Influence of carbon monoxide - Addition to the reaction gas on the hot-filament diamond deposition

Diamond layers were deposited by means of hot-filament chemical vapor deposition from CO/CH4/H-2 gas mixtures. With additions of 1 and 5% CO to the CH4/H-2 mixtures it was possible to obtain faceted diamond layers. CH4 concentrations above 1.5% led to ballas diamond formation. Additions between 10 and 15% CO led to faceted diamond layers with methane concentrations up to 2.0%; these experiments resulted in the highest growth rate of 1.68 mu m/h. Ballas deposition was observed at 2.5% CH4 and above. In conclusion, the addition of CO to the CH4/H-2 gas mixture can increase the growth rates of faceted diamond. This can be explained by the reacativity of oxygen, which obviously reacts with hydrogen under the given diamond deposition conditions.