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O: Fachverband Oberflächenphysik

O 60: Poster Session IV (Solid/liquid interfaces; Semiconductors; Oxides and insulators; Graphene; Plasmonics and nanooptics; Electronic Structure; Surface chemical reactions; Heterogeneous catalysis)

O 60.2: Poster

Mittwoch, 16. März 2011, 17:30–21:00, P4

Potential dependent structural transition of heptyl viologen on Cu(100) studied by in situ STM and IRRAS — •Melanie Röefzaad¹, Min Jiang², and Klaus Wandelt¹ — ¹Institute for Phys. Chem., University of Bonn, Germany — ²Inst. Bioenergy and Bioprocess Technology,Chinese Academy Sciences, P.R. China

The potential dependent adsorption structure of heptyl viologen (1,1*-Diheptyl-4,4*-bipyridinium, DHV) on a chloride precovered Cu(100) electrode has been investigated by Cyclic Voltammetry (CV), in situ electrochemical STM and IR-Reflection Absorption Spectroscopy (IRRAS). The redox-active DHV molecule exhibits pairs of current waves in CV measurements which are ascribed to two typical one-electron transfer steps and phase transformation processes. Between +200 and -100 mV, an ordered 2D dot-array structure in STM images emerges on the Cl- modified Cu(100) electrode surface. One-electron reduction of the dication around -150 mV causes a phase transition from a dot-array assembly to a stripe pattern in STM images which has a double layer structure. With a decrease of the applied electrode potential, the structure of the adlayer undergoes a subsequent change from the double layer phase to a closed packed monolayer of stripes. Orientation analysis with IRRAS of the bipyridine moiety reveals a slight tilt of the long molecular axis to the surface in the dicationic phase and a parallel orientation in the mono cationic striped phases. Calculation of the average angle of the alkyl chains hints to an orientation along the surface within the dot structure while protruding out of the more closely packed stripe phase.