 177 (1986) 314. Heyraud, J.C., Métois, J.J.: Surf. Sci. 177 (1986) 213. Müller, J.E., Wuttig, M., Ibach, H.: Phys. Rev. Lett. 56 (1986) 1583. Richev, J., Lipkowski, J.: J. Electrochem. Soc. 133 (1986) 121. Sano, M., Kawaguchi, M., Chen, Y.-L., Skarlupka, R.J., Chang, T., Zografi, G., Yu, H.: Rev. Sci. Instrum. 57 (1986) 1158. Ackland, G.J., Thetford, R.: Philos. Mag. A 56 (1987) 15. Ackland, G.J., Tichy, G., Vitek, V., Finnis, M.W.: Philos. Mag. A 56 (1987) 735. Lando lt -Bö rnst ein New Series III/42A2
4.4 Surface free energy and surface stress 87Cho 87Erc 87Gen 87Leh 87Nee 87Van 88Ale 88Dau 88Dod 88Doe 88Ida 88Men 88Wor 89Gas 89Mea1 89Mea2 89Nix 89Pay 89Wei 89Yu 90Ada 90Abe 90Fei 90Mar 90Nee 90Sch 90Wol 91Ers 91Gum 91Man 91Nee 91Ove 91San 91Tak 91Wol 92Cam1 92Cam2 92Fei 92Iba 92Met 92San 93Cho 93Fio 93Law 93Mor 93Nee
4.4 -47
Chou, M.Y., Chelikowsky, J.R.: Phys. Rev. B 35 (1987) 2124. Ercolessi, F., Bartoni, A., Garafalo, M., Parrinello, M., Tosatti, E.: Surf. Sci. 189/190 (1987) 636. Gennes, P.G. d.: Compt. Rend. 42 (1987) 547. Lehwald, S., Wolf, F., Ibach, H., Hall, B.M., Mills, D.L.: Surf. Sci. 192 (1987) 131. Needs, R.J.: Phys. Rev. Lett. 58 (1987) 53. Vanderbilt, D.: Phys. Rev. Lett. 59 (1987) 1456. Alerhand, O.L., Vanderbilt, D., Meade, R.D., Joannopoulos, J.D.: Phys. Rev. Lett. 61 (1988) 1973. Daum, W., Stuhlmann, C., Ibach, H.: Phys. Rev. Lett. 60 (1988) 2741. Dodson, B.W.: Phys. Rev. Lett. 60 (1988) 2288. Doerner, M.F., Nix, W.D.: CRC Crit. Rev. Solid State Mater. Sci. 14 (1988) 225. Iida, T., Guthrie, R.I.L.: The Physical Properties of Liquid Metals. Oxford: Clarendon Press, 1988. Men, F.K., Packard, W.E., Webb, M.B.: Phys. Rev. Lett. 61 (1988) 2469. Wortis, M., in: Springer Series in Chemistry and Physics of Solid Surfaces, Vanselow, R., Howe, R. (eds.), New York: Springer, 1988, Vol. 7, p. 367. Gaspar, J.A., Eguiluz, A.G.: Phys. Rev. B 40 (1989) 11976. Meade, R.D., Vanderbilt, D.: Phys. Rev. B 40 (1989) 3905. Meade, R.D., Vanderbilt, D.: Phys. Rev. Lett. 63 (1989) 1404. Nix, W.D.: Metall. Trans. A 20 (1989) 2217. Payne, M.C., Roberts, N., Needs, R.J., Needels, M., Joannopoulos, J.D.: Surf. Sci. 211/212 (1989) 1. Weinert, M., Watson, R.E., Davenport, J.W., Fernando, G.W.: Phys. Rev. B 39 (1989) 12585. Yu, R., Lam, P.K.: Phys. Rev. B 39 (1989) 5035. Adamson, A.W.: Physical Chemistry of Surfaces. New York: John Wiley, 1990. Abermann, R.: Vacuum 41 (1990) 1279. Feibelman, P.J., Hamann, D.R.: Surf. Sci. 234 (1990) 377. Martinez, R.A., Augustyniak, W.M., Golovchenko, J.A.: Phys. Rev. Lett. 64 (1990) 1035. Needs, R.J., Godfrey, M.J.: Phys. Rev. B 42 (1990) 10933. Schell-Sorokin, A.J., Tromp, R.M.: Phys. Rev. Lett. 64 (1990) 1039. Wolf, D.: Surf. Sci. 226 (1990) 389. Erschbaumer, H., Freeman, A.J., Fu, C.L., Podlucky, R.: Surf. Sci. 243 (1991) 317. Gumbsch, P., Daw, M.S.: Phys. Rev. B 44 (1991) 3934. Mansfield, M., Needs, R.J.: Phys. Rev. B 43 (1991) 8829. Needs, R.J., Godfrey, M.J., Mansfield, M.: Surf. Sci. 242 (1991) 215. Over, H., Kleinle, G., Ertl, G., Moritz, W., Ernst, K.-H., Wohlgemuth, H., Christmann, K., Schwarz, E.: Surf. Sci. 254 (1991) L469. Sander, D., Ibach, H.: Phys. Rev. B 43 (1991) 4263. Takeuchi, N., Chan, C.T., Ho, K.M.: Phys. Rev. B 43 (1991) 13899. Wolf, D.: Philos. Mag. A 63 (1991) 337. Cammarata, R.C.: Surf. Sci. 279 (1992) 341. Cammarata, R.C.: Surf. Sci. Lett. 273 (1992) L399. Feibelman, P.J.: Phys. Rev. B 46 (1992) 2532. Ibach, H.: Phys. Bl. 48 (1992) 705. Methfessel, M., Henning, D., Scheffler, M.: Phys. Rev. B 46 (1992) 4816. Sander, D., Linke, U., Ibach, H.: Surf. Sci. 272 (1992) 318.. Chou, M.Y., Wei, S., Vanderbilt, D.: Phys. Rev. Lett. 71 (1993) 461. Fiorentini, V., Methfessel, M., Scheffler, M.: Phys. Rev. Lett. 71 (1993) 1051. Lawn, B.: Fracture of brittle solids. Cambridge: Cambbridge University Press, 1993. Morrison, I., Bylander, D.M., Kleinman, L.: Phys. Rev. Lett. 71 (1993) 1083. Needs, R.J.: Phys. Rev. Lett. 71 (1993) 460.
Landolt -Börnst ein New Series III/42A2
4.4 -48 94Mül 94Pol 94Wol1 94Wol2 94Cam 94Gro 94Iba 94Web 94Sto 94Str1 94Str2 94Sch 94Web 94Wri 94Yam 95Bro 95Fei1 95Fei2 95Gro 95San1 95San2 95Sch 96Des 96Fei 96Gro 96Kok 96Mar1 96Mar2 96Wac 97Bac 97Che 97Deg 97Fei 97Fill 97Hai 97Iba1 97Iba2 97Koc 97Wat 98Ber 98Gra 98Krä 98San 98Vit 99Gut 99Hof 99Hey 99Iba 99Mül
4.4 Surface free energy and surface stress Müller, P., Kern, R.: Surf. Sci. 301 (1994) 386. Polatoglou, H.M., Methfessel, M., Scheffler, M.: Phys. Rev. B 48 (1993) 1877. Wolf, D.: Phys. Rev. Lett. 70 (1993) 627. Wolf, D.: Phys. Rev. Lett. 71 (1993) 462. Cammarata, R.C.: Prog. Surf. Sci. 46 (1994) 1. Grossmann, A., Erley, W., Ibach, H.: Surf. Sci. 313 (1994) 209. Ibach, H.: J. Vac. Sci. Technol. A 12 (1994) 2240. Weber, M., Koch, R., Rieder, K.H.: Phys. Rev. Lett. 73 (1994) 1166. Stoltze, P.: J. Phys. Condens. Matter 6 (1994) 9495. Streitz, F.H., Cammarata, R.C., Sieradzki, K.: Phys. Rev. B 49 (1994) 10699. Streitz, F.H., Cammarata, R.C., Sieradzki, K.: Phys. Rev. B 49 (1994) 10707. Schell-Sorokin, A.J., Tromp, R.M.: Surf. Sci. 319 (1994) 110. Webb, M.B.: Surf. Sci. 299/300 (1994) 454. Wright, A.F., Feibelman, P.J., Atlas, S.R.: Surf. Sci. 302 (1994) 215. Yamamoto, M., Chan, C.T., Ho, K.M.: Phys. Rev. B 50 (1994) 7932. Bross, H., Kauzmann, M.: Phys. Rev. B 51 (1995) 17135. Feibelman, P.J.: Phys. Rev. B 51 (1995) 17867. Feibelman, P.J.: Phys. Rev. B 52 (1995) 16845. Grossmann, A., Erley, W., Ibach, H.: Surf. Rev. Lett. 2 (1995) 543. Sander, D., Enders, A., Kirschner, J.: Rev. Sci. Instrum. 66 (1995) 4734. Sander, D., Enders, A., Kirschner, J.: Appl. Phys. Lett. 67 (1995) 1833. Schöchlin, J., Bohnen, K.P., Ho, K.M.: Surf. Sci. 324 (1995) 113. Desjonquères, M.C., Spanjaard, D.: Concepts in surface physics. Berlin: Springer-Verlag, 1996. Feibelman, P.J.: Phys. Rev. B 53 (1996) 13740. Grossmann, A., Erley, W., Hannon, J.B., Ibach, H.: Phys. Rev. Lett. 77 (1996) 127. Kokko, K., Salo, P.T., Laihia, R., Mansikka, K.: Surf. Sci. 348 (1996) 168. Marcus, P.M.: Surf. Sci. 366 (1996) 219. Marcus, P.M.: Phys. Rev. B 53 (1996) 2481. Wachter, A., Bohnen, K.P., Ho, K.M.: Surf. Sci. 346 (1996) 127. Bach, C.E., Giesen, M., Ibach, H., Einstein, T.L.: Phys. Rev. Lett. 78 (1997) 4225. Che, J.G., Chan, C.T., Kuo, C.H. , Leung, T.C.: Phys. Rev. Lett. 79 (1997) 4230. Degand, G., Müller, P., Kern, R.: Surf. Rev. Lett. 4 (1997) 1047. Feibelman, P.J.: Phys. Rev. B 56 (1997) 2175. Fillipetti, A., Fiorentini, V.: Surf. Sci. 377-379 (1997) 112. Haiss, W., Nichols, R.J., Sass, J.K.: Surf. Sci. 388 (1997) 141. Ibach, H.: Surf. Sci. Rep. 29 (1997) 193. Ibach, H., Bach, C.E., Giesen, M., Grossmann, A.: Surf. Sci. 375 (1997) 107. Koch, R., in: The chemical physics of solid surfaces, King, D., Woodruff, P. (eds.), Amsterdam: Elsevier 1997, Vol. 8, p. 448. Watts, R., Gibbs, M.R. J., Karl, W.J., Szymczak, H.: Appl. Phys. Lett. 70 (1997) 2607. Bermond, J.M., Métois, J.J., Heyraud, J.C. Floret, F.: Surf. Sci. 416 (1998) 430. Graoui, H., Giorgio, S., Henry, C.R.: Surf. Sci. 417 (1998) 350. Kräuter, G., Schumacher, A., Gösele, U.: Sens. Actuators A 70 (1998) 271. Sander, D., Schmidthals, C., Enders, A., Kirschner, J.: Phys. Rev. B 57 (1998) 1406. Vitos, L., Ruban, A.V., Skriver, H.L., Kollár, J.: Surf. Sci. 411 (1998) 186. Gutjahr-Löser, T. Dissertation, Martin-Luther-Universität Halle-Wittenberg, 1999. Gutjahr-Löser, T., Sander, D., Kirschner, J.: private communication. Hofmeister, H., Huisken, F., Kohn, B.: Europ. Phys. J. D 9 (1999) 137 Heyraud, J.C., Métois, J.J., Bermond, J.M.: Surf. Sci. 425 (1999) 48. Ibach, H.: ERRATUM Surf. Sci. Rep. 35 (1999) 71. Müller, J.E., Ibach, H., private communication.
Lando lt -Bö rnst ein New Series III/42A2
4.4 Surface free energy and surface stress 99Mad 99Mar 99Nie 99Plö 99Pas 99Rub 99San1 99San2 2000Bon 2000Dah 2000Mar 2001Dah 2001He
4.4 -49
Madey, T.E., Nien, C.-H., Pelhos, K., Kolodziej, J.J., Abdelheim, I.M., Tao, H.-S.: Surf. Sci. 438 (1999) 191. Marcus, P.M., Qian, X., Hübner, W.: Phys. Rev. B 60 (1999) 16088. Nien, C.-H., Madey, T.E., Tai, Y.W., Leung, T.C., Che, J.G. , Chan, C.T.: Phys. Rev. B 59 (1999) 10335. Plößl, A., Kräuter, G.: Mater. Sci. Eng. R 25 (1999)1. Passerone, D., Tossatti, E., Chiarotti, G.L., Ercolessi, F.: Phys. Rev. B 59 (1999) 7687. Ruban, A.V., Skriver, H.L.: Phys. Rev. B 59 (1999) 15990. Sander, D.: Rep. Prog. Phys. 62 (1999) 809. Sander, D., Enders, A., Kirschner, J.: Europhys. Lett. 45 (1999) 208. Bonzel, H.P., Emundts, A.: Phys. Rev. Lett. 84 (2000) 5804. Dahmen, K., Lehwald, S., Ibach, H.: Surf. Sci. 446 (2000) 161. Marcus, P.M., Qian, X., Hübner, W.: J. Phys. Condens. Matter 12 (2000) 5541. Dahmen, K., Ibach, H., Sander, D.: J. Magn. Magn. Mater. 231 (2001) 74. He, L.H., Lim, C.W.: Surf. Sci. 478 (2001) 203.
Landolt -Börnst ein New Series III/42A2
4.5 Surface phonon dispersion M.A. ROCCA
Acronyms and symbols ARP DFT FT HATOF HREELS IRAS L LDA LDM LEED ML NEXAFS q|| RBS RW (R) SCP SBZ SEXAFS SH SV T ϑi ϑf θ ω
- Angle Resolved Photoemission - Density Functional Theory - Frustrated Translation - He Atoms Time of Flight - High Resolution Electron Energy Loss Spectroscopy - Infrared Reflection Absorption Spectroscopy - Longitudinally polarised mode - Local Density Approximation - Lattice Dynamical Model - Low Energy Electron Diffraction - Monolayer - Near Edge X-rays Absorption Fine Structure - Phonon wavevector - Rutherford Back Scattering - Rayleigh Wave - Self Consistent Pseudopotential - Surface Brillouin Zone - Surface Extended X-rays Absorption Fine Structure - Shear Horizontally polarised mode - Shear Vertically or sagittally polarised mode - Crystal temperature - Angle of incidence of probe particles - Angle of scattering of probe particles - Adsorbate coverage - Phonon frequency
4.5.1 Introduction 4.5.1.1 Background and general layout The surface phonon spectrum consists of the continuum of the projection of the bulk modes onto the two dimensional surface Brillouin zone (SBZ) and of surface modes, localised in the gaps of the bulk bands. The amplitude of such modes is large near to the surface and decreases rapidly towards the bulk. The presence of the surface may moreover modify the amplitude of the bulk modes leading to the formation of so-called surface resonances. In presence of adsorbates, new modes will be present because of the extra degrees of freedom connected with the motion of the adatoms or of the admolecules. If the latter interact with each other, either directly or via the substrate, their vibrations will behave collectively and disperse with parallel wavevector, q||. Depending on the relevant interatomic forces, the adsorbate modes may lie in the frequency domain of the substrate atoms and hybridise with modes of the same symmetry. Energy gaps will then open up in the dispersion curves. If hybridisation takes place with volume modes, the adsorbate vibration becomes a surface resonance and its energy will leak into the substrate and give rise to a finite linewidth. Substrate and adsorbate phonon frequency and dispersion are determined by the interatomic forces, which are intimately linked to the surface structure. The knowledge about the spectrum of surface phonons can therefore provide important clues to understand the structure as well as the nature of forces driving the surface into one particular structure [89Yan, 90Voi2, 97Nag]. Lando lt -Bö rnst ein New Ser ies III/42A2
4.5-2
4.5 Surface phonon dispersion
[Ref. p 4.5-68
Pure surface modes are usually denoted by Sn, where the index n numbers the branches starting from the one at the lowest frequency. Similarly, the surface resonances are denoted by MSn or Rn and numbered with the same criterion. The acoustic mode with slowest velocity is usually, but not always, mainly shear vertically polarised and coincides with the Rayleigh wave (RW) in the elastic continuum limit [1887R]. The adsorbate induced modes are denoted by the chemical symbol of the adsorbate and by a suffix indicating the relevant motion, e.g. || (⊥) for modes polarised primarily parallel (perpendicular) to the surface plane. The surface phonon spectrum is influenced by physisorbed as well as by chemisorbed species, either because of the hybridisation of the adsorbate induced modes with those of the substrate, or because of the modification of the interaction between the substrate atoms induced by adsorption. The latter effect can change the frequency of the substrate modes or induce the spill out of new modes off the bulk bands. Moreover, at a given wavevector, new surface bands will be generated because of the symmetry reduction associated to the backfolding of the surface Brillouin zone. Finally, adsorption can induce the reconstruction of the surface. Dipole active adsorbate and substrate modes had been investigated already in the seventies by infrared absorption spectroscopy (IRAS) and by high resolution electron energy loss spectroscopy (HREELS). The first surface phonon dispersion curves were measured, however, only at the beginning of the '80-ties by inelastic He atom scattering (HATOF, He atom time of flight spectroscopy) and by HREELS in impact scattering. The former technique exploits the supersonic expansion of He from a nozzle source, by which a thermal energy beam (Ei=20-60 meV) is generated with resolutions which can go down to 200 µeV. Phonon measurements with HATOF are therefore limited in the frequency domain by the low energy of the impinging projectiles. He atoms interact with the low density tail of the surface electron density and have therefore an absolute surface sensitivity. On the other hand, HREELS relies on inelastic low energy (20 <Ei<200 eV) electron scattering in the so-called impact scattering regime, in which the energy loss occurs during the short range interaction with the ion cores. Since electrons in this energy range penetrate some 10 to 20 Å below the surface, the inelastic information is mediated over the outermost two or three layers. Modes with maximum amplitude in deeper layers (and especially in the second layer) can thus be excited. The main limitation of HREELS with respect to HATOF is the resolution, which, in spite of the recent improvements, is limited to 2 meV for out-of-specular measurements. The latter problem can be however overcome by exploiting multiple scattering which causes a strong, and mode specific, energy dependence of the inelastic cross section, allowing to tune the spectrometer on each particular phonon branch and thus to distinguish between features whose difference in frequency is smaller than the energy resolution [85Xu, 89Wu]. The comparison of experimental cross sections with the theoretical forecast proved in some cases to be essential for a correct assignment of the loss peaks to the different vibrational modes. The modification of the force constant between surface atoms may indeed shift the different phonon branches to such an extent that the knowledge of the spectrum expected from the bulk force constants can be insufficient to interpret the data. On the theoretical side lattice dynamical models (LDM) based on force constants were developed in the early years [71All, 74Arm] and allowed reliable predictions of the surface phonon spectrum. More recently, thanks to the remarkable advances achieved in the development of computational schemes based on density functional theory (DFT) and to the availability of supercomputers, it became possible to perform ab-initio calculations of the surface phonon spectrum also for adsorbate covered surfaces [96Bun, 99Fri1]. Over the past decades progress in the field of surface phonon dispersion of clean and adsorbate covered surfaces has been surveyed in a number of review articles, including those of Rocca et al. [86Roc1], Ibach [90Iba, 91Iba, 92Iba1, 94Iba], Wöll [91Wöl], Toennies [92Toe], Benedek and Toennies [94Ben], and Fritsch and Schröder [99Fri1]. Worth mentioning is also the book dealing principally with surface phonons of clean surfaces, edited by Kresse and de Wette [91Kre]. A collection of the data available on surface phonons of bare surfaces (research status of 1994) can be found in Landolt Börnstein, New series Vol. III/24 B, Chapt. 4.
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.5-68]
4.5 Surface phonon dispersion
4.5-3
4.5.1.2 Symmetry considerations, energy and momentum conservation and relevant selection rules in inelastic scattering The surface phonon spectrum is usually measured and computed along the border of the irreducible part of the two dimensional surface Brillouin zone, whose principal points and directions are defined in Fig. 1 for the principal fcc and bcc surfaces. Along mirror planes the normal modes will split into two subgroups, whose atomic displacement pattern is, respectively, even (sagittal modes) or odd (shear horizzontal modes) with respect to reflection. For scattering experiments performed with in-plane scattering geometry and for which the scattering plane coincides with a mirror plane of the crystal, only the excitation of sagittally polarised phonons is allowed. Since most experiments take advantage of this selection rule no measurements of the dispersion of SH modes exist for adsorbate covered surfaces, contrary to the case of bare surfaces [92Bal]. Similarly, in presence of glide planes (as e.g. for C, N and CO on Ni(100)) the inelastic scattering selection rules along the glide plane require that the excitable modes are symmetric with respect to glide reflection in the first SBZ and antisymmetric in the second SBZ [88Rah]. Totally symmetric modes are moreover dipole active. Accurate measurements of the frequency of such phonons at vanishing wavevector can therefore be performed with HREELS or with IRAS with sub meV resolution. In inelastic scattering experiments energy and momentum conservation read: !Ȧ T || ) =
!2 2 (k f − k i2 ) 2m
& cosij f & & ǻk || = g || + q || = k f sinș f sinij f
(1) cosij i − k i sinș i . sinij i
(2)
where ω and q|| are the energy and the wavevector of the phonon, respectively. The polar angles ϑi and ϑf are measured from the surface normal and ϕi and ϕf are the azimuth angles in the surface plane usually & & chosen to be zero. k i and k f are the wavevectors of the impinging and of the outgoing particles. A positive value of ∆k(q||) corresponds to the creation of a phonon, a negative value to its destruction. Similarly we will refer to a positive q|| as an event in which a forward directed phonon is created. In an & & usual experiment k i and k f are chosen in the sagittal plane and, in order to take advantage of the selection rules and to compare the experimental results with theoretical predictions, the latter is aligned with a high symmetry crystallographic direction. For this special case the conservation equations can be conveniently visualized with the aid of the Ewald construction, shown in Fig. 2. The vertical bars are the surface reciprocal lattice rods; the circle shows the final momentum states accessible in elastic scattering; and the arrow indicate the wavevectors of incident and reflected particles. For HREELS the impact energy (of the order of several tens of eV) is much larger than the energy loss so that the spectrum recorded for a given scattering angle, ϑf, corresponds effectively to a constant momentum transfer. For HATOF, on the other hand, the measurements correspond to parabolic scan curves in the ω - q|| space. Scattering events corresponding to different values of q|| are therefore present in the same spectrum. For construction reasons HATOF apparatuses usually have the constraint that ϑi + ϑf is constant and the measurements are recorded by rotating the crystal. 4.5.1.3 Folding of the surface Brillouin zone by symmetry reduction, mode mixing, phonon crossing and opening of energy gaps If the adsorbate builds a superstructure or induces a reconstruction with a larger unit cell than the one of the bare substrate, the size of the new Brillouin zone will be reduced. Previously independent reciprocal space regions may therefore coincide after adsorption, a phenomenon that is usually referred to as folding of the zone. The folding process is shown in Fig. 3 for the case of a (100) face covered with c(2x2) and p(2x2) overlayers. As one can see, for the former case the size of the zone is halved so that the Γ and the
M points of the clean substrate coincide, and so do the previously independent ∆ and Υ directions. For Lando lt -Bö rnst ein New Ser ies III/42A2
4.5-4
4.5 Surface phonon dispersion
[Ref. p 4.5-68
the latter case the zone is reduced to one fourth, so that also Χ is folded back to Γ . Frequency gaps will open up at the new zone boundaries or at crossing points of phonon branches of the same symmetry. The new normal modes can then be obtained by linear combinations of the old substrate and/or adsorbate modes. As an example let us discuss the displacement pattern for phonons of the c(2x2) fcc(100) geometry at ī and Χ , which are shown in Fig. 4. The relevant surface point symmetry group is C4v so that the modes belong either to the symmetric representation, A1, or to the antisymmetric representations, B1 and B2 or to the non symmetric degenerate representation, E. For the latter modes linear combinations can be drawn whose displacement pattern is either even or odd with respect to the (1 1 0) mirror plane. The E symmetry modes d and e at Γ originate, respectively, from the longitudinal and from the shear horizontal modes of the clean surface at Γ and M ; the B2 mode comes from the displacement pattern of the Rayleigh wave at the former M point; the A1 mode f exists also for the clean surface, while the E modes g and h are combinations of the previously longitudinal and SH modes. The modes a, b and c correspond principally to the motion of the adsorbate and are in a different frequency range (usually higher for light chemisorbates) than the corresponding substrate modes d, e and f. At X the modes with A and B symmetry arise from the combination of the displacement patterns of the longitudinal and SH phonons previously located at the two Χ points of the clean surface, while the E modes are generated from the Rayleigh wave. In particular the A1 mode is a true surface phonon as it comes from the longitudinal surface mode S6, present in a gap near X , which is preserved upon backfolding. The displacement pattern of the A2 and B2 modes corresponds to established reconstruction patterns. They occur, respectively, for the p4g(2x2) structures of C on Ni(100) [79Onu] and of O on Rh(100) [98Alf, 99Alf], and suggest that the reconstruction takes place via the softening and freezing of such modes. 4.5.1.4 Phonon anomalies 4.5.1.4.1 Effect of mass loading, modification of force constants and surface stress Mode softening and, in general, anomalies of the substrate phonon frequencies can be induced by the adsorbate by modifying the force fields acting between the substrate atoms. This phenomenon was first observed for O/Ni(100) [83Sze]. The phonon dispersion curve for the c(2x2) structure along Γ – Χ is reported in Fig. 5. The frequency of the RW at X , which is equal to 130 cm–1 for the bare surface, decreases to 80 cm–1. The effect cannot be accounted for by the loading of the surface atoms, which reads [67Ben] Ȧ 2 = Ȧ 02 (1 −
ma θ ), ms
(3)
where ma and ms are the adsorbate and substrate mass, respectively, ω0 is the frequency of the mode for the bare surface, and ș is the coverage. A dramatic change in the interaction between the substrate atoms must therefore occur and indeed the frequency shift can be reproduced by LDM either (left panel in Fig. 5) by reducing by 70 % the force constant between the Ni atoms in the first and in the second crystal layer (second derivative of the interaction potential) or (right panel) by introducing a compressive surface stress (first derivative of the pairwise interaction potential) at the surface. The two causes cannot be easily distinguished just by measuring the phonon dispersion curves since both LDM can give best fits of equivalent quality. The adsorbate induced compressive surface stress was however demonstrated to be relevant for the O/Ni(100) system because it explains also other findings: i) the observed frequency shift depends on the order state of the adsorbate and is smaller when the oxygen is adsorbed disorderly [85Roc], an effect that would not be expected if the adsorbate affects only the surface force constants between the substrate atoms; ii) Ni(100) reconstructs with clockwise and anti-clockwise rotations of the substrate atoms around the adsorbate when the latter is C or N instead of O or S. The displacement pattern of such p4g Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.5-68]
4.5 Surface phonon dispersion
4.5-5
reconstruction coincides with the one of the A2 modes at the X point of the c(2x2) structure (see right panel of Fig. 4, mode g), suggesting that the latter gets frozen into the surface by a soft phonon mechanism [85Rah]. Without adsorbate induced stress, however, the freezing of the A2 mode would imply the unphysical result that the force constant between first and second Ni layer, k12, vanishes. Moreover the B2 mode should freeze in first when k12 is reduced [88Sze]. On the contrary in the presence of a compressive stress, the freezing in of the A2 mode occurs first and for a non vanishing value of k12 [86Rah, 90Yan]. The proposed mechanism is hence that the adsorbate pushes against the substrate atoms at the border of the fourfold hollow and that the atoms can adjust to such forces by relaxing for the loose p(2x2) structure and for the disordered phase, but not for the c(2x2) phase, for which therefore a compressive stress builds up. For C or N chemisorption the adsorption distance is much smaller than for O and the stress is correspondingly larger. When a certain threshold is overcome, the stress is released by the lateral shift of the substrate atoms. The stress induced by adsorption on Ni(100) was measured directly in a later experiment [91San, 92San1, 97Iba]. In accord with the above explanation the build up of surface stress has been found indeed to be much larger for the c(2x2)-O than for the p(2x2)-O structure and even larger for C adsorption. It stops as soon as the p4g surface reconstruction sets in at the coverage of 0.3 ML of carbon. Cluster calculations confirm the picture showing that the strong C–Ni bond removes charge from the Ni–Ni bonds that are no longer able to balance the repulsive interaction between the incompletely screened Ni nuclei [86Mül]. The same mechanism was proposed to account also for the stiffening of the Rayleigh wave for the bare Ni(100) surface, which had been previously ascribed to a 20% increase of the force constant between the Ni atoms of first and second crystal plane. Accordingly tensile surface stress is present on the bare surface. This mechanism has the advantage that it does not imply a reduction of the first interlayer spacing which is present for Ni(100) [83Fre1, 83Fre2] but not for Cu(100) [86Wut] that has a comparable stiffening of the Rayleigh wave at X . Surface stress was proposed to play a role also for other phonon anomalies as e.g. for the softening of the RW at Υ on Ni(110) upon H adsorption [87Leh1]. For Rh(100) p4g c(2x2) O, on the other hand, a different mechanism must be active as the stress caused by adsorption is small, the adsorption distance being much larger than for C or N on Ni(100). Indeed the reconstruction pattern corresponds then to the displacements of the B2 mode at X of the c(2x2) overlayer (see Fig. 5), which gets soft because of the adsorbate induced reduction of the force constants between the substrate atoms [98Alf, 99Alf, 99Bar]. Another effect observed quite systematically is the strong reduction of the cross section of the longitudinal surface resonance, which dominates the HATOF spectra for fcc (111) surfaces and which originates from a strong reduction of the in-plane force constant between surface atoms. Especially H is often seen to have the effect of eliminating the anomaly, restoring the surface force constants to the bulk value [87Ber]. This adsorbate was intensively studied also for elemental semiconductors, being important because of technological applications as well as because it enables to study the dynamics of the unreconstructed bare surface [96Grä2]. 4.5.1.4.2 Kohn anomaly Phonon anomalies are induced also by the coupling of phonons with the electronic excitation spectrum. This mechanism, called Kohn anomaly, corresponds to the breakdown of the adiabatic separation of ionic and electronic degrees of freedom and takes place for wavevectors corresponding to significant Fermi surface nesting. This is the case for H/W(110) [92Hul1, 93Hul1, 93Hul2, 94Bal2, 96Bal] and H/Mo(110) [93Hul1, 93Hul2, 97Krö] that show indeed a phonon anomaly. The HATOF data for H/W(110) along the [001] direction is reported in Fig. 6, together with a scan curve crossing the critical region in reciprocal space. For q|| ≤ 0.6 Å–1 two modes are present and correspond to the Rayleigh wave (lower frequency mode) and to the longitudinal resonance (higher frequency points). Around q||c =0.93 Å–1, however, a strong softening of the lower phonon branch occurs, which is accompanied by the appearance of a third branch whose frequency nearly vanishes at q||c. The peaks labeled with 4 and 1 in the bottom panel correspond to the upper and lower branch of the splitted lower frequency mode. Peak 1 is distinctly broader than peak 4. The anomaly is present for all wavevectors whose x-component ([001] direction or –1 Γ – H ) is close to 0.9 Å , indicating that the anomaly has a one-dimensional character. Along Γ – S , –1 e.g. q||c is at 1.225 Å , corresponding to (q||x =1.00, q||y = 0.707) Å–1. Lando lt -Bö rnst ein New Ser ies III/42A2
4.5-6
4.5 Surface phonon dispersion
[Ref. p 4.5-68
HREELS investigation demonstrated that also the longitudinal surface phonon has a shallow dip at the same wavevector [94Bal2, 96Bal]. The lowest branch was however not observed. First principle calculations of the phonon spectrum [96Bun] reproduced the shallow dip and confirmed that branch 1 is the RW. The current understanding of branch 4 is that it corresponds to the excitation of electron holepairs [95Koh], for which He atom scattering is more sensitive than electron scattering. The effect arises because He atoms interact with the low density tail of the electron distribution outside of the surface, while electrons are scattered by the high electron density close to as the nuclei of the substrate. Alternatively it was proposed that the excitation is connected with a plasmon like motion of the H atoms [96Bun]. The latter explanation holds however only for H/W(110) as the H adatoms on Mo(110) are fairly localised [97Krö]. The critical wavevector at which the anomaly occurs for Mo(110) is linked to nesting of the Fermi-surface contours associated to the (d3z2–r2,dxy) band, which has nearly one dimensional character. It runs parallel to Γ – N , and perpendicular to Γ – S , in significant parts of the surface Brillouin zone, and is shifted to lower energies by hydrogen adsorption, thus becoming localised at the surface [95Koh, 96Koh1, 96Koh2, 97Koh]. For H/W(110), on the other hand, the situation is more complicated. Recent angle resolved photoemission (ARP) data [98Rot] demonstrated that two different surface states, arising from the splitting of a surface band due to spin orbit coupling, are present upon H saturation and suggesting that the relevant Fermi nesting is between them. 4.5.1.5 Dispersion of adsorbate induced modes The dispersion of the adsorbate induced modes allows to infer information about the interaction between the adatoms and it is therefore frequently reported also in studies in which the substrate phonons were not investigated. While such studies are omitted from this data collection, they may show some quite general effects. Let us therefore discuss briefly the HREELS investigation of CO adsorption on Ir(100) [91Kis]. A c(2x2) structure is formed when adsorption occurs on the unreconstructed substrate, while the LEED pattern reverts to (1x1) for adsorption on the (5x1) reconstructed substrate indicating that long range order is inhibited. The phonon dispersion is reported in Fig. 7. Four modes are visible. The internal stretching vibration is at 2070 cm–1. Such frequency is indicative of adsorption in on-top sites. The other modes are the dipole active Ir–CO stretch at 500 cm–1, the CO rotational mode at 430 cm–1 and the frustrated translational motion at 55 cm–1. No substrate related modes were detected. The rotational mode, the frustrated translation and the Ir–CO stretch show little or no dispersion, while the internal CO stretch frequency decreases strongly when moving out of Γ . The latter effect is due to the long range dipoledipole interaction and is always present. It is given by [78Mah]: Į ȣ Ȉ 0 (q || ) Ȧ 2 (q || ) = Ȧ 02 1 + 1 + Į e Ȉ 0 (q || )
(4)
where ω0 is the frequency of the isolated adsorbate species, αν and αe are the vibrational and the electronic polarisabilities, respectively, and Σ0(q||) is the so-called dipole sum & & iq || ⋅ ri (5) Ȉ 0 (q || ) = ∑ e U(ri ) i For larger q|| and for adsorbates with smaller dipolar interaction, the dispersion can have either sign and it is determined either by direct interactions between the adsorbates or by interactions via the substrate. In general the dispersion curve of the adsorbate induced modes contains therefore valuable information on the interaction between the adsorbates. The adsorbate induced modes can couple with those of the substrate having the same symmetry, thus leading to avoided crossing and to the opening of energy gaps also for weakly interacting systems. An example is given in Fig. 8 for the HATOF investigation of an incommensurate Xe monolayer adsorbed on Cu(110) [94Zep]. The avoided crossing is between the vertical stretch motion of the adsorbate against the substrate and the Rayleigh wave. The gap at q||=0.3 Å–1 is about 0.5 meV in accord with the small interaction of a physisorbed gas with the substrate. Another example of energy gap, which occurs at the
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.5-68]
4.5 Surface phonon dispersion
4.5-7
zone centre for the longitudinal mode, was observed for the commensurate ( 3 × 3 )R30o structure of Xe on Cu(111) [98Bra]. From the magnitude of the gap information on the corrugation of the Xe-atom potential and on the friction forces was derived. Much effort was dedicated recently to HATOF studies of physisorbed hydrocarbons because of the applied relevance of such topic, e.g. CH4 [97Gra], C2H4 [96Gra1], C2H6 [97Gra], n-hexane, n-octane, ndecane, benzene and cyclohexane [95Wit2] on Cu(100) and d-octane, nonane and decane on Cu(111) were investigated [96Fuh]. The substrate phonon dispersion is then affected because of the presence of the frustrated translation perpendicular to the surface, which hybridises with the RW, opening small energy gaps. Such effect is generally small. This data has not been included in the present collection, unless mass loading leads to significant phonon anomalies. 4.5.1.6 Theoretical models The variety of crystal surfaces for which the surface phonon dispersion was measured entailed the use of a corresponding large variety of theoretical models, as the theoretical approach varies significantly from one class of materials to another. Usually the results for the adsorbate covered surfaces are compared with those obtained for the bare substrate. The major difficulty is thereby the larger unit cell. Otherwise the same models developed for the bare surfaces were applied. In the case of metals the screening of the bare ion-ion interaction by the conduction electrons is difficult to model theoretically. Empirical lattice dynamical models (LDM) were therefore introduced in which the force constants in the interior of the crystal are obtained by fitting the experimental dispersion curves of bulk phonons, while the force constants coupling atoms at and near the surface are modified. Unfortunately, as there is in many cases no consensus on a satisfactory model for the bulk crystal, it is difficult to give a reliable forecast for the changes of the surface force constants. The difficulty can be overcome for sp-bonded materials by carrying out self consistent pseudopotential (SCP) calculations. The method was later extended to noble metal and transition metal surfaces. Such calculations are also addressed as ab-initio or first principles. For semiconductor surfaces calculations were performed either by computing from first principles the electronic structure and using then these results to set up appropriate bond charge models from which the force constants were derived, or by calculating the electronic and atomic structural properties within DFT-LDA and using a total energy Ansatz to determine phonon frequencies and dispersion.
4.5.2 Data collection The data for surface phonon dispersion determined either experimentally or theoretically for adsorbed covered systems is reported and compared with the surface phonon dispersion of the corresponding bare system. The data is organised according to the electrical properties of the material: firstly metals, secondly elemental semiconductors and insulators, and finally compound semiconductors, oxides and salts. The reported systems are collected in Table I. TABLE I Investigated surface phonon dispersion curves of adsorbate covered systems. System Ag(100) bare Ag(100) Cl Ag(110) bare Ag(110) O Ag(110) O
Symmetry (1x1) c(2x2) (1x1) p(2x1) p(3x1)
Al(111) bare Al(111) Na
(1x1)
Lando lt -Bö rnst ein New Ser ies III/42A2
3× 3
Coverage
0.5 ML 0.25 ML
Exp. technique HREELS, HATOF HATOF HATOF HATOF HATOF
Fig. 9 10 11 12 13
0.33 ML
HREELS HREELS
14a 14b
0.5 ML
Ref. 90Mor, 91Che, 94Bun 83Lam, 84Lam 87Bra1, 87Bra2, 89Tat 89Yan 90Bra1, 90Bra2, 91Bra, 93Bra 88Loc, 93Fra, 97Nag 97Nag
4.5-8
4.5 Surface phonon dispersion
System Al(111) Na Cu(100) bare Cu(100) CO Cu(100) N Cu(100) O
Symmetry (2x2) (1x1) c(2x2) c(2x2)
Cu(100) PF3 Cu(100) S Mo(110) bare
c(4x2) p(2x2) (1x1)
0.25 ML 0.25 ML
HATOF 21 HREELS 22 HREELS, HATOF 23
Mo(110) H Mo(110) H Mo(110) H Mo(110) O Ni(100) bare Ni(100) C Ni(100) H Ni(100) N Ni(100) O Ni(100) O Ni(100) S Ni(110) bare Ni(110) CO Ni(110) H Ni(110) H Ni(110) O Ni(111) bare Ni(111) O Pb(111) bare Pb(111) d-octane Pt(111) bare Pt(111) H Pt(111) O Pt(111) O Rh(110) bare Rh(110) O Rh(111) bare Rh(111) H Rh(110) C6H6
(2x1) (2x2) (1x1) p(2x2) (1x1) p4g(2x2) (1x1) p4g(2x2) p(2x2) c(2x2) c(2x2) (1x1) p2mg(2x1) p2mg(2x1) (1x2) p(2x1) (1x1) p(2x2) (1x1)
0.5 ML 0.75 ML 1.0 ML 0.25 ML
HREELS, HATOF HREELS, HATOF HREELS, HATOF HREELS HREELS HREELS HATOF HREELS HREELS, HATOF HREELS, HATOF HREELS HREELS HREELS HREELS HREELS HREELS HREELS HREELS HATOF HATOF HATOF HATOF HATOF HATOF HATOF HATOF HATOF HATOF HATOF
47 48 49 50 50 51 51 52 53 53 54 55 56, 61 57, 61
c( 2 × 2 2 )
Coverage 0.5 ML 0.5 ML 0.5 ML 0.5 ML
0.5ML 0.5 ML 0.25 ML 0.5 ML 0.5 ML 1.0 ML 1.0 ML 1.5 ML 0.5 ML 0.25 ML 1.0 ML
(1x1) (1x1) p(2x2) (1x1) (1x2) (2x2) (1x1) (1x1) (2 3 × 3)
1.0 ML 0.25 ML 1.0 ML 0.5 ML 1.0 ML 1.0 ML
Exp. technique HREELS HREELS, HATOF HATOF HREELS HREELS
Fig. 15 16 17 18 20
24, 25 24, 25 24, 25 26 27 28, 29 30 31 32 34 35 37 40 41 42 43 45 46
Ru(0001) bare Ru(0001) H W(100) bare W(100) H W(110) bare W(110) H
(1x1) (1x1) (1x1) (1x1) (1x1) p(2x1)
0.5 ML
HATOF HATOF HATOF HATOF HREELS, HATOF HREELS, HATOF
W(110) H
p(2x2)
0.75 ML
HREELS, HATOF 57, 61
W(110) H
(1x1)
1.0 ML
HREELS, HATOF 57, 59
C(100) H C(100) H C(111) H
(2x1) (1x1) (1x1)
1.0 ML 2.0 ML 2.0 ML
theory theory HATOF
1.0 ML 2.0 ML
63 64 65
[Ref. p 4.5-68 Ref. 97Nag 86Wut, 93Ben, 94Hof 95Ell 86Fra 89Wut1, 89Wut2 99 Bra 87Fra 97Krö, 98Krö1, 98Krö2, 92Hul2 93Hul2, 97Krö 93Hul2, 97Krö 93Hul2, 97Krö 98Krö1, 98Krö2 83Leh, 86Roc2 87Roc 87Ber 86Dau, 88Rah 84Sze, 91Ber 83Leh, 84Rah, 91Ber 85Leh, 86Leh, 90Yan 87Leh2 90Voi2 89Voi 89Voi, 87Leh1 90Voi2, 91Yan 90Men1, 90Men2 90Voi2, 91Yan 96Fuh 96Fuh 85Har, 86Ker2, 87Neu 89Bor 86Ker1, 86Ker2, 87Ker 87Neu 93Bel 93Bel 95Wit1 95Wit1 93Wit1,93Wit2 97Bra 97Bra 87Ern, 89Ern 92Ern 92Hul1, 92Hul2, 94Bal1 92Hul1, 92Hul2, 94Bal1, 94Bal2, 96Bal 92Hul1, 92Hul2, 94Bal1, 94Bal2, 96 Bal 92Hul1, 92Hul2, 94Bal1, 94Bal2, 96 Bal 96San 96San 96Lan, 98Gle
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.5-68] System Ge(100) S Si(100) bare Si(100) As Si(100) Ge Si(100) Sb Si(100) H Si(100) H Si(111) As Si(111) Ga Si(111) H GaAs(110) bare GaAs(110) H GaP(110) H GaP(110) Sb InAs(110) H InP(110) H MgO(100) CO NaCl(100) CO2 NaCl(100) H2O NaCl(100) C2H2 NaCl(100) OCS
4.5 Surface phonon dispersion Symmetry (1x1) (2x1) (2x1) (2x1) (2x1) (2x1) (1x1) (1x1) ( 3 × 3)
(1x1) (1x1) (1x1) (1x1) (1x1) (1x1) (1x1)
Coverage 1.0 ML 0.5 ML 0.5 ML 0.5 ML 0.5 ML 1.0 ML 1.0 ML 0.3 ML 1.0 ML 1.0 ML 1.0 ML 1.0 ML 1.0 ML 1.0 ML
Exp. technique theory theory theory theory theory theory theory HREELS, HATOF
Fig. 66 67 69 70 71 72 73 74
HREELS, HATOF HREELS, HATOF theory theory theory theory theory theory HATOF HATOF HATOF HATOF HATOF
75 76 77 78 79 80 81 82
4.5-9 Ref. 92Pol 97Tüt 98Grä, 99Tüt 98Tüt2 98Tüt1, 98Tüt2 96Grä1 97Grä 90Doa1, 90Doa2, 92San2, 94Sch 95Sch, 89Doa 92Stu, 92Dum, 90Doa3 99Fri1 99Fri1 99Fri1 99Fri1 99Fri1 95Fri1 95Ger 93Lan, 93Hei, 95Lan 95Bru 98Pic 96Gle, 96Doh
4.5.2.1 Correspondence of units Several units are used for the surface phonon energies. No attempt has been made to convert the data to a single unit, rather the units of the original data are employed. In Table II the conversion factors between the different units, which may be useful for comparing different sets of data, are reported. Table II Energy conversion factors.
1 THz 1 cm–1 1013 rad/sec 1 meV
THz
cm–1
1013 rad/sec
meV
1 0.02998 1.5915 0.2418
33.36 1 53.09 8.066
0.6283 0.01884 1 0.1519
4.136 0.1240 6.583 1
4.5.2.2 Metal surfaces Ag(100) The surface phonon spectrum of the bare surface as measured by HREELS [90Mor, 91Che] and HATOF [94Bun] is reported in Fig. 9. The data shows evidence for a weak stiffening of the RW and for the presence of two longitudinal acoustic surface resonances. The difference between HREELS and HATOF, although systematic, is within experimental error.
Lando lt -Bö rnst ein New Ser ies III/42A2
4.5-10
4.5 Surface phonon dispersion
[Ref. p 4.5-68
Ag(100) Cl Chlorine forms a c(2x2) overlayer on Ag(100). The surface phonon dispersion was investigated by HATOF [83Lam, 84Lam] at a beam energy of 20 meV and of 64 meV showing evidence for the excitation of the RW. Its dispersion, reported in Fig. 10, is not appreciably affected by Cl adsorption. This result is in accord with the absence of interlayer relaxation [76Zan]. No Cl induced high frequency modes were observed. The dispersion of the RW could be recorded only over part of the surface Brillouin zone because of the dramatic dependence of the inelastic cross section on q||. The q|| effect is discussed quantitatively with reference to the theoretical model of ref. [83Bor]. The data along Γ – M are measured near to the ( 1 , 1 ) diffraction peak. The backfolded branch can be seen near M' . Ag(110) The surface phonon spectrum of the bare surface was measured by HATOF [87Bra1, 87Bra2, 89Tat] and it is reported in Fig. 11. Along Γ – X apart from the RW (S1), two surface resonances (MSo and MS+ ) are present. Along Γ – M the lowest frequency mode S1 is L polarised, while S3 is the Rayleigh wave. Ag(110) O The surface reconstructs upon oxygen adsorption forming regularly spaced added Ag–O rows along the <001> direction with p(nx1) symmetry and 2
Ref. p. 4.5-68]
4.5 Surface phonon dispersion
4.5-11
the RW (S1) and two surface resonances (R1 and R2) are observed, which were absent for the bare surface [97Nag]. S1 is strongly softened by adsorption and merges with the resonance R2 at small wavevectors. The resonance R1 is present only near Γ and is dipole active. The result of a LDM calculation assuming a substitutional adsorption site for the Na adatoms is shown in Fig. 14b. LDM calculations were performed also for other adsorption geometries and shown to generate surface phonon spectra incompatible with experiment. The modes R1 and R2 are shown to be associated to the same SV motion of the Na atoms, whereby R1 is the backfolded branch of R2. The frequency of the dipole active phonon R1 was reproduced by ab-initio calculations. The surface phonon dispersion of the (2x2) phase was measured by HREELS [97Nag] and is reported in Fig. 15 together with the data measured for the bare Al surface. For this phase the surface phonon dispersion is modified less than for the 3 × 3 phase although also in this case adsorption is suggested to be substitutional. The surface mode S1 and the resonance R1 are assigned to the RW, R1 being the backfolded branch. Cu(100) The surface phonon dispersion of the clean surface, as measured by HREELS [86Wut] and confirmed by HATOF [93Ben, 94Hof], is reported in Fig. 16. The RW is stiffer than predicted by LDM using the bulk force constant. The phenomenon was ascribed to the presence of tensile surface stress. Cu(100) CO CO forms an ordered c(2x2) overlayer on Cu(100) at a coverage of 0.5 ML. The surface phonon spectrum was measured by HATOF along both high symmetry directions and is shown in Fig. 17. The RW frequency at the zone boundary is found to be shifted from the bare surface value because of mass loading and for a slight modification of the force constants between the underlying Cu atoms. The opening of hybridisation gaps is clearly visible in the data. The analysis is supported by a slab calculation [95Ell]. Cu(100) N Nitrogen forms a c(2x2) overlayer at a coverage of 0.5 ML whose phonon dispersion was measured by HREELS along Γ – X and is shown in Fig. 18. The frequency of the RW (S4-phonon) at X is only slightly changed with respect to the clean surface value. The data are compared to a LDM calculation which shows that an optimum fit to the perpendicular (N⊥) and to the parallel (N||) nitrogen modes is obtained when the nitrogen adatom is placed 0.6 Å above the first copper layer [86Fra]. Cu(100) O Oxygen forms a c(2x2) mesh at a coverage of 0.5 ML and induces a missing row 2 × 2 2 reconstruction of the substrate [89Zen] (see Fig. 19). The oxygen occupies the former fourfold hollows and sits almost coplanar with the Cu atoms of the outermost crystal plane, while rows of Cu atoms are missing along [001]. The critical nucleation coverage for the reconstructed phase is 0.34±0.02 ML. The surface phonon dispersion was investigated by HREELS and is reported in Fig. 20. The modes at 34 meV and 56 meV are dipole active in accord with the local Cs symmetry and correspond to the perpendicular vibration of the adsorbate and to the frustrated translation across the missing rows. The mode at 85 meV, visible for off-specular scattering conditions, corresponds to the frustrated translation along the missing rows. Two branches associated to the Rayleigh wave are observed, the backfolded branch being nearly dispersionless. This behaviour is indicative of a strong reduction of the force constants at the surface, in accord with the missing row reconstruction. The loss at 69 meV is very weak and is assigned to the overtone of the 34 meV mode [89Wut1, 89Wut2].
Lando lt -Bö rnst ein New Ser ies III/42A2
4.5-12
4.5 Surface phonon dispersion
[Ref. p 4.5-68
Cu(100) PF3 PF3 forms a c(4x2) structure on Cu(100) at a coverage of 0.25 ML. The surface phonon dispersion was investigated by HATOF and is reported in Fig. 21 for isolated molecules as well as for the ordered structure. The dispersion shows evidence of a low frequency mode, assigned to the frustrated translation of the adsorbate (FTx), and of the RW. For the ordered structure (see panel b) the modes RW1 at 8.2 meV and RW2 at 10.3 meV, are assigned to the RW and to its backfolded branch. The result of a LDM calculation, for which the surface corner atoms (see inset) were replaced by heavier particles of mass m=mCu+mPF3 is shown in panel c). It demonstrates that the principal effect of phosphor trifluoride adsorption is mass loading [99Bra]. Cu(100) S Sulphur on Cu(100) forms an ordered p(2x2) overlayer, corresponding to a coverage of 0.25 ML. S sits in the fourfold hollow at a perpendicular distance of 1.39 Å from the outermost Cu plane. The surface phonon spectrum of this system was investigated by HREELS along Γ – X and is reported in Fig. 22. The dispersion was recorded also along Γ – M but not published. LDM calculations were performed and compared to the experiment. The data shows evidence for: the RW at 12.5 meV at X and 16.5 meV at M , a surface resonance around 20 meV along both directions and the S–Cu stretching vibration at 42 meV. The LDM calculations show that the force constant between the Cu atoms at the surface retains its bulk value and that the frustrated translation, S|| is expected at about the same frequency as the vertical mode, S⊥ [87Fra]. Further reference [87Wu]. Mo(110) The surface phonon spectrum of bare Mo(110) consists of the RW, of the L mode and of a further resonance at 240 cm–1 (see Fig. 23). The dispersion curves were measured by HREELS (open symbols) [97Krö, 98Krö1, 98Krö2] as well as by HATOF (filled circles) [92Hul2]. Mo(110) H Hydrogen forms three superstructures on Mo(110) characterised by (2x1), (2x2) and (1x1) superstructures corresponding respectively to a coverage of 0.5 ML, 0.75 ML and 1 ML. The adsorbate resides always in the hollow sites. The surface phonon dispersion data are shown in Fig. 24 for HATOF and HREELS measurements. For lower coverage no anomalies are present, while at saturation a dip is observed both for the RW and for the L mode which is ascribed to a Kohn anomaly (see also the case of W(110) (1x1) H and the discussion in the introductory part). A further mode, whose frequency nearly vanishes at the critical wavevector, is observed only with HATOF. It corresponds either to the excitation of electron hole pairs [95Koh] or to a plasmon like motion of the H atoms [96Bun]. The dispersion of the H induced modes is reported in Fig. 25. The Kohn anomaly is due to the nesting of the Fermi surface contours associated to the (d3z2–r2,dxz)-like band, which run parallel to Γ – S and perpendicular to Γ – S over significant parts of the SBZ [95Koh]. The effect of H is to change the potential at the surface and to shift the Mo surface state into a region of reciprocal space where it becomes localised at the surface. The band becomes thus two-dimensional and the nesting one-dimensional. The theoretical calculation for the Fermi contours differs however significantly from the ARP result [89Jeo1, 89Jeo2], which shows nesting at larger wavevectors. The presence of a Kohn anomaly was invoked also for an anomaly observed for Mo(110) Li at 1 ML coverage [00Krö]. A subsequent paper of one of the authors questioned however this interpretation, suggesting that the phonon anomaly can be explained by surface stress [02Dah]. Main References: [93Hul2] and [97 Krö]. Further references: [93Hul1, 93Hul2, 98Krö1].
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.5-68]
4.5 Surface phonon dispersion
4.5-13
Mo(110) p(2x2) O Oxygen forms a p(2x2) structure at saturation, corresponding to 0.25 ML. The surface phonon dispersion is reported in Fig. 26. In spite of the indication by ARP [94Kev, 94Dha] that Fermi surface nesting should occur, no surface phonon anomalies are observed, except for the stiffening of the RW at N (shift from 17 to 19 meV). The solid triangles and the dots in the p(2x2) data along Γ – Η were recorded with the crystal at room temperature, where the additional LEED spots present at low temperature along [1 1 0] have disappeared. The phonon spectrum is however little affected. The oxygen-surface stretch mode was visible only in-specular despite varying the electron impact energy from 2 to 25 eV. Its energy reads 65 meV. The oxygen mode parallel to the surface was not detected. The adsorption site is identified with the long bridge in accord with a previous investigation [92Col]. Residual occupation of the threefold hollows, probably at the boundaries of p(2x2) islands is witnessed by a shoulder at 70 meV in the HREELS spectra [98Krö1,98Krö2]. Ni(100) The surface phonon dispersion on the clean surface was thoroughly investigated by HREELS [83Leh], [86Roc2] as well as HATOF [87Ber]. HREELS data are reported in Fig. 27. HATOF data (not shown) coincide with the HREELS result. The clean surface shows evidence for the RW and for several resonances. The frequency of the RW (S1 along Γ M , S4 along Γ X) at the zone boundary is higher than predicted by LDM’s assuming the bulk value of the force constant also between surface atoms. The effect was attributed to tensile surface stress. An increase of the RW frequency is also in accord with the 3.2% inwards relaxation of the first interplanar distance observed by RBS [83Fre1, 83Fre2]. Ni(100) C Carbon forms above 0.25 ML a weak c(2x2) phase with splitted LEED spots indicative of the presence of antiphase domains with the adsorbate occupying the fourfold hollow. Above of 0.3 ML glide planes form along [1 1 0] and the symmetry becomes p4g. LEED [79Onu] and SEXAFS [87Bad] show that the adsorbate still occupies the fourfold hollows and is 0.1 Å above the Ni atoms in the outermost crystal plane. The geometry of the reconstructed phase implies an ordered clockwise and anticlockwise rotation pattern of the substrate surface atoms around the adsorbates, which coincides with the displacement pattern of the A2 mode of the c(2x2) overlayer at X (see right panel of Fig. 4, mode g). A soft phonon mechanism was therefore proposed for the reconstruction [85Rah]. Subsequent LDM calculations [87Mil, 88Sze, 89Mil, 89Sze] showed however that the B2 mode rather then the A2 mode should freeze in first when the force constant between Ni atoms in first and second crystal plane decreases. Inclusion of a compressive surface stress in the LDM allows to overcome this difficulty and to obtain the correct reconstruction [86Mül]. This model also explains the surprising absence of appreciable softening of the RW with C adsorption [87Roc] (see Fig. 28). The surface phonon dispersion as measured by HREELS is reported in Fig. 29 for a coverage of 0.5 ML. The data are reported for an extended zone scheme, the zone boundary being halfway between Γ and X . By symmetry no energy gaps can form at the zone boundary along the glide planes. The C⊥ modes at 42 meV and 51 meV at Γ and X correspond, respectively, to the in-phase and out of phase vertical stretch motions at Γ of the two C atoms of the unit cell. Four parallel modes are found at around 93 meV. They are doubly degenerate at Γ and X . The avoided crossing of the dispersion of such modes along Γ – X leads to the opening of an energy gap and to the asymmetric form of the dispersion [89Sze]. Such effect is not taken into account in the LDM calculations reported by solid lines. The high frequency of the parallel adsorbate modes is due to the vanishing adsorption distance of the C adatoms. Another consequence of the reconstruction is the splitting of the RW into two modes, the upper branch being R1 (at 18 meV at X ). The dependence on carbon coverage of the RW at X and of the frequency of the adsorbate modes at Γ are reported in Fig. 28. A sharp decrease of the Ni–C stretch at the onset of the weak c(2x2) superstructure and no evident change at the onset of the p4g reconstruction are Lando lt -Bö rnst ein New Ser ies III/42A2
4.5-14
4.5 Surface phonon dispersion
[Ref. p 4.5-68
observed. The strong temperature dependence of the RW frequency is indicative of strong anharmonicity. The same effect was observed for Ni(100) p4g N. See also the introduction for further discussion on this system. Main reference [87Roc]. Further references [89Sze, 89Mil, 88Sze, 87Mil, 85Rah, 87Rah]. Ni(100) H Hydrogen adsorption restores the surface phonon frequencies to the values predicted by LDM calculations using the bulk force constants. In particular, compared to the clean surface case, the RW is softened by 0.7 meV at X and by 1.5 meV at M . The longitudinal resonance disappears almost completely from the spectra. The data are discussed in ref. [87Ber], but no dispersion curves were reported. Ni(100) N Nitrogen adsorption induces a p4g reconstruction at a coverage of 0.5 ML. In close analogy to the case of C/Ni(100) the N atoms sit in a c(2x2) unit mesh in the fourfold hollows, while the substrate reconstruction reduces the symmetry to (2x2). SEXAFS investigation [87Wen] shows that the adsorption site is the fourfold hollow with an adsorption distance of 0.1 Å above the outermost Ni atom plane. The rotational displacement around the adsorbate is 0.68 Å, slightly larger than for C/Ni(100) (0.5 Å [87Bad]). The dispersion of surface phonons as measured by HREELS is reported in Fig. 30. The experimental points are reported for an extended zone scheme, the zone boundary being at X . By symmetry no energy gap can form at the zone boundary along this direction. The N⊥ mode extending from 34 meV at Γ to 51 meV at X corresponds to the in-phase vertical stretch motions of the two N atoms of the unit cell in the first zone and to the out-of-phase stretch motion in the second zone. The inphase mode at Γ falls within the bulk band and is therefore a surface resonance. Four parallel modes are expected, but only two are observed (direct and backfolded branches in the first and second SBZ, respectively) at around 91 meV. The high frequency of the parallel modes is due to the vanishing adsorption distance of the N adatoms. The RW and two surface resonances are observed, too, of which R1, originates from the backfolded branch of the RW and is a true surface mode at X . The lines are the result of a LDM calculation for the reconstructed surface geometry [88Rah]. The RW frequency shows a marked crystal temperature dependence at X , where it reads 13.6±0.4 meV at T=130 K and 12.0±0.6 meV at T=300 K. Main references [86Dau] and [88Rah]. Ni(100) O Oxygen forms two ordered superstructures, p(2x2) and c(2x2), on Ni(100), corresponding to a coverage of 0.25 ML and 0.5 ML, respectively. The adsorbate sits in both cases in the fourfold hollow at a vertical distance of 0.86 Å from the outermost Ni plane (SEXAFS [82Stö, 87Wen], NEXAFS [83Nor], LEED [89Oed, 90Oed]). Using nuclear methods the maximum coverage of the c(2x2) phase was determined to be 0.42±0.04 ML [86Alk]. RBS experiments [83Fre1, 83Fre2] demonstrated that the first interplanar distance increases by 2% for the p(2x2) and 5.2% for the c(2x2) structure. The surface phonon dispersion for the p(2x2) O overlayer is reported in Fig. 31a for HREELS data [84Sze] and in Fig. 31b for HATOF data [91Ber]. The branch at 420 cm–1 is the perpendicular stretch vibration of oxygen, while the frustrated translation is observed at 640 cm–1. The Rayleigh wave is only slightly softened with respect to the clean surface. Two resonances are present near Γ . One of them is dipole active and corresponds to the breathing motion with A1 symmetry which originates from the backfolding of the S6 mode originally at X . The solid lines are the result of a LDM calculation [86He]. The surface phonon dispersion for the c(2x2) O overlayer is reported in Figs 32 a) and b) for HREELS [83Leh, 84Rah] and HATOF [91Ber], respectively. The RW shows a strong softening at X (from 132 cm–1 to 80 cm–1) which is due to the adsorbate induced compressive stress at the surface. A reduction of the force constant between the substrate atoms in first and second crystal layer is also possible in view of the large outwards relaxation of the first interplanar distance. The stress model can however explain several other findings and in Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.5-68]
4.5 Surface phonon dispersion
4.5-15
particular the dependence of the softening of the RW on the order status of the adsorbate (see Fig. 33). See also the introductory part for further discussion on this system. Ni(100) S Sulfur forms at saturation (0.5 ML) a c(2x2) structure on Ni(100). The adsorbate occupies the fourfold hollow sitting at 1.35 Å above the outermost Ni atom plane (LEED [73Dem], SEXAFS [81Bre] and photoelectron spectroscopy [81Ros, 83Bar, 84Ord]). The surface phonon dispersion is reported in Fig. 34. The observed branches correspond to the RW (S4), to S6 and to a surface resonance associated to the backfolding of the RW from the M X direction. The vertical and the parallel mode of the adsorbate are visible above the projection of the bulk phonon bands (hatched area). The LDM calculation was performed with the bulk value of the force constants. In order to obtain a good fit with a LDM an adsorption distance of 1.45 Å had to be assumed. This shortcoming is most probably due to neglecting of the adsorbate induced stress [92San1]. Main reference [85Leh] and [86Leh]. Ni(110) The surface phonon dispersion for the clean surface was measured by HREELS [87Leh2] and is reported in Fig. 35. The RW corresponds to the S1 mode along Γ – X and to S3 along Γ – Υ . Along the latter direction the lowest frequency mode is mainly longitudinally polarised. Ni(110) p2mg (2x1) CO CO forms at saturation a p2mg (2x1) structure at 1 ML coverage on Ni(110). Adsorbate geometry and SBZ are shown in Fig. 36. The CO molecules are adsorbed in atop sites with the axis tilted away from the surface normal. The dispersion curve, measured by HREELS, is reported in Fig. 37 over an extended zone scheme. Two stretch motions are possible corresponding to in-phase and out-of-phase vibration of the two CO molecules of the unit cell. The two modes are degenerate at X and Υ . The latter observation implies that ∆Y, i.e. the lateral displacement of the chemisorption sites with respect to the substrate atoms, is exactly one quarter of the substrate unit cell. The dispersion as well as the low symmetry adsorption sites are caused by the repulsive dipole-dipole interaction between the close packed CO molecules. The dipolar interaction determines the negative dispersion of the in-phase motion with q||. The mode at 400 cm–1 corresponds to the stretch of the CO molecule against the substrate. The two substrate modes are due to the RW and to its backfolded branch [90Voi2]. Ni(110) H Hydrogen forms on Ni(110) a sequence of ordered structures with increasing coverage which were attributed to the increasing density of zig-zag chains along the rows of the first layer Ni atoms (see Fig. 38). At one ML coverage the (2x1) superstructure forms which consists of an unreconstructed surface with H atoms in the three fold sites between two first layer and a second layer atom with equal Ni–H distances (LEED [87Rei]). Saturation coverage is at 1.5 ML. The surface is then (1x2) reconstructed with pairing substrate rows (LEED [87Kle]). Two adsorption sites are occupied corresponding to the previous threefold site and to a Cs site above the paired rows. A strong softening of the S1 mode was found with H adsorption and ascribed to the build up of surface stress. The frequency shift of the phonons at Υ (Figs. 39a and b) indicates a propensity of the surface towards reconstruction. At X on the contrary (see Fig. 39c) the frequency of the RW remains unchanged up to one ML coverage indicating that H adsorption induces a charge rearrangement that influences the substrate interaction only along [001]. The surface phonon dispersion curve for the p2mg (2x1) H overlayer is reported in Fig. 40. The two H atoms, present in the unit cell, are linked by the glide operation. Two modes are dipole active in accord with the reduced symmetry of the adsorption site. A further mode is visible only off specular and along Γ – X . The mode at 630 cm–1 has the strongest dipole character but corresponds to motion mostly parallel to the surface
Lando lt -Bö rnst ein New Ser ies III/42A2
4.5-16
4.5 Surface phonon dispersion
[Ref. p 4.5-68
plane. The perpendicular stretch mode is at 1100 cm–1. The substrate modes S1 and S3 at Υ are softened by 10% with respect to the clean surface [89Voi]. The surface phonon dispersion curve for the (1x2) H overlayer is reported in Fig. 41. The data are reported on an extended zone scheme, the first Brillouin zone ending at Υ ' , halfway between Γ and Υ . At Υ a splitting of the RW and the opening of a gap is observed. The three H atoms per unit cell give rise to four dipole active modes in accord with the reduced symmetry of the adsorption sites. The mode at 450 cm–1 corresponds to the vibration perpendicular to the Ni rows in the [001] direction. Symmetry considerations imply that the modes at 930 cm–1 and 1240 cm–1 are polarised within the Cs plane parallel to the Ni rows. Ab-initio calculations however assign the 1240 cm–1 loss to a vibration predominantly perpendicular and the 930 cm–1 loss to a vibration predominantly parallel to the surface along [1 1 0] [87Fei]. References [89Voi, 87Leh1]. Further reference [87Iba]. Ni(110) O Oxygen adsorption on Ni(110) induces a series of ordered structures leading finally to nickel oxide formation. The (2x1) phase, observed at half a ML coverage, involves a missing row reconstruction of the substrate. The oxygen adatoms sit in the long bridge sites at an estimated height of 0.6 Å above the outermost Ni atoms (EXAFS [86Bab]).The surface phonon dispersion is reported in Fig. 42 for the p(2x1) phase. Three dipole active modes are present. Two of them are associated to adsorbate vibrations, while the one at 118 cm–1 is due to a Ni surface phonon folded back to the Γ point because of the (2x1) reconstruction. The presence of two dipole active adsorbate modes shows that the local adsorption symmetry is Cs, i.e. only one mirror plane is present and the adsorbate is shifted out of the long bridge in the [1 1 0] direction. The adsorbate induced modes are polarised within the mirror plane predominantly parallel (at 239 cm–1) and perpendicular (at 385 cm–1) to the surface in the [1 1 0] direction. The third mode, at 790 cm–1, is polarised parallel to the surface in the [001] direction and shows a particularly strong temperature dependence. The other modes did not change appreciably with T. The assignment is less clear for the substrate modes. The lowest lying phonon at Υ is at 84 cm–1, i.e. close to the frequency of the RW of the clean surface. Similarly the mode at 135 cm–1 is close to the frequency of the S3 mode of the clean surface. Such modes are however unlikely to have survived unchanged the missing row reconstruction. LDM calculations assign the mode at 84 cm–1 to an odd vibration which becomes visible because the symmetry is reduced to Cs and the Γ – Υ direction is no longer a mirror plane. The mode at 118 cm–1 at Γ is dipole active and originates from a mode along X – S which is folded back on Γ – Υ for the reconstructed surface. Along Γ – Χ the two dipole active adsorbate modes show practically no dispersion throughout the SBZ. The lowest frequency substrate mode is assigned to the RW [90Voi2, 91Yan]. Ni(111) The surface phonon dispersion of clean Ni(111) was measured by HREELS and is reported in Fig. 43 [90Men1, 90Men2]. Two surface modes, S1 and S6 and a surface resonance are visible. Modified surface force constants are necessary to reproduce the dispersion with a LDM, as it is the case also for the other Ni surfaces. Ni(111) O The p(2x2) O/ Ni(111) system is reconstructed with a twist deformation of three of the top layer nickel atoms and a vertical displacement of all of the atoms in the top layer of the unit cell (LEED [90Gri]). The oxygen coverage is 0.25 ML. A schematic view of the structure of the p(2x2) overlayer is reported in Fig. 44. The oxygen lifts three of the nickel atoms away from their original bulk positions, while the fourth relaxes towards the second layer Ni atoms. The surface phonon dispersion measured by HREELS is reported in Fig. 45. Five optical modes are observed. The modes at 67 and 71 meV are assigned to oxygen adsorbate vibrations, while the lower modes lie within the bulk bands. The open (filled) circles Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.5-68]
4.5 Surface phonon dispersion
4.5-17
indicate data points recorded at an electron impact energy of 7 (160) eV. LDM calculations are presented, too (thick solid lines). The theoretical dispersion curves for the two lower lying modes is not extended over the whole SBZ as such modes are surface resonances which do not produce sharp spectral density features at large wavevectors. The thin solid lines are best fit curves to the experimental data [94Tis]. Pb(111) The surface phonon dispersion for the clean Pb surface was investigated by HATOF and is indicative of no change in the force constants compared to the bulk value [96Fuh]. The result of the LDM is reported in Fig. 46. Pb(111) d-octane d-octane adsorbs flat on the surface. The surface phonon spectrum was investigated by HATOF and shows evidence for the frustrated translation (FTz) normal to the surface and for the RW (see Fig. 46). The latter is strongly softened because of mass loading. The AOP1 mode corresponds to an internal vibration of the alkane molecule [96Fuh]. Pt(111) The surface phonon dispersion of the bare Pt surface was determined by HATOF and is reported in Fig. 49 (open symbols). The RW (dots) and the L resonance (triangle) are observed. The RW presents anomalies along Γ – K , which were ascribed to the Kohn mechanism [85Har, 86Ker2, 87Neu]. Pt(111) (1x1) H Hydrogen forms a (1x1) overlayer at saturation corresponding to 1 ML coverage. It adsorbs in the threefold fcc hollows causing an expansion of about 1.3±0.4 % of the first interlayer spacing (RBS [80Dav], LEED [76Chr]). Theory [87Fei] predicts that the H atoms lie about 0.95 Å above the surface in agreement with RBS results [86Koe]. The inelastic He scattering data are collected in Fig. 47. They show a significant softening of the RW frequency at the zone boundary (from 11.1 meV to 9.5 meV at K and from 10.8 meV to 9.3 meV at M ). Moreover the longitudinal resonance, present on the clean surface and particularly intense along <110>, has disappeared. These changes imply a strong modification of tangential, radial and three-body force constants especially in the surface plane, connected to a redistribution of the electronic charge at the surface and a reduction of the sp-d hybridisation, responsible for the directed bonding charge between atoms in the bulk [89Bor]. Pt(111) O Oxygen forms at saturation (coverage 0.25 ML) a p(2x2) structure when adsorption occurs at T=300 K, corresponding to a coverage of 0.25 ML. The adatoms are sitting in the three-fold hollows 1.4 Å above the outermost Pt atoms plane as inferred from the oxygen substrate stretch at 59 meV [82Ste]. A (1x1) coverage can be reached when the Pt crystal is annealed at a crystal temperature of 540 K in 5 10–7 mbar of oxygen. The latter phase corresponds to the formation of a subsurface oxide [87Neu]. According to ref. [81Nie, 81Bon] it can only be obtained in presence of silicon impurities. The phonon dispersion of the p(2x2) overlayer was measured by HATOF along ī − M and is reported in Fig. 48. The data (panel a) show evidence for two branches associated to the RW and of a hybridisation gap at the zone boundary of 0.85±0.2 meV. The two dispersionless modes at 9 and 10 meV originate from the backfolding of the RW from the M - K - M' direction. In a comment it was suggested that they might be due to a single mode [87Sze]. Theory is reported in panel b. Inclusion of threebody forces is necessary to reproduce the size of the phonon gap. Reference [86Ker1, 86Ker2, 87Ker]. The phonon dispersion for the (1x1) phase
Lando lt -Bö rnst ein New Ser ies III/42A2
4.5-18
4.5 Surface phonon dispersion
[Ref. p 4.5-68
(coverage 1 ML) was measured by HATOF and is reported in Fig. 49. A strong softening of the RW and of the L mode is observed along ī − M in the last third of the surface Brillouin zone [87Neu]. Rh(110) The surface phonon dispersion of bare Rh(110) was measured by HATOF for the metastable (1x2) missing row reconstructed surface obtained after chemical removal of the oxygen adatoms by hydrogenation at T=360 K. No LDM exists for comparison. The data are reported in Fig. 50a [93Bel]. Rh(110) O Oxygen forms a (2x2) overlayer on Rh(110) at 0.5 ML coverage. The substrate is reconstructed in the same way as for the metastable (1x2) surface whose surface phonon dispersion is reported in Fig. 50a. The surface phonon dispersion was measured by HATOF and is reported in Figs. 50c, d and e [93Bel]. Rh(111) The surface phonon spectrum of bare Rh(111) was measured by HATOF and is reported in Fig. 51a. The RW and a L resonance are observed along both high symmetry directions [95Wit1]. Rh(111) H Hydrogen forms a well ordered (1x1) overlayer at the saturation coverage of 1 ML. The adsorption site is likely to be the three-fold hollow. The dispersion curve was investigated by HATOF and is reported in Fig. 51b [95Wit1]. The intensity of the L-modes is weaker for the hydrogenated phase, while the RW is observed over all the SBZ. Its frequency at K and M reads 16.4 meV and 15.6 meV, respectively, and is thus slightly decreased compared to the clean surface values. Some weak and broad peaks, observed above the RW (open circles marked by B’), are associated to surface resonances. Moreover an additional mode, S2, is split off from the longitudinal bulk bands along both high symmetry directions at energies of 28.5 meV and 29.7 meV at K and M , respectively. Such mode is not hydrogen induced as it does not shift in frequency when deuterium is adsorbed. Three H vibrations were reported by HREELS at 92 meV, 136 meV and 175 meV [86 Mat]. Rh(111) ( 2 3 × 3 ) C6H6 The phonon dispersion curve for the ( 2 3 × 3 ) phase, obtained at saturation (0.16 ML), was investigated by HATOF. The data, reported in Fig. 52, show evidence for the RW and for the frustrated translation of benzene parallel to the surface. The two modes hybridise strongly opening an energy gap [93Wit1, 93Wit2]. Ru(0001) The surface phonon dispersion was measured by HATOF. The data are reported in Fig. 53a. The SBZ is reported in the inset. The two modes correspond to the RW and to the L resonance [97Bra]. No change of surface force constants is necessary to reproduce the data with a LDM. Ru(0001) (1x1) H Hydrogen forms several ordered phases on Ru(0001). Only the more stable (1x1) phase, corresponding to saturation coverage (1ML), was investigated by HATOF to determine the surface phonon dispersion. The dispersion curve for the H saturated surface is reported in Fig. 53b. Apart from the RW and the L mode two further features, denoted by S2, are present [97Bra]. Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.5-68]
4.5 Surface phonon dispersion
4.5-19
W(100) Clean W(100) undergoes reconstruction via a soft phonon mechanism, which was confirmed by HATOF experiments [87Ern, 89Ern]. The surface phonon dispersion curve, reported in Fig. 54, shows a strong Kohn anomaly at M . W(100) H Hydrogen forms a (1x1) phase at saturation (2 ML coverage) whose surface phonon dispersion was investigated by HATOF. The measurements show that H removes the Kohn anomaly and the force constants between surface atoms are restored to their bulk value [92Ern]. The data are shown in Fig. 55 and compared with the result of a LDM. Nearly dispersionless H induced modes were observed by HREELS at: 160 meV - asymmetric stretch, 130 meV - symmetric stretch, 118 meV - optical mode, 80 meV - wagging mode. [87Ers,87Woo]. W(110) The surface phonon dispersion was investigated by HREELS and HATOF and is reported in Fig. 56 [94Bal1, 92Hul1, 92Hul2]. The data show evidence for the RW, for the longitudinal resonance and for a further resonance at 200 cm–1. Contrary to the case of the (100) surface, no phonon anomaly is present. W(110) H Three adsorbed H phases form on W(110): p(2x1) at 0.5 ML coverage, (2x2) at 0.75 ML and (1x1) at saturation (1 ML). The phonon dispersion was investigated for all the phases by HATOF [92Hul1, 92Hul2] as well as by HREELS [96Bal, 94Bal1, 94Bal2]. The H adsorption site is in all cases the threefold hollow, but the saturated phase corresponds to a liquid phase with propensity for onedimensional disorder. Moreover in the latter conditions the surface is reconstructed whereby the topmost layer is shifted with respect to the second layer [86Chu]. The phonon dispersion curves were measured along ī − S , ī − Ǿ and ī − N and are reported in Fig. 57. HREELS data for the RW, for the first layer L mode and for a second layer mode are depicted as triangles, diamonds, circles and squares, respectively. The circles close to the N point for the clean surface could also be due to a vertically polarised phonon in the second crystal layer. Data points due to the backfolded RW, observed only close to Γ are depicted as inverse triangles. The HATOF data are reported as small dots. The difference for the p(2x1) phase at S between HATOF and HREELS is most probably due to a slight difference in coverage. The dispersion of the RW of the p(2x1) phase differs around N and S from the one of the clean surface: a frequency increase from 14.5 meV to 16.5 meV takes place at N , while a decrease from 17 to 14 meV occurs at S . Upon further dosing the RW frequency at N stays constant, while the frequency at S drops further. The RW dispersion shows therefore a maximum at about ζ=0.75 ( ī − S ). As soon as the (1x1) phase forms, a strong anomaly is observed along ī − Ǿ at the incommensurate wavevector q||=0.93 Å–1 both for the RW and for the L-mode. The Rayleigh wave is apparently splitted into two branches, out of which the lower one is not detected by HREELS and is therefore assigned to the excitation of electron hole pairs [97Koh] or of a plasmon-like collective excitation of the hydrogen atoms [96Bun]. As shown in Fig. 58 the anomaly is present for all wavevectors whose component along ī − Ǿ is equal to ∼1 Å–1. The theoretical dispersion determined ab-initio is shown in Fig. 59 [96Bun]. In accord with the electronic origin of the loss, the lowest HATOF branch is not present in the LDM result. The HREEL spectra for the (1x1) phase are show in Fig. 60, while the dispersion data for the H induced modes along ī − Ǿ are collected in Fig. 61 for the three phases. For p(2x1) H three modes are observed, corresponding to the three degrees of freedom of the adsorbate. The modes at 96 meV and at 156 meV are dipole active, implying adsorption in the hollow site. The loss at 156 meV is mainly due to the perpendicular motion [96Bal]. For the (2x2) H
Lando lt -Bö rnst ein New Ser ies III/42A2
4.5-20
4.5 Surface phonon dispersion
[Ref. p 4.5-68
phase, five H related modes are observed in-specular, while a sixth branch is only excited for off-specular conditions. All modes display only a small dispersion, except for the modes at 94 and 106 meV. As three H atoms are present per unit cell, a total of 9 adsorbate induced phonon branches would be expected, but the in-phase and anti-phase modes of two of the H atoms are nearly degenerate. The mode at ∼155 meV is due to the perpendicular stretch motion. For the (1x1) H phase, the stretch vibration is at 163 meV and displays a stronger dispersion than for the other H phases [96Bal]. Its lineshape is anomalous, consisting of a continuum plus a single sharp peak [94Bal2, 96Bal] (see Fig. 60). Surface disorder is not sufficient to explain this finding as no sharp loss for the vertical vibration at 155 meV would then be expected. The effect is ascribed to delocalisation of the adsorbates in the parallel directions. The H atoms were suggested therefore to be in a quasi liquid like phase. [94Bal2]. See also the introduction for further discussion. Main references [92Hul1, 92Hul2, 96Bal, 94Bal1, 94Bal2]. 4.5.2.3 Elemental Semiconductors and Insulators C(100) H Hydrogen on diamond (100) forms a (1x1) 2H phase at saturation (2 ML coverage) and (2x1) H phase (1ML coverage). In both cases two H atoms are present in each unit cell. The optimised surface structures are reported in Fig 62 together with the SBZ. The surface phonon dispersion curves, as predicted by first principle theory [96San], are reported in Figs. 63 and 64 for the two phases. The H atoms are coupled to an essentially ideal bulk truncated diamond substrate lattice for both phases, but the surface phonon dispersion is quite different. The projected bulk phonon bands (hatched area in Figs. 63 and 64) exhibit only small gaps and pockets, which host no surface modes, while several surface resonances are found within the bulk bands. Modes denoted with S and B indicate stretch and bending motions of the adsorbate. Frustrated rotations are marked by the subscript r. Subscripts s and a indicate the symmetric and the antisymmetric motions of the two H atoms in the unit cell. SH modes are denoted by a bar over the symbol. The mode STOX at Χ in Fig. 63 exhibits pronounced contributions of the C atoms in the third layer. Comparison with experiment is possible only at Γ where HREELS data exist. For the (2x1) system [93Aiz, 94Tho] loss peaks were reported at 363 meV and 152 meV [93Aiz] and 363 meV, 155 meV and 137 meV [94Tho], which coincide with the modes Sa (363 meV), BS+ (155 meV) and STOX (133 meV). For the (1x1) system [93Lee] losses were found at 361 and 350 meV, corresponding to the symmetric and antisymmetric H stretch modes, respectively and at 181, 162 and 153 meV. The latter modes fall in the region of the H bending motion. Main reference [96San]. C(111) H Hydrogen forms a (1x1) phase at saturation (2ML coverage) and a (1x2) phase at 1 ML coverage, which is obtained by heating the saturated surface to 1300 K. The structure was investigated by LEED [93Lee] and He atom scattering [97Sch]. The surface phonon dispersion of the (1x1) phase was measured by HATOF [96Lan, 98Gle] and calculated from first principles [95San1, 95San2, 97Maz, 98Gle] and is reported in Fig. 65a. Interestingly substituting H with D (see Fig. 65b) causes quite a large isotopic effect on the surface phonon spectrum and especially on the RW dispersion (at Χ the frequency shifts from 17 meV in presence of H to 15 meV in presence of deuterium). The phenomenon is ascribed to the different contribution of the adatoms to the oscillation amplitude. For the description of the symbols in Fig. 65 see discussion of C(100) H. Main reference [98Gle]. Ge(100) (1x1) S Sulfur is used to passivate the Ge surface and was suggested as a prototype for the development of an intuitive picture of the chemical bond at the semiconductor surface. The structural and electronic properties were calculated within DFT-LDA for the (1x1) phase obtained at saturation (1ML coverage). The adsorption site is identified with the bridge, while the substrate reverts to a nearly ideal bulk termination. The surface phonon spectrum was calculated by a total energy ansatz and is shown in Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.5-68]
4.5 Surface phonon dispersion
4.5-21
Fig. 66. There are localised adsorbate induced modes both above and below the projected bulk phonon band. A prominent resonance, due to the vibration of the S adatoms, is present at Γ and is indicated by the dashed line [92Pol]. Si(100) The surface phonon dispersion for the clean (2x1) reconstructed surface was calculated [97Tüt] and it is reported in Fig. 67. Si(100) As, Ge and Sb The surface undergoes a (2x1) reconstruction when covered with 0.5 ML of As, Ge or Si, forming symmetric dimers with As and Sb and tilted dimers with Ge (see Fig. 68) [90Jed, 93Krü, 94Fra]. The surface phonon dispersion was calculated ab initio. In the case of As two methods were applied and slightly different results were obtained. In the first method, applied also to the Ge and Sb cases, the adiabatic bond charge model was used for which the electronic and structural properties are determined by an ab-initio pseudopotential method [99Tüt]. The second method employs an extension of the semiempirical total energy Ansatz, which includes the electronic properties via a band-structure energy term treated within the empirical tight binding method [98Grä]. All information necessary to determine the parameters of the band structure and of the elastic energy is obtained from first principles total energy and electronic structure calculations. The surface phonon spectrum according to the method of ref. [98Grä]. is shown in Fig. 69a. SH modes are indicated with a bar above the symbol. Three kind of modes are discussed: A-modes, located below the projection of the bulk phonons on the SBZ and mostly dominated by the heavy As adatoms; D-modes, surface resonances within the bulk bands with energies up to 40 meV which involve characteristic movements of the dimer adatoms together with the first substratelayer Si atoms; and S-modes, optical substrate-surface modes above 40 meV to which the As atoms do not take part. The phonon dispersion curve obtained with the method of ref. [99Tüt] is reported in Fig. 69b. The main features agree with the result of the model of ref. [98Grä], but the single features appear at slightly different frequencies. The corresponding spectra for Ge and Sb overlayers are reported in Figs. 70 and 71, respectively [98Tüt1, 98Tüt2]. Experimental results for these systems are still lacking. Si(100)(2x1) H H forms a (2x1) phase at 0.5 ML coverage. This system is characterised by a large misfit between the mass of adsorbate and of substrate atoms, consequently the motion of the adsorbate is nearly decoupled from that of the dimer atoms. The surface phonon dispersion was computed following a semiempirical total energy ansatz [96Grä1] and is reported in Fig. 72. Experimental data for the phonon dispersion are lacking. The symmetric and asymmetric H stretch modes are only marginally split in frequency (62.57 Thz and 62.91 Thz) [84Cha]. The H bending modes couple to the dimer atom motion so that their splitting is larger (ν(Bs)=18.46 Thz, ν(Ba)=18.86 Thz). Such frequencies compare well with the HREELS value of 18.98 Thz [83Stu]. Ds at 10.54 THz and Dt at 5.95 Thz correspond to dimer stretch and tilt motions. The D1 mode at 10.3 Thz and the D2 mode at 13.54 Thz involve mainly a bending of the dimer bond in the xz-plane. SH modes are denoted with a bar over the symbol. Si(110) (1x1) H The hydrogenated Si(110) surface was studied by infrared spectroscopy [96Wat]. Hydrogen adsorption restores the ideal bulk terminated geometry of the Si substrate at 1 ML coverage. The adsorbates sit in atop sites. The surface phonon spectrum was calculated with a semiempirical total energy method. The result is shown in Fig. 73 [97Grä]. Hydrogen stretch modes are denoted by S, hydrogen bending modes by B. C-modes are chain modes of the substrate.
Lando lt -Bö rnst ein New Ser ies III/42A2
4.5-22
4.5 Surface phonon dispersion
[Ref. p 4.5-68
Si(111) (1x1) As In contrast to the inherent instability of the clean Si(111) surface, the As capped surface (1ML coverage) is inert. Each As atom is covalently bonded in an almost bulk-like configuration to the three underlying Si atoms. The surface crystallography was investigated by LEED [86Olm] and medium energy ion scattering [88Cop], which indicate only a slight outwards relaxation of the As atoms (~0.2 Å). The surface phonon spectrum was investigated by HATOF [90Doa1, 90Doa2, 92San2] and by HREELS [94Sch] and is reported in Fig. 74 together with a theoretical prediction. The different surface modes are denoted by different symbols. The As overlayer affects the surface dynamics principally because of the mass defect in the outermost layer. The two acoustic branches were found also for the (1x1) H phase and are therefore intrinsic of the substrate. The surface phonon spectrum was calculated from first principles following total energy schemes and ab-initio calculations based on the local density approximation of density functional theory employing non local, norm conserving, pseudopotential [98Grä]. A similar very good agreement with experiment was obtained independently by Honke et al., who calculated the surface phonon dispersion using density functional perturbation theory [96Hon]. Si(111) ( 3 × 3 ) Ga The ( 3 × 3 ) reconstruction is induced on the Si(111) surface by a number of different metals at a coverage of 0.3 ML and consists of metal atoms occupying half of the T4 sites. Each adatom is located directly above a Si atom in the second layer and is bonded to three Si surface atoms, such that all dangling bonds are saturated. The phonon dispersion for the Ga overlayer was investigated by HREELS [95Sch] as well as by HATOF [89Doa]. The HREELS results and HATOF data are compared with the result of first principle calculations [99Fri2] in Fig. 75. Si(111) (1x1) H The Si(111) (1x1) H surface can be grown at 1 ML coverage with a high degree of perfection and became therefore a prototype system for well defined experimental studies of surface phonon dispersion. HATOF data can be found in refs. [88Har, 90Doa3], HREELS data in refs. [92Stu, 92Dum]. Theoretical calculations were performed in refs. [88Gold, 88Mig, 95San1, 96Grä2, 96Hon]. The HATOF data [90Doa3] are reported in Fig. 76a and compared with the theoretical prediction of ref. [88Mig]. HREELS data [92Stu, 92Dum] are reported in Fig. 76b, together with the theory of ref. [95San1]. The theoretical prediction for the deuterated system is reported in Fig. 76c [96Grä2]. The lowest frequency mode is the RW. Several surface modes are found in the gaps of the projection of the bulk phonons. Due to the large mass mismatch the H vibrational modes are decoupled from those of the substrate. The system behaves therefore as a perfect realisation of the ideal bulk terminated Si(111). 4.5.1.2.4 Compound Semiconductors GaAs(110) Experimentally the surface was investigated by HATOF [87Har, 87Doa]. The result of a theoretical model calculated by ab-initio linear response formalism is shown in Fig. 77 [95Fri1]. GaAs(110) (1x1) H The surface phonon dispersion was determined by means of ab-initio linear response formalism [95Fri1]. No experimental data are yet available for the phonon dispersion curves. HREELS was recorded at Γ for the hydrogen modes [96Gra2]. The hydrogenation is saturated at 1 ML coverage. The 1 ML coverage phase has the (1x1) periodicity of the substrate and causes the removal of the relaxation present for the clean surface and the onset of a slight counter-rotation of the atoms in the first plane of the substrate. Direct information about the structure has been obtained by photoelectron diffraction [95Ruo] and
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.5-68]
4.5 Surface phonon dispersion
4.5-23
grazing incidence X-ray diffraction [94Ruo]. The theoretical prediction for the surface phonon dispersion of GaAs (1x1) H [95Fri1] is shown in Fig. 78. The main differences with respect to the clean surface are: i) the third acoustic phonon mode along Γ – Χ' predicted for the clean surface [93Fri] and confirmed by HATOF [87Doa] is absent in the hydrogenated phase; ii) the surface optic phonon branch, characterised by an opposing motion of the surface cations and of the second layer anions, located above the bulk band for the clean surface (as confirmed by HREELS [94Nie]) is shifted downwards into the optic bulk bands, becoming a surface resonance. The surface localised modes of GaAs(110) covered by 0.5 ML of hydrogen are similar to those of the (1x1) H phase except for a vibration at 35.1 meV appearing at Γ when hydrogen is chemisorbed on the Ga atoms. Further theoretical papers [93Ber, 95Fri1]. GaP(110) H and Sb Similar to the case of GaAs, H and Sb form (1x1) phases at saturation on GaP (1 ML coverage). Contrary to the GaAs case however, the acoustic and optical bulk bands are now well separated. The phonon modes above the bulk continuum (dashed lines) are shifted into the optical bulk bands upon H adsorption. The phonon dispersion curves are reported in Figs. 79 and 80 [99Fri1]. InAs(110) (1x1) H The surface phonon dispersion is reported in Fig. 81 for the (1x1) phase corresponding to 1 ML coverage, as calculated from first principles in ref. [99Fri1]. The modes are similar to those of GaP(110)(1x1) H, to which system we refer for further discussion [99Fri1]. InP(110) (1x1) H The interaction of H with InP(110) leads to complicated surface reactions. At saturation however this system is very similar to GaAs(110). The surface phonon dispersion was determined by means of an abinitio linear response formalism [95Fri1]. No experimental data are yet available for the phonon dispersion curves, while HREELS data [96Nie] were recorded for the Γ point. The main feature in the HREEL spectra (not shown) is the Fuchs-Kliever mode at 54.3 meV. Hydrogen atoms bind simultaneously to In and P atoms in each stage of the adsorption process. The hydrogenation is saturated at 1 ML coverage with two H atoms per surface unit cell. The 1 ML coverage has the (1x1) periodicity of the substrate. Adsorption leads to the removal of the relaxation in the first layer of the substrate and to the onset of a slight counter-rotation of the atoms in the first plane of the substrate. The theoretical prediction for the surface phonon dispersion of InP(110)(1x1)H [95Fri1] is shown in Fig. 82 [95Fri1]. 4.5.2.5 Oxides and Salts Quite a bit of work was performed for physisorbed species on MgO and NaCl. In all cases little or no modification of the surface phonon spectrum occurred. These results are therefore not shown. MgO For the MgO(100) CO system the dispersion of the low energy adsorbate modes was measured by HATOF [95Ger]. No evidence was found for the RW. NaCl Adsorption of several gases was studied on the (100) surface by HATOF: CO2 [93Lan, 93Hei, 95Lan], H2O [95Bru], acetylene [98Pic], and OCS [96Gle,96Doh]. The RW is always a prominent structure in the spectra. The RW dispersion curve is crossed by several modes corresponding only to the frustrated translation parallel to the surface in the case of water admolecules and to several adsorbate induced modes for the other gases.
Lando lt -Bö rnst ein New Ser ies III/42A2
4.5-24
4.5 Surface phonon dispersion
[Ref. p 4.5-68
Acknowledgments The author likes to thank Mariachiara Lupi for critical reading of the manuscript and for helping in its preparation.
Lando lt -Börnst ein New Ser ies III/42 A2
Figures for 4.5
∆ Γ
X
C S D Γ Σ X Y
M
Σ
T
∆
Y
Γ
K T’ M Σ
(0,0)
(110) (001)
Σ Γ ∆
Face centered cubic (fcc) M
N
Y X
Γ
(001)
e −or He
(111)
ϑi
ϑs
e− He
S H
q II
N’
(110) Body centered cubic (bcc)
Fig. 1. Surface Brillouin Zone (SBZ) for the low Miller index surfaces of face centred cubic (fcc) and body centred cubic (bcc) lattices discussed in the present review.
Fig. 2. Ewald sphere construction for the inelastic scattering events. For He atoms the energy loss is comparable to the impact energy of the particles, while for electrons it is negligible on the scale of the figure. The HREELS spectra are therefore effectively constant q|| scans, while HATOF spectra run along the so-called scan curves and include losses with different q|| values.
For Fig. 3, see next page
Surface phonons of (100) c (2×2) surfaces at Γ
Surface phonons of (100) c (2×2) surfaces at X Adsorbate modes
Adsorbate Modes a)
b)
c)
a)
E,odd
E,even
A1,even
E,odd
E,even
A1,even
d)
First layer substrate modes e)
f)
d)
First layer substrate modes e)
f)
E,odd
E,even
A1,even
E,odd
E,even
A1,even
g)
h)
i)
E,odd
B2,even
B1,even
g)
h)
i)
E,odd
E,even
B1,even
b
b)
c)
a Fig. 4a, b. Displacement pattern of the surface phonons of a c(2x2) overlayer on a (100) substrate at: (a) Γ ; (b) X .
Lando lt -Bö rnst ein New Ser ies III/42A2
4.5-26
4.5 Surface phonon dispersion
Adsorbate Substrate
p (2×2)
[Ref. p 4.5-68
c (2×2)
Top View A
A’
A
A’
A
Side View A’ A
A’ X
Γ
M
Γ
Fig. 3. Direct and reciprocal lattice for p(2x2) and c(2x2) superstructures on a fcc(100) surface: SBZ size reduction and folding.
M
X1
with internal stress
500
400
12
400
12
300
9
300
9
200
6
200
6
100
3
100
3
0
0
0 0 Γ
0.5 Red.wavevector coord. ξ
1.0 X
Wavenumber ν [cm−1]
15
Frequency ω [THz]
Wavenumber ν [cm−1]
500
Ni(100) c(2×2)O
without internal stress
0 Γ
15
Frequency ω [THz]
X2
0 0.5 Red.wavevector coord. ξ
1.0 X
Fig. 5. Surface phonon dispersion along Γ – X for Ni(100) c(2x2) O. Two LDM are shown: in the left panel a 70% reduction of the force constant between the Ni atoms in the first and second crystal layer is necessary to reproduce the anomaly; in the right panel the same effect is reached by introducing a compressive stress at the surface [86Rah]. The shaded area indicates the continuum due to the projection of the bulk phonon band. (ξ = Qx/1.26 Å–1)
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.5-68]
4.5 Surface phonon dispersion
25
20
W(110)
clean
15
1
clean 20
T
Intensity I [kHz meV −1 ]
L
Phonon energy hω [meV]
4.5-27
10 2
15
10 2
5 5 1
0
0 0.4 0.6 0.8 1.0 Red.wavevector coord. ξ
0.2
0 a
1.2
1.4
−10 0 Energy loss E loss [meV]
9
20
H-saturated
H-saturated
8
10
20
10
20
2 4
7
15
Intensity I [kHz meV −1 ]
Phonon energy hω [meV]
− 20
a
5 4
10
1 3
5
5 4
3
3
5
2 2
1
0 0
6
0.2
b
0.4 0.6 0.8 1.0 Red.wavevector coord. ξ
1.2
0
1.4 b
1 − 20
−10 0 Energy loss E loss [meV]
Fig. 6a, b. Surface phonon dispersion for clean and H covered W(110) (left panels) and HATOF scan curves recorded for an impact energy Ei = 37.74 meV and ϑ i = 49 °, crossing the critical spectral region (right panel). The solid lines in the left panel represent the lower edges of the surface projected transverse (T) and longitudinal (L) bulk phonons. For the bare surface the data points are assigned to the RW (lowest branch) and to the L resonance (upper branch). For the (1x1) H phase the same two branches are present below q|| ≅ 0.6 Å–1, while at larger wavevectors the lower branch softens and splits. The numbers in the dispersion curves indicate the peaks in the HATOF spectrum [93Hul2].
Lando lt -Bö rnst ein New Ser ies III/42A2
4.5-28
4.5 Surface phonon dispersion Γ
2100
6
I r(100)-(5×1)+16 L CO I r(100)-(1×1)+16 L CO
K
M’
K’
Cu(110):Xe
2050
450
2
RW 4 L H1
3
T
500
T
Phonon energy hω [meV]
5
2000
Wavenumber ν [cm−1]
[Ref. p 4.5-68
H2
2 1
400
0 0
60 20 0.4 0.6 0.8 Red.wavevector coord. ξ
0.2
0 Γ
〈110〉
Γ
2.0
2.5
Fig. 8. Surface phonon dispersion along [ 1 1 0 ] for an incommensurate Xe monolayer deposited on Cu(110) measured with HATOF. The modes H1 and H2 are generated by hybridisation of the vertical vibration of the adsorbate with the RW. The mode L corresponds to the longitudinal motion of the Xe adatoms. The upper dispersionless feature (⊥2) corresponds to the double excitation of the vertical vibration. The short dashed lines are the calculated dispersion curves for vertical (⊥) and longitudinal (L) motion assuming a perfectly hexagonal Xe lattice. The solid lines are the dispersion curves with the actual lattice distortion taken into account. The long dashed line indicates the substrate RW [94Zep].
1.0 M
Fig. 7. HREELS data for the dispersion curves of the CO induced modes on Ir(100). The data are nearly identical for adsorption on the (1x1) surface (crosses) and on the (5x1) reconstructed phase (squares). The main origin of the wavevector dependence of the internal CO stretch frequency is the long range dipoledipole interaction [91Kis]. (ξ = Q||/1.64 Å–1)
X
1.0 0.5 1.5 Wavevector qII [Å−1]
〈100〉
M
Ag(100) Phonon energy hω [meV]
20
L L 10
R R
SH HAS EELS
Fig. 9. Ag(100). Surface phonon dispersion of the bare Ag surface. [91Che, 90Mor, 94Bun].
0 1.0
0.5
0 0.5 Wavevector qII [Å−1]
1.0
1.5
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.5-68]
10
4.5 Surface phonon dispersion
Γ
X
X
Γ
M‘
15
〈110〉
Ag(100) c (2×2)Cl
4.5-29
M‘ 〈001〉
10
Phonon energy ∆ E [meV]
Phonon energy ∆E [meV]
5
0
5 0 −5
−5 −10 −10 −1.0
− 0.5
0
0.5
−15
1.0
(1 1) Wavevector qII [Å−1]
( 23 32 )
Wavevector qII [Å−1]
( 12 12 )
Fig. 10. Ag(100)-c(2x2) Cl. Extended zone plot of the phonon energies measured by HATOF [83Lam,84Lam]. Negative frequencies correspond to phonon annihilation. The dashed lines indicate the bulk band edge, while the solid lines are the surface modes S1 and S4 as calculated by Castiel et al. [76Cas] for bare Ag(001) surface. Along Γ Μ the data were recorded around the ( 1 1 ) diffraction peak.
18
Γ
[ ξ 0]
Γ
X
15
Ag(110)
12 9 MS 0 6 S1
MS 7
0 0.2
0.8 0.6 0.4 Red.wavevector coord. ξ
9
6
S3
S1
3
3
0 [0 0] a
Ag(110)
Y
12 MS 7
Phonon energy hω [meV]
Phonon energy hω [meV]
15
[ 0ξ ]
1.0 [1 0]
b
0 0 [0 0]
0.2
0.8 0.6 0.4 Red.wavevector coord. ξ
1.0 [0 1]
Fig.11a, b. Ag(110). Surface phonon dispersion of the clean Ag(110) surface measured by HATOF along (a) Γ − Χ and (b) Γ − Υ [87Bra1, 87Bra2, 89Tat]. The solid line in (a) is the result of a LDM [89Tat].
Lando lt -Bö rnst ein New Ser ies III/42A2
4.5-30
4.5 Surface phonon dispersion
[Ref. p 4.5-68
10
Ag(110)p(2×1)O Phonon energy hω [meV]
8 MS 7 6 S3 4 S1 2
Fig. 12. Ag(110)-p(2x1)O Surface phonon dispersion curves measured by HATOF (open circles: experimental data, solid lines: LDM fit for the missing row reconstructed surface) [89Yan,87Bra].
MS 0
0 X‘
0.4
0.2
0.2 Γ −1 Wavevector qII[Å ]
Γ
0.4
0.6
Y
X‘
10 Γ
Y
Ag(110)p(3×1)O
8
Phonon energy hω [meV]
Phonon energy hω [meV]
12
6
4
2
0 0 a
0.1
0.2 −1 Wavevector qII[Å ]
9 B 6
0.4 b
3 3 2 1 1 2 2 3 3 3 2 2 3 3 3 2 2 1 1 1 3
1
3
0 0.3
A
0
0.1
0.2
0.3 0.4 0.5 −1 Wavevector qII[Å ]
2
0.6
0.7
Fig. 13a, b. Ag(110)-p(3x1)O. Surface phonon dispersion curves measured by HATOF along (a) Γ − X (folded direction) and (b) Γ − Y (experimental data: open circles - intense structures; triangles - weak features). The lines represent the result of a LDM assuming a missing row reconstructed surface and the bulk value of the force constant between the substrate atoms. Inset in (b): added row model of the reconstructed surface. The Ag atoms are numbered starting from the surface layer and the O atoms are represented by filled circles. Main reference: [93Bra]. Further references: [90Bra1, 90Bra2, 91Bra].
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.5-68]
4.5 Surface phonon dispersion
4.5-31
400
50
400 Al(111)
Al(111) (√3×√3) R 30° Na
40
40 300
300
200
R1
100
10
30
S1
100
10 S1
R2
Γ a
0.5
K’ −1 Wavevector qII[Å ]
0
0
0
0
Phonon energy hω [cm−1]
200 20
Phonon energy hω [meV]
Phonon energy hω [cm−1]
Phonon energy hω [meV]
30
1.0
Γ
M b
0.5
K’ −1 Wavevector qII[Å ]
1.0 M
Fig. 14a, b. Al(111) (√3 x √3) Na. Surface phonon dispersion determined by HREELS along Γ M . (a) clean surface: HREELS data: open circles and LDM results; (b) adsorbate covered surface (HREELS: open circles) and LDM calculation assuming a substitutional adsorption site for the Na adatoms. Shear vertically polarised surface modes are represented by thick solid lines, shear horizontally polarized surface modes by full squares [97Nag].
Lando lt -Bö rnst ein New Ser ies III/42A2
4.5 Surface phonon dispersion 400
Al(111) (2×2)Na
140
[Ref. p 4.5-68 [ξ ξ ]
X
40
Γ
[ξ 0 ]
M 4.0
Cu(100) Phonon wavenumber ν [cm−1]
120
3.5 3.0
100
300
Phonon energy hω [cm−1]
Phonon energy hω [meV]
30
1.0
M’ −1 Wavevector qII[Å ]
0.5
M
10
5
Phonon energy hω [meV]
Phonon energy hω [meV]
〈110〉
〈100〉
0 −5 −10 −15 − 2.0
1.0 [1 0]
10
Ag(100) c (2×2)CO 5
0 0 0 [0 0] Red.wavevector coord. ξ
← Fig. 15. Al(111) (2x2) Na. HREELS data for the high coverage phase as measured by HREELS (filled circles) along Γ M . The open circles and solid lines represent data and LDM calculations for bare Al(111) along the same direction [97Nag].
0 0.5
1.0
Fig. 16. Cu(100). Surface phonon spectrum for the bare surface [86Wut]. The circles are the experimental HREELS data points, dashed and solid lines are the result of the LDM fit with bulk force constants and with modified surface force constants, respectively.
S1
Γ
40
[ 12 12 ]
100
0
1.5
0 0.5
R1
10
2.0 60
20
200 20
2.5
80
Phonon frequency ν [THz]
4.5-32
2.0 1.0 0 Γ Wavevector qII [Å−1]
−5 −10 −15
RW −1.0
0
4.0
3.0 M
−1.0
1.0 0 Γ Wavevector qII [Å−1]
2.0 X
a b Fig. 17. Cu(100) c(2x2) CO. Surface phonon spectrum as measured by HATOF. The solid and the dashed curves are the dispersion of the RW for the clean surface and its backfolded branch. Losses corresponding to the excitation of the RW are plotted as open circles. Filled and open squares denote the frustrated translation mode of the CO molecules in the c(2x2) overlayer and at defects [95Ell].
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.5-68]
4.5 Surface phonon dispersion
Cu(100) c(2×2)N
800
4.5-33
Cu(100) √2×√2 O
24
21
400
12 N
300
9
200
6
Phonon frequency ν [THz]
700
T
Phonon wavenumber ν [cm−1]
NII
O
1st Cu 〈110〉
a 3
100
2nd Cu
RW 0 Γ
0 0.2
0.8 0.6 0.4 Red.wavevector coord. ξ
X
Fig. 18. Cu(100) c(2x2) N. Surface phonon dispersion as measured by HREELS. The shaded area indicates the continuum of bulk modes [86Fra]. The lines indicate surface substrate phonons and adsorbate modes. (ξ = q||/1.23 Å–1) 800
Cu(100)(√2×2√2 ) O
Fig. 19. Cu(100) (√2 x 2√2) O. Schematic model of the missing row reconstructed Cu(100) c(2x2) O phase.
Cu O
700
〈100〉
b
400
Γ
X
12
Cu(100) p(2×2)S ω (S ) 9 ω (S ) T
300
500 400 300 200
Phonon frequency ν [THz]
Wavenumber ν [cm−1]
II
Phonon wavenumber ν [cm−1]
600
200
6
100
3 ω (S4 )
S1
100
0
0
0 0 Γ
0.25
0.50 0.75 M‘ Red.wavevector coord. ξ
1.00 M
Fig. 20. Cu(100) (√2 x 2√2) O. Surface phonon dispersion as measured by HREELS, reported on an extended zone scheme. The insets indicate schematically the motion of the adatoms for each mode. TheRW and two resonances are observed. The RW branch shows no dispersion in the second Brillouin zone [89Wut1, 89Wut2]. (ξ = q||/1.74 Å–1)
Lando lt -Bö rnst ein New Ser ies III/42A2
0
0.5 Red.wavevector coord. ξ
1.0
Fig. 22. Cu(100) p(2x2) S. Surface phonon spectrum as measured by HREELS. Lines are surface modes according to a LDM model. The shaded area represents the projection of the bulk phonons on the SBZ [87Fra]. (ξ = q||/1.23 Å–1)
For Fig. 21, see next page
4.5-34
12
4.5 Surface phonon dispersion
Γ
Γ
X
Cu(100) PF3
isolated PF3
M Γ
9
[Ref. p 4.5-68
X
RW
[100]
6
[110]
FTx 3 a
Phonon energy hω [meV]
0
c(4×2) PF3
RW2 9 RW1
6
FTx 3 b
0
RW2 9
RW 1
6
[110] [110]
3 c
0 0
1.23 −1 Wavevector qII[Å ]
2.46
Fig. 21a-c. Cu(100) c(4x2) PF3. Surface phonon dispersion measured with HATOF: (a) isolated PF3 molecules (exposure 0.4 langmuirs PF3), (b) c(4x2) PF3 overlayer, (c) results of a LDM assuming the bulk radial force constant between nearest neighbour substrate atoms [99Bra].
Mo(110)
250
Phonon energy hω [cm−1]
200
150 Fig. 23. Mo(110). Surface phonon dispersion of the clean surface [97Krö, 98Krö1, 98Krö2, 92Hul2].
100
( S Γ :ξ = q||/1.22 Å–1),
50
( Γ H :ξ = q||/1.50 Å–1) ( N Γ :ξ = q||/1.41 Å–1)
0 1 S
0.5
0 0 0.5 1 1 Γ Γ H N’ N Red.wavevector coord. ξ
0.5
0 Γ
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.5-68]
4.5 Surface phonon dispersion
4.5-35
240 200
Mo(110) H
“(2×1)”H
160 120 80 40 0
Phonon energy hω [cm−1]
240 (2×2)H
200 160 120 80 40 0 240
(1×1)H
200 160 120 80 40 0
1 S
0.5
0 0 0.5 1 1 Γ Γ H N’ N Red.wavevector coord. ξ
0.5
0 Γ
Fig. 24. Mo(110) H. Surface phonon dispersion for the different H superstructures on Mo(110) along three directions of the SBZ. Triangles indicate HREELS data for the RW, circles and diamonds indicate surface resonances. The dots denote HATOF data. A shallow dip is observed for the H saturated phase along N Γ at a critical wavevector of 0.93 Å–1 both for the RW wave and for the L resonance [93Hul2, 97Krö]. ( S Γ :ξ = q||/1.22 Å–1), ( Γ H :ξ = q||/1.50 Å–1) and ( N Γ :ξ = q||/1.41 Å–1)
Lando lt -Bö rnst ein New Ser ies III/42A2
4.5-36
4.5 Surface phonon dispersion
1300
[Ref. p 4.5-68
Mo(110) H
1200 (2×2)H
Phonon energy hω [cm−1]
(1×1)H
“(2×1)”H
1100 1000 900 Fig. 25. Mo(110) H. Dispersion of the H induced modes for the different H phases as measured by HREELS along Γ H
800 700
[97Krö]. (ξ = q||/1.50 Å–1)
0
250
0.3 0.6 0.9 1.2 0 0.3 0.6 0.9 0 Red.wavevector coord. ξ
0.2
0.4
0.6
Mo(110)p(2×2)0 Fig. 26. Mo(110) p(2x2) O. HREELS data for the Mo(110) p(2x2)O phase recorded for a crystal temperature T=110 K. The RW, the L-mode and the dipole active surface resonance are depicted as triangles, circles and diamonds, respectively. The solid triangles and the dots along ( Γ H ) were measured with the crystal at room temperature [98Krö1, 98Krö2].
Phonon energy hω [cm−1]
200
150
100
( S Γ :ξ = q||/1.22 Å–1),
50
( Γ H :ξ = q||/1.50 Å–1)
0 1 S
0.5
0 0 0.5 1 1 Γ Γ H N’ N Red.wavevector coord. ξ
0.5
0 Γ
( N Γ :ξ = q||/1.41 Å–1)
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.5-68]
[ ξξ ]
Ni (100)
280
T
2
nd
2
2
4.5-37
M
nd
R6
+ 2nd II
[ξ 0]
Γ T
X
nd
nd
2 II
T
320
4.5 Surface phonon dispersion
9 8
nd
200
2 II 2
7
R1 S 2
R2
nd 2 II
st
1 II
6
nd T
Phonon wavenumber ν [cm−1]
R5
st
1 II
5
160
R4
st
R3
1 II
4
120 S1 80
3
S4
2
40
1
0 0.5 [ 12 12 ]
0.3
0.4
0.2
0.1
0 0 0.2 0.4 [0 0] Red.wavevector coord. ξ
0.6
0.8
0 1.0 [1 0]
Phonon frequency ν [THz]
S6
240
nd T
2
Fig. 27. Ni(100) Surface phonon dispersion as measured by HREELS [86Roc2]. The solid lines are surface modes, the dashed lines surface resonances according to LDM fit with modified force constants at the surface. 1 and 2 indicate modes with largest amplitude in first and second crystal layer, respectively.
Ni(100)- C 725 c
700
c II super structure p4g
400 375 c
T
Phonon energy hω [cm−1]
675
350
b Fig. 28. Ni(100) C. Carbon coverage dependence of the frequency of the (S4) RW at X (a), of the Ni-C stretch
325 S4
140
a
120 0
0.1
Lando lt -Bö rnst ein New Ser ies III/42A2
0.2 0.3 Carbon coverage θ [ML]
0.4
0.5
at Γ (b) and of the frustrated translation of the C atoms parallel to the surface (c) at ξ = 0.3. The crystal was annealed to 600 K. [87Roc].
Ni(100) p4g C
0.8 c II
X
c II
800
21
700
15 c
T
Wavenumber ν [cm−1]
500
24
12
400
9
300 R4 R3
200 R2
X’
X
Ni(100) p4g N
24
21
N II
500
15 N
400
12 R2
300
9
200
6
6 R1
100
3
S4
0.2
Γ
R1
100
Γ
[Ref. p 4.5-68
Phonon frequency ν [THz]
700
0.4 X’ 0.6
0.2
Phonon wavenumber ν [cm−1]
Γ
Phonon frequency ν [THz]
800
4.5 Surface phonon dispersion
T
4.5-38
0.8 0.6 0.4 Red.wavevector coord. ξ
Γ
X
Fig. 29. Ni(100) p4g (2x2) C. Dispersion of the surface phonons as mea- sured by HREELS. The data are reported for an extended zone scheme, the zone boundary being at X ′ [87Roc]. The lines are the result of a LDM. (ξ = q||/1.26 Å–1)
3
RW
X’ Wavevector qII [Å−1]
X
Fig. 30. Ni(100) p4g (2x2) N. Dispersion of the surface phonons for the p4g reconstructed c(2x2) phase of N along Γ − X . The experimental points, measured by HREELS, are reported for an extended zone scheme, the zone boundary being at X ′ [86Dau, 88Rah]. The lines are the result of a LDM. The squares denote surface resonances, the circles surface modes.
For Figs. 31 and 32, see next pages
150
Ni(100) O ω S (X)
Phonon energy hω [cm−1]
4
100 c(2×2)
50
p(2×2)
c(2×2)
Fig. 33. Ni(100) O. Oxygen coverage dependence of the RW frequency at X for a surface which was annealed to 400 K after oxygen adsorption (crosses) and for the non annealed system (triangles and circles). The dashed line indicates the expected reduction of ωS 4 ( X) given by mass loading. The solid lines are guides to the eye. The coverage regions giving ordered superstructures are shown, too [85Roc].
0
15
30 45 Oxygen coverage θ [%]
60
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.5-68]
4.5 Surface phonon dispersion
Γ 700
X’
X
Ni(100) - p(2×2)O O II
600
21
12
R
200
6
100
S4
0
0.5 Wavevector qII [Å−1]
a
[110]
Phonon frequency ν [THz]
O
T
Phonon wavenumber ν [cm−1]
18
400
3
Fig. 31a, b. Ni(100) p(2x2) O. Surface phonon dispersion measured by (a) HREELS and (b) HATOF. The HREELS data are reported in an extended zone scheme, the zone boundary of the p(2x2) structure being at X ′ [84Sze]. The lines are the result of a LDM. In (a) the backfolded branches are reported as dashed lines. Reference [84Sze, 91Ber, 86He]. Further references [90Col, 85Sze].
1.0
[001]
Ni(100) - p(2×2)O Phonon energy hω [cm−1]
15
Phonon energy hω [meV]
4.5-39
100 10
50 5
Γ 0.1 0.2 0.3 0.4 0.5 b
Lando lt -Bö rnst ein New Ser ies III/42A2
X’ M’ 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 Γ Wavevector qII [Å−1]
4.5-40
4.5 Surface phonon dispersion
500
[Ref. p 4.5-68
15
400
12
300
9
200
6
100
3
0 Γ
a
15
0.5 Red.wavevector coord. ξ
[110]
Phonon frequency ν [THz]
Phonon wavenumber ν [cm−1]
Ni(100) - c(2×2)O
Fig. 32a, b. Ni(100) c(2x2) O. Surface phonon dispersion measured by (a) HREELS and (b) HATOF. The different symbols in (a) denote the different surface modes and resonances. The solid lines are the result of a LDM model including the surface stress field. Apart from the Rayleigh wave an additional mode (dashed curve) is observed by HATOF along both crystallographic directions which shows very little dispersion. Such mode is ascribed to the high concentration of oxygen vacancies on the studied surface. Main references [83Leh, 84Rah, 91Ber]. Further references [86Leh, 90Yan]
1.0 X
[100]
Ni(100) - c (2×2)O
10
50 5
Γ b
0.2 0.4 0.6 0.8 1.0 1.2 X
Phonon energy hω [cm−1]
Phonon energy hω [meV]
100
0.8 0.6 0.4 0.2 Γ M’ Wavevector qII [Å−1]
Lando lt -Börnst ein New Ser ies III/42 A2
12
Geometric structure of Ni(110)/CO(2×1)p2mg
ω
R = 1.45 Å T
ωS
S
Unit cell g ∆Y
T
ω IIS
6
200
First Brillouin zone
Cs
Γ
3.52Å
S6
S
X
[110]
Phonon frequency ν [THz]
Phonon wavenumber ν [cm−1]
ω
4.98Å
ω IIS 9
300
4.5-41
−1
Ni(100) - c(2×2)S
T
400
4.5 Surface phonon dispersion
0.63Å
Ref. p. 4.5-68]
Y
0.893Å
[001]
−1
ω S4 100
3
0
0.5 Red.wavevector coord. ξ
1.0
Fig. 34. Ni(100) c(2x2) S. Surface phonon dispersion measured by HREELS. Crosses denote the RW, triangles and squares the parallel and the vertical vibration of the adsorbate, respectively. The open circles stay for a surface resonance at 4.5 THz and for the S6 mode above 6 THz. The shaded area is the projection of the bulk phonon bands on the SBZ. The lines are the result of a LDM calculation. References [85Leh, 86Leh, 90Yan]. (ξ = q||/1.26 Å–1)
Fig. 36. Ni(110) p2mg (2x1) CO. The (2x1)p2mg adsorption geometry is shown, together with the relevant lattice parameters and symmetry elements and SBZ [90Voi2]. The CO coverage is 1ML.
For Fig. 35 and 37, see next pages [110]
Ni(110)H
[001] 1
1
2
[110]
[001]
cS x
g a
y
cS b
species II
Fig. 38a, b. Ni(110) H. Models for (a) the (2x1) H and (b) the reconstructed (1x2) H covered surfaces. Open and closed triangles indicate the two H adatom moieties.
Lando lt -Bö rnst ein New Ser ies III/42A2
4.5-42
[ξ 0]
Γ
X
Ni(110)
320
[Ref. p 4.5-68
[0 ξ]
Γ
Y
9
9
280
280 8
6
160
5 4 S1
3
Phonon wavenumber ν [cm−1]
Phonon wavenumber ν [cm−1]
MS 7 200
120
240
7
Phonon frequency ν [THz]
S7
240
8
80
0
0 [0 0]
a
0.2
0.4 0.6 0.8 Red.wavevector coord. ξ
6
160
5 4
120
S3
80
2 40
7
MS 7 200
1
40
0 1.0 [1 0]
0 b
0 [0 0]
S1
3
Phonon frequency ν [THz]
320
4.5 Surface phonon dispersion
2 1 0
0.2
0.4 0.6 0.8 Red.wavevector coord. ξ
1.0 [1 0]
Fig. 35. Ni(110). Surface phonon dispersion for clean Ni(110) [87Leh2].
2000
Ni(110)/CO(2×1) p2 mg
1800
Phonon wavenumber ν [cm−1]
[001]
[110]
Γ10 X Γ
S Y
600
400
200
1.0 0.8 Y
0.6 0.4 0.2
0.5 1.0 0 X Γ Red.wavevector coord. ξ
1.5
2.0 Γ10
Fig. 37. Ni(110) p2mg (2x1) CO. Surface phonon dispersion as measured by HREELS [90Voi2] reported for an extended zone scheme. Only modes symmetric with respect to glide reflection are observable in the first SBZ along Γ − X , and the antisymmetric ones in the second. ( Y Γ : ξ = q||/0.893 Å–1), ( Γ Γ10 ξ = q||/0.63 Å–1).
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.5-68] 90
4.5 Surface phonon dispersion 140
Ni(110) H
A1(S3) Phonon at Y
Phonon wavenumber ν [cm−1]
Phonon wavenumber ν [cm−1]
B1(S1) Phonon at Y
80
70
60 0
120
1.5
0
0.5 1.0 H coverage θ [ML]
b
1.5
S1 Phonon at X
135 130
125
Fig. 39a-c. Ni(110) H. Hydrogen coverage dependence of the phonon frequencies of: (a) S1 and (b) A1 at Y ; (c) of the S1 mode at
120
115
X . References [89Voi, 87Leh1]. 0
0.4
0.2
c
0.6 0.8 1.0 H coverage θ [ML]
1.2
1.4
1.6
Ni(110) p2mg(2×1) H
36
H
T
Phonon wavenumber ν [cm−1]
1200
900
27 H II
600
18
300
9
S3 S1 1.0 Y
0.8
Lando lt -Bö rnst ein New Ser ies III/42A2
0.6
0.4
0.2
0 0.2 0.4 Γ Red.wavevector coord. ξ
0.6
0.8
1.0 X Γ10
Phonon frequency ν [THz]
Phonon wavenumber ν [cm−1]
140
130
110
0.5 1.0 H coverage θ [ML]
a
4.5-43
Fig. 40. Ni(110) p2mg (2x1) H. Surface phonon dispersion measured by HREELS at 1ML coverage [89Voi]. ( Y Γ : ξ = q||/0.893 Å–1) ( Γ Γ10 : ξ = q||/1.26 Å–1).
4.5-44
4.5 Surface phonon dispersion
[Ref. p 4.5-68
Ni(110) (1×2) H Phonon wavenumber ν [cm−1]
900
27
600
18
300
9
100
3
1.0 Y Γ01
800
0.8
0.6
0.4
0.2
0.6
0 0.2 0.4 Γ Red.wavevector coord. ξ
Ni(110) - (2×1) O
0.8
Fig. 41. Ni(110) (1x2) H. Surface phonon dispersion measured by HREELS for the reconstructed phase obtained at H saturation coverage (1.5 ML) [89Voi, 87Leh1, 87Iba]. ( Y Γ : ξ = q||/0.893 Å–1) ( Γ X : ξ = q||/1.26 Å–1).
1.0 X
40
24
Phonon frequency ν [THz]
36
1200
[ξ0]
Γ
M
Ni(111)
35 21
300
9
200
6
30 Phonon energy hω [meV]
X‘ Phonon frequency ν [THz]
Phonon wavenumber ν [cm−1]
700
25 R1
20 15
S1
10 5 0 0 [00]
100
S2
0.2
0.4 0.6 Red.wavevector coord. ξ
0.8
1.0 [10]
3
1.0 0.8 0.6 0.4 0.2 0 0.2 0.4 0.6 0.8 1.0 X Γ Y Red.wavevector coord. ξ
Fig 43. Ni(111). Surface phonon dispersion for the bare Ni(111) surface [90Men1, 90Men2]. The solid and dashed lines are the result of a LDM assuming the bulk value for the force constants between surface atoms and modified constants, respectively.
Fig. 42. Ni(110) p(2x1) O. Surface phonon dispersion determined by HREELS [90Voi2, 91Yan]: open circles data recorded at T=120 K, filled circles at T=300 K. ( Y Γ : ξ = q||/0.893 Å–1) ( Γ X : ξ = q||/1.26 Å–1).
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.5-68]
4.5 Surface phonon dispersion
80
4.5-45
Ni(111) p(2×2) O
New position of oxygen bonded atoms Original position of the first nickel layer New position of non - oxygen bonded atoms
Phonon energy hω [meV]
70 60
40 30 20 10 0
a
final parameters experimental data data regression
50
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Red.wavevector coord. ξ
Fig. 45. Ni(111) p(2x2) O. Surface phonon dispersion measured by HREELS. [94Tis]. Γ
M’
M
b
Fig. 44a, b. Ni(111) p(2x2) O. (a) Schematic views of Ni(111) p(2x2) O: upper panel from above; lower panel: cut through the crystal along the dashed line. The arrows indicate that the three nickel atoms bonded to the oxygen atom are shifted by 0.07 Å along the arrow direction. (b) SBZ [90Gri].
15
Phonon energy hω [meV]
Pb (111) d-octane
10
AOP 1
FTz
5
Fig 46. Pb(111) d-octane. Surface phonon spectrum as measured by HATOF [96Fuh]. FTz and AOP1 are the frustrated translation vertical to the surface, and an internal vibration of d-octane, respectively.
RW 0 K
Lando lt -Bö rnst ein New Ser ies III/42A2
Γ Wavevector q
M
4.5-46
4.5 Surface phonon dispersion
Γ
Σ
M
Σ‘
K
[Ref. p 4.5-68
Γ
T
Pt (111) (1×1) H
24
Phonon energy hω [meV]
20
16
12
8
Fig. 47. Pt(111) (1x1) H. Surface phonon dispersion on Pt(111) (1x1) H was measured by HATOF. Filled circles are HATOF data points, lines are the result of LDM calculations [89Bor].
4
0 0
12
0.4
0.8
1.2 1.6 2.0 1.2 Red.wavevector coord. ξ
Γ
M0
0.8
12
0.4
0
Γ
M0
Pt(111) p (2×2) O 10 Phonon energy hω [meV]
Phonon energy hω [meV]
10 8 6 4
8 6 4 2
2
0
0 0
0.2 0.4 Wavevector qII [Å−1]
0.6
0
0.2 0.4 Wavevector qII [Å−1]
0.6
Fig. 48. Pt(111) p(2x2) O. Surface phonon dispersion of the p(2x2) overlayer as measured by HATOF along Γ − M . Open circles refer to data recorded in the first Brillouin zone, while filled circles are for events detected in the second Brillouin zone. The backfolded mode at 10 meV is observed only in the first zone. The result of a LDM is reported in the right panel. Reference [86Ker1, 86Ker2, 87Sze, 87Ker].
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.5-68]
4.5 Surface phonon dispersion
4.5-47
12 12
Pt(111) (1×1) O 10 k12 = 1.1k Phonon energy hω [meV]
Phonon energy hω [meV]
10 8 6 4
8 k12 = 0.8k 6 4 clean Pt(111) Pt(111)”oxide”
2
2
0
0 0 Γ
0.2
0.4
0.6 0.8 1.0 1.2 Wavevector qII [Å−1]
1.4
0 Γ
0.2
0.4
0.6 0.8 1.0 Wavevector qII [Å−1]
1.2
M b a Fig. 49a, b. Pt(111) (1x1) O. Surface phonon dispersion of the (1x1) O phase [87Neu, 86Ker2], along (a) Γ Κ and (b) Γ Μ open symbols: bare surface, filled symbols oxygen saturated phase. In (b) the dashed and solid curves are the result of a LDM implying an increase of 10% and a decrease by 20% of k12, respectively. Γ
10
X‘
K
Γ
10
Y‘
Fig. 50a, b. Rh(110)(2x2) O. Surface phonon dispersion, as measured by HATOF [93Bel], for: (a) the bare (1x2) reconstructed surface; and (b) for the oxygen covered Rh(110) surface. The oxygen coverage is 0.5 ML.
8
Phonon energy hω [meV]
Phonon energy hω [meV]
Rh(110) (1×2)
6 4 2
8 6 4 2
0
0 0
a 10
0.4 0.2 Wavevector qII [Å−1]
Γ
0
0.6
Y‘
10
0.4 0.2 Wavevector qII [Å−1]
Γ
0.6
X‘
6 4
S‘
10
6 4
8 6 4
2
2
2 0
0 0 b
Γ
12
8
Phonon energy hω [meV]
Phonon energy hω [meV]
Phonon energy hω [meV]
Rh(110) (2×2)O 8
14
0.4 0.2 Wavevector qII [Å−1]
Lando lt -Bö rnst ein New Ser ies III/42A2
0.6
0 0
0.4 0.2 Wavevector qII [Å−1]
0.6
0
0.6 0.4 0.2 Wavevector qII [Å−1]
0.8
4.5-48
35
4.5 Surface phonon dispersion
〈110〉
Γ
〈112〉
M
K
[Ref. p 4.5-68
Γ
Rh(111)
Phonon energy hω [meV]
30 25 LR
LR 20
B
15 10
RW
K
5
a
Γ
0 0 35
0.5
1.0
1.35
K
M
1.0
0.5 〈112〉
0 Γ
Rh(111)H(1×1) S2
30
Phonon energy hω [meV]
RW
〈112〉
1.56
〈110〉
Γ
M
〈110〉 M
S2
25
LR
LR 20
B’
B’
15 10
RW
RW
5 0 0 b
0.5
1.0
1.56 1.35 Wavevector qII [Å−1]
1.0
0.5
0
Fig. 51a, b. Rh(111) (1x1) H. (a) Surface phonon spectrum for the bare Rh(111) surface. The dashed lines represent the limits of the projection of the vertically and longitudinally polarised bulk phonons on the surface [95Wit]. (b) The surface phonon dispersion in presence of the (1x1) H overlayer as measured by HATOF [95Wit1]. The inset reports the SBZ.
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.5-68]
[112]
M
20
Phonon energy hω [meV]
4.5 Surface phonon dispersion
Γ
[110]
4.5-49
K
Rh(111)(2√3×3)C 6 H6
15
10 H
C
C
H
5
0 -2.0
-1.5
-1.0
-0.5 0 0.5 Wavevector qII [Å−1]
1.0
1.5
2.0
Fig. 52. Rh(111) (2√3 x 3) C6H6. The phonon dispersion curve as measured by HATOF [93Wit1, 93Wit2]. See inset for the adsorption geometry.
For Fig. 53, see next page
12
[ξ 0]
Γ
W(100) Phonon energy hω [meV]
10
M T = 450K 280K
8 6 4 2
Fig. 54. W(100). Surface phonon dispersion of bare W(100) as measured by HATOF at two surface temperatures [87Ern, 89Ern].
0 0 [0 0]
0.2
Lando lt -Bö rnst ein New Ser ies III/42A2
0.4 0.8 0.6 Red.wavevector coord. ξ
1.0 [1 0]
4.5-50
35
4.5 Surface phonon dispersion
Γ
[1120]
Γ
[1100]
M
K
[Ref. p 4.5-68
Ru(0001)
Phonon energy hω [meV]
30 25 20 LR
LR
15 10
K
RW 5
Γ
M
[1120]
RW
M [1100]
0 0
a 35
0.5
Γ
1.0 [1120]
1.55
1.35
K
M
1.0
0.5 [1100]
0 Γ
Ru(0001)(1×1)H
Phonon energy hω [meV]
30 S2
25
S2
20 15 10
RW
RW
5 0 0 b
0.5
1.0
1.55 1.35 Wavevector qII [Å−1]
1.0
0.5
0
Fig. 53a, b. Ru(0001) (1x1) H. (a) Surface phonon dispersion [97Bra]. The lines are the result of a LDM calculation with bulk force constants. (b) Surface phonon dispersion curve in presence of the (1x1) H overlayer as determined by HATOF. The lines are the result for surface phonon and resonances of a LDM fitting the bulk phonon dispersion [97Bra]. LR denotes the longitudinal resonance. The SBZ is reported in the inset in (a).
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.5-68]
Phonon energy hω [meV]
30
4.5 Surface phonon dispersion
4.5-51
W (100) (1×1) H
20 L Set Ι
10
RW
L
RW
0 Γ
M
X
Γ
Fig. 55. W(100) (1x1) H. HATOF data for the surface phonon dispersion [92Ern]. The lines are the result of a LDM calculation.
Wavevector qII
250
W (110)
Phonon energy hω [cm−1]
200
150
100
50
0 0 Γ
0.5
1.0
1.5 H
2.0 N’
1.0 N Wavevector qII [Å−1]
0.5
0 Γ
0 Γ
0.5
1.0 S
Fig. 56. W(110). Surface phonon dispersion for the clean W(110) surface [94Bal1, 92Hul1, 92Hul2]. HREELS data are reported by open symbols, HATOF data are given by the small filled dots. Different symbols for the HREELS data denote different phonon branches.
Lando lt -Bö rnst ein New Ser ies III/42A2
4.5-52
4.5 Surface phonon dispersion
[Ref. p 4.5-68
W (110)p (2×1) H
200
25
20
150
15 100 10 50 5 0
0 (2×2) H
25
20 150 15 100 10 50
Phonon energy hω [meV]
Phonon energy hω [cm−1]
200
5 0
0
200
(1×1) H
25
20 150 15 100 10 50
0 S
5 0 1.0
0.5
0 Γ
0 Γ
0.5
1.0
Wavevector qII [Å−1]
1.5 H
2.0 N’
1.0 N
0.5
0 Γ
Fig. 57. W(110) H. Phonon dispersion curves for the different H phases, measured along ( Γ − S ) ( Γ − Η ) and ( Γ − Ν ). The data were recorded at T=110 K. The data for the (1x1) H phase along ( Γ − Η ) show evidence for the phonon instability. No temperature dependent frequency shifts were observed. HREELS data are reported as open symbols, HATOF data as filled circles. Main references [92Hul1, 92Hul2, 96Bal, 94Bal1, 94Bal2].
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.5-68]
4.5 Surface phonon dispersion
W (110) (1×1) H H
4.5-53
W(110)(1×1) H
[001]
-1
P
0.9 Å
P
N
N
Γ
[110]
Phonon energy hω
[111]
Fig. 58. W(110) (1x1) H. Position of the critical wavevectors at which the phonon anomaly is observed. The dotted lines indicate the directions along which HATOF data were recorded. Γ
111
0.5
1252
546
768
W (110) H
1323 1056 1223
644 750 885
113
N
Fig. 59. W(110) (1x1) H. Experimental HREELS (dots) and HATOF (diamonds) data are compared with the result of first principle calculations for the substrate modes of the (1x1) H phase [96Bun].
(2×2)H off-spec ×20
0 (1×1)H off-spec 1306
850
Intensity I [1000 c/s]
H
×7
0 2
(2×1)H off-spec
Wavevector qII
2000
850
0 1
1306
×2000
(2×1)H off-spec ×40
0 0
Lando lt -Bö rnst ein New Ser ies III/42A2
500 1500 1000 Energy loss E loss [cm−1]
2000
Fig. 60. W(110) H. HREELS spectra showing the anomalous line shape of the H- and D-induced energy losses for the different phases [94Bal2].
4.5-54
4.5 Surface phonon dispersion
1300
1400
W(110)p(2×1)H
W(110)(2×2)H
1300
Phonon energy hω [cm−1]
1200
Phonon energy hω [cm−1]
[Ref. p 4.5-68
1200
800
700
600
700 600
500 0.5
0 Γ
a
800
1.0 Wavevector qII [Å−1]
500
2.0
1.5 H
b
0 Γ
0.2
0.6 0.4 Wavevector qII [Å−1]
0.8
1.0 H‘
1400
W(110)(1×1)H
Fig. 61a-c. W(110) p(2x1) H. Dispersion of the H induced modes for: (a) p(2x1) H phase, three modes are observed, corresponding to the three degrees of freedom of the adsorbate; (b) (2x2) H phase and (c) (1x1) H phase. The stretch vibration is at 163 meV and displays a stronger dispersion than for the other H phases [96Bal].
Phonon energy hω [cm−1]
1300 1200
800 700 600 500
c
0.5
0 Γ
2.0
1.0 1.5 Wavevector qII [Å−1] H
C(100)(2×1)H H
Fig. 62a, b. C(100) H. Optimised surface structures for (a) C(100) (2x1) H and (b) C(100) (1x1) H and surface Brillouin zones.
C(100)(1×1)2H H
C
C
C
ky Γ2×1
H
ϑ
rCH
J 2×1 kx
d12
C
rCC
ky
H
Γ1×1
C
J 1×1 kx
J ‘2×1 K2×1 a
H
H
J ‘1×1
d12 d23
H H r CH ϑ C
K 1×1
b Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.5-68]
90
4.5 Surface phonon dispersion
C(001)(2×1)H
4.5-55
Sa 360
Ss 80
Bs+
B s1
S TOΓ
B a1
Br1
40
160 STOX
B s-
30
120
B s2 20
80
0
90
Γ2×1
Fig. 63. C(100) (2x1) H. Calculated surface phonon dispersion at 1 ML coverage [96San]. Shaded area: projection of bulk phonon bands; solid curves dispersion of surface modes and resonances.
RW
R TAX R TA B a2
10
Phonon energy hω [meV]
Phonon frequency ν [THz]
320
40 B a2 J’2×1
K 2×1 Wavevector q
J 2×1
0 Γ2×1
C(001)(1×1)H Sa
360
Ss
80
Bs+
Bs
40
160 BΓ
30
B s-
120
B a+ B sr
20
80
10
40 B a-
0
Γ2×1
Lando lt -Bö rnst ein New Ser ies III/42A2
RW J’2×1
K 2×1 Wavevector q
J 2×1
0 Γ2×1
Phonon energy hω [meV]
Phonon frequency ν [THz]
320
Fig. 64. C(100) (1x1) H. Calculated surface phonon dispersion at 2 ML coverage [96San]. Shaded area: projection of bulk phonon bands; solid curves dispersion of surface modes and resonances.
4.5-56
90
4.5 Surface phonon dispersion
C(111)(1×1)H
[Ref. p 4.5-68
370
S 80
330 200
B1 B 2
40
160 R1
B3
R1
B3
30
120 S6
S8
20
Phonon energy hω [meV]
Phonon frequency ν [THz]
50
80
S’8 RW
10
40
0
0 Γ
M
a
70
Γ
K Wavevector q
C(111)(1×1)D 270
S 60
230 200
B1 B 2
40
160 R1
R1
30
120
S6
20
S8
B3
B3
80
S’8 RW 10
0 Γ b
40
0 M
K Wavevector q
Phonon energy hω [meV]
Phonon frequency ν [THz]
50
Fig. 65a, b. C(111) (1x1) H. (a) Calculated surface phonon dispersion for the hydrogenated surface and HATOF data [98Gle]; (b) same as (a) for the deuterated surface and HATOF data [98Gle]. Shaded area: projection of bulk phonon bands; solid curves dispersion of surface modes and resonances.
Γ
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.5-68]
4.5 Surface phonon dispersion
15
4.5-57
60
Ge(001)(1×1)S
10
40
30
0
Fig. 66. Ge(100) (1x1) S. Surface phonon dispersion predicted by theory. No experimental data are available at the moment [92Pol]. Shaded area: projection of bulk phonon bands; solid curves dispersion of surface modes. Surface resonances are reported as dashed lines.
K
Fig. 67. Si(100). Surface phonon dispersion of bare Si(100) (2x1). Shaded area: projection of bulk phonon bands; solid curves dispersion of surface modes and resonances [98Tüt2].
5
20
10
0 Γ
K
J’ K Wavevector q
J
Phonon energy hω [meV]
Phonon frequency ν [THz]
50
Γ
80
Si(100)(2×1)
Phonon energy hω [meV]
70 60 50 40 30 20 10 0
Γ
J’
J
K Wavevector q
Lando lt -Bö rnst ein New Ser ies III/42A2
Γ
4.5-58
4.5 Surface phonon dispersion
Si(100)(2×1) Ge
Si(100)(2×1) Sb
2.35
2.87
2.38
Ge
18.5°
[Ref. p 4.5-68
Sb 0.76 0.81
1.48
Si
2.41
1.58
2.38 Si
1.27
1.20
2.34
2.31
2.37
3.72
3.95
0.14 3.83
Si
Si 2.26
Ge
2.21
3.83
3.83
Sb
1.96
1.94
a
b
Fig. 68. Si(100)(2x1)As. Top view, side view and structural parameters of Si(100)(2x1) Ge and Si(100)(2x1) Sb. The structure for Si(100) (2x1) As [99Tüt] is similar to the one of Sb [98Tüt2].
For Fig. 69, see next page
Si(100)(2×1)Ge 70
Phonon energy hω [meV]
60 50
40
30
Fig. 70. Si(100)(2x1)Ge. Surface phonon dispersion according to ref. [98Tüt2]. Shaded area: projection of bulk phonon bands; solid curves dispersion of surface modes and resonances. The dashed lines indicate selected modes of the bare Si(100)(2x1) surface.
20 10 0
Γ
J’
J
K
Γ
K
Wavevector q
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.5-68]
4.5 Surface phonon dispersion
4.5-59
Si(100)(2×1)As
20
80 S2 S2 S1 S0
S0
Da
10
60
S1
S1
Da 40
Ds Db
Ds
Ds Dt
5
Dt
Ds
A3 D1
A1
A2
Phonon energy hω [meV]
Phonon frequency ν [THz]
15
20
A4
0
0 Γ
J’
Γ
J
K Wavevector q
Si(100)(2×1)As
J‘
K
Γ
J
70
Phonon energy hω [meV]
60 50
40
30 20 10 0
Γ
Lando lt -Bö rnst ein New Ser ies III/42A2
J’
J
K Wavevector q
Γ
K
Fig. 69a, b. Si(100)(2x1)As. Surface phonon spectrum (full lines) and projection of the bulk phonon bands (vertical lines) according (a) to ref. [98Grä] and (b) to ref. [99Tüt]. Prominent modes have been labelled according to their origin and nature. In (b) the dashed lines indicate selected modes of the bare Si(100)(2x1) surface.
4.5-60
4.5 Surface phonon dispersion
[Ref. p 4.5-68
Si(100)(2×1)Sb 70
Phonon energy hω [meV]
60 50
40
30
Fig. 71. Si(100)(2x1)Sb Surface phonon dispersion according to ref. [98Tüt1, 98Tüt2]. Shaded area: projection of bulk phonon bands; solid curves dispersion of surface modes and resonances. The dashed lines indicate selected modes of the bare Si(100)(2x1) surface.
20 10 0
Γ
65
J
K
J’
Γ
K
Wavevector q
Si(100)(2×1)H
Sa
260
Ss 60 Bs
Ba
Ba
Bs Db2
80
15
60 Da
Ds Ds
10
40
Db1
Phonon energy hω [meV]
Phonon frequency ν [THz]
20
Dt 5
20 RW 0
0 Γ
J’
K Wavevector q
J
Γ
Fig. 72. Si(100)(2x1)H. Surface phonon dispersion [96Grä1]. Localised and resonant modes are shown by solid lines.
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.5-68]
65
4.5 Surface phonon dispersion
4.5-61
Si(110)(1×1)H Sa
2100 Ss
60
2000 700
20
Bo Bi Bo Cs
15
500
Cx 10
400
Cy
Ct2 300
Phonon wavenumber ν [cm−1]
Phonon frequency ν [THz]
600 Bi
C t1 200
Fig. 73. Si(110) (1x1) H. Surface phonon dispersion of hydrogenated Si(110). The vertically dashed areas represent the projection of the bulk phonon bands. Localised and resonant modes are shown by solid lines [97Grä].
5 100 0 Γ
Γ
J
K Wavevector q
J’
20
80
Si(111)(1×1)As S4
Phonon frequency ν [THz]
15
R3
S4
60
K4
S3
L1
L1
10 L2
40
L2
K3 K2 K1
5
20
0
0 Γ
Lando lt -Bö rnst ein New Ser ies III/42A2
M
K Wavevector q
Γ
Phonon energy hω [meV]
0
Fig. 74. Si(111) (1x1) As. Surface phonon spectrum of Si(111) (1x1)As: filled circles HREELS data [94Sch], open circles HATOF data [92San1], solid lines surface modes and surface resonances calculated with ab-initio methods [98Grä]. The shaded region is the projection of the bulk phonon bands.
4.5-62
4.5 Surface phonon dispersion
[Ref. p 4.5-68
75
Si(111)(√3×√3)Ga
50
250 25
0
0 Γ
M
K Wavevector q
Γ
Phonon energy hω [meV]
Phonon wavenumber ν [cm −1 ]
500
Fig. 75. Si(111) (√x√3) Ga. Surface phonon dispersion curve. The shaded area is the projection of the bulk phonon bands on the SBZ. Triangles and circles denote HATOF [89Doa] and HREELS [95Sch] data, respectively. The solid lines are the calculated phonon dispersion curves [99Fri2].
For Fg. 76, see next page 40
GaAs(110)
Phonon energy hω [meV]
30
20 Fig. 77. GaAs(110). Surface phonon dispersion predicted for the clean surface [95Fri1]. The shaded area represents the projection of the bulk bands on the SBZ. The surface phonon mode above the bulk optical band splits into two modes along Γ − X . The uppermost mode is marked by the dashed line.
10
0 X
X‘
M
Γ
X
Γ Wavevector q
X‘
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.5-68]
4.5 Surface phonon dispersion
4.5-63
Si(111)(1×1)H 500
50
300
S6 S8
S’8
S8 25
200
100
RW
0
0 Γ
a
Phonon energy hω [meV]
Phonon wavenumber ν [cm −1 ]
LM 400
M
Γ
K Wavevector q
Si(111)(1×1)H 2100
S
260
B
80
600 R3
500
60 LM
400 R1
R2
R1
Phonon energy hω [meV]
Phonon wavenumber ν [cm −1 ]
2000
40
300
S6 S8
S’8
200
Fig. 76a-c. 20
Fig. 76a, b.
100 0 Γ b
Lando lt -Bö rnst ein New Ser ies III/42A2
RW 0 M
K Wavevector q
Γ
For Fig. 76 c and the figure caption, see next page
4.5-64
47
4.5 Surface phonon dispersion
[Ref. p 4.5-68
Si(111)(1×1)D S 180
42 20 80
B2 60 B3
R1
10
B3
B3
R1 40
S6
S’8
S8 5
20 RW
0 c
0 Γ
M
K
Phonon energy hω [meV]
Phonon frequency ν [THz]
B1 15
Fig. 76a-c. Si(111) (1x1) H. (a) HATOF data [90Doa3] and theoretical prediction [88Mig]. (b) HREELS data: filled circles [92Stu], open circles [92Dum]. The solid lines are the theoretical prediction according to ref. [95San1]. The mode marked LM in (a) and (b) is the Lucas mode. It is absent in experimental data being shear horizontally polarised. Surface resonances are denoted by dashed lines. (c) Surface phonon dispersion as forecasted for the deuterated Si(111) surface [96Grä2, 97Maz]. In (b) and (c) the symbols S, B and R refer to adsorbate stretching, bending and rotational motions. Substrate surface modes are denoted by Sn.
Γ
Wavevector q
40
GaAs(110)(1×1)H
Phonon energy hω [meV]
30
20
Fig. 78. GaAs(110) (1x1) H. Surface phonon dispersion curve predicted for the hydrogenated surface by ab-initio linear response formalism [95Fri1]. The shaded area represents the projection of the bulk bands on the surface Brillouin zone.
10
0 X
X‘
M
Γ
X
Γ Wavevector q
X‘
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.5-68]
4.5 Surface phonon dispersion
GaP(110)H stretching modes 272.1 271.9 224.0 223.6 223.2 bending modes 74
Phonon energy hω [meV]
70 66 50
40
30
20
10
0
X‘
M
Γ
X
X
〈110〉
Γ Wavevector q
〈001〉
X
Fig. 79. GaP(110) (1x1) H. Surface phonon dispersion predicted from first principles calculation [99Fri1]. The shaded area represents the projection of the bulk phonon bands on the SBZ. The solid lines are the dispersion curves for surface modes and resonances. The dashed curves indicate the dispersion of selected surface modes of the clean surface. The dots report the position of these modes for the unrelaxed bulk geometry.
Lando lt -Bö rnst ein New Ser ies III/42A2
4.5-65
4.5-66
4.5 Surface phonon dispersion
[Ref. p 4.5-68
For Fig. 80, see next page
InAs(110)H stretching modes 264.0 263.8 204.4 204.0 203.6 bending modes
Phonon energy hω [meV]
65 60 55
30
25
20
15 10 5
0 X
X‘
M
Γ
X
〈110〉
Γ Wavevector q
〈001〉
X‘
Fig. 81. InAs(110) (1x1) H. Surface phonon dispersion curve predicted in ref. [99Fri1]. The shaded area represents the projection of the bulk phonon bands on the SBZ. The solid lines are the dispersion curves for surface modes and resonances. The dotted lines in the gap between the bulk phonon bands are selected surface modes of the clean surface. The dashed lines within the bulk bands are weak surface resonances. The dots indicate the position of these modes for the unrelaxed bulk geometry of the bare surface.
Lando lt -Börnst ein New Ser ies III/42 A2
Ref. p. 4.5-68]
4.5 Surface phonon dispersion
4.5-67
60
GaP(110)(1×1)Sb
Phonon energy hω [meV]
50
40
30
20
10
0 Γ Wavevector q
X
X‘
Fig. 80. GaP(110) (1x1) Sb. Surface phonon dispersion predicted from first principles in ref. [99Fri1]. The shaded area represents the projection of the bulk bands. The solid lines are surface modes and surface resonances. Above the bulk optical phonon band two surface modes are present. The uppermost mode is evidenced by a dotted line.
50
InP(110)(1×1)H
Phonon energy hω [meV]
40
30
20
10
0
X‘
M
Γ
X
X
Lando lt -Bö rnst ein New Ser ies III/42A2
Γ Wavevector q
X‘
Fig. 82. InP(110) (1x1) H. Surface phonon dispersion curve predicted for the hydrogenated surface by ab-initio linear response formalism [95Fri1]. The shaded area represents the projection of the bulk bands on the surface Brillouin zone. The solid lines are the surface modes. The dotted curves indicate the dispersion of two surface-localised gap modes of clean InP(110). The diamonds denote the frequency of these modes for a bare unrelaxed surface.
References for 4.5 1887R 67Ben 71All 73Dem 74Arm 76Cas 76Chr 76Zan 78Mah 79Onu 80Dav 81Bon 81Bre 81Nie 81Ros 82Ste 82Stö 83Bar 83Bor 83Fre1 83Fre2 83Lam 83Leh 83Stu 83Sze 84Cha 84Lam 83Nor 84Ord 84Rah 84Sze 85Har 85Leh 85Roc 85Rah 85Sze 85Xu 86Alk
Lord Rayleigh, J.W.: Proc. London Math. Soc. 17 (1887) 4. Benedek, G., Nardelli, G.: Phys. Rev. 155 (1967) 1004. Alldredge, G.P., Allen, R.E., de Wette, F.W.: Phys. Rev. B 4 (1971) 1682. Demuth, J.E., Jepsen, D.W., Marcus, P.M.: Phys. Rev. Lett. 31 (1973) 540. Armand, G., Theeten, J.B.: Phys. Rev. B 9 (1974) 3969. Castiel, D., Dobrzynski, L, Spanjaard, D.: Surf. Sci. 59 (1976) 252. Christmann, K., Ertl, G., Pignet, T.: Surf. Sci. 54(1976) 365. Zanazzi, E., Jona, F., Jepsen, D.W., Marcus, P.M.: Phys. Rev. B 14 (1976) 432. Mahan, G.D., Lucas, A.A.: J. Chem. Phys. 68 (1978) 1344. Onuferko, J.H., Woodruff, D.P., Holland, B.W.: Surf. Sci. 87 (1979) 357. Davies, J.A., Jackson, D.P., Narton, P.R., Posner, D.E., Unertl, W.N.: Solid State Commun. 34 (1980) 41. Bonzel, H.P., Franken, A.M., Pirug, G.: Surf. Sci. 104 (1981) 625. Brennan, S., Stöhr, J., Jaeger, R.: Phys. Rev. B 24 (1981) 4871. Niehus, H., Comsa, G.: Surf. Sci. 102 (1981) L14. Rosenblatt, D.H., Tobin, J.G., Mason, M.G., Davis, R.F., Shirley, D.A., Li, C.H., Tong, S.Y.: Phys. Rev. B 23 (1981) 3828. Steininger, H., Lehwald, S., Ibach, H.: Surf. Sci. 123 (1982) 1. Stöhr, J., Jäger, R., Kendelewicz, T.: Phys. Rev. Lett. 49 (1982) 142. Barton, J.J., Bahr, C.C., Hussain, Z., Robey, S.W.,Tobin, J.G., Klebanoff, L.E., Shirley, D.A.: Phys. Rev. Lett. 51 (1983) 272. Bortolani, V., Franchini, A., Nizzoli, F., Santoro, G., Benedek, G., Celli, V.: Surf. Sci. 128 (1983) 249. Frenken, J.W.M., van der Veen, J.F., Allan, G.: Phys. Rev. Lett. 51 (1983) 1876. Frenken, J.W.M., Smeenk, R.G., van der Veen, J.F.: Surf. Sci. 135 (1983) 147. Lambert, W.R., Trevor, P.L., Doak. R.B., Cardillo M.J.: J. Vac. Sci. Technol. A 2 (1984) 1066. Lehwald, S., Szeftel, J., Ibach, H., Rahman, T.S., Mills, D.L.: Phys. Rev. Lett. 50 (1983) 518. Stucki, F., Schaefer, J.A., Anderson, J.R., Lapeyre, G.J., Göpel, W.: Solid State Commun. 47 (1983) 795. Szeftel, J., Lehwald, S., Ibach, H., Rahman, T.S., Black, J.E., Mills, D.L.: Phys. Rev. Lett. 51 (1983) 268. Chabal, Y.C., Raghavachari, K.: Phys. Rev. Lett. 53 (1984) 282. Lambert, W.R., Cardillo, M.J., Trevor, P.L., Doak, R.B.: Surf. Sci. 145 (1984) 519. Norman, D., Stöhr, J., Jaeger, R., Durham, P.J., Pendry, J.P.: Phys. Rev. Lett. 51 (1983) 2052. Orders, P.J., Sinkovic, B., Fadley, C.S., Trehan, R., Hussain, Z., Lecante, J.: Phys. Rev. B 30 (1984) 1838. Rahman, T.S., Mills, D.L., Black, J.E., Szeftel, J., Lehwald, S., Ibach, H.: Phys. Rev. B 30 (1984) 589. Szeftel, J., Lehwald, S.: Surf.Sci. 143 (1984) 11. Harten, U., Toennies, J.P., Wöll, Ch., Zhang, G.: Phys. Rev. Lett. 55 (1985) 2308. Lehwald, S., Rocca, M., Ibach, H., Rahman, T.S.: Phys. Rev. B 31 (1985) 3477. Rocca, M., Lehwald, S., Ibach, H.: Surf. Sci. Lett. 163 (1985) L738. Rahman, T.S., Ibach, H.: Phys. Rev. Lett. 54 (1985) 1933. Szeftel, J.: Surf. Sci. 152/153 (1985) 797. Xu, M.L., Hall, B.M., Tong, S.Y., Rocca, M., Ibach, H., Lehwald, S., Black, J.E.: Phys. Rev. Lett. 54 (1986) 1171. Alkemade, P.F.A., Turkenburg, W.C., van der Weg, W.F.: Nucl. Instrum. Methods B 15 (1986) 126. Lando lt -Bö rnst ein. New Ser ies III/42A2
4.5 Surface phonon dispersion 86Bab 86Chu 86Dau 86Fra 86He 86Ker1 86Ker2 86Koe 86Lah 86Leh 86Mat 86Mül 86Olm 86Rah 86Roc1 86Roc2 86Wut 87Bad 87Ber 87Bra1 87Bra2 87Doa 87Ern 87Ers 87Fei 87Fra 87Har 87Iba 87Ker 87Kle 87Leh1 87Leh2 87Mil 87Neu 87Rei 87Rah 87Roc 87Sze 87Wen 87Woo
4.5-69
Baberschke, K., Döbler, U., Wenzel, L., Arvanitis, D.: Phys. Rev. B 33 (1986) 5910. Chung, J.W., Ying, S.C., Estrup, P.J.: Phys. Rev. Lett. 56 (1986) 749. Daum, W., Lehwald, S., Ibach, H.: Surf. Sci. 178 (1986) 528. Franchy, R., Wuttig, M., Ibach, H.: Z. Phys. B 64 (1986) 453 . He, J., Rahman, T.S.: Phys. Rev. B 34 (1986) 5017. Kern, K., David, R., Palmer, R.L., Comsa, G., He, J., Rahman, T.S.: Phys. Rev. Lett. 56 (1986) 2064. Kern, K., David, R., Palmer, R.L., Comsa, G., Rahman, T.S.: Surf. Sci. 178 (1986) 537. Koeleman, B.J.J., de Zwart, S.T., Beers, A.L., Poelsema, B., Verheij, L.K.: Phys. Rev. Lett. 56 (1986) 1152. Lahee, A.M., Toennies, J.P., Wöll, Ch.: Surf. Sci. 177 (1986) 371. Lehwald, S., Rocca, M, Ibach, H., Rahman, T.S.: J. Electron. Spectrosc. Relat. Phenom. 38 (1986) 29. Mate, C.M., Somorjai, G.,: Phys. Rev. B 34 (1986) 7417. Müeller, J.E., Wuttig, M., Ibach, H.: Phys. Rev. Lett. 56 (1986) 1583. Olmstead, M.A., Bringans, R.D., Uhrberg, R.I.G., Bachrach, R.Z.: Phys. Rev. B 34 (1986) 6041. Rahman, T.S., Rocca M., Lehwald, S., Ibach, H.: J. Electron. Spectrosc. Relat. Phenom. 38 (1986) 45. Rocca, M., Ibach, H., Lehwald, S., Rahman, T.S.: in Structure and Dynamics of Surface I, Schommers, W., von Blankenhagen, P. (eds.),Topics in Current Physics 41 (1986) 245. Rocca, M., Lehwald, S., Ibach, H., Rahman, T.S.: Surf. Sci. 171 (1986) 632. Wuttig, M., Franchy, R., Ibach, H.: Solid State Commun. 57 (1986) 445. Bader, M., Ocal, C., Hillert, B., Haase, J., Bradshow, A.M.: Phys. Rev. B 35 (1987) 5900. Berndt, R., Toennies, J.P., Wöll, Ch.: J. Electron. Spectrosc. Relat. Phenom. 44 (1997) 183. Bracco, G., Tatarek, R., Terreni, S., Tommasini, F., Linke, U.: J. Electron. Spectrosc. Relat. Phenom. 44 (1997) 197. Bracco, G., Tatarek, R., Tommasini, F., Linke, U., Persson, M.: Phys. Rev. B 36 (1987) 2928. Doak, R.B., Nguyen, D.B.: J. Electron. Spectrosc. Relat. Phenom. 44 (1987) 205. Ernst, H.J., Hulpke, E., Toennies, J.P.: Phys. Rev. Lett. 58 (1987) 1941. Erskine, J.L., Woods, J.P., Kulkarni, A.D., de Wette, F.W.: J. Electron. Spectrosc. Relat. Phenom. 44 (1987) 27. Feibelman, P.J., Hamann, D.R.: Surf. Sci. 182 (1987) 411. Franchy, R.,Wuttig, M., Ibach, H., Rahman, T.S., He, J.: Surf. Sci. 187 (1987) 58. Harten, U., Toennies, J.P.: Europhys. Lett. 4 (1987) 833. Ibach, H., Lehwald, S., Voigtländer, B.: J. Electron. Spectrosc. Relat. Phenom. 44 (1987) 263. Kern, K, David, R., Palmer, R.L., Comsa, G., He, J., Rahman, T.S.: Phys. Rev. Lett. 58 (1987) 1050 C. Kleinle, G., Penka, V., Behm, R.J., Ertl, G., Moritz, W.: Phys. Rev. Lett. 58 (1987) 148. Lehwald, S., Voigtländer, B., Ibach, H.: Phys. Rev. B 36 (1987) 2446. Lehwald, S., Wolf, F., Ibach, H., Hall, B.M., Mills, D.L.: Surf. Sci. 192 (1987) 131. Mila, F., Szeftel, J., Auby, N.: J. Electron. Spectrosc. Relat. Phenom. 44 (1987) 383. Neuhaus, D., Joo, F., Feuerbacher, B.: Phys. Rev. Lett. 58 (1987) 694. Reimer, W., Penka, V., Skottke, M., Behm, R.J., Ertl, G., Moritz, W.: Surf. Sci. 186 (1987) 45. Rahman, T.S.: Phys. Rev. B 35 (1987) 9494. Rocca, M., Lehwald, S., Ibach, H., Rahman, T.S.: Phys. Rev. B 35 (1987) 9510. Szeftel, J.: Phys. Rev. Lett. 58 (1987) 1049 C. Wenzel, L., Arvanitis, D., Daum, W., Rotermund, H.H., Stöhr, J., Baberschke, K., Ibach, H.: Phys. Rev. B 36 (1987) 7689. Woods, J.P., Kulkarni, A.D., Erskine, J.L., de Wette, F.W.: Phys. Rev. B 36 (1987) 5848.
Lando lt -Börnst ein. New Ser ies III/42 A2
4.5-70 87Wu 88Cop 88Har 88Loc 88Mig 88Rah 88Sze 89Bor 89Doa 89Ern 89Gay 89Jeo1 89Jeo2 89Mil 89Oed 89Sze 89Tat 89Voi 89Wu 89Wut1 89Wut2 89Yan 89Zen 90Bra1 90Bra2 90Col 90Doa1 90Doa2 90Doa3 90Gri 90Iba 90Jed 90Men1 90Men2 90Mor 90Oed 90Voi1 90Voi2 90Yan 91Bra 91Ber
4.5 Surface phonon dispersion Wu, Z.Q., Xu, M.L., Chen, Y., Tong, S.Y., Mohamed, M.H., Kesmodel, L.L.: Phys. Rev. B 36 (1987) 9329. Copel, M., Tromp, R.M., Köhler, U.K.: Phys. Rev. B 37 (1988) 10756. Harten, U., Toennies, J.P., Woell, Ch., Miglio, L., Ruggerone, P., Colombo, L., Benedek, G.: Phys. Rev. B 38 (1988) 3305. Lock, A., Toennies, J.P., Wöll, Ch., Bortolani, V., Franchini, A., Santoro, G.: Phys. Rev. B 37 (1988) 7087. Miglio, L., Ruggerone, P., Benedek, G.: Phys. Scr. 37 (1988) 768. Rahman, T.S.: Phys. Rev. B 38 (1988) 10387. Szeftel, J., Mila, F.: J. Phys. C Solid State Phys. 21 (1988) L1131. Bortolani, V., Franchini, A., Santoro, G., Toennies, J.P., Wöll, Ch., Zhang, G.: Phys. Rev. B 40 (1989) 3524. Doak, R.B.: J. Vac. Sci. Technol. B 7 (1989) 1252. Ernst, H.J., Hulpke, E., Toennies, J.P.: Europhys. Lett. 10 (1989) 747. Gaylord, R.H., Jeong, K.H., Kevan, S.D.: Phys. Rev. Lett. 62 (1989) 2036. Jeong, K.H., Gaylord, R.H., Kevan, S.D.: Phys. Rev. B 39 (1989) 2973. Jeong, K.H., Gaylord, R.H., Kevan, S.D.: J. Vac. Sci. Technol. A 7 (1989) 2199. Mila, F., Szeftel, J., Auby, N.: Surf. Sci. 216 (1989) 139. Oed, W., Lindner, H., Starke, U., Heinz, K., Müller, K., Pendry, J.B.: Surf. Sci. 224 (1989) 179. Szeftel, J., Mila, F., Khater, A.: Surf. Sci. 216 (1989) 125. Tatarek, R., Bracco, G., Tommasini, F., Franchini, A., Bortolani, V., Santoro, G., Wallis, R.F.: Surf. Sci. 211/212 (1989) 314. Voigtländer, B., Lehwald, S., Ibach, H.: Surf. Sci. 208 (1989) 113. Wu, Z.Q., Chen, Y., Xu, M.L., Tong, S.Y., Lehwald, S., Rocca, M., Ibach, H: Phys Rev. B 39 (1989) 3116. Wuttig, M., Franchy, R., Ibach, H.: Surf. Sci. 224 (1989) L979. Wuttig, M., Franchy, R., Ibach, H.: Surf. Sci. 213 (1989) 103. Yang, L., Rahman, T.S., Bracco, G., Tatarek, R.: Phys. Rev. B 40 (1989) 12271. Zeng, H.C., McFarlene, R.A., Mitchell, K.A.R.: Surf. Sci. 208 (1989) L7. Bracco, G., Tatarek, R., Vandoni, G.: Phys. Rev. B 42 (1990) 1852. Bracco, G., Masseti, E., Tatarek, R.: J. Electron. Spectrosc. Relat. Phenom. 54/55 (1990) 317. Colin de Verdière, Szeftel, J., Soukiassian, P.: Phys. Rev. B 42 (1990) 7234. Doak, R.B., Nguyen, D.B.: Phys. Rev. B 41 (1990) 3578. Doak, R.B.: J. Electron Spectrosc. Relat. Phenom. 54/55 (1990) 281. Doak, R.B., Chabal, Y.J., Higashi, G.S., Dumas, P.: J. Electron Spectrosc. Relat. Phenom. 54/55 (1990) 291. Grimsby, D.T.V., Wu, Y.K., Mitchell, K.A.R.: Surf. Sci. 232 (1990) 51. Ibach, H., in: Interaction of atoms and molecules with solid surfaces, Bortolani, V., March, N.H., Tosi, M.P. (eds.), Plenum Publishing Corporation, 1990, p. 325. Jedrecy, N., Sauvage-Simkin, M., Pinchaux, R., Massies, J., Gresier, N., Etgens, V.H.: Surf. Sci. 230 (1990) 197. Menezes, W. Knipp, P., Tisdale, G., Sibener, S.J.: Phys. Rev. B 41 (1990) 5648. Menezes, W. Knipp, P., Tisdale, G., Sibener, S.J.: J. Electr. Spectrosc. Relat. Phenom. 54/55 (1990) 373. Moretto, P., Rocca, M., Valbusa, U., Black, J: Phys. Rev. B 41 (1990) 12905. Oed, W., Lindner, H., Starke, U., Heinz, K., Müller, K., deAndres, P., Saldin, D.K., Pendry, J.B.: Surf. Sci. 225 (1990) 242. Voigtländer, B., Bruchmann, D., Lehwald, S., Ibach, H.: Surf. Sci. 225 (1990) 151. Voigtländer, B., Lehwald, S., Ibach, H.: Surf. Sci. 225 (1990) 162. Yang, L., Rahman, T.S., Mills, D.L.: Phys. Rev. B 42 (1990) 2864. Bracco, G., Tatarek, R.: Surf. Sci. 251/252 (1991) 498. Berndt, R., Toennies, J.P., Wöll, Ch.: Surf. Sci. 244 (1991) 305. Lando lt -Bö rnst ein. New Ser ies III/42A2
4.5 Surface phonon dispersion 91Che 91Iba 91Kis 91Kre 91San 91Toe 91Wöl 91Yan 92Bal 92Ben 92Col 92Dum 92Ern 92Hul1 92Hul2 92Iba1 92Pol 92San1 92San2 92Stu 92Toe 93Aiz 93Bel
93Ben 93Ber 93Bra 93Dif 93Fra 93Fri 93Hei
93Hul1 93Hul2 93Krü 93Lan 93Lee 93Wit1 93Wit2 94Bal1 94Bal2 94Ben 94Bun
4.5-71
Chen, Y., Tong, S.Y., Rocca, M., Moretto, P., Valbusa, U., Bohnen, K.P., Ho, K.M.: Surf. Sci. Lett. 250 (1991) L389. Ibach, H.: Phys. Scr. T 39 (1991) 323. Kisters, G., Chen, J.G., Lehwald, S., Ibach, H.: Surf. Sci. 245 (1991) 65. Kress, W., de Wette, F.W., (eds.): Surface Phonons, Springer Series in Surface Science, Vol. 21, Berlin: Springer-Verlag, 1991. Sander, D., Ibach, H.: Phys. Rev. B 43 (1991) 4263. Toennies, J.P., in: Surface Phonons, Springer Series in Surface Science, Vol. 21, p. 111, Berlin: Springer-Verlag, 1991. Wöll, Ch.: Appl. Phys. A 53 (1991) 377. Yang, L., Rahman, T.S.: Surf. Sci. 241 (1991) 25. Balden, M., Lehwald, S., Ibach, H., Ormeci, A., Mills, D.L.: Phys. Rev. B 46 (1992) 4172. Benedek, G, Ellis, J., Reichmut, A., Ruggerone, P, Schlief, H, Toennies, J.P.: Phys. Rev. Lett. 69 (1992) 2951. Colaianni, M.L., Chen, J.G., Weinberg, W.H., Yates, J.T. Jr.: Surf. Sci. 279 (1992) 211. Dumas, P., Chabal, Y.J.: J. Vac. Sci. Technol. A 10 (1992) 2160. Ernst, H.J., Hulpke, E., Toennies, J.P., Wöll, Ch.: Surf. Sci. 262 (1992) 159. Hulpke, E., Lüdecke, J.: Phys. Rev. Lett. 68 (1992) 2846. Hulpke, E., Lüdecke, J.: Surf. Sci. 272 (1992) 289. Ibach, H.: Phys. Bl. 48 (1992) 705. Pollmann, J., Krüger, P., Mazur, A.: Appl. Surf. Sci. 56-58 (1992) 193. Sander, D., Linke, U., Ibach, H.: Surf. Sci. 272 (1992) 318. Santini, P., Ruggerone, P., Miglio, L., Doak, R.B.: Phys. Rev. B 46 (1992) 9865. Stuhlmann, Ch., Bogdányi, G., Ibach, H.: Phys. Rev. B 45 (1992) 6786. Toennies, J.P.: Europhys. News 23 (1992) 63. Aizawa, T., Ando, T., Kamo, M., Sato, Y.: Phys. Rev. B 48 (1993) 18348. Bellman, A.F., Cvetko, D., Dhanak, V.R., Polli, M., Tommasini, F., Prince, K.C., in: Inelastic Energy Transfer in Interactions with Surfaces and Adsorbates, Gumhalter, B., Levi, A.C., Flores, F. (eds.), Singapore: World Scientific, 1993, p. 49. Benedek, G., Ellis, J., Luo, N.S., Reichmut, A., Ruggerone, P., Toennies, J.P.: Phys. Rev. B 48 (1993) 4917. Bertoni, C.M., Shkrebtii, A.I., di Felice, R., Finocchi, F.: Prog. Surf. Sci. 42 (1993) 319. Bracco, G. Tatarek, R.: Nuovo Cimento 15 D (1993) 471. Di Felice, R., Shkrebtii, A.I., Finocchi, F., Bertoni, C.M., Onida, G.: J. Electron. Spectrosc. Relat. Phenom. 64/65 (1993) 697. Franchini, A., Bortolani, V., Santoro, G., Celli, V., Eguiluz, A.G., Gasper, J.A., Gester, M., Lock, A., Toennies, J.P.: Phys. Rev. B 47 (1993) 4691. Fritsch, J., Pavone, P., Schröder, U.: Phys. Rev. Lett. 71 (1993) 4194. Heidberg, J., Kampshoff, E., Kühnemuth, R., Schönekäs, O., Lange, G., Schmicker, D., Toennies, J.P., Vollmer, R., Weiss, H.: J. Electron. Spectrosc. Relat. Phenom. 64/65 (1993) 341. Hulpke, E., Lüdecke, J.: J. Electron. Spectrosc. Relat. Phenom. 64/65 (1993) 641. Hulpke, E., Lüdecke, J.: Surf. Sci. 287/288 (1993) 837 . Krüger, P., Pollmann, J.: Phys. Rev. B 47 (1993) 1898. Lange, G., Toennies, J.P., Vollmer, R., Weiss, H.: J. Chem. Phys. 98 (1993) 10096. Lee, S.-T., Apai, G.: Phys. Rev. B 48 (1993) 2684. Witte, G., Range, H., Toennies, J.P., Wöll, Ch.: J. Electron. Spectrosc. Relat. Phenom. 64/65 (1993) 715. Witte, G., Range, H., Toennies, J.P., Wöll, Ch.: Phys. Rev. Lett. 71 (1993) 1063. Balden, M., Lehwald, S., Preuss, E., Ibach, H.: Surf. Sci. 307-309 (1994) 1141. Balden, M., Lehwald, S., Ibach, H., Mills, D.L.: Phys Rev. B. 73 (1994) 854. Benedek, G., Toennies, J.P.: Surf. Sci. 299/300 (1994) 587. Bunjes, N., Luo, N.S., Ruggerone, P., Toennies, J.P., Witte, G.: Phys. Rev. B 50 (1994) 8897.
Lando lt -Börnst ein. New Ser ies III/42 A2
4.5-72 94Dha 94Fra 94Hof 94Iba 94Kev 94Nie 94Ruo 94Sch 94Tis 94Tho 94Zep 95Bru 95Ell 95Koh 95Fri1 95Fri2 95Ger 95Lan 95Ruo 95San1 95San2 95San3 95Sch 95Wit1 95Wit2 96Bal 96Bun 96Doh 96Fuh 96Gle 96Gra1 96Gra2 96Grä1 96Grä2 96Hon 96Koh1 96Koh2 96Lan 96Nie 96San 96Wat 97Bra 97Gra 97Grä 97Iba
4.5 Surface phonon dispersion Dhar, S., Smith, K.E., Kevan, S.D.: Phys. Rev. Lett. 73 (1994) 1448. Franklin, G.E., Fontes, E., Qian, Y., Bedzyk, M.J., Golovchenko, J.A., Patel, J.R.: Phys. Rev. B 50 (1994) 7483. Hofmann, F., Toennies, J.P., Manson, J.R.: J.Chem. Phys. 101 (1994) 10155. Ibach H., Surf. Sci. 299/300 (1994) 116. Kevan, S.D.: Surf. Sci. 307/309 (1994) 832. Nienhaus, H., Mönch, W.: Phys. Rev. B 50 (1994) 11750. Ruocco, A., Nannarone, S., Sauvage-Simkin, M., Jedrecy, N., Pinchaux, R., Waldhauer, A.: Surf. Sci. 307 (1994) 662. Schmidt, J., Ibach, H.: Phys. Rev. B 50 (1994) 14354. Tisdale, G., Sibener, S.J.: Surf. Sci. 311 (1994) 360. Thoms, B.D., Butler, J.E.: Phys. Rev. B 50 (1994) 17450. Zeppenfeld, P., Buechel, M., David, R., Comsa, G., Ramseyer, C., Girardet, G.: Phys. Rev. B 50 (1994) 14667. Bruch, L., Glebov, A., Toennies, J.P., Weiss, H.: J. Chem. Phys. 103 (1995) 5109. Ellis, J., Toennies, J.P., Witte, G.: J. Chem. Phys. 102 (1995) 5059. Kohler, B., Ruggerone, P., Wilke, S., Scheffler, M.: Phys. Rev. Lett. 74 (1995) 1387. Fritsch, J., Eckert, A., Pavone, P., Schröder, U.: J. Phys. Condens. Matter 7 (1995) 7717. Fritsch, J., Pavone, P.: Surf. Sci. 344 (1995) 159. Gerlach, R., Glebov, A., Lange, G., Toennies, J.P., Weiss, H.: Surf. Sci. 331 (1995) 1490. Lange, G., Schmicker, D., Toennies, J.P., Vollmer, R., Weiss, H.: J. Chem. Phys. 103 (1995) 2308. Ruocco, A., Biangini, M., Di Bona, A., Gambacorti, N., Valeri, S., Nannarone, S., Santoni, A., Bonnet, J.: Phys. Rev. B 51 (1995) 2399. Sandfort, B., Mazur, A., Pollmann, J.: Phys. Rev. B 51 (1995) 7139. Sandfort, B., Mazur, A., Pollmann, J.: Phys. Rev. B 51 (1995) 7150. Sandfort, B., Mazur, A., Pollmann, J.: Phys. Rev. B 51 (1995) 7168. Schmidt, J., Ibach, H., Müller, J.E.: Phys. Rev. B 51 (1995) 5233. Witte, G., Wöll, Ch.: J. Chem. Phys. 103 (1995) 5860. Witte, G., Toennies, J.P., Wöll, Ch.: Surf. Sci. 323 (1995) 228. Balden, M., Lehwald, S., Ibach, H.: Phys. Rev. B 53 (1996) 7479. Bungaro, C., de Gironcoli, S., Baroni, S.:Phys. Rev. Lett. 77 (1996) 2491. Dohrmann, J., Glebov, A., Toennies, J.P., Weiss, H.: Surf. Sci. 368 (1996) 118. Fuhrmann, D., Wöll, Ch.: Surf. Sci. 368 (1996) 20. Glebov, A., Toennies, J.P., Weiss, H.: Surf. Sci. 351 (1996) 200 53. Graham, A.P., Bertino, M.F., Hoffmann, F., Toennies, J.P.: J. Chem. Soc. Faraday Trans. 92 (1996) 4749. Grabowski, S.P., Nienhaus, H., Mönch, W.: Surf. Sci. 352/354 (1996) 310. Gräschus, V., Mazur, A., Pollmann, J.: Proceedings of the 23rd Internationl Conference on the Physics of Semiconductors, ICPS 23, Singapore: World Scientific, 1996, p. 931. Gräschus, V., Mazur, A., Pollmann, J.: Surf. Sci. 368 (1996) 179. Honke, R., Pavone, P., Schröder, U.: Surf. Sci. 367 (1996) 75. Kohler, B., Ruggerone, S., Scheffler, M., Tosatti, E.: Z. Phys. Chem. 197 (1996) 193. Kohler, B., Ruggerone, S., Scheffler, M.: Surf. Sci. 368 (1996) 213. Lange, G., Toennies, J.P.: Phys. Rev. B 53 (1996) 9614. Nienhaus, H., Grabowski, S.P., Mönch, W.: Surf. Sci. 368 (1996) 196. Sandfort, B., Mazur, A., Pollmann, J.: Phys. Rev. B 54 (1996) 8605. Watanabe, S.: Surf. Sci. 351 (1996) 149. Braun, J., Kostov, K.L., Witte, G., Surnev, L., Skofronick, J. G., Safron, S.A., Wöll, Ch.: Surf. Sci. 372 (1997) 132. Graham, A.P., Bertino, M.F., Hoffmann, F., Silvestri, W., Toennies, J.P.: J. Chem. Phys. 106 (1997) 2502. Gräschus, V., Mazur, A., Pollmann, J.: Phys. Rev. B 56 (1997) 6482. Ibach, H.: Surf. Sci. Rep. 29 (1997) 193. Lando lt -Bö rnst ein. New Ser ies III/42A2
4.5 Surface phonon dispersion 97Koh 97Krö 97Maz 97Nag 97Nie 97Sch 97Tüt 98Alf 98Bra 98Gle 98Grä 98Krö1 98Krö2 98Pic 98Rot 98Tüt1 98Tüt2 99Alf 99Bar 99Bra 99Fri1 99Fri2 99Mor 99Tüt 00Krö 02Dah
4.5-73
Kohler, B., Ruggerone, P., Scheffler, M.: Phys. Rev. B 56 (1997) 13503. Kröger, J., Lehwald, S., Ibach, H.: Phys. Rev. B 55 (1997) 10895. Mazur, A., Sandfort, B., Gräschus, V., Pollmann, J.: Festkörperprobleme/Adv. Solid State Phys. 36 (1997) 181. Nagao, T., Iizuka, Y., Shimazaki, T., Oshima, C.: Phys. Rev. B 55 (1997) 10064. Nienhaus, H., Grabowski, S.P., Mönch, W.: Surf.Sci. 368 (1996) 196. Schaich, Th., Braun, J., Toennies, J.P., Buck, M., Wöll, Ch.: Surf. Sci. Lett. 385 (1997) L958. Tütüncü, H.M., Jenkins, S.J., Srivastava, G.P.: Phys. Rev. B 56 (1997) 4656. Alfé, D., de Gironcoli, S., Baroni, S.: Surf. Sci. 410 (1998) 151. Braun, J., Fuhrmann, D., Siber , A., Gumhalter, B., Wöll, Ch.: Phys. Rev. Lett. 80 (1998) 125. Glebov, A., Toennies, J.P., Vollmer, S., Safron, S.A., Skofronick, J.G., Gräschus, V., Mazur, A., Pollmann, J.: Phys. Rev. B 57 (1998) 10082 . Gräschus, V., Mazur, A., Krüger, P., Pollmann, J.: Phys. Rev. B 57 (1998) 13175. Kröger, J., Lehwald, S., Ibach, H.: Surf. Sci. 402/404 (1998) 496. Kröger, J., Lehwald, S., Ibach, H.: Phys. Rev B 58 (1998) 1578. Picaud, S., Hoang, P.N.M., Girardet, C., Glebov, A., Miller, R.E., Toennies, J.P.: Phys. Rev. B 57 (1998) 10090. Rotenberg, E., Kevan, S.D.: Phys. Rev. Lett. 80 (1998) 2905. Tütüncü, H.M., Jenkins, S.J., Srivastava, G.P.: Surf. Sci. 402-404 (1998) 42. Tütüncü, H.M., Jenkins, S.J., Srivastava, G.P.: Phys. Rev. B 58 (1998) 10754. Alfé, D., de Gironcoli, S., Baroni, S.: Surf. Sci. 437 (1999) 18. Baraldi, A., Cerda, J., Martin Gago, J.A., Comelli, G., Linit, S., Paolucci, G., Resei, R.: Phys. Rev. Lett. 82 (1999) 4874. Braun, J., Bishop, G.G., Ermakov, A.V., Goncharova, L.V., Hinch, B.J.: J. Chem. Phys. 110 (1999) 5337. Fritsch, J., Schröder, U.: Phys. Rep. 309 (1999) 209. Fritsch, J., Arnold, M., Eckl, C., Honke, R., Pavone, P., Schröder, U.: Surf. Sci. 428 (1999) 58. Moritz, T., Menzel, D., Widdra, W.: Surf. Sci. 427-428 (1999) 64. Tütüncü, H.M., Gay, S.C.A., Srivastava, G.P.: Physica B 263-264 (1999) 424. Kröger, J., Bruchmann, D., Lehwald, S., Ibach, H.: Surf. Sci. 449 (2000) 227. Dahmen, K., Ibach, H.: Surf. Sci. (to be publisched).
Lando lt -Börnst ein. New Ser ies III/42 A2
