A theoretical study of the nucleation, size, and structure of diamond phase carbon clusters on Si(111) substrates is presented. Molecular mechanics analysis has been utilized to predict energetically and entropically feasible pathways for nucleation of the carbon clusters. Several mechanistic pathways for nucleation of carbon clusters are examined with CH3and/orC2H2as the nucleation precursors. A possible model for the nucleation mechanism of diamond-phase carbon clusters on the &bgr;-SiC(111) surface, which forms epitaxially on Si(111) substrates, is presented. The critical size of the carbon clusters is computed based on the atomistic theory of nucleation and the proposed nucleation mechanisms. ©1997 American Institute of Physics.