21 February 2013 Large area selective emitters/absorbers based on 2D tantalum photonic crystals for high-temperature energy applications
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Abstract
We report highly selective emitters based on high-aspect ratio 2D photonic crystals (PhCs) fabricated on large area (2 inch diameter) polycrystalline tantalum substrates, suitable for high-temperature operation. As an example we present an optimized design for a selective emitter with a cut-off wavelength of 2μm, matched to the bandgap of an InGaAs PV cell, achieving a predicted spectral selectivity of 56.6% at 1200K. We present a fabrication route for these tantalum PhCs, based on standard microfabrication processes including deep reactive ion etch of tantalum by an SF6 based Bosch process, achieving high-aspect ratio cavities (< 8:1). Interference lithography was used to facilitate large area fabrication, maintaining both fabrication precision and uniformity, with a cavity diameter variation of less than 2% across the substrate. The fabricated tantalum PhCs exhibit strong enhancement of the emittance at wavelengths below cut-off wavelength, approaching that of blackbody, and a steep cut-off between high and low emittance spectral regions. Moreover, detailed simulations and numerical modeling show excellent agreement with experimental results. In addition, we propose a surface protective coating, which acts as a thermal barrier coating and diffusion inhibitor, and its conformal fabrication by atomic layer deposition.
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V. Rinnerbauer, V. Rinnerbauer, Y. X. Yeng, Y. X. Yeng, J. J. Senkevich, J. J. Senkevich, J. D. Joannopoulos, J. D. Joannopoulos, M. Soljačić, M. Soljačić, I. Celanovic, I. Celanovic, } "Large area selective emitters/absorbers based on 2D tantalum photonic crystals for high-temperature energy applications", Proc. SPIE 8632, Photonic and Phononic Properties of Engineered Nanostructures III, 863207 (21 February 2013); doi: 10.1117/12.2005202; https://doi.org/10.1117/12.2005202
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