Dimple-assisted dewetting: heterogeneous nucleation in undercooled wetting films

Undercooled wetting films near a first-order wetting transition exhibit an unusually long lifetime: the thermal nucleation barrier for formation of a critical hole in a film of thickness F diverges according to Gamma similar to exp (epsilon (c)/k(B)T) where the excess free energy epsilon (c) similar to F-xi with xi greater than or equal to 2. Localized perturbations of the liquid-vapor interface ('dimples') are shown to be a useful tool in reducing Gamma in a controlled way: they act as heterogeneous nucleation centers for thermal critical nuclei. For He-4 wetting films on weak-binding alkali substrates (Cs, Rb) dimples can be generated either by vortices in a superfluid film or by surface electrons. The theory of the heterogeneous nucleation process initiated by the presence of surface dimples ('dimple-assisted dewetting') is developed, accompanied by quantitative predictions for experiment.