Brownian Motion of Vacancy Islands on Ag(111)

The motion of monatomic deep vacancy islands on crystal surfaces is studied both theoretically and experimentally. We develop a new theoretical model which allows us to deduce the microscopic mechanism of mass transport from measuring the diffusion coefficients of the vacancy islands as a function of their size. This model is applied to experimental results obtained with a fast scanning tunneling microscope on Ag(111) at room temperature. The observed scaling is consistent with a mechanism where the microscopic mass transport is dominated by diffusion of adatoms across the vacancy island rather than along the island boundary.