The effect of H2/C2H2 ratio on the structure and tribological properties of carbon thin films prepared by PBII

Carbon thin films have been prepared on Si by plasma-based ion implantation (PBII) with H2 and C2H2 mixed gases with various H2/C2H2 ratios. The effect of the H2/C2H2 ratio on the structure and tribological properties of the thin films has been investigated. XPS composition depth profile shows that a H2/C2H2 ratio of about 1.0 corresponds to the just appearance of a carbon film growing on a C–Si transition layer showing gradually compositional and structural changes between the carbon film and the substrate, and above the ratio of 1.0 corresponds to no carbon film but a carbon-implanted layer. As the H2/C2H2 ratio increases, the carbon film shows the rapidly decreasing thickness. Raman spectra show that the carbon films are diamond-like carbon (DLC) films rich in Sp3 bonds carbons. A H2/C2H2 ratio of approximately 0.1 corresponds to the maximal Sp3/Sp2 ratio. The H2/C2H2 ratio in the range of 0–0.3 corresponds to larger Sp3/Sp2 ratio than the ratio of 0 (without H2 additive). AFM morphologies exhibit that the DLC films are smooth and compact, and the H2/C2H2 ratio of 0.08 corresponds to the smallest roughness. On the other hand, ball-on-disk sliding wear experiments show that the H2/C2H2 ratio of 0–0.15 exhibit more significant improvement in tribological properties of the DLC films than the ratio of 0. In particular, at low sliding load of below 0.5 N the DLC films present more than 3 h-wear life and near to zero-wear rate. It is found that the H2/C2H2 ratio of about 0.08 corresponds to the best tribological properties. The influences of sliding load, sliding frequency, film thickness and counter-ball materials on the tribological properties are also presented.