Structure and Mechanical Properties of Diamond-Like Carbon Films Prepared from C2H2 and H2 Mixtures by Pulse Plasma Chemical Vapor Deposition

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Diamond-like carbon (DLC) films were prepared by dc pulse plasma chemical vapor deposition (CVD). The hydrogen flow ratio [$\text{H$_{2}$}/(\text{C$_{2}$H$_{2}$}+\text{H$_{2}$})$] was varied from 0 to 0.75, and the pulse frequency was varied from 1 to 20 kHz. Then, the relationship between film structure and hardness was investigated. At $\text{H$_{2}$}/(\text{C$_{2}$H$_{2}$}+\text{H$_{2}$})=0$, films prepared at 10 kHz have the greatest hardness because a further increase in pulse frequency leads to an increase in the number of regular sixfold ring structures in the film and excessive ion peening on the growth face. The hardness at $\text{H$_{2}$}/(\text{C$_{2}$H$_{2}$}+\text{H$_{2}$})=0.5$ is greater than that at $\text{H$_{2}$}/(\text{C$_{2}$H$_{2}$}+\text{H$_{2}$})=0$ because the effect of ion peening and the number of regular sixfold ring structures at $\text{H$_{2}$}/(\text{C$_{2}$H$_{2}$}+\text{H$_{2}$})=0.5$ are suitable for fabricating hard films. In contrast, at $\text{H$_{2}$}/(\text{C$_{2}$H$_{2}$}+\text{H$_{2}$})=0.75$, the hardness is lower than that at $\text{H$_{2}$}/(\text{C$_{2}$H$_{2}$}+\text{H$_{2}$})=0$ because of the reduced effect of ion peening; thus, the effect of an increase in the number of polymer bonds becomes significant.
2010-07-25