Study of signal-to-background ratio of surface-enhanced Raman scattering: Dependences on excitation wavelength and hot-spot gap

Signal-to-background ratio of surface-enhanced Raman scattering (SERS) plays an important role in the analytic applications of SERS. Its dependences on excitation wavelength and gap between metal particles were studied theoretically and experimentally. We show that this ratio is higher at smaller gaps for the same excitation wavelength and is higher for the wavelengths having higher values of the absolute values of the dielectric function of the metal. This study thus results in design guidelines in the fabrication of SERS-active substrates with high signal-to-background ratio.