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)) o n 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 m ethane (6 scc min(-1)) and oxygen (0 or 2 scc min(-1)) have been emplo yed. Scanning electron microscopy and laser Raman spectroscopy have be en utilised for the characterisation of the deposit. Intermediate hydr ogen flow rates are found to give maximum crystallite size, crystallit e density and better quality of diamond deposit. The presence of oxyge n does not affect the trend but it increases the deposition rate and i mproves the quality of the deposit. It has been brought out that atomi c hydrogen besides etching also plays a role in the formation of diamo nd nuclei and their growth.