Insights into the Growth of (Ultra)nanocrystalline Diamond by Combined Molecular Dynamics and Monte Carlo Simulations

In this paper, we present the results of combined molecular dynamics Metropolis Monte Carlo (M D-M MC) simulations of hydrocarbon species at flat diamond (100)2 x 1 and (111)1 x 1 surfaces. The investigated species are considered to be the most important growth species for (ultra)nanocrystalline diamond ((U)NCD) growth, When applying the NI MC algorithm to stuck species at monoradical sites, bonding changes are only seen for CH(2). The sequence of the bond breaking and formation as put forward by the MMC simulations mimics the insertion of CH, into a surface dimer as proposed in the standard growth model of diamond. For hydrocarbon species attached to two adjacent radical (biradical) sites, the MMC simulations give rise to significant changes in the bonding structure. For UNCD, the combinations of C(3) and C(3)H(2), and C(3) and C(4)H(2) (at diamond (100)2 x 1) and C and C(2)H(2) (at diamond (111)1 x 1) are the most successful in nucleating new crystal layers. For NCD, the following combinations pursue the diamond structure the best: C(2)H(2) and C(3)H(2) (at diamond (100)2 x 1) and CH(2) and C(2)H(2) (at diamond (111)1 x 1). The different behaviors of the hydrocarbon species at the two diamond surfaces are related to the different sterical hindrances at the diamond surfaces.