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Abstract:
Employing transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX) and X-ray photoelectron spectroscopy (XPS) we have studied tantalum clusters on a thin Al2O3 film epitaxially grown on NiAl(110). Our data reveal that the clusters are three dimensional, growing epitaxially on the oxide film with their [110] directions parallel to the surface normal and Ta[001]‖NiAl[001]. From the observed moiré fringes the tantalum lattice constant could be determined as a function of the cluster size. We found that the lattice constant decreases with decreasing cluster size with the highest observed reduction being 4.5% for a cluster with a diameter of 12.5 Å. Interestingly the clusters are only partly oxidized as concluded from XPS, TEM and EDX data although the samples were exposed to air after cluster deposition.
