Effect of five typical vacancy defects on the tribological behaviors of MoS2 sheet: A molecular dynamics study

The tribological behavior of the defective MoS2 sheet has been investigated under different normal loads by molecular dynamics simulations. Five typical vacancy defects have been introduced to estimate the anti-friction and anti-wear properties of defective MoS2 sheets. The existence of vacancy defects increases the local friction of the MoS2 sheet and accelerates wear failure. The degree of vacancy defect influence on the anti-friction and anti-wear properties of MoS2 is as follows: VMo < VS < VS2 < VMoS3 < VMoS6. The atomic frictional deviation of the a-C tip and the potential energy surfaces of the defective MoS2 sheet have been analyzed to reveal the potential mechanisms of the atomic pinning effect. The enhancements of atomic pinning and energy barrier induced by vacancy defects are the main contributions for the increased local friction in the MoS2 sheet. The S atomic vacancies in the bottom S layer have been further considered. The top layer S atom tends to transfer and fill the bottom S vacancy under a certain normal load of 130nN. The transformation of vacancy defect further increases the surface friction of defective MoS2 sheets.