Effect of feed gas composition effects on the nanotribological properties of diamond-like carbon films

A series of experimental nanoindentation, nanowear and nanoscratch tests was conducted to investigate the relationship between the nanotribological characteristics of diamond-like carbon (DLC) and feed gas composition used for the deposition. The DLC films were deposited on silicon substrates in radio-frequency plasma enhanced chemical vapor deposition system with a mixture of hydrogen and methane gases. Raman spectroscopy results show that the integrated intensity ratios (ID/IG) of each profile correlate with sp2/sp3 ratios. The result also indicates that the hydrogen content in the source gas has a significant influence upon the sp2/sp3 ratio and hydrogen-to-carbon ratio in DLC films. It is demonstrated that the sp2/sp3 ratio decreases with increasing hydrogen content in the DLC film. Our result also reveals that a significant relationship between the hydrogen content and the nanotribological characterizations of the DLC films, namely lower hydrogen-to-carbon ratio leads to higher hardness, elastic modulus, friction coefficient, and lower wear depth. The surface reinforcement can be attributed to the fact that variation of surface energy arises from the different carbon hybridized states (sp2/sp3 ratio), which improve the surface properties via the hydrogen content in the source gas and associated nanotribological characteristics.

► Tribological diamond-like carbon (DLC) coatings were prepared.
► RF-plasma-enhanced chemical vapor deposition with H2 and CH4 gas mixture
► Integrated intensity ratios (ID/IG) have been correlated with sp2/sp3 ratios.
► Tribological properties of DLC films studied by nanoindentation