Macroscopically Aligned Carbon Nanotubes as a Refractory Platform for Hyperbolic Thermal Emitters
Macroscopically Aligned Carbon Nanotubes as a Refractory Platform for Hyperbolic Thermal Emitters
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DOI：
10.1021/acsphotonics.9b00452
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发表时间：
2019-03
期刊：
影响因子：
7
通讯作者：
Weilu Gao;C. Doiron;Xinwei Li;J. Kono;G. Naik
中科院分区：
文献类型：
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作者：
Weilu Gao;C. Doiron;Xinwei Li;J. Kono;G. Naik
耐火纳米光子学，或高温纳米光子学，可以彻底改变许多应用，包括数据存储和废热回收。特别是，由双曲材料制成的纳米光子器件由于其近乎无限的光子态密度（PDOS）而具有广阔的应用前景。然而，在现有的耐火双曲材料中，特别是在宽光谱范围内，实现突出的PDOS是具有挑战性的。在这里，我们证明了排列碳纳米管的宏观薄膜和结构作为优异的耐火双曲材料。我们发现，排列的碳纳米管在$1600^{\circ}$ C以下具有热稳定性，并表现出极端的各向异性——在一个方向上是金属的，而在另两个方向上是绝缘的。这种极端的各向异性使该系统成为双曲材料，在中红外宽带频谱范围内（长于$4.3\mu$ m）具有特别大的PDOS，在深度亚波长大小的腔中表现出强烈的共振。我们观察到了定向碳纳米管薄膜的极化、光谱选择性热发射，以及体积小至$\sim\lambda^3/700$的定向碳纳米管的无限空腔，这些空腔在$700^{\circ}$ C下工作。这些实验表明，排列的碳纳米管具有天然的大PDOS，导致热光子密度提高了两个数量级以上，使其成为一个有前途的难熔纳米光子平台。
Refractory nanophotonics, or nanophotonics at high temperatures, can revolutionize many applications, including data storage and waste heat recovery. In particular, nanophotonic devices made from hyperbolic materials are promising due to their nearly infinite photonic density of states (PDOS). However, it is challenging to achieve a prominent PDOS in existing refractory hyperbolic materials, especially in a broad spectral range. Here, we demonstrate that macroscopic films and architectures of aligned carbon nanotubes work as excellent refractory hyperbolic materials. We found that aligned carbon nanotubes are thermally stable up to $1600^{\circ}$C and exhibit extreme anisotropy - metallic in one direction and insulating in the other two directions. Such extreme anisotropy makes this system a hyperbolic material with an exceptionally large PDOS over a broadband spectrum range (longer than $4.3\mu$m) in the midinfrared, exhibiting strong resonances in deeply sub-wavelength-sized cavities. We observed polarized, spectrally selective thermal emission from aligned carbon nanotube films as well as indefinite cavities of aligned carbon nanotubes with volume as small as $\sim\lambda^3/700$ operating at $700^{\circ}$C . These experiments suggest that aligned carbon nanotubes possess naturally large PDOS that leads to thermal photon densities enhanced by over two orders of magnitude, making them a promising refractory nanophotonics platform.