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Gmelin Handbook of Inorganic and Organometallic Chemistry

8th Edition

Gmelin Handbook of Inorganic and Organometallic Chemistry

PREPARED

AND ISSUED BY

FOUNDED BY

8TH EDITION

CONTINUED BY

8th Edition

GmeLin Handbuch der Anorganischen Chemie

Achte, völlig neu bearbeitete Auflage

Gmelin-Institut für Anorganische Chemie der Max-Planck-Gesellschaft zur Förderung der Wissenschaften

Director: Ekkehard Fluck

Leopold Gmelin

8th Edition begun under the auspices of the Deutsche Chemische Gesellschaft by R. J. Meyer

E. H. E. Pietsch and A. Kotowski, and by Margot Becke-Goehring

Springer-Verlag Berlin Heidelberg GmbH 1993

GmeLin-lnstitut für Anorganische Chemie der Max-Planck-Gesellschaft zur Förderung der Wissenschaften

ADVISORY BOARD

Min.-Rat Dr. H. Bechte (Bundesministerium für Forschung und Technologie, Bonn), Prof. Dr. K. Dehnicke (PhiLipps-Universität, Marburg), Prof. Dr. H. Grünewald (Bayer AG, Lever-kusen), Prof. Dr. H. Harnisch, Chairman (Hoechst AG, FrankfurtlMain-Höchst), Prof. Dr. H. Nöth (Ludwig-MaximiLians-Universität, München), Prof. Dr. H. Offermanns (Degussa AG, Frankfurt/Main), Prof. Dr. A. Simon (Max-PLanck-Institut für Festkörperforschung, Stuttgart), Prof. Dr. Dr. h.c. mult. G. Wilke (Max-Planck-Institut für Kohlenforschung, Mülheim/Ruhr), Prof. Dr. H. F. Zacher (Präsident der Max-Planck-Gesellschaft, München)

DIRECTOR

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EMERITUS MEMBER OF THE INSTITUTE Prof. Dr. Dr. E.h. Margot Becke

CORRESPONDENT MEMBERS OF THE INSTITUTE Prof. Dr. Dr. h.c. Hans Bock, Prof. Dr. Dr. Alois Haas, Sc. D. (Cantab.)

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Volumes published on "Tungsten" (Syst. No. 54)

Tungsten Main VoLume - 1933

Tungsten SuppL. VoL. A 1 Metal, TechnoLogy - 1979

Tungsten SuppL. VoL. A 2 PhysicaL Properties - 1987

Tungsten SuppL. VoL. A 3 PhysicaL Properties - 1989

Tungsten SuppL. VoL. A 4 Surface Properties. ELectron Emission - 1993 (present voLume)

Tungsten SuppL. VoL. A 5a ELectrochemistry - 1990

Tungsten SuppL. VoL. A 5b Metal, ChemicaL Reactions with Nonmetals Nitrogen to Arsenic - 1993

Tungsten SuppL. VoL. A 6a Metal, ChemicaL Reactions with Metals Antimony to Barium - 1991

Tungsten SuppL. VoL. A 6b Metal, ChemicaL Reactions with Metals Zinc to Lawrencium - 1988

Tungsten SuppL. VoL. A 7 Metal, ChemicaL Reactions with Inorganic and Organic Compounds - 1987

Tungsten SuppL. VoL. B 1 Systems with NobLe Gases, Hydrogen, and Oxygen - 1978

Tungsten SuppL. VoL. B 2 Oxides - 1979

Tungsten SuppL. VoL. B 3 Compounds of Tungsten with Oxygen and Antimony, Bismuth; ALkali Tungstates - 1979

Tungsten SuppL. VoL. B 4 Tungstates of Group IIA and IIB Metals - 1980

Tungsten SuppL. VoL. B 5 Tungstates of Group 111 A and 111 B Metals - 1984

Tungsten SuppL. VoL. B 6 Anhydrous Tungstates of Group IV A and VI B Metals - 1984

Gmelin Handbook of Inorganic and Organometallic Chemistry

AUTHORS

EDITORS

CHIEF EDITOR

8th Edition

W

Tungsten SuppLement VoLume A4

Surface Properties. Electron Emission

With 53 illustrations

Gerhard Czack, Gerhard Kirschstein, Wolfgang Kurtz, Frank Stein

Wolfgang Huisl, Wolfgang Kurtz, Frank Stein

Wolfgang Huisl

System Number 54

Springer-Verlag Berlin Heidelberg GmbH 1993

LITERATURE CLOSING DATE: 1992 IN SOME CASES MORE RECENT DATA HAVE SEEN CONSIDERED

Library 01 Congress CataLog Card Number: Agr 25-1383

ISBN 978-3-662-10156-8 ISBN 978-3-662-10154-4 (eBook) DOI 10.1007/978-3-662-10154-4

This work is subject to copyright. ALL rights are reserved, whether the whoLe or part 01 the materiaL is concerned, specilicaLly those 01 transLation, reprinting, reuse 01 illustrations, broadcasting, reproduction by photocopying machine or simiLar means, and storage in data banks. Under § 54 01 the German Copyright Law where copies are made lor other than private use, a lee is payabLe to "VerwertungsgeseLlschaft Wort", Munieh.

© by Springer-Verlag Berlin Heidelberg 1993 OriginaLly published by Springer-Verlag Berlin in 1993. Softcover reprint ofthe hardcover 8th edition 1993

The use 01 registered names, trademarks, etc., in this publication does not impLy, even in the absence 01 a specilic statement, that such names are exempt Irom the reLevant protective Laws and reguLations and therelore Iree lor generaL use.

Preface

This voLume continues the description of the physicaL properties of tungsten metaL and covers specificaLLy surface properties, eLectron emission, and fieLd evaporation.

Tungsten surfaces are probabLy the most extensiveLy studied metaL surfaces. RecentLy, experimentaLists and theorists have focused their interest on the atomic structure, Lattice dynamics, and eLectronic properties of the W(100) surface. WhiLe the structure of the recon-structed Low-temperature surface is weLL estabLished, there are still unresoLved probLems concerning the structure at and above room temperature, the nature of the phase transition, and the driving force for the reconstruction. Other Low-index tungsten surfaces have been studied in much Less detail.

There are numerous and partLy confLicting data on the surface energy, the seit-diffusion parameters, and the work function of singLe-crystaL and poLycrystaL tungsten surfaces. ELec-tron emission, which is of fundamentaL importance for many appLications, comprises therm-ionic, fieLd, photofieLd, and photoeLectric emission as weLL as emission induced by impinging eLectrons, atoms, or ions. Pioneering work in areas Like thermionic or fieLd emission is comprehensiveLy discussed. Very recent studies of vaLence-band and core-LeveL spectra moreover provide detaiLed information on intrinsic surface properties. FieLd evaporation phenomena are treated at the end of this voLume.

Frankfurt am Main November 1993

Woltgang HuisL

fable of Contents

Page

1 Atomic Structure, LaHice Dynamies, and Electronic Structure of Tungsten Surfaces 1

1.1 W(100) . . . . . . . . . . . . . . . . . . . 1.1.1 Atomic Structure. Reconstruction and Relaxation

Survey ................. . Phase Diagram ............... . Structure of the Low-Temperature (L T) Surface

Lateral Atom Shifts (Reconstruction) and Interlayer Spacings (Relaxation) Reconstruction Domains ........ .

Structure of the High-Temperature (HT) Surface Lateral Structure of the HT Surface . . . . . Relaxation of the HTW(100) Interlayer Spacing

Phase Transition . . . . . . . . . . . . . . Driving Forces for Reconstruction and Relaxation

1.1.2 Lattice Dynamies . . . . . . . . . . . . Surfaee Debye Temperature. Thermal Mean Square Displacements Phonons ................. .

Survey ................. . Experimental Surfaee Phonon Dispersion Curves Simulation of the Surfaee Dynamies

1.1.3 Surfaee Eleetronie Strueture Introduetion . . . . . . . . . . . Surfaee Core-Level Shifts . . . . . Eleetronie Surfaee Density of States (SOOS) Surfaee States and Surfaee Resonanees

Surfaee States and Resonanees above EF Surfaee States and Resonanees below EF or Dispersing through EF

Synoptie Charaeterization of States and Resonanees; Dispersion Curves Charaeterization of Prominent Surface Bands

Theoretical Studies . . . . . Charge Density Contour Plots

Fermi Surfaee . . . . . . . .

1.2 W(110) ....... . 1.2.1 Atomie Strueture. Reeonstruction and Relaxation 1.2.2 Surfaee Debye Temperature. Surface Atom Vibrations 1.2.3 Surfaee Electronie Structure . . . .

Surface Core-Level Shifts . . . . . . . Surface States. Eleetronie Band Strueture Fermi Surfaee

1.3 W(lll) . . . . . . . . 1.3.1 Atomie Strueture. Relaxation 1.3.2 Surface Debye Temperature 1.3.3 Surfaee Electronic Strueture

Surface Core-Level Shifts . . . Surfaee States. Eleetronic Band Strueture

1.4 W(211) and Other Surfaces 1.4.1 Atomie Structure. Relaxation

4 6 6

11 13 13 18 20 25 30 30 31 31 33 36 40 40 40 41 43 43 45 45 48 51 53 55

56 56 59 61 61 62 64

66 66 67 67 67 67

70 70

XII

1.4.2 Surface Debye Temperature 1.4.3 Surface ELectronic Structure

Surface Core-LeveL Shifts Surface ELectronic States

2 Surface Free Energy. Surface Tension

2.1 Single-Crystal Studies Involving Several Surfaces

2.2 Single-Crystal Studies on Particular Surfaces

2.3 Polycrystals. Average Field EmiHer Tips

2.4 Mett

3 Surface Self-Oiffusion

3.1 Atomic Oisplacement Studies 3.1.1 Survey ..... 3.1.2 Diffusion on W(110) 3.1.3 Diffusion on W (211) 3.1.4 Diffusion on W(100) 3.1.5 Diffusion on W (111) 3.1.6 Diffusion on W (321) 3.1.7 Diffusion on Other Surfaces

3.2 Surface Self-Oiffusion with Appreciable Mass Transport 3.2.1 Diffusion Studies on W AdLayers . . . . . . . . . . 3.2.2 Grain-Boundary Grooving, Smoothing of Scratches, and Thermo- and

ELectrotransport Studies . . . . . . . . . . . . . . 3.2.3 Blunting of W Tips. Ring Rate Studies . . . . . . . . 3.2.4 Build-Up of Emitter Tips and Formation of Protrusions

Build-Up ................. . Protrusions ................ .

3.2.5 lon-Bombardment-Induced Surface Diffusion

4 Work Function

4.1 Survey. Reviews

4.2 Experimental Work Function Oata 4.2.1 SingLe-CrystaL Surfaces

W (110) W (211) W(100) W (111) W (311) W(611) W(310) Other Surfaces

4.2.2 PoLycrystal Surfaces and Average Tip Studies

4.3 Calculated Work Function Oata

Page

72 72 72 73

74

74

76

77

78

82

82 82 83 85 88 88 89 90

93 93

94 96

100 100 103 105

107

107

108 108 108 111 112 113 114 114 115 115 121

124

4.4 Influence 01 Delects on the Work Funclion

4.5 Temperature CoeHicient 01 the Work Function

5 Electron Emission . .

5.1 Thermionic Emission 5.1.1 Introduction 5.1.2 The Richardson Constant 5.1.3 InfLuence of Surface Nonuniformity 5.1.4 Energy Distribution . . . . . . . 5.1.5 Schottky Deviations . . . . . . . 5.1.6 Emission Current Anomalies near TM 5.1.7 Potential and Temperature Gradients inside the Crystal

5.2 Field Emission ..... 5.2.1 Reviews. . . . . . . . . . . . 5.2.2 Total Energy Distributions . . . . 5.2.3 Fowler-Nordheim Characteristics 5.2.4 Single-Electron vs. Multiple-Electron Tunneling 5.2.5 Energy Exchange Effects ......... . 5.2.6 Field Emission in Magnetic Fields. Polarized Electron Emission 5.2.7 Flicker Noise

5.3 Thermal Field Emission

5.4 Photofleld Emission 5.4.1 Introduction 5.4.2 Photofield Emission Energy Distributions (PFEEDs) 5.4.3 Yield Studies ....... . 5.4.4 Current-Field Characteristics 5.4.5 Temperature Dependence of PFE

5.5 Photoelectric Emission . 5.5.1 Photoelectric Yields 5.5.2 Valence-Band Spectra

Introduction . . . . . . . Studies Comparing Different Surfaces W(hkl) UPS Studies on W(110) Surfaces UPS Studies on W(100) Surfaces . . . . . . UPS Studies on W(111) Surfaces ..... . UPS Studies on Surfaces of Tungsten Polycrystals

5.5.3 Core-Level Spectra Introduction . . . . . . Surface Core-Level Shifts

Experimental Data Comparison with Theoretical Results

Angle-Resolved Spectra (Photoelectron Diffraction) Line Shapes and Widths. Background

5.5.4 Photoelectric Schottky Deviations

5.6 Laser-Induced Electron Emission

XIII

Page

126

128

132

132 132 132 134 135 137 138 139

142 142 142 149 151 152 153 154

156

158 158 159 161 162 165

167 167 169 169 171 173 178 184 185 185 185 187 187 190 194 196 197

197

XIV

5.7 Electron-Induced Electron Emission 5.7.1 Secondary Electron Emission Yield

Polycrystals . . . . . . . . . . . . Single Crystals . . . . . . . . . . .

5.7.2 Inelastic Secondary Electron Emission Spectra Polycrystals . . . . . . . . Single Crystals . . . . . . .

5.7.3 Elastic Electron Scattering Introduction . . . . . . . . Fine-Structure in LEED Intensity Profiles Spin-Polarization Profiles . . . . . . .

5.8 lon- and Atom-Induced Electron Emission 5.8.1 Introduction . . . . . . . . . . . . . 5.8.2 Electron Emission under Impact of Noble Gases

Helium He Atoms He Ions .

Neon Ne Atoms Ne Ions .

Argon ... Ar Atoms Ar Ions

Krypton . . Xenon ...

Xe Atoms Xe Ions

5.8.3 ELectron Emission under Impact of Other Nonmetals Hydrogen Oxygen Nitrogen . HaLogens Carbon Nonmetal Compounds

5.8.4 Electron Emission under Impact of Metals Lithium Sodium . Potassium Rubidium Caesium Calcium . Zinc Cadmium Mercury . Bismuth .

6 Field Evaporation

6.1 Survey ....

6.2 Charge States and Charge State Distributions

Page

202 202 203 205 210 211 211 214 214 216 220

225 225 227 227 227 228 232 232 233 235 235 236 241 243 243 243 245 245 248 248 250 250 251 251 251 251 252 252 252 253 253 253 253 253

255

255

256

6.3 Post-Ionization

6.4 Tunneling vs. Thermal Activation

6.5 Evaporation Rates . . . . . . .

6.6 Activation Energies and Frequency Pre-exponential Factors

6.7 Evaporation Fields . . . . . . . . . .

xv

Page

258

258

260

261

262

6.8 Energy Distributions and Energy Deficits 264

6.9 Field Adsorption and Promotion of Field Evaporation by Image and Residual Gases 266

6.10 Field Desorption (Evaporation) Micrographs 268

6.11 Field-Evaporated Endform . . . . . 270

Physical Constants and Conversion Factors 276