The characterisation of model Cu/Ru(001) bimetallic catalysts by static SIMS with XPS and TPD

The deposition of Cu onto Ru(001) at 540 and 1080 K has been studied by SSIMS supplemented by XPS and TPD. The SSIMS mass spectrum of the Cu/Ru surfaces showed the presence of Cu⁺ and Ru⁺ ions as well as the cluster ions RuCu⁺, Ru⁺₂, Cu⁺₂ and lower intensities of Cu⁺₃, RuCu⁺₂ and Ru₂Cu⁺. Copper coverage was independently monitored by XPS and TPD. It was shown that Cu coverage in the sub-monolayer region was directly proportional to $\text{RuCu}{}^{\mathrm{+}}\text{Ru}{}^{\mathrm{+}}$. Secondary ion emission was strongly influenced by work function changes consequent on Cu adsorption.Studies of the variation of the elemental and cluster ion intensities as a function of Cu coverage, at the two temperatures, has provided detailed information on the dispersion of Cu in the sub-monolayer region, and on the physical form of the ad-layer above a monolayer coverage.