Ultralow friction regime from the in situ production of a richer fullerene-like nanostructured carbon in sliding contact

Hitherto, among carbon-based thin films, fullerene-like hydrogenated carbon (FL-C:H) films exhibit unique ultralow friction and wear in open or humid air, but the mechanisms responsible for the friction regime are still not clear. Here, we provide definitive experimental evidences obtained from the wear tracks and debris of FL-C: H films, and show that FL-C: H films' surface undergoes gradual transformation into a richer and more stable fullerene-like nanostructure, due to the increasing content of pentagonal and heptagonal carbon rings in addition to the six-membered graphene rings, as a result of thermal and strain effects from the repeated friction. The sliding-induced in situ promotion of the FL structures at frictional contact leads to ultralow friction and wear in open air. The results establish an excellent low friction and wear regime for the structural film, and develop the lubrication mechanisms of carbon-based films.