Over-coupled resonator for broadband surface enhanced infrared absorption (SEIRA)

Abstract

Detection of molecules is a key issue for many applications. Surface enhanced infrared absorption (SEIRA) uses arrays of resonant nanoantennas with good quality factors which can be used to locally enhance the illumination of molecules. The technique has proved to be an effective tool to detect small amount of material. However, nanoresonators can detect molecules on a narrow bandwidth so that a set of resonators is necessary to identify a molecule fingerprint. Here, we introduce an alternative paradigm and use low quality factor resonators with large radiative losses (over-coupled resonators). The bandwidth enables to detect all absorption lines between 5 and 10 μm, reproducing the molecular absorption spectrum. Counterintuitively, despite a lower quality factor, the system sensitivity is improved and we report a reflectivity variation as large as one percent per nanometer of molecular layer of PMMA. This paves the way to specific identification of molecules. We illustrate the potential of the technique with the detection of the explosive precursor 2,4-dinitrotoluene (DNT). There is a fair agreement with electromagnetic simulations and we also introduce an analytic model of the SEIRA signal obtained in the over-coupling regime.

2D Silver-Nanoplatelets Metasurface for Bright Directional Photoluminescence, Designed with the Local Kirchhoff’s Law

“…To enhance the absorptivity in the NPLs, we aimed at reducing the losses in the metal and thus chose silver. As discussed in ref , the bare plasmonic grating must be in the overcoupled regime (radiative losses are larger than material losses) in order to ensure that material losses are equal to radiative losses when adding a layer of NPLs.…”

Wavelength Tunable Infrared Perfect Absorption in Plasmonic Nanocrystal Monolayers

“…Simulated spectra for the 25 nm sample indicate that it lies close to the critical coupling regime (d ITO ≈ t critical ) with very low reflection values (absorption above 98% from 3.1 to 3.6 μm), while the 31 nm sample shows obvious splitting of the reflection dips (positioned at 3 and 3.8 μm), indicating that this configuration is operating in the overcoupled regime (d ITO > t critical ). Although overcoupling does not lead to perfect absorption directly at the CPR wavelength, overcoupling could be advantageous for molecular detection 59 and hot electron transfer schemes. 60 The experimental results (Figure 3f) closely match the simulated predictions, demonstrating the applicability of the model to these ITO NC-based metamaterials and the feasibility of using NC size to achieve thickness-controlled coupling strength.…”

Surface-Enhanced Infrared Absorption Spectroscopy by Resonant Vibrational Coupling with Plasmonic Metal Oxide Nanocrystals

“…Other photonic-coupled NC assembly architectures have been investigated where the plasmonic response of gold NCs and the confined photons within the NC assembly generate a polaritonic response. , Polariton interactions with molecules can significantly enhance SEIRA . More broadly, integration of plasmonic nanostructures in photonic superstructures can enhance plasmon-vibration coupling strength by optimizing the radiative and nonradiative damping ratios. − We anticipate such benefits could be realized with ITO NC monolayers in various photonic structures where the tunability of the NCs provides additional degrees of freedom beyond those available with conventional plasmonic metals to control and significantly enhance SEIRA. Beyond sensing, strong plasmon-vibration coupling may lead to strategies for manipulating chemical reactivity and other physicochemical properties of NC-bound molecules …”