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SYSA: Symposium Tayloring Organic Interfaces: Molecular Structures and Applications

SYSA 5: Poster Session SYSA

SYSA 5.4: Poster

Dienstag, 26. Februar 2008, 14:30–20:00, Poster A

Pentacene film growth on HOPG — •Jan Götzen, Daniel Käfer, Christof Wöll, and Gregor Witte — Physikalische Chemie I, Ruhr-Universität Bochum, 44780 Bochum

Recent studies have shown that the structure and molecular orientation in organic thin films depends sensitively on the interaction with the substrate which is of vital interest for an understanding and optimization of organic thin film electronic devices. Here we report a characterization of the microstructure, morphology and thermal stability of pentacene films grown by OMBD onto freshly cleaved HOPG by employing STM, AFM, NEXAFS, XRD and TDS. Despite a rather weak, essentially van-der Waals-type substrate interaction pentacene molecules adsorb with their planes oriented parallel to the surface and form a commensurate monolayer due to the close match of the molecular carbon frame and the underlying graphite lattice. This packing motive, however, is not maintained in multilayer films where instead molecules in subsequent layers are tilted around their long axis. The mutlilayer growth is further characterized by the formation of individual, elongated crystalline islands exhibiting the Siegrist bulk polymorphism and thus parallels the growth scenario observed previously for pentacene on Au(111). Identical structures were observed for rather different growth conditions (rate and temperature) and therefore indicate the presence of equilibrium film structures. In contrast films with upright oriented molecules were obtained if the graphite had been briefly sputtered to roughen the substrate surface and thus emphasizes the importance of micro-roughness on the resulting film growth.