Speed dependence of friction on single-layer and bulk MoS2 measured by atomic force microscopy

We perform atomic force microscopy (AFM) experiments on mechanically exfoliated, single-layer and bulk molybdenum disulfide (MoS2) in order to probe friction forces as a function of sliding speed. The results of the experiments demonstrate that (i) friction forces increase logarithmically with respect to sliding speed, (ii) there is no correlation between the speed dependence of friction and the number of layers of MoS2, and (iii) changes in the speed dependence of friction can be attributed to changes in the physical characteristics of the AFM probe, manifesting in the form of varying contact stiffness and tip-sample interaction potential parameters in the thermally activated Prandtl–Tomlinson model. Our study contributes to the formation of a mechanistic understanding of the speed dependence of nanoscale friction on two-dimensional materials.