Step-edge versus interior barriers to atom incorporation at lattice steps

Observations of the spatial distribution of individual atoms over close-packed (111) clusters of the fcc metals platinum as well as iridium reveal that atoms preferentially populate the inner region. The inner region is separated by an energy barrier from the step edge, leaving empty of adatoms a ring approximately three nearest-neighbor distances wide. The effect of such an interior energy barrier upon the lifetime to atom incorporation into steps is explored for one- as well as two-dimensional clusters. Interior barriers are found to increase the lifetime to incorporation much more than the conventional step-edge barrier, and may significantly affect the morphology of growing surfaces.