Angular Correlation of the Annihilation Radiation Method in Comparative Analysis of the Atomic–Electron Structure of Various Carbon Materials

Abstract

The atomic–electronic and defect structure of various carbon materials—crystalline diamond and CVD diamond films, single-crystal and polycrystalline graphite, technical carbons with different specific surface areas and oxidation states, activated carbons, and carbon nanofibers—has been studied using the positron annihilation method. It has been found that the shape of the angular distribution of annihilation radiation (ACAR) for carbon nanofibers differs from that of both graphite and diamond materials. A noticeable broadening of the ACAR compared to that of polycrystalline graphite has been recorded. It has been shown that the carbon–carbon bonds are stressed and the shortest distance between adjacent carbon atoms is reduced compared to graphite. The presence of adjacent planes in the helical structure of the nanofiber also increases the degree of localization of annihilating valence electrons. All this leads to the observed broadening of the ACAR in nanofibers.