The remarkable flexibility, stable chemical structure, and extraordinary thermal, electrical, and optical properties of carbon nanotubes (CNTs) are promising for a variety of applications in flexible and/or high-temperature electronics, optoelectronics, and thermoelectrics, including wearables, refractory photonics, and waste heat harvesting [1]. However, the long-standing goal in the preparation of CNT ensembles is how to maintain the extraordinary properties of individual CNTs on a macroscopic scale. The polydispersity and randomness remain two main challenges.

Here, we will discuss different methods for creating macroscopically aligned CNTs, including spontaneous formation of wafer-scale aligned CNT films via controlled vacuum filtration [2-4] and production of ultrahigh-conductivity CNT fibers and films through solution spinning and coating [5,6]. We will then describe the optical [2,7-11], dc and ac electrical [2,12-17], thermal [18], and thermoelectric [19-21] properties of these materials. These results are promising for device applications in various fields such as flexible CNT broadband detectors [22-26], spectrally selective thermal emitters [11], and thermoelectric devices [20,21].

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2. X. He et al., “Wafer-Scale Monodomain Films of Spontaneously Aligned Single-Walled Carbon Nanotubes,” Nature Nanotechnology 11, 633 (2016).
3. W. Gao and J. Kono, “Science and Applications of Wafer-Scale Crystalline Carbon Nanotube Films Prepared through Controlled Vacuum Filtration,” Royal Society Open Science 6, 181605 (2019).
4. N. Komatsu et al., “Groove-Assisted Global Spontaneous Alignment of Carbon Nanotubes in Vacuum Filtration,” Nano Letters 20, 2332 (2020).
5. N. Behabtu et al., “Strong, Light, Multifunctional Fibers of Carbon Nanotubes with Ultrahigh Conductivity,” Science 339, 182 (2013).
6. L. W. Taylor et al., “Improved Properties, Increased Production, and the Path to Broad Adoption of Carbon Nanotube Fibers,” Carbon 171, 689 (2021).
7. K. Yanagi et al., “Intersubband Plasmons in the Quantum Limit in Gated and Aligned Carbon Nanotubes,” Nature Communications 9, 1121 (2018).
8. W. Gao et al., “Continuous Transition between Weak and Ultrastrong Coupling through Exceptional Points in Carbon Nanotube Microcavity Exciton–Polaritons,” Nature Photonics 12, 362 (2018).
9. M. E. Green et al., “Bright and Ultrafast Photoelectron Emission from Aligned Single-Wall Carbon Nanotubes through Multiphoton Exciton Resonance,” Nano Letters 19, 158 (2019).
10. F. Katsutani et al., “Direct Observation of Cross-Polarized Excitons in Aligned Single-Chirality Single-Wall Carbon Nanotubes,” Physical Review B 99, 035426 (2019).
11. W. Gao et al., “Macroscopically Aligned Carbon Nanotubes as a Refractory Platform for Hyperbolic Thermal Emitters,” ACS Photonics 6, 1602 (2019).
12. X. Wang et al., “High-Ampacity Power Cables of Tightly-Packed and Aligned Carbon Nanotubes,” Advanced Functional Materials 24, 3241 (2014).
13. A. Zubair et al., “Carbon Nanotube Fiber Terahertz Polarizer,” Applied Physics Letters 108, 141107 (2016).
14. D. Tristant et al., “Enlightening the Ultrahigh Electrical Conductivities of Doped Double-Wall Carbon Nanotube Fibers by Raman Spectroscopy and First-Principles Calculations,” Nanoscale 18, 19668 (2016).
15. N. Komatsu et al., “Modulation-Doped Multiple Quantum Wells of Aligned Single-Wall Carbon Nanotubes,” Advanced Functional Materials 27, 1606022 (2017).
16. F. R. G. Bagsican et al., “Terahertz Excitonics in Carbon Nanotubes: Exciton Autoionization and Multiplication,” Nano Letters 20, 3098 (2020).
17. A. Baydin et al., “Giant Terahertz Polarization Rotation in Ultrathin Films of Aligned Carbon Nanotubes,” Optica 8, 760 (2021).
18. S. Yamaguchi et al., “One-Directional Thermal Transport in Densely Aligned Single-Wall Carbon Nanotube Films,” Applied Physics Letters 115, 223104 (2019).
19. K. Fukuhara et al., “Isotropic Seebeck Coefficient of Aligned Single-Wall Carbon Nanotube Films,” Applied Physics Letters 113, 243105 (2018).
20. Y. Ichinose et al., “Solving the Thermoelectric Trade-Off Problem with Metallic Carbon Nanotubes,” Nano Letters 19, 7370 (2019).
21. N. Komatsu et al., “Macroscopic Weavable Fibers of Carbon Nanotubes with Giant Thermoelectric Power Factor,” Nature Communications 12, 4931 (2021).
22. S. Nanot et al., “Broadband, Polarization-Sensitive Photodetector Based on Optically-Thick Films of Macroscopically Long, Dense, and Aligned Carbon Nanotubes,” Scientific Reports 3, 1335 (2013).
23. X. He et al., “Photothermoelectric p-n Junction Photodetector with Intrinsic Broadband Polarimetry Based on Macroscopic Carbon Nanotube Films,” ACS Nano 7, 7271 (2013).
24. X. He et al., “Carbon Nanotube Terahertz Detector,” Nano Letters 14, 3953 (2014).
25. X. He, F. Léonard, and J. Kono, “Uncooled Carbon Nanotube Photodetectors,” Advanced Optical Materials 3, 989 (2015).
26. A. Zubair et al., “Carbon Nanotube Woven Textile Photodetector,” Physical Review Materials 2, 015201 (2018).