Surface-enhanced Raman scattering spectra of p-nitrobenzoic acid (PNBA) on the Ag electrode of a Ag/AlOx/Al tunnel junction are measured under application of a bias voltage. The bands caused by the adsorbed PNBA- at the active junction's area increase in intensity with bias voltage and a new band attributable to the azo-group emerges at voltages greater than +2.2 eV. The intensity profile of the new band is similar to the junction's Tafel plot. In contrast, the non-active electrode surface shows no change in the bands. These results indicate the tunnel junction might furnish a surface template for an anisotropic molecular structure.
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