Linear optical and surface-enhanced Raman scattering study on metallic membranes with subwavelength complementary patterns

An efficient technique is developed to fabricate optically thin metallic films with subwavelength patterns and their complements simultaneously. By comparing the spectra of the complementary films, we show that Babinet´s principle nearly holds in the optical domain. A discrete-dipole approximation can qualitatively describe their spectral dependence on the illuminating polarization. Using pyridine as probe molecules, we studied surface-enhanced Raman scattering (SERS) from the complementary structures. Although the complementary structures possess closely related linear spectra, they have quite different near-field behaviors. For hole arrays, their averaged local field gains as well as the SERS enhancements are strongly correlated to their transmission spectra. We therefore can use cos⁴θ to approximately describe the dependence of the Raman intensity on the excitation polarization angle θ, while the complementary particle arrays present maximal local field gains at wavelengths generally much larger than their localized surface plasmonic resonant wavelengths.