The authors review the development of extended x-ray absorption fine structure (EXAFS) within the last decade. Advances in experimental techniques have been largely stimulated by the availability of synchrotron radiation. The theory of EXAFS has also matured to the point where quantitative comparison with experiments can be made. The authors review in some detail the analysis of EXAFS data, starting from the treatment of raw data to the extraction of distances and amplitude information, and they also discuss selected examples of applications of EXAFS chosen to illustrate both the strength and limitations of EXAFS as a structural tool.

Extended x-ray absorption fine structure—its strengths and limitations as a structural tool

Calculations of ground-state and excited-state properties of materials have been one of the major goals of condensed matter physics. Ground-state properties of solids have been extensively investigated for several decades within the standard density functional theory. Excited-state properties, on the other hand, were relatively unexplored in ab initio calculations until a decade ago. The most suitable approach up to now for studying excited-state properties of extended systems is the Green function method. To calculate the Green function one requires the self-energy operator which is non-local and energy dependent. In this article we describe the GW approximation which has turned out to be a fruitful approximation to the self-energy. The Green function theory, numerical methods for carrying out the self-energy calculations, simplified schemes, and applications to various systems are described. Self-consistency issue and new developments beyond the GW approximation are also discussed as well as the success and shortcomings of the GW approximation.

https://iopscience.iop.org/article/10.1088/0034-4885/61/3/002/pdf

The GW method

Electronic structure of solids

The structure and properties of metal-semiconductor interfaces

1 Introduction.- 1. History.- 2. Scope of Present Book and Review of Past Books.- 3. Name-Calling.- 4. Areas Related to Electron Spectroscopy Not to be Discussed in Detail.- 4.1. Electron-Impact Spectroscopy.- 4.2. Photoemission.- 4.3. Penning Ionization Spectroscopy.- 4.4. Ion Neutralization Spectroscopy.- 5. Fields Related to Electron Spectroscopy.- 2 Instrumentation and Experimental Procedures.- 1. Source Volume.- 1.1. Excitation Devices.- 1.1.1. Electron Gun.- 1.1.2. X-Ray Tube.- 1.1.3. Synchrotron Radiation.- 1.1.4. Vacuum-UV Sources.- 1.2. Target Sample.- 1.2.1. Gases.- 1.2.2. Solids.- 1.2.3. Condensed Vapors, Liquids, and Targets at Other Than Room Temperature.- 1.3. Chamber for Angular Distribution Studies.- 1.4. Preacceleration and Deceleration.- 2. Analyzer.- 2.1. Cancellation of Magnetic Fields.- 2.1.1. Helmholtz Coils.- 2.1.2. Magnetic Shielding.- 2.2. Types of Analyzers.- 2.2.1. Retarding Grid.- 2.2.2. Dispersion.- 3. Detector Systems and Data Analysis.- 3.1. Single-Channel Detector.- 3.2. Position-Sensitive Detector.- 3.3. Scanning the Spectrum.- 3.4. Data Analysis.- 4. New Developments.- 5. Review of Commercial Instruments.- 5.1. AEI.- 5.2. Du Pont.- 5.3. Hewlett-Packard.- 5.4. McPherson.- 5.5. Perkin-Elmer.- 5.6. Physical Electronics.- 5.7. McCrone-RCI.- 5.8. Vacuum Generators, Inc..- 5.9. Varian.- 5.10. Others.- 3 Fundamental Concepts.- 1. Photoelectric Effect.- 2. Binding Energy.- 3. Final States and the Sudden Approximation.- 3.1. Spin-Orbit Splitting.- 3.2. Multiplet Splitting.- 3.3. Jahn-Teller Splitting.- 3.4. Electron Shakeoff and Shakeup.- 3.5. Configuration Interaction.- 3.6. Koopmans' Theorem and the Sudden Approximation.- 3.7. Vibrational and Rotational Final States.- 4. Atomic Wave Functions.- 5. Molecular Orbital Theory.- 5.1. Theoretical Models.- 5.1.1. Ab Initio Calculations.- 5.1.2. Semiempirical Calculations.- 5.2. Basis Set Extension and MO Mixing.- 5.3. Atomic and Molecular Orbital Nomenclature.- 5.3.1. Atoms.- 5.3.2. Molecules.- 4 Photoelectron Spectroscopy of the Outer Shells.- 1. Introduction.- 2. Energy Level Scheme.- 2.1. Binding Energy.- 2.2. Final States.- 2.2.1. Spin-Orbit Splitting.- 2.2.2. Multiplet Splitting due to Spin Coupling.- 2.2.3. Jahn-Teller Effect.- 2.2.4. Electron Shakeoff and Shakeup.- 2.2.5. Configuration Interaction.- 2.2.6. Resonance Absorption.- 2.2.7. Collision Peaks.- 3. Identification of the Orbital.- 3.1. Ionization Potentials.- 3.1.1. Characteristic Ionization Bands.- 3.1.2. Effects of Substituents.- 3.1.3. Sum Rule.- 3.1.4. The Perfluoro Effect.- 3.1.5. Dependence on Steric Effects.- 3.2. Identification of Orbitals by Vibrational Structure.- 3.3. Identification of Molecular Orbitals from Intensities of Ionization Bands.- 3.4. Identification of Molecular Orbitals by Angular Distribution.- 4. Comparison of PESOS with Other Experimental Data.- 4.1. Optical Spectroscopy.- 4.2. Mass Spectroscopy.- 5. Survey of the Literature on PESOS.- 5.1. Atoms.- 5.2. Diatomic Molecules.- 5.2.1. H2.- 5.2.2. N2 and CO.- 5.2.3. O2 and NO.- 5.2.4. Diatomic Molecules Containing Halogen.- 5.3. Triatomic Molecules.- 5.3.1. Linear Triatomic Molecules.- 5.3.2. Bent Triatomic Molecules.- 5.4. Organic Molecules.- 5.4.1. Methane, Alkanes, and Tetrahedral Symmetry.- 5.4.2. Unsaturated Aliphatics.- 5.4.3. Ring Compounds.- 5.4.4. Multiring Compounds.- 5.4.5. Organic Halides.- 5.4.6. Miscellaneous Organic Compounds Containing Oxygen, Nitrogen, Sulfur, and Phosphorus.- 5.5. Organometallics and Miscellaneous Inorganic Polyatomic Molecules.- 5.6. Ions, Transient Species, and Other Special Studies in PESOS.- 6. Studies on Solids.- 7. Analytical Applications of PESOS.- 5 Photoelectron Spectroscopy of the Inner Shells.- 1. Atomic Structure.- 2. Theoretical Basis of Chemical Shifts of Core Electrons.- 2.1. Valence Shell Potential Model.- 2.2. Effect of Neighboring Atoms.- 2.3. Calculation of Net Charge from Electronegativity.- 2.4. Calculation of Net Charge from Semiempirical MO.- 2.5. Use of Ab Initio Calculations for Chemical Shifts.- 2.6. Correlation of Chemical Shift with Thermochemical Data.- 3. Summary of Data on Chemical Shifts as a Function of the Periodic Table.- 3.1. Carbon.- 3.2. Nitrogen and Phosphorus.- 3.3. Sulfur and Oxygen.- 3.4. Group IIIA, IVA, VA, and VIA Elements.- 3.4.1. Group IIIA: B, Al, Ga, In, and Tl.- 3.4.2. Group IVA: C, Si, Ge, Sn, and Pb.- 3.4.3. Group VA: N, P, As, Sb, and Bi.- 3.4.4. Group VIA: O, S, Se, and Te.- 3.5. Halides and Rare Gases.- 3.6. Alkali Metals and Alkaline Earths.- 3.7. Transition Metals.- 3.7.1. First Transition Metal Series: Sc, Ti, V, Cr, Mn, Fe, Co, Ni.- 3.7.2. Second Transition Metal Series: Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd.- 3.7.3. Third Transition Metal Series: Hf, Ta, W, Re, Os, Ir, Pt.- 3.8. Groups IB and IIB: Cu, Ag, Au, Zn, Cd, Hg.- 3.9. Rare Earths and Actinides.- 4. Special Topics on Shifts in Core Binding Energies.- 4.1. Experimental and Interpretive Problems in PESIS.- 4.1.1. Comparative Problems in the Gas and Solid Phases.- 4.1.2. Charging.- 4.1.3. Definition of Binding Energy for Insulators.- 4.1.4. Binding Energy of Surface Atoms.- 4.1.5. Radiation Effects.- 4.1.6. Linewidths.- 4.2. Inorganic Compounds.- 4.2.1. Multiple Chemical Environment.- 4.2.2. Coordination Complexes.- 4.3. Organic Compounds.- 4.3.1. Resonance.- 4.3.2. Substituent Effects.- 4.3.3. Group Analysis.- 4.3.4. Specific Studies on Organic Molecules.- 4.4. Comparison of Core Electron Binding Energy Shifts with Other Physical Quantities.- 4.4.1. Mossbauer Isomer Shift.- 4.4.2. NMR.- 4.4.3. Other Physical Data.- 5. Other Applications of PESIS.- 5.1. Multicomponent Structure.- 5.1.1. Multiplet or Exchange Splitting.- 5.1.2. Electron Shakeoff and Shakeup.- 5.1.3. Configuration Interaction.- 5.1.4. Characteristic Energy Losses.- 5.1.5. Determining the Nature of Multicomponent Structure.- 5.2. PESIS for Surface Studies.- 5.3. Angular Studies with PESIS.- 6. Use of PESIS for Applied Research.- 6.1. PESIS as an Analytical Tool.- 6.2. Biological Systems.- 6.3. Geology.- 6.4. Environmental Studies.- 6.5. Surface Studies.- 6.6. Polymers and Alloys.- 6.7. Radiation Studies.- 6.8. Industrial Uses.- 6 Auger Electron Spectroscopy.- 1. Theory of the Auger Process.- 2. Comparison of the Auger Phenomenon with the Photoelectric Effect and X-Ray Emission.- 3. Use of Auger Spectroscopy for Gases.- 3.1. Atoms.- 3.2. Molecules.- 3.3. Study of Ionization Phenomena by Auger Spectroscopy.- 3.4. Autoionization.- 3.5. Auger Spectroscopy for Use in Gas Analysis.- 4. Use of Auger Spectroscopy in the Study of Solids.- 4.1. Special Problems Encountered on Using AES with Solids.- 4.1.1. Variables Concerned with Production of Auger Electrons.- 4.1.2. High-Energy Satellite Lines.- 4.1.3. Characteristic Energy Losses.- 4.1.4. Charging in Nonconducting Samples.- 4.2. High-Resolution Auger Spectroscopy with Solids.- 4.3. General Analytical Use of Auger Spectroscopy.- 4.4. Use of Auger Spectroscopy in the Study of Surfaces.- 4.4.1. General Considerations.- 4.4.2. Literature Survey of Surface Applications.- 4.5. Other Methods for Surface Analysis.- 4.5.1. Comparison of PESIS and Auger Spectroscopy for Surface Studies.- 4.5.2. Methods of Surface Analysis Other than AES and PESIS.- Appendixes.- 1. Atomic Binding Energies for Each Subshell for Elements Z = 1-106.- 3. Compilation of Data on Shifts in Core Binding Energies.- 4. Acronyms and Definitions of Special Interest in Electron Spectroscopy.- References.

Photoelectron and Auger Spectroscopy

We present experimental evidence of a unique, ordered chemisorption phase in the initial interaction of oxygen with the Al(111) surface. At high oxygen exposure or high temperature, this phase is shown to transform irreversibly to a bulklike aluminum oxide. The measured temperature dependence, as well as the low-energy electron diffraction, suggests a threefold, centered bonding site. A comparison between calculated and experimental valence-band density of states for the oxygen-covered Al(111) surface is made for the estimated oxygen-atom-substrate-surface distance.

Ordered oxygen overlayer associated with chemisorption state on Al(111)

Experimental Evidence for One Highly Dispersive Dangling-Bond Band on Si(111) 2 × 1

Angle-resolved energy distributions for photoelectrons emitted from the (111), (110), and (100) crystal faces of Au are presented for photon energies in the range 7.0-11.6 eV. The variation of peak-energy positions as a function of photon energy and electron emission angle has been studied. We have found very good qualitative agreement between the experimental results and the predictions of the three-step model applied to a relativistic-augmented-plane-wave band structure. To fit the theoretical peak-energy positions to the experimental data, it is necessary to lower bands Nos. 3, 4, and 5 (numbered from the bottom of the valence-band complex) by on the average 0.2 eV and to raise band No. 6 by 0.2 eV along the $\ensuremath{\Gamma}K$ symmetry line. Considerable emission must also be attributed to nondirect processes such as phonon-assisted nondirect transitions, scattering of electrons excited in direct transitions, and surface photoemission. A shoulder due to nondirect processes is always seen at -2.3 eV, whenever the emission due to direct transitions is low. The dispersion of the surface state in the $L$ gap has been measured. A parabolic fit to the data gives ${E}_{0}=0.45\ifmmode\pm\else\textpm\fi{}0.05$ eV and ${m}^{*}=(0.37\ifmmode\pm\else\textpm\fi{}0.05){m}_{0}$. We also report measurements on the local work function for the three low-index crystal faces.

Photoemission study of the bulk and surface electronic structure of single crystals of gold

Photoemission study of the surface and bulk electronic structures of Si(111)7×7 and Si(111)<=3̄×<=3̄:Al

Substrate core chemical shifts upon chemisorption of oxygen on aluminum are observed using variable-excitation-energy photoelectron spectroscopy. At low exposures a unique intermediate oxidation state evolves where the $\mathrm{Al} 2p$ level is shifted by only 1.3 eV toward higher binding energy as compared to the 2.6-eV shift observed for heavily oxidized aluminum (${\mathrm{A}1}_{2}$ ${\mathrm{O}}_{3}$). Simultaneous observation of the $\mathrm{O} 2p$ resonance shows evidence for a sharp phase change at exposures close to monolayer formation.

S. A. Flodström

Papers

Ordered oxygen overlayer associated with chemisorption state on Al(111)

Experimental Evidence for One Highly Dispersive Dangling-Bond Band on Si(111) 2 × 1

Photoemission study of the bulk and surface electronic structure of single crystals of gold

Photoemission study of the surface and bulk electronic structures of Si(111)7×7 and Si(111)<=3̄×<=3̄:Al

Multiple Oxidation States of Al Observed by Photoelectron Spectroscopy of Substrate Core Level Shifts