Gaseous precursors of diamond-like carbon films in CH4/Ar plasmas

We have investigated by numerical simulations the gas-phase chemistry of a typical radio frequency, low pressure CH4/Ar plasma used for the deposition of diamond and diamond-like carbon films. We find that CH3 is the most abundant carbon containing radical in pure methane discharges, while it is the carbon dimer C2 in discharges of methane highly diluted by argon. Thus, we propose that the gaseous precursor of the film is CH3 in methane plasmas, and C2 in CH4/Ar plasmas.