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

Ir-Pd alloys were formed on Pd(110) by evaporation of Ir and subsequen t heating in vacuo. Ir overlayers were stable up to 600 K. At higher t emperatures 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 homogeneo us distribution of the two metals was obtained was probed with angle-r esolved 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 high er temperatures. Mixed surface layers could thus be formed which varie d 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 w ith an increased amount of oxygen desorbing from subsurface sites.