Directional surface enhanced Raman scattering on gold nano-gratings

Abstract : Directional plasmon excitation and SERS emission were demonstrated for 1D and 2D gold nanostructure arrays deposited on flat gold layer. Extinction spectrum of both arrays exhibits intense resonance bands that are red shifted when the incident angle is increased. Systematic extinction analysis of different grating periods revealed that this band can be assigned to a propagated surface plasmon of the flat gold surface that fulfills the Bragg condition of the arrays (Bragg mode). Directional SERS measurements demonstrated that the SERS intensity can be improved by one order of magnitude, when the Bragg mode positions matched with either the excitation or the Raman wavelengths. Hybridized numerical calculations of Finite Element Method and Fourier Modal Method also proved the presence of Bragg mode plasmon and illustrated that the enhanced electric field of the Bragg mode is particularly localized on the nanostructures regardless of their size.