Synthesis of carbon films with ultra-low friction in dry and humid air

Using pulsed dc magnetron sputtering, we synthesized hydrogenated amorphous carbon films with and without sulfur doping. These films were smooth and amorphous, with low compressive stress (< 1 GPa). Auger electron spectroscopy confirmed the incorporation of sulfur, and X-ray photoelectron spectroscopy showed that sulfur atoms are chemically bound. Most significant, ball-on-flat tribo-testing showed that hydrogenated carbon films doped with 5 at.% sulfur have ultra-low friction coefficients (< 0.01) in air with relative humidity from 0% to 50%.