Origin of Surprising Attractive Interactions between Electronegative Oxygen Adatoms on Aluminum Surfaces

Abstract

When electronegative atoms adsorb on a more electropositive metal surface, charge transfer occurs and adatoms become negatively charged, typically resulting in repulsive lateral interactions. However, in the case of O on Al surfaces, the opposite occurs and the lateral interactions between adatoms are attractive. We demonstrate that the surprising attractive interactions are a consequence of a simple electrostatic stabilization that stems from an interplay between Coulombic interactions and geometric effects; that is, there exists a critical adatom height above the surface below which the lateral interactions are attractive. We argue that this picture is generally applicable for electronegative adatoms on metal surfaces provided that (i) the adsorption bonding is sufficiently ionic and (ii) the adatoms are sufficiently small to come close enough to the surface.