Ultra-Narrow SPP Generation from Ag Grating.

Gerald Stocker,Andreas Tortschanoff,Reyhaneh Jannesari,Elmar Aschauer,Thang Duy Dao,Clement Fleury,Thomas Grille,Florian Dubois,Cristina Consani,Parviz Saeidi,Gerald Pühringer,Bernhard Jakoby,Jasmin Spettel

doi:10.3390/s21216993

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

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

Methods

Results

Conclusion