Observation of a novel nucleation mechanism at step edges: LiF molecules on Ag(1 1 1)

Abstract

Growth of LiF on Ag(1 1 1) at low temperatures has been investigated by scanning tunnelling microscopy. It is found that, upon deposition at 77 K and for a large range of incidence fluxes, nucleation of LiF molecules begins on both the upper and the lower side of the step-edges. This behaviour is very different to the well-known case of metal-on-metal growth, on which nucleation is restricted to the lower side of step edges. This new mechanism is explained by the localized charge redistribution at step sites, which favours adsorption of polar molecules on both the upper and lower step edges, and should in principle be also present in the growth of other insulator-on-metal systems at low temperatures.