Studies of Model Nanostructured Materials : Geometric and Electronic Structure, and sub-10 fs Charge Transfer Dynamics

A number of nanostructured systems has been investigated by means of Photoemission and X-ray absorption spectroscopies and by Scanning tunneling microscopy with emphasis on the geometric and electronic structure and the excited-state charge transfer dynamics. These systems comprise aromatic molecules on semiconductor surfaces (titanium dioxide), metal clusters, and an alkali-C60 compound. Electronic and geometric structure are complementary to each other, and changes in the geometric structure are accompanied by changes in the electronic structure. Therefore, a detailed investigation of the latter makes it possible to draw conclusions on the former. In particular, this close relationship has been used to characterise the adsorbate geometry of the pyridine-carboxylic acid monomers on rutile TiO2(110), which is determined by the strong substrate bond as well as interadsorbate interactions. Similarly, it has been found that bi-isonicotinic acid adsorbs on a nanostructured anatase TiO2 film by forming strong bonds between both carboxylic groups and the substrate titanium atoms. For deposited metal clusters, the core binding energies are found to mirror the cluster size. Resonant core electron spectroscopies have been employed to elucidate the excited-state charge transfer dynamics with respect to the transfer of an excited electron from the bi-isonicotinic acid and isonicotinic acid adsorbates to a titanium dioxide semiconductor surface. An important aspect has been the development of new variations of the method in order to be able to unravel the spectra of these relatively complex systems. While a strong excitonic effect localises the excited electron on the adsorbate for the lowest excited state, excitation to the higher excited states leads to an ultrarapid charge transfer on a low- to sub-femtosecond timescale. In LiC60 the character of the alkali-C60 bond has been investigated. The balance between the different energy contributions points to an ionic bond with an important element of covalency