Well-aligned Carbon Nanotubes Research Articles

On line construction of carbon nanotube/polytriazole composite films with high tensile and heat resistant properties

Carbon nanotubes (CNTs) have low densities and excellent mechanical properties due to their unique one-dimensional tubular structures, and are thus considered as an ideal reinforcement for lightweight and high-strength resin-based composites. However, it is still difficult to prepare high-performance composites with a high content of well-aligned CNTs. Besides, limited by the poor heat resistance of epoxy resin, it is still challenging to prepare composites with both high strength and heat resistance. In the present study, a simple on-line process is proposed to prepare CNT/polytriazole composite films. That is, a CNT assembly just having formed in a high temperature reactor is pulled through solution containers for shrinking and resin infiltration and subsequently winded on a drum to form a composite film. By optimizing the resin content and CNT alignment for better densification and inter-binding, the tensile strength of the composite film can reach a high level of 2.52 GPa with a decent elongation of 4.3 %. Associated with the use of the polytriazole resin, the composite could be cured at a low temperature of 80 °C but have a high glass transition temperature of 298 °C. Thus, the present technique is useful for preparing high-strength composite materials which are required to be able to be cured at low temperature but applied at high temperature.

High-Density Well-Aligned Single-Walled Carbon Nanotubes for Application as a Saturable Absorber with a High-Pass Filter Effect in an Erbium-Doped Ultra-Short-Pulse Fiber Laser

High-Density Well-Aligned Single-Walled Carbon Nanotubes for Application as a Saturable Absorber with a High-Pass Filter Effect in an Erbium-Doped Ultra-Short-Pulse Fiber Laser

Gas flow–directed growth of aligned carbon nanotubes from nonmetallic seeds

Kite growth is a process that utilizes laminar gas flow in chemical vapor deposition to grow long, well-aligned carbon nanotubes (CNTs) for electronic application. This process uses metal nanoparticles (NPs) as catalytic seeds for CNT growth. However, these NPs remain as impurities in the grown CNT. In this study, nanodiamonds (NDs) with negligible catalytic activity were utilized as nonmetallic seeds instead of metal catalysts because they are stable at high temperatures and facilitate the growth of low-defect CNTs without residual metal impurities. Results demonstrate the successful growth of over 100-μm-long CNTs by carefully controlling the growth conditions. Importantly, we developed an analysis method that utilizes secondary electron (SE) yield to distinguish whether or not CNTs grown from metal impurities. The absence of metallic NPs at the CNT tips was revealed by the SE yield mapping, whereas the presence of some kind of NPs at the same locations was confirmed by atomic force microscopy (AFM). These results suggest that most of the aligned CNTs were grown from nonmetallic seeds, most likely ND-derived NPs, via the tip-growth mode. Structural characterizations revealed the high crystallinity of CNTs, with relatively small diameters. This study presents the first successful use of nonmetallic seeds for kite growth and provides a convincing alternative for starting materials to prepare long, aligned CNTs without metal impurities. The findings of this study pave the way for more convenient fabrication of aligned CNT-based devices, potentially simplifying the production process by avoiding the need for the removal of metal impurities.

Hierarchical Nickel–Cobalt Hydroxide Composite Nanosheets-Incorporated Nitrogen-Doped Carbon Nanotubes Embedded with Nickel–Cobalt Alloy Nanoparticles for Driving a 2 V Asymmetric Supercapacitor

A class of electrode materials with favorable structures and compositions and powerful electrochemical (EC) properties are needed to boost the supercapacitor capacity significantly. In this study, an inventive technique was established to produce a well-aligned nickel-cobalt alloy nanoparticles-encapsulated N-doped carbon nanotubes with porous structure and good conductivity on carbon cloth (NiCo@NCNTs/CC) as a substrate. Then, nanosheets of nickel-cobalt layered double hydroxide (NiCo-LDH) were grown on NiCo@NCNTs/CC via a simple EC deposition method to construct a self-supported monolithic hierarchical nanosheets/nanotubes composite electrode of NiCo-LDH/NiCo@NCNTs/CC. In such a composite electrode, the NiCo@NCNTs can act as a good conductor and structural scaffold to grow NiCo-LDH nanosheets with a three-dimensional open and porous structure, which helps to improve the electron/ion-transfer performance, increase the number of exposed reactive sites, and inhibit the aggregation of NiCo-LDH nanosheets, thereby boosting the capacitance and stability. As a positive electrode, the NiCo-LDH/NiCo@NCNTs/CC hierarchical nanosheets/nanotubes electrode displays 1898 mF cm-2 (1262 A g-1) of high capacitance, long-term stability with a capacitance retention of around 100% after 8000 cycles, and nearly 103% Coulombic efficiency. After assembling into an asymmetric supercapacitor with a Co(OH)2/NiCo@NCNTs/CC negative electrode, 2 V of operating voltage with 73.1 μW h cm-2 (52.8 W h kg-1) of energy density was achieved. Our investigation gives a potential approach for constructing the integrated composite electrode of transition-metal compounds-carbon materials for high-performance supercapacitors.

Femtosecond Er-Doped All-Fiber Laser with High-Density Well-Aligned Carbon-Nanotube-Based Thin-Film Saturable Absorber.

We have studied the ultrafast saturation behavior of a high-density well-aligned single-walled carbon nanotubes saturable absorber (HDWA-SWCNT SA), obtained by a high-pressure and high-temperature treatment of commercially available single-wall carbon nanotubes (SWCNTs) and related it to femtosecond erbium-doped fiber laser performance. We have observed the polarization dependence of a nonlinear optical saturation, along with a low saturation energy level of <1 fJ, limited to the detector threshold used, and the ultrafast response time of <250 fs, while the modulation depth was approximately 12%. We have obtained the generation of ultrashort stretched pulses with a low mode-locking launching threshold of ~100 mW and an average output power of 12.5 mW in an erbium-doped ring laser with the hybrid mode-locking of a VDVA-SWNT SA in combination with the effects of nonlinear polarization evolution. Dechirped pulses with a duration of 180 fs were generated, with a repetition rate of about 42.22 MHz. The average output power standard deviation was about 0.06% RMS during 3 h of measurement.

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

Abstract 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.

Simultaneous production of hydrogen and carbon nanotubes from biogas: On the effect of Ce addition to CoMo/MgO catalyst

In this study, hydrogen and carbon nanotubes (CNTs) are simultaneously produced via a synergistic combined process of CO2 methanation (METH) and chemical vapor deposition (CVD) processes using biogas as a feedstock. METH process could upgrade CO2 containing biogas into CH4-rich gas which then decomposed into H2 and forming CNTs over CoMo/MgO catalyst by CVD process. The effects of Ce addition to CoMo/MgO were investigated. Comprehensive characterization confirms that all as-synthesized samples composed of well-aligned multi-walled carbon nanotubes (MWCNTs) with a narrow size distribution. The Ce addition improved CoMo dispersion on MgO, resulting in smaller and uniform CNTs. The small addition of Ce into CoMo/MgO catalyst could enhance the production CNTs yield. The higher Ce addition would, however, result in the CNTs yield decreased, attributed to a high basicity of CeO2 surface and a large coverage of CeO2 on the catalyst surface. The IG/ID increased with increased Ce addition, while the surface area monotonically decreased, attributed to a decrease in defects of nanotubes. In addition, this wisely combined process could result in a remarkable 100%CO2 elimination, while high CH4 conversion of 90% was obtained. The H2 production yield could gain more than 30 vol% with respect to H2 in the feed stream. The H2 yield and purity in the effluent gas stream were approximately 90%.

High-strength carbon nanotube/epoxy resin composite film from a controllable cross-linking reaction

Carbon nanotubes (CNTs) have been considered as potential reinforcements for various composites due to their excellent mechanical properties. However, it is still a challenge to prepare high-performance CNT/resin composites, resulting from the weak interfacial bonding between individual CNTs or that between CNTs and resin. Herein, a facile and effective method for preparing high-strength CNT/epoxy resin (EP) composite films is put forward, consisting of a controllable cross-linking treatment to the well-aligned CNT films and subsequent chemical filling with EP. Benefiting from the synergistic effects of optimized cross-linked CNTs and further enhancement by EP, the tensile strength of the obtained CNT/EP composite film reaches 2.5 GPa, which is about 5 times that of the raw CNT film. Our study might provide an effective strategy toward the preparation of high-performance CNT composite materials.

Direct growth of vertically well-aligned carbon nanotube arrays on atomic layer deposition of ZnO films

Plasma-enhanced chemical vapor deposition (PECVD) was used to prepare vertically well-aligned carbon nanotube arrays on atomic layer deposition (ALD) of zinc oxide (ZnO) films with acetylene (C2H2) and ammonia (NH3). The mechanisms of their nucleation and initial growth were analyzed on ZnO films, and the activation energy was also calculated to be about 60.7 kJ/mol. Generally, the reactivity of NH2 radicals was higher than that of H2 molecules and H radicals, so the activation energy was lower for the nucleation and initial growth of vertically aligned carbon nanotube arrays (VACNTs) with NH2 radicals, compared with H radicals and H2 molecules.

An Ingenious Strategy to Integrate Multiple Electrocatalytically Active Components within a Well-Aligned Nitrogen-Doped Carbon Nanotube Array Electrode for Electrocatalysis

In this paper, an ingenious strategy was developed to construct a well-aligned nitrogen-doped carbon nanotube (NCNT) array electrode integrated with multiple electrocatalytically active components ...

Aligning dense carbon nanotube arrays

Device Technology Although semiconducting carbon nanotubes (CNTs) are promising candidates to replace silicon in transistors at extremely small dimensions, their purity, density, and alignment must be improved. Liu et al. combined a multiple dispersion sorting process, which improves purity, and a dimension-limited self-alignment process to produce well-aligned CNT arrays on a 10-centimeter silicon wafer. The density is sufficiently high (100 to 200 CNTs per micrometer) that large-scale integrated circuits could be fabricated. With ionic liquid gating, the performance metrics exceeded those of conventional silicon transistors with similar dimensions. Science , this issue p. [850][1] [1]: /lookup/doi/10.1126/science.aba5980

Aligned, high-density semiconducting carbon nanotube arrays for high-performance electronics.

Single-walled carbon nanotubes (CNTs) may enable the fabrication of integrated circuits smaller than 10 nanometers, but this would require scalable production of dense and electronically pure semiconducting nanotube arrays on wafers. We developed a multiple dispersion and sorting process that resulted in extremely high semiconducting purity and a dimension-limited self-alignment (DLSA) procedure for preparing well-aligned CNT arrays (within alignment of 9 degrees) with a tunable density of 100 to 200 CNTs per micrometer on a 10-centimeter silicon wafer. Top-gate field-effect transistors (FETs) fabricated on the CNT array show better performance than that of commercial silicon metal oxide-semiconductor FETs with similar gate length, in particular an on-state current of 1.3 milliamperes per micrometer and a recorded transconductance of 0.9 millisiemens per micrometer for a power supply of 1 volt, while maintaining a low room-temperature subthreshold swing of <90 millivolts per decade using an ionic-liquid gate. Batch-fabricated top-gate five-stage ring oscillators exhibited a highest maximum oscillating frequency of >8 gigahertz.

Construction of porous interface on CNTs@NiCo-LDH core-shell nanotube arrays for supercapacitor applications

Carbon-based materials have always been a research hotspot in the field of supercapacitors due to their unique stability under a wide range of potential. However, most of carbon-based materials used in supercapacitors cannot maximize the intrinsic capacitance performance due to the limited internal mass transfer. Herein, hierarchical well-aligned nanotube arrays with porous diffusive interfaces are in-situ fabricated by the self-templated effect of ZnO nanorod and ZIF-8 nano-shell. In this unique architecture, the well-aligned carbon nanotubes (CNTs) growing firmly on carbon fibers (CFs) can not only improve the mass transfer of ions onto the NiCo-LDHs surfaces, but also used as good backbones for the subsequent loading of NiCoLDHs nanosheets with high capacity. The optimized core-shell electrode displays an excellent capacity of 176.33 mAh g−1 at 1 A g−1. The as-prepared CNTs@NiCo-LDH//ZIF-8 derived carbon asymmetric supercapacitor (ASC) exhibits a high energy density of 37.38 Wh kg−1 at 800 W kg−1 and an outstanding cycling stability (90.22% retention after 5200 cycles), which offers a new synthesis strategy for design of carbon-based materials in superior electrochemical energy storage applications.

Identification of appropriate catalyst system for the growth of multi-walled carbon nanotubes via catalytic chemical vapor deposition process in a single step batch technique

Large quantities of well-aligned and purified Carbon nanotubes (CNTs) are to be produced for commercial applications. For this purpose, the design of an efficient catalyst system is very essential, which should have high catalytic activity, stability, and high diffusion of carbon. In this investigation, an attempt has been made to find a possible catalyst system that supports high yield with a defect-less structure of CNTs. Catalytic chemical vapor deposition (CCVD) single step batch process was used to synthesize CNTs in a single experiment (run) using six different mono-metallic and bi-metallic catalysts (NiO, CoO, CuO, NiO/CuO, NiO/CoO, CoO/CoO) systems. The catalyst materials were synthesized by the impregnation method. The mono-metallic and bi-metallic catalyst particles were characterized by SEM, XRD, and TGA. The carbon products obtained from different catalysts compositions were analyzed using FESEM, HRTEM, and Raman spectroscopy. The yield percentage of multi-walled CNTs was calculated. The aerial density of the CNTs grown on different catalyst compositions was found using image J technique. The diameter distribution of both catalyst compositions and grown CNTs were evaluated using their respective SEM and FESEM images. From this investigation, it was found that NiO/CuO produced higher yield of CNTs with well-aligned structure. CuO/CoO catalyst system produced amorphous carbon. The bi-metallic catalyst compositions grow higher yield and well-aligned CNTs as compared to mono-metallic catalyst systems.

Controllable synthesis of N-doped aligned carbon nanotubes from melamine-based carbon by water-assisted chemical vapor deposition

N-doped well-aligned thin multiwall carbon nanotubes (CNTs) have been prepared by a facile water-assisted chemical vapor deposition (CVD) process using melamine as both the carbon precursor and N-dopant and ferrocene as both the catalyst and carbon precursor. It is shown that the synthetic temperature has strong effects on the growth of carbonaceous structure. Carbon films started to grow at reaction temperature of 700 °C, and the optimal temperature for the synthesis of aligned CNTs, based on the experiment results, was found to be 900 °C. The lengths of the CNTs can be tuned by changing the annealing time of the pyrolysis process, it could reach as long as 40.2 μm. The atomic percentage of nitrogen doping in aligned CNTs could be achieved to 1.71%. It was found that there were many joints and defects in the as-prepared CNTs which may offer more nucleation sites on the chemically inert CNT surface for various specialized applications such as supercapacitor.

An optimized resistive CNT-based gas sensor with a novel configuration by top electrical contact

The paper proposes a new fabrication method of a resistive gas sensor made of vertically aligned carbon nanotubes (CNT) by the perforated electrode. This new configuration can be also utilized with vertically aligned nanomaterial such as ZnO wires. This method contains two aspects, which are getting top electrical contact from MWCNTs and devising hexagonal pattern holes on the sensor surface to ease the gas flow through the sensor. Reaching ambient molecules to these dense CNT forests is always of the essence; also, the top electrical contact of the CNTs is a fabrication challenge. The high sensitivity of proposed CNT-based sensor is attributed to their collective large porous surface along with etched circular holes located at the apexes and center of a hexagonal pattern on sensor top contact. For optimal sensor performance, the simulation approach by ANSYS-FLUENT software has optimized circular holes diameters and distances. The fabrication process proposes an oxygenated plasma treated CNTs with top electrical contact devised by a certain simple method for the very first time. Top electrical contact has been fabricated possible by the procedure of immersing the CNTs in viscosity liquid and providing electrical contact using conductive paste. Well-aligned multi-walled carbon nanotubes (MWCNT) have been grown on glass substrate placed into DC-PECVD unit bearing approximately temperature of 350 °C. In this paper, the resistivity of carbon nanotubes at different temperatures for the ambient gas and linear sensitivity to oxygen gas has been investigated. The sensors with larger diameter nanotubes are more sensitive. Etching patterned holes with 200 μm diameter enhances the sensitivity up to 50%.

Realizing Controllable Carbon Nanotube Arrays for Soft Devices by Asymmetric Langmuir–Blodgett and Hydrophilization Process

Well-aligned Carbon nanotube (CNT) arrays are expected by flexible and stretchable devices. In this paper, an asymmetric Langmuir-Blodgett (LB) method and inorganic hydrophilization method have been proposed, with which well-aligned CNT arrays on soft substrates like polyethylene naphthalate, polyimide and polydimethylsiloxane have been realized. After depositing 50 nm SiO2 for hydrophilization, the water contact angle has been significantly reduced for different substrates. The surface roughness and flexibility have also been characterized to analyze their effect on device performance. The nanotube density in the arrays can be controlled to 10-25 tubes/μm 2 , 25-35 tubes/μm 2 or 35-45 tubes/μm 2 by tuning the surface pressure during the LB process. With aligned semiconducting CNT arrays as channel and anisotropic metallic CNT network as gate/source/drain electrodes, all-carbon nanotube transistors on PI substrate have been fabricated for demonstration. The fabricated devices show a subthreshold swing of 92.9 mV/dec, a carrier mobility of 15.32 cm 2 /Vs, and an on/off current ratio of 4.51 × 10 2 . More importantly, with 50 nm thick gate dielectrics, the changes of threshold voltage and carrier mobility are within 16.62% and 28.78%, respectively, even after bending 1000 times under a curvature radius of 3.66 mm.

Facile active control of a pulsed erbium-doped fiber laser using modulation depth tunable carbon nanotubes

Short pulsed fiber lasers have been widely made using single-walled carbon nanotubes as a saturable absorber (SA). However, most of the currently used devices can only operate in one determined operation state with an unchangeable modulation SA depth in the cavity, which significantly limits their application in photonic devices. In this paper, well-aligned carbon nanotube arrays are synthesized using zeolite AlPO4-5 as a template, which features anisotropic optical absorption. The linear optical absorption of the as-synthesized carbon nanotube arrays can easily be tuned by adjusting a polarization controller, thus providing a tunable modulation depth for the carbon nanotube SA. By exploiting this SA in an erbium-doped fiber laser cavity, both Q-switched and mode-locked pulsed lasers are achieved by simply adjusting a polarization controller under a fixed pump power of 330 mW. In addition, the repetition rate of the Q-switching and pulse duration of the mode-locking can be tuned according to the variation of modulation depth. Moreover, soliton molecules can be obtained when the modulation depth of the SA is 4.5%.

A New Mitigation Method for Space Robot Charging Effect Based on CNTs

Autonomous space robot will be widely used to complete various space missions in future. Unfortunately electrostatic surface discharge (ESD) induced by space plasma environment may produce one of the most common anomaly in space robots. Liquid Metal Ion Source (LMIS) is one of the effective mitigation methods for space robot charging effect. But as a devices for space-robots charging mitigation equipment, has strict requirements to its weight and volume. The present LMIS can only work at a very high voltage, so the weight and volume of LMIS isn’t suitable for space robot. Here we propose that carbon nanotubes (CNTs) can be used as capillary-type emitters in LMIS to meet the challenge. Well-aligned CNT arrays are synthesized on self-ordered hexagonal porous anodic aluminum oxide (AAO) template using chemical vapor deposition (CVD) method. The CNTs obtained are monodispersed and have open tip, which indicates that they have the similar geometry to the present capillary-type emitters in LMIS. So the LMIS made of CNTs can emit ions at a very lower voltage. A new mitigation device for space robot charging effects with very small weight and volume can be developed. The key steps for fabricating CNT emitters are presented.

Aligned-SWCNT film laminated nanocomposites: Role of the film on mechanical and electrical properties

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.