Single-Molecule Conductance of Redox Molecules in Electrochemical Scanning Tunneling Microscopy

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• 作者：W. Haiss ; T. Albrecht ; H. van Zalinge ; S. J. Higgins ; D. Bethell ; H. H&ouml ; benreich ; D. J. Schiffrin ; R. J. Nichols ; A. M. Kuznetsov ; J. Zhang ; Q. Chi ; J. Ulstrup
• 刊名：Journal of Physical Chemistry B
• 出版年：2007
• 出版时间：June 21, 2007
• 年：2007
• 卷：111
• 期：24
• 页码：6703 - 6712
• 全文大小：184K
• 年卷期：v.111,no.24(June 21, 2007)
• ISSN：1520-5207

文摘

Experimental data and theoretical notions are presented for 6-[1'-(6-mercapto-hexyl)-[4,4']bipyridinium]-hexane-1-thiol iodide (6V6) "wired" between a gold electrode surface and tip in an in situ scanning tunnelingmicroscopy configuration. The viologen group can be used to "gate" charge transport across the molecularbridge through control of the electrochemical potential and consequently the redox state of the viologenmoiety. This gating is theoretically considered within the framework of superexchange and coherent two-step notions for charge transport. It is shown here that the absence of a maximum in the I_tunneling versuselectrode potential relationship can be fitted by a "soft" gating concept. This arises from large configurationalfluctuations of the molecular bridge linked to the gold contacts by flexible chains. This view is incorporatedin a formalism that is well-suited for data analysis and reproduces in all important respects the 6V6 data forphysically sound values of the appropriate parameters. This study demonstrates that fluctuations of isolatedconfigurationally "soft" molecules can dominate charge transport patterns and that theoretical frameworksfor compact monolayers may not be directly applied under such circumstances.