Investigation of nanostructured materials by positron annihilation

Nanostructured materials with grain sizes around 10 nm (maximum similar to 100 nm) have maximum number of interfacial vacancy-like defects and microvoids - clusters of 10 to 15 vacancies, at the intersection of the interfaces. Each of these defects has a size distribution. A large inter-atomic distance distribution and reduced atomic density in the grain boundaries, compared to that within the crystallites, have been proposed. Positron annihilation spectroscopy, which is one of the most effective non-destructive tools to study the type and concentration of the defects in solids, has been extensively used to investigate the nature of nanostructured materials. In this review the author has attempted to summarize the information obtained so far on these materials from positron studies.