Impact of Microstructure on MoS2 Oxidation and Friction

This work demonstrates the role of microstructure in the friction and oxidatidn behavior of the lamellar solid lubricant molyhderiurn disulfide (MoS2). We report on systematic investigations of oxidation and friction for two MoS2 films with distinctively different microstructures amorphous and planar/highly-ordered before and after exposure to atomic oxygen (AO) and high-temperature (250 degrees C) molecular oxygen. A combination of experimental tribology, molecular dynamics simulations, X-ray photoelectron spectroscopy (XPS),, and high sensitivity low-energy ion scattering (HS-LEIS) was used to reveal new insights about the links between structure and properties of these, widely utilized low-friction materials. Initially, ordered MoS2 films showed a surprising resistance to both,atomic and molecular oxygens (even at elevated temperature), retaining characteristic low friction, after exposure to extreme Oxidative environments. XPS shows comparable oxidation Of both coatings via, AO; however, monolayer resolved compositional depth profiles from HS-LEIS,reveal that the microstructure of the ordered coatings limits oxidation to the first atomic layer.