Surface-Enhanced Infrared Absorption: Pushing the Frontier for On-Chip Gas Sensing.

Surface-enhanced infrared absorption (SEIRA) is capable of identifying molecular fingerprints by resonant detection of infrared vibrational modes through the coupling with plasmonic modes of metallic nanostructures. However, SEIRA for on-chip gas sensing is still not very successful due to the intrinsically weak light-matter interaction between photons and gas molecules and the technical challenges in accumulating sufficient gas species in the vicinity of the spatially localized enhanced electric field, namely, the "hot-spots", generated through plasmonics. In this paper, we present a suspended silicon nitride (Si3N4) nanomembrane device by integrating plasmonic nanopatch gold antennas with metal-organic framework (MOF), which can largely adsorb carbon dioxide (CO2) through its nanoporous structure. Unlike conventional SEIRA sensing relying on highly localized hot-spots of plasmonic nanoantennas or nanoparticles, the device reported in this paper engineered the coupled surface plasmon polaritons in the metal-Si3N4 and metal-MOF interfaces to achieve strong optical field enhancement across the entire MOF film. We successfully demonstrated on-chip gas sensing of CO2 with more than 1800× enhancement factors by combining the concentration effect from the 2.7 μm MOF thin film and the optical field enhancement of the plasmonic nanopatch antennas.