Recent developments in surface-enhanced Raman scattering (SERS) enable observation of single-bond vibrations in real time at room temperature.By contrast,mid-infrared (MIR) vibrational spectroscopy is limited to inefficient slow detection.Here we develop a new method for MIR sensing using SERS.This method utilizes nanoparticle-on-foil(NPoF) nanocavities supporting both visible and MIR plasmonic hotspots in the same nanogap formed by a monolayer of molecules.Molecular SERS signals from individual NPoF nanocavities are modulated in the presence of MIR photons.The strength of this modulation depends on the MIR wavelength,and is maximized at the 6-12 μm absorption bands of SiO2 or polystyrene placed under the foil.Using a single-photon lock-in detection scheme we time-resolve the rise and decay of the signal in a few 100 ns.Our observations reveal that the phonon resonances of SiO2 can trap intense MIR surface plasmons within the Reststrahlen band,tuning the visible-wavelength localized plasmons by reversibly perturbing the localized few-nm-thick water shell trapped in the nanostructure crevices.This suggests new ways to couple nanoscale bond vibrations for optomechanics,with potential to push detection limits down to single-photon and single-molecule regimes.

NanoPhotonics Centre,Cavendish Laboratory,Department of Physics,JJ Thompson Avenue,University of Cambridge,Cambridge CB3 OHE,UK;Empa,Swiss Federal Laboratories for Materials Science and Technology,Laboratory for Mechanics of Materials and Nanostructures,Thun,Switzerland

[1]Rohit Chikkaraddy;Angelos Xomalis;Lukas A.Jakob;Jeremy J.Baumberg-.Mid-infrared-perturbed molecular vibrational signatures in plasmonic nanocavities)[J].光：科学与应用（英文版）,2022(01):127-135

NPoF,nanogap,Reststrahlen,crevices

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