The tribological properties of nanometre carbon films prepared by plasma-based ion implantation at various implanting voltages

Abstract

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.