Macroscopically Aligned Carbon Nanotubes as a Refractory Platform for Hyperbolic Thermal Emitters

Abstract

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 • 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 µm) in the midinfrared, exhibiting strong resonances in deeply subwavelength-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 ∼ λ 3 /700 operating at 700 • 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. * guru@rice.edu † These authors contributed equally. arXiv:1903.06063v1 [physics.optics]

Emergent Properties of Macroscale Assemblies of Carbon Nanotubes

“…That nanotube films could function as hyperbolic metamaterials is intuitive: along the nanotube alignment direction, free charges can oscillate freely (a metal-like optical permittivity), whereas perpendicular to the film, free charge conductivity is relatively suppressed (leading to a dielectric-like permittivity). Recently, this property been experimentally verified: by using ellipsometry [33] and reflectometry, [34] two separate studies found hyperbolic dispersion in aligned nanotube films One of the unique functionalities of nanotube hyperbolic metamaterials is that their optical properties are a strong function of carrier concentration-thus they function as tunable hyperbolic metamaterials. This functionality is virtually nonexistent in natural crystals and extremely rare even in engineered hyperbolic metamaterials.…”

“…That nanotube films could function as hyperbolic metamaterials is intuitive: along the nanotube alignment direction, free charges can oscillate freely (a metal‐like optical permittivity), whereas perpendicular to the film, free charge conductivity is relatively suppressed (leading to a dielectric‐like permittivity). Recently, this property been experimentally verified: by using ellipsometry [ 33 ] and reflectometry, [ 34 ] two separate studies found hyperbolic dispersion in aligned nanotube films…”

Fenntarthatóság – fenntartásokkal

“…Egy új német tanulmány szerint a szélerőművek -megfelelő támogatási politika esetén -elvileg egész Európa ellátását megoldhatnák (Rydberg et al, 2019). A fotovoltaikus energia-előállításban is vannak arra mutató jelek, hogy a jelenlegi 22-36%-os energiaátalakítási hatékonyság a Rice University újabb szén nanocsöves kutatási eredményei szerint (Gao et al, 2019) az infravörös hányadnak a látható fotonspektrumba konvertálásával elvileg akár 80%-ra is emelhető. A 3. ábrán szembetűnő, hogy ma az azonos energiamennyiség előállítására képes energiaforrások létesítésének fajlagos anyagigénye (t/TWh) a hagyományos (cement, beton, acél, üveg és egyéb) anyagokból milyen óriási eltérést mutat!…”

“…Csakhogy, mint láttuk, a voksok megszerzéséért folytatott versenyben a rendkívül komplex globális ökoszisztéma egy-egy elemének tudományosan megalapozatlan, "kampányszerű" fejlesztésével a környezetben is nagyobb kárt okozhatunk, mint a kezelni kívánt probléma maga. Az üdvözlendő napenergia-hasznosító nanotechnológiai fejlesztések mellett (Gao et al, 2019) a technológiai lehetőségek mindenhatóságának túlhangsúlyozása a káros folyamatok megfékezésében, például nanorendszerek fejlesztése a légköri CO 2 -koncentráció globális megkötésére (Han-Zhien, 2019), sokszor a legkézenfekvőbb természetes megoldásokat szorítja háttérbe.…”

Tunable Hyperbolic Plasmons in Self-Assembled Carbon Nanotube Metamaterials

“…hyperbolic resonances across this wavelength range could be combined with the unique functional capabilities of nanotubes for new applications. The temperature stability and low thermal mass of carbon nanotubes could be combined with resonant spectral selectivity at multiple frequencies to enable thermal emitters with tailored spectral properties [20,[34][35][36][37][38]. Nanotubes supporting multiple resonances could be used for multiband surface-enhanced infrared absorption (SEIRA) with actively tunable resonant frequencies [39,40].…”