STRUCTURAL CHARACTERIZATION OF A MODEL CATALYST - PT AL2O3/NIAL(110)/

By using STM, LEED and ISS we have studied the condensation of Pt on c lean NiAl(110) and on a thin ordered Al2O3 film grown on NiAl(110). On Al2O3/NiAl(110) and up to a coverage of one monolayer Pt forms highly dispersed two-dimensional islands with an average diameter of 10-30 A ngstrom whose density increases with the coverage. For higher Pt cover age the formation of three-dimensional Pt clusters is observed. Anneal ing of the Pt-covered surface leads to a diffusion of Pt into the oxid e film. On clean NiAl(110) and up to one monolayer we found two-dimens ional growth of Pt the density of the islands remaining approximately constant.