Transition from one-dimensional to two-dimensional island decay on an anisotropic surface

We have investigated the decay of two-dimensional islands on the anisotropi c Ag(110) surface using variable temperature scanning tunneling microscopy. Contrary to predictions from traditional Ostwald ripening theory, a quasi- one-dimensional decay mode is observed at low temperatures, 175-220 K. A su rprisingly sharp transition to the quasi-two-dimensional decay mode is obse rved around 220 K. This transition is accompanied by a fast equilibration o f the island shape. These findings have tentatively been rationalized withi n a simple model to identify the underlying rate limiting atomistic process es.