Free-standing Carbon Nanotube Research Articles

Heteroatom doped graphitic carbon nanotubes as freestanding anodes for advanced potassium-ion batteries

Owing to its higher earth element reserve and similar chemical properties to lithium, potassium ion batteries (PIBs) have been regarded as a potential alternative to lithium-ion batteries. And considering the relatively larger ionic radius of potassium, available electrode materials need to be equipped with enough space for volume expansion during charge-discharge cycles, thus graphitic carbon nanomaterials with adjustable layer spacing gradually come into researcher's version. Here with copper nanowires serving as growth template and organic polyvinyl pyrrolidone (PVP) providing carbon source, freestanding and ultra-light graphitic carbon nanotube (GCNT) aerogels were simply assembled and annealed, which were directly used as anodes of PIBs. Annealing parameters (temperature and atmosphere) were adapted to regulate the lattice order and interlayer spacing of GCNTs, and N, O heteroatoms derived from PVP were directly doped into the carbon lattice during thermal annealing, to optimize and enhance the cycle capacity and rate performance of GCNT anodes. The electrochemical potassium storage mechanism of GCNTs was also quantitatively analyzed. Most of the potassium ions are reversibly stored by squeezing into and escaping from the carbon lattice, and simultaneously oxygen-containing functional groups with different chemical states also offer active redox sites and dedicate partial capacity. Therefore, our assembled GCNTs with large lumen are expected to sandwich-like load with active substances efficiently, further constructing next-generation PIBs with excellent performance.

Improvement of Electrical and Thermal Properties of Carbon Nanotube Sheets by Adding Silver Nanowire and Mxene for an Electromagnetic-Interference-Shielding Property Study.

Hybrid carbon nanotube (CNT) sheets were fabricated by mixing CNTs with silver nanowires (AgNWs) and MXene to study their electromagnetic-interference (EMI)-shielding properties. CNT/AgNW and CNT/MXene hybrid sheets were produced by ultrasonic homogenization and vacuum filtration, resulting in free-standing CNT sheets. Three different weight ratios of AgNW and MXene were added to the CNT dispersions to produce hybrid CNT sheets. Microstructure characterization was performed using scanning electron microscopy, and the Wiedemann-Franz law was used to characterize transport properties. The resulting hybrid sheets exhibited improved electrical conductivity, thermal conductivity, and EMI-shielding effectiveness compared to pristine CNT sheets. X-band EMI-shielding effectiveness improved by over 200%, while electrical conductivity improved by more than 1500% in the hybrid sheets due to a higher charge-carrier density and synergistic effects between nanomaterials. The addition of AgNW to CNT sheets resulted in a large improvement in electrical conductivity and EMI shielding; however, this may also result in increased weight and sample thickness. Similarly, the addition of MXene to CNT sheets may result in an increase in weight due to the presence of the denser MXene flakes.

N-doped carbon nanotube arrays Encapsuled with cobalt‑nickel alloy as superior free-standing electrodes for ultrahigh-rate hydrogen peroxide production

Electrocatalytic oxygen reduction via the two-electron pathway (2e−-ORR) is an environmentally friendly and promising route for hydrogen peroxide (H2O2) production. Carbon-based catalysts with transition metal species have been widely investigated due to their high tunability. However, the H2O2 production performance of such catalysts is still far from the requirement of practical applications, owing to their contradiction between durability and ORR activity/selectivity. In this work, metal alloy is encapsulated within the free-standing N-doped carbon nanotube arrays, named NiCo-CNTs-x (x represents the duration of the cation substitution process in hours), to precisely regulate the activity and selectivity of nitrogen sites on the surface of the carbon layer, meanwhile hindering the dissolution of alloy inside the CNTs, thus realizing long-term stability and high-activity catalysis for 2e−-ORR. Therefore, the NiCo-CNTs-30 demonstrates high activity (onset potential around 0.7 V) and selectivity (greater than 85% within the range of 0–0.8 V), and delivers a high yield of 11.7 mg L−1 h−1 with no current decay or structural damage within 24 h, showcasing its exceptional long-term stability. The catalyst can also effectively degrade organic dyes, making it highly promising for industrial applications.

Scalable, flexible, ultra-strong, free-standing papery all carbon nanotube membrane with excellent separation and antifouling properties

Carbon nanotube (CNT) based membranes have shown tremendous promise for water purification. However, fabricating free-standing all CNT membranes with excellent separation and antifouling properties remains challenging. Here, a densified flexible, ultra-strong, free-standing papery all CNT membrane with excellent separation and antifouling properties is reported. The chemically densified free-standing CNT membrane has an extremely high tensile strength up to 330 MPa, four times higher than the original CNT membrane and one order of magnitude higher than most polymeric membranes. The negatively charged surface of the densified CNT membrane enables efficient separation of two dyes even with similar molecular sizes. Meanwhile, the densified CNT membrane exhibits superior antifouling performance during the filtration of dyes, humic acid and bovine serum albumin solutions, and oil-in-water emulsions due to its reinforced hydration layer induced by the hydrophilic functional groups resulting from chemical densification. The chemically densified CNT membrane shows not only excellent separation and antifouling performance, but also superior long-term stability and regeneration performance in the filtration of foulant-containing solutions. This study may pave the way for large-scale application of densified free-standing all CNT membranes in the realm of water treatment.

Free-Standing Carbon Nanotube Embroidered Graphene Film Electrode Array for Stable Neural Interfacing.

Implantable neural probes that are mechanically flexible yet robust are attractive candidates for achieving stable neural interfacing in the brain. Current flexible neural probes consist mainly of metal thin-film electrodes integrated on micrometer-thick polymer substrates, making it challenging to achieve electrode-tissue interfacing on the cellular scale. Here, we describe implantable neural probes that consist of robust carbon nanotube network embroidered graphene (CeG) films as free-standing recording microelectrodes. Our CeG film microelectrode arrays (CeG_MEAs) are ultraflexible yet mechanically robust, thus enabling cellular-scale electrode-tissue interfacing. Chronically implanted CeG_MEAs can stably track the activities of the same population of neurons over two months. Our results highlight the potential of ultraflexible and free-standing carbon nanofilms for stable neural interfacing in the brain.

Enhanced Thermal Conductivity of Free-Standing Double-Walled Carbon Nanotube Networks.

Nanomaterials are driving advances in technology due to their oftentimes superior properties over bulk materials. In particular, their thermal properties become increasingly important as efficient heat dissipation is required to realize high-performance electronic devices, reduce energy consumption, and prevent thermal damage. One application where nanomaterials can play a crucial role is extreme ultraviolet (EUV) lithography, where pellicles that protect the photomask from particle contamination have to be transparent to EUV light, mechanically strong, and thermally conductive in order to withstand the heat associated with high-power EUV radiation. Free-standing carbon nanotube (CNT) films have emerged as candidates due to their high EUV transparency and ability to withstand heat. However, the thermal transport properties of these films are not well understood beyond bulk emissivity measurements. Here, we measure the thermal conductivity of free-standing CNT films using all-optical Raman thermometry at temperatures between 300 and 700 K. We find thermal conductivities up to 50 W m-1 K-1 for films composed of double-walled CNTs, which rises to 257 W m-1 K-1 when considering the CNT network alone. These values are remarkably high for randomly oriented CNT networks, roughly seven times that of single-walled CNT films. The enhanced thermal conduction is due to the additional wall, which likely gives rise to additional heat-carrying phonon modes and provides a certain resilience to defects. Our results demonstrate that free-standing double-walled CNT films efficiently dissipate heat, enhancing our understanding of these promising films and how they are suited to applications in EUV lithography.

Free-Standing CNT Film for Interlaminar Toughening: Insight into Infiltration and Thickness Effects.

Carbon fiber reinforced polymer composites have the advantages of being lightweight, having high strength and designability, and having been extensively used. However, the interlaminar toughness and delamination resistance of these composites are relatively poor due to their laminated structure and intrinsic brittleness of resin matrix. In this paper, commercialized free-standing carbon nanotube (CNT) films, drawn from CNT forests, were used to toughen the interlaminar interfaces of the composites. The effects of resin infiltration state and thickness of CNT films on the interlaminar toughening effect were systematically investigated. The results show that the pre-infiltration treatment of CNT films with acetone diluted epoxy resin solution can effectively improve the degree of resin infiltration. Compared with the samples containing untreated CNT film, the Mode I and Mode II interlaminar fracture toughness of the treated samples were significantly improved. The GIC reached a maximum of 1412.42 J/m2 at a CNT film thickness of 5 µm, which was about 61.38% higher than that of the baseline. At a CNT film thickness of 15 µm, the GIIC reached a maximum value of 983.73 J/m2, approximately 67.58% higher than that of the baseline. The corresponding toughening mechanisms were also systematically analyzed.

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.

“Wane and wax” strategy: Enhanced evolution kinetics of liquid phase Li2S4 to Li2S via mutually embedded CNT sponge/Ni-porous carbon electrocatalysts

The lithium-sulfur battery (Li-S) has been considered a promising energy storage system, however, in the practical application of Li-S batteries, considerable challenges remain. One challenge is the low kinetics involved in the conversion of Li2S4 to Li2S. Here, we reveal that highly dispersed Ni nanoparticles play a unique role in the reduction of Li2S4. Ni-porous carbon (Ni-PC) decorated in situ on a free-standing carbon nanotube sponge (CNTS/Ni-PC) enriches the current response of liquid phase Li2S4 and Li2S2 around the cathode more than 8.1 and 5.7 times higher than that of the CNTS blank sample, respectively, greatly boosting the kinetics and decreasing the reaction overpotential of Li2S4 reduction (lower Tafel slope and larger current response). Thus, with the same total overpotential, more space is provided for the concentration difference overpotential, allowing the more soluble polysulfide intermediates farther away from the surface of the conductive materials to be reduced based on the “wane and wax” strategy, and significantly improving the sulfur utilization. Consequently, S@CNTS/Ni-PC delivers excellent rate performance (812.4 mAh·g−1 at 2C) and a remarkable areal capacity of 10.1 mAh·cm−2. This work provides a viable strategy for designing a target catalyst to enhance the conversion kinetics in the Li2S4 reduction process.

Plasma-enhanced atomic layer deposition of ruthenium metal on free-standing carbon nanotube forest for 3D flexible binder-less supercapacitor electrodes

Plasma-enhanced atomic layer deposition of ruthenium on functionalized free-standing multi-walled carbon nanotube (MWCNT) forest directly grown on a stainless steel mesh as a flexible supercapacitor electrode is done by a zero-oxidation state precursor and nitrogen plasma. Using this method for the fabrication of 3D flexible supercapacitor electrodes eliminates the need for any binder component and solution-based synthesis step as well as the production of any toxic by-products. Moreover, it enables the utilization of the entire high-surface-area MWCNTs and it alleviates the Ru agglomeration issue typically found in solution-based synthesis techniques. Accordingly, ruthenium is successfully deposited on the entire length of the carbon nanotubes in various process temperatures and plasma exposure durations with a thickness range of 15–60 nm. Electrochemical characterization of the electrodes shows a significant improvement in the capacitance of Ru coated MWCNT compared to bare MWCNT due to the additional surface faradaic redox reactions. Cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical impedance spectroscopy (EIS) are carried out to evaluate the electrochemical performance of the fabricated electrodes. The capability of the 3D flexible electrode is evaluated in different bending angles of 60, 80, and 180° and twisting conditions. Capacitance as high as 1834.5 mF.cm−2 (393 F.g−1) with a very low charge transfer resistance of 5.49 Ω.cm−2 is achieved that shows >400 % improvement in capacitance compared to bare MWCNTs. A capacitance retention of 92 % after 1000 CV cycles is achieved.

Defect-Induced Adsorption Switching (p- to n- Type) in Conducting Bare Carbon Nanotube Film for the Development of Highly Sensitive and Flexible Chemiresistive-Based Methanol and NO2 Sensor.

Lightweight and flexible gas sensors are essentially required for the fast detection of toxic gases to pass on the early warning to deter accident situations caused by gas leakage. In view of this, we have fabricated a thin paper-like free-standing, flexible, and sensitive carbon nanotube (CNT) aerogel gas sensor. The CNT aerogel film synthesized by the floating catalyst chemical vapor deposition method consists of a tiny network of long CNTs and ∼20% amorphous carbon. The pores and defect density of the CNT aerogel film were tuned by heating at 700 °C to obtain a sensor film, which showed excellent sensitivity for toxic NO2 and methanol gas in the concentration range of 1-100 ppm with a remarkable limit of detection ∼90 ppb. This sensor has consistently responded to toxic gas even after bending and crumpling the film. Moreover, the film heat-treated at 900 °C showed a lower response with opposite sensing characteristics due to switching of the semiconductor nature of the CNT aerogel film to n-type from p-type. The annealing temperature-based adsorption switching can be related to a type of carbon defect in the CNT aerogel film. Therefore, the developed free-standing, highly sensitive, and flexible CNT aerogel sensor paves the way for a reliable, robust, and switchable toxic gas sensor.

Polyoxometalate-immobilized carbon nanotube constructs triggered by host-guest assembly result in excellent electromagnetic interference shielding.

In the era of fifth-generation networks and the Internet of Things, new classes of lightweight, ultrathin, and multifunctional electromagnetic interference (EMI) shielding materials have become inevitable prerequisites for the protection of electronics from stray electromagnetic signals. In the present study, for the first time, we have designed a unique nanohybrid composed of a copper-based polyoxometalate (Cu-POM)-immobilized carbon nanotube construct, having a micron (∼100 μm)-level thickness, through a facile vacuum-assisted filtration technique. In this course of study, a total of four Cu-POMs, two from each category of Keggin and Anderson bearing opposite charges, i.e., positive and negative, have been rationally selected to investigate the effects of the host-guest electrostatic interaction between CNT and POMs in the EMI shielding performance. This approach of the host-guest electrostatic assembly between Cu-based polyanionic oxo clusters and counter-charged CNTs in the construct synergistically enhances the EMI shielding performance compared to the individual components dominated by 90% absorption in the X-band (8.2-12.4 GHz) frequency regime. Further, mutable EMI SE can be achieved by tuning the concentration of POMs and CNTs with different weight ratios. Such Cu-POM-immobilized CNT constructs demonstrating excellent shielding (∼45 dB) are not amenable via any other conventional routes, including flakes and dispersion.

Micro- and Macrostructures of Aligned Boron Nitride Nanotube Arrays.

Boron nitride nanotubes (BNNTs) possess a broad range of applications because of several engineering-relevant properties, including high specific strength and stiffness, thermal stability, and transparency to visible light. The morphology of these nanoscale fibers must be controlled to maximize such properties, which can be achieved by synthesizing long aligned arrays of crystalline hexagonal boron nitride (hBN) nanotubes. Herein, we synthesize high-quality millimeter length, vertically aligned (VA-) BNNTs using free-standing carbon nanotube (CNT) arrays as scaffolds. In addition to high optical transparency of the VA-BNNTs, we also demonstrate several micro- and macrostructures of BNNTs via patterning and/or postprocessing of the arrays, including engineering of either disconnected or interconnected tubes in VA-, horizontally aligned (HA-), or coherently buckled BNNTs. The internanotube spacings and interconnections between aligned BNNT can thus be tailored to create BN macrostructures with complex shapes and advantaged morphologies for hierarchical materials and devices.

Controlled optical near-field growth of individual free-standing well-oriented carbon nanotubes, application for scattering SNOM/AFM probes.

Exploiting localized heat-generation density and the resulting enhanced temperature-rise for controlled growth of carbon nanotubes (CNTs) is reported, and its potentials for batch-production of high-quality CNT probes are demonstrated. Optical near field chemical vapor deposition (ONF-CVD) benchtop fabrication schemes are developed for the localized integration of individual well-aligned carbon nanotubes without bending/buckling exactly at desired nanoscale sites. It is demonstrated that generating self-aligned catalyst nanoparticles superimposed on top of silicon nanotips, along with near-field induced absorption confinement, provide the ability to localize the generated heat at the nanotips apexes, and control the CNT growth locations. The nanoscale maskless controllability of the growth site is shown by properly tailoring ONF-CVD conditions to overcome overall heat exposure of the substrate for selective activation of catalyst nanoparticles located at apexes, from those dispersing all over the tips. The calculated local power densities and temperature profiles of the simulated tips, clearly demonstrate the confined heat and optimal gradient of generated temperature rise as the main factors affecting the growth. In addition to determining necessary processing conditions to control the localization and orientation of the growth, parameters affecting the length and diameter of the localized individually grown nanotubes are also presented. Optical near-field-based growth schemes can be extended for localized maskless fabrication of other nanoscale devices, beyond the diffraction limit, using photothermal effects.

Facile electro-thermal igniters based on freestanding CNTs films for the ignition of energetic materials

Facile electro-thermal igniters based on freestanding carbon nanotubes (CNTs) films are investigated for exploring the use of igniting energetic materials. Increases in electro-thermal temperature, dynamic pictures of ignition process, and temporal changes of voltage, current and resistance as well as the ignition ability of freestanding CNTs film–based igniters with different film thickness are compared with their counterparts with paper-like substrate. The results demonstrated that freestanding CNTs film–based igniters had faster rise in electro-thermal temperature and better ignition ability than their counterparts. The ignition delay of loaded energetic materials employing freestanding CNTs film based–igniters was only 40%–67% of their counterparts depending on the film thickness. Freestanding CNTs film–based igniters with larger thicknesses were more suitable for the rapid ignition of energetic materials. The shortest ignition delay for igniters of 8 × 8 mm bridge area under 20 V was less than 80 ms. The initial temperature rise rate of igniters was crucial for deciding the ignition delays of loaded energetic materials. The presence of substrates in CNTs film–based igniters impeded their temperature rise rate and thus increased the ignition delay of loaded energetic materials. Moreover, due to the property of negative resistance-temperature coefficient, freestanding CNTs film–based igniters are favourable for the realization of low voltage ignition of energetic materials.

The Effect of Ionic Carriers and Degree of Solidification on the Solid-State Electrolyte Performance for Free-Standing Carbon Nanotube Supercapacitor

To eliminate electrolyte leakage, the development of safe and flexible supercapacitors necessitates solid-state electrolytes which integrate both high mechanical and electrochemical capabilities. Quasi-solid-state electrolytes, which constitute a polymer matrix along with an aqueous electrolytic phase, are a viable answer to this problem. Recently, gel electrolytes have gained a lot of attention in flexible and wearable electronic devices due to their remarkable advancements. However, the limitation in the multi-functional abilities and high-performance in such gels hinders the practical usage of such devices. On the electrochemical perspective, the performance of the gel electrolyte depends on the type of ionic carrier (acidic, alkaline, or salt-based), size of the ion, solvent concentration, type of polymer, as well as the interaction between the polymer and other components. Moreover, the performance of the electrolyte differs with the electrode-electrolyte interface and thus is highly dependent on the electrode material. For this reason, it is vital to carry a parametric study to evaluate the effect of the above stated. The aim of this study is to investigate the effect of changing the ionic carrier (namely H3PO4, KOH and LiCl) as well as the solvent concentration on architecturally engineered PVA-based electrolytes’ performance in free-standing CNT supercapacitor using a bio-based compound, cellulose as a binder. The dependence of the electrolyte’s mechanical structure for long term stability is further evaluated by using the optimized concentration of each (H3PO4, KOH and LiCl) by freezing and de-freezing the gel to form membrane-like films, as a result of the increased physical cross-linking. The supercapacitors are studied for their capacitance, charge/discharge capabilities as well their long-term stability and also compared with aqueous electrolyte for the three aforementioned ionic carriers.

Pore structure changes in free-standing single-wall carbon nanotube film on vacuum high-temperature annealing

• Highly pure and crystalline free-standing SWCNT films were fabricated. • Impurities can be removed completely by vacuum high-temperature annealing. • Vacuum annealing can improve crystallinity of SWCNT film. • Vacuum annealing eliminates nanowindows and other defects from SWCNT film. The fabrication of free-standing single-wall carbon nanotube (SWCNT) film is promising for better understanding of SWCNT and many applications. Here we fabricated highly pure and crystalline free-standing SWCNT film using vacuum high-temperature annealing. Impurities can be removed thoroughly by vacuum annealing at 2073 K and 10 −1 Pa for 3 h. Also, the vacuum annealing was quite efficient for removing nanowindows and improving crystallinity of the SWCNT film. The transmission electron microscopic observation and X-ray diffraction confirmed almost no change in the average tube diameter and bundle structure of SWCNT. The vacuum high-temperature annealing decreases the N 2 adsorption amount at 77 K by more than half, supporting closing nanowindows on graphene wall of SWCNT by the vacuum annealing. Our free-standing SWCNT film is expected to promote a fundamental understanding of electrochemical energy issues by the application these films as the well-characterized electrodes.

Morphology investigation on direct growth ultra-long CNTs by chemical vapour deposition method for high performance HER applications

Carbon nanotube (CNT) is prepared by chemical vapor deposition method and their electrochemical behaviors for instance oxygen evolution (OER) and hydrogen evolution (HER) reaction have been successfully studied. In recent times, Pt-free electrocatalysts have been greatly attractive in electrochemical hydrogen evolution reactions for the replacement of fossil fuels and development of sustainable energy carriers. Chemical vapor deposition method was used as an efficient way to synthesize CNTs directly. The as prepared free-standing and multifunctional CNT electrodes are used for overall water splitting applications. In this work, we have designed CNT as electrode material as well as current collector using Ni-foil and Ni-foam substrate and their fundamental characterizations confirm the structural, morphological behaviors of CNTs. Moreover, the well-ordered growth of CNT was obtained in Ni-foam CNTs 1 and 2, whereas in the Ni foil CNTs 1 and 2 less growth of CNT and amorphous carbon sponge was exceeded, which was further confirmed by the SEM images. The achieved electrochemical HER results displayed that the Ni-foam-CNT-2 exhibited lower overpotential, smallest Tafel slope and lower resistance value of 110 mV, 240 mV/dec and 0.24 Ω respectively. Moreover, Ni-foam-CNT-2 revealed excellent stability with 86.6 % retention over 20 h. Hence, it is one of the cost-effective and reliable materials for electrochemical hydrogen evolution reaction.

Multiwalled Carbon Nanotube-Based Freestanding Filters for Efficient Removal of Fine Particulate Matters (PM0.3), Microplastics (MP0.3), and Bioaerosols

Air pollution caused by various hazards such as particulate matters (PM), microplastics (MP), bioaerosols (BA), etc. has become a global concern for public health across the globe. In recent decades, nanofiltration-based air purification techniques have rapidly evolved as a viable solution to address worldwide air pollution challenges. Herein, we report a simple, cost-effective, and scalable technique for the fabrication of lightweight, freestanding, and flexible multiwalled carbon nanotube (MWCNT) membranes for air filter applications. The developed membrane filter possesses excellent capturing efficiency of more than 99% for PM0.3, MP0.3, and BA. Additionally, the developed membrane has also been well investigated in terms of hydrophobic behavior (contact angle ∼148 ± 7°), narrow pore size (∼16 nm), packing density (∼0.65 g/cc), porosity (∼56%), pressure drop (∼139.7 Pascal), flexibility, and reusability, reflecting its self-cleaning feature, physical sieve characteristics, adaptability, and commercialization. Thus, the filter developed in this work shows its potential utility toward the removal of indoor pollution and in air filter industries as well.

High-Performance Cold Cathode X-ray Tubes Using a Carbon Nanotube Field Electron Emitter.

A cold cathode X-ray tube was fabricated using a carbon nanotube (CNT) field electron emitter made by a free-standing CNT film which is composed of a highly packed CNT network. A lot of CNT bundles with a sharp tip are vertically aligned at the edge of the thin CNT film with a length of 10 mm and a thickness of 7 μm. The cold cathode X-ray tube using the CNT field emitter presents an extremely high tube current density of 152 A/cm2 (corresponding to tube current of 106.4 mA), the electron beam transmittance of 95.2% and a small focal spot size (FSS) of 0.5 mm. In addition, the cold cathode X-ray tube also shows stable lifetime during 100 000 shots. High emission current density of the cold cathode X-ray tube is mainly attributed to a lot of electron emission sites at an edge of the CNT film. The small FSS is caused by an ensemble of the CNT field electron emitter made by a free-standing thin CNT film and the optimized curve-shape elliptical focusing lens. Based on obtained results, the cold cathode X-ray tube can be widely used for various X-ray applications such as medical diagnosis systems and security check systems in the future.