Friction properties of WS2/graphite fluoride thin films grown by pulsed laser deposition

Abstract Graphite fluoride (CF x ) is investigated as an additive for WS 2 thin films to reduce its sensitivity to moisture. The films are grown onto hardened 440C stainless steel disks by pulsed laser deposition using the 248 nm line from an excimer laser. Substrate temperature and additive concentration are varied to control film chemistry and crystal structure. The effect of relative humidity (i.e., x exhibit ultralow friction (ULF) behavior in dry air (i.e., μ ⩽ 0.01), but friction increases with RH. Mechanisms for the ULF behavior are proposed which suggest that further reductions in friction are possible. Films grown at 300 °C or with higher concentrations of CF x are relatively insensitive to humidity, but have more typical friction coefficients (μ ⩽ 0.04) in dry air.