SPATIALLY-RESOLVED CHEMISTRY ON BIMETALLIC SURFACES

The local chemical properties of bimetallic surfaces, which are often drastically different from those of each of the components, will be di scussed. Using CO adsorption as a probe molecule it will be shown for two model systems, Au/Pd(111) and Pt/Ru(0001), that their chemical pro perties depend decisively on the local surface structure and that the correct interpretation of area integrating spectroscopic and kinetic d ata obtained from such surfaces requires detailed knowledge of their ( defect) structure and of the distribution of the different components in the surface layer. It will further be shown that information on the local chemical properties of specific structural elements such as mon olayer islands and monolayer island edges, and specific surface ensemb les can be gained by applying high resolution scanning tunneling micro scopy imaging and area integrating spectroscopic techniques in combina tion to bimetallic surfaces whose morphology and composition is varied in a systematic and controlled way. Based on experimental results ads orption on a monolayer A / substrate B system is suggested as a model for gaining information on the modifications in chemical properties of AB alloy surfaces due to metal-metal interactions.