Some aspects of SERS temporal fluctuations: analysis of the most intense spectra of hydrogenated amorphous carbon deposited on silver

Surface-enhanced Raman scattering (SERS) spectra of hydrogenated amorphous carbon (a-C: H) deposited on silver substrates have been recorded with a confocal Raman microscope. When scattered radiation is collected during a short time from an area of a few square micrometres, the subsequently measured SERS spectra often exhibit strong temporal changes (fluctuations). In this paper we present examples of spectra for which the intensity maxima of the fluctuating narrow Raman bands are significantly higher than that of the background (the background is usually dominated by two broad Raman bands centred at about 1350 and 1590 cm(-1)). In a series of successively measured spectra, one can find spectra with noticeably different total integral intensity. This suggests that the results of averaging the spectra revealing strong and weak fluctuations may be different (at least in intensity). The influence of some electrolytes on the SERS spectral fluctuations is also analysed. Our experiments revealed that the efficiencies of quenching of the SERS spectral fluctuations by various electrolytes are significantly different. We suggest that only anions directly interacting with the metal surface quench strong SERS fluctuations, and that the large differences between chloride and perchloride solutions are caused by differences in the strength of interaction of Cl- and ClO4- anions with the silver surface. Copyright (C) 2007 John Wiley & Sons, Ltd.