Carbon Nanotube Arrays Research Articles

W Clusters In Situ Assisted Synthesis of Layered Carbon Nanotube Arrays on Graphene Achieving High-Rate Performance.

W atoms/clusters are employed to in situ assist the development of layered vertically aligned carbon nanotube arrays (VACNTs) through hot-filament-assisted chemical vapor deposition (HFCVD) with liquid binary Fe3O4/AlOx catalysts. The hot W filament was utilized to in situ evaporate atomic W and form W clusters on Fe catalysts, which have a strong impact on the growth of layered VACNT arrays. The migration and Ostwald ripening of Fe catalysts are found to be suppressed immediately with more W clusters deposition during CNT growth. Through controlling the deposition of W clusters, the electrochemical energy storage performance of as-prepared layered VACNT arrays is also tunable as electrodes of ion-based supercapacitors. The layered VACNT arrays can achieve a high capacity of 83.1 mF cm-2 and possess desirable rate performance due to the suitable hot filament condition (55 W for 90 s). This work provides a new perspective to in-depth understand the behavior of W filament during HFCVD and the significant role of the in situ generated W clusters on the growth of CNTs by maintaining the catalytic activity and structure of catalysts.

Harmonic generation by an interaction of laser with an array of anharmonic carbon nanotubes

A scheme of second and third harmonic generation from laser irradiated anharmonic carbon nanotubes (CNTs) embedded in silica is proposed. An intense ultra short laser pulse interacting with the array of CNTs displaces its electrons. When this displacement becomes comparable to the radius of electrons of CNTs, the restoring force of electrons varies nonlinearly with the displacement. As a result, plasmon resonance gets broadened and the large resonance absorption of the laser by the electrons of CNTs occurs. The power conversion efficiency of harmonic generation due to the anharmonicity of CNTs is much higher than that due to the ponderomotive force nonlinearity. The effect of amplitude modulated parameter on the amplitude of second and third harmonic is studied. The high amplitude of generated harmonics can be realized with the amplitude modulated laser as compared to ordinary unmodulated laser.

In-situ Growing Carbon Nanotubes on Nickel Modified Glass Fiber Reinforced Epoxy Composites for EMI Application

Glass fiber (GF) reinforced polymer composites have attracted increasing attention due to their excellent performance. In this study, GF was coated by a thin layer of nickel, and then grafted carbon nanotubes (CNTs) array by a chemical vapor deposition method (CVD). The CNT contents can be varied by changing the CVD conditions. Three types of fillers, nickel coated GF (GF@Ni), GF with CVD grown CNTs (GF-CNTs) and nickel-coated GF with CVD grown CNTs (GF@Ni-CNTs), were used to prepare the epoxy composites. The electromagnetic interference shielding performances were investigated as a function of CNT contents. The GF@Ni-CNTs reinforced epoxy composites, which had the CNTs mass ratio of 9.2 wt% to the hybrids, showed the best EMI shielding performance among the composites. Their total EMI shielding effectiveness (SE) was higher than 35 dB in the range of 1–18 GHz, and above 50 dB in the X band. By incorporating the nickel layer on the GF surface, the same EMI performance can be achieved with lower CNTs content. For achieving a SE value of 35 dB in the X band, it needed GF@Ni-CNTs/epoxy with CNTs mass ratio of 3.8 wt% to the hybrids, instead of GF-CNTs/epoxy composites with CNTs mass ratio of 5.2 wt% to the hybrids.

Design and theoretical study of novel multifunctional 3D-BC2N polymorphs

We constructed a series of novel 3D-BC2N structures that can be obtained by compressing well-mixed carbon nanotube and boron nitride nanotube arrays. Sequential theoretical calculations indicated a variety of electronic and mechanical properties, such as superhardness, tunable band gap, and ductility, for these novel 3D-BC2N polymorphs. In specific, 3D (6,6)-Ⅱ, 3D (4,4)-Ⅱ, 3D (8,8), 3D (6,6)-Ⅰ and 3D (8,0) are energetically more favorable than previously proposed diamond-like β-BC2N; the hardness of 3D (6,6)-Ⅱ can reach a remarkably high value of 72 GPa; 3D (6,0) and 3D (8,0) are direct gap superhard phases; and 3D (10,0) has a semimetallic nature.

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.

Near-perfect absorber consisted of a vertical array of single-wall carbon nanotubes and engineered multi-wall carbon nanotubes

An extensive study on the optical characteristics of vertically aligned single-wall carbon nanotubes (SWCNTs) and engineered multi-wall carbon nanotubes (MWCNTs) using finite-difference time-domain (FDTD) simulation technique is presented in this work. We investigated absorption characteristics for SWCNTs, MWCNTs, dual-diameter MWCNTs, and cone MWCNTs with the changes in the occupation area and incident angle of light in the visible wavelength range. The enhancement of absorption was achieved by changing the geometrical shapes. Our study suggests that 99.569 % of the total light energy is absorbed in SWCNTs and 99.883 % in cone-shaped-top MWCNTs with an occupation area of 20 % and 50 %, respectively, at 450 nm wavelength and 5000 nm tube height. Moreover, for both SWCNTs and MWCNTs, reflectance increases with the increase of the occupation area due to the larger reflecting top surface area. We found that a drastic reduction of absorption occurs as the angle between the tube axis of aligned carbon nanotubes (CNTs) and the incoming light source increases above 30 °. Our study will be valuable for further investigation of the optical properties of shape-engineered CNTs and will promote CNT-based ultra-broadband absorber devices and systems for multifunctional optoelectronic applications.

Optimization and simulation of a carbon nanotube arrangement for transparent conductive electrodes with record-high direct current to optical conductive ratios

Carbon nanotube (CNT) meshes have optical and electrical properties that make them suitable for use in next-generation transparent conductive electrodes (TCEs). Although circuit modeling of CNT meshes has been studied widely, very few researchers have modeled the optical properties of the horizontally and regular arrangement of CNT arrays. The behavior of light propagating through a CNT mesh is complex, with no straightforward rules established to provide simple analytical solutions. In this study, we used the three-dimensional finite difference time domain (3D-FDTD) method to model the optical properties of regular arrays of CNTs, based on the calculated refractive indices and extinction coefficients of multi-walled CNTs (MWCNTs). One-dimensional regular arrays of CNTs displayed strong anisotropic optical behavior. Moreover, by adjusting the spacing and arrangement of two-dimensional regular arrays of CNTs, we could identify the optimal structure for a CNT-based TCE displaying excellent optical and electrical performance. We have also developed the concept of the “optical threshold,” which defines the most effective charge transport channels possessing sufficiently open areas. This concept solves the trade-off between the two key parameters—the light transmittance and the sheet resistance—in TCEs. The optimal geometry provided a CNT mesh with not only the most effective charge transport channels but also very high optical transmittance, CNT network with a diameter of 10 nm (specific conductivity of 0.385 Ω−1 nm−1) has light transparency and low sheet resistance T > 90% and Rs < 1.6 Ω/sq, such that the ratio of the direct current conductivity to the optical conductivity (σDC/σop) reached as high as 2077. This value is far greater than previously reported simulated and experimental values for TCEs based on various materials.

Growth of Homogeneous High‐Density Horizontal SWNT Arrays on Sapphire through a Magnesium‐Assisted Catalyst Anchoring Strategy

AbstractIn‐situ growth of high‐density single‐walled carbon nanotube (SWNT) arrays with homogeneity is highly desirable for integrated circuits. However, disastrous migration and aggregation of catalyst nanoparticles on substrate has greatly limited the area of as‐grown SWNT arrays. Herein, we develop a magnesium‐assisted catalyst anchoring strategy to restrain catalyst nanoparticles sintering on substrate. Magnesium modification ameliorates sapphire surface by high temperature solid reaction and thus provides a stronger metal‐support interaction (SMSI). Hereby, we realize the direct growth of high‐density SWNT arrays that fully cover an entire 10×10 mm2 substrate with the local highest density of ≈110 tubes μm−1 using iron as catalyst. This strategy was also proven universal when employing solid carbide catalysts.

Growth of Homogeneous High-Density Horizontal SWNT Arrays on Sapphire through a Magnesium-Assisted Catalyst Anchoring Strategy.

In-situ growth of high-density single-walled carbon nanotube (SWNT) arrays with homogeneity is highly desirable for integrated circuits. However, disastrous migration and aggregation of catalyst nanoparticles on substrate has greatly limited the area of as-grown SWNT arrays. Herein, we develop a magnesium-assisted catalyst anchoring strategy to restrain catalyst nanoparticles sintering on substrate. Magnesium modification ameliorates sapphire surface by high temperature solid reaction and thus provides a stronger metal-support interaction (SMSI). Hereby, we realize the direct growth of high-density SWNT arrays that fully cover an entire 10×10 mm2 substrate with the local highest density of ≈110 tubes μm-1 using iron as catalyst. This strategy was also proven universal when employing solid carbide catalysts.

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 ...

Resistivity of mesopore-confined ionic liquid determined by electrochemical impedance spectroscopy

Ordered carbon nanotube (CNT) arrays with pore diameter 24.4 ± 4.6 nm formed within anodized aluminum oxide (AAO) bonded to Si were used as electrodes for supercapacitors with neat EMIM-BF4 ionic liquid as the electrolyte. A series of devices with increasing AAO thickness (equal to CNT length) were tested using electrochemical impedance spectroscopy (EIS). Data were fit using the de Levie model of porous electrodes to determine the electrochemically active surface area and the in-pore electrolyte resistivity. The results indicate that uncatalyzed chemical vapor deposition (CVD) of CNTs in AAO can lead to blocked CNTs and reduced active area. The average resistivity of the electrolyte within the pores across the four devices tested was determined to be approximately 383 Ω cm, more than five times higher than the reported bulk resistivity of 70.9 Ω cm. It is possible that the enhanced resistivity is due to hydrophilic surface functionalities on the surface of the CNTs.

Piezoresistive Flexible Sensor Based on Microscopic Observation of Suspended Single-walled Carbon Nanotube Array

<p style="text-align: justify;"><span style="font-family: "times new roman";">With the continuous progress of science and technology, piezoresistive flexible sensors have been widely used in aerospace, energy detection, military confrontation, medical and health services and life services. In this paper, the piezoresistive flexible sensor based on a single-walled carbon nanotube array suspended under a microscope is studied. This research is mainly to combine suspended single-walled carbon nanotubes, nucleic acid molecular hybridization technology and electrochemical analysis technology to develop a piezoresistive flexible sensor with high sensitivity and good selectivity based on microscope observation. Selective detection of nanotube array fragments. Using carbon nanotubes as the tip of STM/AFM effectively improves the resolution of piezoresistive flexible sensors. Experimental data shows that when the first device array structure is adopted, the sensitivity is 0.3412 in the interval of 0-15KPa; and the sensitivity is 0.4502 in the interval of 15-30KPa. Later, as the pressure continues to increase, its sensitivity tends to zero. The experimental results show that the piezoresistive flexible sensor based on the single-walled carbon nanotube array suspended under a microscope is within a certain range. As the pressure increases, the sensitivity also increases; beyond a certain range, as the pressure increases, the pressure the sensitivity of the resistive flexible sensor tends to zero.</span>

Highly Aligned Array of Heterostructured Polyflourene-Isolated Boron Nitride and Carbon Nanotubes.

Boron nitride nanotubes (BNNTs) have attracted increasing attention for their exceptional thermal, electronic, and optical properties. However, the progress in BNNTs applications has largely been limited by the low purity of as-synthesized BNNTs and inefficient solution-processing protocols due mainly to the instability of BNNTs in most of the solvents. Therefore, fabrication of highly pure, stable, and fully individualized BNNTs in a rational manner is required. Here, we report a significant improvement in the preparation of well-dispersed BNNTs, utilizing conjugated polymers that interact with BNNTs, allowing selective sorting and individualization of the nanotubes. Evidence of strong interactions between the polymers and BNNTs was observed by optical absorption and photoluminescence spectroscopies, while effective individualization was observed by electron microscopy. The sorted BNNTs were successfully used in a solution-processing protocol called dose-controlled, floating evaporative self-assembly (DFES) previously established for single-walled carbon nanotubes (SWCNT) array fabrication. A device fabricated via DFES from the sorted BNNTs mixed with polymer-wrapped, semiconducting single-walled carbon nanotubes (s-SWCNTs) exhibited an on-state conductance of 253 ± 6 μS μm-1 and an on/off ratio of 106.6±0.4 for a gate voltage of -0.1 V. This breakthrough in BNNT dispersion and isolation is a significant advancement toward the exploitation of BNNTs in future applications.

LED Device Based on Single-Walled Carbon Nanotube Arrays

The migration model of the (n, 0) zigzag SWNT is established on the basis of Mathiessen’s law to calculate carrier mobility, which are the foundation for performance analysis of electroluminescence light emission. The split-gate technique is used to create p-and n-doped regions in the single-walled carbon nanotube (SWNT) arrays that are separated by a gap with a width of several microns. The LED devices based on SWNT arrays using split-gate technique are fabricated and tested by using an optical measurement system. Compared to the LED with the central gate, the split-gate SWNT LED has enhanced the light generation efficiency of the intrinsic SWNT array segment by decreasing the potential barrier across the junction of the intrinsic SWNT array segment. The results demonstrate the luminescent principle of LED based on SWNT array in theoretical simulation and device measurement.

Collective Excitations and Optical Response of Ultrathin Carbon-Nanotube Films

We present a theoretical study of the collective quasiparticle excitations responsible for the electromagnetic response of ultrathin plane-parallel homogeneous periodic single-wall carbon nanotube arrays and weakly inhomogeneous single-wall carbon nanotube films. We show that in addition to varying film composition, the collective response can be controlled by varying the film thickness. For single-type nanotube arrays, the real part of the dielectric response shows a broad negative refraction band near a quantum interband transition of the constituent nanotube, whereby the system behaves as a hyperbolic metamaterial at higher frequencies than those classical plasma oscillations have to offer. By decreasing nanotube diameters it is possible to push this negative refraction into the visible region, and using weakly inhomogeneous multi-type nanotube films broadens its bandwidth.

N-doped carbon nanotube arrays on reduced graphene oxide as multifunctional materials for energy devices and absorption of electromagnetic wave

Considering serious exhausted non-renewable energy resources and electromagnetic radiation pollution issues, it is quite urgent to exploit multifunctional material for realizing both the conversion sustainable energy sources and protection of electromagnetic radiation pollution. Herein, we develop a facile and high-yield preparation route to fabricate a multifunctional material consisted of CoFe alloy nanoparticles encapsulated in nitrogen doped carbon nanotubes arrays grown on both sides of reduced graphene oxide (CoFe@N-CNT/rGO). CoFe@N-CNT/rGO displays excellent properties in the field of rechargeable Zn-air battery and electromagnetic wave absorption. CoFe@N-CNT/rGO shows bifunctional electrocatalytic performances toward oxygen reduction reaction and oxygen evolution reaction, favorably comparable to that of commercial catalysts (Pt/C and IrO2). Furthermore, the assembled liquid and all-solid-state rechargeable Zn-air batteries with CoFe@N-CNT/rGO as air cathode display good charging–discharging performance. As electromagnetic wave absorbing material, CoFe@N-CNT/rGO shows the minimal reflection loss of −33.2 dB at 13.3 GHz, superior to reported carbon-based electromagnetic wave absorbing materials. Based on excellent electromagnetic absorption performance, electromagnetic energy conversion device is designed to realize reasonable utilization and conversion of the absorbed electromagnetic energy. These encouraging results lay a solid foundation for development the multifunctional material and provide an effective strategy for simultaneously solving energy crisis and electromagnetic radiation problems.

Dynamic characteristics of droplet impingement on carbon nanotube array surfaces with varying wettabilities

This work experimentally investigated the water droplet impingement behaviors on carbon nanotube (CNT) array surfaces characterized by different wettabilities from hydrophilicity to superhydrophobicity. By varying the impact velocity, six typical dynamic behaviors of droplet impact were identified and a related droplet regime map was developed under different wettabilities. To further investigate the evolution behavior of droplet impact, the dynamic contact angle (DCA) and spreading factor were measured and analyzed. The damped oscillations of DCA were observed for wettable and mildly hydrophobic CNT array surfaces, while the approximate impact inertia independence was verified for high hydrophobicity or even superhydrophobicity. The contact line velocity in the vicinity of triple phase interface was found to be highly related to the DCA variation at the initial stage of spreading. The discrepancy of DCA on different wettable surfaces reduced significantly with the increase of Weber number. The reduction in post-impact CAs and resultant wettability enhancement after droplet impingement was mainly attributed to self-assembly structures caused by the capillary action during the spreading phase.

Insight into MoS2–MoN Heterostructure to Accelerate Polysulfide Conversion toward High‐Energy‐Density Lithium–Sulfur Batteries

AbstractLithium–sulfur batteries are deemed as optimal energy devices for the next generation of high‐energy‐density energy storage. However, several problems such as low energy density and short cycle life hinder their application in industry. Here, MoS2–MoN heterostructure nanosheets grown on carbon nanotube arrays as free‐standing cathodes are reported. In this heterostructure, MoN works as a promoter to provide coupled electrons to accelerate the redox reaction of polysulfides while the MoS2, with a two‐dimensional layered structure, provides smooth Li+ diffusion pathways. Through their respective advantages, both MoN and MoS2 could mutually boost the process of “adsorption‐diffusion‐conversion” of polysulfides, which have a synergy enhancement effect to restrain the lithium polysulfides from shuttling. The designed cathodes show excellent long‐term cycling performances of 1000 cycles at 1C with a low decay rate of 0.039% per cycle and a high rate capability up to 6C. A high initial areal capacity of 13.3 mAh cm−2 is also achieved under a low electrolyte volume/sulfur loading (E/S) ratio of 6.3 mL g−1. This strategy of promoting polysulfide conversion by heterostructure MoS2–MoN as presented in this work can provide a more structured design strategy for future advanced Li–S energy storage systems.

External light control of three-dimensional ultrashort far-infrared pulses in an inhomogeneous array of carbon nanotubes

We present a study of the propagation of three-dimensional (3D) bipolar electromagnetic ultrashort pulses in an inhomogeneous array of semiconductor carbon nanotubes (CNTs) in the presence of a control high-frequency (HF) electric field. The inhomogeneity is present in the form of a layer with an increased concentration of conduction electrons, which acts as a barrier for the propagation of ultrashort electromagnetic pulses through the CNT array. The dynamics of the pulse is described by a nonlinear equation for the vector potential of the electromagnetic field (it takes the form of a 3D generalization of the sine-Gordon equation), derived from the Maxwell's equations and averaged over the period of the HF control field. By means of systematic simulations, we demonstrate that, depending on the amplitude and frequency of the HF control, the ultrashort pulse approaching the barrier layer either passes it or bounces back. The layer's transmissivity for the incident pulse is significantly affected by the amplitude and frequency of the HF control field, with the reflection coefficient nearly vanishing in intervals that make up a discrete set of transparency windows, which resembles the effect of the electromagnetically-induced transparency. Having passed the barrier, the ultrashort pulse continues to propagate, keeping its spatiotemporal integrity. The results may be used for the design of soliton valves, with the transmissivity of the soliton stream accurately controlled by the HF field.

Monolithic wood biochar as functional material for sustainability

AbstractTrees are crucial to humankind's survival, releasing the oxygen we breathe, growing the fruits we eat, and supplying wood to build and warm our shelters. Heating wood at 300°C‐800°C with little or no oxygen creates wood biochar, a carbonaceous product. Wood biochar monoliths have a continuous carbon matrix and morphological features that resemble anatomical elements in a tree, including xylem and phloem, which transport water from the root and deliver sugars from leaves to individual cells. Structurally and chemically, monolithic wood biochar belongs to nanoporous carbons (NPCs) consisting of carbon nanotubes arrays and integrated graphene sheets. Researchers have extensively explored NPCs as functional materials for applications essential to sustainability, including electrical energy storage, water purification, and CO2 capture. However, the lack of scalable manufacturing technology continues to hinder the large‐scale utilization of NPCs despite their demonstrated superiority in enhancing materials performance. Derived from abundant woody biomass with simple processes, wood biochar monoliths offer a new opportunity for overcoming this limitation. This review documents recent progress in applying wood biochar monoliths in areas critical to sustainability, focusing on electrical energy storage and water purification. This progress has revealed the potential of monolith wood biochar as a greener, more cost‐effective, and scalable NPC in enhancing sustainability and opened the door to a new field that is both exciting and relevant. The review concludes with a perspective on the future research direction.