Superlow friction behavior of Si-doped hydrogenated amorphous carbon film in water environment

Si-doped hydrogenated amorphous carbon (a-C:H:Si) film was prepared using hybrid radio frequency plasma-enhanced chemical vapor deposition (R.F. PECVD) and non-balanced magnetron sputtering deposition technique. The microstructure of the film was characterized by means of Raman spectrometry, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD), while its friction behavior in water environment was investigated using a ball-on-disc tribometer. Results show that the a-C:H:Si film has typical diamond-like characteristics, and Si doped with a relative atomic concentration of about 3.9% in the film mainly exists in the form of Si, SiC, and SiO2, while it shows a superlow friction coefficient of about 0.005 in water environment when sliding against Si3N4 ball. The superlow friction behavior of the hybrid diamond-like-carbon (DLC) film could be attributed to the formation of a tribochemical reaction film and boundary lubrication layer mainly consisting of colloidal silica generated from tribochemical reactions between silicides and water molecules.