Friction-induced chemical and structural modifications of molybdenum disulphide thin films

The present work investigates chemical and structural modifications of molybdenum disulphide thin coatings induced by macroscale friction in both reactive (air) and inert conditions. Chemical and micro-structural modifications were analyzed in detail by Raman spectroscopy. We found no traces of oxide formation even when sliding was performed in the air. However, the formation of a well-adhered tribofilm, related to superior lubricating properties, was detected only in inert conditions. We can conclude that, in ambient condition, it is water physisorption and not oxidation, which impairs good lubrication. At the same time, Raman spectra indicated a re-crystallization effect induced by sliding.