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Research Papers: Micro/Nanoscale Heat Transfer

# Extraordinary Coherent Thermal Emission From SiC Due to Coupled Resonant Cavities

[+] Author and Article Information
Nir Dahan, Avi Niv, Gabriel Biener, Yuri Gorodetski, Vladimir Kleiner

Faculty of Mechanical Engineering, Micro and Nanooptics Laboratory, Russell Berrie Nanotechnology Institute, Technion-Israel Institute of Technology, Haifa 32000, Israel

Erez Hasman

Faculty of Mechanical Engineering, Micro and Nanooptics Laboratory, Russell Berrie Nanotechnology Institute, Technion-Israel Institute of Technology, Haifa 32000, Israelmehasman@tx.technion.ac.il

J. Heat Transfer 130(11), 112401 (Sep 03, 2008) (5 pages) doi:10.1115/1.2955475 History: Received October 10, 2007; Revised March 26, 2008; Published September 03, 2008

## Abstract

In high temperature and vacuum applications, when heat transfer is predominantly by radiation, the material’s surface texture is of substantial importance. Several micro- and nanostructure designs have been proposed to enhance a material’s emissivity and its radiative coherence, as control of thermal emission is of crucial concern in the design of infrared sources, optical filters, and sensing devices. In this research, an extraordinary coherent thermal emission from an anisotropic microstructure is experimentally and theoretically presented. The enhanced coherency is due to coherent coupling between resonant cavities obtained by surface standing waves, wherein each cavity supports a localized field that is attributed to coupled surface phonon polaritons. We show that it is possible to obtain a polarized quasimonochromatic thermal source from a SiC microstructure with a high quality factor of 600 at the resonant frequency of the cavity and a spatial coherence length of 716 wavelengths, which corresponds to an angular divergence of $1.4mrad$. In the experimental results, we measured a quality factor of 200 and a spatial coherence length of 143 wavelengths. We attribute the deviation in the experimental results to imperfections in the fabrication of the high quality factor cavities.

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## Figures

Figure 9

(a) Spectral emissivity observed in normal direction for TE polarized wave and (b) angular emissivity at the peak wavelength at 11.6μm, obtained in (a).

Figure 8

(a) Dispersion relation of SPPs at SiC flat surface k∥, i.e., delocalized (solid); slab waveguide β (dashed); standing waves inside the cavity ksw (dots). (b) Decay length of delocalized SPPs in air as a function of frequency.

Figure 7

The magnitude of the electric field components in the x-z plane, (a) ∣Ex∣ and (b) ∣Ez∣, for normal incident wavelength λ0=11.6μm. The calculations were performed for the realized cavity profile as shown in Fig. 1: periodicity Λ=11.6μm, fill factor q=0.56, and depth h=4.6μm.

Figure 6

Calculated reflectivity of CRC as a function of the cavity depth, for normal incident wavelength λ0=11.6μm

Figure 5

(a) Spectral emissivity observed in (thick line) a normal direction and in (thin line) θ=1deg for TM polarized wave; (solid) calculated emissivity for the realized cavity profile as illustrated in the inset, (dash) experiment, and (circle) corrected emissivity obtained from (b). (b) Angular emissivity at the peak wavelengths obtained in (a); (solid) theory and (dash) experiment obtained by deconvolution analysis. The inset shows (dots) the measured emissivity and the (solid) curve fitting to the experimental results obtained by convolving the dash curve in (b) and the angular resolution.

Figure 4

(a) Calculated emissivity, ε, for rectangular cavity profile shown in Fig. 1 and (b) measured emissivity, ε¯, distribution as a function of frequency in the spectral range in which SiC supports SPPs, and the observation angle near the normal direction. The bright colors represent high emissivity.

Figure 3

Experimental setup used to measure spectral directional emissivity. P-polarizer; BB-blackbody; M1-flat mirror on rotating stage; M2-parabolic mirror, focal length=250mm; D-angular resolution diaphragm in the focal plane of M2, diameter=1mm; A-field of view aperture; diameter=10mm.

Figure 2

The magnitude of the electric field components in the x-z plane, (a) ∣Ex∣ and (b) ∣Ez∣, for normal incident wavelength λ0=11.6μm. The calculations were performed for a SiC CRC with periodicity Λ=11.6μm, fill factor q=0.5, and depth h=14.85μm.

Figure 1

(a) CRCs geometry with a coordinate system. (b) SEM image of CRC structure. (c) SEM image of a single cavity cross section embedded in SiC with periodicity Λ=11.6μm, fill factor q=0.56, and depth h=4.6μm; to observe the cavity profile in a high contrast (the dark region indicates SiC), a Pt was deposited and ion milling with a focused ion beam was performed.

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