The Role of Intermediate States in Low-Velocity Friction between   Amorphous Surfaces
  Simulated sliding between an oxidized silicon tip and surface over six decades of velocity using accelerated molecular dynamics reproduces the experimentally observed velocity dependence of the friction force. Unlike in the crystalline case, as increasing force is applied to the amorphous tip intermediate states arise. These intermediate states serve as critical transition pathways. The emergence of such states leads to the emergence of a plateau in sliding velocity at lower sliding speeds and higher temperatures. A simple theory based on these observations successfully describes both the experimental and the simulated data. 
Woo Kyun Kim and Michael L. Falk
cond-mat.mtrl-sci cond-mat.stat-mech