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. Show more