Temperature control of thermal radiation from composite bodies

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Temperature control of thermal radiation from composite bodies

Weiliang Jin, Athanasios G. Polimeridis, and Alejandro W. Rodriguez

Phys. Rev. B 93, 121403(R) – Published 9 March 2016

Abstract

We demonstrate that recent advances in nanoscale thermal transport and temperature manipulation can be brought to bear on the problem of tailoring thermal radiation from wavelength-scale composite bodies. We show that such objects—complicated arrangements of phase-change chalcogenide ( ${Ge}_{2} {Sb}_{2} {Te}_{5}$ ) glasses and metals or semiconductors—can be designed to exhibit strong resonances and large temperature gradients, which in turn lead to large and highly directional emission at midinfrared wavelengths. We find that partial directivity depends sensitively on a complicated interplay between shape, material dispersion, and temperature localization within the objects, requiring simultaneous design of the electromagnetic scattering and thermal properties of these structures. Our calculations exploit a recently developed fluctuating-volume current formulation of electromagnetic fluctuations that rigorously captures radiation phenomena in structures with strong temperature and dielectric inhomogeneities, such as those studied here.

Received 1 July 2015

DOI:https://doi.org/10.1103/PhysRevB.93.121403

Physics Subject Headings (PhySH)

Thermal conductivity

Chalcogenides

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Weiliang Jin¹, Athanasios G. Polimeridis², and Alejandro W. Rodriguez¹

¹Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
²Skolkovo Institute of Science and Technology, Moscow, Russia

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Issue

Vol. 93, Iss. 12 — 15 March 2016

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Images

Figure 1
Schematic of two composite bodies, involving GST (blue) hemispheroids coated with Ti (green), AZO (red), or ${Si}_{3} N_{4}$ (orange) shells, which rest on a low-index, transparent substrate in contact with a heat reservoir at 300 K. The GST is heated from below by a conductive 2D material (e.g., a carbon-nanotube wall or graphene sheet), leading to temperature gradients within the structure. The presence of boundary resistance at material interfaces is captured by effective thermal resistances (see text). Figure 2 explores radiation from GST-Ti and GST- ${Si}_{3} N_{4}$ bodies with parameters $L_{0} = 1.7 μ m, t_{0} = 0.3 μ m, h_{0} = 0.5 μ m$ and $L_{0} = 1.3 μ m, t_{0} = 1.3 μ m, h_{0} = 2.6 μ m$ , respectively, and under various heating conditions (see text); here we show the temperature profile corresponding to scenario (iii).
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Figure 2
Spectral emissivity $ε (ω) = Φ (ω) / Φ_{BB} (ω)$ (blue dots) from heterogeneous bodies comprising ${Ge}_{2} {Sb}_{2} {Te}_{5}$ (GST) hemispheroids coated with either (a) ${Si}_{3} N_{4}$ or (b) Ti shells and resting on a low-index substrate (object dimensions are specificed in Fig. 1). The structures are heated from the GST-substrate interface by a 2D thin-film conductor under heating scenario (iii), described in the text, with an interface temperature $T_{GST} = 870$ K. The resulting temperature profiles $T (x)$ are shown in Fig. 1 and in the insets. $ε$ is defined as the ratio of the thermal flux $Φ (ω)$ of each body normalized to the flux $Φ_{BB} = \frac{A}{4 π^{2}} {(ω / c)}^{2} Θ (ω, T)$ from a corresponding blackbody of the same surface area $A$ but uniform $T = 870$ K (green lines, arb. units). Also shown are the partial directivities $η_{\pm} = Φ_{\pm} / Φ$ (red line), defined as the ratios of the outgoing flux into the upper/lower hemisphere $Φ_{\pm} = 2 π \int_{\mp π / 2}^{π \mp π / 2} d θ Φ (ω, θ)$ to the total flux, where $θ$ is defined in Fig. 1. (c) Angular radiation intensity $Φ (θ)$ normalized by the total flux $Φ$ , for the structures in (a) (solid red line) and (b) (solid blue line) under scenario (iii), compared to emission under uniform-temperature conditions (dashed lines). (d) Total (frequency-integrated) partial directivity $P_{-} = H_{-} / H$ as a function of $T_{GST}$ , with $H_{-} = \int d ω Φ_{-}$ , for the Ti structure under different heating conditions, corresponding to multiple degrees of temperature localization in the GST (see text).
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Figure 3
(a), (b) Peak directivity $η_{-}$ (dashed lines, right axes) and emissivity $ε$ (solid lines, left axes) associated with the resonance closest to the peak of the BB spectrum of Ti-shell hemispheroids (Fig. 1) as a function of various shape/size parameters, including aspect ratio $2 h / D$ (magenta), overall size $D$ (black), metal thickness $t$ with a fixed GST size $L = L_{0}$ (red), and GST size $L$ with a fixed overall size $D = D_{0}$ (blue). Here, the subscripts “0” and the vertical dashed lines denote size parameters specified in Fig. 1. (c) Angular radiation intensity $Φ (θ)$ from various heterogeneous bodies—composite GST (blue), AZO (red), and ${Si}_{3} N_{4}$ (orange) mushrooms and cylinders—at selected frequencies $ω$ and normalized by the total flux $Φ$ . All plots assume perfect $T = 870$ K localization in the GST, while other materials are held at 300 K.
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