Tribo-Induced Interfacial Material Transfer of AFM Probe Assisting Superlubricity in WS 2 /Graphene Heterojunction.

Robust superlubricity of 2D materials could be obtained by transferring graphene on the tip surface for the formation of interlayer friction of heterojunction, owing to the availability of stable interfacial incommensurate contact. Nevertheless, the material transfer mechanisms assisting superlubricity via atomic force microscopy (AFM) probe are still hardly comprehended. In this work, we reported a superlow friction coefficient (0.003) of WS/graphene heterojunction governed by graphene flake-transferred AFM tips and achieved a superlubricity state of velocity-independence. Both low adhesion of heterojunction and excellent wear-resistance for tip were also observed, which were attributed to the extremely low interface interaction during the incommensurate contact. The in-depth investigation on the frictional contact zones of probes was performed through high-resolution transmission electron microscopy (HRTEM). The observations emphasize the prevailing mechanisms of tribo-induced interfacial material transfer when AFM probes scanning on the surface of 2D materials. The evolution of superlubricity state principally depends on the establishment of interfacial nanostructures in the self-adaptive running-in period, by different contact mechanics and tribo-reconstructing pathways. These results stimulate a technical route to develop superlubricious tribopairs of 2D materials and guide a promising perspective in engineering system.