Understanding the Surface-Enhanced Raman Spectroscopy 'Background'

Even 35 years after the discovery of surface-enhanced Raman spectroscopy (SERS) much remains to be learned about the phenomenon.(1-3) Despite broad consensus on the mechanism of SERS, many features remain poorly understood and in particular much less effort has been put into understanding the continuum emission called the 'background' observed in SERS spectra. Here the SERS background is studied systematically on sphere segment void (SSV) plasmonic substrates. We establish the physicochemical dependence of the background on plasmons, the identity of the adsorbate, adsorbate coverage and electrochemical potential. In particular, by exchanging electron-donating and electron-withdrawing adsorbates, we demonstrate predictable modulation of the SERS background. Using these observations, we propose a model for the origin of the SERS background. Finally, we test the proposed model against its predictions for anti-Stokes SERS spectra.