Transition from thermal to athermal friction under cryogenic conditions.

Atomic scale frictional forces encountered as a function of temperature for the contact of a Si3N4 probe tip and the basal plane of MoS2 have been measured with atomic force microcopy over the temperature range 100-500 K. Friction is observed to increase exponentially with decreasing temperature from 500 to 220 K. An Arrhenius analysis of the temperature dependent friction over this range yields an effective activation energy of approximately 0.3 eV for the thermally activated stick-slip motion of the probe tip on this surface. As temperature is reduced further below 220 K, a distinct transition to a largely athermal behavior is detected and is shown to result from the onset of interfacial wear, entailing an alternative energy dissipation pathway.