Enhanced and tunable double Fano resonances in plasmonic metasurfaces with nanoring dimers

Abstract

Abstract The appearance of the double-resonance substrate has promoted the application of surface-enhanced Raman scattering (SERS). By controlling the frequencies of the double resonances to match the excitation and Raman scattering frequencies, the detection of the object to be measured can be more effective. For the double-resonance substrate, while the resonance frequencies can be highly controllable, the electric field enhancement is also one of the important factors affecting the application in SERS. In this paper, we designed a metasurface composed of a nanoring dimer array, silica dielectric and gold film. The nanoring dimer array and gold film are separated by the silica dielectric to form a resonant cavity. The localized surface plasmon resonance generated in the nanoring dimer array is coupled with the cavity mode of the resonant cavity. Double Fano resonance with strong electric field enhancement is generated at the gap of the nanoring dimer. The electric field enhancement value can reach 100, which is an order of magnitude larger than that of the nanoring metasurface without the gap structure. The double Fano resonance peaks can be flexibly adjusted while maintaining large electric field enhancements by changing the following parameters: the period of the nanoring dimer array along the direction of the short axis, the ratio of the inner and outer radius of the nanoring and the length of the resonant cavity. Therefore, the proposed metasurface-enhanced Raman scattering substrate provides both the enhanced and tunable double Fano resonances necessary for high-sensitivity, high-selectivity and high-throughput detection. In addition, we proved that the length of the cavity can be determined by theoretical calculation, which avoids a lot of simulation processes.