PARAMETRIC STUDY OF ATMOSPHERIC-PRESSURE DIAMOND SYNTHESIS WITH AN INDUCTIVELY-COUPLED PLASMA TORCH

Polycrystalline diamond coatings have been deposited on molybdenum and silicon substrates using an inductively coupled, atmospheric-pressure plasma torch. Growth rates are on the order of 10 mum/hr. The inductively coupled plasma reactor is found to produce a uniform, well-characterized growth environment for experimental and computational study of the atmospheric-pressure diamond growth regime. Growth morphology is found to be sensitive to reactor conditions such as substrate surface temperature and methane-to-hydrogen feed ratio. An experimental parametric study of these variables is performed and the resultant growth analyzed by scanning electron microscopy, Raman spectroscopy, and X-ray diffraction. Spectroscopic analysis of the gas phase is also performed Results indicate that the substrate temperature range over which diamond growth occurs shifts toward higher temperatures as the methane-to-hydrogen feed ratio is increased The growth rate is observed to reach a maximum with varying methane-to-hydrogen feed ratio at constant substrate temperature. Raman analysis of the deposits indicates that higher-quality diamond is achieved at the highest limits of substrate temperature for a given methane-to-hydrogen ratio. Higher-quality diamond is also observed to be formed al lower methane-to-hydrogen feed ratios.