Diamond synthesis from CO-H2 mixed gas plasma

Particulate or film-like diamond was prepared on silicon substrates from CO-H₂ mixed gas using a microwave plasma technique. The growth rate of diamond without graphite and amorphous carbon, as measured by Raman spectroscopy, was 9m h^–1 for particles and 4mh^–1 for flims. These values were larger than those in other source gas systems, such as CH₄-H₂, CH₄-H₂-H₂O and CH₃OH-H₂. The good formation rate and high quality of diamond in the CO-H₂ system was attributed to acceleration of methyl radical formation by the reaction of excited CO and H₂ molecules and removal of by-product graphite by OH radicals in the plasma.