Material transfer mechanism for fabrication of superlubricity interface by reciprocating rubbing on graphite under high contact stress

Superlubricity is attractive in many scientific and technological fields due to energy-saving and wear reduction. Two incommensurate contacting surfaces (superlubricity interface) slide against each other exhibiting ultralow dynamic friction coefficient below 10−3. Fabrication of the superlubricity interface is the essence to obtain superlubricity. Here we developed a plasma-assisted mechanical exfoliation and tribo-transfer method to fabricate graphene nanoflake wrapped atomic force microscopy (AFM) tips. Superlubricity between graphene-wrapped tips with different diameters and graphite was achieved with a friction coefficient as low as 10−4. Systematic investigations were conducted on material transfer mechanism mainly including delamination, deformation and lateral displacement, and fracture and transfer of graphene nanoflake from thick graphene. Negative friction-load phenomenon and abnormal stick-slip motion on graphene were observed, demonstrating top layers of graphene were deformed and delaminated during rubbing process. Weakened strengthening effect on monolayer graphene and bubble on thick graphene after reciprocating rubbing may prove interlayer sliding and lateral displacement. The general nature of the results may apply to other 2D materials. These results not only provide a technical route to acquire superlubricity interface but also intensify the understanding of superlubricity which is the basis of its application in moving mechanical systems.