PNNL

Abstract

Molecular Dynamics methods with a modified Tersoff potential have been used to simulate Si displacement cascades with energies up to 50 keV and to compare clustering behavior for Si and Au recoils in beta-SiC. The results show that the lifetime of thermal spike is very short (0.7 ps) compared to metals and that the surviving defects are dominated by C interstitials and vacancies. Only 19% of the interstitial population is contained in clusters, with the the largest cluster containing only 4 interstitial atoms. The energy dependence of stable defect formation exhibits a power-law relationship. The high energy recoils generate multiple cascades and form dispersed defect configurations. These results suggest that the amorphization in SiC does not occur during the cascade lifetime. On the other hand, large disordered domains are created in cascades produced by 10 keV Au recoils. Structure analysis indicates that these highly disordered regions have amorphous characteristics. The data for the cluster spectra have been used to calculate relative cross sections for in-cascade amorphization and defect-stimulated amorphization. The ratios of these cross sections for Si and Au are in excellent agreement with those derived from a fit of the direct-impact/defect-stimulated model to experimental data.