About 30 nm thick nanometre carbon films have been prepared on Si wafers by plasma-based ion implantation at various implanting voltages. The ball-on-disc sliding friction experiments show that the tribological properties of these carbon films are in good agreement with the corresponding structure characteristics which strongly depend on the implanting voltage. These structure characteristics include the film roughness, the film thickness, the C–Si transition layer between the carbon film and the Si substrate and the sp3/sp2 ratio. As the implanting voltage increases, the roughness and the thickness decrease, the C–Si transition layer thickens and the sp3/sp2 ratio first increases to the maximum value at about 30 kV and then decreases. 3 kV and below correspond to bad tribological properties owing to polymer-like carbon (PLC) film and no C–Si transition layer with poor adhesion to the Si substrate. When the implanting voltage increases to over 3 kV, a C–Si transition layer is gradually formed and thickens with increasing adhesion, and the PLC film is gradually turned into a diamond-like carbon (DLC) film, and hence the tribological properties are gradually improved and reach the best values at 30 kV. 10–50 kV correspond to two orders of increase in wear life, close to zero volume wear rate, but about 0.3 friction coefficient at 0.1 N applied load. With the increase in the applied load, the wear life and the friction coefficient decrease and the wear rate increases. For Si wafers coated with the DLC films at 30 kV, in the range of 0.5–1 N, there is an appropriate value corresponding to the wear life of above 18 000 s, friction coefficient of about 0.1 and wear rate of 10−9 mm3 N−1 m−1 level. Additionally, the wear mechanism is discussed.

Ultrathin diamond-like carbon (DLC) films with thicknesses of 5–60 nm have been prepared on Si by plasma-based ion implantation. Raman spectrum and x-ray photoelectron spectroscopy (XPS) show that these DLC films present high sp3/sp2 ratios. XPS also displays that each DLC film firmly adheres to the Si substrate owing to a C–Si transition layer. Atomic force microscopy shows that the DLC films are smooth and compact with average roughness (Ra) of about 0.25 nm. Sliding friction experiments reveal that these DLC films show significantly improved tribological performance. With increase of DLC film thickness, the sp3/sp2 ratio increases, the roughness decreases, the hardness increases, the adhesive wear lightens and thereby the tribological performance becomes enhanced. Also, the effects of the applied load and the reciprocating frequency on the tribological performance are discussed.