A MICROSCOPIC MODEL FOR SURFACE-INDUCED DIAMOND-TO-GRAPHITE TRANSITIONS

GRAPHITIZATION of diamond at ambient pressure,vas first observed in th e 1920s(1,2), but the mechanisms responsible for this transformation a nd, in particular, those underlying the nucleation and growth of graph ite in diamond, remain controversial(3-5). In addition to their fundam ental interest, these processes have technological relevance-for examp le, for the growth by chemical vapour deposition(6) of diamond-like fi lms, which sometimes include graphitic islands(7), Here we report the results of first-principles molecular dynamics simulations of a surfac e-induced diamond-to-graphite transition, which provide a microscopic model for the early stages of the graphitization process, We find that a well defined diamond/graphite interface forms during the transition ; the electronic properties of the atoms at this interface suggest tha t they are highly chemically active sites. In addition to its relevanc e to graphite inclusion in diamond films, our model should yield insig ht into the process of selective etching in vapour-deposited carbon fi lms, and possibly also into diamond nucleation.