How asymmetric islands become symmetric

Scanning tunneling microscopy reveals that sputtering of the Au(110) surface results in the formation of vacancy islands with a broken mirror symmetry These islands exhibit two types of steps on opposite sides: a lower energy (111) step and a higher energy (331) step. We analyze the thermal fluctuations and especially the kink distribution of such vacancy islands. Despite the broken symmetry, which they adopt internally, these islands show a symmetric average outer contour. Their coarsening proceeds via a variety of pathways, often leading to new, symmetric structures, with exclusively (111) steps. The lowest energy vacancy configuration is a bound pair of two vacancy lines or islands.