title: Nucleation and growth of Ag islands on the (√3 × √3)R30° phase of Ag on Si(111).
abstract: We use scanning tunneling microscopy to measure densities and characteristics of Ag islands that form on the (√3 × √3)R30°-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 µm. 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 ∼ 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≈3-4 in the regime 180-250 K, where island density varies strongly with temperature.
authors.affiliation: Ames Laboratory, Iowa State University, Ames, IA 50011, USA.
authors.forename: A
authors.initials: A
authors.lastname: Belianinov
authors.forename: B
authors.initials: B
authors.lastname: Unal
authors.forename: K-M
authors.initials: KM
authors.lastname: Ho
authors.forename: C-Z
authors.initials: CZ
authors.lastname: Wang
authors.forename: J W
authors.initials: JW
authors.lastname: Evans
authors.forename: M C
authors.initials: MC
authors.lastname: Tringides
authors.forename: P A
authors.initials: PA
authors.lastname: Thiel