Abstract
Crystal growth in a microwave plasma CVD was studied using as seeds crystalline diamond particles produced by an HP-HT technique. Reaction pressure and hydrogen gas flow rate were fixed at 3.3kPa and 2.8cm3/s, respectively, while the methane concentration and reaction duration were variable. A microwave power of 220W was used for most of the runs. Results were evaluated in terms of increase in linear grain dimension. The growth rate reached a maximum at a microwave power of around 220W (1170K estimated) and a methane concentration of about 5.4%. There was a tendency for growth rate to be high in the early stage and to decrease as the process went on, with larger seeds growing more slowly. It was also observed that the growth rate was significantly affected by the surface condition in the early stage.
Based on observation of deposited particles and analysis by X-ray diffraction and Raman spectroscopy, methane concentrations not exceeding 1.0% are necessary for producing idiomorphic diamond crystals. Specifically, at concentrations higher than 1.8%, the product was round, with amorphous carbon co-deposited.
