An optical dustbin made by the subwavelength-induced super-black carbon aerogels
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Super-black carbon aerogel sleeves (CAS) with different reflectivities and a clear aperture had been made, by the sol–gel polycondensation of resorcinol (R) and formaldehyde (F) under the catalysis of sodium carbonate (C), and was used to eliminate stray light. We explained that the subwavelength structure is the main factor that leads to the low reflectivity of CA and constructed a simple optical system to measure the exit power from CAS in different directions. We proved that different CASs have different matting effects, and all of these CASs have better matting effects than that of monolithic graphite that has higher reflectivity. To show the fine angular resolution ability of CAS, we measured the faculae from the reflected light of a compact disc and found that the CAS with a clear aperture of 1.0 mm is the best. The super-black CAS could be used in precision optical instruments and to eliminate stray light in the optical.
I. INTRODUCTION
Carbon aerogel was introduced in 1989 (Pekala) by carbonization of resorcinol-formaldehyde aqueous gels1; they are highly porous materials with a three-dimensional microporous and mesoporous network. Carbon aerogels had been extensively studied by researchers due to its many excellent properties, such as a large surface area, a tunable, high porosity, and a low bulk density.2–13 Carbon aerogels are promising materials for hydrogen storage14–17 and had been widely investigated as electrode materials for supercapacitors and electrochemical double-layer capacitors18–22 because their high packing density and microstructure yield a good electrochemical performance. Metal-doped carbon aerogels are also used to remove poisonous gases.23,24 Carbon aerogels are also ideal super-black materials, Steven R. Meier, Michelle L. Korwin, and Celia I. Merzbacher measured the directional hemispherical reflectance (DHR) of carbon aerogels and found that the HDR is 1.0–1.2 6 0.2% throughout the 2.5–14.3 lm infrared wave length region, when the incident angle changed from 8° to 30°, and the DHR increased by only 0.2%.25 They also found that low-density carbon aerogels have low reflectivity.26 In general, researchers believe that the blackness of materials with low reflectivity has been attributed to strongly absorbing pigmentation alone. Vukusic, Sambles, and
Contributing Editor: Winston V. Schoenfeld Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/jmr.2017.347
Lawrence found that the nanostructure of the butterfly wing contributes significantly to their black appearance.27 Chen, Hubbard, Shields et al. fabricated the subwavelength silicon moth-eye structures and discovered that the fabricated nanocone array form a broadband antireflecting surface had an average reflection less than 3% in the spectral range from 400 to 1000 nm.28 Qibin Zhao, Tongxiang Fan, Jian Ding et al. fabricated a superblack amorphous carbon film with 99% optical absorption in visible light, by borrowing the inverse V-type antireflection nanoarchitecture from the bla
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