Theoretical Studies of Growth of Diamond (110) from Dicarbon

A mechanism for growth on the diamond (110) surface, with dicarbon (C 2 ) as the growth species, is examined. Reaction energies and activation energies of the various steps in the mechanism were investigated on model systems using molecular quantum mechanics, including the AM1 semiempirical method and the BLYP/6-31G* density functional method. The BLYP/6-31G* method yielded reaction energies and activation barriers in reasonable agreement with the results of G2 theory on some simple, related reactions. Two models for a hydrogen-terminated diamond (110) surface were employed, one with 18 carbon atoms (C 18 H 26 ) and another with 46 carbon atoms (C 46 H 50 ). The results indicate that C 2 addition to diamond (110) is highly exothermic with small activation barriers (<5 kcal/mol). Insertion of C 2 into CH bonds on the model surface to form an ethylene-like adsorbate is energetically favorable, resulting in energy lowerings of 150−180 kcal per mole of C 2 . Formation of single bonds between adjacent adsorbed C 2 units can be initiated by the addition of a hydrogen atom to one of the adsorbed, ethylene-like C 2 moieties. The linking of two C 2 units by this process is exothermic. The formation of single bonds between adjacent adsorbed C 2 units can also occur directly, without initiation by hydrogen addition, and is exothermic for the linking of three or more C 2 units. By either pathway the formation of a C−C single bond on the surface is exothermic by 40−50 kcal/mol.