Effect of source gas chemistry on tribological performance of diamond-likecarbon films

In this study, we investigated the effects of various source gases (methane , ethane? ethylene, acetylene, and methane + hydrogen) on the friction and wear performance of diamond-like carbon (DLC films produced from the source gases. Specifically, we described the anomalous nature and fundamental fri ction and near mechanisms of DLC films derived from gas discharge plasmas w ith very low to very high hydrogen content. The films were deposited on ste el substrates by a plasma-enhanced chemical vapor deposition process at roo m temperature and the tribological tests were performed in dry nitrogen. Th e tribological tests revealed a close correlation between the source gas ch emistry and the friction and wear coefficients of the DLC films. Specifical ly, films grown in source gases with higher hydrogen-to-carbon ratios had m uch lower friction coefficients and wear rates than did films derived from source gases with lower hydrogen-to-carbon ratios. The lowest friction coef ficient (0.002) was achieved with a him derived from 25% methane +75% hydro gen, whereas a coefficient of 0.15 was seen in films derived from acetylene . Similar correlations were observed for wear rates. Films derived from hyd rogen-rich plasmas had the least wear, whereas films derived from pure acet ylene suffered the highest wear. We used a combination of scanning and tran smission electron microscopy and Raman spectroscopy to characterize the str uctural chemistry of the resultant DLC films. 2000 Elsevier Science S.A. Al l rights reserved.