Electronic nature of step-edge barriers against adatom descent on transition-metal surfaces.

By studying a series of adatoms on representative transition-metal surfaces through first-principles calculations, we establish a clear correlation between the preferred mechanism and activation energy for adatom descent at a step and the relative degree of electronic shell filling of the adatom and the substrate. We also find an approximate linear relation between the adatom step-edge hopping barriers and the adatom-surface bonding strength with slope roughly proportional to the number of the adatom's nearest neighbors initially. These results may serve as simple guiding rules for predicting precise atomic surface morphologies in heteroepitaxial growth, as in formation of nanowires.