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.
The conductance of single-molecule junctions is affected by the structure of the
molecule and how it is bound to the electrodes, which may be examined using Raman
spectroscopy. Liu
et al. have developed 'fishing-mode' tip-enhanced Raman spectroscopy, which allows the
simultaneous determination of conductance and Raman spectra.