Coaxial Carbon Nanotubes Research Articles

Characterization and Investigating the Effect of Gate-Insulator Thickness on Co-Axial Cylindrical Carbon Nanotube Field Effect Transistor

Characterization and Investigating the Effect of Gate-Insulator Thickness on Co-Axial Cylindrical Carbon Nanotube Field Effect Transistor

ELECTRODE: An electrochemistry package for atomistic simulations.

Constant potential methods (CPMs) enable computationally efficient simulations of the solid-liquid interface at conducting electrodes in molecular dynamics. They have been successfully used, for example, to realistically model the behavior of ionic liquids or water-in-salt electrolytes in supercapacitors and batteries. CPMs model conductive electrodes by updating charges of individual electrode atoms according to the applied electric potential and the (time-dependent) local electrolyte structure. Here, we present a feature-rich CPM implementation, called ELECTRODE, for the Large-scale Atomic/Molecular Massively Parallel Simulator, which includes a constrained charge method and a thermo-potentiostat. The ELECTRODE package also contains a finite-field approach, multiple corrections for nonperiodic boundary conditions of the particle-particle particle-mesh solver, and a Thomas-Fermi model for using nonideal metals as electrodes. We demonstrate the capabilities of this implementation for a parallel-plate electrical double-layer capacitor, for which we have investigated the charging times with the different implemented methods and found an interesting relationship between water and ionic dipole relaxations. To prove the validity of the one-dimensional correction for the long-range electrostatics, we estimated the vacuum capacitance of two coaxial carbon nanotubes and compared it to structureless cylinders, for which an analytical expression exists. In summary, the ELECTRODE package enables efficient electrochemical simulations using state-of-the-art methods, allowing one to simulate even heterogeneous electrodes. Moreover, it allows unveiling more rigorously how electrode curvature affects the capacitance with the one-dimensional correction.

Coaxial vibrations of electrostatically actuated DWCNT resonators: Amplitude–voltage​ response of parametric resonance

This paper investigates the amplitude–voltage response of parametric resonance of coaxial vibrations of double-walled carbon nanotubes (DWCNTs) under electrostatic actuation. The system under investigation consists of a DWCNT parallel to a ground plate and under AC voltage. This voltage produces a nonlinear electrostatic force leading the DWCNT into vibrations. There is a nonlinear intertube van der Waals force between the two coaxial carbon-nanotubes. In coaxial vibration, the two concentric nanotubes move together synchronously. The AC frequency is near the fundamental coaxial natural frequency of the DWCNT. This leads to parametric resonance. The case of small damping, soft electrostatic actuation, and DWCNTs with a high length to diameter ratio (Euler–Bernoulli beam model), is considered. Modal analysis is performed to decouple the equations of free vibrations in their linear part. The solution of the nonlinear problem is then found in terms of modal coordinates. Reduced Order Models (ROMs) using from one to five modes of vibration are used for investigation. Three methods are used to solve these models, (1) the Method of Multiple Scales used to solve the ROM using one mode of vibration, (2) continuation and bifurcation analysis of the five modes of vibration (5T) Reduced Order Model (ROM) using AUTO-07P, and (3) numerical integration of 5T ROM using Matlab. All models and methods are in excellent agreement for amplitudes lower than 0.4 of the gap, while at amplitudes larger than 0.4 only 5T-ROM provide reliable results. The effects of detuning frequency and damping on the amplitude–voltage response of DWCNTs under electrostatic actuation are reported. The importance of the results in this paper are the effect of damping and detuning frequency on the subcritical and supercritical bifurcations, as they define the voltage intervals DWCNT reaches nonzero steady-state amplitudes.

Connecting effect on the charge transport and nonlinear optical properties of heteronanotubes

Carbon/boron nitride heteronanotubes are now at the centre of experimental and theoretical studies because of their tunable properties and diverse applications. Herein, we investigate the charge transport and optical properties of carbon/boron nitride hybrid single- and double-walled nanotubes on the basis of first-principles calculations. Our results reveal that the C/BN heterojunctions with radial junctions parallel (horizontal) to the tube axis have more effects than the perpendicular (vertical) junctions on the charge transport properties of heteronanotubes. Furthermore, we find that the nonlinear optical response can be meaningfully controlled by altering the C/BN content and junction arrangement. In double-walled coaxial heteronanotubes, the interwall interaction is also found to increase the electron and hole transport rates noticeably and to have a major effect on the first hyperpolarizabilities of C/BN heteronanotubes. In contrast with coaxial carbon nanotubes, where the inner constituent is totally shielded by the outer tube, in our studied C/BN coaxial heteronanotubes, the inner shell is only partially shielded by the outer constituent. This study suggests a strategy to high-efficient design heteronanotubes with high charge transport properties and tunable nonlinear optical responses. Moreover, the designed C/BN heteronanotubes can discrete electrons and holes, suggesting their application in solar cell materials.

Stability and electronic properties of hybrid coaxial carbon nanotubes–boron nitride nanotubes under the influence of electric field

Stability and electronic properties of hybrid coaxial carbon nanotubes–boron nitride nanotubes under the influence of electric field

Zeolite-supported synthesis, solution dispersion, and optical characterizations of single-walled carbon nanotubes wrapped by boron nitride nanotubes

Zeolite-supported carbon nanotube (CNT) synthesis provides a route for its mass production due to the porous surfaces accommodating a large number of catalytic particles and maintaining the fine particle sizes during high-temperature growth. Coaxial single-walled carbon nanotubes (SWCNTs) and boron nitride nanotube (BNNT) van der Waals heterostructures have been produced recently on the CNT thin-film template. To achieve a high yield of the one-dimensional heterostructure, BNNT-wrapped SWCNTs were synthesized on zeolite support coated with catalytic nanoparticles. They were then dispersed in solution and examined by absorption, photoluminescence, and Raman spectroscopy. A robust thermal stability enhancement was observed, and optical characterizations revealed the composition of dispersed SWCNTs wrapped by BNNTs before air annealing includes individual SWCNTs, BNNT-wrapped SWCNT bundles, and BNNT-wrapped individual SWCNTs. Furthermore, the outside wrapping by BNNTs caused a significant down-shift of the photoluminescence spectrum in semiconducting SWCNTs, suggesting that BNNT-wrapped SWCNTs can be preserved after harsh dispersion treatments.

Performance analysis of an enclosed, coaxial carbon nanotube (CNT) speaker in presence of flow using COMSOL Multiphysics

Performance analysis of an enclosed, coaxial carbon nanotube (CNT) speaker in presence of flow using COMSOL Multiphysics

A continuum study of ionic layer analysis for single species ion transport in coaxial carbon nanotubes

In this letter, we employ the Poisson-Nernst-Planck equation and the continuum molecular model to investigate the ionic layers formation in coaxial carbon nanotubes, which are crucial for understanding the ion transport in nanomaterials, as well as modern solar cells and batteries. Owing to the curvature of nanotubes and the strong ion-nanotubes interactions, our simulations show that stable ionic multi-layers can always be formed inside nanotubes under a wide range of external electric fields and operating temperatures. Approximate solutions have also been deduced to support our numerical results. Most importantly, our hybrid model enjoys rapid and efficient computational times and hence fluid flow, conductivity and VI curve can be extracted almost instantaneously, which opens up a new research direction for the ion transport in nanomaterials.

Design and characterization of an enclosed coaxial carbon nanotube speaker.

Automotive mufflers are heavy, large, and loud at low frequencies. Carbon nanotube (CNT) speakers are solid-state, lightweight, flexible, and capable of handling high temperatures. This makes them suitable as loudspeakers in active exhaust noise cancellation applications. A coaxial CNT speaker designed for active noise control in an exhaust system is developed. Test results for resistance, in-pipe axial sound pressure level, and efficiency are presented. The maximum in-pipe sound pressure level was above 120 dB (re 20 μPa) using 105 W of electrical power. The maximum power efficiency was 0.008%. The weight, dimensions, and sound pressure level of the speaker show promise for active exhaust noise cancellation applications.

Multi-Physics and CFD Analysis of an Enclosed Coaxial Carbon Nanotube Speaker for Automotive Exhaust Noise Cancellation

<div class="section abstract"><div class="htmlview paragraph">Automotive exhaust noise is one of the major sources of noise pollution and it is controlled by passive control system (mufflers) and active control system (loudspeakers and active control algorithm). Mufflers are heavy, bulky and large in size while loudspeakers have a working temperature limitation. Carbon nanotube (CNT) speakers generate sound due to the thermoacoustic effect. CNT speakers are also lightweight, flexible, have acoustic and light transparency as well as high operating temperature. These properties make them ideal to overcome the limitations of the current exhaust noise control systems. An enclosed, coaxial CNT speaker is designed for exhaust noise cancellation application. The development of a 3D multi-physics (coupling of electrical, thermal and acoustical domains) model, for the coaxial speaker is discussed in this paper. The model is used to simulate the sound pressure level, input power versus ambient temperature and efficiency. The 3D model provides accurate results of the temperature profile and heat flow as compared to a 2D model. Also, the flow of exhaust gases can be efficiently modeled using a 3D model. The flow analysis would help understand any flow penetration into the speaker as well as the effect of heat transfer due to the flow. The model is validated by comparing the experimental results with the simulation results. Along with multi-physics simulation, CFD analysis of the coaxial speaker is also studied in this paper. The CFD analysis is focused on the backpressure generated by the speaker and the flow path of the exhaust gases inside the CNT speaker.</div></div>

Correction to Coaxial Carbon Nanotube Supported TiO2@MoO2@Carbon Core-Shell Anode for Ultrafast and High-Capacity Sodium Ion Storage.

Correction to Coaxial Carbon Nanotube Supported TiO2@MoO2@Carbon Core-Shell Anode for Ultrafast and High-Capacity Sodium Ion Storage.

Coaxial Carbon Nanotube Supported TiO2@MoO2@Carbon Core-Shell Anode for Ultrafast and High-Capacity Sodium Ion Storage.

The sluggish kinetic in electrode materials is one of the critical challenges in achieving high-power sodium ion storage. We report a coaxial core-shell nanostructure composed of carbon nanotube (CNT) as the core and TiO2@MoO2@C as shells for a hierarchically nanoarchitectured anode for improved electrode kinetics. The 1D tubular nanostructure can effectively reduce ion diffusion path, increase electrical conductivity, accommodate the stress due to volume change upon cycling, and provide additional interfacial active sites for enhanced charge storage and transport properties. Significantly, a synergistic effect between TiO2 and MoO2 nanostructures is investigated through ex situ solid-state nuclear magnetic resonance. The electrode exhibits a good rate capability (150 mAh g-1 at 20 A g-1) and superior cycling stability with a reversibly capacity of 175 mAh g-1 at 10 A g-1 for over 8000 cycles.

Mechanical and thermal properties of the coaxial carbon nanotube@boron nitride nanotube composite

The mechanical and thermal properties of a novel one dimensional nanocomposite, a coaxial (10,0) carbon nanotube inside a (19,0) boron nitride nanotube (CNT@BNNT), are studied by molecular dynamics (MD) simulations. Results show that the CNT@BNNT composites possess excellent mechanical strength and high thermal conductivity, both of which are comparable to that of individual CNT. The calculated Young's Modulus is about 0.856 TPa and the critical strain and the maximum stress can be increased by increasing the inter-tube coupling strength while decreased by increasing the tube length. Due to its larger tube densities, the overall thermal conductivity of the CNT@BNNT arrays is estimated to be 2.36 times that of the CNT arrays when used as the thermal interface materials (TIMs) and also exhibits better thermal stability at high temperatures owing to the presence of the BNNT sheath. Compression stress leads to a decrease in the thermal conductivity of the CNT@BNNT, and the thermal conductivity drops rapidly near the critical strain. However, when the compression strain exceeds the critical one, the thermal conductivity changes slowly with further increase of the compression strain. Phonon spectrum demonstrates that high frequency phonons play a dominate role in the thermal conductivity of the CNT@BNNT nanocomposite.

Uniform coaxial CNT@Li2MnSiO4@C as advanced cathode material for lithium-ion battery

The rational design of the nano structure is crucial for overcoming the inherent defect and engineering high performance of Li2MnSiO4 cathode material. In the present study, uniform coaxial carbon nanotube CNT@Li2MnSiO4@C has been designed and synthesized by an efficient step-by-step strategy and applied as high-performance cathode for lithium ion battery. It is demonstrated that the product has a uniform coaxial structure, the thickness of Li2MnSiO4 shell and outermost carbon layer is about 20 nm and 4.5 nm, respectively. This properly design can effectively improve the electric conductivity, shorten the Li ion diffusion length, relax volume change upon charge/discharge and relieve the manganese dissolution. Benefit from its unique structural features, the CNT@Li2MnSiO4@C electrode material overcomes the intrinsic disadvantage of Li2MnSiO4 of poor electronic/ionic conductivity and fast capacity fading rate, and hence exhibiting promising improvement on reversible capacity and cycling properties.

Coaxial carbon nanotubes: from springs to ratchet wheels and nanobearings

Quantum mechanical calculations are performed for double-walled and triple-walled carbon nanotubes (DWCNTs, TWCNTs). We show how the DWCNTs may be modelled by mechanical analogues with interactions mediated by spring forces with weakening elastic constants in addition to a weak van der Waals -like interaction. This enables us to predict the natural frequency of longitudinal oscillations of the DWCNTs, their elastic spring constant and the corresponding interaction between the CNTs. Results of the interaction energy ΔE for the DWCNT system obtained from the mechanical model are in remarkable agreement with those obtained from our quantum mechanical calculations, and we obtain functional dependencies of ΔE on axial elongation and inter-wall separation of the DWCNTs. Our density functional theory calculations reveal that the armchair-armchair systems are significantly more stable than both the corresponding armchair-chiral configurations, as well as the corresponding stacked graphene sheets. The results obtained for translational and rotational motion (slide / roll) of the CNTs indicate a potential use of DWCNTs as springs, ratchet wheels, nanogears and bearings in miniaturized devices. Our work enables us to predict the behavior of DWCNTs of different dimensions and would be of practical importance in the actual construction of nanoscale mechanical parts.

Measuring the Density of States of the Inner and Outer Wall of Double-Walled Carbon Nanotubes.

The combination of ultraviolet photoelectron spectroscopy and metastable helium induced electron spectroscopy is used to determine the density of states of the inner and outer coaxial carbon nanotubes. Ultraviolet photoelectron spectroscopy typically measures the density of states across the entire carbon nanotube, while metastable helium induced electron spectroscopy measures the density of states of the outermost layer alone. The use of double-walled carbon nanotubes in electronic devices allows for the outer wall to be functionalised whilst the inner wall remains defect free and the density of states is kept intact for electron transport. Separating the information of the inner and outer walls enables development of double-walled carbon nanotubes to be independent, such that the charge transport of the inner wall is maintained and confirmed whilst the outer wall is modified for functional purposes.

Li-ion and lead-acid battery applications push global battery materials market toward $43.2 bn by 2023

The rational design of the nano structure is crucial for overcoming the inherent defect and engineering high performance of Li2MnSiO4 cathode material. In the present study, uniform coaxial carbon nanotube [email protected]2MnSiO4@C has been designed and synthesized by an efficient step-by-step strategy and applied as high-performance cathode for lithium ion battery. It is demonstrated that the product has a uniform coaxial structure, the thickness of Li2MnSiO4 shell and outermost carbon layer is about 20 nm and 4.5 nm, respectively. This properly design can effectively improve the electric conductivity, shorten the Li ion diffusion length, relax volume change upon charge/discharge and relieve the manganese dissolution. Benefit from its unique structural features, the [email protected]2MnSiO4@C electrode material overcomes the intrinsic disadvantage of Li2MnSiO4 of poor electronic/ionic conductivity and fast capacity fading rate, and hence exhibiting promising improvement on reversible capacity and cycling properties.

Two Sprayer CVD Synthesis of Nitrogen-doped Carbon Sponge-type Nanomaterials

Nitrogen-doped carbon sponge-type nanostructures (N-CSTNs) containing coaxial multiwalled carbon nanotubes are synthesized at 1020 °C by using a modified chemical vapor deposition (CVD) arrangement. Here, the CVD reactor is supplied by two flows coming from two independent sprayers (called sprayer A and sprayer B). The nebulized material in each sprayer is transported by two different gases with different flow velocities. The synthesis of carbon N-CSTNs is performed using different precursors: sprayer A contains a solution composed of ethanol, thiophene and ferrocene, whereas sprayer B contains a solution of benzylamine, thiophene and ferrocene. Samples are classified according to the position inside the reactor and characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and thermogravimetric analysis (TGA). Samples collected at the beginning of the reactor contain curly structures with diameters of 10–100 nm. At the end of the reactor, the sample is mainly formed by one type of structure. A spongy-type material is mainly formed in the hottest zone of the tubular furnace. The N-CSTNs are highly hydrophobic with oil sorption properties, which could be used for adsorption of oil spills.

Vibration and Stability Analysis of DWCNT-Based Spinning Nanobearings

This paper aims at investigating free vibrations and stability of double-walled carbon nanotube (DWCNT)-based spinning nanobearings. The so-called nanobearing consists of two coaxial carbon nanotubes (CNTs) where either of the two CNTs can be a rotor while the other takes the role of stator. Euler–Bernoulli beam model along with the Eringen’s nonlocal theory of elasticity are employed to obtain governing equations of transverse vibrations for the CNTs. The coupling of the two CNTs originates from the van-der-Waals (vdW) forcing present in the interface of the two CNTs. The coupling is taken into account as distributed spring foundation with an equivalent elastic stiffness. Based on the obtained model, effects of small-scale parameter, vdW interaction between CNTs and the diameter ratio of CNTs on the critical spinning speed are investigated. Finally, the stability margins of the nanobearings are determined and some general conclusions are drawn.

Carbon nanotube coaxial thermophone for automotive exhaust noise cancellation

Exhaust noise from automobiles is a major concern and needs to be controlled. Current noise control systems, mainly mufflers, have significant size, weight, and performance limitations at low frequencies. Passive control systems are unable to cancel noise efficiently over the entire frequency spectrum. Active noise control system helps to overcome the above limitation. This paper deals with the design and testing of a coaxial carbon nanotube speaker for active cancellation of automotive exhaust noise. Carbon nanotubes are virtually massless and work on the thermo-acoustic principle. Their ability to sustain heat makes them suitable for use in elevated temperature environments such as automotive exhausts. Analytical calculations are performed using transfer matrix method to evaluate the effect of coaxial thermo-phone and side branch speakers on the sound pressure level in the exhaust tailpipe. Design of the coaxial CNT thermophone and testing of it by mounting on an automotive exhaust tailpipe are discussed. Low frequencies (20 Hz–1000 Hz) are considered to evaluate the performance of the thermophone. For active cancellation of exhaust noise, Filtered-X Least Mean Square (FXLMS) algorithm is developed and implemented using NI LabVIEW.