Edge orientation dependent nanoscale friction.

Nanoscale friction is generally found to be a function of the contact area. However, little is known whether and how it is dependent on the contact area shape. In this study, based on molecular dynamics (MD) simulations about a rectangular graphene flake sliding on a diamond-supported graphene substrate, we show that the friction between the flake and the substrate is significantly dependent on the flake edge oriented perpendicular to the sliding direction, but less dependent on the edge along the sliding direction. As a result, the friction between the flake and the substrate is closely related to the aspect ratio of the flake. We propose a novel nanoscale friction formula for the translational motion of a rectangular slider. The simulation data fit the formula well and the effect of the aspect ratio on nanoscale friction can thus be efficiently captured. We discuss also the origin of the edge orientation dependent nanoscale friction. The present findings provide not only a preliminary evaluation of the contact area shape dependent nanoscale friction, but also a quite important guide for modeling the friction properties of nanodevices based on two-dimensional (2D) materials.