Substrate influence on the polarization dependence of SERS in crossed metal nanowires†
The influence of polarization dependence is an unavoidable problem in surface-enhanced Raman spectroscopy (SERS) applications, especially for anisotropically-enhanced structures with strong surface plasmon coupling. In this work, the polarization dependence of SERS in crossed nanowires (NWs) on metal or dielectric films was investigated both experimentally and theoretically. The measured SERS spectra indicated that the strong polarization dependence of the crossed NWs was greatly influenced by the substrate, which was determined by only the direction of the bottom NWs for a metal film or the top NWs for a dielectric film. The studies further demonstrated that this polarization dependence was not related to the diameter ratio or intersecting angle of the NWs. The present work not only improves the applications of SERS but also increases our understanding of surface plasmon excitation in complicated metal nanostructures.