  Morphological instability of a planar surface ([111], [011], or [001]) of an
ultra-thin metal film is studied in a parameter space formed by three major
effects (the quantum size effect, the surface energy anisotropy and the surface
stress) that influence a film dewetting. The analysis is based on the extended
Mullins equation, where the effects are cast as functions of the film
thickness. The formulation of the quantum size effect (Z. Zhang et al., PRL 80,
5381 (1998)) includes the oscillation of the surface energy with thickness
caused by electrons confinement. By systematically comparing the effects, their
contributions into the overall stability (or instability) is highlighted.
