Fabrication of plasmonic nanoparticle structures on planar substrates

Studying the optical properties of coupled plasmonic systems is important for both fundamental understanding and optimization of plasmon-enhanced optical sensing applications such as surface enhanced Raman scattering (SERS), near-field optical microscopy (NSOM) and surface plasmon resonance (SPR) sensing. Two nanoparticle structures of particular interest include nanoshell dimers and nanoparticles suspended over a metal film. We present a bench-top wet-chemistry method for nanoparticle dimer fabrication. The significant optical near-field enhancement in the gap between nanoparticles in a dimer structure could make it a powerful tool for enhanced spectroscopy applications. A simple geometry of nanoparticles suspended over a metal film is fabricated and its optical response is probed at various film thicknesses using optical transmission spectroscopy. A virtual resonance state emerged from interaction between discrete nanoparticle plasmons and the effective continuum of film plasmons shows a strong red-shift as the film thickness is decreased.