Scanning tunnelling microscopy was used to measure densities and characteristics of Ag islands that formed on the (√3 x √3)R30°-Ag phase on Si(111), as a function of deposition temperature. Nucleation theory predicted that the logarithm of island density varied linearly with inverse deposition temperature. The data showed two linear regimes. At 50 to 125K, islands were relatively small, and island density decreased only slightly with increasing temperature. At 180 to 250K, islands were larger and polycrystalline, and island density decreased strongly with increasing temperature. At 300K, Ag atoms could travel for distances of the order of 1µm. Assuming that Ag diffusion occurred via thermally activated motion of single atoms between adjacent sites, the data could be explained as follows. At 50 to 25K, the island density did not follow conventional Arrhenius scaling due to limited mobility and a consequent breakdown of the steady-state condition for the adatom density. At about 115 to 125K, a transition to conventional Arrhenius scaling with critical nucleus size (i = 1) began and, at 180 to 250K, i > 1 prevailed. The transition points indicated a diffusion barrier of 0.20 to 0.23eV and a pair-wise Ag-Ag bond strength of 0.14eV. These energy values led to an estimate of i≈3 to 4 in the regime 180 to 250K, where island density varies strongly with temperature.

Nucleation and Growth of Ag Islands on the (√3 x √3)R30° Phase of Ag on Si(111). A.Belianinov, B.Ünal, K.M.Ho, C.Z.Wang, J.W.Evans, M.C.Tringides, P.A.Thiel: Journal of Physics - Condensed Matter, 2011, 23[26],  265002