CO adsorption on PtxPd1−x(1 1 1) single crystal alloy surfaces: a core level and valence band photoemission study

We present a photoelectron spectroscopy study of three single crystal PtxPd1−x(1 1 1) alloy surfaces (x=0.1, 0.5, 0.9) using synchrotron radiation. The surface and chemical sensitivity of core level photoemission allows us to quantify an oscillatory depth concentration profile and the palladium segregation at the surface of each alloy. The experimental results are compared to theory based on regular solution and tight binding Ising model formalisms, a good agreement is found. In the second part of the paper the effect of CO adsorption on the alloy surfaces is investigated. The variety of adsorption site geometry and chemistry as a function of surface segregation and bulk alloy concentration is revealed in both valence band and core level spectra.