Berlin 2008 – scientific programme

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O: Fachverband Oberflächenphysik

O 34: Metal Substrates: Adsorption of Organic/Bio Molecules II

O 34.4: Talk

Tuesday, February 26, 2008, 14:30–14:45, MA 043

Analysis of structural and electronic properties of complex molecular phases: Tetracene on Ag(111) — •Sergey Soubatch, Ruslan Temirov, and Stefan Tautz — Forschungszentrum Jülich, Jülich, Germany

Formation and properties of disordered and ordered phases of tetracene on Ag(111) surface have been studied using LT-STM. At sub-monolayer coverage, tetracene forms a disordered phase due to repulsive interactions between flat-laying molecules on the metal surface. As the coverage rises, the tetracene phase starts to order. This process is driven by a balancing of intermolecular repulsion, attraction between molecules and the substrate, and competition between the positional and rotational entropy. Two long range ordered phases can appear at the surface. The alpha-phase represents a compact monolayer of flat-lying molecules, those electronic properties are strongly affected by interaction with the metal. It is revealed by significant shift of LUMO level registered by differential conductance spectroscopy. The beta-phase has more complex structure including interfacial layer and additional layer and molecular chains on top. Whilst the molecules in more planar configuration at the interface are strongly coupled to metallic electron states of the substrate, the molecules tilted out of the metal surface and/or separated from the metal by interfacial layer are found to be decoupled. For such molecules strong effect of local environment and intermolecular interaction on the energy of LUMO level is observed. The structural model for complex tetracene beta-phase has been proposed.