Gaseous precursors of diamond-like carbon films: chemical composition of CH4/Ar plasmas

Abstract We have implemented a gas-phase chemistry numerical simulation of a typical radio frequency, low-pressure plasma. We have applied it to the study of CH 4 /Ar plasmas used for the deposition of diamond and diamond-like carbon films. Our results show that CH 3 is the most abundant carbon-containing radical in pure methane discharges and in CH 4 /Ar mixtures at low argon concentrations, indicating that the gaseous precursor of the film is CH 3 . On the contrary, in discharges of methane highly diluted by argon, we find evidence of a transition in the gas-phase composition. Since the most abundant carbon-containing radical becomes the carbon dimer C 2 , while CH 3 gets completely removed from the gas phase, we are led to the conclusion that an alternative growth mechanism should act in highly diluted CH 4 /Ar plasmas, where the role of the gaseous precursor of the film is played by C 2  radicals.