Deformation Of Carbon Nanotubes Research Articles

Welded Carbon Nanotube-Graphene Hybrids with Tunable Strain Sensing Behavior for Wide-Range Bio-Signal Monitoring.

Carbon nanotubes (CNTs) and graphene have commonly been applied as the sensitive layer of strain sensors. However, the buckling deformation of CNTs and the crack generation of graphene usually leads to an unsatisfactory strain sensing performance. In this work, we developed a universal strategy to prepare welded CNT-graphene hybrids with tunable compositions and a tunable bonding strength between components by the in situ reduction of CNT-graphene oxide (GO) hybrid by thermal annealing. The stiffness of the hybrid film could be tailored by both initial CNT/GO dosage and annealing temperature, through which its electromechanical behaviors could also be defined. The strain sensor based on the CNT-graphene hybrid could be applied to collect epidermal bio-signals by both capturing the faint skin deformation from wrist pulse and recording the large deformations from joint bending, which has great potential in health monitoring, motion sensing and human-machine interfacing.

Flow through Deformed Carbon Nanotubes Predicted by Rigid and Flexible Water Models.

In this study, using nonequilibrium molecular dynamics simulation, the flow of water in deformed carbon nanotubes is studied for two water models TIP4P/2005 and simple point charge/FH (SPC/FH). The results demonstrated a nonuniform dependence of the flow on the tube deformation and the flexibility imposed on the water molecules, leading to an unexpected increase in the flow in some cases. The effects of the tube diameter and pressure gradient are investigated to explain the abnormal flow behavior with different degrees of structural deformation.

Water flow rate quantification through an experimental CNT membrane: A molecular dynamics simulation approach

The comprehension of water flow rate within carbon nanostructures holds great importance in both theoretical understanding and engineering design of microscale and nanoscale devices. This study presents a comprehensive numerical model for analyzing the water flow rate in Carbon Nanotube (CNT) membranes. The outcomes of this model have particular relevance in predicting the performance and designing CNT membranes for water desalination, which offer the potential for remarkably rapid transport. By investigating the characteristics of the CNT membrane, various geometric properties that influence the overall flow rate are quantified. Apart from the diameter and length, attention is also given to non-ideal factors associated with the deformation of CNTs from their original structures. Specifically, the impact of eccentricity and bending on the flow rate through CNTs is examined, revealing limited but noteworthy effects. Additionally, a simplified model is developed to characterize the membrane using statistical data pertaining to CNT synthesis. The results of the total water flow rate demonstrate that the existing numerical model closely aligns with the reported experimental values.

Geometric nonlinear analysis of large rotation behavior of a curved SWCNT

ABSTRACT Nanotubes form clusters and are found in curved bundles in nanotube films and nanocomposites. Separation phenomenon is suspected to occur in these curved bundles. In this study, the deformation of a single-wall carbon nanotube (SWCNT) interacting with curved bundle nanotubes is analyzed. It is assumed that the bundle is rigid and only van der Waals force acts between the nanotube and the bundle of nanotubes. A new method of modeling geometric nonlinear behavior of the nanotube due to finite rotation and the corresponding van der Waals force is developed using co-rotational finite element method (CFEM) formulation, combined with small deformation beam theory, with the inclusion of axial force. Current developed CFEM method overcomes the limitation of linear Finite Element Method (FEM) formulation regarding large rotations and deformations of carbon nanotubes. This study provides a numerical tool to identify the critical curvature influence on the interaction of carbon nanotubes due to van der Waals forces and can provide more insight into studying irregularities in the electronic transport properties of adsorbed nanotubes in nanocomposites.

Pyrrole-like defects as origin of piezoelectric effect in nitrogen-doped carbon nanotubes

In this work, it is shown for the first time that nitrogen-doped carbon nanotubes (CNTs) exhibit anomalous piezoelectric properties that depend on the concentration of pyrrolic N, which can be used in the development of energy-efficient nanogenerators. The results are supported by studies of CNTs using X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, and piezoresponse force microscopy. We proposed a mechanism for appearance of a piezoelectric response in CNTs associated with the formation of an uncompensated dipole moment as a result of curvature of the graphene sheet surface due to the formation of pyrrole-like defects and bamboo-like “bridges” in the nanotube cavity. It was found that with an increase in the concentration of pyrrolic N from 20 to 27 at. %, the magnitude of the piezoelectric strain coefficient of CNTs increases from 30 to 92 pm/V, and the magnitude of the current generated during the deformation of the CNTs increases from 16 to 129 nA. Experimental and theoretical estimates of the output voltage arising at 1% deformation of nitrogen-doped CNTs are performed. The output voltage of CNTs ranged from 85 to 259 mV, depending on the pyrrolic N concentration. The established regularities make it possible to take into account the influence of the CNT defect types on its electrical properties in the process of creating various nanoelectronic devices.

Deformation Mechanism of Carbon Nanotubes with Dislocation Array

Carbon nanotubes (CNTs) have attracted attention as a nanocarbon material with excellent mechanical properties. The formation process of CNTs can not prevent the introduction of lattice defects. Various studies have conducted that the presence of lattice defects has a great influence on the properties of CNTs. In this study, we aim to elucidate the deformation mechanism of CNTs with dislocation arrays by fusing molecular dynamics simulation and differential geometry calculation, and investigate the possibility of controlling the mechanical properties by the lattice defects. The deformation of the models and simulation results show that the shape change is caused by the spontaneous deformation of lattice defects and the cylindrical shape of CNT. Using differential geometry, we discuss the bending of the curved surface, and the deformation mechanism was clarified by the mechanical properties expressed as equivalent bending stiffness. Furthermore, it was suggested that the deformation of CNTs could be designed by controlling the lattice defects and the size of CNT.

Electron transport properties of carbon nanotubes with radial compression deformation

In this paper, molecular dynamics simulation method is used to investigate the contacting configuration of carbon nanotubes with open ends and metal, thereby obtaining the law of radial compression deformation of carbon nanotubes. The obtained results show that after horizontally contacting the metal surface, the radial compression deformation is affected by the contact length, the diameter of the tube, the type of metal and the number of layers. Based on the first principles combining tight-binding density functional theory and non-equilibrium Green's function, the electron transport properties of carbon nanotubes with different diameters, chiralities, lamellar deformations and radial deformations are systematically studied. The obtained results show that the current of metallic single-walled carbon nanotubes presents linear change in a bias voltage range between –2 V and 2 V, and the current-voltage curve is symmetrical about the origin. The magnitude of the current is only related to the bias voltage, but not to the diameter; when the carbon nanotubes are deformed by radial compression, the current growth trend is downward and even plateau effect may appear under a larger bias voltage. The current flowing in the semiconducting single-walled carbon nanotubes decreases with the increase of radial compression deformation, and the current-voltage curve gradually transforms from semiconductor characteristics into metallic characteristics. The trend of the current-voltage curve of double-walled carbon nanotubes is consistent with that of metallic single-walled carbon nanotubes. However, the non-linear variation amplitude of the current-voltage curve of double-walled carbon nanotubes is less affected by the radial compression deformation. Owing to the increase of walls of nanotubes, the current of double-walled carbon nanotubes is twice as high as that of single-walled carbon nanotubes under the same bias voltage. The electrons can produce transitions through rapid vibration between adjacent tubes, in view of the fact that interlayer coupling characteristics of three-walled carbon nanotubes reduce the degeneracy of the energy level and larger system increases the density of states near the Fermi level, resulting in large oscillations and asymmetry about the origin of the current-voltage curve.

Strain-induced band modulation of thermal phonons in carbon nanotubes

We show that carbon nanopeapods are an ideal artificial superlattice to induce band modulation of thermal phonons. Based on spectral energy density analysis, we found that a periodic deformation in carbon nanotubes induced by fullerene encapsulation leads to zone folding of phonon dispersions up to near the maximum frequency. The zone-folding effect gives rise to phonon band gaps caused either by Bragg reflection or mode hybridization, and this reduces group velocity. This was quantified to play the leading role in reduction of thermal conductivity by the fullerene encapsulation. The strain modulation of thermal phonon bands opens a possibility to control material thermal conductivity.

Structure and stability of deformed partially hydrogenated carbon nanotubes

In this paper, we study the effect of the axial deformation of carbon nanotubes in the zigzag and armchair directions on the stability of the interface between hydrogenated and non-hydrogenated regions. We analyze the specific energy of this interface as a function of the axial strain. We found that the clear interface can be obtained at a wider temperature range due to tube stretching. The energy barriers characterizing the process of hydrogen migration from the hydrogenated region of the nanotube to the pristine tube are calculated. It is concluded that the tube deformation significantly affects the stability of the system. For some tubes applied strain can qualitatively change the regularity of hydrogenation, changing the sign of the interface energy.

Ultrahigh adhesion between carbon nanotube and free-standing monolayer graphene

Using a self-prepared individual carbon nanotube (CNT) mechanical force sensor, we measured the adhesion between CNT and free-standing monolayer graphene and other bulk substrates. All the measurements were made by using the same CNT force sensor under the same conditions, such as moving speed, observation angle, temperature, and vacuum pressure, confirming the reliability and accuracy of experimental data. The adhesion at contact is proportional to the deformation of the curved CNT, which can be directly measured in a scanning electron microscope. It was found that the deformation of CNT was the largest on the suspended graphene, showing that the suspended graphene has the largest adhesion on CNT. This unusually high adhesion on suspended monolayer graphene is related to the low bending stiffness and extreme flexibility of this atomically thin layer. The main contribution of this work is to demonstrate the unusually high adhesion on suspended graphene experimentally. More advanced modeling needs complicated molecular dynamics simulation and surface energy computation in our future work.

Ultra-highly stretchable and anisotropic SEBS/F127 fiber films equipped with an adaptive deformable carbon nanotube layer for dual-mode strain sensing

We delicately designed and fabricated an anisotropic fibrous film-based strain sensor with remarkable dual-mode sensing capabilities to respectively achieve an ultra-wide workable range and high sensitivity in two loading directions.

Water diffusion in carbon nanotubes: Interplay between confinement, surface deformation, and temperature.

In this article, we investigate, through molecular dynamics simulations, the diffusion behavior of the TIP4P/2005 water confined in pristine and deformed carbon nanotubes (armchair and zigzag). To analyze different diffusive mechanisms, the water temperature was varied as 210 ≤ T ≤ 380 K. The results of our simulations reveal that water presents a non-Arrhenius to Arrhenius diffusion crossover. The confinement shifts the diffusion transition to higher temperatures when compared with the bulk system. In addition, for narrower nanotubes, water diffuses in a single line, which leads to its mobility independent of the activation energy.

Effect of external pressure on the vibration analysis of higher order shear deformable FG-CNTRC spherical panels

The numerical investigation is performed on the vibration of the higher order shear deformable carbon nanotube reinforced composite (CNTRC) spherical panels subjected to the initial external pressure. The functionally graded nanocomposite is reinforced with the non-uniform distribution of CNTs. The problem is formulated following the higher order shear deformation shell theory (HSDT) within the variational differential quadrature numerical approach. For this purpose, the direct discretization of Hamilton’s principle is carried out with the aid of differential quadrature operators. Derivation of the variational formulation of nanocomposite spherical panels based on the HSDT and studying the effects of external pressure on the vibration behavior are the main novel aspects of this research. Several numerical examples are provided to survey the impacts of geometrical and material factors on the vibration of pressurized functionally graded CNTRC spherical panels. It is shown that the internal pressure has the most influence on the vibrational behavior of the thicker panel.

Nonlinear vibrations of magneto-electro-elastic doubly curved shells reinforced with carbon nanotubes

In this article, the study on the geometrically nonlinear free vibration behaviour of higher order shear deformable Carbon nanotube reinforced magneto-electro-elastic (CNTMEE) doubly curved shells has been performed. The displacement fields and geometric nonlinearity are assumed to follow Donnell Shell theory and von-Karman’s relation, respectively. Using Hamilton’s principle the governing equations of motion are derived. A special attention has been paid to investigate the effect of electro-magnetic circuits on the nonlinear frequency response of CNTMEE shells for the first time. Numerical examples are illustrated to assess the influence of different parameters including shell geometry, CNT distribution, volume fraction, shallowness ratio, thickness ratio, aspect ratio in detail. Also, the contribution of combined/individual coupling fields on nonlinear free vibrations has been examined. The results suggest that the geometric and material parameters alter the nonlinear characteristics of CNTMEE shells significantly.

High-temperature vacuum pressure sensor using carbon nanotubes

I studied sensors using carbon nanotubes (CNTs) powered by van der Waals forces with the objective of developing a pressure sensor that can work in harsh environments. To achieve this, the deformation of CNTs was investigated under vacuum. The sensitivity of developed sensors increased with an increase in the temperature. The sensors with single-wall CNTs were more sensitive than the ones with multi-wall CNTs with reasonable repeatability. I interpreted previous theoretical reports on the deformation of CNTs at metal interconnections using the results and suggested that the deformation primarily depended on temperature.

Rollable and transparent subpixelated electrochromic displays using deformable nanowire electrodes with improved electrochemical and mechanical stability

Electrochromic displays (ECDs) have advantages that are required for next-generation wearable devices, but they are limited in terms of electrochromic (EC) material pixelation and application in deformable electrodes. Therefore, in this study, rollable and transparent subpixelated-ECDs with deformable single-walled carbon nanotube (SWCNT)/Pd-coated Ag nanowire (PCSN) bilayer electrodes were developed and successfully confirmed to achieve high electrochemical and mechanical stability. Chemically enhanced PCSN with the Pd thickness controlled to 5 nm was synthesized, and the SWCNTs were deposited to a thickness of 50 nm as bilayers on PCSNs for further chemical and mechanical improvement. To implement deformable displays, the electrode materials and emitting layers must be deformable. The EC gels were elastically deformed even under the condition of an applied external strain of 70%, and to have a Poisson’s ratio of ~0.43. The viologen-based EC gels were used to realize various colors (magenta, blue, and green), and characteristics of the ECDs such as the response time, coloration efficiency, and repeatability were excellent. The redox stability of the rollable ECDs using bilayer electrodes exhibit >100-fold improvement in the redox stability compared with devices with pristine-Ag NWs. The subpixelated-rollable ECDs were simultaneously implemented with subpixels of three colors and were stable in repeated rollable tests for 500 cycles at a curvature radius of 2.5 mm. Consequently, these results indicate that EC materials can be applied to wearable devices, while retaining the advantages of ECDs, by solving the problems related to pixelation and electrodes.

Water diffusion in rough carbon nanotubes.

We use molecular dynamics simulations to study the diffusion of water inside deformed carbon nanotubes with different degrees of deformation at 300 K. We found that the number of hydrogen bonds that water forms depends on nanotube topology, leading to enhancement or suppression of water diffusion. The simulation results reveal that more realistic nanotubes should be considered to understand the confined water diffusion behavior, at least for the narrowest nanotubes, when the interaction between water molecules and carbon atoms is relevant.

Length-controllable picking method and conductivity analysis of carbon nanotubes

In this paper, a length-controllable picking-up method of carbon nanotubes (CNTs) is proposed and the electrical performance data utilized for the conductivity analysis of CNT are also obtained. The micro-nano-operation system inside scanning electron microscope (SEM) is composed of 4 manipulation units each with 3 degrees of freedom, which is driven by piezoelectric ceramics and flexure hinges. In this micro manipulation system, an atomic force microscope (AFM) probe is used as the end effector to adjust the spatial pose of the CNT based on van der Waals force and two tungsten needles are used to cut the CNT from the target length and to measure the <i>I-V</i> characteristic data simultaneously. At first, the AFM probe is moved in the <i>z</i> direction to approach to the CNT until the end of the CNT is adsorbed onto the surface of the AFM probe. And then the AFM probe moves alternately in the <i>x</i> and <i>z</i> direction in order to stretch the CNT into a horizontal straight line, only in this way can the length of the CNT be measured accurately and can the cutting position be determined. Two tungsten needles cleaned by using hydrofluoric acid to remove the oxide layer are controlled to contact both sides of the cutting position on CNT and connected to the TECK 2280S power supply through the electric cabinet to apply a gradually increasing DC voltage, and the current in the circuit is measured and recorded by the TECK DMM7510 until the current abruptly changes to zero which indicates that the CNT between the tungsten needles has been cut off. The stress of the CNT in contact with the tungsten needles and the AFM probe are analyzed. The modeling of van der Waals force between AFM probe and CNT which can influence the pick-up length error caused by the deformation of CNT under the force of tungsten needles is completed. It is found that the contact length of them and the pick-up length error decrease while the van der Waals force between the AFM probe and CNT increases. The circuit models for contact between the tungsten needles and three operating objects, such as semiconducting CNT, metallic CNT and CNT bundle, are also established. In addition, the <i>I-V</i> characteristic equations of circuit model which can be used to fit the <i>I-V</i> data are derived separately. The CNT pick-up experiment is carried out and the results demonstrate that the proposed picking method can control the length of CNT effectively, but the conductivity of CNT can also be judged by fitting the <i>I-V</i> obtained experiment data through the derived <i>I-V</i> characteristic equations.

Demonstration and Understanding of Nano-RAM Novel One-Time Programmable Memory Application

In prior researches, carbon nanotube (CNT)-based nano-random access-memory (NRAM) uses reset initialization which obtains >1011 high write endurance for large-time programmable (LTP) application. In this paper, for the first time, NRAM one-time programmable (OTP) application is proposed by using set initialization for data archive. Specifically, virgin NRAM cells are all in high resistance state (HRS) for storing bit “0.” In contrast, set initialization uses reversed polarity voltage to obtain low resistance state (LRS) for bit “1.” Furthermore, physical models of set initialization and retention current degradation are proposed for the first time. The current increment during set initialization can be attributed to electron tunneling and CNT deformation. Retention current degradation may be due to variation of paralleled CNT contacts in bottleneck zone. As for OTP performance, median NRAM bit and 1% tail bit demonstrate more than 1 billion years and 15 years data retentions, respectively, on 150 °C. The tail bit activation energy is 2.41 eV. Finally, no LRS read disturb is found after 10 s 0.5-V stress on both polarities. The virgin NRAM cells in HRS should be more stable than set initialized NRAM cells in LRS for both retention time and read disturb.

Effect of Structural Defect on Cross-sectional Deformation of Carbon Nanotubes

Effect of Structural Defect on Cross-sectional Deformation of Carbon Nanotubes