Environmental Effects on the Tribology and Microstructure of MoS2-Sb2O3-C Films

The tribology of molybdenum disulfide (MoS2)-Sb2O3-C films was tested under a variety of environmental conditions (ambient 50% RH, 10(-7) Torr vacuum, 150 Torr oxygen, and 8 Torr water) and correlated with the composition of the surface composition expressed while sliding. High friction and low friction modes of behavior were detected. The lowest coefficient of friction, 0.06, was achieved under vacuum, while sliding in 8 Torr water and ambient conditions both yielded the highest value of 0.15. Water vapor was determined to be the environmental species responsible for high friction performance. XPS evaluations revealed a preferential expression of MoS2 at the surface of wear tracks produced under vacuum and an increase in Sb2O3 concentration in wear tracks produced in ambient air (50% RH). In addition, wear tracks produced by sliding in vacuum exhibited the lowest surface roughness as compared to those produced in other environments, consistent with the picture of low friction originating from well-ordered MoS2 layers produced through sliding in vacuum.