Plasmon Hybridization in Compressible Metal-Insulator-Metal Nano-Cavities: an Optical Approach for Sensing Deep Sub-Wavelength Deformation

We present a pressure-induced deformation-sensitive device based on 2D matrices of plasmonic gold nanodisks coupled to a metal thin layer through a compressible dielectric spacer, namely a deformable metal-insulator-metal (MIM) nanocavity, to report deep sub-wavelength size variations (< λ/200). The system is characterized by two hybrid branches, which are resonant in the visible/near infrared spectral region. The fundamental mode, owing to the near-field interaction between the plasmonic nanostructures and the metal film, exhibits a remarkable sensitivity to the gap size, exceeding that of a planar “macroscopic” optical cavity and extending its operational domain to the sub-wavelength range, where excellent opportunities towards truly multiscale MIMs-based pressure sensors can be envisioned. Concurrently, its intrinsic plasmonic nature synergistically combines into a single platform multi-purpose functionalities, such as ultrasensitive detection, remote temperature readout etc., with practical perspectives in ultra-compact inspection tools for structural and functional information at the nanoscale.