Electron Spectroscopy for Surface Analysis

The development of surface physics and surface chemistry as a science is closely related to the technical development of a number of methods involving electrons either as an excitation source or as an emitted particle carrying characteristic information. Many of these various kinds of electron spectroscopies have become commercially available and have made their way into industrial laboratories. Others are still in an early stage, but may become of increasing importance in the future. In this book an assessment of the various merits and possible drawbacks of the most frequently used electron spectroscopies is attempted. Emphasis is put on prac­ tical examples and experimental design rather than on theoretical considerations. The book addresses itself to the reader who wishes to know which electron spectroscopy or which combination of different electron spectroscopies he may choose for the particular problems under investigation. After a brief introduction the practical design of electron spectrometers and their figures of merit important for the different applications are discussed in Chapter 2. Chapter 3 deals with electron excited electron spectroscopies which are used for the elemental analysis of surfaces. Structure analysis by electron diffrac­ tion is described in Chapter 4 with special emphasis on the use of electron diffrac­ tion for the investigation of surface imperfections. For the application of electron diffraction to surface crystallography in general, the reader is referred to Volume 4 of "Topics in Applied Physics".

1. Introduction.- 1.1 Electron Spectroscopy and Its Importance in Surface Science.- 1.2 The Information Depth.- 1.3 Electron Spectroscopies.- References.- 2. Design of Electron Spectrometers for Surface Analysis.- 2.1 Specific Requirements of the Various Electron Spectroscopies for Surface Analysis.- 2.2 General Principles and Characteristics of Electron Spectrometers.- 2.2.1. Basic Principles of Energy Analysis.- 2.2.2. Characteristics Related to Energy Resolution and Sensitivity.- 2.2.3. Figures of Merit.- 2.3 Design Principles of Electron Spectrometers.- 2.3.1 Electron Optics for Energy Analysis.- 2.3.2 Optimization of Electron Monochromators and Analyzers.- 2.3.3 Detection Methods and Data Processing.- 2.3.4 Further Practical Considerations.- 2.4 Description of the Electron Spectrometers and the Methods of Energy Analysis for Surface Studies.- 2.4.1 Electrostatic Deflection Spectrometers.- 2.4.2 Magnetic Deflection Spectrometers.- 2.4.3 Crossed-Field Deflection Spectrometers.- 2.4.4 Retarding Potential Spectrometers.- 2.4.5 Other Techniques.- 2.5 Comparison of Electron Spectrometers.- 2.6 List of Abbreviations and Acronyms.- References.- 3. Electron-Excited Core Level Spectroscopies.- 3.1 Basic Processes.- 3.1.1 Free Atoms.- 3.1.2 Surface Atoms.- 3.2 Threshold Spectroscopies.- 3.2.1 Oberserving the Excitation: Disappearance Potential Spectroscopy (DAPS).- 3.2.2 Observing the Deexcitation.- 3.3 Ionization Loss Spectroscopy (ILS).- 3.4 Auger Electron Spectroscopy (AES).- 3.4.1 Influence of the Atomic Environment.- 3.4.2 Quantitative Auger Analysis.- 3.4.3 Auger Microanalysis.- 3.4.4 Combined Auger/X-Ray Microanalysis.- 3.5 Comparisons.- 3.5.1 Threshold Spectroscopies Inter Se.- 3.5.2 Threshold Spectroscopies Versus ILS.- 3.5.3 Elemental Analysis.- References.- 4. Electron Diffraction and Surface Defect Structure.- 4.1 Principles of Defect Detection by Electron Diffraction.- 4.1.1 Validity of the Kinematical Approximation.- 4.1.2 Construction and Calculation of the Ideal LEED Pattern.- 4.1.3 Instrumental Limitations.- 4.1.4 Diffraction Pattern of Simple Defect Structures.- 4.1.5 The Kind of Information in the Diffraction Pattern.- 4.2 Point Defects.- 4.2.1 Variation of Scattering Factor.- 4.2.2 Variation of Atom Position.- 4.3 Atomic Steps.- 4.3.1 Regular Step Arrays on Primitive Lattices.- 4.3.2 Irregular Step Arrays.- 4.3.3 Nonprimitive Lattices.- 4.3.4 Examples of Stepped Surfaces.- 4.4 Domains and Facets.- 4.4.1 Superstructures and Domains.- 4.4.2 LEED Patterns of Domain Structures.- 4.4.3 Quantitative Description of LEED Patterns.- 4.4.4 Facets.- 4.5 The Interpretation of a LEED Pattern.- 4.5.1 Parameters to be Observed.- 4.5.2 Interrelation of Defects and Effects.- References.- 5. Photoemission Spectroscopy.- 5.1 Principles of Photoemission.- 5.1.1 Parameters and Ranges.- 5.1.2 Basic Processes.- 5.2 Instrumentation.- 5.2.1 Light Sources.- 5.3 Theoretical and Practical Aspects.- 5.3.1 Electron Excitation and Emission.- 5.3.2 Surface Sensitivity.- 5.3.3 Relaxation and Chemical Shift.- 5.3.4 Photoemission from Adsorbates.- 5.4 Measurement Methods.- 5.4.1 Energy-Resolved Spectroscopy.- 5.4.2 Angle-Resolved Photoemission.- 5.4.3 Yield Spectroscopies.- 5.4.4 Spin-Polarized Photoemission.- References.- 6. Electron Energy Loss Spectroscopy.- 6.1 Definition of ELS.- 6.2 Theory of Inelastic Scattering.- 6.2.1 The Classical Theory (Concept of the “Dielectric Theory”).- 6.2.2 Quantum Mechanical Description of the Dielectric Theory.- 6.2.3 The Excitation of Optical Surface Phonons in Infrared-Active Material.- 6.2.4 Excitation of Optical Surface Phonoms on Noninfrared-Active Substrates.- 6.2.5 Excitation of Plasma Waves.- 6.2.6 Electronic Surface Transitions.- 6.2.7 Data Reduction.- 6.2.8 Anisotropic Effects of ELS.- 6.3 Experimental Studies of Surface Vibrations (Clean Surfaces).- 6.3.1 The Apparatus.- 6.3.2 Infrared Active Material.- 6.3.3 Noninfrared Active Material.- 6.4 Vibrational Modes on Gas-Covered Surfaces.- 6.4.1 Apparatus.- 6.4.2 Information.- 6.4.3 Oxygen Adsorption on Si (111) 2 × 1.- 6.4.4 Adsorption of Hydrogen on Si (111) 2 × 1.- 6.4.5 Hydrogen Adsorption on W(100).- 6.4.6 Adsorption of Oxygen on W(100).- 6.4.7 The Adsorption of CO on Tungsten (100).- 6.5 Experimental Studies of Electronic Transitions.- 6.5.1 The Apparatus.- 6.5.2 Relationship Between the Spectrometer and the Interpretation of the Loss Spectra.- 6.5.3 Excitations of Electronic Transitions at Clean Silicon Surfaces.- 6.5.4 Electronic Excitations at Ge(111) Surfaces.- 6.5.5 Galliurn Arsenide.- 6.5.6 Selection Rule Effects Observed at Ge and GaAs.- 6.5.7 Electronic Transitions at SiO and SiO2.- 6.6 Conclusion.- References.