Theoretical Studies on Nanocrystalline Diamond: Nucleation by Dicarbon and Electronic Structure of Planar Defects

Abstract

Density functional theory and ab initio molecular orbital theory have been used to calculate the energetics of C2 insertion into C9H12 and C9H14 clusters that model unhydrided and monohydrided (100) diamond surfaces, respectively. The reaction of C2 with either the C9H12 or C9H14 cluster is exothermic by more than 100 kcal/mol, but the lowest energy product is different for the two clusters. The reaction of singlet C2 with the CC double bond of the C9H12 cluster leads to either carbene structures or a cyclobutyne-like structure, with the former having the lower energy at both the HF/6-31G* and B3LYP/6-31G* levels of theory. No barrier for insertion into the CC double bond of the C9H12 cluster was found at the HF/6-31G* and B3LYP/6-31G* levels of theory. The reaction of singlet C2 with the HC−CH single bond or C−H bonds of the C9H14 cluster leads to a structure having a cyclobutene-like geometry. We propose that the disparate nucleation rates of diamond crystallites grown in hydrogen-rich vs hydrogen-poor ...