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Observations of individual iridium atoms diffusing over Ir(111) planes with an iridium cluster at the center reveal an empty zone, {~}3 nearest-neighbor spacings wide, around the cluster. In this zone adatoms are never seen. Quantitative studies of the probability of atom incorporation at the cluster, compared to the probability of being trapped at the plane edge, suggest that the empty zone comes about because in the vicinity of the cluster, diffusion toward an ascending step is much more rapid than on a flat terrace, so that adatoms are funneled to the cluster.
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Wang et al. (1993) studied this question.
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