Computer simulations of damage due to passage of a heavy fast ion through diamond

Abstract

We present tight-binding molecular dynamics simulations of the structural modifications that result from the “thermal spike” that occurs during the passage of a heavy fast ion through a thin diamond or amorphous carbon layer, and the subsequent regrowth upon cooling. The thermal spike and cooling down are simulated by locally heating and then quenching a small region of carbon, surrounded either by diamond or by a mostly $s{p}^3$ bonded amorphous carbon network. For the case of the thermal spike in diamond we find that if the “temperature” (kinetic energy of the atoms) at the center of the thermal spike is high enough, an amorphous carbon region containing a large fraction of threefold coordinated C atoms ($s{p}^2$ bonded) remains within the diamond network after cooling. The structure of this amorphous layer depends very strongly on the “temperature” of heating and on the dimensions of the thermal spike. Scaling is found between curves of the dependence of the percentage of $s{p}^2$ bonded atoms in the region of the thermal spike on the heating “temperature” for different volumes. When the thermal spike occurs in an initially amorphous sample the structure of the damaged region after cooling exhibits the above dependencies and is found to be a function of the structure of the original amorphous carbon layers.