STM ANALYSIS OF TRIOSMIUM CARBONYL CLUSTER ADSORPTION AT HOPG

The study of metallic carbonyl clusters as precursors in tailoring the heterogeneous metal catalysts has been of great importance. The catal ytic nature of the adsorbed clusters in thin film form depends on the chemical properties of the substrate used. The metal-support interacti on will determine various properties such as the surface morphology, a dsorption features and the structural orientations. We report a scanni ng tunneling microscopy (STM) study of an osmium carbonyl duster (Os-3 (CO)(11)(NCCH3)) adsorbed on highly oriented pyrolytic graphite (HOPG) . STM measurements showed that the osmium carbonyl cluster interacts w ith HOPG in such a way that it adsorbs on the basal plane showing regu lar lattice structure, whereas the axial planes of the HOPG surface sh ows no ordered structure. The regular cluster lattice structure of the carbonyl cluster on the basal plane of the graphite has lattice param eters of a = 1.4 nm and b = 1.5 nm. We believe that the regular orient ation of the cluster indicates a monolayer adsorption of the cluster o n the graphite basal planes. Scanning tunneling spectroscopy (STS) mea surements also indicated an insulating behavior for the cluster molecu les on HOPG, with a significant energy gap value of ca. 300 mV. The cl uster interaction at the active sites, i.e. axial planes of the graphi te, was also observed by in situ STM measurements.