THERMAL PLASMA SYNTHESIS OF DIAMOND

A numerical model was used to examine experimental data in which a gas chromatograph measured the composition of gas sampled through a 70-mu m orifice in the growth substrate during atmospheric-pressure RF plas ma diamond CVD. Substantial discrepancies were found between the measu rements and the predicted species mole fractions at the surface, but t he data were in much better accord with predicted mole fractions simil ar to 0.2 mm above the surface. This may possibly be due to the pertur bation caused by the orifice; The model was also used to examine the: predicted effects of freestream and substrate temperatures on the surf ace concentrations ratios of H, CH3 and C2H2. Different trends versus substrate temperature were found according to whether the freestream t emperature was 3000 K or 4000 K.