Binding sites and diffusion barriers of single-height Si(001) steps

Using molecular-dynamics simulations, we have mapped out the potential-energy surface of a Si adatom over the ${\mathit{S}}_{\mathit{A}}$ and ${\mathit{S}}_{\mathit{B}}$ Si(001) steps. This identifies the likely binding sites for step growth and provides estimates for the diffusion barriers over the step edges. We find that the barriers at the step edge do not differ substantially from those on the flat terraces. Surprisingly, the ${\mathit{S}}_{\mathit{A}}$ and rebonded ${\mathit{S}}_{\mathit{B}}$ steps are only weak sinks for adatoms. In contrast, the nonbonded ${\mathit{S}}_{\mathit{B}}$ step is a good sink.