Surface Analysis - The Principal Techniques Edited by John C. Vickerman Surface Analysis Research Centre, Department of Chemistry UMIST, Manchester, UK JOHN WILEY & SONS Chichester New York Weinheim Brisbane Singapore Toronto
Contents List of Contributors Preface xiii xv Chapter 1 Introduction 1 JOHN С VICKERMAN 1 How do we define the surface? 1 2 How many atoms in a surface? 2 3 Information required 3 4 Surface sensitivity 5 5 Radiation effects surface damage 6 Chapter 2 Vacuum Technology for Applied Surface Science... 9 ROD WILSON 1 Introduction: gases and vapours 9 2 The pressure regions of vacuum technology and their characteristics 15 3 Production of a vacuum 17 3.1 Types of pump 17 3.2 Evacuation of a chamber 29 3.3 Choice of pumping system 30 3.4 Determination of the size of backing pumps 31 3.5 Flanges and their seals 31 4 Measurement of low pressures 32 4.1 Gauges for direct pressure measurement... 33 4.2 Gauges using indirect means of pressure measurement 35 4.3 Partial pressure measuring instruments 39 Chapter 3 Electron Spectroscopy for Chemical Analysis 43 BUDDY RATNER DAVID CASTNER
vi CONTENTS 1 Overview 43 1.1 The basic ESCA experiment 43 1.2 A history of the photoelectric effect and ESCA 44 1.3 What information is learned from ESCA? 45 2 X-ray interaction with matter, the photoelectron effect, and photoemission from solids 46 3 Binding energy and the chemical shift 49 3.1 Koopmans' Theorem 49 3.2 Initial state effects 50 3.3 Final state effects 52 3.4 Binding energy referencing 53 3.5 Charge compensation in insulators 55 3.6 Peak widths 56 3.7 Peak fitting 57 4 Inelastic mean free path and sampling depth 58 5 Quantitation 61 5.1 Quantitation methods 63 5.2 Quantitation standards 63 5.3 Quantitation example 66 6 Spectral features 67 7 Instrumentation 74 7.1 Vacuum systems for ESCA experiments... 75 7.2 X-ray sources 76 7.3 Analyzers 77 7.4 Data systems 79 7.5 Accessories 79 8 Spectral quality 80 9 Depth profiling 81 10 X-Y Mapping 85 11 Chemical derealization 87 12 Valence Band 89 13 Perspectives 90 13.1 Energy resolution and spectral interpretation 90 13.2 Low-temperature ESCA studies 91 13.3 Photoelectron diffraction 91 13.4 Low-cost ESCA 91 13.5 Imaging ESCA 91 14 Conclusions 92
CONTENTS Chapter 4 Auger Electron Spectroscopy 99 HANS JÖRG MATHIEU 1 Introduction 99 2 Principle of the Auger Process 100 2.1 Kinetic energies of Auger peaks 101 2.2 Ionization cross-section 103 2.3 Comparison of Auger and photon emission.. 104 2.4 Electron backscattering 106 2.5 Escape depth 108 2.6 Chemical shifts 109 3 Instrumentation 110 3.1 Electron sources Ill 3.2 Spectrometers 112 3.3 Modes of acquisition 113 3.4 Detection limits 118 4 Quantitative analysis 119 5 Depth profile analysis 122 5.1 Thin film calibration standard 122 5.2 Depth resolution 123 5.3 Sputter rates 125 5.4 Preferential sputtering 129 5.5 A-correction 130 5.6 Chemical shifts in AES profiles 130 6 Summary 132 vii Chapter 5 Secondary Ion Mass Spectrometry-the Surface Mass Spectrometry 135 JOHN С VICKERMAN ANDREW SWIFT 1 Introduction 135 2 Basic concepts 137 2.1 The basic equation 137 2.2 Monolayer lifetime and the static limit 137 2.3 Surface charging 140 3 Experimental requirements 140 3.1 Primary beam 140 3.1.1 Electron bombardment 142 3.1.2 Plasma 143
viii CONTENTS 3.1.3 Surface ionisation 144 3.1.4 Field ionisation sources 144 3.2 Mass analysers 145 3.2.1 Magnetic sector 146 3.2.2 The quadrupole mass analyser 147 3.2.3 Time of Flight Mass Spectrometers.. 149 4 Mechanism of secondary ion generation 153 4.1 Models of sputtering 153 4.2 Ionisation 157 4.2.1 Nascent ion molecule model 157 4.2.2 The desorption ionisation model... 158 5 Static SIMS-the relationship between spectra and surface structure 158 5.1 Surface science studies of the adsorbate state 159 5.1.1 CO adsorption on metals 159 5.1.2 Adsorption of complex hydrocarbons 162 5.1.3 Surface reactions 164 5.2 Surface chemistry of organic materials 164 5.2.1 Static conditions for organic analysis. 165 5.2.2 Spectral interpretation 167 5.3 Examples of surface characterisation 169 5.3.1 Surface analysis of an adhesive system 170 5.3.2 Quantification of surface composition 173 5.4 MS/MS studies of the ion generation process 177 6 SIMS imaging or scanning SIMS 181 7 Depth profile analysis by dynamic SIMS 186 7.1 The dynamic SIMS experiment 186 7.1.1 Depth Profiling the Ion Beam... 187 7.1.2 Depth Profiling the mass analyser. 188 7.2 Quantitative analysis 188 7.2.1 Sensitivity 189 7.2.2 Dynamic range 191 7.3 Depth resolution 193 7.3.1 Instrumental effects 194 7.3.2 Surface topography 194 7.3.3 Radiation induced effects 195
CONTENTS ix 8 Sputtered Neutral Mass Spectrometry 197 8.1 Electron post-ionisation 198 8.1.1 Electron beam post-ionisation 198 8.1.2 SNMS basic equation for elemental analysis 201 8.1.3 Electron plasma SNMS 201 8.2 Photon induced post-ionisation 202 8.2.1 SNMS by resonant multi-photon ionisation (REMPI) 204 8.2.2 SNMS using non-resonant multi-photon ionisation 206 8.3 Summary 208 Chapter 6 Low-energy Ion Scattering and Rutherford Backscattering 215 EDMUND TAGLAUER 1 Introduction 215 2 Physical basis 217 2.1 The scattering process 217 2.2 Collision kinematics 218 2.3 Interaction potentials and cross-sections... 220 2.4 Shadow cone 224 3 Rutherford backscattering 227 3.1 Energy loss 227 3.2 Apparatus 230 3.3 Beam effects 232 3.4 Quantitative layer analysis 233 3.5 Structure analysis 236 3.6 The value of RBS and comparison to related techniques 240 4 Low-energy ion scattering 242 4.1 Neutralisation 242 4.2 Apparatus 245 4.3 Surface composition analysis 248 4.3.1 Adsorbates 250 4.3.2 Catalysts 252 4.3.3 Alloys 253 4.4 Structure analysis 255 4.4.1 Principles (ICISS) 255 4.4.2 Surface reconstruction 258 4.4.3 Direct recoil spectroscopy (DRS)... 259 4.5 Conclusions 262
X CONTENTS Chapter 7 Vibrational Spectroscopy from Surfaces 267 MARTYN PEMBLE 1 Introduction 267 2 Infrared spectroscopy from surfaces 268 2.1 Transmission IR spectroscopy 269 2.2 Photoacoustic spectroscopy 272 2.3 Reflectance methods 273 2.3.1 Attenuated total (internal) reflection (ATR) 274 2.3.2 Diffuse reflectance 275 2.4 Reflection-absorption IR spectroscopy (RAIRS) 278 2.4.1 The RAIRS experiment 280 2.4.2 Signal enhancement techniques in RAIRS 282 2.5 Spatial resolution in surface IR spectroscopy. 285 3 Electron energy loss spectroscopy (EELS) 285 3.1 Inelastic or impact scattering 286 3.2 Elastic or dipole scattering 289 3.3 The EELS experiment 291 3.4 Spatial resolution in EELS 292 4 The group theory of surface vibrations 292 4.1 The general approach 292 4.2 Group theory analysis of ethyne adsorbed on to a flat surface 293 4.3 Group theory analysis of ethyne adsorbed on a (100) surface of an FCC metal 296 4.4 The form of the RAIRS and dipole EELS spectrum 298 5 Laser Raman Spectroscopy from surfaces 299 5.1 The theory of Raman scattering 300 5.2 The study of collective surface vibrations (phonons) 301 5.3 Raman spectroscopy from metal surfaces... 302 5.4 Spatial resolution in Raman Spectroscopy... 304 5.5 Fourier transform Raman techniques 304 6 Inelastic neutron scattering (INS) 304 6.1 Introduction to INS 304 6.2 The INS spectrum 305 6.3 INS spectra of hydrodesulphurisation catalysts 305 7 Sum-frequency generation methods 307
CONTENTS Chapter 8 Surface Structure Determination by Interference Techniques 313 WENDY R. FLAVELL 1 Introduction 313 1.1 Basic theory of diffraction three dimensions 314 1.2 Extension to surfaces two dimensions... 319 1.2.1 Notation for surface structures 321 1.2.2 The Ewald sphere construction in two dimensions 321 2 Electron diffraction techniques 323 2.1 General introduction 323 2.2 Low energy electron diffraction (LEED)... 324 2.2.1 Development 324 2.2.2 Experimental arrangement 324 2.2.3 Elements of the theory of LEED... 326 2.2.4 Applications of LEED 334 2.3 Reflection high energy electron diffraction (RHEED) 339 2.3.1 Introduction 339 2.3.2 Experimental arrangement 339 2.3.3 Elements of the theory of RHEED... 340 2.3.4 Applications of RHEED: Temporal intensity variations in RHEED patterns during film growth of semiconductors by Molecular Beam Epitaxy (MBE) 342 3 Absorption/Scattering techniques 346 3.1 Introduction 346 3.1.1 X-ray absorption in solids 346 3.1.2 Fine structure in X-ray absorption spectra 348 3.2 Extended X-ray absorption fine structure (EXAFS) 348 3.2.1 The importance of EXAFS 350 3.2.2 Basic theory of EXAFS 351 3.2.3 Experimental techniques 356 3.2.4 Data handling 359 3.2.5 Applications of EXAFS 361 3.3 Extension to surfaces surface exafs (SEXAFS) 364 3.3.1 Experimental techniques 364 xi
xii CONTENTS Chapter 9 3.3.2 Applications of SEXAFS 366 3.3.3 NEXAFS (XANES) in surface structure determination 369 4 Additional techniques for surface structure determination 371 4.1 Two-dimensional X-ray diffraction (surface X-ray diffraction) 371 4.2 X-ray standing waves (XSW) or standing X-ray wavefield absorption (SXW) 376 4.3 Photoelectron diffraction (PD) 379 Scanning Tunnelling Microscopy and Atomic Force Microscopy 393 GRAHAM LEGGETT 1 Introduction 393 2 Basic principles of operation 394 2.1 Operation of the STM 395 2.1.1 Quantum tunnelling 395 2.1.2 The role of tip geometry. 397 2.1.3 Instrumentation and basic operating parameters 402 2.2 Operation of the AFM 403 3 Atomic resolution and spectroscopy: surface crystal and electronic structure 407 3.1 Studies of gold surfaces 408 3.2 Graphite surfaces 412 3.3 The silicon (111) 7 x 7 reconstruction 413 3.4 Scanning tunnelling spectroscopy 414 3.5 Crystal growth 418 3.6 Lithography and micromanipulation 419 3.7 Atomic resolution by AFM 422 4 Molecules at surfaces 423 4.1 Liquid crystals and organic liquids 423 4.2 Self-assembled monolayers 429 4.3 Other adsorbate and film structures 430 5 Studies of polymer surfaces 432 6 Biological applications 438 7 Conclusions 444 Index 451