Sliding speed-induced nanoscale friction mosaicity at the graphite surface

The kinetic friction of the (0001) graphite surface has been mapped at different speeds and scales by means of an atomic force microscope. The maps show nanoscale domains of various sizes and friction strengths. Each domain presents a transition between two friction regimes and a specific logarithmic scaling of friction with speed. The gradient of this variation is determined by the angle between the macroscopic sliding direction and a stiff crystal axis of the surface lattice. The experimental results are analyzed by considering thermally activated sliding regimes within the puckering friction mechanism.