Scaling laws of structural lubricity.

"Structural lubricity" refers to a unique friction state in which two flat surfaces are sliding past each other with ultralow resistance due to incommensurate atomic lattice structures. In this case, theory anticipates sublinear scaling for the area dependence of friction. Here, we experimentally confirm these predictions by measuring the sliding resistance of amorphous antimony and crystalline gold nanoparticles on crystalline graphite. For the amorphous particles a square root relation between friction and contact area is observed. For crystalline gold particles we find a more complex scaling behavior related to variations in particle shape and orientation. These results allow us to link mesoscopic friction to atomic principles.