Amplification of surface-enhanced Raman scattering due to substrate-mediated localized surface plasmons in gold nanodimers

Surface-enhanced Raman scattering (SERS) is ubiquitous in chemical and biochemical sensing, imaging and identification. Maximizing the SERS enhancement is a continuous effort focused on the design of appropriate SERS substrates. Here we show that a significant improvement in a SERS signal can be achieved with substrates combining localized surface plasmon resonances and a nonresonant plasmonic substrate. By introducing a continuous gold (Au) film underneath Au nanodimer antenna arrays, over 10-fold increase in the SERS enhancement is demonstrated. Triangular, rectangle and disc dimers were studied, with the bowtie antenna providing the highest SERS enhancement. Simulations of electromagnetic field distributions of the Au nanodimers on the Au film support the observed enhancement dependences. The hybridization of localized plasmonic modes with the image modes in a metal film provides a straightforward way to improve the SERS enhancement in designer SERS substrates.