Surface-Enhanced Raman Spectroscopy of Electrochemically Characterized Interfaces. Relations between Raman Scattering Intensity and Surface Coverage for Simple Anionic Adsorbates

摘要

Surface-Enhanced Raman Scattering (SERS) obtained as a function of electrode potential for chloride, bromide, iodide, thiocyanate, azide, and cyanide adsorbed at roughened silver electrodes are compared with corresponding surface concentration-potential data extracted from differential capacitance measurements in order to examine the relation between SERS and surface coverage for these structurally simple adsorbates. After generating SERS by means of an oxidation-reduction cycle, it was found that altering the potential to a more negative value, where the adsorbate coverage fell below a monolayer, corresponded closely in most cases to the onset of a potential-dependent decay in the SERS intensity. Monitoring the potential dependence of the Raman intensity with an Optical Multi-channel Analyzer as well as with a conventional scanning spectrometer allowed a rapid reversible component of the potential dependence to be separated from an additional irreversible signal decay associated with the loss of Raman-active sites. The present results suggest that the adsorption energetics of the Raman-active surface sites do not differ substantially from those for the sites occupied by the majority of the adsorbate.