Chemical origins of surface-enhanced Raman scattering by water on silver- and carbon-overlayered silver electrodes

Abstract

Enhanced Raman scattering (ERS) from H₂O on silver-electrode surfaces appears to arise from a contaminant carbon-rich laser microzone. The carbon appears to originate in electrolyte salt contaminants. Carbon-free silver-electrode surfaces exhibit no detectable H₂O-ERS. Also, extensively precarbonized silver and surfaces exhibit more intense H₂O-ERS than ERS recorded from a conventional surface. Auger electron spectroscopic data for such conventional silver/H₂O-ERS surfaces reveal a non-illuminated surface which is relatively rich in carbon and which at high laser flux incorporates a zone of almost pure carbon. These results are interpreted in terms of an H₂O intercalate of an expanded graphitic oxide (highly oxidized carbon) structure. Such negatively charged graphitic oxide surfaces can internally accumulate both polar molecules (e.g. H₂O) and cations. The unexpected sensitivity of H₂O-ERS to both the electrolyte cation and the presence of anions forming insoluble silver(I) salts can be understood in terms of graphitic oxide adsorption.