The interaction of hydrogen with CeO${}_2$ (111)/Ru (0001) and surface action spectroscopy. Setup and first experiments

The first part of this thesis describes the setup of an apparatus for vibrational surface action spectroscopy as well as first experiments with this new method employing infrared radiation from the free electron laser of the Fritz Haber Institute. Vibrational action spectroscopy has been used previously mostly for the characterization of clusters in the gas phase. We have extended this method towards an application to solid surfaces with a V${}_2$O${}_3$(0001) film on Au(111) as a model system for the first studies. This oxide has vanadyl groups at the surface but not in the bulk, and therefore these groups could be used to show that the method is surface sensitive. The second part of my thesis treats the interaction of hydrogen with CeO${}_2$(111) thin films on Ru(0001). Experiments are carried out under UHV conditions using different surface science techniques such as low energy electron diffraction (LEED), thermal desorption spectroscopy (TDS), high resolution electron energy loss spectroscopy (HREELS) and scanning tunneling microscopy (STM). Cerium oxide (ceria) plays a crucial part in catalytic reactions due to its ability to store and release oxygen. There are many studies about the interaction of atomic hydrogen with ceria, but a comprehensive picture is still lacking. Hydrogen was dosed at pressures of at least 10 mbar in the studies discussed here. Stoichiometric CeO${}_2$(111) is not very much affected by exposure to hydrogen at room temperature, while, contrary to results found in the literature, exposure to reduced CeO${}_2$(111) does not lead to the formation of hydroxyl groups but to hydride species. Moreover, the Ce${}^{3+}$ in the reduced oxide is re-oxidized to Ce${}^{4+}$. At elevated temperatures, hydrogen additionally reduces the sample. This thesis confirms that oxygen vacancies play an important role in the interaction of hydrogen molecules with CeO${}_2$(111), and it confirms that hydrogen may be stored as a hydride species in the oxide. The electronic and morphological changes through the hydrogenation process are discussed.