Mass selected copper clusters on well-ordered aluminum oxide layers

Clusters are objects built of up to several thousand atoms which are interesting concerning applications in catalysis, information technology or medicine. Depending on their size, i.e. the exact number of atoms, unique features may arise. For any application these clusters have to be deposited on a surface. Here, a Ni3Al single crystal is used to grow a thin, well-ordered ’-Al2O3 film. This oxide film exhibits two superstructures, which serve as binding sites for clusters. By depositing size selected clusters on the oxidized surface, a functionalization should be achievable leading ideally to equally spaced clusters of exact the same size. The experiments presented here focus on the arrangement of copper clusters deposited on the mentioned oxide film. Furthermore, the stability is investigated by applying different heating procedures to the sample system up to 600 K. A series of different geometrical magic cluster was deposited respectively. Low Energy Electron Diffraction (LEED) reveals the (oxidized) substrate quality while Scanning Tunneling Microscopy (STM) is used to determine the position and height of deposited clusters. It could be shown that the arrangement of clusters is in good accordance with simulated data, obtained by Monte-Carlo methods. Thus, a strong indication for an alignment with the template structure (superstructure of the oxide film) is found, even if the clusters are not equally space, one cluster per binding site, due to the limitations of coverage in this investigation. The height, in turn, allows to show the stability of deposited clusters. Here, a clear maximum after every heating procedure can be identified in the height histograms. Supported by local height spectroscopy measurements Z(V), this maximum exactly belongs to the deposited cluster size. The present results suggest that the sample system is remarkably suited for any application that requires mass selected clusters homogeneously arranged on a surface