Single-walled Carbon Nanotube Films Research Articles

Aerosol doping of SWCNT films with p- and n-type dopants for optimizing thermoelectric performance

We investigate the aerosol doping method for a thermoelectric performance enhancement of single-walled carbon nanotube (SWCNT) films. A study of doping behavior by depositing an aerosolized dopant solution and real-time optimization of thin film properties focuses on thermoelectric characteristics. Achieving precise control over doping results, we demonstrated the thermoelectric power factor of 657 and 708 μW/mK2 for, respectively, p-type and n-type doped SWCNT films. The proposed doping strategy offers superior flexibility for device design and comparable performance to solution-based doping, paving the way to efficient and scalable thermoelectric generator production based on carbon nanotube materials.

A new method for evaluation of nanotube growth kinetics in aerosol CVD

Aerosol chemical vapor deposition (CVD) – a particular case of floating catalyst CVD method with an extreme dilution of catalyst – has been demonstrated to be one of the most advanced one-stage and continuous techniques for the production of single-walled carbon nanotubes (SWCNTs) for various applications in electronics, optics, energy storage, etc. Nevertheless, rational scaling of the aerosol CVD reactor is often limited by a fundamental problem of tracking the growth kinetics, in particular, the nanotube growth rate and the catalyst deactivation rate. We propose a robust method for the assessment of nanotube growth kinetics (growth rate and catalyst lifetime) based on the analysis of the SWCNT film equivalent sheet resistance (R90) versus residence time (τ) dependencies. We have demonstrated identical trends of R90-vs-τ and length-vs-τ curves at different concentrations of CO2 used as a promoter in the Boudouard reaction- (CO-) based synthesis. As a result, we have revealed the mechanisms behind the CO2 effect on the catalyst deactivation rate not reported before. In particular, we observed an increase in CO2 concentration to provide a faster growth rate but an earlier catalyst deactivation. We believe this work might be useful for researchers from both academia and industry and facilitate more active development of aerosol CVD methods for the production of new materials.

Utilization of Interfacial Films of Organo‐Modified Carbon Nanotubes as Adsorption Templates for a Number of Biomolecules while Maintaining their Activity

AbstractWe investigated the versatility of a monolayer of organo‐modified single‐walled carbon nanotubes (SWCNTs) on a water surface as a template to maintain activity by adsorbing various biomolecules from the subphase. Organo‐modified SWCNTs with amphiphilic properties formed a Langmuir film on the subphase containing biomolecules, and adsorbed and immobilized biomolecules via electrostatic interactions. In this study, the interactions of trypsin, lysozyme, cytochrome C protein, glucose oxidase sugar chain polymer, deoxyribonucleic acid, and chitosan with SWCNTs at the air/water interface were investigated. The uniqueness of this study is that it shows the possibility of wide‐ranging applications by utilizing an organo‐modified SWCNT interfacial film as an adsorption template for various biomolecules. The expansion behavior of the surface pressure‐area isotherms indicated the existence of interactions between the organo‐modified SWCNTs monolayer on the water surface and the biomolecules. The morphology and spectroscopic properties of the films transferred onto solid substrates clearly indicate the adsorption and immobilization of biomolecular groups. DNA and chitosan were not immobilized on the organo‐modified SWCNTs film template; however, the other four enzyme/protein molecules were adsorbed onto the solid substrate and maintained their fine second‐order structures, even under harsh conditions.

Highly Conductive Robust Carbon Nanotube Networks for Strong Buckypapers and Transparent Electrodes

AbstractWhile individual single‐wall carbon nanotubes (SWCNTs) have remarkable strength and electrical conductivity, SWCNT networks fabricated from dispersions have inferior properties due to nanotube bundling, limiting the potential applications of SWCNT materials. Herein, a common dye molecule (purpurin) is used to exfoliate SWCNTs via noncovalent functionalization and to fabricate SWCNT materials by a simple solution‐based process. The advantageous noncovalent interactions result in efficient exfoliation and metallic SWCNT enrichment, affording SWCNT materials with high mechanical robustness and electrical conductivity. This method is used to prepare mechanically robust SWCNT films and flexible transparent conductive electrodes.

Improved Characterization of Aqueous Single-Walled Carbon Nanotube Dispersions Using Dynamic Light Scattering and Analytical Centrifuge Methods.

Aqueous dispersions of single-walled carbon nanotubes (SWCNTs) with a surfactant were studied by using a combination of differential sedimentation and dynamic light scattering methods. When applied to elongated particles like SWCNTs, the differential sedimentation method makes it possible to measure their diameters in dispersions, while the dynamic light scattering method allows to measure their lengths. Both methods have logarithmic dependence on the ratio between the length and diameter of the particles, and their simultaneous use improves the accuracy of measuring particles' dimensions. It was shown that sonication of dispersions leads not only to unbundling of agglomerates into individual nanotubes but also to a decrease in their lengths and the appearance of new defects detectable in increasing the D/G ratio in the Raman spectra. Unbundling into individual nanotubes occurs after exposure to 1 kWh/L energy density, and the single nanotube diameter with SDBS is ca. 3.3 nm larger than that of the naked nanotubes. Conductivity of thin SWCNT films made out of individual nanotubes demonstrates a power law dependence with the exponent close to the theoretical one for rigid rods.

Boosting CO-based synthesis of single-walled carbon nanotubes with hydrogen

Aerosol (floating catalyst) chemical vapor deposition method based on CO disproportionation (the Boudouard reaction) is one of the most promising techniques for the synthesis of single-walled carbon nanotubes (SWCNTs), especially in the form of thin films. However, despite its advantages (i.e., high quality of nanotubes, absence of double- or multi-walled nanotubes, and high controllability of the process), synthesis based on CO disproportionation fails to provide high-yield production. In this work, we examined the effect of hydrogen, admixed to the CO atmosphere as a growth promoter, on the synthesis and properties of SWCNTs. Using optical spectroscopy techniques, conductivity tests, TEM and SEM analysis, and thermodynamic calculations, we revealed hydrogen affects both catalyst activation and nanotube growth. We found a positive H2 effect in two different temperature regimes: the yield increased by a factor of ∼15 at a low temperature (880 °C), which, after doping, led to one of the lowest ratios of the equivalent sheet resistance (R90) and yield (i) and SWCNT lengthening by a factor of 2.4 leading to a 3-fold decrease in an R90 coupled with a noticeable increase in the yield at a high temperature (1000 °C) (ii). We believe the presented results are fruitful for the fundamental understanding of the mechanism for nanotube growth and practical opportunity to fine-tune the production rate of SWCNT films.

High-Performance Infrared Detectors Based on Black Phosphorus/Carbon Nanotube Heterojunctions.

Infrared detectors have broad application prospects in the fields of detection and communication. Using ideal materials and good device structure is crucial for achieving high-performance infrared detectors. Here, we utilized black phosphorus (BP) and single-walled carbon nanotube (SWCNT) films to construct a vertical van der Waals heterostructure, resulting in high-performance photovoltaic infrared detectors. In the device, a strong built-in electric field was formed in the heterojunction with a favored energy-band matching between the BP and the SWCNT, which caused a good photovoltaic effect. The fabricated devices exhibited a diode-like rectification behavior in the dark, which had a high rectification ratio up to a magnitude of 104 and a low ideal factor of 1.4. Under 1550 nm wavelength illumination, the 2D BP/SWCNT film photodetector demonstrated an open-circuit voltage of 0.34 V, a large external power conversion efficiency (η) of 7.5% and a high specific detectivity (D*) of 3.1 × 109 Jones. This external η was the highest among those for the photovoltaic devices fabricated with the SWCNTs or the heterostructures based on 2D materials and the obtained D* was also higher than those for most of the infrared detectors based on 2D materials or carbon materials. This work showcases the application potential of BP and SWCNTs in the detection field.

Nitrogen-Doped Single-Walled Carbon Nanotubes by Floating-Catalyst CVD Process

Due to the properties of single-walled carbon nanotube (SWCNT), thin film SWCNTs have been used for many versatile applications. Direct synthesis of the nanotube films with desired electronic structures without prerequisite of post treatment process then becomes one important step. Here, we present the synthesis of nitrogen-doped SWCNTs by floating-catalyst chemical vapor deposition process. With low nitrogen level incorporated into the sp2 carbon network, substitutional and pyridinic nitrogens become predominance. The electronic structure of N-doped SWCNT film could be changed into n-type doping. The localized structures of carbon and nitrogen bonding environments were also revealed by x-ray absorption spectroscopy. The formation of p-n junction was also obtained from the I-V characteristic of N-doped SWCNT heterojunction diode revealing n-type behavior of the sample.

A Study on the O2 Plasma Etching Method of Spray-Formed SWCNT Films and Their Utilization as Electrodes for Electrochemical Sensors.

In this study, we analyzed the morphological changes and molecular structure changes on the surface of single-walled carbon nanotube (SWCNT) films during oxygen plasma (O2) etching of SWCNT surfaces formed by the spray method and analyzed their potential use as electrochemical electrodes. For this purpose, a SWCNT film was formed on the surface of a glass substrate using a self-made spray device using SWCNT powder prepared with DCB as a solvent, and SEM, AFM, and XPS analyses were performed as the SWCNT film was O2 plasma etched. SEM images and AFM measurements showed that the SWCNT film started etching after about 30 s under 50 W of O2 plasma irradiation and was completely etched after about 300 s. XPS analysis showed that as the O2 plasma etching of the SWCNT film progressed, the sp2 bonds representing the basic components of graphite decreased, the sp3 bonds representing defects increased, and the C-O, C=O, and COO peaks increased simultaneously. This result indicates that the SWCNT film was etched by the O2 plasma along with the oxygen species. In addition, electrochemical methods were used to verify the damage potential of the remaining SWCNTs after O2 plasma etching, including cyclic voltammetry, Randles plots, and EIS measurements. This resulted in a reversible response based on perfect diffusion control in the cyclic voltammetry, and an ideal linear curve in the Randles plot of the peak current versus square root scan rate curve. EIS measurements also confirmed that the charge transfer resistance of the remaining SWCNTs after O2 plasma etching is almost the same as before etching. These results indicate that the remaining SWCNTs after O2 plasma etching do not lose their unique electrochemical properties and can be utilized as electrodes for biosensors and electrochemical sensors. Our experimental results also indicate that the ionic conductivity enhancement by O2 plasma can be achieved additionally.

Stress-Strain and Resistance-Strain Hysteresis in Single-Wall Carbon Nanotube Films for Stretchable Battery Electrodes

The need to protect the vulnerable and limited resources that are naturally available while meeting the growing energy demand of the world makes the sustainable development of renewable energy of paramount importance. To address these needs, a new type of battery electrode has been developed at Honda Research Institute (HRI), based on free-standing single-wall carbon nanotube (SWNT) films containing active battery materials as dispersed nanoparticles. The SWNT films provide both mechanical support and electrical conductivity, removing the need for metal electrodes (increasing the energy density of the battery) and binder materials (making the process environmentally friendly).Under cyclic strain, the SWNT-based electrodes show hysteretic behaviors in both stress-strain and electrical resistance-strain relations. The electrical resistance-strain behavior shows a different trend from the previously observed behavior on 2D SWNT films (on elastic substrate). We hypothesize that this change can be attributed to the differences in the SWNT network structures in the 2D and 3D films. To understand the microscopic origin of the hysteresis, we performed coarse-grained molecular statics (CGMS) simulations of the SWNT film. The simulations show that the intrinsic Van der Waals interaction between SWNTs is responsible for the observed robust mechanical properties of the electrodes. In addition, our study also reveals that the sparsity of the 3D morphology results in the current being carried across the simulation box only by a few paths. As a consequence, the resistance hysteresis is governed entirely by the change in the power-carrying capacity of the network due to the breaking and formation of contacts between the SWNTs during loading-unloading. The qualitative nature of the resistance-strain hysteresis can thus be attributed to the rapid formation of inter-nanotube contacts, as the nanotube bundles (elongated by initial loading) buckle during unloading.

(Invited) Anisotropy in Complex Refractive Index Spectra of Single-Chirality-Enriched Carbon Nanotube Films

Toward macroscopic applications of exceptional optical properties of single-walled carbon nanotubes (SWCNTs), we reported in-plane complex refractive index spectra [1] of various single-chirality-enriched [2] SWCNTs films in which the SWCNTs are mostly oriented in two dimensions parallel to the film surface. However, in order to describe the anisotropic optical responses of such SWCNT films for incident light from all the directions, out-of-plane refractive index spectra are also required, in addition to the in-plane ones. We will report complete broadband complex refractive index spectra of single-chirality-enriched SWCNTs films for in-plane and out-of-plane optical responses. [1] T. Nishihara, A. Takakura, M. Shimasaki, K. Matsuda, T. Tanaka, H. Kataura, and Y. Miyauchi, Nanophotonics 11, 1011 (2022). [2] Y. Yomogida, T. Tanaka, M. Zhang, M. Yudasaka, X. Wei, and H. Kataura, Nat. Commun. 7, 12056 (2016).

(Invited) Highly Transparent and Mechanically Robust Energy-Harvestable Piezocomposite with Embedded One-Dimensional P(VDF-TrFE) Nanofibers and Single-Walled Carbon Nanotubes

Here, highly transparent, flexible, and ultrathin piezocomposite, in which electrospun poly(vinylidene fluoride-co-trifluoroethylene) [P(VDF-TrFE)] nanofibers (NFs) and aerosol-synthesized single-walled carbon nanotubes (SWCNTs) are embedded in elastomer matrix, is fabricated. The P(VDF-TrFE) NF mat is exploited as a piezoelectric layer of the piezocomposite while the SWCNT film is applied as a transparent conductive electrode (TCE) thereof. The use of these one-dimensional (1D) nanomaterials allows the piezocomposite not only to have a high transparency along with low diffusivity, but also to exhibit enhanced mechanical properties. In addition, the coupling effect of piezo- and flexoelectricity exhibited from the electrospun NFs and the acid-doping effect conducted on the SWCNTs facilitate a significant improvement in kinetic energy-harvesting performance, leading to a maximum output voltage of 26.8 V. Moreover, electrospinning and aerosol chemical vapor deposition (CVD) methods employed here are facile, scalable, and cost-effective, thus are expected to accelerate the development of industrially feasible next-generation wearable electronics.

Radial Alignment of Carbon Nanotubes Via Dead-End Filtration

Dead-end filtration is a facile method to globally align single wall carbon nanotubes (SWCNTs) in large area films with a two-dimensional order parameter, , approaching unity. Uniaxial alignment has been achieved using pristine and hot-embossed membranes but more sophisticated geometries have yet to be investigated. In this work, we create three different patterns with radial symmetry and an area of 3.8 cm². Two of these patterns are replicated by the filtered SWCNTs and values of » 0.85 are obtained. Each of the radially aligned SWCNT films are characterized by scanning cross-polarized microscopy in reflectance and laser imaging in transmittance with linear, radial and azimuthal polarized light fields. The former is used to define a novel indicator akin to the two-dimensional order parameter using Malu’s law, yielding 0.82 for the respective film. The films are then transferred to a flexible printed circuit board and terminal two-probe electrical measurements are conducted to explore the potential of those new alignment geometries. Figure 1

Assembly and Characterization of Length-Sorted, Aligned Boron Nitride/Carbon Nanotube Thin Film Composites Via Slow Vacuum Filtration

Globally aligned single-wall carbon nanotubes (SWCNTs) are a promising, scalable platform for studying fundamental physical phenomena and an important vehicle for optoelectronic device applications. Recent work by Rust et al. [1] has identified nanotube length as an important mediating factor in the degree and scale of SWCNT alignment via slow vacuum filtration (SVF).Building on this work and that of Walker et al. [2,3], we explore the co-assembly of length-sorted SWCNTs and boron nitride nanotubes (BNNTs) atop polycarbonate track-etched membranes. BNNTs have recently gained interest as a chirality-agnostic, wide-bandgap material for encapsulation, insulation, thermal/mechanical robustness, and visible-light transparency, while also having a similar high aspect ratio morphology, making them an exceptional and alignable host matrix for individualized CNT species. To prepare such hybrid assemblies, a polymer-assisted, depletion-based method was first used to length-sort different diameter SWCNT (alkane filled electric-arc, CoMoCAT, metallic-sorted Tuball), and BNNT nanotube populations. Thereafter, we investigated the impacts of tube lengths, relative BN/C fraction, mass loading, and presence of a global director force on the multi-scale assembly behavior. A combination of birefringence microscopy and polarized Raman spectroscopy probed and identified trends in global and local ordering under these conditions.[1] Rust, C., Shapturenka, P., Spari, M., Jin, Q., Li, H., Bacher, A., Guttmann, M., Zheng, M., Adel, T., Hight Walker, A. R., Fagan, J. A., & Flavel, B. S. (2022). The Impact of Carbon Nanotube Length and Diameter on their Global Alignment by Dead-End Filtration. Small (forthcoming).[2] Walker, J. S., Fagan, J. A., Biacchi, A. J., Kuehl, V. A., Searles, T. A., Hight Walker, A. R., & Rice, W. D. (2019). Global Alignment of Solution-Based Single-Wall Carbon Nanotube Films via Machine-Vision Controlled Filtration. Nano Letters, 19(10), 7256–7264.[3] Walker, J. S., Macdermid, Z. J., Fagan, J. A., Kolmakov, A., Biacchi, A. J., Searles, T. A., Walker, A. R. H., & Rice, W. D. (2022). Dependence of Single‐Wall Carbon Nanotube Alignment on the Filter Membrane Interface in Slow Vacuum Filtration. Small, 18, 2105619.

Sensitivity enhancement of SWCNT gas sensors by nitrogen plasma treatment

Single-walled carbon nanotubes (SWCNTs) hold promise for detecting toxic and chemically aggressive gases due to their unique 1D structure. However, the limited sensitivity of as-produced SWCNT films hampers their practical application as gas sensors. To enhance sensitivity, various functionalization methods, including nitrogen doping, have been explored. In this study, we investigated the impact of low-frequency nitrogen plasma treatment on SWCNT films for sensing reducing and oxidizing air pollutants—specifically, NO2 and NH3—at concentrations ranging from 10 to 50 ppm. TEM and UV-vis-NIR unveiled the etching of the SWCNT structure, and Raman spectroscopy showed the formation of defects following nitrogen plasma treatment. XPS analysis confirmed the presence of amine, pyridinic, and quaternary N-containing defects within the graphitic structure. Upon treating pristine SWCNT films with a 32 W·h dose of plasma, the average chemiresistive response to 50 ppm analyte (in air) at room temperature increased significantly by 100x, rising from 0.2% to 20% (NO2) and from 0.05% to 17% (NH3). Density functional tight-binding modeling corroborated the experimental findings, revealing a correlation between plasma dose and sensor signal. Moreover, the modeling suggested that analyte molecule adsorption on defects is favored over basal plane adsorption.

Hybrid Silicon Nitride Photonic Integrated Circuits Covered by Single-Walled Carbon Nanotube Films.

The integration of low-dimensional materials with optical waveguides presents promising opportunities for enhancing light manipulation in passive photonic circuits. In this study, we investigate the potential of aerosol-synthesized single-walled carbon nanotube (SWCNT) films for silicon nitride photonic circuits as a basis for developing integrated optics devices. Specifically, by measuring the optical response of SWCNT-covered waveguides, we retrieve the main SWCNT film parameters, such as absorption, nonlinear refractive, and thermo-optic coefficients, and we demonstrate the enhancement of all-optical wavelength conversion and the photoresponse with a 1.2 GHz bandwidth.

Ultrathin transparent carbon nanotube/LiMn2O4 and carbon nanotube/MoS2 film electrodes for Li-ion full batteries

The increasing demands for wearable devices have significantly facilitated the development of transparent electronics. Serving as key components of fully integrated transparent devices, transparent batteries are urgently needed yet their development is largely hindered by the difficulties of fabricating transparent electrode materials. Here, we successfully designed the transparent cathodes and anodes through combining transparent single-walled carbon nanotubes (SWNTs) films with lithium manganate (CNT/LMO) and molybdenum disulfide (CNT/MoS2), respectively. We found that the fabricated cathode and anode composite films exhibit excellent transmittances of 75% and 80%, respectively. Also, the interconnected SWNT networks in the composite films provide an efficient channel for fast electron transport that significantly contribute to their electrochemical performance. Specifically, when employed as battery electrodes, the highly transparent CNT/LMO cathode and CNT/MoS2 anode show initial areal capacities of 13 and 66 μAh cm−2 at current densities of 0.05 and 0.2 mA cm−2, respectively. More impressively, a full cell, which is constructed with transparent CNT/LMO and CNT/MoS2 composite films as electrodes, shows the capacity retention up to 90% after 100 cycles. The demonstration of transparent electrodes in this study provides a promising strategy to realize the fabrication of fully transparent wearable devices.

Enhancing the Electrical Conductivity and Strength of PET by Single-Wall Carbon Nanotube Film Coating.

Single-wall carbon nanotubes (SWCNTs) with excellent physicochemical properties are considered a promising candidate for the electrical and mechanical reinforcements of polymers. However, the poor dispersion of SWCNTs in plastics seriously limits their application and their achieved performance enhancement. Here, we coat a freestanding, highly conductive SWCNT film onto the surface of a polyethylene terephthalate (PET) film by a hot-pressing method. Due to the uniform SWCNT network structure and strong interfacial interaction, the SWCNT/PET hybrid film showed notably enhanced electrical and mechanical properties even though with a very low SWCNT weight fraction of 0.066%. The surface square resistance of the SWCNT/PET film decreased to 120-140 Ω/□ from 1016 Ω. In addition, Young's modulus and tensile strength of the SWCNT/PET film reached 4.6 GPa and 148 MPa, which are 31.3 and 24.4%, respectively, higher than the pure PET film. The SWCNT/PET film shows excellent mechanical durability and thermal stability, demonstrating its potential use as an antistatic material.

Partial dehydration-mediated selective ion-permeation through subnanometer-scale windows in highly crystalline single walled carbon nanotube walls

We propose single-atom catalytic oxidation method for production of subnanometer-scale windows on the graphene layer of single walled carbon nanotubes (SWCNTs) in this study. We used the free-standing SWCNT films which had merits for reliable measurements and applicability to electrochemical measurements for determination of the nanowindow size. Copper(II) 2,3,9,10,16,17,23,24-octakis(octyloxy)-29H,31H-phthalocyanine (CuPc) was adsorbed on SWCNT bundles using liquid-phase adsorption at surface coverage of 0.9. Then, nanowindows were produced by oxidation above 550 K being higher than the decomposition temperature of the bulk CuPc. The oxidation of CuPc-adsorbed SWCNT film markedly increased the surface area from N2 adsorption at 77 K due to access of N2 to the internal tube space through the nanowindows. The nanowindow size was estimated to be the molecular size of N2 through the evident low-pressure adsorption hysteresis of the N2 adsorption isotherm and TEM observation. The selective ion permeability through the nanowindows for H3O+, Li+, Na+, K+, Mg2+, Ca2+, and Ba2+ ions was determined by the inside-capacitance being the capacitance difference of SWCNT between with and without nanowindows. The selective permeation of the hydrated ions depended on the oxidation conditions for production of nanowindows, showing less than 1 nm of the nanowindow size. The relationship between the inside-capacitance and hydrated ion diameter for the selective permeation of hydrated ions indicated partial dehydration of the hydrated ions just only on their permeation through the nanowindows under the accelerated conditions.

Characterization and application of flexible, highly conductive freestanding films of SWCNT and PMMA nanocomposite prepared by facile solution method

The aim of this work was to prepare single-walled carbon nanotube (SWCNT)-embedded polymethyl methacrylate (PMMA) freestanding polymer films and investigate their mechanical and electrical properties. PMMA is widely used in various applications; however, its poor mechanical and electrical properties limit its use. The electrical and mechanical performance of PMMA can be effectively improved by producing nanoparticle-reinforced PMMA composites. Carbon nanotubes (CNTs) are highly attractive nanoparticles used to develop polymer nanocomposite films with novel properties useful for diverse technological applications. The superior electrical and mechanical properties of CNTs can enhance the corresponding properties of the CNT/PMMA nanocomposite. The SWCNT/PMMA nanocomposite films were prepared with a simple sonication technique by employing ethanol and water as solvents. The prepared films were characterized by X-ray diffraction, photoluminescence, Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy, and scanning electron microscopy analysis to examine the structural, morphological, and optical properties as well as chemical composition of the films. In addition, nanoindentation and current vs. voltage studies were also conducted. Further, the hydrogen evaluation reaction effect of the prepared electrode was evaluated to investigate the catalytic activity of the films. This technologically attractive SWCNT/PMMA nanocomposite freestanding film prepared first time via a simple low-cost technique showed good conductivity, photosensitivity and flexibility with catalytic property.