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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 42.66: Poster

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

Structural transitions of Heptyl Viologen adlayers on a Cu(1 0 0) electrode: In situ STM study — •Min Jiang, Knud Gentz, and Klaus Wandelt — Institute for Physical and Theoretical Chemistry, University of Bonn, Wegelerstr.12, D-53115 Bonn

Surface redox processes and structural transitions of heptyl viologen (1,1’-Diheptyl-4,4’-bipyridinium dichloride, DHV²⁺) was studied on a Cu(1 0 0) electrode by cyclic voltammetry (CV) and in situ scanning tunneling microscopy (STM). Typical for a redox-active molecule, DHV in KCl electrolyte solution exhibited two pairs of spike-like current waves and two-step one-electron redox processes. The DHV²⁺ species spontaneously formed four kinds of highly ordered phases on the preadsorbed chloride c(2 × 2) adlayer under non-reactive condition, which were composed of two mirror domains and two rotational domains. One-electron reduction of the dication DHV²⁺ caused a phase transition to a stripe pattern which arises from a π−π stacking of the corresponding monocation radical DHV^{· +} species. This phase transition involved not only reduction of the pre-adsorbed DHV²⁺ species but also a further adsorption and reduction of DHV²⁺ species from the solution phase. During the cathodic sweep, the stripe pattern of the cation radicals changed from a loose array to a more compact structure. At more negative potential, the ordered stripe pattern disappeared gradually and a reversible order-disorder transition happened. This is caused by chloride desorption-adsorption through the viologen film.