Chung Y.-W. Practical guide to surface science and spectroscopy
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Practical Guide to
SURFACE SCIENCE AND
SPECTROSCOPY
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Practical Guide to
SURFACE SCIENCE AND
SPECTROSCOPY
Yip-Wah Chung
Northwestern University
Evanston, Illinois
San Diego San Francisco New York Boston
London Sydney Tokyo
This book is printed on acid-free paper. 䡬
∞
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CONTENTS
Preface xi
1 Fundamental Concepts in Ultrahigh Vacuum,
Surface Preparation, and Electron Spectroscopy 1
1.1 Introduction 1
1.2 The Need for Ultrahigh Vacuum 2
1.3 Achieving Ultrahigh Vacuum 4
1.4 Pressure Measurement 7
1.5 Preparation of Clean Surfaces 9
1.6 Need for Electron Spectroscopy 10
1.7 Electron Scattering from Solid Surfaces 12
1.8 Electron Energy Analyzers 13
1.8.1 Retarding Field Analyzer 14
1.8.2 Cylindrical Mirror Analyzer 16
1.8.3 Concentric Hemispherical Analyzer 17
1.9 Other Considerations 19
Problems 19
v
vi
CONTENTS
2 Auger Electron Spectroscopy 23
2.1 Auger Electron Emission 23
2.2 Experimental Aspects 24
2.3 Sensitivity of Auger Electron Spectroscopy 26
2.4 Energies and Shapes of Auger Peaks 27
2.5 Chemical State Effects 28
2.6 Intensity of Auger Electron Emission 29
2.7 Profile Analysis 33
2.8 Scanning Auger Microprobe 33
2.9 Quantitative Analysis 35
2.10 Case Study: Surface Composition of a 5 at% Al–Fe Alloy 39
Problems 40
3 Photoelectron Spectroscopy 45
3.1 One-Electron Description of the Photoelectric Effect 45
3.2 Photon Sources 47
3.3 Detectors 50
3.4 Element Identification 51
3.5 Chemical Shift 51
3.6 Relaxation Shift and Multiplet Splitting 53
3.7 Chemical Bonding on Surfaces 54
3.8 Band Structure Studies 56
3.9 Extended X-Ray Absorption Fine Structure 60
3.10 Special Applications 62
3.10.1 Auger Electron and Photoelectron Forward Scattering 62
3.10.2 Photoemission of Adsorbed Xenon 63
Problems 64
4 Inelastic Scattering of Electrons
and Ions 69
4.1 One-Electron Excitation of Core and Valence Electrons 69
4.2 Plasmon Excitations 71
4.3 Surface Vibrations 72
4.4 Ion Scattering Spectroscopy 75
4.5 Secondary Ion Mass Spectrometry 77
Problems 80
vii
CONTENTS
5 Low-Energy Electron Diffraction 83
5.1 Introduction 83
5.2 Electron Diffraction 83
5.3 Naming Conventions for Surface Structures 85
5.4 Experimental Aspects 87
5.5 Selected Properties of the Surface Reciprocal Space 88
5.6 Kinematic Theory 89
5.7 Applications of the Kinematic Theory 92
5.7.1 Determination of Real Space Lattice from LEED
Pattern 92
5.7.2 Angular Spread of Diffracted Beams 93
5.7.3 Steps 95
5.7.4 Surface Vibrations 96
Problems 97
Appendix
Diffraction Intensity as a Function of Temperature 98
6 Scanning Probe Microscopy 101
6.1 Introduction 101
6.2 Historical Perspective 102
6.3 Review of Electron Tunneling 103
6.4 Principle of STM Imaging 104
6.5 STM Image Interpretation 106
6.6 STM Implementation 107
6.6.1 Coarse Motion Control 107
6.6.2 Fine Motion Control 107
6.6.3 Tip Preparation 109
6.6.4 Vibration Isolation 110
6.6.5 Data Acquisition and Analysis 111
6.7 Applications of STM 112
6.7.1 High-Resolution Imaging of Surfaces 112
6.7.2 Spectroscopy 113
6.7.3 Lithography 113
6.7.4 Current Fluctuations 114
6.8 Limitations of STM and Solutions 114
6.9 Scanning Capacitance Microscopy 115
6.10 Atomic Force Microscopy 115
6.10.1 Equations of Interest 116
Problems 116
Additional Reading 117
viii
CONTENTS
7 Interfacial Segregation 119
7.1 Introduction 119
7.2 Gibbs Adsorption Equation 119
7.3 One Component Systems 123
7.4 Surface Segregation in Binary Alloys 124
7.5 Relationship Between Surface and Bulk Composition of Binary
Alloys 127
7.6 The Unified Segregation Model 129
7.6.1 Surface Energy and Heat of Mixing 129
7.6.2 Elastic Strain Energy 130
7.6.3 Entropy Change 131
7.6.4 Comparison with Experiment 131
7.7 Environmental Effects on Surface Segregation 131
Problems 133
8 Metal–Semiconductor Interfaces 137
8.1 Surface States 137
8.2 Semiconductor Surfaces 141
8.2.1 The Space Charge Region 141
8.2.2 Fermi-Level Pinning 144
8.3 Work Function Measurements 146
8.3.1 Photoemission 147
8.3.2 Kelvin Method 147
8.3.3 Retarding Field Technique 148
8.4 The Metal–Semiconductor Interface 148
8.4.1 The Schottky Model 148
8.4.2 Surface States and the Defect Model 152
8.4.3 Case Study: Gold on InP 153
Problems 153
Appendix
Useful Information for Semiconductors 156
9 Gas–Surface Interactions 157
9.1 Introduction 157
9.2 Heat of Adsorption 159
ix
CONTENTS
9.3 The Langmuir Adsorption Isotherm 167
9.3.1 Noninteracting Atoms 167
9.3.2 Interacting Atoms 170
9.3.3 Effect on Surface Tension 171
9.4 Pressure Effects 172
9.5 Promoters, Poisons, and Ensemble Effects 172
9.6 Surface Compounds 173
9.7 Case Studies 174
9.7.1 Strong Metal–Support Interaction 174
9.7.2 Ductility of Ni
3
Al 177
Problems 178
Index 181