Carbon association of surface‐enhanced Raman scattering (SERS) by pyridine on gold electrodes: A Raman and Auger spectroscopic study

Abstract

AbstractSurface‐enhanced Raman scattering (SERS) by pyridine on gold electrode surfaces to arise from the adsorption of pyridine in or on surface carbon present after the oxidation‐reduction cycle (ORC). Similar Raman ring‐breathing mode spectra for both gold and silver electrodes and sols indicate a common intensely scattering phase which is independent of the metal substrate. The common phase proposed is [carbon‐pyridine]. Auger electron spectroscopy indicates that the SERS spectrum arises from a surface microzone having a C to Au ratio of ca 7. Cathodic elimination of microzone carbon results in the elimination of pyridine SERS. Carbon‐enriched (sputtered) gold surfaces exhibit the same ring‐breathing mode pattern as for the conventional SERS surface. Laser carbonization effects are suggested by differences in the SERS intensities observed for the presence and absence of laser flux during the ORC. Laser decarbonization appears to be the origin of the characteristic decay of SERS from gold electrodes. It is proposed that the decay is instantaneous for 514.5 nm Ar+ excitation and slower for 647.1 nm Kr+. Differences in pyridine SERS intensities from silver and gold electrodes are attributed to differences detected by Auger spectroscopy in the extent of laser microzone carbonization. On the basis of these findings Au/pyridine SERS has been classified as Type I.