A PHOTOEMISSION-STUDY OF THE ADSORPTION OF THE 1ST AND THE 2ND LAYER OF XENON ON PT(332)

Xenon adsorption on Pt(332) has been studied by photoemission, LEED and TPD at 90 and 70 K. Step blocking by either CO or H-2 adsorption has been used to assign the different components of the Xe 5p spectra to different adsorption sites. At 90 K, the step-down sites are populated first. By increasing the xenon coverage, xenon atoms are then adsorbed on the (111) terraces. Under these conditions, no xenon induced LEED superstructure is observed. By lowering the temperature, a new Xe 5p peak appears before the growing of the Xe 5p peak attributed to the second layer. Consequently, an incommensurate aligned xenon superstructure is observed. Two models are discussed to assign the adsorption sites related to this new peak. The first one considers the completion of the first monolayer before the formation of the second xenon layer involving sites located at the step-up sites. We believed that this model is more reasonable. In the second model, a step induced clustering is considered. In the absence of an absolute coverage determination, this model cannot be definitively ruled out.