Acknowledgements ............................................. xiii
Introduction .................................................... 1
1.1. Heterogeneous Catalysis ................................. 2
1.2. Why Surfaces? ........................................... 3
1.3. Where are Heterogeneous Reactions Important? ............ 4
1.3.1. Haber-Bosch Process .............................. 4
1.3.2. Fischer-Tropsch Chemistry ........................ 4
1.3.3. Three-way Catalyst ............................... 5
1.4. Semiconductor Processing and Nanotechnology ............. 5
1.5. Other Areas of Relevance ................................ 6
1.6. Structure of the Book ................................... 6
References ................................................... 9
1. Bulk and Surface Structure .................................. 11
1.1. Clean Surface Structure ................................ 12
1.1.1. Ideal Flat Surfaces ............................. 12
1.1.2. High Index and Vicinal Planes ................... 17
1.1.3. Faceted Surfaces ................................ 19
1.1.4. Bimetallic Surfaces ............................. 19
1.1.5. Porous Solids ................................... 20
1.1.6. Oxide Surfaces .................................. 23
1.2. Reconstruction and Adsorbate Structure ................. 27
1.2.1. Implications of Surface Heterogeneity for
Adsorbates ...................................... 27
1.2.2. Clean Surface Reconstructions ................... 27
1.2.3. Adsorbate Induced Reconstructions ............... 28
1.2.4. Islands ......................................... 32
1.2.5. Chiral Surfaces ................................. 32
1.3. Band Structure of Solids ............................... 35
1.3.1. Bulk Electronic States .......................... 35
1.3.2. Metals, Semiconductors and Insulators ........... 35
1.3.3. Energy Levels at Metal Interfaces ............... 40
1.3.4. Energy Levels at Metal-Semiconductor
Interfaces ...................................... 41
1.3.5. Surface Electronic States ....................... 43
1.3.6. Size Effects in Nanoscale Systems ............... 46
1.4. The Vibrations of Solids ............................... 48
1.4.1. Bulk Systems .................................... 48
1.4.2. Nanoscale Systems ............................... 50
1.5. Summary of Important Concepts .......................... 50
1.6. Frontiers and Challenges ............................... 51
1.7. Further Reading ........................................ 51
1.8. Exercises .............................................. 52
References .................................................. 54
2. Experimental Probes and Techniques .......................... 57
2.1. Ultrahigh Vacuum ....................................... 57
2.1.1. The Need for UHV ................................ 57
2.1.2. Attaining UHV ................................... 58
2.2. Light and Electron Sources ............................. 60
2.2.1. Types of Lasers ................................. 61
2.2.2. Atomic Lamps .................................... 61
2.2.3. Synchrotrons .................................... 61
2.2.4. Free Electron Laser (FEL) ....................... 63
2.2.5. Electron Guns ................................... 64
2.3. Molecular Beams ........................................ 64
2.3.1. Knudsen Molecular Beams ......................... 64
2.3.2. Free Jets ....................................... 66
2.3.3. Comparison of Knudsen and Supersonic Beams ...... 68
2.4. Scanning Probe Techniques .............................. 71
2.4.1. Scanning Tunnelling Microscopy (STM) ............ 71
2.4.2. Scanning Tunnelling Spectroscopy (STS) .......... 76
2.4.3. Atomic Force Microscopy (AFM) ................... 77
2.4.4. Near-field Scanning Optical Microscopy (NSOM) ... 81
2.5. Low Energy Electron Diffraction (LEED) ................. 84
Advanced Topic: LEED Structure Determination ................ 86
2.6. Electron Spectroscopy .................................. 91
2.6.1. X-ray Photoelectron Spectroscopy (XPS) .......... 92
2.6.2. Ultraviolet Photoelectron Spectroscopy (UPS) .... 97
Advanced Topic: Multiphoton Photoemission (MPPE) ........... 102
2.6.3. Auger Electron Spectroscopy (AES) .............. 103
2.6.4. Photoelectron Microscopy ....................... 107
2.7. Vibrational Spectroscopy .............................. 109
2.7.1. IR Spectroscopy ................................ 111
2.7.2. Electron Energy Loss Spectroscopy (EELS) ....... 116
2.8. Other Surface Analytical Techniques ................... 118
2.9. Summary of Important Concepts ......................... 118
2.10.Frontiers and Challenges .............................. 119
2.11.Further Reading ....................................... 119
2.12.Exercises ............................................. 120
References ................................................. 123
3. Chemisorption, Physisorption and Dynamics .................. 127
3.1. Types of Interactions ................................. 127
3.2. Binding Sites and Diffusion ........................... 128
3.3. Physisorption ......................................... 133
Advanced Topic: Theoretical Description of
Physisorption ......................................... 133
3.4. Nondissociative Chemisorption ......................... 134
3.4.1. Theoretical Treatment of Chemisorption ......... 134
3.4.2. The Blyholder Model of CO Chemisorption
on a Metal ..................................... 138
3.4.3. Molecular Oxygen Chemisorption ................. 141
3.4.4. The Binding of Ethene .......................... 142
3.5. Dissociative Chemisorption: H2 on a Simple Metal ...... 143
3.6. What Determines the Reactivity of Metals? ............. 145
3.7. Atoms and Molecules Incident on a Surface ............. 148
3.7.1. Scattering Channels ............................ 148
3.7.2. Nonactivated Adsorption ........................ 151
3.7.3. Hard Cube Model ................................ 153
3.7.4. Activated Adsorption ........................... 156
3.7.5. Direct versus Precursor Mediated Adsorption .... 157
3.8. Microscopic Reversibility in Ad/desorption
Phenomena ............................................. 161
3.9 The Influence of Individual Degrees of Freedom on
Adsorption and Desorption ............................ 166
3.9.1. Energy Exchange ................................ 167
3.9.2. PES Topography and the Relative Efficacy of
Energetic Components ........................... 168
3.10.Translations, Corrugation, Surface Atom Motions ....... 169
3.10.1.Effects on Adsorption .......................... 169
3.10.2.Connecting Adsorption and Desorption with
Microscopic Reversibility ...................... 172
3.10.3. Normal Energy Scaling ......................... 174
3.11.Rotations and Adsorption .............................. 176
3.11.1.Nonactivated Adsorption ........................ 176
3.11.2. Activated Adsorption .......................... 178
3.12.Vibrations and Adsorption ............................. 178
3.13.Competitive Adsorption and Collision Induced
Processes ............................................. 179
Advanced Topic: High-Energy Collisions ..................... 181
3.14.Classification of Reaction Mechanisms ................. 182
3.14.1.Langmuir-Hinshelwood Mechanism ................. 183
3.14.2.Eley-Rideal Mechanism .......................... 185
3.14.3.Hot Atom Mechanism ............................. 186
3.15.Measurement of Sticking Coefficients .................. 187
3.16.Summary of Important Concepts ......................... 191
3.17.Frontiers and Challenges .............................. 192
3.18.Further Reading ....................................... 192
3.19.Exercises ............................................. 193
References ................................................. 201
4. Thermodynamics and Kinetics of Adsorption and Desorption ... 207
4.1. Thermodynamics of Ad/desorption ....................... 207
4.1.1. Binding Energies and Activation Barriers ....... 207
4.1.2. Thermodynamic Quantities ....................... 209
4.1.3. Some Definitions ............................... 210
4.1.4. The Heat of Adsorption ......................... 211
4.2. Adsorption Isotherms from Thermodynamics .............. 213
4.3. Lateral Interactions .................................. 216
4.4. Rate of Desorption .................................... 217
4.4.1. First-order Desorption ......................... 218
4.4.2. Transition State Theory Treatment of
First-order Desorption ......................... 219
4.4.3. Thermodynamic Treatment of First-order
Desorption ..................................... 223
4.4.4. Nonfirst-order Desorption ...................... 225
4.5. Kinetics of Adsorption ................................ 226
4.5.1. CTST Approach to Adsorption Kinetics ........... 226
4.5.2. Langmuirian Adsorption: Nondissociative
Adsorption ..................................... 227
4.5.3. Langmuirian Adsorption: Dissociative
Adsorption ..................................... 230
4.5.4. Dissociative Langmuirian Adsorption with
Lateral Interactions ........................... 231
4.5.5. Precursor Mediated Adsorption .................. 232
4.6. Adsorption Isotherms from Kinetics .................... 234
4.6.1. Langmuir Isotherm .............................. 235
4.6.2. Classification of Adsorption Isotherms ......... 236
4.6.3. Thermodynamic Measurements via Isotherms ....... 238
4.7. Temperature Programmed Desorption (TPD) ............... 238
4.7.1. The Basis of TPD ............................... 238
4.7.2. Qualitative Analysis of TPD Spectra ............ 240
4.7.3. Quantitative Analysis of TPD Spectra ........... 243
4.8. Summary of Important Concepts ......................... 246
4.9. Frontiers and Challenges .............................. 247
4.10.Further Reading ....................................... 247
4.11.Exercises ............................................. 248
References ................................................. 252
5. Liquid Interfaces .......................................... 255
5.1. Structure of the Liquid/Solid Interface ............... 255
5.1.1. The Structure of the Water/Solid Interface ..... 258
5.2. Surface Energy and Surface Tension .................... 260
5.2.1. Liquid Surfaces ................................ 261
5.2.2. Curved Interfaces .............................. 263
5.3. Liquid Films .......................................... 265
5.3.1. Liquid-on-solid Films .......................... 265
5.4. Langmuir Films ........................................ 267
5.5. Langmuir-Blodgett Films ............................... 269
5.5.1. Capillary Condensation and Meniscus
Formation ...................................... 269
5.5.2. Vertical Deposition ............................ 272
5.5.3. Horizontal Lifting (Shaefer's Method) .......... 273
5.6. Self-assembled Monolayers (SAMs) ...................... 274
5.6.1.Thermodynamics of Self-assembly ................. 275
5.6.2. Amphiphiles and Bonding Interactions ........... 277
5.6.3. Mechanism of SAM Formation ..................... 277
Advanced Topic: Chemistry with Self-Assembled Monolayers ... 281
5.7. Thermodynamics of Liquid Interfaces ................... 281
5.7.1. The Gibbs Model ................................ 281
5.7.2. Surface Excess ................................. 283
5.7.3. Interfacial Enthalpy and Internal, Helmholtz
and Gibbs Surface Energies ..................... 283
5.7.4. Gibbs Adsorption Isotherm ...................... 285
5.8. Electrified and Charged Interfaces .................... 285
5.8.1. Surface Charge and Potential ................... 285
5.8.2. Relating Work Functions to the
Electrochemical Series ......................... 288
5.9. Summary of Important Concepts ......................... 290
5.10.Frontiers and Challenges .............................. 291
5.11.Further Reading ....................................... 291
5.12.Exercises ............................................. 292
References ................................................. 293
6. Heterogeneous Catalysis .................................... 295
6.1. The Prominence of Heterogeneous Reactions ............. 295
6.2. Measurement of Surface Kinetics and Reaction
Mechanisms ............................................ 296
6.3. Haber-Bosch Process ................................... 302
6.4. From Microscopic Kinetics to Catalysis ................ 306
6.4.1. Reaction Kinetics .............................. 307
6.4.2. Kinetic Analysis using De Donder Relations ..... 308
6.4.3. Definition of the Rate Determining Step (RDS) .. 309
6.4.4. Microkinetic Analysis of Ammonia Synthesis ..... 310
6.5. Fischer-Tropsch Synthesis and Related Chemistry ....... 313
6.6. The Three-way Automotive Catalyst ..................... 317
6.7. Promoters ............................................. 320
6.8. Poisons ............................................... 321
6.9. Bimetallic and Bifunctional Catalysts ................. 323
6.10.Rate Oscillations and Spatiotemporal Pattern
Formation ............................................. 324
Advanced Topic: Cluster Assembled Catalysts ................ 326
6.11.Sabatier Analysis and Optimal Catalyst Selection ...... 327
6.12.Summary of Important Concepts ......................... 329
6.13.Frontiers and Challenges .............................. 330
6.14.Further Reading ....................................... 330
6.15.Exercises ............................................. 331
References ................................................. 333
7. Growth and Epitaxy ......................................... 337
7.1. Stress and Strain ..................................... 337
7.2. Types of Interfaces ................................... 341
7.2.1. Strain Relief .................................. 341
7.3. Surface Energy, Surface Tension and Strain Energy ..... 343
7.4. Growth Modes .......................................... 345
7.4.1. Solid-on-Solid Growth .......................... 345
7.4.2. Strain in Solid-on-Solid Growth ................ 346
7.4.3. Ostwald Ripening ............................... 348
7.4.4. Equilibrium Overlayer Structure and Growth
Mode ........................................... 349
7.5. Nucleation Theory ..................................... 351
7.6. Growth Away from Equilibrium .......................... 354
7.6.1. Thermodynamics versus Dynamics ................. 354
7.6.2. Nonequilibrium Growth Modes .................... 355
7.7. Techniques for Growing Layers ......................... 359
7.7.1. Molecular Beam Epitaxy (MBE) ................... 359
7.7.2. Chemical Vapour Deposition (CVD) ............... 362
7.7.3. Ablation Techniques ............................ 364
7.8. Catalytic Growth of Nanotubes and Nanowires ........... 364
7.9. Etching ............................................... 369
7.9.1. Classification of Etching ...................... 369
7.9.2. Etch Morphologies .............................. 374
7.9.3. Porous Solid Formation ......................... 375
7.9.4. Silicon Etching in Aqueous Fluoride
Solutions ...................................... 377
7.9.5. Coal Gasification and Graphite Etching ......... 380
7.9.6. Selective Area Growth and Etching .............. 381
Advanced Topic: Si Pillar Formation ........................ 384
7.10.Summary of Important Concepts ......................... 384
7.11.Frontiers and Challenges .............................. 386
7.12.Further Reading ....................................... 386
7.13.Exercises ............................................. 387
References ................................................. 389
8. Laser and Nonthermal Chemistry: Photon and Electron
Stimulated Chemistry and Atom Manipulation ................. 395
8.1. Photon Excitation of Surfaces ......................... 396
8.1.1. Light Absorption by Condensed Matter ........... 396
8.1.2. Lattice Heating ................................ 398
Advanced Topic: Temporal Evolution of Electronic
Excitations ................................................ 402
8.1.3. Summary of Laser Excitations ................... 409
8.2. Mechanisms of Electron and Photon Stimulated
Processes ............................................. 410
8.2.1. Direct versus Substrate Mediated Processes ..... 410
8.2.2. Gas-Phase Photochemistry ....................... 412
8.2.3. Gas-Phase Electron Stimulated Chemistry ........ 414
8.2.4. MGR and Antoniewicz Models of DIET ............. 414
8.2.5. Desorption Induced by Ultrafast Excitation ..... 418
8.3. Photon and Electron Induced Chemistry at Surfaces ..... 419
8.3.1. Thermal Desorption, Reaction and Diffusion ..... 419
8.3.2. Stimulated Desorption/reaction ................. 420
8.3.3. Ablation ....................................... 428
8.4. Charge Transfer and Electrochemistry .................. 431
Advanced Topic: Semiconductor Photoelectrodes and the
Gratzel Photovoltaic Cell .................................. 434
8.5. Tip Induced Process: Mechanisms of Atom
Manipulation .......................................... 438
8.5.1. Electric Field Effects ......................... 439
8.5.2. Tip Induced ESD ................................ 439
8.5.3. Vibrational Ladder Climbing .................... 441
8.5.4. Pushing ........................................ 443
8.5.5. Pulling ........................................ 444
8.5.6. Atom Manipulation by Covalent Forces ........... 444
8.6. Summary of Important Concepts ......................... 446
8.7. Frontiers and Challenges .............................. 447
8.8. Further Reading ....................................... 448
8.9 Exercises ............................................. 448
References ................................................. 451
Appendix I. Fundamental Constants and Conversion Factors .... 455
Appendix II. Abbreviations ................................... 459
Appendix III. Symbols ......................................... 463
Appendix IV. Useful Mathematical Expressions ................. 469
Index ......................................................... 473
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