GROWTH OF DIAMOND FROM CO2-(C2H2, CH4) GAS SYSTEMS, WITHOUT SUPPLYING ADDITIONAL HYDROGEN GAS

Recently, we have been searching for a new reaction path in diamond growth and discovered that diamond films can grow without adding extra hydrogen gas to the hydrocarbon feed. Using high pressure microwave chemical vapour deposition and gas systems of CH4-CO2 or C2H2-CO2, icosahedral polycrystalline particles were deposited and the surface of the films revealed a polycrystalline morphology with smooth (111) facets. The growth rate of the film is 3.11-mu-m h-1 in the CH4-CO2 system and 0.98-mu-m h-1 in the C2H2-CO2 system. The carbon ratio range of the former, which grows crystalline diamond, is broader than the latter ratio range. Furthermore, the growth rate of films in the C2H2-CO2 system is twice that of the CH4-H2 System, and similar to the maximum rate in the CO-H2 system. In the CH4-CO2 system, the maximum rate which resulted in crystalline diamond films is about 2-mu-m h-1, which is about four times that of the CH4-H2 system and twice that of the CO-H2 system. We believe that the crystallinity and quality of the film as determined by X-ray diffraction and cathodoluminescence spectral analysis are comparable with those of naturally occurring type IIa diamond.