Nucleation and growth of Ag islands on the (root 3 x root 3)R30 degrees phase of Ag on Si(111)

TitleNucleation and growth of Ag islands on the (root 3 x root 3)R30 degrees phase of Ag on Si(111)
Publication TypeJournal Article
Year of Publication2011
AuthorsBelianinov A, Unal B, Ho KM, Wang CZ, Evans JW, Tringides MC, Thiel PA
Journal TitleJournal of Physics-Condensed Matter
Date Published07/06
ISBN Number0953-8984
Accession NumberISI:000291658700003
Keywords3x root 3-ag, competing processes, controlling energies, epitaxial-growth, LOW-TEMPERATURES, restructuring process, root-3-ag surface, scanning-tunneling-microscopy, si(111)-root-3x-root-3-ag surface, small-cluster mobility

We use scanning tunneling microscopy to measure densities and characteristics of Ag islands that form on the (root 3 x root 3) R30 degrees-Ag phase on Si(111), as a function of deposition temperature. Nucleation theory predicts that the logarithm of island density varies linearly with inverse deposition temperature. The data show two linear regimes. At 50-125 K, islands are relatively small, and island density decreases only slightly with increasing temperature. At 180-250 K, islands are larger and polycrystalline, and island density decreases strongly with increasing temperature. At 300 K, Ag atoms can travel for distances of the order of 1 mu m. Assuming that Ag diffusion occurs via thermally activated motion of single atoms between adjacent sites, the data can be explained as follows. At 50-125 K, the island density does not follow conventional Arrhenius scaling due to limited mobility and a consequent breakdown of the steady-state condition for the adatom density. At similar to 115-125 K, a transition to conventional Arrhenius scaling with critical nucleus size (i = 1) begins, and at 180-250 K, i > 1 prevails. The transition points indicate a diffusion barrier of 0.20-0.23 eV and a pairwise Ag-Ag bond strength of 0.14 eV. These energy values lead to an estimate of i approximate to 3-4 in the regime 180-250 K, where island density varies strongly with temperature.

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Alternate JournalJ Phys-Condens MatJ Phys-Condens Mat