Much understanding exists regarding chirality-dependent properties of single-wall carbon nanotubes (SWCNTs), primarily obtained through single-tube studies. However, macroscopic manifestations of chirality dependence have been limited, especially in electronic transport. Here, recent progress in our optical and electronic transport studies of single-chirality SWCNT thin films will be reviewed. We observed pronounced chirality-dependent electronic localization in temperature and magnetic field dependent conductivity measurements on macroscopic films of single-chirality SWCNTs [1]. We also performed optical absorption measurements in aligned single-chirality (6,5) SWCNT films, and through comparison with detailed theoretical calculations based on the Boltzmann scattering equation, we demonstrated that the background absorption is due to phonon-assisted transitions from the semiconductor vacuum to finite-momentum continuum states of excitons [2]. Furthermore, we conducted terahertz emission and photocurrent studies on films of aligned single-chirality semiconducting SWCNTs and found that excitons autoionize, i.e., spontaneously dissociate into electrons and holes [3]. Some of these studies were enabled by our recent improvement of the controlled vacuum filtration technique [4,5], which allows us to fabricate wafer-scale aligned SWCNTs with extremely anisotropic optical properties [6-9].

1. W. Gao et al., “Band Structure Dependent Electronic Localization in Macroscopic Films of Single-Chirality Single-Wall Carbon Nanotubes,” Carbon 183, 774 (2021).
2. S. Dal Forno et al., “Origin of the Background Absorption in Carbon Nanotubes: Phonon-Assisted Excitonic Continuum,” Carbon 186, 465 (2021).
3. F. R. G. Bagsican et al., “Terahertz Excitonics in Carbon Nanotubes: Exciton Autoionization and Multiplication,” Nano Letters 20, 3098 (2020).
4. X. He et al., “Wafer-Scale Monodomain Films of Spontaneously Aligned Single-Walled Carbon Nanotubes,” Nature Nanotechnology 11, 633 (2016).
5. 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).
6. F. Katsutani et al., “Direct Observation of Cross-Polarized Excitons in Aligned Single-Chirality Single-Wall Carbon Nanotubes,” Physical Review B 99, 035426 (2019).
7. W. Gao et al., “Macroscopically Aligned Carbon Nanotubes as a Refractory Platform for Hyperbolic Thermal Emitters,” ACS Photonics 6, 1602 (2019).
8. N. Komatsu et al., “Groove-Assisted Global Spontaneous Alignment of Carbon Nanotubes in Vacuum Filtration,” Nano Letters 20, 2332 (2020).
9. A. Baydin et al., “Giant Terahertz Polarization Rotation in Ultrathin Films of Aligned Carbon Nanotubes,” Optica 8, 760 (2021).