Significantly Increased Solubility of Carbon Nanotubes in Superacid by Oxidation and Their Assembly into High‐Performance Fibers

This study demonstrates that small amount of oxygen incorporated into carbon nanotubes (CNTs) during the purification process greatly increases their solubility in chlorosulfonic acid (CSA). Using as‐purchased and unpurified CNT powders, the optimal purification process is established to significantly increase the solubility of CNTs in CSA, and spin CNT fibers with high mechanical strength (0.84 N tex^?1) and electrical conductivity (1.4 MS m^?1) from the CNT liquid crystal dope with high concentration of CNTs in CSA. The knowledge obtained here may guide development of a way to dissolve extremely long CNTs at high concentration and thereby to enable production of CNT fibers with ultimate properties.     

Failure analysis and the optimal toughness design of carbon nanotube-reinforced composites

The combined analysis of the fracture toughness enhancement of carbon nanotube (CNT)-reinforced composites is herein carried out on the basis of atomistic simulation, shear-lag theory and facture mechanics. It is found that neither longer reinforced CNTs nor stronger CNT/matrix interfaces can definitely lead to the better fracture toughness of these composites. In contrast, the optimal interfacial chemical bond density and the optimal CNT length are those making the failure mode just in the transition from CNT pull-out to CNT break. To verify our theory, an atomic/continuum finite element method (FEM) is applied to investigate the fracture behavior of CNT-reinforced composites with different interfacial chemical bond densities. Our analysis shows that the optimal interfacial chemical bond density for (6,6) CNTs is about 5–10% and that increasing the CNT length beyond 100 nm does not further improve fracture toughness, but can easily lead to the self-folding and clustering of the CNTs. The proposed theoretical model is also applicable to short fiber-reinforced composites.     

Preparation and characterization of a novel hydroxyapatite/carbon nanotubes composite and its interaction with osteoblast-like cells

Hydroxyapatite (HA) and its based biomaterials could chemically bond directly to bone when implanted, resulting in the formation of a strong bone-implant interface. Carbon nanotubes (CNT) are believed to be very promising in the enhancement ceramic matrix and played an important role as reinforcement for imparting strength and toughness to brittle HA bioceramic. Here we demonstrate the potential use in reinforcing biomaterials through an attempt to use CNT strengthen brittle HA bioceramic. This work aims to study the optimum sintering conditions of CNT modified HA to get CNT–HA composite with improved mechanical properties using a rapid spark plasma sintering system. The microstructure, phases, chemical compositions and mechanical properties of the ceramic samples were characterized by various advanced methods. Though no obvious chemical reaction between CNT and HA has been detected, the physical crosslink caused by the presence of CNT resulted in that a CNT–HA composite with a relatively high value of modulus (~ 131.1 GPa) and hardness (~ 6.86 GPa) achieved at the sintering temperature of 1100 °C. In vitro cellular responses to the composites were assessed to investigate the proliferation and morphology of a human osteoblast cell line cultured on the various composites.     

Rapid, Sensitive Detection of Neurotransmitters at Microelectrodes Modified with Self-assembled SWCNT Forests

Carbon nanotube (CNT) modification of microelectrodes can result in increased sensitivity without compromising time response. However, dip coating CNTs is not very reproducible and the CNTs tend to lay flat on the electrode surface which limits access to the electroactive sites on the ends. In this study, aligned CNT forests were formed using a chemical self-assembly method, which resulted in more exposed CNT ends to the analyte. Shortened, carboxylic acid functionalized single-walled CNTs were assembled from a dimethylformamide (DMF) suspension onto a carbon-fiber disk microelectrode modified with a thin iron hydroxide-decorated Nafion film. The modified electrodes were highly sensitive, with 36-fold higher oxidation currents for dopamine using fast-scan cyclic voltammetry than bare electrodes and 34-fold more current than electrodes dipped in CNTs. The limit of detection (LOD) for dopamine was 17 ± 3 nM at a 10 Hz repetition rate and 65 ± 7 nM at 90 Hz. The LOD at 90 Hz was the same as a bare electrode at 10 Hz, allowing a 9-fold increase in temporal resolution without a decrease in sensitivity. Similar increases were observed for other cationic catecholamine neurotransmitters, and the increases in current were greater than for anionic interferents such as ascorbic acid and 3,4-dihydroxyphenylacetic acid (DOPAC). The CNT forest electrodes had high sensitivity at 90 Hz repetition rate when stimulated dopamine release was measured in Drosophila . The sensitivity, temporal resolution, and spatial resolution of these CNT forest modified disk electrodes facilitate enhanced electrochemical measurements of neurotransmitter release in vivo.     

Mechanical properties of carbon nanotubes and their polymer nanocomposites

More than 10 years have passed since carbon nanotubes (CNT) have been found during observations by transmission electron microscopy (TEM). Since then, one of the major applications of the CNT is the reinforcements of plastics in processing composite materials, because it was found by experiments that CNT possessed splendid mechanical properties. Various experimental methods are conducted in order to understand the mechanical properties of varieties of CNT and CNT-based composite materials. The systematized data of the past research results of CNT and their nanocomposites are extremely useful to improve processing and design criteria for new nanocomposites in further studies. Before the CNT observations, vapor grown carbon fibers (VGCF) were already utilized for composite applications, although there have been only few experimental data about the mechanical properties of VGCF. The structure of VGCF is similar to that of multi-wall carbon nanotubes (MWCNT), and the major benefit of VGCF is less commercial price. Therefore, this review article overviews the experimental results regarding the various mechanical properties of CNT, VGCF, and their polymer nanocomposites. The experimental methods and results to measure the elastic modulus and strength of CNT and VGCF are first discussed in this article. Secondly, the different surface chemical modifications for CNT and VGCF are reviewed, because the surface chemical modifications play an important role for polymer nanocomposite processing and properties. Thirdly, fracture and fatigue properties of CNT/polymer nanocomposites are reviewed, since these properties are important, especially when these new nanocomposite materials are applied for structural applications.     

Non-destructive characterization of structural hierarchy within aligned carbon nanotube assemblies

Understanding and controlling the hierarchical self-assembly of carbon nanotubes (CNTs) is vital for designing materials such as transparent conductors, chemical sensors, high-performance composites, and microelectronic interconnects. In particular, many applications require high-density CNT assemblies that cannot currently be made directly by low-density CNT growth, and therefore require post-processing by methods such as elastocapillary densification. We characterize the hierarchical structure of pristine and densified vertically aligned multi-wall CNT forests, by combining small-angle and ultra-small-angle x-ray scattering (USAXS) techniques. This enables the nondestructive measurement of both the individual CNT diameter and CNT bundle diameter within CNT forests, which are otherwise quantified only by delicate and often destructive microscopy techniques. Our measurements show that multi-wall CNT forests grown by chemical vapor deposition consist of isolated and bundled CNTs, with an average bundle diameter of 16 nm. After capillary densification of the CNT forest, USAXS reveals bundles with a diameter >4 μm, in addition to the small bundles observed in the as-grown forests. Combining these characterization methods with new CNT processing methods could enable the engineering of macro-scale CNT assemblies that exhibit significantly improved bulk properties.     

High performance natural rubber composites with a hierarchical reinforcement structure of carbon nanotube modified natural fibers

A simple and facile method for depositing multiwall carbon nanotubes (MWCNTs) onto the surface of naturally occurring short jute fibers (JFs) is reported. Hierarchical multi-scale structures were formed with CNT-networks uniformly distributed and fully covering the JFs (JF–CNT), as depicted by the scanning electron microscopy (SEM) micrographs. The impact of these hybrid fillers on the mechanical properties of a natural rubber (NR) matrix was systematically investigated. Pristine JFs were cut initially to an average length of 2.0 mm and exposed to an alkali treatment (a-JFs) to remove impurities existing in the raw jute. MWCNTs were treated under mild acidic conditions to generate carboxylic acid moieties. Afterward, MWCNTs were dispersed in an aqueous media and short a-JFs were allowed to react with them. Raman spectroscopy confirmed the chemical interaction between CNTs and JFs. The JF–CNT exposed quite hydrophobic behavior as revealed by the water contact angle measurements, improving the wettability of the non-polar NR. Consequently, the composite interfacial adhesion strength was significantly enhanced while a micro-scale “mechanical interlocking” mechanism was observed from the interphase-section transmission electron microscopy (TEM) images. SEM analysis of the composite fracture surfaces demonstrated the interfacial strength of NR/a-JF and NR/JF–CNT composites, at different fiber loadings. It can be presumed that the CNT-coating effectively compatibillized the composite structure acting as a macromolecular coupling agent. A detailed analysis of stress-strain and dynamic mechanical spectra confirmed the high mechanical performance of the hierarchical composites, consisting mainly of materials arising from natural resources.     

Hybrid Films of Graphene and Carbon Nanotubes for High Performance Chemical and Temperature Sensing Applications

A hybrid composite material of graphene and carbon nanotube (CNT) for high performance chemical and temperature sensors is reported. Integration of 1D and 2D carbon materials into hybrid carbon composites is achieved by coupling graphene and CNT through poly(ionic liquid) (PIL) mediated‐hybridization. The resulting CNT/PIL/graphene hybrid materials are explored as active materials in chemical and temperature sensors. For chemical sensing application, the hybrid composite is integrated into a chemo‐resistive sensor to detect a general class of volatile organic compounds. Compared with the graphene‐only devices, the hybrid film device showed an improved performance with high sensitivity at ppm level, low detection limit, and fast signal response/recovery. To further demonstrate the potential of the hybrid films, a temperature sensor is fabricated. The CNT/PIL/graphene hybrid materials are highly responsive to small temperature gradient with fast response, high sensitivity, and stability, which may offer a new platform for the thermoelectric temperature sensors.     

Optimized network of multi-walled carbon nanotubes for chemical sensing

This work reports the design of a resistive gas sensor based on 2D mats of multi-walled carbon nanotubes (MWCNTs) grown by aerosol-assisted chemical vapour deposition. The sensor sensitivity was optimized using chlorine as analyte by tuning both CNT network morphology and CNT electronic properties. Optimized devices, operating at room temperature, have been calibrated over a large range of concentration and are shown to be sensitive down to 27 ppb of chlorine. The as-grown MWCNT response is compared with responses of 2000?°C annealed CNTs, as well as of nitrogen-doped CNTs and CNTs functionalized with polyethyleneimine (PEI). Under chlorine exposure, the resistance decrease of as-grown and annealed CNTs is attributed to charge transfer from chlorine to CNTs and demonstrates their p-type semiconductor behaviour. XPS analysis of CNTs exposed to chlorine shows the presence of chloride species that confirms electron charge transfer from chlorine to CNTs. By contrast, the resistance of nitrogen-doped and PEI functionalized CNTs exposed to chlorine increases, in agreement with their n-type semiconductor nature. The best response is obtained using annealed CNTs and is attributed to their higher degree of crystallinity.     

Template synthesis and growth mechanism of metal nanowire/carbon nanotube heterojunctions

Copper (Cu) and Cobalt (Co) with remarkable difference in the catalytic activity for the growth of carbon nanotubes (CNTs) have been used to prepare metal-nanowire/CNT heterojunctions. The ordered arrays of Cu nanowire/CNT (CuNW/CNT) and Co nanowire/CNT (CoNW/CNT) heterojunctions were prepared by combining electrochemical deposition and chemical vapor deposition. The interfaces between CNTs and Cu or Co nanowires have been examined and compared. At the interface of CuNW/CNT heterojunction, the tip of CuNW is encapsulated by carbon material (named "cap") and connected the CNT consisting of amorphous carbon (a-C). Two-segment CuNW/amorphous CNT (CuNW/a-CNT) hybrid nanostructure was obtained for the CuNW/CNT heterojunctions due to low catalytic activity of Cu. It is also interesting that a hollow gap was observed between the "cap" and the CuNW. By contrast with the case of Cu, multi-walled CNT (MWCNT) was achieved and no hollow gap was observed at the interface of CoNW/CNT heterojunctions. Three-segment CoNW/MWCNT/a-CNT hybrid nanostructure was observed for the CoNW/CNT heterojunctions because of high catalytic activity of Co. Because no stable copper carbides are observed, we infer that the growth mechanism of CuNW/CNT heterojunctions is different from that of CoNW/CNT. Possible growth models of CuNW/CNT and CoNW/CNT heterojunctions are proposed based on experimental results, respectively.     

Ultra‐High Optical Absorption Efficiency from the Ultraviolet to the Infrared Using Multi‐Walled Carbon Nanotube Ensembles

The optical absorption efficiencies of vertically aligned multi‐walled (MW)‐carbon nanotube (CNT) ensembles are characterized in the 350?7000 nm wavelength range where CNT site densities > 1 × 10¹¹/cm² are achieved directly on metallic substrates. The site density directly impacts the optical absorption characteristics, and while high‐density arrays of CNTs on electrically insulating and non‐metallic substrates have been commonly reported, achieving high site‐densities on metals has been challenging and remains an area of active research. These absorber ensembles are ultra‐thin (<10 μm) and yet they still exhibit a reflectance as low as ～0.02%, which is 100 times lower than the reference; these characteristics make them potentially attractive for high‐sensitivity and high‐speed thermal detectors. In addition, the use of a plasma‐enhanced chemical vapor deposition process for the synthesis of the absorbers increases the portfolio of materials that can be integrated with such absorbers due to the potential for reduced synthesis temperatures. The remarkable ruggedness of the absorbers is also demonstrated as they are exposed to high temperatures in an oxidizing ambient environment, making them well‐suited for extreme thermal environments encountered in the field, potentially for solar cell applications. Finally, a phenomenological model enables the determinatiom of the extinction coefficients in these nanostructures and the results compare well with experiment.     

Nanotube-Based Chemical and Biomolecular Sensors

We present a brief review about recent results regarding carbon nanotube （CNT）-based chemical and biomolecular sensors. For the fabrication of CNT-based sensors, devices containing CNT channels between two metal electrodes are first fabricated usually via chemical vapor deposition （CVD） process or ＂surface programmed assembly＂ method. Then, the CNT surfaces are often functionalized to enhance the selectivity of the sensors. Using this process, highly-sensitive CNT-based sensors can be fabricated for the selective detection of various chemical and biological molecules such as hydrogen, ammonia, carbon monoxide, chlorine gas, DNA, glucose, alcohol, and proteins.     

A General Method for the Chemical Synthesis of Large‐Scale,Seamless Transition Metal Dichalcogenide Electronics

The capability to directly build atomically thin transition metal dichalcogenide (TMD) devices by chemical synthesis offers important opportunities to achieve large‐scale electronics and optoelectronics with seamless interfaces. Here, a general approach for the chemical synthesis of a variety of TMD (e.g., MoS₂, WS₂, and MoSe₂) device arrays over large areas is reported. During chemical vapor deposition, semiconducting TMD channels and metallic TMD/carbon nanotube (CNT) hybrid electrodes are simultaneously formed on CNT‐patterned substrate, and then coalesce into seamless devices. Chemically synthesized TMD devices exhibit attractive electrical and mechanical properties. It is demonstrated that chemically synthesized MoS₂–MoS₂/CNT devices have Ohmic contacts between MoS₂/CNT hybrid electrodes and MoS₂ channels. In addition, MoS₂–MoS₂/CNT devices show greatly enhanced mechanical stability and photoresponsivity compared with conventional gold‐contacted devices, which makes them suitable for flexible optoelectronics. Accordingly, a highly flexible pixel array based on chemically synthesized MoS₂–MoS₂/CNT photodetectors is applied for image sensing.     

纳米碳管阵列

在概括纳米碳管阵列特异的场发射效应及在场发射器方面应用前景的基础上，介绍了合成纳米碳管阵列的研究历程以及化学气相沉积法在纳米碳管阵列合成方面的重要意义，就当前纳米碳管阵列的快速合成与低温合成两个发展方向进行了概述，并指出等离子体化学气相沉积法能有效地用于纳米碳管阵列的低温合成。     

The fabrication of vertically aligned and periodically distributed carbon nanotube bundles and periodically porous carbon nanotube films through a combination of laser interference ablation and metal-catalyzed chemical vapor deposition

Scalable fabrication of carbon nanotube (CNT) bundles is essential to future advances in several applications. Here, we report on the development of a simple, two-step method for fabricating vertically aligned and periodically distributed CNT bundles and periodically porous CNT films at the sub-micron scale. The method involves laser interference ablation (LIA) of an iron film followed by CNT growth via iron-catalyzed chemical vapor deposition. CNT bundles with square widths ranging from 0.5 to 1.5 μm in width, and 50-200 μm in length, are grown atop the patterned catalyst over areas spanning 8 cm(2). The CNT bundles exhibit a high degree of control over square width, orientation, uniformity, and periodicity. This simple scalable method of producing well-placed and oriented CNT bundles demonstrates a high application potential for wafer-scale integration of CNT structures into various device applications, including IC interconnects, field emitters, sensors, batteries, and optoelectronics, etc.     

Catalytic-free growth of VACNTs for energy harvesting

Abstract

The present study introduces a process to grow micro-honeycomb (µ-HC) vertically aligned carbon nanotubes (VACNTs) using thermal chemical vapor deposition technique. Methane is used as a source of carbon and hydrogen gas as a reducing agent. Where, the fabricated µ-HC structure reported in literature involves complex synthesis process and requires a catalyst layer, the novelty of the process used here lies in the fact that no catalyst layer is used for the growth of CNT network, rather copper foil is used as a substrate. The in-situ cracking of CNTs due to water treatment leads to the formation of µ-HC CNT network, which is confirmed by Raman spectroscopy. Further scanning electron microscopy analysis shows that the length of developed µ-HC CNT is ～5?µm. Hexagonal µ-HC network shows more than 94% absorption in UV-Vis-NIR wavelength region. The designed process provides high-yield with a low-cost synthesis of vertically aligned CNTs having 3?D microarchitecture. The fabricated CNT network can be used as an electrode for supercapacitor, as an active layer in a photovoltaic cell and most of the energy harvesting devices.     

Building desired heterojunctions of semiconductor CdS nanowire and carbon nanotube via AAO template-based approach

Heterojunctions of CdS nanowire (CdSNW) and carbon nanotube (CNT) have been achieved in the nanochannels of anodic aluminum oxide (AAO) templates via sequentially electrodepositing CdSNWs and chemical vapor depositing CNTs. Transport measurements reveal that Ohmic-like behavior has been achieved, which may result from a very low energy barrier in the junction of CdSNW/CNT. Furthermore, three-segment heterostructures of CNT/CdSNW/CNT have also been obtained by adding a procedure of selectively etching part of the deposited CdSNWs before chemical vapor depositing CNTs. The approach could be exploited to build nanodevices and functional networks consisting of well-interconnected two- or three-segment nanoheterostructures.     

Flexible High‐Conductivity Carbon‐Nanotube Interconnects Made by Rolling and Printing

Applications of carbon nanotubes (CNTs) in flexible and complementary metal‐oxide‐semiconductor (CMOS)‐based electronic and energy devices are impeded due to typically low CNT areal densities, growth temperatures that are incompatible with device substrates, and challenges in large‐area alignment and interconnection. A scalable method for continuous fabrication and transfer printing of dense horizontally aligned CNT (HA‐CNT) ribbon interconnects is presented. The process combines vertically aligned CNT (VA‐CNT) growth by thermal chemical vapor deposition, a novel mechanical rolling process to transform the VA‐CNTs to HA‐CNTs, and adhesion‐controlled transfer printing without needing a carrier film. The rolling force determines the HA‐CNT packing fraction and the HA‐CNTs are processed by conventional lithography. An electrical resistivity of 2 mΩ · cm is measured for ribbons having 800‐nm thickness, while the resistivity of copper is 100 times lower, a value that exceeds most CNT assemblies made to date, and significant improvements can be made in CNT structural quality. This rolling and printing process could be scaled to full wafer areas and more complex architectures such as continuous CNT sheets and multidirectional patterns could be achieved by straightforward design of the CNT growth process and/or multiple rolling and printing sequences.     

Highly Flexible and Efficient Solar Steam Generation Device

Solar steam generation with subsequent steam recondensation has been regarded as one of the most promising techniques to utilize the abundant solar energy and sea water or other unpurified water through water purification, desalination, and distillation. Although tremendous efforts have been dedicated to developing high‐efficiency solar steam generation devices, challenges remain in terms of the relatively low efficiency, complicated fabrications, high cost, and inability to scale up. Here, inspired by the water transpiration behavior of trees, the use of carbon nanotube (CNT)‐modified flexible wood membrane (F‐Wood/CNTs) is demonstrated as a flexible, portable, recyclable, and efficient solar steam generation device for low‐cost and scalable solar steam generation applications. Benefitting from the unique structural merits of the F‐Wood/CNTs membrane—a black CNT‐coated hair‐like surface with excellent light absorbability, wood matrix with low thermal conductivity, hierarchical micro‐ and nanochannels for water pumping and escaping, solar steam generation device based on the F‐Wood/CNTs membrane demonstrates a high efficiency of 81% at 10 kW cm^?2, representing one of the highest values ever‐reported. The nature‐inspired design concept in this study is straightforward and easily scalable, representing one of the most promising solutions for renewable and portable solar energy generation and other related phase‐change applications.     

Nano Temperature Sensor Using Selective Lateral Growth of Carbon Nanotube Between Electrodes

This paper presents lateral growth of carbon nanotube (CNT) between two electrodes and its use as nano temperature sensor. Fabrication of electrodes is made by MEMS techniques. The CNT is grown selectively by microwave plasma chemical vapor deposition between two electrodes. After wire bonding, the grown CNT is tested and calibrated. The growth conditions of CNT, such as the flow rate of CH₄ or N₂ gas, are varied to obtain a high-quality CNT sensor. SEM is used to observe the shape and structure of CNT, while Raman spectrum analysis is used to indicate the degree of graphitization or amorphous structure in the CNT. The I-V curve of CNT is measured at different temperature, and a linear relationship between the electric resistance of CNT and the temperature is obtained. This result indicates that CNT can be used as a temperature sensor