Universal growth of islands driven by ion beams: Theory and measurements on Pt(111)

We report quantitative measurements of island growth on Pt(111) driven by irradiation with self ions. These processes take place on pans or mesas that isolate the active terrace from the remaining crystal by a surrounding step bunch. The observed evolution takes a universal form common to both growth and shrinkage, dependent on the ion beam energy, for both adatom and advacancy islands. We explore both the functional form and the absolute time scale of the island development. A theory that includes defect reactions is presented to explain the universality, using a quasistatic approximation for the transient defect population. For reasons that are explained, neither the functional form nor the absolute time scale of the evolution depends on the defect diffusion coefficient. Within the uncertainties, the experiments confirm the predicted universal form of the driven island evolution. The quantitative agreement makes studies of island growth an attractive future means for determining the number of surface thermal defects created per incident ion. It also confirms the precision of the molecular dynamics simulations that were employed in earlier research to calibrate the rates at which mobile thermal defects are created during irradiation by self-ion beams of various energies.