Probing superlubricity of layered Van der Waals contact junctions by colloidal probe Atomic Force Microscopy

This chapter reviews Colloidal Probe—Atomic Force Microscopy (CP- AFM) friction experiments probing superlubricity in layered Van der Waals (meso-scopic) contact junctions. Specifically, we cover all the aspects of these experiments, from the preparation of the probes to the modeling required to achieve insight into the physical mechanisms underlying the observed phenomenology. The main fabrication methods of the graphene-coated colloidal probes are comprehensively described. We also report on key features that accompany the emergence of superlubricity for graphene-based homo-junctions, as well as for hetero-junctions of graphene with common transition metal dichalcogenides. Finally, we discuss atomic friction data in light of the single-asperity thermally-activated Prandtl-Tomlinson (PT) model. The PT model is shown to effectively rationalize the results of CP-AFM experiments involving different colloidal probes, material substrates and sliding regimes. In particular, nearly-dissipationless sliding occurs only for the lower corrugated interface of graphene homo-junctions, as a result of the load-controlled transition from dissipative stick–slip to continuous superlubric sliding taking place in the low-loads limit.