Point defect movement and annealing in collision cascades

The effect of collision cascades on preexisting point defects in crystalline materials was studied by simulating 5 keV collision cascades in gold, copper, aluminum, platinum, and silicon. The results indicate that collision cascades do not significantly affect interstitials or vacancies outside the liquid core of the cascade, although in the fee metals 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 region when it resolidifies and recombine or cluster there. At elevated temperatures, random jumps of interstitials during the thermal-spike phase can cause significant additional trapping of interstitials in the liquid. In contrast to the annealing effects of preexisting damage in the fee metals, in silicon the amount of new damage created by st cascade is roughly independent of the number of initial point defects. The difference is attributed to the nature of the bonding in the materials.