Diffusion mechanism on a double-layer stepped Si(001) surface without (with) a surfactant

We study the diffusion mechanism on island in the presence of a surfactant using ab initio molecular dynamics method. We first find an equilibrium structure from an ideally stepped structure which favors the rebonded D_B step edge with p(2×2) phase. We then study the diffusion mechanism on D_B step which emulates the island with {311} facets. In contrast with the prevailing role of a surfactant on a flat surface where the diffusion of adatoms is suppressed by the site-exchange mechanism, we find that the surfactant significantly reduces the additional Schwoebel barrier near the step edge such that the island formation is severely suppressed and the layer-by-layer growth mode is promoted.