Single Carbon Nanotubes Research Articles

3D waviness effect of carbon nanotubes on fundamental natural frequency and modeling of resonance of nanocomposite structure

Optimum waviness of carbon nanotubes (CNTs) inside a matrix composite beam and composite bridge is endeavor to obtain its utmost natural frequencies considering a volume fraction of CNTs. 3D FE model of the beam is generated via ABAQUS along with Python programming and thereafter to calculate an optimal waviness under encastre boundary conditions and different vibration modes. The effect of waviness and the number of waves on mode shapes, natural frequency, and corresponding stiffness of a beam are examined, and the outcomes are compared to those of a pure polymer beam, straight CNT-based composite beam and nanobridge value. It was decided to conduct a convergence analysis and the optimum value of the number of elements and nodes was studied and found that 19666 nodes are reliable to give correct results. The FE analysis results reveal that the waviness effect of CNTs significantly depends on mode shapes. The fundamental natural frequency, as well as other related vibrational properties, is observed to be enhanced. By decreasing the waviness from 50 to 25, there is an increment in natural frequency in the 3rd mode by 68.68, 5th mode by 44.6 and 6th mode by 62.4, but in other modes, there is negligible difference. When single-wave CNTs were compared, the sine wave produced more frequency in the third mode by 206.03, 4th mode by 199.8 and 6th mode by 478.6 Hz. After comparing the results of different waviness types, single sine waviness, multi-waved CNTs, straight CNTs and neat matrix, it is found that for the highest value of waviness of CNT fiber-based nanocomposites, the natural frequency of CNT-reinforced nanocomposite reaches the frequency of the neat matrix and further adding of CNTs does not increase the value of frequency. The result showed that the finite element model (FEM) is a good simulation of the vibratory system.

Rotating Flow in a Nanofluid with CNT Nanoparticles over a Stretching/Shrinking Surface

The steady three-dimensional rotating flow past a stretching/shrinking surface in water and kerosene-based nanofluids containing single and multi-walled carbon nanotubes (CNTs) is investigated. The governing equations are converted to similarity equations, and then numerically solved using MATLAB software. The impacts of rotational, suction, and nanoparticle volume fraction on the flow and the thermal fields, as well as velocity and temperature gradients at the surface, are represented graphically and are analyzed. Further, the friction factor and the heat transfer rate for different parameters are presented in tables. It is found that the heat transfer rate increases with increasing nanoparticle volume fraction as well as suction parameter in water and kerosene-based nanofluids of single and multi-walled CNTs. However, the increment in the rotating flow parameter decreases the rate of heat transfer. Multi-walled carbon nanotubes and kerosene-based nanofluid contribute to heat transfer rates better than single-walled carbon nanotubes and water-based nanofluid, respectively. A unique solution exists for the stretching surface, while two solutions are obtained for the shrinking surface. Further analysis of their stabilities shows that only one of them is stable over time.

Aerosol Jet Printing of Graphene and Carbon Nanotube Patterns on Realistically Rugged Substrates.

Direct-write additive manufacturing of graphene and carbon nanotube (CNT) patterns by aerosol jet printing (AJP) is promising for the creation of thermal and electrical interconnects in (opto)electronics. In realistic application scenarios, this however often requires deposition of graphene and CNT patterns on rugged substrates such as, for example, roughly machined and surface-oxidized metal block heat sinks. Most AJP of graphene/CNT patterns has thus far however concentrated on flat wafer- or foil-type substrates. Here, we demonstrate AJP of graphene and single walled CNT (SWCNT) patterns on realistically rugged plasma-electrolytic-oxidized (PEO) Al blocks, which are promising heat sink materials. We show that AJP on the rugged substrates offers line resolution of down to ∼40 μm width for single AJP passes, however, at the cost of noncomplete substrate coverage including noncovered μm-sized pores in the PEO Al blocks. With multiple AJP passes, full coverage including coverage of the pores is, however, readily achieved. Comparing archetypical aqueous and organic graphene and SWCNT inks, we show that the choice of the ink system drastically influences the nanocarbon AJP parameter window, deposit microstructure including crystalline quality, compactness of deposit, and inter/intrapass layer adhesion for multiple passes. Simple electrical characterization indicates aqueous graphene inks as the most promising choice for AJP-deposited electrical interconnect applications. Our parameter space screening thereby forms a framework for rational process development for graphene and SWCNT AJP on application-relevant, rugged substrates.

Asymmetric carbon nanotube dimers embedded in a dielectric slab: new plasmonic resonance behavior

All prior work on modeling the full-wave electromagnetic response of carbon nanotubes (CNTs) have focused on CNTs in free-space, whereas in most practical applications, CNTs are embedded in a dielectric substrate. In this work, we use full-wave simulations to study the plasmonic resonances of CNT dimers embedded in a lossy dielectric slab with a finite thickness. The numerical results show that the finite thickness dielectric slab leads to the emergence of new CNT resonance behavior that is not present in a homogeneous environment. As a single CNT approaches the dielectric slab interfaces, the resonance frequency of the CNT increases due to reduced dielectric loading. The resonance behavior changes completely when two CNTs in proximity form a dimer near the slab interface. The bonding and antibonding resonances of CNT dimers and the absorbed power vary significantly with the distance between the slab interface and the CNT dimer. Using this phenomenon, we show that symmetric CNT dimers can behave like asymmetric CNT dimers. Also, the antibonding resonance of an asymmetric CNT dimer can be suppressed by adjusting the length and depth of the CNT dimer inside the slab. This work can guide future sensing modalities based on CNT dimer as well as can provide an accurate assessment of the proximity of a CNT network to the interface of the embedding substrate.

Intelligent supervised learning for viscous fluid submerged in water based carbon nanotubes with irreversibility concept

This article examined the Silver based Di‑hydrogen carbon nanotubes flow model (SDH-CNTFM) between two stretchable coaxially disks by utilizing the Method of Levenberg Marquardt with Back-propagated Neural Networks (MLM-BPNN). Here the base liquid is silver (Ag) and the nanoparticles are SWCNTs and MWCNTs (single and multiwall carbon nanotubes). The governing PDEs for SDH-CNTFM are transformed into ODEs by utilizing similarity transformation. Energy equations are developed through heat generation and viscous dissipation joule heating. Also calculated the total entropy optimization. Flow parameters velocity, entropy optimization, temperature, Nusselt number and Bejan number are discussed for both single and multi-walls carbon nanotubes (SWCNTs and MWCNTs) graphically and in Tabular form. The reference dataset is calculated through implementation of Optimal Homotopy Analysis method (OHAM) for variants of SDH-CNTFM. For the variation of different parameters this reference dataset is utilized in MATLAB to clarify the solution and error analysis plots. Moreover, the approximated solution is assessed through adopting training/testing/validation procedure and comparing it with standard solution which is endorsed by performance study based on MSE convergence, error histogram and regression studies. Heat transfer rate and surface drag force are discussed for both SWCNTs and MWCNTs numerically by using different flow parameters. From obtained outcomes, it is observed that entropy rate boosts up for higher approximation of nanoparticles of volume friction and Brickman number (Br) which is controlled due to the minimization of Brickman number.

A Compact Physical Drain Current Model of Multitube Carbon Nanotube Field Effect Transistor Including Diameter Dispersion Effects

Carbon nanotube field-effect transistor (CNTFET) shows great potential for digital and analog applications due to the unique 1-D ballistic carrier transport in carbon nanotubes (CNTs). A new compact physical model for CNT Schottky-barrier transistors is proposed in this article. The Schottky barrier between the contact metal and CNTs is described by using an effective barrier height, and more importantly, the influence of using CNT arrays or networks rather than a single CNT as the device channel is considered in this model. Moreover, the trapping effect is investigated and modeled by adding <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RC</i> delay element to the equivalent circuit. The model is proposed in a concise form to avoid complex operations such as integration and is compatible with circuit simulation. The simulation results of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}-{V}$ </tex-math></inline-formula> characteristics are verified to be in agreement with experimental data.

Entropy Generation Analysis of Radiated Magnetohydrodynamic Flow of Carbon Nanotubes Nanofluids with Variable Conductivity and Diffusivity Subjected to Chemical Reaction

The purpose of this article is to analyze the entropy generation and heat and mass transfer of carbon nano-tubes (CNTs) nanofluid by considering the applied magnetic field under the influence of thermal radiation, variable thermal conductivity, variable mass diffusivity, and binary chemical reaction with activation energy over a linearly stretching cylinder. Convective boundary conditions on heat and mass transfer are considered. An isothermal model of homogeneous-heterogeneous reactions is used to regulate the solute concentration profile. It is assumed that the water-based nanofluid is composed of single and multi-walled carbon nanotubes. Employing a suitable set of similarity transformations, the system of partial differential equations is transformed into the system of nonlinear ordinary differential equations before being solved numerically. Through the implementation of the second law of thermodynamics, the total entropy generation is calculated. In addition, entropy generation for fluid friction, mass transfer, and heat transfer is discussed. This study is specially investigated for the impact of the chemical reaction, and activation energy with entropy generation subject to distinct flow parameters. It is found that the slip parameters greatly influence the flow characteristics. Fluid temperature is elevated with higher radiation parameters and thermal Biot number. Entropy and Bejan number are found to be an increasing function of solid volume fraction, magnetic field, and curvature parameters. Binary chemical reaction and activation energy on concentration profile have opposite effects.

Plane vibrational modes and localized nonlinear excitations in carbon nanotube bundle

Bulk nanomaterials made of carbon nanotubes (CNTs) possess unique physical and mechanical properties that are used in a number of applications, for example, for creating mass or force sensors, protection against shock and vibration. One of the specific implementations of such materials is a CNT bundle in which aligned CNTs are held together due to van der Waals interactions. Linear and nonlinear dynamic excitations in such materials are still poorly understood. Here we study plane waves and spatially localized nonlinear dynamic modes in a CNT bundle under plane strain conditions, when the CNT cross sections completely determine the deformed state of the bundle. In particular, we analyze vibration spectrum of single CNT, dispersion curves of phonons propagating along the close packed direction of CNT bundle, compressive solitons and discrete breathers in the form of single CNT oscillating at large amplitude in the CNT bundle. It is shown that compressive solitons can propagate long distances in the bundles of CNTs having radius no more than about 0.8 nm. Discrete breathers can exist in bundles of CNTs of any radius. The results obtained revealed new channels of energy localization and transport in CNT bundles, which is important for their use in various technologies.

Using static linear response theory to describe field emission field enhancement and a field-induced insulator-conductor transition

Experiments on field electron emission (FE) of single carbon nanotubes (CNTs) indicate that they exhibit a nearly linear Fowler–Nordheim plot, and the field enhancement factor (FEF) near the CNT apex is independent of the applied (macroscopic) field (FM) for small radii field emitters. Recent results, based on density functional theory calculations considering CNTs with small radii, retrieved the constancy of the FEF defined in terms of the corresponding induced electron density. As a consequence, it has been reported that the constancy of the FEF with FM could be connected with the linear response of the CNT. In this paper, we reinforce this connection, considering the problem of a floating (6,6) hybrid single-walled nanotube, whose cylindrical body is an insulating one and composed of alternating boron and nitrogen atoms end-capped with carbon atoms. Our results show that the constancy of the FEF is achieved when a linear dependence between the longitudinal component of the induced system dipole moment (μi,z) and FM is observed. Two regimes of constant polarizabilities have been found at sufficiently low and high FM-values. In the intermediate range 0.3V/nm≲FM≲5 V/nm, a crossover from insulating-to-conducting behavior, exhibiting a nonlinear dependence of μi,z on FM, is found accompanied by an increase of the FEF with FM. This result reveals circumstances that could lead to dependence of the FEF on FM, being timely for interpretation of FE characteristics in the context of vacuum nanoelectronic devices.

Joint-Free Single-Piece Flexible Thermoelectric Devices with Ultrahigh Resolution p–n Patterns toward Energy Harvesting and Solid-State Cooling

Joints widely exist in traditional organic electronic devices that are composed of p–n modules, including organic thermoelectric (TE) devices. They often harm the performance of the devices by increasing their electrical resistance and thermal resistance. Recently, a few joint-free approaches have been reported to fabricate TE devices with a single carbon nanotube (CNT) composite film. However, the resolution of p–n patterns is low, e.g., >100 μm, with a conventional printing/drop-casting method. Herein, a plasma treatment method was reported to fabricate joint-free TE devices with a single-piece flexible CNT composite film whose performance was higher than that of traditional devices in energy harvesting and solid-state cooling. In addition, this method provided p–n patterns with a high resolution of ∼1–2 μm which is promising for making future high integration level TE devices. This method can be extended to fabricate a broad range of high integration level organic electronic devices composed of p–n modules.

Building a Bridge for Carbon Nanotubes from Nanoscale Structure to Macroscopic Application.

Through 30 years of research, researchers have gained a deep understanding of the synthesis, characteristics, and applications of carbon nanotubes (CNTs). However, up to now, there are still few industries using CNT as the leading material. The difficulty of CNTs to be applied in industry is the gap between the properties of CNT-based aggregates and those of a single carbon nanotube. Therefore, how to maintain the intrinsic properties of CNTs when they are assembled into aggregates is of great significance. Herein, we summarize and analyze the research status of CNT materials applied in different fields from proven techniques to potential industries, including energy storage, electronics, mechanical and other applications. For each application, the intrinsic properties of CNTs and the real performances of their aggregates are compared to figure out the key problems in CNT synthesis. Finally, we give an outlook for building a bridge for CNTs from nanoscale structure to macroscopic application, giving inspiration to researchers making efforts toward the real application of carbon nanotubes.

Electrochemical impedimetric analysis of different dimensional (0D–2D) carbon nanomaterials for effective biosensing of L-tyrosine

Electrochemical biosensors employing nano-transduction surfaces are considered highly sensitive to the morphology of nanomaterials. Various interfacial parameters namely charge transfer resistance, double layer capacitance, heterogeneous electron transfer rate and diffusion limited processes, depend strongly on the nanostructure geometry which eventually affects the biosensor performance. The present work deals with a comparative study of electrochemical impedance-based detection of L-tyrosine (or simply tyrosine) by employing carbon nanostructures (graphene quantum dots, single walled carbon nanotubes (CNTs) and graphene) along with tyrosinase as the bio-receptor. Specifically, the role of carbon nanostructures (i.e. 0D, 1D and 2D) on charge transfer resistance is investigated by applying time-varying electric field at the nano-bioelectrode followed by calculating the heterogeneous electron transfer rate, double layer capacitor current and their effects on limits of detection and sensitivities towards tyrosine recognition. A theoretical model based on Randel’s equivalent circuit is proposed to account for the redox kinetics at various carbon nanostructure/enzyme hybrid surfaces. It was observed that, the 1D morphology (single walled CNTs) exhibited lowest charge transfer resistance ∼2.62 kΩ (lowest detection limit of 0.61 nM) and highest electron transfer rate ∼0.35 μm s−1 (highest sensitivity 0.37 kΩ nM−1 mm−2). Our results suggest that a suitable morphology of carbon nanostructure would be essential for efficient and sensitive detection of tyrosine.

Mechanical Behavior of Single and Bundled Defect-Free Carbon Nanotubes

ConspectusSuperstrong materials can be utilized in many fields such as bulletproof vests, airframes, suspension bridges, flywheel energy storage, etc. As one of the strongest materials, carbon nanotubes (CNTs) can potentially be used to fabricate superstrong fibers. However, the tensile strength of CNTs is impaired a lot by defects, and the CNT fibers prepared so far have strengths much lower than that of a single CNT, showing a “size effect”. The conventional study of solid mechanics is usually based on the assumption that materials contain defects. Defect-free ultralong CNTs can hopefully help us avoid the “size effect” of nanomaterials and produce superstrong CNT fibers. They would also provide a system for the study of the mechanical behavior of ideal solids with a nonlocalized “quantum stress singularity”.In this Account, we discuss our recent studies on the mechanical behavior of defect-free single CNTs and CNT bundles. First, we introduce the defect-free structure of ultralong CNTs, which is one type of ideal solid. Second, we review the investigation of the static tensile properties and dynamic fatigue resistance and their temperature-dependence of single centimeters long defect-free CNTs. The results showed that defect-free CNTs have superior comprehensive mechanical properties, including superstrength, -toughness, and -durability. Different from traditional materials, the fatigue lifetime and fracture of CNTs are dominated by the first single-bond-sized defect (quantum stress singularity), showing “superbrittleness”. Third, by using a gas flow focusing in situ synthesis method as well as a synchronous tightening and relaxing strengthening strategy, we successfully fabricated CNT bundles with tensile strengths approaching that of single CNTs and showed that the “size effect” can be avoided. In addition, the advantages and promising future of using CNTs in flywheel energy storage are discussed. Finally, we provide our perspectives on the challenges and future directions in this field.

Device design and optimization of CNTFETs for high-frequency applications

Carbon nanotube (CNT) field-effect transistors (FETs) have recently reached high-frequency (HF) performance similar to that of silicon RF-CMOS at the same gate length despite a tube density and current per tube that are far from the physical limits and suboptimal device architecture. This work reports on an investigation of the optimal device design for practical HF applications in terms of cut-off frequencies, power gain, and linearity. Different fundamental designs in the gate contact arrangement are considered based on a 3D device simulation of both CNTs and contacts. First, unit cells with a single CNT and minimal contact sizes are compared. The resulting simulation data are then extended toward a structure with two gate fingers and realistic contact sizes. Corresponding parasitic capacitances, as well as series and contact resistances, have been included for obtaining realistic characteristics and figures of merit that can be used for comparison with corresponding silicon RF MOSFETs. Finally, a sensitivity analysis of the device architecture with the highest performance is performed in order to find the optimal device design space.

Controlled growth of a single carbon nanotube on an AFM probe

Carbon nanotubes (CNTs) can be used as atomic force microscopy (AFM) tips for high-resolution scanning due to their small diameter, high aspect ratio and outstanding wear resistance. However, previous approaches for fabricating CNT probes are complex and poorly controlled. In this paper, we introduce a simple method to selectively fabricate a single CNT on an AFM tip by controlling the trigger threshold to adjust the amount of growth solution attached to the tip. The yield rate is over 93%. The resulting CNT probes are suitable in length, without the need for a subsequent cutting process. We used the CNT probe to scan the complex nanostructure with a high aspect ratio, thereby solving the long-lasting problem of mapping complex nanostructures.

Self-assembly behavior of ultra-high molecular weight in-situ anionically synthesized polymer matrix composite materials “grafted from” single- or multi-wall CNTs

A pioneering synthetic approach for the design of novel composite materials is reported. The final products are consisting of high number average molecular weight diblock copolymers which are surface initiated (“grafting from” approach) from either single or multi-wall carbon nanotubes (SWCNTs or MWCNTs respectively). In-situ anionic polymerization results in nanocomposites, exhibiting narrow dispersity indices which are in accordance with anionic polymerization standards, able to self-assemble when studied in bulk. The polymer matrices are diblock copolymers of the PS-b-PI type [PS: polystyrene and PI: poly(isoprene)]. The successful “grafting from” the corresponding CNTs is verified by Raman and Χ-Ray Photoelectron spectroscopy, while the structure/properties relationship of the composites is determined employing High Resolution Transmission Electron Microscopy (HR-TEM). HR-TEM characterization is very important for the successful identification of the MWCNTs as well as for the justified conformation of the polymeric chains grafted from the CNTs.

Influence of carbon nanotubes on the dielectric and electro-optical properties of a proto-type ferroelectric mixture used in display devices

Doping of different concentrations of single and multi-walled carbon nanotubes (CNTs) is found to influence considerably the dielectric and electro-optical properties of a room temperature FLC mixture. However, the comparative change of such properties between the two types of CNT doped systems is marginal. Dispersion of CNTs produces not enough change in the molecular ordering as revealed by the small decrease in the phase transition temperatures and tilt angles. Spontaneous polarization is also found to decrease due to the screening of the molecular dipole moments by the π–π electron system of the CNTs. Both the dielectric increments and absorption strengths are found to decrease remarkably due to the trapping of ions by the CNTs. Trapping also decreases ac and dc conductivities and the local electric field which in turn fastens the switching time considerably making the CNT-doped systems more suitable for FLC-based applications.

An effect of MHD and radiation on CNTS-Water based nanofluids due to a stretching sheet in a Newtonian fluid

The present article makes on the presence of the magnetohydrodynamic (MHD) flow of an electrically conducting Newtonian fluid over a superlinear stretching/shrinking sheet. A similarity transformation is utilized to interpret the representing construction of nonlinear PDEs by nonlinear ODEs. These equations are solved analytically along with the corresponding boundary conditions. The impact of radiation, mass transpiration, and carbon nanotube (CNT) volume fraction on MHD Newtonian fluid flow and heat transfer is under investigation. Water, ethylene glycol, and engine oil are used as base liquids in the sample along with single and multi-walled carbon nanotubes (MCNTs). Heat transfer in an electrically conducting fluid, including internal heat generation and absorption, is evaluated over a continuously stretching/shrinking sheet with power-law surface temperature or heat flux. Furthermore, the heat equation is solved analytically via the Kummer’s function and WKB method, respectively. The studied results verify that CNTs have significant properties in improving heat transfer processes which have been extensively developed in manufacturing industrial applications, especially in nanomedicine, where the use of carbon nanotubes as drug-carriers is being pursued, particularly in cancer treatment.

Conductive, sensing stable and mechanical robust silicone rubber composites for large‐strain sensors

AbstractConductive polymer composites (CPCs) with carbon nanotubes (CNTs) have exhibited desirable sensing capacities to external stimuli. In this study, it is found that poor dispersion of single‐wall CNTs gives rise to low mechanical strength and unsteady responsive signal outputs of CPCs as strain sensing materials. With attempt to solve this problem, we prepare the conductive silicone rubber composites with hybrid CNT masterbatch and carbon black (CB) fillers (CNT/CB composites) by drying mixing method. Hybrid CBs separate and loosen the entanglement of CNTs in CNT/CB composites which forms more conductive paths and better dispersion of CNTs than those only with single CNTs (CNT‐composites). CNT/CB composite achieves a good conductivity, sufficient mechanical strength and high elasticity. In contrast with CNT‐composite, its reproducibility of resistance responsivity was remarkably improved at strain cycles, which display stable sensing properties for mechanically strain sensor applications. Importantly, CNT/CB composites show outdoor usage robustness, including excellent salt‐spray resistance, hot‐humidity stability and a wide operation temperature range of −40 to +50°C. It is believed that our work offers a simple approach to fabricate stable and flexible strain sensing materials, which is useful for sensor products.

A thermal conductivity model for hybrid heat and mass transfer investigation of single and multi-wall carbon nano-tubes flow induced by a spinning body

The enhancement of thermal heat transfer utilizing the hybrid nanofluids is explored widely by numerous researchers over the years. Because of these exciting characteristics features of hybrid nanofluids, the prime focus of this article is the investigation of engine oil and mineral oil-based hybrid nanofluids consisting of carbon nanotubes (SWCNT-MWCNT) over a rotating cone present in a convectively heated permeable environment. In the flow supposition, a mathematical model is formulated, Boundary layer approximations are used to minimize the structure of partial differential equations. The dimensionless system of highly non-linear partial differential equations is obtained through boundary layer approximation. The findings obtained showed a rise in temperature for both CNT's, the thickness of the thermal boundary layer has increased under the impact of solid volume fraction of nanotubes. SWCNTs provide a reduction in skin friction and enhancement in Nusselt number. The hybrid nanofluid with EO (engine oil) base has demonstrated a greater heat transfer coefficient and reduced fluid motion's skin friction than MO (mineral oil) based. The model hybrid flow can be used in industries like turbine heat production, wind energy generation, and pharmaceutical processes.