# Frontiers in Energy

 Front. Energy    2020, Vol. 14 Issue (3) : 482-509     https://doi.org/10.1007/s11708-020-0693-0
 REVIEW ARTICLE
Spectral emittance measurements of micro/nanostructures in energy conversion: a review
Shiquan SHAN1, Chuyang CHEN2, Peter G. LOUTZENHISER2, Devesh RANJAN2, Zhijun ZHOU3(), Zhuomin M. ZHANG2()
1. State Key Laboratory of Clean Energy Utilization, Zhejiang University, Hangzhou 310027, China; George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta GA 30332, USA
2. George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta GA 30332, USA
3. State Key Laboratory of Clean Energy Utilization, Zhejiang University, Hangzhou 310027, China
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 Abstract Micro/nanostructures play a key role in tuning the radiative properties of materials and have been applied to high-temperature energy conversion systems for improved performance. Among the various radiative properties, spectral emittance is of integral importance for the design and analysis of materials that function as radiative absorbers or emitters. This paper presents an overview of the spectral emittance measurement techniques using both the direct and indirect methods. Besides, several micro/nanostructures are also introduced, and a special emphasis is placed on the emissometers developed for characterizing engineered micro/nanostructures in high-temperature applications (e.g., solar energy conversion and thermophotovoltaic devices). In addition, both experimental facilities and measured results for different materials are summarized. Furthermore, future prospects in developing instrumentation and micro/nanostructured surfaces for practical applications are also outlined. This paper provides a comprehensive source of information for the application of micro/nanostructures in high-temperature energy conversion engineering. Corresponding Author(s): Zhijun ZHOU,Zhuomin M. ZHANG Online First Date: 28 August 2020    Issue Date: 14 September 2020
 Cite this article: Shiquan SHAN,Chuyang CHEN,Peter G. LOUTZENHISER, et al. Spectral emittance measurements of micro/nanostructures in energy conversion: a review[J]. Front. Energy, 2020, 14(3): 482-509. URL: http://journal.hep.com.cn/fie/EN/10.1007/s11708-020-0693-0 http://journal.hep.com.cn/fie/EN/Y2020/V14/I3/482
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 Fig.1  Schematic diagram. Fig.2  Schematic diagram of a high-temperature spectral emisso-meter (reprinted from Ref. [27] with permission). Fig.3  Experimental setup of PTB for measuring the spectral directional emittance. Fig.4  Schematic of the infrared spectral emittance characterization facility at NIST (reprinted from Ref. [24] with permission). Fig.5  Optical layout of the high-temperature spectral emisso-meter at the Georgia Institute of Technology (reprinted from Ref. [25] with permission). Fig.6  The vacuum emissiometry setup at the National Institute of Optics in Italy (reprinted from Ref. [26] with permission). Tab.1  Summary of direct emittance measurement instruments Fig.7  Schematic with details of the indirect measurement method at NIST (reprinted from Ref. [28] with permission). Fig.8  Solar facility for optical properties characterization at PROMES laboratory (reprinted from Ref. [76] with permission). Fig.9  Experimental setup for characterizing spectral normal optical properties with FTIR fiber optics technique at elevated temperatures (reprinted from Ref. [77] with permisssion). Fig.10  Illustration of different micro/nanostructures. Fig.11  Representative spectra for the spectral solar irradiance (AM1.5), blackbody emissive power at 1000 K, and the “ideal” absorptance/emittance spectrum for a solar absorber. Fig.12  Spectral absorptance of an all-ceramic solar selective absorber. Tab.2  Summary of spectral selective solar absorbers Fig.13  Metamaterial solar absorber. Fig.14  Spectral EQE of an InAsSbP TPV cell, spectral emissive power of a blackbody at 1500 K, and the emittance spectra of ideal broadband and narrowband selective emitters. Tab.3  Summary of spectral selective TPV emitters Fig.15  Measured spectral emittance of microcavities. Fig.16  (a) Schematic of the fabricated Fabry-Perot cavity resonator; (b) and (c) the emittance spectra for TE and TM waves, respectively, at different temperatures for $θ=$ 30°; (d) schematic of the metamaterial emitter made of a gold grating and SiO2 spacer on an optically opaque Au film; (e) emittance measured with a DTGS detector; (f) emittance measured with an InSb detector for TM wave at 700 K for different zenith angles (adapted with permission from Ref. [25] for (a, b, c); and from Ref. [50] for (d, e, f)). Fig.17  SEM images.