Real-time tuning of plasmonic nanogap cavity resonances through solvent environments

Nanogap cavity metasurfaces - an array of metallic nanoparticles separated from a metal plane by a nanometer-scale dielectric material - can manipulate electromagnetic waves across a wide wavelength range. Through this, they can profoundly modify the optical processes of molecules and materials relevant to quantum communications, photocatalysis, and optoelectronics. Interactions between nanocavities and light, however, require overlap between the cavity resonance and the energy of the incident photon or optical transition, demanding labor-intensive fabrication of bespoke metasurfaces for each desired application. Here, we dynamically tune the resonance wavelength of nanogap cavity metasurfaces by modulating the refractive index of the surrounding medium using solvents. We achieve precise, reversible, and broadband resonance control for narrow nanogap cavity resonances (full width half max <500 nm) over a range of 1-5 µm, while maintaining high absorption efficiency (60-98 %). Resonance tuning up to 300 nm for a single metasurface was achieved by changing the dielectric environment from air to solvents with controlled refractive indexes n = 1.3-1.7 without any discernable metasurface degradation. This opens new possibilities for applications in optical sensing with significantly increased nanofabrication tolerances, such as tunable photonic devices and adaptive optical systems, where precise control over light-matter interactions is critical.