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

The structural modifications that a highly damaged region in diamond underg oes upon thermal annealing have been studied by molecular dynamic simulatio ns. We verified our use of the Tersoff potential and our computational meth ods for describing the thermally driven transition of diamond to graphite b y calculating the thermal graphitization of a diamond slab and comparing th e results with those of recently published [Alessandro De Vita et al., Natu re (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 sa me 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 anne aled, 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 re arrange as threefold coordinated atoms in a planar graphitic structure orie nted along the [111] directions of the diamond. Threefold coordinate atoms in the center of the damage region, where the damage density is high, tende d to convert to a fourfold coordinated configuration, i.e., regrow to diamo nd. This behavior was not found for a lightly damaged diamond region, creat ed by the energetic dislodgement of just one C atom. The findings of the pr esent study are in agreement with experimental data on the annealing/graphi tization of diamond, damaged by energetic heavy ions as encountered during ion implantation of diamond. [S0163-1829(99)07509-8].