MICROWAVE DIAMOND SYNTHESIS WITH HIGH OXYGEN HYDROCARBONS (CARBON-DIOXIDE, OXYGEN)

Abstract

Our previous study demonstrated that a higher growth rate and improved crystallinity resulted from using CH4-CO(2)s in diamond deposition. The possibility of diamond synthesis using a high oxygen-containing liquid hydrocarbon, dimethyl carbonate (C3H6O3) supplemented by CO2 or 0(2) was therefore explored in the present study. Well-faceted diamond was deposited when the ratios of the respective flow rates for CO2/C3H6O3 and O-2/C3H6O3 were 6%-8% and 1.5%-2.25%. The growth rates of the diamond films, which were of high quality, were 3.6 and 1.7 mu m h(-1) respectively. The diamond films displayed different surface morphology and crystal features in these gas mixtures, i.e. the diamond film possessed more (311) and (100) facets in the O-2-C3H6O3 mixture at a power of 400 W. The diamond film deposited from 6.75% CO2 in C3H6O3 was indicated by the roughness determination not only to possess a higher growth rate but also to attain a smooth surface with a roughness of 0.048 mu m (R(a)). The surface roughness of the diamond film was 0.083 mu m for 2% O-2 in C3H6O3. The intensities of CO, OH and O produced from O-2-C3H6O3 mixtures were observed by optical emission spectroscopy measurements to be greater than those produced from CO2-C3H6O3 mixtures, but the intensities of C(2)d CH showed the opposite trend. This was the main difference between the CO2-C3H6O3 and O-2-C3H6O3 mixtures. Therefore a larger amount of etching agents appears to block the nucleation of diamond in O-2-C3H6O3 mixtures. The complete results of our study, including Raman and X-ray diffraction analyses, are presented here.