Superacids such as chlorosulfonic acid (CSA) and oleum spontaneously dissolve carbon nanotubes (CNT) in high concentrations without damaging their structure. Despite protonation-induced electrostatic repulsion being the driving force in this process, relatively little is known about the actual protonation of individual CNT. Furthermore, numerous claims describing diameter and chiral selectivity (or lack thereof) during the acid-induced doping of CNT are in direct conflict and must be reconciled. Herein, we present direct measurement of charge transfer in solution phase CNT over a broad range of CNT diameters and acid compositions. We find that in CSA, the charge density of commercial CNT ranges from near 0.007 for small diameter semiconductors to more than 0.04 holes per carbon atom for the largest diameter mixed chirality sample. The significant difference in CNT charge transfer is explained according to diameter dependence of the CNT work function, and interfacial p-type doping by the superacid without changes to the CNT density of states. Theoretical results predict a simple diameter and acidity dependent charging behavior, which is experimentally confirmed via Raman spectroscopy. In CSA, the CNT fractional charge, f(c,CSA), as a function of RBM, ?(RBM) in cm(-1), is found to be f (c,CSA) (?(RBM)) = (0.268 - (5.77 x 10(-4))?(RBM))(2) or, equivalently, f(c,CSA) (d(t) ) = ( 0.268 - (( 0.143 ))/(dt) )(2) as a function of nanotube diameter, d ( t ) in nm. This equation relates the CSA-induced CNT charge to the CNT diameter and indicates that the larger diameter CNTs may be better suited for solution processing.

Boron nitride nanotubes (BNNTs) have attracted attention for their predicted extraordinary properties; yet, challenges in synthesis and processing have stifled progress on macroscopic materials. Recent advances have led to the production of highly pure BNNTs. Here we report that neat BNNTs dissolve in chlorosulfonic acid (CSA) and form birefringent liquid crystal domains at concentrations above 170 ppmw. These tactoidal domains merge into millimeter-sized regions upon light sonication in capillaries. Cryogenic electron microscopy directly shows nematic alignment of BNNTs in solution. BNNT liquid crystals can be processed into aligned films and extruded into neat BNNT fibers. This study of nematic liquid crystals of BNNTs demonstrates their ability to form macroscopic materials to be used in high-performance applications.

Chlorosulfonic acid and oleum are ideal solvents for enabling the transformation of disordered carbon nanotubes (CNTs) into precise and highly functional morphologies. Currently, processing these solvents using extrusion techniques presents complications due to chemical compatibility, which constrain equipment and substrate material options. Here, we present a novel acid solvent system based on methanesulfonic or p -toluenesulfonic acids with low corrosivity, which form true solutions of CNTs at concentrations as high as 10 g/liter (≈0.7 volume %). The versatility of this solvent system is demonstrated by drop-in application to conventional manufacturing processes such as slot die coating, solution spinning continuous fibers, and 3D printing aerogels. Through continuous slot coating, we achieve state-of-the-art optoelectronic performance (83.6 %T and 14 ohm/sq) at industrially relevant production speeds. This work establishes practical and efficient means for scalable processing of CNT into advanced materials with properties suitable for a wide range of applications.

We report on the latest properties of solution spun carbon nanotube fiber (CNTF) and discuss these results in the context of the field of CNTF, as well as the broader field of high-performance fibers. Using high aspect ratio, high purity carbon nanotubes (CNTs), we have produced neat CNTF with an electrical conductivity of 10.9 MS/m and a tensile strength of 4.2 GPa. We find that properties for solution spun CNTF have doubled every three years since the first reports in the mid-2000s. Companies are driving up the scale and lowering the costs of CNT and CNTF production. If the recent improvement trends in properties, cost, and scale can be sustained for the next several years, CNTF will be uniquely poised for large-scale market adoption.

Manufacturing of printed electronics relies on the deposition of conductive liquid inks, typically onto polymeric or paper substrates. Among available conductive fillers for use in electronic inks, carbon nanotubes (CNTs) have high conductivity, low density, processability at low temperatures, and intrinsic mechanical flexibility. However, the electrical conductivity of printed CNT structures has been limited by CNT quality and concentration, and by the need for nonconductive modifiers to make the ink stable and extrudable. This study introduces a polymer-free, printable aqueous CNT ink, and, via an ambient direct-write printing process, presents the relationships between printing resolution, ink rheology, and ink-substrate interactions. A model is constructed to predict printed feature sizes on impermeable substrates based on Wenzel wetting. Printed lines have conductivity up to 10 000 S m(-1). The lines are flexible, with <5% change in DC resistance after 1000 bending cycles, and <3% change in DC resistance with a bending radius down to 1 mm. Demonstrations focus on i) conformality, via printing CNTs onto stickers that can be applied to curved surfaces, ii) interactivity using a CNT-based button printed onto folded paper structure, and iii) capacitive sensing of liquid wicking into the substrate itself. Facile integration of surface mount components on printed circuits is enabled by the intrinsic adhesion of the wet ink.

We introduce a new method for fabricating fiber-like field emitters using pointwise deposition of aqueous suspensions of carbon nanotubes (CNTs). Liquid ink is held between a flat base and an upper locating pin as the ink solvent dries and CNTs densify via capillary forces. The resulting field emitters have high aspect ratios, dense packing of CNTs and, importantly, a large base providing mechanical stability and enhanced thermal/electrical contact compared to emitters fabricated from wet-spun CNT fibers and CNT forests. These attributes enable excellent field emission properties—namely, a high field enhancement factor and low turn-on voltage—for a range of tested emitter sizes. The noteworthy improvements in emission from these CNT structures alongside the versatile fabrication process motivates future work on emitter array manufacturing and device integration.

A monofilament fiber spun from individual carbon nanotubes is an arbitrarily long ensemble of weakly interacting, aligned, discrete nanoparticles. Despite the structural resemblance of carbon nanotube monofilament fibers to crystalline polymeric fibers, very little is known about their dynamic collective mechanics, which arise from van der Waals interactions among the individual carbon nanotubes. Using ultrafast stroboscopic microscopy, we study the collective dynamics of carbon nanotube fibers and compare them directly with nylon, Kevlar, and aluminum monofilament fibers under the same supersonic impact conditions. The in situ dynamics and kinetic parameters of the fibers show that the kinetic energy absorption characteristics of the carbon nanotube fibers surpass all other fibers. This study provides insight into the strain-rate-dependent strengthening mechanics of an ensemble of nanomaterials for the development of high-performance fibers used in body armor and other protective nanomaterials possessing exceptional stability in various harsh environments.

Early work on carbon nanotube (CNT) antennas indicated that their performance could not match that of metals such as copper. However, recent improvements in fluid phase CNT processing have yielded macroscopic CNT materials with better alignment and conductivity. There is currently a gap in the literature on CNT antennas for direct experimental measurements of radiation efficiency. In this study, we conducted radiation efficiency measurements of microstrip patch antennas made of shear-aligned CNT films. We measured a radiation efficiency of 94% at 10 GHz and 14 GHz, matching equivalent copper antennas. Furthermore, the minimum CNT film thickness required to match the performance of copper drops with increasing frequency due to reduced losses from the skin effect. These findings pave the way for applications of aligned CNT patch antennas in the aerospace industry, where low weight, mechanical durability, and temperature-independent performance are critically important.

Single‐walled carbon nanotubes (SWCNTs) are a class of 1D nanomaterials that exhibit extraordinary electrical and optical properties. However, many of their fundamental studies and practical applications are stymied by sample polydispersity. SWCNTs are synthesized in bulk with broad structural (chirality) and geometrical (length and diameter) distributions; problematically, all known post‐synthetic sorting methods rely on ultrasonication, which cuts SWCNTs into short segments (typically <1 µm). It is demonstrated that ultralong (>10 µm) SWCNTs can be efficiently separated from shorter ones through a solution‐phase “self‐sorting”. It is shown that thin‐film transistors fabricated from long semiconducting SWCNTs exhibit a carrier mobility as high as ≈90 cm 2 V −1 s −1 , which is ≈10 times higher than those which use shorter counterparts and well exceeds other known materials such as organic semiconducting polymers (<1 cm 2 V −1 s −1 ), amorphous silicon (≈1 cm 2 V −1 s −1 ), and nanocrystalline silicon (≈50 cm 2 V −1 s −1 ). Mechanistic studies suggest that this self‐sorting is driven by the length‐dependent solution phase behavior of rigid rods. This length sorting technique shows a path to attain long‐sought ultralong, electronically pure carbon nanotube materials through scalable solution processing.

Heterojunctions of carbon nanotubes interfaced with silicon and doped with AuCl3 can achieve attractive power conversion efficiencies when operated in the photovoltaic regime; however, the cost and long-term stability of such devices must be improved before they could become commercially viable. Here, we investigate the role of chemical treatment of the carbon nanotube/silicon interface with either SOCl2 or HNO3, prior to AuCl3 doping, on the stability of the photovoltaic devices. We find that while both treatments initially lead to similar device performance, devices treated with HNO3 are significantly more stable. Using X-ray photoemission spectroscopy, we demonstrate that pretreatment with the powerful organic oxidant SOCl2 generates a variety of low-oxidation state silicon species at the nanotube silicon interface that are not generated by exposure to HNO3. These species and their evolution over time are implicated in the reduced device stability, highlighting the importance of silicon oxidation states in determining the stability of carbon nanotube silicon photovoltaic devices.

We have characterized the conductivity of carbon nanotubes (CNT) fibers enriched in semiconducting species as a function of temperature and pulsed laser irradiation of 266 nm wavelength. While at high temperatures the response approaches an Arrhenius law behavior, from room temperature down to 4.2 K the response can be framed, quantitatively, within the predictions of the fluctuation induced tunneling which occurs between the inner fibrils (bundles) of the samples and/or the elementary CNTs constituting the fibers. Laser irradiation induces an enhancement of the conductivity, and analysis of the resulting data confirms the (exponential) dependence of the potential barrier upon temperature as expected from the fluctuation induced tunneling model. A thermal map of the experimental configuration consisting of laser-irradiated fibers is also obtained via COMSOL simulations in order to rule out bare heating phenomena as the background of our experiments. (*) Author

Lightweight materials for next-generation electrical and mechanical applications are expected to have significant impacts on aerospace and ground transportation by reducing fuel consumption. Assessing the potential of novel wiring or fibers requires accurate measurement of linear density. The linear densities of fibers are measured by determining the fiber's resonant frequency vibroscopically, which requires complex mechanical equipment for vibrating the fiber. Here, we leverage the electrical conductivity of carbon nanotube (CNT) fibers to induce vibrations by applying an alternating current (AC) to a fiber under a known tension in the presence of a permanent magnetic field, eliminating the need for mechanical actuation. The fiber vibrates at maximum amplitude when the AC frequency matches the fiber's fundamental resonant frequency, creating an audible sound and inducing measurable changes in the fiber electrical properties. Linear density can be calculated accurately from the resonant frequency or the changes in electrical properties in this simplified apparatus during a tensile test.

In this study, well-aligned single-walled carbon nanotube (SWCNT) films were utilized as lamellae to prepare a multifunctional nanocomposite by a feasible 'layer-by-layer' preparation method. This structural design can not only dramatically reduce the agglomeration effect of SWCNTs, but also achieve high in-plane stiffness. It was found that the well-aligned SWCNT films contribute to the high stress-transfer between CNTs and present good wettability with epoxy matrix, thereby improving the mechanical enhancement. Interestingly, this laminated structure possesses distinct electrical behaviors under different loading conditions. The electrical resistance linearly increases with the increase of in-plane tensile strain but is insensitive to bending. This work could provide in-depth understanding on the mechanical and electrical properties of CNT-based laminated nanocomposites.

The electrical behaviors under mechanical deformation of an aligned single-walled carbon nanotube (SWCNT) film nanocomposite have been systematically investigated in this work. Electrical signals along the CNT axis (‖) and perpendicular to the CNT axis (⊥) follow a specific pattern, which enables the mechanical motion to be determined by vector analysis of such signals. The unique electrical behaviors of the sandwiched nanocomposites originate from the anisotropic characteristics of the CNT films. By combining in situ mechanical investigation with a coarse-grained molecular dynamics simulation, the shearing effect between SWCNTs is found to play a key role in stress-transfer along the ‖ direction, resulting in arc-shape cracks, while the peeling effect is dominant along the ⊥ direction, leading to unifom SWCNT bar bridging at cracks. The fabricated CNT based sandwiched nanocomposite is believed to have great potential in building flexible all-direction sensors.

Carbon nanotubes (CNTs) have many uses in energy storage, electron emission, molecular electronics, and optoelectronics. Understanding their light-matter interactions is crucial to their development. Here, we study a film of single-walled CNTs with a thickness of 1.67 mu m and a 2D orientational order parameter of 0.51, measured by polarized Raman spectroscopy. The film is expected to have a work function of about 5.1 eV. In this study, similar to 100-fs pulses with 1.5 ((h) over bar omega) and 3 eV (2 (h) over bar omega) photon energy are used to pump the CNT film while observing its electron emission in vacuum. Ultrafast pulses produce nonlinear phenomena in enhanced field emission, as the CNTs absorb strongly enough that thermally excited carriers can tunnel through the potential barrier. Through curve fitting of the power dependence for each pump energy, we find that the light at (h) over bar omega is absorbed via 5-photon absorption, and the light at 2 (h) over bar omega is absorbed via a combination of 2- and 3-photon absorption. Further study reveals a space-charge limited regime with low applied bias, a photoemission regime with moderate bias, and a laser-assisted field emission regime when the bias is high enough that the photon pump is no longer important. Cross-correlation pumping with the two colors simultaneously shows 4x enhancement of the emission, with a FWHM that suggests a lifetime of similar to 190 fs, similar to the dephasing time of electrons in CNTs. These studies help illuminate the properties of CNTs as a nonlinear optical material and go towards a more thorough understanding of their optoelectronic properties.

We report ultrafast photoelectron emission from aligned single-wall carbon nanotubes utilizing strong exciton resonances inherent in this prototypical one-dimensional material. These results establish SWCNT films as novel and promising ultrafast photocathode material. © 2019 The Author(s)

Dispersing carbon nanotubes (CNTs) using surfactants into water requires ultrasonication that supplies mechanical energy to debundle and exfoliate CNTs. However, sonication is known to damage CNTs and to cut them into short fragments. Also, the CNT concentration in water dispersion is typically limited to up to 1.0 wt %. Here, we show that by using a sulfuric acid pretreatment, we can enhance the debundling of CNTs and reduce subsequent sonication to achieve homogeneous dispersions without damaging CNTs. Additionally, using a progressive and controlled dialysis, we are able to increase the CNT concentration up to 1.8 wt %. We demonstrate that such highly concentrated dispersions can be used as spin dopes to fabricate continuous fibers. Our fibers have an electrical conductivity up to 580 kS/m, a tensile strength of similar to 1 GPa, and a Young's modulus of 123 GPa, exceeding the mechanical properties of related fibers made from conventional surfactant-stabilized dispersions of sonicated CNTs.

At the microscopic scale, carbon nanotubes (CNTs) combine impressive tensile strength and electrical conductivity; however, their macroscopic counterparts have not met expectations. The reasons are variously attributed to inherent CNT sample properties (diameter and helicity polydispersity, high defect density, insufficient length) and manufacturing shortcomings (inadequate ordering and packing), which can lead to poor transmission of stress and current. To efficiently investigate the disparity between microscopic and macroscopic properties, a new method is introduced for processing microgram quantities of CNTs into highly oriented and well-packed fibers. CNTs are dissolved into chlorosulfonic acid and processed into aligned films; each film can be peeled and twisted into multiple discrete fibers. Fibers fabricated by this method and solution-spinning are directly compared to determine the impact of alignment, twist, packing density, and length. Surprisingly, these discrete fibers can be twice as strong as their solution-spun counterparts despite a lower degree of alignment. Strength appears to be more sensitive to internal twist and packing density, while fiber conductivity is essentially equivalent among the two sets of samples. Importantly, this rapid fiber manufacturing method uses three orders of magnitude less material than solution spinning, expanding the experimental parameter space and enabling the exploration of unique CNT sources.

We study nonlinear above-threshold photoemission (ATPE) in single-wall carbon nanotubes at two wavelengths. NIR photoemission demonstrates 5-photon ATPE, while UV ATPE is dominantly a 2nd process. Two-pulse correlation exhibits enhanced photoemission with a very short lifetime less than 200 fs.

Individual carbon nanotubes (CNTs) are highly conducting (both electrically and thermally), mechanically strong, and ultralight. These characteristics make them promising for use in various applications, including renewable energy, electronics, and aerospace. However, in macroscopic form, i.e., in the form of CNT bundles, these outstanding properties mostly vanish. Recently, fibers consisting of iodine-doped aligned CNTs with conductivities close to that of copper have been produced. Many studies have assumed polyiodide ions, such as tri-iodide (I 3 - ) and penta-iodide (I 5 - ), to be the origin of doping, but the observed large conductivity values cannot be explained with only polyiodides. Here, we quantitatively determine the doping level due to iodine and estimate the number of activated conductive channels in the double-wall CNTs (DWCNTs) that form the fibers. The CNT fibers used in this study were produced by the wet-spinning process, during which the nanotubes were doped with chlorosulfonic acid. The fibers were annealed for dedoping and then were kept in an iodine vapor chamber for 24 hours for doping. To quantify the conductivity increase due to iodine doping, we measured the current carrying capacity of the fibers. To determine the doping level, Raman experiments were performed at room temperature with 568 nm excitation on both iodine-doped and dedoped fibers. The figure shows G-band Raman spectra for (a) an iodine-doped DWCNT fiber and (b) a dedoped DWCNT fiber. These Raman spectra were fit with four Lorentzian peaks using the decomposition method developed from multiwavelength Raman spectroscopy studies on doped samples and high-pressure Raman experiments. These four peaks represent the upper (G + ) and lower (G - ) branches of the inner (G i ) and outer (G o ) tubes, characteristics of the G-band of DWCNTs. For the iodine-doped fiber, G o - , G i + and G o + are upshifted compared to the dedoped fiber. The G-band shift associated with the inner tube is due to the lattice contraction of the outer tube. From these shifts, it is possible to estimate the charge transfer per carbon atom, f C , to be 0.029 and the average Fermi level shift to be 1 eV. Due to the high level of doping, the number of conductive channels increases. To estimate the number of conductive channels, rough estimation was possible using E i (eV) = 0.38 i / d (nm) (for metallic tubes i = 0, 3, 6, ..., and for semiconducting tubes i = 1, 2, 4, 5, 7, 8, ...). Before doping, a statistical analysis gives 1/3 metallic (2 channels) and 2/3 semiconducting (0 channel) for inner and outer tubes, which suggests that the average number of conductive channels for a DWCNT is 4/3. As the outer diameter is ~2 nm, by moving the average Fermi level by 1 eV, we obtain i = ~5, which indicates that the number of conductive channels for a doped DWCNT is 26/3 on average. This conductance improvement is significant. By first-principles calculations based on the density functional theory (DFT), using the Vienna ab initio simulation package (VASP), the structural and electronic properties of both CNT systems were obtained. The plane-wave basis set cutoff energy was set to be 400 eV with a Gaussian smearing method of 0.005 eV width, in order to assure well-converged total energy and force values. All the atoms were allowed to relax until the maximum of forces acting on them became smaller than 0.01 eV/Angstrom. After optimization, the charge transfer of isolated CNTs and CNT bundles, respectively, was determined using Henkelman's group’s program for Bader charge analysis. This calculation proves that two I 2 in contact with CNTs can interact to form metastable I 3 - and I - with a large charge transfer to the carbon nanotube, considerably increasing the doping to a level compatible with experimental observations. Finally, another set of samples were prepared with iodine inside the DWCNTs in order to clearly observe the arrangements of the iodine atoms. We observe, through transmission electron microscopy (TEM), isolated I adjacent to I 3 species. Thus, large charge transfer due to I - and detection of I - through TEM explains the high conductivity achieved through iodine doping. Figure 1