The atomic-scale smoothness of the interface determines whether the growth mode is essentially "continuous" (molecules add anywhere) or "lateral" (addition occurs only at ledges, which sweep laterally across the interface).

Try changing DS_f/k to see how the nature of the interface is established ( The desorption probability for any particular molecule is given by ). Systems with atomically smooth interfaces tend to form facets during growth, i.e. to expose preferentially certain crystallographic planes. These are the atomically "smoothest" planes, on which growth occurs most slowly.

Metallic phases do not usually exhibit facets, although they may do so if they form directly from vapour or from dilute solution.