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BookDOI

Positrons in solids

Pekka J. Hautojärvi
- Vol. 12
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TLDR
Positron decomposition has been studied extensively in the literature as mentioned in this paper, with a focus on the effect of free positrons and their formation and removal in the presence of free Positrons.
Abstract
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.

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Journal ArticleDOI

Positron study of native vacancies in doped and undoped GaAs

TL;DR: In this article, the authors used positron lifetime measurements to study various doped and undoped GaAs samples in the as-grown state and concluded that positron trapping by acceptor-type Ga-vacancy-dopant complexes is the main cause of vacancy defects.
Journal ArticleDOI

Precipitation and dissolution processes in age-hardenable Al alloys — a comparison of positron annihilation and X-ray small-angle scattering investigations I. Al—Zn(x) (x = 3, 4.5, 6, 10, and 18 at%)

TL;DR: In this paper, the precipitation and dissolution processes in four AlZn(4.5)Mg alloys are studied by means of XSAS, TEM, and PAS investigations.
Journal ArticleDOI

Relaxation and crystallization behavior of the Zr50Cu40Al10 metallic glass

TL;DR: In this paper, the authors examined relaxation and crystallization behavior of the ternary Zr50Cu40Al10 metallic glass by using positron annihilation and transmission electron microscopy (TEM).
Journal ArticleDOI

Defect analysis in FeAl and FeSi with positron lifetime spectroscopy and Doppler broadening

TL;DR: In this paper, the authors used positron lifetime spectroscopy and Doppler broadening to measure the defect formation in intermetallic compounds of FeAl and FeSi.
Journal ArticleDOI

Defect types and defect properties in FeAl alloys

TL;DR: In this paper, the authors measured the migration enthalpy using the fast Doppler broadening technique and showed that the formation volume of the defects increases from 0.88 Ω in Fe-7at to 1.42 Ω at Fe-40at.
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