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 temperature programmed desorption, ion scattering spectroscopy, scanning tunneling microscopy, and scanning tunneling spectroscopy. Three dimensional growth has been observed at 300 K for both cases. The adsorption energy of Au on the TiO2(001) surface has been measured to be 50 kcal/mol using temperature programmed desorption, compared to the adhesive energy of 90 kcal/mol for the bulk Au metal. At an equivalent Au coverage of 1.8 ML, very homogenous, hemispherical Au particles with an average 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 equivalent monolayers produces similar to 60 Angstrom diameter clusters. The scanning tunneling spectroscopy measurements show a gradual development of the metallic character of the Au clusters with increasing cluster size. Very similar results have been obtained for the Pd clusters supported on the MgO(100)/Mo(100) surface. (C) 1997 American Vacuum Society.