Molecules and Clusters on Oxide Surfaces

In this thesis X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, scanning tunneling microscopy,and density functional theory have been used to study the fundamental interactions between model oxidesurfaces and either organic, mixed organic/inorganic, or purely inorganic adsorbate layers. As model oxidesurfaces have served the rutile TiO2(110) surface and an in-situ grown iron oxide film supported by a Pt(111)surface. It is found that the amino acids L-cysteine, L-cystine, and S-methyl-L-cysteine as well as thezinc-protoporphyrin IX adsorb on the rutile TiO2(110) surface as carboxylates. This suggests a bidentate bondbetween the equivalent oxygen atoms of the deprotonated carboxylic groups of the molecules andfivefold-coordinated surface titanium atoms. All molecules, except S-methyl-L-cysteine, suffer from furtherdissociation on the surface. The thiol group of L-cysteine is deprotonated at surface defects, the disulfide bondof a fraction of the L-cystine adsorbates breaks at surface defects and in stoichiometric sites, and the centralzinc atom of the protoporphyrin is displaced as a result of a strong surface interaction. Gold clusters with a size on the nanometer scale have been grown on the adsorbate-modified rutile TiO2(110)surface as well as on a partly reduced ultrathin FeO(110) film grown on the Pt(111) surface. It is shown that bothsurfaces can be used as templates for growing small clusters. On the partly L-cysteine-covered rutile TiO2(110)surface the gold clusters nucleate mostly on the molecules, and the clusters are smaller as compared toclusters grown after deposition of the same amount of gold on the clean TiO2(110) surface. On the ultrathinFeO(111)/Pt(111) surface oxygen dislocation loops are nucleation sites for gold clusters, which are found to beactive for CO adsorption. An interesting proton transfer behavior is observed among the functional groups of L-cysteine in thick films ofL-cysteine prepared at 100 K. In this film L-cysteine forms zwitterions, but with most of the protons provided bythe thiol groups rather than the carboxylic groups, as would have be expected from common textbookknowledge. This is the first unambiguous identification of this particular form of L-cysteine zwitterion. (Less)