Anomalous load dependence in single-asperity tribological behaviour of anodic aluminium oxide nanohoneycombs

Nanoscratch tests on porous alumina with a Berkovich diamond tip reveal a very strong load dependence of the sliding friction coefficient in the submicronewton load range. The friction coefficient is generally >10 under loads below 0.1 mN, and this drops to ∼1 under larger loads. This peculiar behaviour is thought to be due to the row-by-row failure of the solid walls in the nanohoneycomb structure, which leads to a nearly linear scaling of the scratch resistance with scratch width.