title: High-temperature stability and selective thermal emission of polycrystalline tantalum photonic crystals.
abstract: We present the results of extensive characterization of selective emitters at high temperatures, including thermal emission measurements and thermal stability testing at 1000 °C for 1h and 900 °C for up to 144 h. The selective emitters were fabricated as 2D photonic crystals (PhCs) on polycrystalline tantalum (Ta), targeting large-area applications in solid-state heat-to-electricity conversion. We characterized spectral emission as a function of temperature, observing very good selectivity of the emission as compared to flat Ta, with the emission of the PhC approaching the blackbody limit below the target cut-off wavelength of 2 μm, and a steep cut-off to low emission at longer wavelengths. In addition, we study the use of a thin, conformal layer (20 nm) of HfO(2) deposited by atomic layer deposition (ALD) as a surface protective coating, and confirm experimentally that it acts as a diffusion inhibitor and thermal barrier coating, and prevents the formation of Ta carbide on the surface. Furthermore, we tested the thermal stability of the nanostructured emitters and their optical properties before and after annealing, observing no degradation even after 144 h (6 days) at 900 °C, which demonstrates the suitability of these selective emitters for high-temperature applications.
authors.affiliation: Research Laboratory of Electronics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, MA, Cambridge 02139, USA. vrinner@mit.edu
authors.forename: Veronika
authors.initials: V
authors.lastname: Rinnerbauer
authors.forename: Yi Xiang
authors.initials: YX
authors.lastname: Yeng
authors.forename: Walker R
authors.initials: WR
authors.lastname: Chan
authors.forename: Jay J
authors.initials: JJ
authors.lastname: Senkevich
authors.forename: John D
authors.initials: JD
authors.lastname: Joannopoulos
authors.forename: Marin
authors.initials: M
authors.lastname: Soljačić
authors.forename: Ivan
authors.initials: I
authors.lastname: Celanovic
mesh_terms: D003460:Crystallization / Q000379:methods*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D006358:Hot Temperature; D008422:Materials Testing; D017785:Photons; D012031:Refractometry; D020349:Surface Plasmon Resonance / Q000295:instrumentation*; D013635:Tantalum / Q000737:chemistry*; D013696:Temperature
chemical_list: D013635:Tantalum