Ab InitioStudies of the Diffusion Barriers at Single-Height Si(100) Steps

The binding sites and diffusion barriers for a Si adatom moving over a buckled Si(100) surface and single-height steps were calculated using ab initio methods. Surprisingly, the diffusion barriers may be sensitive to the local buckling of the dimers. The adatom binding energies and escape barriers at step edges depend strongly on the type of the step. The SA step edge is a relatively poor sink for adatoms, while adatoms can be easily trapped at the SB edge. These results explain the fast growth observed at the ends of the dimer rows.