Absence of surface enhanced Raman scattering (SERS) by pyridine on cleaned roughened silver electrodes

Abstract

AbstractAnodically roughened silver electrode surfaces which have been cathodically cleaned exhibit virtually no pyridine surface spectrum i.e. no surface enhanced Raman scattering (SERS) effect. Scanning electron microscopy (SEM) reveals no detectable change in the surface roughness features as a result of the cathodic surface cleaning. The absence of SERS has been confirmed for cathodically‐cleaned flat (unanodized), roughened (anodized) and massively roughened (repetitively anodized) silver surfaces. These findings appear to rule out flat‐surface or roughened‐surface (metal‐particle) enhancement of the pyridine spectrum itself. Other evidence confirms that the intensely scattering SERS phase is [carbon‐pyridine] and not pyridine itself. The carbon and pyridine SERS intensities are shown to coincide on the potential scale and to exhibit a stoichiometric interdependence. These results rule out coadsorption and argue strongly in favour of internal trapping rather than external adsorption of pyridine on carbon. The insensitivity of pyridine SERS to the presence of a radical scavenger confirms the absence of radical ion resonance enhancement. These results are consistent with parallel Auger studies which reveal that localized laser damage (producing a zone of pure carbon in the case of pyridine) is probably the primary factor in SERS from silver electrodes. The implications of these and other results for a reduced silver‐generated enhancement factor are considered.