Sputtered tantalum photonic crystal coatings for high-temperature energy conversion applications

Thick sputtered tantalum (Ta) photonic crystal (PhC) coatings on Inconel were investigated as a potential replacement for bulk refractory metal substrates used for high-temperature emitters and absorbers in thermophotovoltaic energy conversion applications, where high-temperature stability and high reflectance of the surface in the infrared wavelength range are critical in order to sustain high operational temperatures and reduce losses due to waste heat. A selective emitter and solar absorber 2D PhC were fabricated in 8 and 30 micron sputtered Ta coatings, respectively, using standard semiconductor processes as a proof of concept. The fabricated PhCs showed high spectral selectivity in good agreement with the numerical simulations. The PhCs, coated with a thin HfO2 protective layer, sustained one hour anneals at 700, 900, and 1100°C with very little structural degradation or change in their optical properties. This study presents a promising alternative to bulk substrates as a relatively low-cost and easily integrated platform for nano-structured devices for high-temperature applications.