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    Fabrication of Asymmetric Molecular Junctions by the Oriented Assembly of Dithiocarbamate Rectifiers

    Year: 2011

    Journal: J. Am. Chem. Soc., 2011, 133 (15), pp 5921–5930, 20111221

    Authors: Deqing Gao, † Frank Scholz, † Heinz-Georg Nothofer, † William E. Ford, † Ullrich Scherf, § Jurina M. Wessels, † Akio Yasuda, † and Florian von Wrochem,†

    Organizations: † Sony Deutschland GmbH, Materials Science Laboratory, Hedel?nger Strasse 61, 70327 Stuttgart, Germany § Bergische Universität Wuppertal, Makromolekulare Chemie und Institut für Polymertechnologie, Gauss-Strasse 20, 42097 Wuppertal, Germany

    The oriented assembly of molecules on metals is a requirement for rectification in planar metal−molecule−metal junctions. Here, we demonstrate how the difference in adsorption kinetics between dithiocarbamate and thioacetate anchor groups can be utilized to form oriented assemblies of asymmetric molecules that are bound to Au through the dithiocarbamate moiety. The free thioactate group is then used as a ligand to bind Au nanoparticles and to form the desired metal−molecule−metal junction. Besides allowing an asymmetric coupling to the electrodes, the molecules exhibit an asymmetric molecular backbone where the length of the alkyl chains separating the electrodes from a central, para-substituted phenyl ring differs by two methylene units. Throughout the junction fabrication, the layers were characterized by photoelectron spectroscopy, infrared spectroscopy, and scanning tunneling microscopy. Large area junctions using a conducting polymer interlayer between a mercury-drop electrode and the self-assembled monolayer prove the relationship between electrical data and molecular structure.