Carbon Nanotubes Grow on the C Face of SiC (0001̄) during Sublimation Decomposition: Quantum Chemical Molecular Dynamics Simulations

Abstract

High-temperature quantum chemical molecular dynamics simulations (QM/MD) based on the density functional tight binding (DFTB) method were performed on SiC surfaces and compared with experimental observations. Following the nucleation of nanocaps on the C face of SiC(0001), substantial carbon nanotube (CNT) growth is observed during evaporation of Si between 2000 and 3000 K, while the Si face appears not capable of nanocap formation and perpendicular tube growth under otherwise identical conditions. Instead, graphene sheet growth parallel to the surface is observed in this case. Si evaporation is modeled by two approaches to Si atom removal, one where all Si atoms in one surface layer are removed simultaneously and another one where Si atoms are individually removed from random positions in selected surface layers. The tubes directly “grown” in our simulations display many sidewall defects, consistent with experimental findings. During random removal of Si on the C face, we also observe first indications ...