Clusters obtained by sputter deposition of cobalt atoms on alumina

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Abstract
We report on aggregation of Co on a smooth amorphous alumina surface, during sputter deposition of Co atoms at room temperature. The atomic structure of the Co grains appears to be size dependent: hep in the larger bean-shaped clusters (greater than 3 nm), and often fee in the smaller, almost spherical clusters. The deposits show relatively narrow distributions of the cluster sizes and of the intercluster distances, which results in a noticeable local order and explains how charge blocking (the so-called Coulomb blockade) could be observed in large sets of such particles by Schelp et al. (1997, Phys. Rev. B, 56, R5747). Electrical percolation occurs at a nominal thickness of about 2 nm.