Positrons in solids
01 Jan 1979-Vol. 12
TL;DR: 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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TL;DR: In this article, the positron potential is constructed from the full lattice electrostatic potential, and a local-density approximation for the correlation potential, in order to reliably predict annihilation characteristics for positrons trapped at defect clusters of varying size, geometry and impurity environment.
Abstract: A new, versatile method of calculating positron states in solids is described. The main purpose is to develop a practical scheme accurate enough to reliably predict annihilation characteristics for positrons trapped at defect clusters of varying size, geometry and impurity environment, in order to help analyse experimental data. The positron potential is constructed from the full lattice electrostatic potential, and a local-density approximation for the correlation potential. The three-dimensional positron Schrodinger equation is solved by finite-element techniques. Enhancement effects in the annihilation rate are parametrised in a simple way, both for simple and transition metals. The applications discussed include vacancies, vacancy clusters and impurity-vacancy complexes in a number of metals. Good agreement with experiment in cases where comparison is possible suggests a good predictive power for the scheme.
571 citations
TL;DR: Positron annihilation spectroscopy is particularly suitable for studying vacancy-type defects in semiconductors and combining state-of-the-art experimental and theoretical methods allows for detailed identification of the defects and their chemical surroundings as mentioned in this paper.
Abstract: Positron annihilation spectroscopy is particularly suitable for studying vacancy-type defects in semiconductors. Combining state-of-the-art experimental and theoretical methods allows for detailed identification of the defects and their chemical surroundings. Also charge states and defect levels in the band gap are accessible. In this review the main experimental and theoretical analysis techniques are described. The usage of these methods is illustrated through examples in technologically important elemental and compound semiconductors. Future challenges include the analysis of noncrystalline materials and of transient defect-related phenomena.
534 citations
TL;DR: In this article, the positron annihilation spectroscopy (PAS) was used as a non-destructive probe to examine defects in technologically important Si-based structures, including the quality of overlayers, formation and annealing of defects after ion implantation, identification of defect complexes, and evaluation of the distribution of internal electric fields.
Abstract: In the past few years, there has been rapid growth in the positron annihilation spectroscopy (PAS) of overlayers, interfaces, and buried regions of semiconductors. There are few other techniques that are as sensitive as PAS to low concentrations of open‐volume‐type defects. The characteristics of the annihilation gamma rays depend strongly on the local environment of the annihilation sites and are used to probe defect concentrations in a range inaccessible to conventional defect probes, yet which are important in the electrical performance of device structures. We show how PAS can be used as a nondestructive probe to examine defects in technologically important Si‐based structures. The discussion will focus on the quality of overlayers, formation and annealing of defects after ion implantation, identification of defect complexes, and evaluation of the distribution of internal electric fields. We describe investigations of the activation energy for the detrapping of hydrogen from SiO2−Si interface trap centers, variations of interface trap density, hole trapping at SiO2−Si interfaces, and radiation damage in SiO2−Si systems. We also briefly summarize the use of PAS in compound semiconductor systems and suggest some future directions.
288 citations
TL;DR: In this article, the study of thermal vacancy formation in pure metals by positron annihilation and the determination of vacancy formation enthalpies is reviewed with particular emphasis to the potential of positron lifetime spectroscopy.
Abstract: The study of thermal vacancy formation in pure metals by positron annihilation and the determination of vacancy formation enthalpies is reviewed with particular emphasis to the potential of positron lifetime spectroscopy. The investigation of high-temperature vacancy migration by positron annihilation in pulse-heating experiments is outlined and first results are reported.
Es wird ein Uberblick gegeben uber die Untersuchung von Leerstellen im thermischen Gleichgewicht in reinen Metallen mit Hilfe der Positronenzerstrahlung und uber die dabei gewonnenen Resultate der Leerstellenbildungsenthalpie. Hierbei wird insbesondere auf die spezifischen Moglichkeiten der Positronlebensdauerspektroskopie hingewiesen. Es wird zudem uber die Ergebnisse von Messungen der Positronenzerstrahlung in schnellen Aufheizexperimenten berichtet, mit denen die Leerstellenwanderung bei hohen Temperaturen untersucht werden kann.
286 citations
TL;DR: Positron annihilation spectroscopy (PAS) has become an increasingly valuable tool for the study of the electronic and defect struc- tures of materials as discussed by the authors, due to the ability of the positron to annihilate from a variety of specific states in solids, ranging from an extended state in a defect-free lattice to highly localized states in lattice defects.
Abstract: Positron annihilation spectroscopy (PAS) has in recent years become an increasingly valuable tool for the study of the electronic and defect struc tures of materials. Owing to the ability of the positron to annihilate from a variety of specific states in solids, ranging from an extended state in a defect-free lattice to highly localized states in lattice defects, PAS can yield unique information regarding various properties of materials. The unique aspects of PAS arise from the fact that the positron-electron pair annihilation process, which proceeds by the emission of y rays, can yield detailed information regarding both the electron density and the electron momenta in the region from which the positron annihilates. The physical basis of positron annihilation in condensed matter and the applications of PAS to the study of solids have been extensively reviewed elsewhere (1-4). In addition, several reviews of various aspects of the application of PAS to the study of electronic structure (5-10) and defects in materials (1 1-20) have been published. The present paper is intended as a brief introduction to positron annihilation, and its recent literature, and to the applications of PAS in the area of materials science, with particular emphasis on metals and alloys. As such, this review will use selected examples from the literature to discuss some recent advances in this relatively new research area as well as some of the future potential of PAS for the study of materials. The present work is based, in part, on a previous short review (20) by this author.
254 citations