Restructuring in step decorations grown by simulated epitaxy of Cu on a bcc W(110) surface

Abstract

The submonolayer growth of Cu deposit at an ascending step oriented in the [001] direction on a W(110) surface is studied by kinetic Monte Carlo simulations at temperatures ranging from 60 to 280 K and fluxes from 10 - 1 9 to 10 - 3 ML/s. A lattice-gas model that simulates deposition of adatoms, diffusion of monomers, diffusion along deposit edges, and reversible aggregation of adatoms is employed. The growth conditions are chosen in such a way that the growing deposit accumulates only at the step edge. Randomly ramified step decorations are found to grow in extended temperature regimes. The deposit morphology changes from an open branched aggregate with fractal dimension equal to 1.71′0.04 at low temperatures to a stripe of a compact shape at the highest temperature considered. With increasing temperature of deposition the partial restructuring processes yield widening of aggregate branches. The onset of the restructuring processes takes place at 90 K when single-coordinated adatoms become mobile. Twofold- and threefold-coordinated adatoms become mobile at 180 and at 250 K; respectively. There is a temperature window, 150 K<T<190 K, where the deposit equilibration slows down because the average number of hops performed by single-coordinated adatoms is nearly constant and the hops from twofold-coordinated sites do not start yet. At these temperatures, step decorations with a nearly constant average branch width of 3-4 atoms are obtained. The high-temperature region of crossover into the compact growth, existing above 200 K, results in aggregates called fat fractals with branches widened up to 10 or more atoms. These fat fractals resemble closely step decorations observed in molecular beam epitaxy experiments.