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 Ni Al(110). Our data reveal that the clusters are three dimensional, grow ing 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 functio n of the cluster size. We found that the lattice constant decreases wi th 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 d ata although the samples were exposed to air after cluster deposition. (C) 1998 Elsevier Science B.V. All rights reserved.