Revisiting Surface-Enhanced Raman Scattering on Realistic Lithographic Gold Nanostripes

In this article, we investigate the Surface-Enhanced Raman Scattering (SERS) efficiency of methylene blue (MB) molecules deposited on gold nanostripes which, due to their fabrication by electron beam lithography and thermal evaporation, present various degrees of crystallinity and nanoscale surface roughness (NSR). By comparing gold nanostructures with different degrees of roughness and crystallinity, we show that the NSR has a strong effect on the SERS intensity of MB probe molecules. In particular, the NSR features of the lithographic structures significantly enhance the Raman signal of MB molecules, even when the excitation wavelength lies far from the localized surface plasmon resonance (LSPR) of the stripes. These results are in very good agreement with numerical calculations of the SERS gain obtained using the discrete dipole approximation (DDA). The influence of NSR on the optical near-field response of lithographic structures thus appears crucial since they are widely used in the context of nano-optics or/and molecular sensing.