Theory of depinning of monolayer films adsorbed on a quartz crystal microbalance.

In quartz crystal microbalance studies of the friction between an adsorbed monolayer film and a metallic substrate, the films are observed to slide relative to the substrate under inertial forces of order 10(-14) dyn per film atom, a force much smaller than all existing theoretical estimates of the force that surface defects are capable of exerting on the film. We argue that defect potentials with a range comparable to an atomic spacing or more will produce a pinning force below the inertial force.