Dispersion‐Engineered Deep Sub‐Wavelength Plasmonic Metasurfaces for Broadband Seira Applications

Abstract Surface enhanced infrared absorption (SEIRA) spectroscopy is a powerful tool in which plasmonically enhanced electromagnetic fields provide high‐sensitivity molecular detection. Most SEIRA platforms operate at a single resonant frequency, which must be tuned to match that of the target molecule, and commonly rely on time‐consuming lithographic techniques. This study presents a high‐throughput and cost‐effective plasmonic metasurface for broadband, tunable, and strong infrared signal enhancement. The platform is built upon the principle of dispersion‐engineered plasmonic Fabry–Pérot (FP) nanocavity arrays. It offers 1) tight squeezing of infrared (IR) photons into deep sub‐wavelength nano‐volumes and 2) spectrally tunable near‐field enhancements of up to ≈10⁶, two to three orders of magnitude higher than most optical metasurface systems. By coupling multilayer nano‐thin film deposition and nanoskiving fabrication techniques, the dispersive FP metasurfaces can be rapidly and reproducibly constructed in a scalable and lithography‐free manner. Using IR spectroscopy, the selective and sensitive label‐free detection of a molecular monolayer is achieved at a range of frequencies. An enhancement factor of nearly 10⁵ is measured at the carbonyl (C = O) vibrational marker band of the molecule. The confluence of high field enhancement, broadband plasmonic response, and facile fabrication makes this metasurface a promising platform for SEIRA spectroscopy.