Adatom binding at the surface ledges of a jellium metal

Abstract

The nature of a surface ledge on a jellium metal has been simulated by sharply cutting the uniform positive charge into the prescribed ledge and allowing the negative electronic charge to show a compensating modulation, falling off tangentially to the surface. The size of the associated fall-off parameter was determined by energy minimization and turned out to be quite independent of step height and comparable to that for the charge fall-off perpendicular to the surface. To this ledge a model adatom was brought, consisting of a Topp-Hopfield ion core and a single valence electron distribution. When approaching the ledge from the lower terrace, the adatom binding increased by about 40% more than its flat surface value. Conversely, the adatom approaching the ledge across the upper terrace experienced a decrease in binding (balustrade effect) also of about 40% of the flat surface binding. A particular application of the results to condensation from the vapor phase is the prediction that the spacing between a series of ledges will tend to become more uniform as the condensation proceeds.