SERS detection of the vibrational Stark effect from nitrile-terminated SAMs to probe electric fields in the diffuse double-layer.

The vibrational Stark effect is observed in the surface-enhanced Raman scattering spectra of self-assembled monolayers functionalized with pendant nitrile groups. Stark tuning of the nitrile-stretching frequency serves as a localized probe of the electric field in the diffuse double layer of a SAM-modified electrochemical interface. Stark-tuning rates at low ionic strength correspond to reasonable values of the local electric (E) field in the double layer. The nitrile-stretching frequency converges on its isotropic value at applied potentials approaching the PZC, which indicates that Stark-tuning of the frequency is a direct probe of the E field at the interface. Loss of the local electric field at high ionic strengths shows that the probe responds to changes in the Debye length of the double layer. The results demonstrate the applicability of this electric-field probe for characterizing the diffuse double-layer region.