Hydrogen flow rate dependence of diamond crystallite size, density and quality in ''jet flow'' HFCVD employing CH4-H-2-O-2 gaseous mixture

The effect of variation of hydrogen flow rate (300-2000 sec min(-1)) on the crystallite size, crystallite density and the quality of diamond deposited on tungsten and silicon substrates has been investigated in ''jet-flow'' HFCVD technique. In these studies, fixed flow rates of methane (6 scc min(-1)) and oxygen (0 or 2 scc min(-1)) have been employed. Scanning electron microscopy and laser Raman spectroscopy have been utilised for the characterisation of the deposit. Intermediate hydrogen flow rates are found to give maximum crystallite size, crystallite density and better quality of diamond deposit. The presence of oxygen does not affect the trend but it increases the deposition rate and improves the quality of the deposit. It has been brought out that atomic hydrogen besides etching also plays a role in the formation of diamond nuclei and their growth.