Atom condensation at lattice steps and clusters

The deposition of individual Ir atoms on an Ir(111) surface with a central iridium cluster on it has been observed in the field ion microscope. Around Ir clusters of both 12 and 59 atoms at T=20 K there is an empty zone, {~}2 nearest-neighbor spacings wide, in which condensed atoms are not found. From quantitative measurements of the distribution of adatoms over the surface it appears that atoms from the vapor striking this region skitter over the surface, even at T{~}20 K, and are collected at cluster edges. Atoms from the vapor striking the cluster condense without damage to the cluster.