Effect of temperature-induced contact quality evolution on nanoscale friction

Multiple subcontacts formation/rupture and puckering the evolution of contact quality play crucial roles in modulating friction on two-dimensional lamellar materials but have up to now been studied separately in the field of nanotribology. In this work, by using variable temperature friction force microscopy in ultrahigh-vacuum conditions, we investigate friction on graphite surfaces with different numbers of free edges as a function of temperature from 295.0 to 100.0 K. We introduce subcontacts formation/rupture simply by changing temperature and tune the out-of-plane deformation compliance by changing the number of free edges. It is found that friction on a plane with large deformation compliance is constantly larger than that with small deformation compliance at cryogenic temperatures. While appearing to be influenced secondly by deformation compliance, the coefficients of friction increase, however, linearly with temperature. By performing systematic stick-slip measurements, the aforementioned separate friction mechanisms have been linked, where the temperature-induced increase of subcontacts rupture force can give rise to the frictional contact quality which additionally becomes more prominent on a plane with large deformation compliance at cryogenic temperatures. These results emphasize a way to vary the contact quality via temperature and demonstrate that the subcontacts formation/rupture and the contact quality must be correlatively accounted for.