Parameters Of Carbon Nanotubes Research Articles

Interaction of obliquely incident lasers with anharmonic CNTs acting as dipole antenna to generate resonant THz radiation

The present paper explores the terahertz (THz) generation by the interaction of obliquely incident laser beams with the array of vertically aligned anharmonic carbon nanotubes (CNTs) acting as dipole antennas. In the scheme, anharmonicity arises due to the nonlinear variation of restoration force on the various electrons of CNTs and it plays a key role in the enhancement of THz generation. The anharmonic CNTs help in broadening the resonance peak, which paves the way for the enhancement of the normalized THz amplitude. The laser beams incident obliquely on the close-packed array of vertically aligned anharmonic CNTs grown over the glass substrate and set oscillations in the CNTs so that each CNT act as the oscillatory dipole to generate THz radiation. The THz electric field shows enhancement at surface plasmon resonance frequency , where is the characteristic parameter of CNTs, is the relative permittivity of lattice and is the plasma frequency. This scheme is quite suitable to generate THz radiations in the milliwatt range of optimized values of the laser and CNTs parameters. We also explore the impact of polarization, S-parameter, critical angle, and length-matching effects of CNT antennas on the THz generation.

Influence of thermal contact resistance on the field emission characteristics of a carbon nanotube

A recent algorithm developed by Tripathi et al. [J. Appl. Phys. 128, 025017 (2020); Erratum, J. Appl. Phys. 131, 169901 (2022)] is modified to study the effects of thermal contact resistance on the field emission (FE) properties of a carbon nanotube (CNT). The model takes into account the temperature dependence of the CNT electrical and thermal conductivities. The boundary condition proposed by Huang et al. [Phys. Rev. Lett. 93, 7 (2004)] is used to include the effects of thermal contact resistance at a CNT/chuck interface located at x=0, i.e., Tc=T(x=0)=λπr2κ(Tc)(∂T/∂x)x=0+T0, where r is the CNT radius, κ(Tc) is the heat conduction coefficient at x=0, and λ is the thermal resistivity of the CNT/chuck interface. The chuck is assumed to be a perfect heat sink at temperature T0. For a given set of CNT parameters and values of the applied external electric field, it is shown that current constriction at the CNT/chuck contact point leads to self-heating effects which increase with the value of the thermal contact resistance, leading to an increase in the temperature profile along the CNT (including the temperature at its tip) and the FE current above their values obtained assuming the CNT/chuck interface is at the heat sink temperature T0. The fractional change of the emission current versus applied external electric field is calculated for increasing values of the parameter λ.

Indirect Exchange Coupling in Carbon Nanotubes

Nanostructured magnetic composites based on carbon nanotubes (CNTs) and ferromagnetic nanoparticles (FNPs) are of great interest both from an applied and fundamental point of view. In particular, one of the features of CNTs with FNPs is the possibility of magnetic interaction of nanoparticles through the conducting medium of CNTs. For a detailed description of this special type of interaction, which is the indirect exchange coupling, it is necessary to establish the relationship between the macroscopic and microscopic parameters of the physical system. In nanostructured ferromagnets, these dependences are described within the framework of a random magnetization model in which the spin system and, consequently, the main macroscopic characteristics (coercivity, susceptibility, and saturation magnetization) are determined by such microscopic parameters as the exchange interaction constant, the FNP magnetization, the local magnetic anisotropy constant, and the grain size. In this paper, on the basis of the previously obtained microscopic parameters of CNT – FNP nanocomposites, the possibility of obtaining long-range magnetic correlations through the indirect exchange coupling (IEC) between FNP embedded inside a multi-wall CNT (MWCNT) is considered. A model Hamiltonian is used that takes into account the diameter, chirality, chemical potential and spin-orbit interaction (SOI) in the system. The reason for the appearance of a noticeable SOI in CNTs is the curvature of the tubes, which significantly increases the SOI compared to graphene, as well as possible defects and the presence of FNP. IEC is realized by means of p-electrons of the inner wall of the MWCNT. The propagation of the spin susceptibility along the MWCNT axis is calculated and it is shown that a long-range magnetic order is realized under the condition that the chemical potential enters the gap opened by the SOI. Coherence is realized at distances up to micrometers. The proposed approach also made it possible to estimate the energy of the exchange interaction between the FNP belonging to one CNT. The results obtained indicate the prospects for the use of CNT– FNP nanocomposites in carbon spintronics.

Tensile mechanics of buckypaper: Bridging the disconnect between disordered structure and carbon nanotube properties

Carbon nanotubes (CNTs) are the building blocks of a variety of meso- and macro-scale assemblies. Buckypaper (BP) is a typical mesoscopic material that can possess tensile strength and modulus of up to three to four orders of magnitude lower than constituent CNTs. Identifying the “ruler” that not only predicts the realistic tensile properties of BP but also enables the scaling up of these characteristics with the aid of key CNT and structural parameters remains an open challenge. Herein, we propose a comprehensive theoretical framework to devise detailed tensile mechanics of the highly complex and fundamentally challenging random network of multi-walled carbon nanotubes (MWCNTs). A shell-based analytical model comprising intertube sliding and stretching as key modes of deformation has been constructed that successfully reduced Young's modulus of MWCNTs from 1 TPa to a few hundred megapascals in BP. Further, the tensile strength of BP has been modeled based upon the intertube sliding of MWCNTs at a stress that is well below their individual failure strength. A good agreement between the theoretical and experimental stress-strain curves of BPs justified that the predictive model is sufficiently robust. The parametric analysis on various metrics obtained from the analytical model has also been performed.

Alignment of carbon nanotubes under the influences of nematic liquid crystals and electric fields — an analytical study

Carbon nanotubes (CNTs) have benefits in various fields, they are disadvantageous due to their tendency to form aggregates and poorly controlled alignment of the CNT molecules (characterized by order parameters). These deficiencies can be overcome by dispersing the CNTs in nematic liquid crystal (LC) and placing the mixture under the influence of an electric field. In this study, Doi and Landau–de Gennes free energy density equations are used to analytically confirm that an electric field increases the order parameters of CNTs and LCs in a dispersion mixture. The anchoring strength of the nematic LC is also found to affect the order parameters of the CNTs and LC. Further, increasing the length-to-diameter ratio of the CNTs increases their alignment without affecting the LC alignment. These findings indicate that CNT molecular alignment can be controlled by adjusting the CNT length-to-diameter ratio, anchoring the LCs, and adjusting the electric field strength.

Piezoelectric response of aligned carbon nanotubes depending on sublayer material

The results of experimental studies of the effect of the sublayer material on the piezoelectric response and sensitivity to mechanical deformations of aligned carbon nanotubes (CNTs) are presented. It is shown that the highest piezoelectric response (136 nA at a pressing force of 4 μN) and best sensitivity are demonstrated by CNTs grown on a Mo sublayer. This dependence is probably due to the geometric parameters of CNTs and the structure of the CNT array as a whole. The results obtained can be used to develop energy-efficient nanogenerators based on CNT arrays.

Torsional Characteristics of Carbon Nanotubes: Micropolar Elasticity Models and Molecular Dynamics Simulation.

Efficient application of carbon nanotubes (CNTs) in nano-devices and nano-materials requires comprehensive understanding of their mechanical properties. As observations suggest size dependent behaviour, non-classical theories preserving the memory of body’s internal structure via additional material parameters offer great potential when a continuum modelling is to be preferred. In the present study, micropolar theory of elasticity is adopted due to its peculiar character allowing for incorporation of scale effects through additional kinematic descriptors and work-conjugated stress measures. An optimisation approach is presented to provide unified material parameters for two specific class of single-walled carbon nanotubes (e.g., armchair and zigzag) by minimizing the difference between the apparent shear modulus obtained from molecular dynamics (MD) simulation and micropolar beam model considering both solid and tubular cross-sections. The results clearly reveal that micropolar theory is more suitable compared to internally constraint couple stress theory, due to the essentiality of having skew-symmetric stress and strain measures, as well as to the classical local theory (Cauchy of Grade 1), which cannot accounts for scale effects. To the best of authors’ knowledge, this is the first time that unified material parameters of CNTs are derived through a combined MD-micropolar continuum theory.

Влияние параметров метода PECVD на рост углеродных нанотрубок для устройств нанопьезотроники

The results of experimental studies of the influence of the growth temperature and the thickness of the catalytic layer on the geometric and structural parameters of carbon nanotubes (CNTs) are presented. It is shown that the use of a TiN-based sublayer makes it possible to provide a low resistivity during the direct growth of CNTs on a conducting contact. It was found that for the formation of the best piezoelectric response, it is necessary to form the most defective CNTs. It is shown that the degree of defectiveness of CNTs can be controlled during their growth. A relationship has been established between the geometric and structural parameters of CNTs that affect the piezoelectric response. The potential applicability of CNTs for the creation of nanopiezotronic devices (nanogenerators, energy nanocarvesters) on their basis is shown.

Structural Damping Model for Composite Rotorcraft Blades with Carbon Nanotube Interlayers

Traditional lag dampers used in rotorcraft applications are unable to produce adequate levels of damping for high-speed coaxial compound rotorcraft that use rigid, hingeless blades. The current paper shows the possibility of having an intrinsic passive damping solution through the use of carbon nanotubes (CNTs) embedded in the interlayer region of a carbon-fiber-reinforced epoxy composite laminate. The CNTs are assumed to have a reversible stick–slip damping mechanism in the composite. The dissipation caused by the slip between the CNTs and the epoxy matrix is proportional to the slippage length of the CNTs. A laminated composite model is used to simulate a spar with alternating plies and CNT interlayers. The model is used to predict the stresses, strains, and damping associated with the plies and interlayers. The laminated composite damping model is validated by comparing the predictions with experimental results from the literature. The model is used to demonstrate the effect of the CNT interlayers on the damping of the composite blade. The effects of blade rotational speed and key CNT parameters (such as aspect ratio and critical shear stress on the damping of the blade) are also investigated. Loss factors of over 8 and 6% were observed with optimally configured parameters for soft and stiff in-plane rotors, respectively (0.138% for the baseline blade). Overall, the results suggest significant damping augmentation is achievable from the use of CNT interlayers in carbon/epoxy blades.

Multifield Coupled Dynamics Model of Resonant Carbon Nanotube Mass Sensor Based on Nonlocal Elastic and Electromagnetic Effects

Resonant mass sensors based on carbon nanotube (CNT) can measure the mass of individual molecules or atoms, and have broad application prospects in biological, medical, chemical, and physical research. Performance of CNT resonator depends on coupling of the multiphysical fields and nonlocal effects. Here, the equation of the nonlocal electromagnetic effects in the CNT is deduced. Combining it with the nonlocal elastic theory, a multifield coupled dynamics model for CNT resonant mass sensor with molecular adsorption is established. Using the model, effects of nonlocal elastic parameter, nonlocal electromagnetic parameter, molecular force, electromagnetic force, size parameters of CNTs, the position of adsorption molecules on the natural frequencies, and modes of CNT are studied. Coupled effects of the physical parameters on the natural frequency of the CNT resonator are analyzed. Molecular dynamics simulation of CNT vibration is carried out, and the results are compared with ones of nonlocal model, which illustrates the nonlocal coupled model. Results show that the coupling between the nonlocal elastic parameter and electromagnetic force has a great effect on the natural frequency of the CNT, and the coupling decreases with nonlocal elastic parameter but increases with electromagnetic force.

Frequency study on panel type of FG-CNTRC joined conical-conical structures

In this paper, frequency behavior of the joined conical-conical panels is investigated while the structures are reinforced with uniform or functionally graded (FG) embedment of carbon nanotubes (CNTs). To consider both rotary inertia and in-plane effects, the formulation is developed upon FSDT considerations. By means of Hamilton’s principle the dynamic equations for two cones are derived. To attach two individual panels accurately, continuity conditions is performed at the junctions to satisfy the compatibility of displacements and stress resultants. After imposing simply supported boundary conditions at the straight edges, the set of governing equations are discretized meridionally on the basis of generalized differential quadrature (GDQ) technique. The proposed discretization approach is applicable for arbitrary boundary types imposed on the two curved edges at the initiating and terminating points of the structure. The validation of results is primarily assessed via some comparisons between present data and those previous researches in the favor of individual conical panels and also finite element model for joined conical-conical type. Thereafter, the significant roles of semi-vertex angle, embrace angle, CNT parameters and boundary types on the vibrational features are discussed.

Optimization of CNT and TFT Parameters for Maximum Transconductance and Safe Temperature Operation of Carbon Nanotube Thin-Film Transistors (CNT-TFTs) Employed in Flat Panel Displays

Thin Film Transistors (TFTs) have lived to see its significant technological improvement for various display applications in recent years. Carbon nanotube (CNT) based TFT technologies have been found to be a promising component for next generation flexible electronics and flat panel displays in view of CNTs high carrier mobility, device stability and mechanical flexibility. However, the design of CNT-TFT is still not well established, especially with a view to achieve the best performance still protecting thermal stability. In this study, the authors had analysed the device structure and operation of transistor in which carbon nanotubes act as active channel region. CNT-TFT with different device geometrics and CNT physical parameters such as channel length, channel width, CNT tube length, network density and its orientation have been extensively studied using NanoNet simulation tool. This study has thrown new insight into the device performance characteristics of CNT-TFTs. The results show that it is essential to fix the length of the channel more than 5 µm for restricting the device temperature at 300 K and it can be brought down as low as 3 µm if the maximum operating temperature can be 400 K. Comparison with already reported experimental results show that the TFT parameters returned by the simulation experiments and presented in this paper match closely.

Investigation of Parameters for Schottky Barrier (SB) Height for Schottky Barrier Based Carbon Nanotube Field Effect Transistor Device

The design and development of Schottky Barrier Carbon Nanotube Field Effect Transistor (SB CNTFET) is still in the primitive research phase for its utilization in digital design. There is an immediate requirement for the analysis of parametric relations with structural factors to benefit the researchers working in this field. This work helps in the improvement of SB based CNTFET devices to be used in the development of various circuit applications. In this work, investigation of Schottky Barrier height on the performance of SB CNTFET for various geometrical and physical design parameters at the device level has been reported. The analysis of various device parameters of carbon nanotube, i. e., chirality, diameter, band gap, oxide thickness and dielectric constant has been carried out viz. subthreshold conduction, and ION/IOFF ratio. The paper also reports the effect of high dielectric constant material in SB CNTFET with oxide thickness along with Schottky Barrier Height Variation. The performance of SB CNTFET with variation in Schottky Barrier height and temperature variation is also reported. The results obtained indicate that performance of SB based CNTFET can be modified by the proper choice of chirality, dielectrics, oxide thickness and operating temperature. The SB parameter can be optimized by proper choice of metal contact in case of CNTFET.

Influence of ammonia flow and sublayer material on adhesion properties of carbon nanotubes

The results of experimental studies of the effect of the sublayer material and the ammonia buffer gas flow on the adhesion force of carbon nanotubes (CNTs) are presented. It is shown that the best adhesion is shown by CNT arrays grown on a chromium sublayer, which is due to the hierarchy of their structure. The influence of ammonia flow on the geometric parameters of CNT is shown. The nonlinear dependence of CNT adhesion force on ammonia flow is established. The results obtained can be used to create adhesive coatings of high strength.

Theoretical study on the effect of electric field for carbon nanotubes dispersed in nematic liquid crystal

Nematic liquid crystal (NLC) plays an important role in the controlled alignment of carbon nanotubes (CNTs). When nematogens are strongly anchored over the surfaces of CNTs, the Liquid Crystal (LC) order parameter is greatly influenced. Moreover, the electro-optic properties of the medium are significantly improved. Application of electric field further modifies these novel properties. The effect of electric field not only changes the phase behavior but also influences the ordering of both LC molecules and CNTs. Utilizing Doi and Landau–de Gennes type free energy mechanism, we have investigated in detail the changes incurred by the electric field. Order parameters of both LC and CNTs are calculated and modified phase diagrams are drawn. Finally, we have employed Landau–Khalatnikov equation to calculate rotational viscosity of the medium. It is found that rotational viscosity decreases with increasing volume fraction of CNTs in accordance with experimental results.

DFT based estimation of CNT parameters and simulation-study of GAA CNTFET for nano scale applications

The device dimensions have been consistently scaling down since many developing technologies need smaller and faster integrated circuits for advancement and improvement in both performance and device density. Device dimensions have been decreased drastically from micron to sub nanometer regime. Traditionally, miniaturizing and performance improvement was obtained by tweaking the MOSFET- reducing the channel lengths and gate oxide thickness, increasing dielectric constants etc Unfortunately at 22 nm node it reached a dead end. However, at 22 nm node the tri-gate FinFET introduced by Intel Corporation have provided many possibilities for scaling the dimensions with satisfactory device performance. Further, the gate all around (GAA) carbon nano tube field effect transistor (CNTFET) provides high gain, high trans-conductance, reduced short channel effects and conditions for scaling the technology to sub nano scale. Due to surround gate structure this GAA CNTFET offers better control with integration of high_k stacked dielectric wrapped around the channel. In this paper, first properties of Carbon nanotube (CNT) have been comprehensively studied for various chirality and diameter and parameters viz. Density of States (DoS) and Band gap (Eg) are extracted by using MedeA tool’s VASP 5.3 module. The various CNT chirality have been optimized and the extracted parameters used to model and simulate CNTFET using Silvaco’s Devedit3D, Atlas and Atlas3D modeling and simulation modules. The device input (ID-VGS ) and output (ID-VDS) characteristics have been intensively studied and parameters including ION /IOFF ratio, DIBL, sub threshold slope extracted and compared with the conventional devices. The GAA CNTFET device at 0.8 V supply voltage exhibits threshold voltage (VTH) 0.254 V, drain induced barrier lowering (DIBL) 72 mV/V, sub-threshold swing (SS) 63.29 mV/dec, and ION/ IOFF ratio 7.17e + 06. The results demonstrate improvement in device parameters for the GAA CNTFET device as compared to bulk silicon and FinFET devices.

Effect of Carbon Nanotube Diameter and Stiffness on Their Phase Behavior in Crowded Solutions.

The unique carbon nanotube (CNT) properties are mainly determined by their geometry, e.g., their aspect ratio, diameter, and number of walls. So far, chlorosulfonic acid is the only practical true solvent for carbon nanotubes, forming thermodynamically stable molecular solutions. Above a critical concentration the system forms an ordered, nematic liquid-crystalline phase. That phase behavior is the basis for liquid-phase processing and the optimal translation of the carbon nanotube molecular properties to the macroscopic scale. The final material properties depend on the phase behavior of the "dope" from which it is prepared, which depends on the CNT parameters themselves. Earlier work determined that CNT aspect ratio controls the phase behavior, in accordance with classical rigid-rod theories. Here we use cryogenic transmission electron microscopy and Raman spectroscopy to understand the relation between the geometry of the CNTs, the chemical interaction with chlorosulfonic acid, and the phase behavior of crowded solutions. We show that the CNT diameter and number of walls also play an independent role in the phase transition and phase morphology of the system because of their effect on the CNT bending stiffness.

Simulation studies on effect of CNT physical parameters on carbon nanotube thin-film transistors (CN-TFTS)

Limitations faced in scaling of silicon-based transistors were expelled using carbon nanotube as channel material. The Carbon nanotube-based thin-film transistor (CN-TFTs) is one of the most promising devices to become successor of silicon devices in near future because of its enhanced device performance in all aspects in nano-regime. The carbon nanotube parameters such as tube length, orientation of tubes between the source and drain terminals, tube density along with channel width and length decide the drain current and device temperature primarily. Therefore, the authors had studied the influence of CNT physical parameters on the CN-TFT device performance in this work. The studies clearly bring out the influence of these parameters on device performance and temperature in addition to suggesting the need to optimize these parameters of the device.

The effect of carbon nanotube chirality on the electrical conductivity of polymer nanocomposites considering tunneling resistance

In this study, the effect on the conductance of polymer nanocomposites considering quantum tunneling resistance is investigated with respect to the chirality of carbon nanotubes (CNTs) and uncertainties in the geometric parameters of CNTs by using Monte Carlo simulations. The random spatial placement for CNTs was accomplished with a one-dimensional line segment and the periodic boundary conditions were applied to CNTs in the two-dimensional representative volume element. Intersection points between each CNT were calculated to obtain connectivity lists of the connected network path. Both the intrinsic resistance of the CNT and the inter-CNT tunneling resistance were considered in this model. In addition, the in-house code developed was validated by comparison with several experimental datasets from the literature. Unlike past studies, uncertainties in the chiral index of single-wall CNTs concerning armchair and zig–zag structures have been considered here and the electrical conductivity and percolation threshold are predicted.

Electrical percolation of silicone rubber filled by carbon black and carbon nanotubes researched by the Monte Carlo simulation

ABSTRACTElectrical percolation of carbon black (CB) and carbon nanotubes (CNTs) filled into silicone rubber (SR) is analyzed by the three‐dimensional (3D) Monte Carlo simulation. First, the 3D models and simulation parameters of CB and CNTs are researched to narrow the deviation between simulation and experimental results of CB/SR and CNTs/SR. The degree of agglomeration is the most important parameter in simulation for CB. The 3D model of CNTs is the most important factor in simulation for CNTs. Then, the 3D Monte Carlo simulation for CB/CNTs/SR is developed based on the optimized 3D models and parameters of CB and CNTs. The results yielded by the simulation with optimized parameters are similar to the experiments and synergistic conductive effect of two hybrid fillers in nanocomposites exists. This work has demonstrated that the quantification of the electrical percolation of two hybrid fillers in nanocomposites by Monte Carlo simulation is feasible. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48222.