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Nat Commun. 2011;2:305. doi: 10.1038/ncomms1310.

Revealing the molecular structure of single-molecule junctions in different conductance states by fishing-mode tip-enhanced Raman spectroscopy.

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State Key Laboratory of Physical Chemistry of Solid Surfaces and Key Laboratory of Analytical Sciences, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China.


The conductance of single-molecule junctions may be governed by the structure of the molecule in the gap or by the way it bonds with the leads, and the information contained in a Raman spectrum is ideal for examining both. Here we demonstrate that molecule-to-surface bonding may be characterized during electron transport by 'fishing-mode' tip-enhanced Raman spectroscopy (FM-TERS). This technique allows mutually verifiable single-molecule conductance and Raman signals with single-molecule contributions to be acquired simultaneously at room temperature. Density functional theory calculations reveal that the most significant spectral change seen for a gold-4,4'-bipyridine-gold junction results from the deformation of the pyridine ring in contact with the drain electrode at high voltage, and these calculations suggest that a stronger bonding interaction between the molecule and the drain may account for the nonlinear dependence of conductance on bias voltage. FM-TERS will lead to a better understanding of electron-transport processes in molecular junctions.

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