Plasmonic Metasurface for Directional and Frequency-Selective Thermal Emission

D. Costantini, A. Lefebvre, A.-L. Coutrot, I. Moldovan-Doyen, J.-P. Hugonin, S. Boutami, F. Marquier, H. Benisty, and J.-J. Greffet

Phys. Rev. Applied 4, 014023 – Published 30 July 2015

Abstract

Incandescent filaments and membranes are often used as infrared sources despite their low efficiency, broad angular emission, and lack of spectral selectivity. Here, we introduce a metasurface to control simultaneously the spectrum and the directivity of blackbody radiation. The plasmonic metasurface operates reliably at $600 ° C$ with an emissivity higher than 0.85 in a narrow frequency band and in a narrow solid angle. This emitter paves the way for the development of compact, efficient, and cheap IR sources and gas detection systems.

Received 5 November 2014

DOI:https://doi.org/10.1103/PhysRevApplied.4.014023

Authors & Affiliations

D. Costantini^1,*, A. Lefebvre², A.-L. Coutrot¹, I. Moldovan-Doyen¹, J.-P. Hugonin¹, S. Boutami², F. Marquier¹, H. Benisty¹, and J.-J. Greffet^1,†

¹Laboratoire Charles Fabry, Institut d’Optique, CNRS, Université Paris-Sud, 2 avenue Augustin Fresnel, 91127 Palaiseau cedex, France
²Université Grenoble Alpes F-38000 Grenoble, France CEA, LETI, MINATEC Campus, F-38054 Grenoble, France

^*Present address: Saint Gobain Recherche, 39 quai L. Lefranc, 93303 Aubervilliers Cedex, France.
^†jean-jacques.greffet@institutoptique.fr

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Vol. 4, Iss. 1 — July 2015

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Images

Figure 1
(a) Direct measurement of the emissivity at $600 ° C$ as a function of the frequency and the angle of the metasurface reported in this paper ( $W / SiN / Pt$ ). The emissivity peak is located at $ω = 2353 {cm}^{- 1}$ ( $λ = 4.25 μ m$ ) and between 0° and 26°. The complete characterization of the structure is shown in Fig. 5. (b) Schematics of the ideal source in the frequency angle plane. The emissivity should be 1 in the useful window and 0 elsewhere.
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Figure 2
Calculated absorption at normal incidence obtained with RCWA of a 2D MIM square grating (period of $3 μ m$ ) as a function of the SiN thickness and of the MIM side. The calculation is performed on the $Au / SiN / Au$ structure (see inset with the electric-field absolute value map at a cross section; minimum is blue, maximum is red) under normal incidence at $λ = 4.25 μ m$ and provides, at this specific wavelength, the geometrical parameters ensuring maximum MIM absorption (critical coupling conditions). The 100% absorption takes place for $L = 900 nm$ and $h_{SiN} = 120 nm$ (black dot).
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Figure 3
(a) Calculated absorptivity as a function of the frequency and the incident $K$ . The absorptivity is averaged over the two polarizations. The parameters of the simulated structure are $L = 900 nm$ , $h_{SiN} = 120 nm$ , and $p = 3 μ m$ . The MIM resonance displays an absorption peak at $ω = 2353 {cm}^{- 1}$ ( $λ = 4.25 μ m$ ) for all incident wave vectors (angles). The oblique line $ω = 2 π c / p - c K$ ( $c$ being the speed of light) cuts the horizontal resonance line in two parts, with large absorption on the side of smaller $K$ . (b) Schematics to explain the reduction of the absorption for large $K$ : (i) for small $K$ values, there is a single diffracted order, whereas (ii) for larger $K$ values, there are two diffracted orders. The existence of the $- 1$ order introduces an additional radiative decay channel so that the critical coupling condition is no longer fulfilled. (c) Calculated absorptivity at $λ = 4.25 μ m$ as a function of the normalized $k_{x}$ and $k_{y}$ . It is clearly seen that the presence of the grating allows controlling of the directivity of the absorption and emission.
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Figure 4
(a) SEM image of the MIM grating showing the size of the square side and of the period. (b) Measured reflectivity $R_{0}$ normalized by a gold surface, plotted as the map of $1 - R_{0}$ . The experimental measurement spans from 13° to 90° and allows observation of the anticrossing point due to strong coupling between the MIM resonance and the plasmon. On the left side (smaller $K$ ) of this crossing line, the quantity $1 - R_{0}$ equals the absorption, and the figure can be compared to Fig. 3. (c) Enlarged anticrossing zone in the measured $1 - R_{0} map$ in $p$ polarization for samples with $L = 900 nm$ and different periods, (i) $p = 2.7 μ m$ , (ii) $p = 3 μ m$ . By decreasing the period, the anticrossing point shifts towards higher $K$ (vertical dashed line).
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Figure 5
Characterization of the $W / SiN / Pt$ metasurface, with height $h_{SiN} = 210 nm$ and patch side $L = 855 nm$ , as a function of the frequency and wave vector $K$ . (a) Measured map of $1 - R_{0}$ normalized by a gold surface (from 13° to 90°). (b) Measured emissivity at $600 ° C$ obtained by normalizing with a blackbody reference (from 0° to 70° angles, with the 13° line as a guide to the eye). (c) Calculated absorption for a direct comparison with the emissivity. (d) The calculated blackbody radiance at $600 ° C$ with the frequency interval of the ${CO}_{2}$ absorption (from 4.16 to $4.36 μ m$ ).
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