Preface ........................................................ xi
Chapter 1 Introduction to surface processes .................... 1
1.1 Elementary thermodynamic ideas of surfaces ................. 1
1.1.1 Thermodynamic potentials and the dividing surface ... 1
1.1.2 Surface tension and surface energy .................. 3
1.1.3 Surface energy and surface stress ................... 4
1.2 Surface energies and the Wulff theorem ..................... 4
1.2.1 General considerations .............................. 5
1.2.2 The terrace-ledge-kink model ........................ 5
1.2.3 Wulff construction and the forms of small crystals .. 7
1.3 Thermodynamics versus kinetics ............................. 9
1.3.1 Thermodynamics of the vapor pressure ............... 11
1.3.2 The kinetics of crystal growth ..................... 15
1.4 Introduction to surface and adsorbate reconstructions ..... 19
1.4.1 Overview ........................................... 19
1.4.2 General comments and notation ...................... 20
1.4.3 Examples of (1×1) structures ....................... 22
1.4.4 Si(001) (2×1) and related semiconductor
structures ......................................... 24
1.4.5 The famous 7×7 structure of Si(111) ................ 27
1.4.6 Various 'root-three' structures .................... 28
1.4.7 Polar semiconductors, such as GaAs(111) ............ 28
1.4.8 Ionic crystal structures, such as NaCl, CaF2, MgO
or alumina ......................................... 30
1.5 Introduction to surface electronics ....................... 30
1.5.1 Work function, φ ................................... 30
1.5.2 Electron affinity, χ and ionization potential Φ .... 30
1.5.3 Surface states and related ideas ................... 31
1.5.4 Surface Brillouin zone ............................. 32
1.5.5 Band bending, due to surface states ................ 32
1.5.6 The image force .................................... 32
1.5.7 Screening .......................................... 33
Further reading for chapter 1 ............................. 33
Problems for chapter 1 .................................... 33
Chapter 2 Surfaces in vacuum: ultra-high vacuum techniques
and processes .................................................. 36
2.1 Kinetic theory concepts ................................... 36
2.1.1 Arrival rate of atoms at a surface ................. 36
2.1.2 The molecular density, n ........................... 37
2.1.3 The mean free path, λ .............................. 37
2.1.4 The monolayer arrival time, τ ...................... 38
2.2 Vacuum concepts ........................................... 39
2.2.1 System volumes, leak rates and pumping speeds ...... 39
2.2.2 The idea of conductance ............................ 41
2.2.3 Measurement of system pressure ..................... 42
2.3 UHV hardware: pumps, tubes, materials and pressure
measurement ............................................... 42
2.3.1 Introduction: sources of information ............... 42
2.3.2 Types of pump ...................................... 43
2.3.3 Chambers, tube and flange sizes .................... 44
2.3.4 Choice of materials ................................ 45
2.3.5 Pressure measurement and gas composition ........... 46
2.4 Surface preparation and cleaning procedures: in situ
experiments ............................................... 47
2.4.1 Cleaning and sample preparation .................... 47
2.4.2 Procedures for in situ experiments ................. 50
2.4.3 Sample transfer devices ............................ 51
2.4.4 From laboratory experiments to production
processes .......................................... 52
2.5 Thin film deposition procedures: sources of information ... 54
2.5.1 Historical descriptions and recent compilations .... 54
2.5.2 Thermal evaporation and the uniformity of
deposits ........................................... 54
2.5.3 Molecular beam epitaxy and related methods ......... 57
2.5.4 Sputtering and ion beam assisted deposition ........ 57
2.5.5 Chemical vapor deposition techniques ............... 59
Further reading for chapter 2 ............................. 60
Problems for chapter 2 .................................... 60
Chapter 3 Electron-based techniques for examining surface and
thin film processes ............................................ 63
3.1 Classification of surface and microscopy techniques ....... 63
3.1.1 Surface techniques as scattering experiments ....... 63
3.1.2 Reasons for surface sensitivity .................... 64
3.1.3 Microscopic examination of surfaces ................ 65
3.1.4 Acronyms ........................................... 69
3.2 Diffraction and quasi-elastic scattering techniques ....... 70
3.2.1 LEED ............................................... 70
3.2.2 RHEED and THEED .................................... 72
3.2.3 Elastic, quasi-elastic and inelastic scattering .... 14
3.3 Inelastic scattering techniques: chemical and electronic
state information ......................................... 76
3.3.1 Electron spectroscopic techniques .................. 76
3.3.2 Photoelectron spectroscopies: XPS and UPS .......... 79
3.3.3 Auger electron spectroscopy: energies and atomic
physics ............................................ 81
3.3.4 AES, XPS and UPS in solids and at surfaces ......... 84
3.4 Quantification of Auger spectra ........................... 88
3.4.1 General equation describing quantification ......... 88
3.4.2 Ratio techniques ................................... 92
3.5 Microscopy-spectroscopy: SEM, SAM, SPM, etc. .............. 95
3.5.1 Scanning electron and Auger microscopy .............. 95
3.5.2 Auger and image analysis of 'real world' samples ... 98
3.5.3 Towards the highest spatial resolution: (a) SEM/
STEM .............................................. 100
3.5.4 Towards the highest spatial resolution: (b)
scanned probe microscopy-spectroscopy ............. 104
Further reading for chapter 3 ............................ 105
Problems, talks and projects for chapter 3 ............... 105
Chapter 4 Surface processes in adsorption .................... 108
4.1 Chemi-and physisorption .................................. 108
4.2 Statistical physics of adsorption at low coverage ........ 109
4.2.1 General points .................................... 109
4.2.2 Localized adsorption: the Langmuir adsorption
isotherm .......................................... 109
4.2.3 The two-dimensional adsorbed gas: Henry law
adsorption ........................................ 110
4.2.4 Interactions and vibrations in higher density
adsorbates ........................................ 113
4.3 Phase diagrams and phase transitions ..................... 114
4.3.1 Adsorption in equilibrium with the gas phase ...... 115
4.3.2 Adsorption out of equilibrium with the gas phase .. 118
4.4 Physisorption: interatomic forces and lattice dynamical
models ................................................... 119
4.4.1 Thermodynamic information from single surface
techniques ........................................ 119
4.4.2 The crystallography of monolayer solids ........... 120
4.4.3 Melting in two dimensions ......................... 124
4.4.4 Construction and understanding of phase diagrams .. 125
4.5 Chemisorption: quantum mechanical models and chemical
practice ................................................. 128
4.5.1 Phases and phase transitions of the lattice gas ... 128
4.5.2 The Newns- Anderson model and beyond .............. 130
4.5.3 Chemisorption: the first stages of oxidation ...... 133
4.5.4 Chemisorption and catalysis: macroeconomics,
macromolecules and microscopy ..................... 135
Further reading for chapter 4 ............................ 141
Problems and projects for chapter 4 ...................... 141
Chapter 5 Surface processes in epitaxial growth .............. 144
5.1 Introduction: growth modes and nucleation barriers ....... 144
5.1.1 Why are we studying epitaxial growth? ............. 144
5.1.2 Simple models - how far can we go? ................ 145
5.1.3 Growth modes and adsorption isotherms ............. 145
5.1.4 Nucleation barriers in classical and atomistic
models ............................................ 145
5.2 Atomistic models and rate equations ...................... 149
5.2.1 Rate equations, controlling energies, and
simulations ....................................... 149
5.2.2 Elements of rate equation models .................. 150
5.2.3 Regimes of condensation ........................... 152
5.2.4 General equations for the maximum cluster
density ........................................... 154
5.2.5 Comments on individual treatments ................. 155
5.3 Metal nucleation and growth on insulating substrates ..... 157
5.3.1 Microscopy of island growth: metals on alkali
halides ........................................... 157
5.3.2 Metals on insulators: checks and complications .... 159
5.3.3 Defect-induced nucleation on oxides and
fluorides ......................................... 161
5.4 Metal deposition studied by UHV microscopies ............. 651
5.4.1 In situ UHV SEM and LEEM of metals on metals ......
5.4.2 FIM studies of surface diffusion on metals ........ 167
5.4.3 Energies from STM and other techniques ............ 169
5.5 Steps, ripening and interdiffusion ....................... 174
5.5.1 Steps as one-dimensional sinks .................... 174
5.5.2 Steps as sources: diffusion and Ostwald ripening .. 176
5.5.3 Interdiffusion in magnetic multilayers ............ 179
Further reading for chapter 5 ............................ 181
Problems and projects for chapter 5 ...................... 181
Chapter 6 Electronic structure and emission processes at
metallic surfaces ............................................. 184
6.1 The electron gas: work function, surface structure and
energy ................................................... 184
6.1.1 Free electron models and density functionals ...... 184
6.1.2 Beyond free electrons: work function, surface
structure and energy .............................. 190
6.1.3 Values of the work function ....................... 193
6.1.4 Values of the surface energy ...................... 196
6.2 Electron emission processes .............................. 200
6.2.1 Thermionic emission ............................... 201
6.2.2 Cold field emission ............................... 202
6.2.3 Adsorption and diffusion: FES, FEM and thermal
field emitters .................................... 206
6.2.4 Secondary electron emission ....................... 207
6.3 Magnetism at surfaces and in thin films .................. 210
6.3.1 Symmetry, symmetry breaking and phase transitions .. 210
6.3.2 Anisotropic interactions in 3D and '2D' magnets ... 211
6.3.3 Magnetic surface techniques ....................... 213
6.3.4 Theories and applications of surface magnetism .... 218
Further reading for chapter 6 ............................ 224
Problems and projects for chapter 6 ...................... 224
Chapter 7 Semiconductor surfaces and interfaces ............... 227
7.1 Structural and electronic effects at semiconductor
surfaces ................................................. 227
7.1.1 Bonding in diamond, graphite, Si, Ge, GaAs, etc. .. 227
7.1.2 Simple concepts versus detailed computations ...... 229
7.1.3 Tight-bindingpseudopotential and ab initio
models ............................................ 230
7.2 Case studies of reconstructed semiconductor surfaces ..... 232
7.2.1 GaAs(110), a charge-neutral surface ............... 232
7.2.2 GaAs(111), a polar surface ........................ 234
7.2.3 Si and Ge(111): why are they so different? ........ 235
7.2.4 Si, Ge and GaAs(001), steps and growth ............ 239
7.3 Stresses and strains in semiconductor film growth ........ 242
7.3.1 Thermodynamic and elasticity studies of surfaces .. 242
7.3.2 Growth on Si(001) ................................. 245
7.3.3 Strained layer epitaxy: Ge/Si(001) and
Si/Ge(001) ........................................ 249
7.3.4 Growth of compound semiconductors ................. 252
Further reading for chapter 7 ............................ 256
Problems and projects for chapter 7 ...................... 257
Chapter 8 Surface processes in thin film devices ............. 260
8.1 Metals and oxides in contact with semiconductors ......... 260
8.1.1 Band bending and rectifying contacts at
semiconductor surfaces ............................ 260
8.1.2 Simple models of the depletion region ............. 263
8.1.3 Techniques for analyzing semiconductor
interfaces ........................................ 265
8.2 Semiconductor heterojunctions and devices ................ 270
8.2.1 Origins of Schottky barrier heights ............... 270
8.2.2 Semiconductor heterostructures and band offsets ... 272
8.2.3 Opto-electronic devices and 'band-gap
engineering' ...................................... 274
8.2.4 Modulation and δ-doping, strained layers,
quantum wires and dots ............................ 279
8.3 Conduction processes in thin film devices ................ 280
8.3.1 Conductivity, resistivity and the relaxation
time .............................................. 281
8.3.2 Scattering at surfaces and interfaces in
nanostructures .................................... 282
8.3.3 Spin dependent scattering and magnetic
multilayer devices ................................ 284
8.4 Chemical routes to manufacturing ......................... 289
8.4.1 Synthetic chemistry and manufacturing: the case
of Si-Ge-C ........................................ 289
8.4.2 Chemical routes to opto-electronics and!or
nano-magnetics .................................... 291
8.4.3 Nanotubes and the future offlat panel TV .......... 293
8.4.4 Combinatorial materials development and analysis .. 294
Further reading for chapter 8 ............................ 295
Chapter 9 Postscript - where do we go from here? ............. 297
9.1 Electromigration and other degradation effects in
nanostructures ........................................... 297
9.2 What do the various disciplines bring to the table? ...... 299
9.3 What has been left out: future sources of information .... 301
Appendix A Bibliography ...................................... 303
Appendix В List of acronyms .................................. 306
Appendix С Units and conversion factors ...................... 309
Appendix D Resources on the web or CD-ROM .................... 312
Appendix E Useful thermodynamic relationships ................ 314
Appendix F Conductances and pumping speeds, С and 5 .......... 318
Appendix G Materials for use in ultra-high vacuum ............ 320
Appendix H UHV component cleaning procedures ................. 323
Appendix J An outline of local density methods ............... 326
Appendix К An outline of tight binding models ................ 328
References .................................................... 331
Index ......................................................... 363
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