THE PREPARATION, CHARACTERIZATION AND OXYGEN-ADSORPTION ON IR/PD(110) ALLOYS

Ir-Pd alloys were formed on Pd(110) by evaporation of Ir and subsequent heating in vacuo. Ir overlayers were stable up to 600 K. At higher temperatures Pd diffusion to the surface occurred, which resulted in a Pd-dominated surface over a range of Ir coverages. The transformation of the surface initially dominated by Ir to one where a more homogeneous distribution of the two metals was obtained was probed with angle-resolved XPS. This showed that above 600 K a rapid loss of Ir from the surface region took place, which was followed by a slower loss at higher temperatures. Mixed surface layers could thus be formed which varied in composition depending on the initial amounts of Ir deposited. At low Ir coverages, these surfaces showed an oxygen adsorption behaviour resembling that of Pd(110) in terms of desorption temperatures, but with an increased amount of oxygen desorbing from subsurface sites.