Gas-phase kinetics during microwave plasma-assisted diamond deposition: Is the hydrocarbon product distribution dictated by neutral-neutral interactions?

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Abstract
The mole fractions of H, H2, CH3, CH4, and C2H2 that were generated in a microwave plasma under conditions typical for diamond deposition are reported. When the methane percentage in the feed gas was 4+H↔CH3+H2 reaction was found to be at the same level of nonequilibrium as in the hot‐filament case. These results, plus arguments based on general principles of plasma chemistry, are taken as indications that the hydrocarbon chemistry in the microwave system is as strongly dictated by neutral‐neutral reactions as in a thermal system. The primary effect of the plasma is perhaps its role in dissociating hydrogen molecules to H atoms without having to raise the gas temperature significantly.