Dewetting dynamics of ultrathin silver films on Si(111)

Continuous silver films of nanometer thickness, grown at room temperature on $(7\mathrm{}\times 7)-\mathrm{Si}\mathrm{}\left(111\right),$ display a wormlike morphology and thermally decay into isolated three-dimensional crystallites. We have tracked the dewetting process in real time using variable-temperature scanning tunneling microscopy. In this ultrathin regime, a range of transitional morphologies are observed, dependent on the substrate step density, annealing time and temperature. Initial film morphology is modulated by the underlying step structure and the growing crystallites show a corresponding step-induced deformation. During the initial stages of dewetting, the Ag-denuded areas transform to the $(\sqrt{3}\times \sqrt{3})R30\mathrm{}°-\mathrm{A}\mathrm{g}/\mathrm{S}\mathrm{i}\mathrm{}\left(111\right)\mathrm{}$ surface, and spatially nonuniform denuded zones appear around the growing crystallites. Enhanced dewetting rates are observed in areas of lower step density, largely because steps act as kinetic obstacles. A simple form to relate the energy gain in dewetting to the density of crystallographic steps is provided. On preprepared $(\sqrt{3}\times \sqrt{3})R30\mathrm{}°-\mathrm{A}\mathrm{g}/\mathrm{S}\mathrm{i}\mathrm{}\left(111\right)\mathrm{}$ substrates, dewetting occurs spontaneously even at room temperature.