Binding and diffusion of a Si adatom around the type A step on Si(001) c(4×2)

Abstract

The results of a simulation are described, using a density functional method, of the diffusion of adatoms on a flat Si(001)c(4×2) surface and around one type of surface step (the SA step). These indicate that there is a moderate additional energy barrier (0.2±0.1 eV) to cross the SA step as compared to the energy for diffusion on a flat surface. The dimer-top lattice site on the lower terrace adjacent to the step edge is stabilized (by 0.15±0.1 eV) with respect to the flat surface result although the most stable binding sites near the step are unaffected. This behavior can be understood based on the disruption of dimer tilt near the step. The results suggest that adatoms are more likely to stop on lattice sites at the SA step edge than on lattice sites on the open surface. This may affect the relative dimer formation rate near the step with respect to the behavior on the flat surface even in the absence of a clear change in binding energy. The effect of the SA step terrace edge on adatom behavior is very short ranged and weak. This is consistent with the relatively small strain field and lack of change in dangling bond density associated with the step edge.