Variation in formation and migration of self-interstitial atom clusters in electron irradiated copper with material purity and specimen preparation method

Abstract

ABSTRACT In situ observation with high-voltage electron microscopy was used to survey effects of impurity atoms on the formation and one-dimensional (1D) migration of self-interstitial atom (SIA) clusters in copper under electron irradiation at 300 K. Specimens were prepared from copper materials of five nominal purities (9N, 6N, 5N, 4N, and 3N) using three methods with different annealing conditions. In standard (STD) specimens prepared through cold rolling and annealing in vacuum, SIA cluster formation and 1D migration depended little on the nominal purity. In non-annealed (NA) specimens prepared from high-purity materials (9N and 6N) using mechanical processing and electropolishing, the defect structure was found to be coarser than in STD specimens. In fact, SIA clusters in NA specimens had number density of more than an order of magnitude lower and an average size more than four times greater. Furthermore, 1D migration had the frequency of about an order of magnitude higher and distance extending more than twice longer. Results of bulk annealing (BA) specimens showed that annealing of as-received block material had minor effects. Distributions of 1D migration distance for all specimens were described using an earlier proposed trap model. These results were discussed assuming that SIA clusters are trapped by impurity atoms existing in as-received materials and those induced by annealing.