MIES-studies on size-selected clusters deposited on oxide surfaces

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This project aims to study the electronic structure of pure and ligated clusters on oxide surfaces by means of the metastable impact electron spectroscopy, MIES, in combination with the ultraviolet photoelectron spectroscopy, UPS, in order to understand their chemical properties. We focus in the first term of the project on well-defined metal clusters with well-known, different and specific chemical properties. The following systems will be investigated in detail spectroscopically: (a) Au3Sr, Au4 und Au8 supported on ultrathin MgO-films: In this example we first characterize the electronic states of the three clusters spectroscopically and compare the obtained results with existing ab initio calculations. Second, we study the binding behavior of 02 to these clusters and a possible activation of the adsorbant. These studies will give important information on the different chemical properties of the three clusters with respect to the oxidation of CO. (b) Pd-atoms supported on ultrathin Mg0-films: Here we study to what extent the oxidation of CO occurs via carbonate formation and/or coadsorption of CO and 02. In the first phase of the project a highly intense source for metastable He atoms will be built at the Technical University of Clausthal. This source will then be integrated into the analysis chamber of the existing cluster deposition experiment at the University of Ulm. In this experimental setup the hemispherical analyzer, necessary for the MIESS studies, is already available. In future these experiments will be extended to other systems. We will grow thin Ti02 and Si02 films onto Mo(110) and Mo(112), respectively, characterize existing defects of these surfaces and study the same cluster systems on these different support materials.