The dispersion of copper adsorbed on a Ru(001) substrate has been investigated by using Fourier transformhyphen;infrared reflection absorption spectroscopy (FThyphen;IRAS) and carbon monoxide as a molecular probe. Copper films evaporated at 85 K show a drastically different CO adsorption behavior compared to annealed films and exhibit a variety of adsorption sites. Characteristic Cndash;O stretching frequencies allow us to identify small copper clusters of 1ndash;4 atoms (2138ndash;2123 cmminus;1), twohyphen;dimensional (2120ndash;2110 cmminus;1) and threehyphen;dimensional (2098 cmminus;1) copper aggregates. After annealing to 250 K copper films at subhyphen; and monolayer coverages form wellhyphen;ordered small twohyphen; and threehyphen;dimensional copper aggregates. Formation of the epitaxial monolayer or islands of copper (2082 cmminus;1) requires a surprizingly mild annealing temperature of 350 K. Further annealing to 540 K results in increasing domain size of the copper islands or annealing of defect sites of the epitaxial monolayer. Multilayer coverages of copper evaporated at 85 K exhibit Cndash;O stretching frequencies found for highhyphen;index copper single crystal surfaces, e.g., (211) and (755). This indicates a large number of surface steps and protruding copper atoms associated with rough films. Annealing to 540 K results in a smooth copper layer with preferential (111) orientation (2075 cmminus;1). The vibrational data presented here for Cundash;Ru(001) agree well with previous reports of CO adsorption on copper single crystals, supported or evaporated films, and matrixhyphen;isolated clusters. They further allow us to determine the dispersion of supported Cundash;Pt and Cundash;Ni catalysts from data in the literature.
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