Direct Visualization of Plasmonic Hotspots of Silver Nanowire Dimers using SERS

Abstract

Visualization of surface plasmon polaritons (SPP) is essential for characterization of plasmonic waveguides which are building blocks for photonic circuits with subwavelength scale. Currently, well-established techniques such as fluorescence- or tip-based microscopy usually improper for being applied to narrow-gap plasmonic structures. In this case, surface-enhanced Raman scattering (SERS) microscopy can be an alternative tool for visualizing highly localized electric field of gap plasmon waveguides. In this work, we report on SERS imaging of chemically synthesized silver nanowire (AgNW) dimers, which shows spatial modulation of intensity patterns along NW-axis. We interpret that such unusual SERS patterns arise from mode beating between two distinct SPP eigenmodes of NW-dimers, generating oscillating intensity distributions. Also, we discuss the validity of the concept that SERS intensity at far-field region directly represents the intensity of local electric field generated from plasmon excitation process, contrary to usual nanoparticle dimers cases.