Water adsorption and desorption on ultra-low friction sulfur-doped hydrogenated carbon films

Water adsorption on hydrogenated carbon film surfaces can drastically affect friction behaviour. In this work, we investigate water adsorption and desorption properties of sulfur-doped hydrogenated films, which we have observed to retain ultra-low friction properties of hydrogenated carbon films in humid air. Water adsorption studies using a quartz crystal microbalance show that there is an almost threefold reduction in equilibrium water coverage at room temperature on hydrogenated carbon films doped with 5 at.% sulfur. Thermal desorption studies indicate that sulfur doping weakens the binding of water molecules on hydrogenated carbon film surfaces.