Role of inert gas in the low-temperature CVD nano-crystalline diamond process.

We report a systematic investigation of the effect of different inert gases on chemical vapour deposition (CVD) of nano-crystalline diamond. \textit{In situ} optical emission measurement was employed to monitor the plasma chemistry, which possibly influences the film growth. Our result indicates that C$_{2}$ is not necessarily the key growth species for nano-crystalline diamond and we will demonstrate here that the nano-crystalline diamond film can be grown under conditions where the C$_{2}$ concentration is very small. Modelling results support the trend in number density changes for intermediate radicals with the volume percentage of argon variation for CH$_{4}$/H$_{2}$/Ar plasma.