POINT-DEFECT MOVEMENT AND ANNEALING IN COLLISION CASCADES

The effect of collision cascades on preexisting point defects in cryst alline materials was studied by simulating 5 keV collision cascades in gold, copper, aluminum, platinum, and silicon. The results indicate t hat collision cascades do not significantly affect interstitials or va cancies outside the liquid core of the cascade, although in the fee me tals the heating of the crystal due to the cascade causes some thermal migration of the interstitials. Within the liquid cascade core, both interstitials and Vacancies move towards the center of the molten regi on when it resolidifies and recombine or cluster there. At elevated te mperatures, random jumps of interstitials during the thermal-spike pha se can cause significant additional trapping of interstitials in the l iquid. In contrast to the annealing effects of preexisting damage in t he fee metals, in silicon the amount of new damage created by st casca de is roughly independent of the number of initial point defects. The difference is attributed to the nature of the bonding in the materials .