Dresden 2011 – wissenschaftliches Programm

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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 60.3: Poster

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

Phase transitions of adsorbed viologen monolayers in the presence and absence of specifically adsorbed halides — •Knud Gentz, Min Jiang, and Klaus Wandelt — Institute for Physical und Theoretical Chemistry, Uni Bonn

The structure and stability of self-assembled organic monolayers are scientifically and technologically very timely research subjects. In those cases where larger organic molecules may not be intact volatile and therefore not be deposited by vapor deposition, adsorption from solution may be an alternative route. Here we present results on heptylviologen layers on HOPG and Cu(1 0 0) surfaces as obtained with cyclic voltametry and in-situ scanning tunneling microscopy in solution. Heptylviologen was adsorbed on the HOPG- and Cu(1 0 0) electrode surfaces from a supporting electrolyte. In the CV spikes characteristic of surface phase transitions of HV monolayers on HOPG were observed. The STM images clearly show a stripe structure on the surface in the regime negative of the spike peaks indicating the presence of the radical cationic phase HV^•+ stabilized by π–π-interaction of the individual molecules. On HOPG a single row and a double row structure were found showing a herringbone-like arrangement of the molecules. Additionally, on copper a second layer adsorption of HV molecules was observed the concentration and structure of which depending on the applied electrode potential. In the regime positive of the spike peak an ordered viologen layer was observed only on copper, where chloride is specifically adsorbed on the surface, which stabilizes the dicationic species on the positively charged electrode.