Decoration criteria for surface steps

Abstract

The criterion derived by Chakraverty and Pound for preferential nucleation of vapour condensation at macroscopic steps upon a crystalline substrate is generalized to apply to steps of any angle. For small included step angles nucleation can occur on steps even under unsaturated conditions so that they are always decorated; for intermediate step angles the degree of preference for nucleation at steps decreases as the vapour supersaturation is increased. Decoration is most easily achieved with a condensate whose contact angle on the substrate is either less than the complement of half the included angle of the step or else approximately 90°.