Characterization of nanometer scale wear and oxidation of transition metal dichalcogenide lubricants by atomic force microscopy

Atomic force microscopy has been used to characterize wear and oxidation of transition metal dichalcogenide surfaces. Sequential images recorded on molybdenum disulfide (MoS2) and niobium diselenide (NbSe2) surfaces show that wear proceeds at defects, and that MoS2 wears at least five times more slowly than NbSe2. Images of thermally treated MoS2 and NbSe2 further demonstrate that oxidation creates surface defects on both materials. However, for similar oxidation conditions, NbSe2 surfaces show extensive degradation, while MoS2 surfaces only exhibit isolated defects. The implications of these results to understanding the tribological properties of the transition metal dichalcogenides are discussed.