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Assemblies of single-walled carbon nanotubes with a specific chiral structure are promising future optofunctional materials because of their strong light–matter coupling arising from sharp optical resonances of quasi-one-dimensional excitons. Their strong optical resonances, which lie in the infrared-to-visible wavelength region, can be selected by their chiralities, and this selectivity promises a wide range of applications including photonic and thermo-optic devices. However, the broadband complex optical spectra of single-chirality carbon nanotube assemblies are scarce in the literature, which has prevented researchers and engineers from designing devices using them. Here, we experimentally determine broadband complex refractive index spectra of single-chirality carbon nanotube assemblies. Free-standing carbon nanotube membranes and those placed on sapphire substrates were fabricated via filtration of the nanotube solution prepared by the separation method using gel chromatography. Transmission and reflection spectra were measured in the mid-infrared to visible wavelength region, and the complex refractive indices of nanotube assemblies were determined as a function of photon energy. The real and imaginary parts of the refractive indices of the nanotube membrane with a bulk density of 1 g cm−3 at the first subband exciton resonance were determined to be approximately 2.7–3.6 and 1.3i–2.4i, respectively. We propose an empirical formula that phenomenologically describes the complex refractive index spectra of various single-chirality nanotube membranes, which can facilitate the design of photonic devices using carbon nanotubes as the material.

Zeolite-supported carbon nanotube (CNT) synthesis provides a route for its mass production due to the porous surfaces accommodating a large number of catalytic particles and maintaining the fine particle sizes during high-temperature growth. Coaxial single-walled carbon nanotubes (SWCNTs) and boron nitride nanotube (BNNT) van der Waals heterostructures have been produced recently on the CNT thin-film template. To achieve a high yield of the one-dimensional heterostructure, BNNT-wrapped SWCNTs were synthesized on zeolite support coated with catalytic nanoparticles. They were then dispersed in solution and examined by absorption, photoluminescence, and Raman spectroscopy. A robust thermal stability enhancement was observed, and optical characterizations revealed the composition of dispersed SWCNTs wrapped by BNNTs before air annealing includes individual SWCNTs, BNNT-wrapped SWCNT bundles, and BNNT-wrapped individual SWCNTs. Furthermore, the outside wrapping by BNNTs caused a significant down-shift of the photoluminescence spectrum in semiconducting SWCNTs, suggesting that BNNT-wrapped SWCNTs can be preserved after harsh dispersion treatments. [ABSTRACT FROM AUTHOR]

The microscopic structure and photosensitive function of encapsulated dye in the single-wall carbon nanotubes (SWCNTs) are studied. The findings suggest that the photoexcitation of such dyes leads to the enhancement of transient absorption saturation in the nanotubes, which also proves the transfer of ultrafast energy from the dye to SWCNTs.

A Kelvin-probe force microscopy method is used to characterize the band structure of a single-walled carbon nanotube (SWNT)/metal system, including a shift in the vacuum level that appears at the SWNT/metal interfaces. The results have shown that easy hole injection can be expected for all SWNT/ferromagnet systems.

Author(s): Hiroyoshi Ishii [1]; Hiromichi Kataura (corresponding author) [1]; Hidetsugu Shiozawa [1]; Hideo Yoshioka [2]; Hideo Otsubo [1]; Yasuhiro Takayama [1]; Tsuneaki Miyahara [1]; Shinzo Suzuki [1]; Yohji Achiba [1]; [...]

The population of valence-band electronic states of fullerene peapods (C60@SWCNT and C70@SWCNT) was studied electrochemically in 0.2 M LiClO4 + acetonitrile. All the relevant Raman modes of intratubular C70 show symmetric charge-transfer bleaching as the tube-related modes.

The intersubband plasmons (ISBPs) of single‐wall carbon nanotubes (SWCNTs) endow SWCNT‐based optoelectronic devices with more functions. However, the structural dependence of the ISBPs of SWCNTs is not fully understood. Here, the effect of electronic types and diameters of SWCNTs on the energy and intensity of their ISBPs is investigated systematically. The results show that the ISBP energy of semiconducting SWCNTs is ≈50–250 meV larger than that of metallic SWCNTs with the same diameters, while the ISBP integral intensity is approximately 1.25 to 4 times stronger. Diameter dependence of ISBPs for both semiconducting and metallic SWCNTs is also observed. With a decrease in diameter, the ISBPs shift to higher energies, while the intensity decreases dramatically. When the diameter is reduced to less than 1 nm, the ISBPs become unobservable. Interestingly, the energy separation between the ISBPs and interband transition S22 (M11) decreases with an increase in diameter. Theoretical calculations show that the structure‐dependent ISBP characteristics are dominated by the electronic states of SWCNTs. Based on the ISBP characteristics of different SWCNTs, high‐performance SWCNT‐based near‐infrared electrochromic devices are fabricated by mixing small‐diameter metallic SWCNTs with semiconducting SWCNTs due to their high conductivity and negligible ISBP signals. [ABSTRACT FROM AUTHOR]

Simultaneous controlling of the threshold voltage of both p- and n-type transistors, comprising complementary integrated circuits, is required to develop low-voltage and low-power flexible electronics. In this study, we report tuning the threshold voltage of carbon nanotube thin-film transistors with organic and metal-ion complex salts as dopants, and using device passivation to secure air-stability. Chemical doping affords simple yet precise control of the dopant level and enables the threshold voltages to be finely tuned. Complementary inverters were fabricated on a plastic substrate. Operation at a low supply voltage of 0.5 V was achieved with fairly high gain and noise margins. [ABSTRACT FROM AUTHOR]

Stretchable devices, which can intimately contact dynamic free‐form surfaces, show great promise for wearable and implantable devices for human beings and multifunctional electronic skins for soft robotics. Although some successful stretchable devices have been reported, there are still remaining issues; in particular, the fundamental requirements for wearable devices, including low‐voltage operation, operation speed, mechanical stretchability and robustness, and easy circuit design, are needed to be satisfied simultaneously. Here, a local strain suppression layer (L‐SSL) is introduced into all‐carbon nanotube (CNT) stretchable thin‐film transistors (TFTs) and integrated circuits (ICs) to address these issues. The L‐SSL, which has a high Young's modulus, is placed on top of the active channel region to suppress the induced local strain. The resulting CNT TFTs show no drain current degradation under externally applied tensile strain of up to 35%. Furthermore, stretchable all‐CNT ICs, such as inverters and ring oscillators, can operate at low supply voltage as 0.7 V, because high‐k material can be used underneath the L‐SSL. Biaxial stretching, an indispensable ability for wearable devices on 3D deformable surfaces such as the human body, is also achieved. The all‐CNT devices, equipped with an L‐SSL, demonstrate potential for strain‐insensitive stretchable devices with low‐voltage operation. [ABSTRACT FROM AUTHOR]

Controlled carrier doping of single-wall carbon nanotubes (SWCNTs) is highly demanded for SWCNT electronic device applications. In this study, we propose a method for the controlled filling of n- and p-type dopant molecules in SWCNTs by co-encapsulating dopant and dummy molecules. The SWCNT dispersion was refluxed in 1,4-dioxane dissolving dopant and dummy molecules. The amount of encapsulated dopant molecules can be controlled by the ratio of dopant/dummy molecules in the solution. The relationship is not linear but resembles positive azeotrope behavior. This suggests that the mixed molecules form a condensed phase at the SWCNT wall, during the encapsulation process. [ABSTRACT FROM AUTHOR]