Nanostructure evolution during cluster growth: Ag on H-terminated Si(111) surfaces.

The size of small clusters has a large effect on cluster growth and structure. Using Ag clusters of sizes from approximately 1 to 10 nm grown on H-Si(111), we found that the cluster structure evolves in stages showing (1) irregular shapes at coverage <or=1 ML (monolayer), (2) mostly single crystal of faceted-hut-like shapes from 2 to 5 ML, and (3) defective disklike islands above 5 ML. We show that the rapid coalescence of small clusters drives the nanostructure transition and leads to a steplike growth of nanoclusters that is different from the predictions of scaling theory.