Eigenschaften fluorierter Aromaten an Metall/Organik-Grenzflächen

The scope of this dissertation was to study the influence of fluorination on the interface properties of aromatic molecules. In a multi-technique approach two model systems were systematically characterized concerning their structural and electronic properties. In conclusion fluorination was found to be a successful route to tailor properties like sample-workfunction, intermolecular interactions and electronic properties. However, also unwanted side-effcts of fluorination were found. Surprisingly, it turned out that perfluorination leads to an unexpectedly high reactivity at the organic/metal-interface in the case of both studied systems. SAMs on Cu(100) formed by differently fluorinated on the one hand and perfluoropentacene (PFP) on the surfaces Au(111), Ag(111) and Cu(111) on the other hand served as modelsystems. These systems differ in their attachment to the surface, since SAMs are covalently bound to the metal via their sulfur-anchor, while PFP is only physisorbed. The first part of this work uses the approach of tailoring the Cu(100) workfunction by differently fluorinated BTs. In order to do so, the system of non-fluorinated BT on Cu(100) was first studied in depth, concerning microscopical structure and long term film stability. As a consequence the provision of a new structure model was enabled after unrevealing severe weaknesses of the model existing in literature. Furthermore it turned out that such BT SAMs degrade rapidly under UHV-conditions at room temperature depending on the grade on fluorination. For perfluorinated BT, this leads to a pure sulfur-overlayer. Such degradations were not considered in earlier studies on BT SAMs and their description in this work now allows to avoid them by cooling and sufficiently fast experiments. Changes of the the Cu(100) workfunction of ±1 eV were reached by systematic va- riation of BT-fluorination. Based on a full structural characterization of all investigated SAMs, it was possible to describe the dependence of the workfunction on molecular dipoles, bond dipoles and intermolecular depolarization quantitatively in an empirical model. In the second part of this work the effect of fluorination of the well known organic semiconductor pentacene (PEN) on its properties at interfaces was tested. Monolayers of PFP on Ag(111) were characterized, which were prepared by thermal desorption of excessive multilayers. This way of preparation which leads to densely packed monolayers in case of PEN ends in a more complex system for PFP. A co-structure of highly ordered dense PFP islands and free substrate areas is found at low temperatures. Thawing the sample to more than 145 K, molecules start to diffuse, forming a low density phase with random lateral orientation, but still parallel orientation to the surface. This phase transition was investigated with different experimental techniques concerning its structural and electronic impacts. Furthermore an unusual parallel orientation of PFP molecules in multilayers on Ag(111) which was suggested from earlier XRD and XSW experiments was confirmed by NEXAFS. At higher temperatures PFP-molecules decompose on Cu(111) and Ag(111). In contrast, only intact desorption is found from PFP-monolayers on Au(111). By combining XPS, NEXAFS and DFT the intermediate binding of fluorine to the metal-substrate can be seen as an essential step. Furthermore surface defects largely promote decomposition of PFP on silver. As a result, for possible device applications of PFP and similar fluorinated aromatics, gold electrodes seem to be the only valuable choice.In the development of organic electronic or photovoltaic devices based on donor-acceptor-systems, frequently π − π-interactions are named as key properties. To study such effects in the case of PFP and PEN, bi-layered PFP/PEN-systems were investigated in the last part of this work. First evidence for a real π − π-interaction in such a system was found and compared to studies from other groups of bulk-blends of PFP and PEN. Interestingly the appearance of a π − π-interaction can be suppressed by a strongly interacting metal substrate. Both modelsystems prove that the concept of fluorination can be successfully employed to influence electronic and structural properties. However, both systems show that even though fluorination stabilizes aromatic molecules against ambient conditions (e.g. O2), particular care has to be taken of chemical reactions at metal/organic interfaces. The quantitative evaluation of the first F1s-NEXAFS-resonances of PFP is described in this work. This may help to analyze blended films of fluorinated acenes and nonfluorinated acenes, because it addresses the fluorinated species separately.