Positron Spectroscopy

Abstract

An overview of the historical development of positron spectroscopy as a probe of condensed matter on the atomic and nano‐scale is followed by an introduction to the fundamentals of positron annihilation and interactions with condensed matter. The experimental techniques of positron lifetime and Doppler broadening spectroscopies, angular correlation of annihilation radiation, and their derivatives, are presented. The development of positron beams of controllable energy for the study of surfaces, interfaces and thin films and layers is described. Finally, examples are given which illustrate how the application of positron annihilation spectroscopy to probe the electronic structure of materials–in the bulk or at or near the surface–yields information not only of a fundamental nature, but also on technologically‐important structural, chemical and electronic properties such as open‐volume defects, nano‐structures, free volumes and phase changes.

High-intensity positron microprobe at the Thomas Jefferson National Accelerator Facility

“…Furthermore, there is great interest from the solid state and atomic physics communities in exploring fundamental and applied research areas that are not accessible with the currently existing low-energy positron intensities. [1][2][3][4][5] There are many experiments that would benefit from a high-intensity high-brightness slow positron source. For example, the 2D-Angular Correlation of Annihilated Radiation (2D-ACAR) measurement to determine fragile Fermi surface pieces of complex materials is source limited and may require several months of data accumulation.…”

Laser Powder Bed Fusion of Molybdenum and Mo-0.1SiC Studied by Positron Annihilation Lifetime Spectroscopy and Electron Backscatter Diffraction Methods

“…Measurements using positrons have the advantage over the other techniques used in evaluating AM materials because they probe a three-dimensional subsurface volume that can be hundreds of microns deep instead of a small, select surface area found in electron and optical microscopy. Advancements in measurement and analysis have developed the ability of PAS techniques to identify single-atom vacancy-type defects [ 18 ] and can characterize microstructures at defect concentrations from 10 to 10 per atom [ 19 ]. They are highly sensitive to open-volume vacancy-type defects such as dislocations, monovacancies, divacancies, and clusters of vacancies at the atomic scale due to the lower electron density found here than in the bulk metal.…”