How asymmetric islands become symmetric

Scanning tunneling microscopy reveals that sputtering of the Au(110) surfac e 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 fluctuat ions and especially the kink distribution of such vacancy islands. Despite the broken symmetry, which they adopt internally, these islands show a symm etric average outer contour. Their coarsening proceeds via a variety of pat hways, often leading to new, symmetric structures, with exclusively (111) s teps. The lowest energy vacancy configuration is a bound pair of two vacanc y lines or islands.