Preferential cluster nucleation on long-range superstructures on Al2O3/Ni3Al(111)

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 cluste rs this pinning operates only at low metal coverage, whereas higher coverag es lead to large agglomerates of the clusters. This is attributed to the re latively weak bonding of Ag to the alumina film. Conversely, in the case of Mn clusters the pinning persists even for moderate metal coverages owing t o the much stronger bond between metal and oxide film. Finally, at high met al coverage the pinning is lost, the Mn clusters do, however, not agglomera te. (C) 2001 Elsevier Science B.V. All rights reserved.