Microscale superlubricity of graphite under various twist angles

The relative rotation and translation of graphene and graphite layers lead to remarkable physical and mechanical phenomena. One such phenomenon for graphite corresponds to the ultralow static and dynamic friction between incommensurate graphene layers, referred to as superlubricity. Even though many studies have been dedicated to this promising phenomenon in recent years, an experimental characterization and a quantitative determination of the effect of relative twist angles on microscale superlubricity are still lacking. The present paper investigates the superlubric properties of microscale graphite under different twist angels by shearing graphite with respect to a substrate. Experimentally, it is surprisingly found that the superlubricity of microscale graphite is almost invariant within a wide range of bicrystal twist angles (6 degrees <= theta <= 59 degrees). This result is confirmed by carrying out molecular dynamics simulations. Further, the influences of twist angles and normal load on the incommensurate-to-commensurate transition are revealed. The estimated critical transition angle is less than 0.1 degrees. These results allow a better understanding of mesoscopic scale superlubricity and extend its application field.