CHARACTERIZATION OF METAL-CLUSTERS (PD AND AU) SUPPORTED ON VARIOUS METAL-OXIDE SURFACES (MGO AND TIO2)

Au clusters supported on the TiO2(001)/Mo(100) surface and Pd clusters supported on the MgO(100)/Mo(100) surface have been studied using tem perature programmed desorption, ion scattering spectroscopy, scanning tunneling microscopy, and scanning tunneling spectroscopy. Three dimen sional growth has been observed at 300 K for both cases. The adsorptio n energy of Au on the TiO2(001) surface has been measured to be 50 kca l/mol using temperature programmed desorption, compared to the adhesiv e energy of 90 kcal/mol for the bulk Au metal. At an equivalent Au cov erage of 1.8 ML, very homogenous, hemispherical Au particles with an a verage diameter of 25 Angstrom and a height of 10 Angstrom are present on a TiO2(001)/Mo(100) surface. Increasing the Au coverage to 3 equiv alent monolayers produces similar to 60 Angstrom diameter clusters. Th e scanning tunneling spectroscopy measurements show a gradual developm ent of the metallic character of the Au clusters with increasing clust er size. Very similar results have been obtained for the Pd clusters s upported on the MgO(100)/Mo(100) surface. (C) 1997 American Vacuum Soc iety.