Tribological performance of ultrathin diamond-like carbon films prepared by plasma-based ion implantation

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 sp(3)/sp(2) 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 sp(3)/sp(2) 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.