Positron beam investigations of natural cubic and coated diamonds

Positron beam and 2D-ACAR investigation of cubic and coated diamonds are re ported. In type IIA diamonds, positrons are mostly trapped in vacancies in the carbon lattice; in type Ia diamonds, two main defect-related annihilati on sites are nitrogen-vacancy complexes (H2, H3) and the vicinity of split interstitial atoms. No correlation between principal nitrogen defects and a nnihilation rate was found. PAS data indicate the presence of a significant amount of vacancies in all studied diamonds, which increases the rate of n itrogen aggregation. It is shown that pressurised fluid inclusions may serv e as a positron trap, giving rise to the long component in the lifetime spe ctra. (C) 2000 Elsevier Science Ltd. All rights reserved.