Abstract

In this study, we investigate the potential of one-dimensional plasmonic grating structures to serve as a platform for, e.g., sensitive refractive index sensing. This is achieved by comparing numerical simulations to experimental results with respect to the excitation of surface plasmon polaritons (SPPs) in the mid-infrared region. The samples, silver-coated poly-silicon gratings, cover different grating depths in the range of 50 nm–375 nm. This variation of the depth, at a fixed grating geometry, allows the active tuning of the bandwidth of the SPP resonance according to the requirements of particular applications. The experimental setup employs a tunable quantum cascade laser (QCL) and allows the retrieval of angle-resolved experimental wavelength spectra to characterize the wavelength and angle dependence of the SPP resonance of the specular reflectance. The experimental results are in good agreement with the simulations. As a tendency, shallower gratings reveal narrower SPP resonances in reflection. In particular, we report on 2.9 nm full width at half maximum (FWHM) at a wavelength of 4.12 µm and a signal attenuation of . According to a numerical investigation with respect to a change of the refractive index of the dielectric above the grating structure, a spectral shift of can be expected, which translates to a figure of merit (FOM) of about 1421 . The fabrication of the suggested structures is performed on eight-inch silicon substrates, entirely accomplished within an industrial fabrication environment using standard microfabrication processes. This in turn represents a decisive step towards plasmonic sensor technologies suitable for semiconductor mass-production.

Highlights

  • Plasmonics in the mid-infrared (MIR) region and their usage for sensor applications have emerged as a field of interest in the recent years [1]

  • The angle-measurement results are presented and discussed in Section 3 where we show the strategy how to control the grating depth for the narrowband surface plasmon polaritons (SPPs) resonance

  • The wavelength of the quantum cascade laser (QCL) can be adjusted with such an accuracy that no error contribution from wavelength uncertainty is included in the discussion

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Summary

Introduction

The miniaturization of existing sensor concepts is one way to meet the demand of integrated sensors In this context, plasmonics in the mid-infrared (MIR) region and their usage for sensor applications have emerged as a field of interest in the recent years [1]. Plasmonics in the mid-infrared (MIR) region and their usage for sensor applications have emerged as a field of interest in the recent years [1] These surface effects allow monitoring different physical or chemical properties at material interfaces in a non-invasive way [2,3,4,5] or even several physical properties at once [6,7]. These properties, together with the fabrication capabilities determine the usability in particular applications

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