Structural investigation of palladium clusters on gamma-AlO3(111)/NiAl(110) with transmission electron microscopy

For Pd clusters on gamma-Al2O3 epitaxially grown on NiAl(110) the lattice c onstant has been determined as a function of the cluster size by evaluating patterns induced by double diffraction involving the NiAl substrate and th e cluster lattice. Similar to results reported previously for platinum and tantalum clusters on the same substrate (Surf. Sci. 1997, 391, 27; Surf. Sc i. 1998, 413, 192), we observe a reduction of the distances within the latt ice with decreasing cluster size. The highest observed reduction is 5% for clusters with a diameter of about 12 Angstrom. Within the limits of the exp erimental errors the reduction of the lattice distances is isotropic. Altho ugh the samples have been exposed to air prior to investigation, the cluste rs are only weakly oxidized as concluded from XPS data.