Characteristics Of Single-walled Carbon Nanotubes Research Articles

Analog monolayer SWCNTs-based memristive 2D structure for energy-efficient deep learning in spiking neural networks

Advances in materials science and memory devices work in tandem for the evolution of Artificial Intelligence systems. Energy-efficient computation is the ultimate goal of emerging memristor technology, in which the storage and computation can be done in the same memory crossbar. In this work, an analog memristor device is fabricated utilizing the unique characteristics of single-wall carbon nanotubes (SWCNTs) to act as the switching medium of the device. Via the planar structure, the memristor device exhibits analog switching ability with high state stability. The device’s conductance and capacitance can be tuned simultaneously, increasing the device's potential and broadening its applications' horizons. The multi-state storage capability and long-term memory are the key factors that make the device a promising candidate for bio-inspired computing applications. As a demonstrator, the fabricated memristor is deployed in spiking neural networks (SNN) to exploit its analog switching feature for energy-efficient classification operation. Results reveal that the computation-in-memory implementation performs Vector Matrix Multiplication with 95% inference accuracy and few femtojoules per spike energy efficiency. The memristor device presented in this work opens new insights towards utilizing the outstanding features of SWCNTs for efficient analog computation in deep learning systems.

Torsional vibrational analysis of irregular single-walled carbon nanotube with elastic-support boundary conditions

Understanding the torsional vibration characteristics of Single-Walled Carbon Nanotubes (SWCNTs) is of great interest to ensure the reliable design of various nanodevices in which SWCNT is a common structural component. The previous studies were usually limited to uniform SWCNTs under classical boundary conditions. Motivated by this limitation, a practical, accurate solution is created for the torsional vibration of an irregular SWCNT with elastic-support boundary conditions. The torsional vibration of an irregular single-walled carbon nanotube with elastic-support boundary conditions is modeled by Flügge's principle. Unlike the uniform carbon nanotube, effects of irregularity and stiffness parameters are considered within the framework of Flügge's model. Stiffness parameters are defined as a function of complex torsional wave number, which makes all the subsequent calculations be treated precisely and efficiently. The governing equations are derived using Flügge's principle, and the wave propagation approach is applied to solve these equations. The accuracy and efficiency of the current model are then illustrated by a variety of numerical examples. The impact of various parameters, including surface irregularity, stiffness, and nanotube thickness, on the torsional vibration of irregular SWCNT, is examined. According to this study, the results indicate that the frequency calculated is influenced by the irregularity parameter compared with the case of uniform SWCNT. The effects of the parameters of irregularity, stiffness, and nanotube thickness are investigated and discussed. The results show that, an increase in irregularity's parameter leads to a decrease in the natural frequency of irregular SWCNT with elastic-support boundary conditions. In addition, an increase in nanotube's thickness leads to a notable decreasing in the natural frequency of irregular SWCNT. The finding obtained in this work may serve as valuable references for the designs of Nano-oscillators and nanodevices, where the torsional vibration of the irregular SWCNT has a remarkable effect on the functioning of these devices.

Calculation of the Single-Walled Carbon Nanotubes' Elastic Modulus by Using the Asymptotic Homogenization Method

This article uses the asymptotic homogenization method to investigate the mechanical characteristics of single-walled carbon nanotubes. The asymptotic homogenization method has been used to derive the equations for the homogenized elastic properties matrix. Then, MATLAB is used to model nanotubes and implement the finite element simulation. Two types of chiralities, including armchair and zigzag, are taken into account in this regard. Young's modulus and shear modulus have been estimated for both armchair and zigzag nanotubes in accordance with the relationships between the derived coefficients and molecular mechanical characteristics. Investigations have been done into how diameter and orientation affect the mechanical characteristics of carbon nanotubes. The research's findings are corroborated and generally consistent with those found in other articles.

Morphology and Electrical Characteristics of Single-Walled Carbon Nanotubes Film Prepared by Air Brush Technique

This study is to investigate the morphology and electrical characteristics of single-wall carbon nanotubes (SWCNTs) thin film deposition using air brush technique. A deposition setup consisting of a conventional artist air brush was developed and used to deposit SWCNT thin films and therefore the resulting film’s characteristics need to be investigated to gauge its suitability in producing uniform monolayer. The SWCNTs used were synthesized via Direct Injection Pyrolytic Synthesis (DIPS) method, with diameters ranging from 0.8 to 3 nm. The substrate was deposited using an airbrush with varying nozzle to study its effect to the resulting SWCNTs thin films’ characteristics. Subsequently, scanning electron microscope (SEM) were used to inspect the morphology and surface topography, and followed by preliminary electrical measurements. The result shows that good dispersion promotes uniform distribution of SWCNTs over large area of glass substrate. Moreover, the electrical measurement revealed that at 1 V, best morphology produced highest current at a nozzle distanceof 10 mm (15.3 μA) and the lowest current at a nozzle height of 4 mm (3.24 μA). From the results presented, it is demonstrated that conventional artist airbrush setup can be effectively used to deposit monolayer thin film of SWCNT with high degree of uniformity. This research is necessary for the process of depositing-controlled CNT thin film network, which can influence the material characteristics and performance of the variety of CNT-based device applications.

Nanojunction Material Effect on the Photoelectric Response of Single-Wall Carbon Nanotube Rectennas.

To optimize the performance of carbon nanotube (CNT)-based rectennas, we have studied the effect of metal work function on the photodetection characteristics. Two materials of conducting nanoprobes, namely, gold (Au) and platinum (Pt), have been used to form a rectifying diode at the interface with the CNT. The electrical and optical characteristics of single-wall carbon nanotubes (SWCNTs) dispersed on top of a SiO2/Si substrate have been investigated using a conductive mode atomic force microscope (C-AFM). The I–V measurements performed for both diodes have exhibited an explicit rectification behavior with high sensitivity of a CNT-based rectenna to light. It has been observed that the lower work function metal (Au) leads to a higher on/off current ratio than the high work function metal (Pt). These experimental observations will be explained using the material characterization of the complete system along with representative energy-band diagrams.

A non-local modeling for the influence of fluid forces on vibration characteristics of carbon nanotubes

This paper studies the effects of fluid forces and magnetic fields on the vibration characteristics of single-walled carbon nanotube (SWCNT). The force of the fluid on the SWCNT tube wall is derived by using the Hamilton’s variation principle, and the Lorentz magnetic force obtained from Maxwell's relationship. The governing equations of motion are based on the non-local beam model under the action of fluid and longitudinal magnetic field. Moreover, in the present investigation, an analytical approach is also proposed to study the effect of fluid, small-scale effect and longitudinal magnetic field on the vibration frequency of single-walled fluid-conveying carbon nanotube. The numerical results show that the fluid has a significant influence on the vibration characteristics of SWCNTs, and the effect of the high-speed fluid on the carbon nanotube (CNT) wall cannot be neglected.

Comparison of characteristics of single-walled carbon nanotubes obtained by super-growth CVD and improved-arc discharge methods pertaining to interfacial film formation and nanohybridization with polymers

A comparison of single-walled carbon nanotubes (SWCNTs) produced by super-growth chemical vapor deposition (CVD) and improved-arc discharge methods was performed as it pertains to the formation of their Langmuir-Blodgett films and polymer-based nanocomposite preparation. Two kinds of SWCNTs indicated amphipathic properties after surface chemical modification using long-chain phosphonic acids. The modification rates of the two types of organo-modified SWCNTs were almost the same, impurities were removed to the same extent, and the influence of the tube length distribution was considered to be low. However, it was expected that the SWCNTs made via improved-arc discharge would be superior in regularity in the two-dimensional film. Specifically, the arrangement regularity of the modified chains was high, and as a result, the layering regularity of SWCNTs itself was considered to be high. Owing to organo-modification, SWCNTs manufactured via the super-growth CVD method tended to be dispersed into finer fibers even in a monolayer. Compared to other organic polymers, this organo-modified SWCNT formed a composite material with higher dispersibility. The significant difference in the physical properties of both SWCNTs constitutes a trade-off relationship between dispersibility and two-dimensional regularity. The difference in the physical properties of the two types of SWCNTs could be related to the strength of the interaction between the exposed SWCNT-specific surfaces, even after organo-modification.

Gate Quantum Capacitance Effects in Nanoscale Transistors

As the physical dimensions of a transistor gate continue to shrink to a few atoms, performance can be increasingly determined by the limited electronic density of states (DOS) in the gate and the gate quantum capacitance (CQ). We demonstrate the impact of gate CQ and the dimensionality of the gate electrode on the performance of nanoscale transistors through analytical electrostatics modeling. For low-dimensional gates, the gate charge can limit the channel charge, and the transfer characteristics of the device become dependent on the gate DOS. We experimentally observe for the first time, room-temperature gate quantization features in the transfer characteristics of single-walled carbon nanotube (CNT)-gated ultrathin silicon-on-insulator (SOI) channel transistors; features which can be attributed to the Van Hove singularities in the one-dimensional DOS of the CNT gate. In addition to being an important aspect of future transistor design, potential applications of this phenomenon include multilevel transistors with suitable transfer characteristics obtained via engineered gate DOS.

Vibration analysis of single-stranded DNA-wrapped single-walled carbon nanotubes using finite element method

We analyzed the vibration characteristics of single-walled carbon nanotubes (SWCNTs)1 wrapped with single-stranded DNA (ssDNA) using the finite element method. The SWCNT model was calculated from the 1st-bending mode of 0.98 GHz to the radial breathing mode of 10.2 THz under free boundary conditions. The natural frequency of the SWCNTs was consistent with the well-known Bernoulli-Euler beam theory, and with the experimental relationship between the wave number and diameter of the SWCNTs. Additionally, the vibration modes and conditions for coupling with the 1st-bending mode of the ssDNA-SWCNTs were obtained under vacuum and water conditions.

Transversely Isotropic Rod for Modeling Elastic Characteristics of Single-Walled Carbon Nanotube

Single-walled carbon nanotubes (SWCNT) are a seamless cylindrical structure formed by folding a single-walled graphene sheet. Nanotubes are of great interest due to their unique thermo-mechanical characteristics. Such objects can be applied in the energy, rocket and aerospace engineering as a filler of advanced structural composite materials.One of the most important SWCNT characteristics is a complex of its elastic properties. The most reliable way to determine the elastic characteristics of a nanotube is to conduct an experiment. However, due to high cost and lengthy time of the experiment completion, it is more preferable to use mathematical modeling of these properties of SWCNT with which the paper deals.The paper proposes a mathematical model that is constructed by methods of generalized continuum mechanics. To use these methods, the nanotube, on the assumption of its transverse isotropy, is presented simultaneously as a cylindrical shell and a continuous circular rod.As a result of consideration of various stress-strain states of the shell and rod, are obtained relations to establish a quantitative relation between the elements of the matrix of compliance coefficients of a rod that simulates a single-walled carbon nanotube, and the elastic characteristics of graphene taken as its basis in the isotropy plane. Also, the constructed mathematical model allows us to define the influence of the nanotube configuration (chiral indices) on its elastic characteristics.The paper presents the application results of the model proposed, using as an example, a SWCNT with chirality indices (7, 0), for which were constructed mutually inverse matrices of compliance and elasticity coefficients that completely describe the elastic properties of the nanotube.Using the proposed mathematical model significantly reduces the time and cost for estimation of the elastic characteristics of the SWCNT, that is especially important at the design stage of new materials based on them.

Effect of DNA on Fundamental Characteristics of Single-Walled Carbon Nanotubes; Length Distribution and Thermal Stability

Single-stranded DNA has been demonstrated to enable single-particle exfoliation of single-walled carbon nanotubes (SWCNTs) in aqueous environments as well as suppress their known toxicological effects. The resultant fundamental properties of DNA-SWCNT hybrids are significant when these nanomaterials are applied to mechanical and biological systems. Accurate characterization of their length distributions is of great importance regarding their application as a clinical diagnostic agent. Here, we show that DNA-SWCNT hybrids differentially bind to freshly-cleaved mica in a manner that significantly depends upon the sequence of DNA. By displacing the DNA from the SWCNTs, we show that the length distributions of the resulting surfactant-coated SWCNTs are statistically identical and suggest that a DNA-wrapping can give inaccurate length distributions in image-derived approaches. Secondly, enhancing the thermal stability of SWCNTs is crucial when these materials are applied to high temperature applications. We examined the thermal decomposition temperature and rate of DNA functionalized carbon nanomaterials using thermogravimetric analysis and found that functionalization with DNA significantly increases the thermal decomposition temperature of all examined carbon nanomaterials in the order SWCNTs > C60 > RGO > MWCNTs. We attribute these increases in decomposition temperature to the fact that DNA, an intumescent molecular entity that increases in volume upon heating, shields the hybridized carbon nanomaterials from flame and elevated temperatures. Enhancing the thermal decomposition properties of carbon nanomaterials with non-toxic flame retardants enables the realization of environmentally friendly high temperature sensing and electronics applications.

Systematic investigation of the catalyst composition effects on single-walled carbon nanotubes synthesis in floating-catalyst CVD

Enormous technological promise of single-walled carbon nanotubes (SWCNTs) can only be harnessed with the premise of controllable synthesis of SWCNTs, where catalyst composition thermodynamically plays a vital role. Herein, we have systematically investigated the effects of catalyst composition on SWCNTs synthesis, using a novel floating-catalyst chemical vapor deposition (FCCVD) system, consisting of catalyst synthesis via spark generator, FCCVD reactor and a real-time monitor of catalysts and SWCNTs. We synthesized SWCNTs from both monometallic (Fe, Co, Ni), bimetallic (Co-Ni, Co-Fe) catalyst particles and kinetically optimized yield and performance of SWCNTs films. We found that the highest yield of SWCNTs from Fe is 15 times as that of Ni SWCNTs and the Co-Ni SWCNTs film possesses best opto-electronic performance. Interestingly, the mean diameter of SWCNTs was found related to the catalyst particle size distributions, but not composition. Moreover, detailed atomic structures determination revealed that SWCNTs from Fe and Co have a wide chirality distribution spanning from zig-zag to armchair edges. However, Co-Ni SWCNTs have comparatively narrower chirality distribution having 71% SWCNTs in the chiral angle of 15–30°. Our results indicate that catalyst composition can efficiently tune yield and characteristics of SWCNTs, but it does not dramatically shift chirality of FCCVD SWCNTs.

Application of the coherent spectroscopy method for the study of biosensor test systems based on nanomarkers

A new class of fluorescent markers, nanocomposites with a high quantum yield, which appeared in the last decade, opens up broad prospects for their use in medicine, in particular, to create on their basis highly sensitive biosensor test systems. It is of interest to use these markers as luminescent sources when conducting immunoenzymatic analysis for specific metabolites. We made a comparison between the optical characteristics of single-walled carbon nanotubes and lanthanide porphyrins. Based on the method that we developed earlier using nonlinear optical effects, we developed recommendations for using functionalized single-layer carbon nanotubes as a fluorescent marker for immunoreactions with high signal characteristics noise in the region of 800 nm and to determine the stability of nanomarkers.

Tensile characteristics of single-walled carbon nanotubes endohedrally decorated with gold nanowires: A molecular dynamics study

Young's modulus and the fracture of gold nanowires (GNWs) encapsulated inside single-walled carbon nanotubes (SWCNTs) are studied using molecular dynamics (MD) simulations. To investigate the mechanical behavior, two important parameters, i.e. ultimate tensile force and strain, are calculated. The obtained results from aforementioned nanostructures are compared with those of pure GNWs and SWCNTs. The results illustrate that SWCNTs filled with GNWs (GNWs@SWCNTs) and pure GNWs possess lower Young's moduli than those of pure SWCNTs in a similar length. As the length increases, Young's modulus of pure GNWs and GNWs@SWCNTs is reduced. In a particular length, the highest and lowest ultimate forces belong to the multishell GNWs@SWCNTs and pure multishell GNWs, respectively. Moreover, it is found that pure SWCNTs have the highest ultimate strains. Also, by rising the length, the ultimate tensile strain increases. To study the effect of selected boundaries on the tensile characteristics, the tensile loads are applied to the boundaries of surrounding SWCNTs instead of whole configuration (B model). The obtained results demonstrated that in the similar length, Young's modulus and ultimate force for B model are higher than those of A model, i.e. the model that the whole system is under the tensile loads. By contrast, in the particular length, B model shows lower ultimate strain compared to that of A model.

Nonlinear vibrations characteristics of single-walled carbon nanotubes by nonlocal elastic shell model

The model of single-walled carbon nanotubes nonlinear vibrations, which is based on shell theory, is derived. The system of partial differential equations with respect to three displacements projections is obtained using the Sanders–Koiter shell theory and nonlocal elasticity. The system of nonlinear ordinary differential equations, which describes the nanotubes vibrations, is obtained by the Galerkin method. The harmonic balanced method is used to calculate free nonlinear vibrations. The bifurcation behavior of CNT vibrations owing to the Naimark–Sacker bifurcation is analyzed. Almost periodic vibrations of carbon nanotubes are investigated numerically. The nanotube periodic and almost periodic vibrations have three displacements projections u,v,w, which are commensurable. This is essential difference of the nanotube vibrations from macroshells.

A Fluorescent Carbon Nanotube Sensor Detects the Metastatic Prostate Cancer Biomarker uPA.

Therapeutic outcomes in patients with prostate cancer are hindered by the inability to discern indolent versus aggressive disease. To address this problem, we developed a quantitative fluorescent nanosensor for the cancer biomarker urokinase plasminogen activator (uPA). We used the unique fluorescent characteristics of single-walled carbon nanotubes (SWCNT) to engineer an optical sensor that responds to uPA via optical bandgap modulation in complex protein environments. The sensing characteristics of this construct were modulated by passivation of the hydrophobic SWCNT surface with bovine serum albumin (BSA). The sensor enabled quantitative detection of known uPA concentrations in human blood products. These experiments potentiate future use of this technology as a rapid, point-of-care sensor for biomarker measurements in patient fluid samples. We expect that further work will develop a method to discern aggressive vs indolentprostate cancer and reduceovertreatment of this disease.

Influence of magnetic field and thermal radiation on convective flow of SWCNTs-water and MWCNTs-water nanofluid between rotating stretchable disks with convective boundary conditions

We have studied MHD boundary layer flow and heat transfer characteristics of single-wall carbon nanotubes (SWCNTs) and multi-wall carbon nanotubes (MWCNTs) with water as the base fluid between two rotating disks with different rotating and stretching velocities by taking thermal radiation and convective boundary conditions numerically in the present analysis. Suitable similarity conversions are employed to reduce non-linear partial differential equations into system of ordinary differential equations and these equations together with boundary conditions are solved numerically using Finite element method. The sway of various pertinent parameters on velocity and temperature distributions as well as skin-friction coefficient and Nusselt number are examined in detail and the results are displayed graphically and in tabular form. It is perceived that the values of Nusselt number escalates near lower disk as the values of nanoparticles volume fraction parameter (φ) increases and rise is remarkably higher in water based multi-wall carbon nanotubes than the single-wall carbon nanotubes. Temperature of the fluid remarkably enhances and is more in SWCNTs-water than MWCNTs-water based nanofluid with higher values of thermal biot number (B4). With increasing values of B2 the rate of heat transfer at lower disk Nu1 improves, whereas, the rate of heat transfer at upper disk Nu2 diminishes in the both nanofluids.

Dependence of the Dipole Moment of Functionalized Carbon Nanotubes of Chair Type on Their Length

The dependence of the electronic energy characteristics of single-walled carbon nanotubes of the chair type (3, 3) and (4, 4) functionalized by the boundary hydrogen and fluorine atoms on the tube length was studied by the semiempirical MNDO quantum-chemical method within the framework of the molecular cluster model. The results of calculations showed a tendency toward saturation of the charges of the boundary atoms at a length of 20 unit cells along the tube axis. The dipole moment of the functionalized carbon nanotubes reached saturation at a length of 40 unit cells along the axis. The dipole moment of saturation increased with the tube diameter. This effect is manifested for various one-dimensional structures.

An Immunologically Modified Nanosystem Based on Noncovalent Binding Between Single-Walled Carbon Nanotubes and Glycated Chitosan.

Functionalized single-walled carbon nanotubes are currently being explored as novel delivery vehicles for proteins and therapeutic agents to treat various diseases. In order to maximize treatment efficacy, a strong binding between single-walled carbon nanotubes and their functionalized molecules is necessary. Glycated chitosan, a polymer with potent immunostimulatory properties for cancer treatment, has been used as a surfactant of single-walled carbon nanotubes to form an immunologically modified nanosystem for biomedical applications. In this study, we investigated the binding characteristics of single-walled carbon nanotube and glycated chitosan using molecular dynamics simulations. The mean square displacement, radius of gyration, interaction energy, and radial distribution function of the single-walled carbon nanotube-glycated chitosan system were analyzed. The results from the simulations demonstrated that glycated chitosan was bound to single-walled carbon nanotubes by a strong, noncovalent interaction. The stability of glycated chitosan on the single-walled carbon nanotubes surface was enhanced by the length of glycated chitosan, and the binding energy of the 2 molecules was closely related to the diameter and chirality of single-walled carbon nanotubes, with the most stable single-walled carbon nanotube-glycated chitosan system being formed by the combination of long polymer, large single-walled carbon nanotube, and armchair single-walled carbon nanotube. The understanding of the interactions between single-walled carbon nanotube and glycated chitosan and the structure of single-walled carbon nanotube-glycated chitosan allows the modifications of the novel nanosystem for disease diagnostics and therapeutics.

Effect of Longitudinal Magnetic Field on Vibration Characteristics of Single-Walled Carbon Nanotubes in a Viscoelastic Medium

The effect of longitudinal magnetic field on vibration response of a sing-walled carbon nanotube (SWCNT) embedded in viscoelastic medium is investigated. Based on nonlocal Euler-Bernoulli beam theory, Maxwell’s relations, and Kelvin viscoelastic foundation model, the governing equations of motion for vibration analysis are established. The complex natural frequencies and corresponding mode shapes in closed form for the embedded SWCNT with arbitrary boundary conditions are obtained using transfer function method (TFM). The new analytical expressions for the complex natural frequencies are also derived for certain typical boundary conditions and Kelvin-Voigt model. Numerical results from the model are presented to show the effects of nonlocal parameter, viscoelastic parameter, boundary conditions, aspect ratio, and strength of the magnetic field on vibration characteristics for the embedded SWCNT in longitudinal magnetic field. The results demonstrate the efficiency of the proposed methods for vibration analysis of embedded SWCNTs under magnetic field.