Microspheres on a Silver Film over Nanoparticle Arrays as Optoplasmonic Hybrid Materials for Surface-Enhanced Raman Spectroscopy

We propose a simple approach to fabricate large-scale optoplasmonic hybrid materials (OHMs) as substrates for surface-enhanced Raman spectroscopy (SERS) with high sensitivity. The OHM is composed of a metal film over a monolayer of nanoparticles (MFON) and a microsphere placed on the top of the MFON. The excited wavelength of the localized surface plasmon resonance in the MFON can be tuned by the nanoparticle size and the additional dielectric layer deposited above the silver layer. When this excited wavelength is slightly longer than the wavelength of the laser, the Raman signal of methylene blue as low as 10^–16 M can be detected. Numerical simulations reveal that the additional electric field enhancement in the OHM compared with the plasmonic nanostructure improves the sensitivity in SERS applications.