Dresden 2009 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 42: Poster Session II (Nanostructures at surfaces: arrays; Nanostructures at surfaces: Dots, particles, clusters; Nanostructures at surfaces: Other; Nanostructures at surfaces: Wires, tubes; Metal substrates: Adsorption of O and/or H; Metal substrates: Clean surfaces; Metal substrates: Adsorption of organic/bio moledules; Metal substrates: Solid-liquid interfaces; Metal substrates: Adsorption of inorganic molecules; Metal substrates: Epitaxy and growth; Heterogeneous catalysis; Surface chemical reactions; Ab-initio approaches to excitations in condensed matter; Organic, polymeric, biomolecular films– also with adsorbates; Particles and clusters)

O 42.61: Poster

Mittwoch, 25. März 2009, 17:45–20:30, P2

Surface mobility and its impact on the stability of oligopyridine mono- and multilayer phases on HOPG - a thermal desorption study — •Michael Roos, Harry E. Hoster, and R. Jürgen Behm — Institute of Surface Chemistry and Catalysis, Ulm University, D-89069 Ulm, Germany

We report on the temperature and coverage dependent desorption rates from layers of two types of Bis(terpyridine)derivatives (BTP) on HOPG [1-4]. These rates are much higher for thicker films than for monolayers. These variations do not predominantly arise from changes in the energetic desorption barriers but are dominated by the frequency factors. Due to the large mass (618 amu) and the correspondingly large moments of inertia of the BTP molecules, the frequency factor approaches 10²⁶ Hz for desorption from an immobile initial state (multilayer), whereas it is changed by a factor of 10⁻⁹ for desorption out of a mobile state (monolayer). This fits to STM observations at 300 K, which revealed that the most stable phase for both molecules is not a close packed hydrogen bonded one, but a dilute 2D gas, where translation and planar rotation are active. We compare the frequency factors and activation energies for desorption of the two types of BTP, which differ in the position of the peripheral N atoms, and discuss possible reasons for the differences.
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