The room temperature growth of metal clusters on well-ordered alumina films on Ni3Al(111) was investigated by scanning tunneling microscopy (STM). The electronic superstructures that appear in the STM images of the bare oxide films, constitute nucleation centers for the cluster growth. For Ag clusters this pinning operates only at low metal coverage, whereas higher coverages lead to large agglomerates of the clusters. This is attributed to the relatively weak bonding of Ag to the alumina film. Conversely, in the case of Mn clusters the pinning persists even for moderate metal coverages owing to the much stronger bond between metal and oxide film. Finally, at high metal coverage the pinning is lost, the Mn clusters do, however, not agglomerate. (C) 2001 Elsevier Science B.V. All rights reserved. References: 11
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