Superlow friction of titanium/silicon codoped hydrogenated amorphous carbon film in the ambient air

Titanium/silicon codoped hydrogenated carbon film was deposited on the n-Si (100) substrates by reactive magnetron sputtering Ti80Si20 target in a mixture of argon and methane. Microstructure of the film was investigated using x-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, Raman spectroscopy, and attenuated total reflectance Fourier transform infrared spectroscopy. The investigations have revealed that the film has an amorphous structure and consists of high sp2 hybridized carbon atoms and bonding hydrogen atoms. The mechanical and tribological properties were evaluated using a nanoindentor and a ball-on-disk tribometer, respectively. The film exhibits hardness of 9.6 GPa, high elastic recovery of 73.0% and high H/E ratio of 0.156. Most significant, the superlow friction (μ<0.01) and special low wear rate (2.4x10-7 mm3 N-1 m-1) was observed in ambient air with 40% relative humidity. Combining the results of scanning electron microscopy and Raman analyses of the worn surface, it is concluded that some mechanisms, e.g., transfer films, friction-induced graphitization, hydrogen-terminated carbon surface, tribochemical reaction, etc., could be together responsible for this superlow friction in the ambient air.