The complex refractive index of polydimethylsiloxane (PDMS) is determined in the wavelength range between 2.5 μm and 16.7 μm. The parameters of a Drude-Lorentz oscillator model (with 15 oscillators) are extracted from Fourier transform infrared spectroscopy reflectance measurements made on both bulk PDMS and thin films of PDMS deposited on the gold coated silicon substrates. It is shown that thin films of PDMS atop gold exhibit selective emission in the 8 μm to 13 μm atmospheric transmittance window, which demonstrates that PDMS, especially due to its ease of deposition, may be a viable material for passive radiative cooling applications.
Selective thermal emitters are materials which emit in narrow wavelength bands, unlike blackbody emitters which emit uniformly over all wavelengths. Materials with tailored emission/absorption characteristics can be useful for applications in energy conversion, energy conservation, chemical, and bio-chemical sensing. In this paper, we show that thin films of polar dielectric materials can act as selective emitters in two frequency bands on either side of the restrahlen band(s) of the polar material due to multiple reflections within the thin films.
The gap dependence of radiative energy transfer due to propagating waves between two identical metallic half-spaces separated by vacuum is investigated. The dielectric function of the metallic half-spaces is described by the Drude model. Analytical expressions for the minimum radiative heat transfer coefficient, h min , and the gap, d min , at which the minimum value of radiative transfer is attained are determined in terms of the parameters of the dielectric function and the absolute temperature T. We show that h min ∝ T 2 in the high temperature limit and h min ∝ T 7/2 in the low temperature limit.
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