Stability and mobility of interstitial-type defect clusters generated from displacement cascades in copper and gold by in-situ transmission electron microscopy

In-situ TEM observations were carried out in copper and gold under 100keV C+, 240keV Cu+, 600keV Kr2+, and 900keV Xe3+ irradiations from 573 to 823K, in order to obtain direct experimental insights into the defect accumulation processes. Defect clusters corresponding to displacement cascades were observed to be unstable depending on the temperature, ion species, and fluence. Multiple (2 or 3) defect clusters showing up with their contrast in the same video frames were considered to be features associated with subcascades and high mobility of these clusters when located within 20 nm and from 20 to 140 nm, respectively. Instability and diffusion of defect clusters were also detected under ion irradiation. The directions of the cascade-driven and instability-driven motions of he defect clusters were strongly related to crowdion directions, suggesting that the underlying mechanism is based on the motion of crowdion-related glissile defects. This instability is interpreted as the transition of sessile defects into glissile ones. The effects of intra- and inter-cascades on the formation of glissile defects are suggested based on their dependence on the ion species and flux.