Plasmonic coupling of SiO_2-Ag 'post-cap' nanostructures and silver film for surface enhanced Raman scattering

摘要

We demonstrate a surface enhanced Raman scattering (SERS) substrate consisting of SiO_2-Ag "post-cap" nanostructures with an underlying silver film fabricated by the glancing angle deposition technique. Electromagnetic simulations predict that SERS enhancement is strongly polarization-dependent, consistent with experimental measurements. Optimized coupling between Ag cap nanoparticles and the underlying silver film can be achieved by controlling the thickness of SiO_2 post sandwiched between them to significantly enhance local electric-field intensity and to increase the density of electromagnetic hot spots. A maximum SERS enhancement factor of 2.38 X 10~9 within the hot spot region is demonstrated, providing sufficient sensitivity for many important applications.