A negative friction coefficient is observed for graphite using atomic force microscopy. The magnitude of the friction coefficient increases with adhesion, which we control by exposing graphite to different conditions. We demonstrate that the negative coefficient is a mechanical effect arising from changes in the bending stiffness of the top layer of graphite with applied load, and not a result of a change in atomic corrugation. We further show that the adhesive force at which the onset of this negative friction-load dependence occurs is determined by the interlayer binding energy.
Citation: Nature Materials
Pub Type: Journals
nanoscale friction, nanoscale adhesion, graphite, interlayer binding energy, atomic force microscopy, friction force microscopy