Binding and diffusion of a Si adatom around type B steps on Si(001) c(4 × 2)

Maps of the binding energy of an adatom on Si(001) c(4 × 2) around the nonbonded and bonded type B surface steps are presented. The results suggest that the nonbonded type B step should accumulate adatoms rapidly both from above and below. The energy barrier to cross the nonbonded step is ∼0.2 eV greater than for diffusion on the flat surface. The binding sites along the nonbonded step edge are similar to those on the flat surface but are paired and connected by a low-energy diffusion pathway that may facilitate formation of dimers along the step edge. The bonded step attracts adatoms ∼0.5±0.2 eV more strongly than any other site on the surface. However, these sites are relatively inaccessible due to surrounding high energy barriers. Based on the results, the upper side of the bonded step should be repulsive to adatoms. The diffusion barrier for adatoms approaching the step rises and the binding sites become less favorable there. Hence, growth of the bonded step is probably much slower than the nonbonded step, which explains its observed predominance on Si(001) surfaces.