Designing and fabricating double resonance substrate with metallic nanoparticles-metallic grating coupling system for highly intensified surface-enhanced Raman spectroscopy.

Recently, nanoparticle-film coupling systems in which metal nanoparticles (supported localized surface plasmons, LSPs) are separated from a flat metal film (supported surface plasmon polaritons, SPPs) by a spacer have been widely reported due to its strong local enhancement field. However, there is are limited studies, which employ the design of combing metal grating into the nanoparticle-film gap system. Here, we propose and fabricate a novel double-resonance SERS system by strategically assembling Au NPs separated by a MoO3 nanospacer from an Ag grating film. The Ag grating with clear SPP effect is used for the first time in a double-resonance system, and the monolayer Au NPs array is well assembled onto the top of the Ag grating with a compact and uniform distribution (inter-particles gap of about 5 nm). As a result, we experimentally and theoretically demonstrate a significant near-field enhancement. The very strong near-field produced in the proposed SERS substrates is due to multiple couplings, including the Au NPs-Ag grating film coupling and Au NPs-Au NPs coupling. In addition, the as-proposed SERS substrates show good reproducibility of SERS, which have potential applications in plasmonic sensing and analytical science.