STEP-EDGE DIFFUSION AND THE STRUCTURE OF NANOMETER-SIZE IR ISLANDS ONTHE IR(111) SURFACE

We report an FIM study of the structure of nanometer-size Ir islands o n the Ir(lll) surface. In this experiment, the number of atoms in an i sland is carefully controlled by field evaporation and vapor depositio n. When this number can be fitted to a hexagonal atomic arrangement, t he stable structure is found to be a perfect hexagon. In other cases, an addition of one ledge atom can reverse the symmetry of a small isla nd or change its shape. We also compare diffusion of adatoms on the Ir (311) and (331) surfaces to that of ledge-atoms along the A- and B-typ e steps of the (111) layer, and the relative binding energies of a led ge atom at these steps.