Shape and evolution of vacancy islands on a missing row reconstructed surface: Au( [formula omitted

Abstract

We show that the removal of 0.2 monolayers of a clean, well-ordered Au(1 1 0) surface at room temperature leads to the formation of vacancy islands with two different types of steps along one direction: a so-called (1 1 1)-step on one side and a (3 3 1)-step on the other side, both along the [1 1 ̄ 0] -direction. We consider the consequences of this broken mirror symmetry, and find that these vacancy islands have a twofold symmetric equilibrium shape, in spite of their structure with only onefold symmetry. The coarsening of the islands proceeds via a variety of pathways that involve rather different time scales, and we show that this is a direct consequence of the broken symmetry. One pathway is a transformation into new symmetric structures. Two vacancy islands can transform into a bound island pair and narrow, single vacancy islands can spontaneously split up into a symmetric pair of ‘vacancy lines’. We determine the formation energy of this particular structure, and find that it is the lowest-energy vacancy configuration.