Positrons in Solids

ISBN-13: 9783642813184 / Angielski / Miękka / 2011 / 258 str.

P. Hautoj Rvi; A. Dupasquier

Opis

In condensed matter initially fast positrons annihilate after having reached equi librium with the surroundings. The interaction of positrons with matter is governed by the laws of ordinary quantum mechanics. Field theory and antiparticle properties enter only in the annihilation process leading to the emergence of energetic photons. The monitoring of annihilation radiation by nuclear spectroscopic methods provides valuable information on the electron-positron system which can directly be related to the electronic structure of the medium. Since the positron is a positive electron its behavior in matter is especially interesting to solid-state and atomic physi cists. The small mass quarantees that the positron is really a quantum mechanical particle and completely different from any other particles and atoms. Positron physics started about 25 years ago but discoveries of new features in its interac tion with matter have maintained continuous interest and increasing activity in the field. Nowadays it is becoming part of the "stock-in-trade" of experimental physics."

Spis treści

1. Introduction to Positron Annihilation.- 1.1 Positron Method.- 1.2 Annihilation of Free Positrons.- 1.3 Experimental Techniques.- 1.3.1 Lifetime Measurements.- 1.3.2 Angular Correlation Measurements.- 1.3.3 Line-Shape Measurements.- 1.3.4 Correlation Between Lifetime and Momentum.- 1.4 Positroniurn Formation and Annihilation.- 1.5 Topics of Positron Studies.- 1.5.1 Metals.- 1.5.2 Metal Defects.- 1.5.3 Ionic Crystals.- 1.5.4 Slow Positrons and Positronium.- 1.5.5 Gases and Low-Temperature Phenomena.- 1.5.6 Molecular Sol ids.- 1.5.7 Positronium Chemistry.- 1.6 Summary.- References.- 2. Electron Momentum Densities in Metals and Alloys.- 2.1 Theory.- 2.1.1 Momentum Density.- 2.1.2 Many-Body Effects.- 2.1.3 Positron Thermalization, Effective Mass and Other Thermal Effects.- a) Thermalization.- b) Effective Mass.- c) Other Thermal Effects.- 2.2 Wave Functions.- 2.2.1 Positron Wave Function.- 2.2.2 Electron Band Structure and Wave Functions.- a) OPW Method.- b) APW Method.- c) KKR and Related Methods.- d) Other Methods.- 2.2.3 Symmetry Properties of Aj(?,k).- a) Radial Behavior.- b) Directional Symmetry.- 2.3 Experimental Techniques.- 2.3.1 2? Angular Correlation Measurements.- 2.3.2 Rotating Specimen Method.- 2.3.3 Doppler Broadening.- 2.3.4 Specimen Preparation.- 2.3.5 Corrections.- a) “Beam Profile” Correction.- b) Diffraction Effect.- c) Angular Resolution and Positron Thermal Motion.- d) Finite Slit Length.- 2.3.6 Analysis.- 2.4 Momentum Density Work in Metals.- 2.4.1 Alkali Metals.- 2.4.2 Other Simple Metals.- 2.4.3 Oriented Graphite, Diamond, Silicon, and Germanium.- 2.4.4 Noble Metals.- 2.4.5 Transition Metals and Rare Earths.- 2.5 Disordered Alloys and Ordered Metallic Compounds.- 2.5.1 Disordered Alloys.- 2.5.2 Metallic Compounds.- 2.6 Conclusion.- References.- 3. Positron Studies of Lattice Defects in Metals.- 3.1 Annihilation Parameters for Defect Studies.- 3.1.1 The Defect Trapping Phenomenon and Its Effect.- 3.1.2 Positron States and Lifetime Spectra.- 3.1.3 Momentum Density Parameters.- 3.2 Monovacancies in Equilibrium.- 3.2.1 The Naive Approach to Temperature Effects.- 3.2.2 Prevacancy Effects.- 3.2.3 Other Complications.- 3.2.4 Vacancy Formation Enthalpy Measurements.- 3.2.5 Characteristic or Threshold Temperatures.- 3.2.6 Pressure Experiments.- 3.3 Nonequilibrium Studies.- 3.3.1 The “Many Defects” Problem.- 3.3.2 Deformation, Quenching, and Irradiation Experiments.- 3.3.3 Annealing Studies.- 3.3.4 Positron Studies of Voids.- 3.4 Defect Studies in Alloys.- 3.4.1 Defect vs Impurity Problems.- 3.4.2 Vacancy Studies.- 3.4.3 Phase Transitions and Boundary Effects.- 3.5 Liquid and Amorphous Metals.- References.- 4. Positrons in Imperfect Solids: Theory.- 4.1 Positron Distribution, Mobility, and Trapping.- 4.1.1 Positron Implantation, Slowing Down, and Thermalization.- 4.1.2 Mobility and Diffusion.- 4.1.3 Positron Distribution in Solids.- 4.1.4 Annihilation Characteristics and Electron-Positron Correlation in Pure Metals.- 4.1.5 Effect of Temperature on Annihilation Characteristics.- 4.1.6 Trapping at Defects.- 4.1.7 Self-trapping.- 4.2 Defects in Metals.- 4.2.1 Electronic Structure of Defects.- 4.2.2 Positron-Defect Interaction.- 4.2.3 Annihilation Characteristics.- 4.2.4 Applications.- a) Vacancies.- b) Dislocations.- c) Impurities and Alloys.- d) Vacancy Clusters.- e) Surfaces.- 4.3 Nonmetals.- 4.4 Conclusions.- References.- 5. Positrons in Ionic Solids..- 5.1 Experimental Methods.- 5.1.1 Standard Experimental Techniques.- 5.1.2 Special Experimental Techniques.- a) Two-Parameter Age-Momentum Measurements.- b) Magnetic Quenching Measurements.- 5.1.3 Experimental Difficulties.- a) Analysis of Multicomponent Lifetime Spectra.- b) Analysis of Multicomponent Momentum Distributions.- c) Source and Surface Contributions to Lifetime Spectra.- d) Radiation Damage Due to the Positron Source.- 5.2 Annihilation Characteristics in Alkali Halides.- 5.2.1 Room Temperature Measurements on Crystals with Low Defect Concentration.- a) Lifetime Spectra.- b) Angular Correlation Curves.- c) Doppler-Broadened Annihilation Line Shape.- d) Three-Quantum Annhi1ation.- 5.2.2 Temperature Effects.- 5.2.3 Annihilation in Crystals with High Defect Concentration.- a) Thermal Defect Generation.- b) Thermal Quenching.- c) Additive Coloration.- d) F ? F-Conversion.- e) Aggregation of F Centers.- f) Doping with Divalent Impurities.- g) Defect Creation by Ionizing Radiation.- h) Plastic Deformation.- i) Mixed Crystals.- 5.2.4 Magnetic Field Effects.- a) Crystals with Low Defect Concentration.- b) Additively Colored Crystals.- c) Doped Crystals.- 5.3 Positron States in Alkali Halides.- 5.3.1 Intrinsic States.- a) Nearly Free Positrons in a Perfect Lattice.- b) Quasi-Positronium in Perfect Crystals.- 5.3.2 Annihilation Centers.- a) CA Center.- b) aA+ Center.- c) CA- and cA-(Ca2+) Centers.- d) aA Center.- e) a2A+ and a3A+ Centers.- 5.3.3 Kinetics of State Formation.- a) Slowing Down.- b) Quasi-Positronium Formation in Perfect Crystals.- c) Formation of A Centers.- 5.4 Annihilation in Other Ionic Compounds.- 5.4.1 Hydrides of Alkali and Alkaline-Earth Metals.- 5.4.2 Copper, Silver, Gold, Thallium Halides.- 5.4.3 Alkaline-Earth Halides.- 5.4.4 Alkaline-Earth Oxides.- References.- Additional References with Titles.