Regensburg 2007 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 44: Poster Session II (Semiconductors; Oxides and Insulators: Adsorption, Clean Surfaces, Epitaxy and Growth; Surface Chemical Reactions and Heterogeneous Catalysis; Surface or Interface Magnetism; Solid-Liquid Interfaces; Organic, Polymeric, Biomolecular Films; Particles and Clusters; Methods: Atomic and Electronic Structure; Time-resolved Spectroscopies)

O 44.70: Poster

Mittwoch, 28. März 2007, 17:00–19:30, Poster C

Potential dependent structures of adsorbed viologens on Cu(100) — •Knud Gentz, Peter Broekmann, Simone Koßmann, Barbara Kirchner, and Klaus Wandelt — Institut für Physikalische und Theoretische Chemie, Uni Bonn

The structures of two different viologens (1,1’-disubstituted 4,4’-Bipyridins) adsorbed on a bromide-modified Cu(100) surface in an electrochemical environment have been studied by cyclic voltammetry (CV) and Scanning Tunneling Microscope (STM) studies. Upon adsorption, both viologens arrange in characteristic structures, dependent on the potential of the electrochemical cell. Via potential variation various structures are accessible and have been characterized. The phase transition are completely reversible between the DBV²⁺ dication and the DBV^{• +} radical cation of Dibenzylviologen and the DPV²⁺ and DPV^{• +} of the Diphenylviologen respectively. For the DPV molecule, this phase transisition proceeds in two steps. First, the bulk phase is oxidized through the adsorbed layer of the DPV^{• +} radical cation. Only at a significantly higher potential the adsorbed viologen is oxidized. In the cathodic sweep a corresponding surface reduction peak can be observed in the cv at higher potential than the bulk reduction peak. The reduction to the neutral DBV and DPV molecules occurs only at low potentials beyond the onset of the hydrogen evolution reaction. Based on DFT calculations of the structure of individual and groups of Viologen molecules, models for the observed structures are proposed.