Anisotropic growth of step decorations during simulated epitaxy on a bcc(1 1 0) surface

The non-equilibrium growth of Cu deposited at ascending steps on W(1 1 0) oriented in [0 0 1] and [1 1 0] directions is studied by kinetic Monte Carlo simulations. A lattice gas model that simulates deposition of adatoms, diffusion of monomers, diffusion along island edges and reversible aggregation is employed. The step decorations with a fractal geometry and a branch width which increases with temperature are found at temperatures between 130 and 230 K. The shape of step decoration depends on the orientation of the step. The anisotropy of growth exists in the temperature range where onefold coordinated adatoms are unstable. The preferential directions into which branching occurs are identified and explained by an asymmetry in jump probability of onefold coordinated adatoms towards twofold coordinated sites at the tip of the growing aggregate.