Computer simulation of damage in diamond due to ion impact and its annealing

The structural modifications that a highly damaged region in diamond undergoes upon thermal annealing have been studied by molecular dynamic simulations. We verified our use of the Tersoff potential and our computational methods for describing the thermally driven transition of diamond to graphite by calculating the thermal graphitization of a diamond slab and comparing the results with those of recently published [Alessandro De Vita et al., Nature (London) 379, 523 (1996)] ab initio calculations. A deeply buried damage region in diamond was obtained by imparting high momenta (corresponding to a kinetic energy of 416 eV) to up to 12 lattice atoms aimed towards the same point in the crystal. This led to the partial amorphization of a volume of a radius of 1.4 nm. The samples with these damage regions were then annealed, with molecular dynamics, at 3000 K for up to 20 ps. It was found that dislodged carbon atoms in the periphery of the damaged region tended to rearrange as threefold coordinated atoms in a planar graphitic structure oriented along the [111] directions of the diamond. Threefold coordinate atoms in the center of the damage region, where the damage density is high, tended to convert to a fourfold coordinated configuration, i.e., regrow to diamond. This behavior was not found for a lightly damaged diamond region, created by the energetic dislodgement of just one C atom. The findings of the present study are in agreement with experimental data on the annealing/graphitization of diamond, damaged by energetic heavy ions as encountered during ion implantation of diamond. [S0163-1829(99)07509-8].