| Abstract Scope |
I will discuss friction behavior of nanocontacts with 2D materials studied with atomic force microscopy (AFM) and molecular dynamics (MD) simulations. Graphite exhibits a nonmonotonic dependence of friction on humidity. From MD, we attribute this to adsorbed water molecules that, when sparse, act as pinning sites, but when plentiful, form a quasi-ordered, incommensurate, low-friction layer [https://doi.org/10.1103/PhysRevMaterials.2.126001]. We also discuss 2D transition metal dichalcogenide (TMD) films, which exhibit intrinsically low friction, although not as low as graphene, attributable to the interfacial potential energy corrugation [https://doi.org/10.1021/acs.nanolett.9b02035]. Friction is measured for sliding on MoS2 from cryogenic to elevated temperatures, with the paradoxical observation that sometimes friction decreases dramatically with temperature (thermolubricity), but other times is athermal. Finally, we compared MoS2, MoSe2, and MoTe2 in bulk and monolayer forms. AFM and MD show that MoS2 has the highest friction and MoTe2 the lowest. Simulations unlock the key to this dependence [https://doi.org/10.1021/acsnano.0c07558]. |