Previous work has established that vacancy islands or pits fill much more quickly when they were in contact with a step edge, such that the common boundary was a double step. The present work focuses on the effect of the orientation of that step, with two possibilities existing for a face centered cubic (111) surface: A- and B-type steps. It was found that the following features could depend on the orientation: (1) the shapes of islands while they shrink; (2) whether the island remains attached to the step edge; and (3) the rate of filling. The first two effects could be explained by the different rates of adatom diffusion along the A- and B-steps that define the pit, enhanced by the different filling rates. The third observation—the difference in the filling rate itself—is explained within the context of the concerted exchange mechanism at the double step. This process was facile at all regular sites along B-steps, but only at kink sites along A-steps, which explains the different rates. It was also observed that oxygen could greatly accelerate the decay process, although it has no apparent effect on an isolated vacancy island (i.e. an island that was not in contact with a step).

Rapid Decay of Vacancy Islands at Step Edges on Ag(111) - Step Orientation Dependence. M.Shen, C.J.Jenks, J.W.Evans, P.A.Thiel: Journal of Physics - Condensed Matter, 2010, 22[21], 215002