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O: Fachverband Oberflächenphysik

O 59: Poster Session II (Nanostructures at surfaces: Dots, particles, clusters; Nanostructures at surfaces: arrays; Nanostructures at surfaces: Wires, tubes; Nanostructures at surfaces: Other; Plasmonics and nanooptics; Metal substrates: Epitaxy and growth; Metal substrates: Solid-liquid interfaces; Metal substrates: Adsoprtion of organic / bio molecules; Metal substrates: Adsoprtion of inorganic molecules; Metal substrates: Adsoprtion of O and/or H; Metal substrates: Clean surfaces; Density functional theory and beyond for real materials)

O 59.68: Poster

Mittwoch, 24. März 2010, 17:45–20:30, Poster B1

Structural transitions of heptyl viologen adlayers on Cu(1 0 0) – an electrochemical and in situ STM study — •Min Jiang, Knud Gentz, and Klaus Wandelt — Institute for Physical and Theoretical Chemistry, University of Bonn, Wegelerstr. 12, 53115 Bonn

The redox behaviour and potential dependent adsorption structure of heptyl viologen (abbreviated as DHV²⁺) on a Cu(1 0 0) electrode have been investigated in a chloride-containing electrolyte solution by in situ electrochemical scanning tunneling microscopy (EC-STM). After injecting DHV²⁺ molecules into the KCl electrolyte solution, a highly ordered 2D dot-array structure in STM images emerges on a c(2× 2) chloride modified Cu(1 0 0) electrode surface. DHV²⁺ molecules spontaneously arrange themselves with their molecular planes facing to the electrode surface and their long molecular axis parallel to a step edge. Such adsorption structure can be described by mirror domains and rotational domains which stably exist between 200mV and −100mV. One-electron reduction of dication DHV²⁺ around −150mV causes a phase transition from a dot-array assembly to a stripe pattern in STM images which has a bilayer structure. With a decrease of the applied electrode potential, the structure of DHV^{• +} adlayer undergoes a change from a loose stripe phase to a more compact stripe phase, and a subsequent decay of the compact structure, and then a formation of new dimer phase. A further electron transfer reaction at −400mV causes the appearance of an amorphous phase on the electrode surface.