Near-field thermal radiation between doped silicon plates at nanoscale gaps

Mikyung Lim, Seung S. Lee, and Bong Jae Lee

Phys. Rev. B 91, 195136 – Published 26 May 2015

Abstract

Radiative heat transfer can be significantly enhanced via photon tunneling through a nanometer-scale gap to the point that it exceeds the blackbody limit. Here we report quantitative measurements of the near-field thermal radiation between doped-Si plates ( $width = 480 μ m$ and $length = 1.34 cm$ ). A novel MEMS-based platform enables us to maintain doped-Si plates at nanoscale gap distances that cannot be achieved by other methods. The measured radiative heat transfer coefficient was found to be 2.91 times greater than the blackbody limit at a 400-nm vacuum gap.

Received 27 October 2014
Revised 29 April 2015

DOI:https://doi.org/10.1103/PhysRevB.91.195136

Authors & Affiliations

Mikyung Lim, Seung S. Lee, and Bong Jae Lee^*

Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology, Daejeon 305-701, South Korea

^*bongjae.lee@kaist.ac.kr

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Issue

Vol. 91, Iss. 19 — 15 May 2015

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Images

Figure 1
Proposed MEMS-based platform for measuring the near-field thermal radiation between doped-Si plates. (a) Cross-sectional view of the MEMS-based platform consisting of the source (i.e., doped-Si film of 590- $μ m$ width $\times$ 1.34-cm length $\times$ 600-nm thickness) and the receiver (i.e., doped-Si film of 480- $μ m$ width $\times$ 1.34-cm length $\times$ 600-nm thickness). The width of the source is intentionally designed to be wider than that of the receiver in order to assure that the receiver is fully covered by the source during the alignment. The actual heat transfer area was measured to be $480 μ m \times 1.34 cm$ by an optical microscope. (b) Three-dimensional schematic of the MEMS-based platform. (c) The displacement distribution in the source and the receiver parts under an arbitrary normal load.
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Figure 2
Fabricated MEMS-based platform and experimental setup. Photographs of the fabricated (a) source and (b) receiver parts. (c) Detailed experimental setup. The red line connects the receiver to a DMM, and blue line connects the source to a DMM. One electrode for each of the source and the receiver are connected to a capacitance meter to estimate the vacuum gap during the experiments. A U-shaped wire is connected to a dc power supply to increase the temperature of the source.
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Figure 3
Near-field radiative heat transfer coefficient. (a) The increase in the receiver temperature as predicted by a COMSOL simulation with respect to the radiative heat transfer coefficient when the source temperature is fixed at 371 K. (b) The measured radiative heat transfer coefficients from $d = 400$ nm to $d = 1030$ nm (red open circles). The reference datum used to remove the conduction contribution is denoted with a blue filled circle. The vacuum gap width is estimated from the average value of capacitance during 10 s for each point and the standard deviation of the measured capacitance is denoted as an error bar in the vacuum gap. The black line represents the radiative heat transfer coefficient obtained from the two-body formulation with modified Fresnel coefficients. The inset describes the linearity between the calculated radiative heat transfer coefficient and the inverse of the vacuum-gap width.
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Figure 4
Fabrication processes of the MEMS-based platform.
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Figure 5
The direction of a bare fused-silica wafer.
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Figure 6
Schematic illustration of variation in the separation distance $d (x)$ along the source/receiver films.
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