MODEL CATALYSTS OBTAINED BY CLUSTER DEPOSITION OF PALLADIUM ONTO HOPG- TEM AND STM CHARACTERIZATION

Supported particles (model catalysts used in hydrogenation reactions) are obtained by cluster beam deposition onto HOPG and characterised by transmission electron microscopy (TEM) and scanning tunneling microsc opy (STM). TEM shows the formation of groups of particles on the surfa ce and the decoration of the steps of graphite. The groups of particle s on the surface are well separated from each other. STM large scale o bservations agree with these observations. A detailed experimental stu dy of the (square-root 3 x square-root 3)R30-degrees periodic charge d ensity modulations of the graphite observed around the particles is pr esented and these modulations are interpreted in terms of a perturbati on introduced by the particle to the degenerate wave functions of grap hite, lifting up the degeneracy and yielding the (square-root 3 x squa re-root 3)R30-degrees superstructure.