TEM study of tantalum clusters on Al2O3/NiAl(110)

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 him with their [110] directions parallel to the surface normal and Ta[001]//NiAl[001]. From the observed moire 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 Angstrom. 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. (C) 1998 Elsevier Science B.V. All rights reserved.