Experimental and molecular dynamics simulation studies of friction behavior of hydrogenated carbon films

Hydrogenated carbon (CH_x) films were grown by reactive magnetron sputtering of graphite in an argon-hydrogen plasma. Pulsed d.c. bias was applied to both the carbon target and the substrate to maintain a stable process and reasonable deposition rate. The resulting films were smooth and stress-free. The influence of hydrogen concentration and relative humidity on friction properties of the films was investigated. At 5% relative humidity, the lowest friction coefficient of 0.01 was obtained at a sputter-gas composition containing 25% hydrogen. Excessive incorporation of hydrogen produces softening and degrades its friction performance at high contact stresses. Molecular dynamics simulation studies showed the reduction of friction coefficient with surface hydrogenation. These studies indicate that pulsed d.c. magnetron sputtering can produce hydrogenated carbon films with friction properties similar to those prepared by chemical vapor deposition methods.