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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.National Science Foundation (U.S.) (NSF award No. ECS-0335765)United States. Army Research Office. Institute for Soldier Nanotechnologies (Contract Nos. DAAD-19-02-D0002)United States. Army Research Office (Contract No. W911NF-07-D000)United States. Dept. of Energy (MIT S3TEC Energy Research Frontier Center, Grant No. DE-SC0001299)Austrian Science Fund (FWF: J3161-N20

Large area selective emitters/absorbers based on 2D tantalum photonic crystals for high-temperature energy applications