Diameter Of Carbon Nanotubes Research Articles

Informatics-based design of polyaniline-carbon nanotube thermoelectric nanocomposite using ANN and GA

Abstract Conducting polymer and carbon nanotube (CNT) based nanocomposites have emerged as prospective thermoelectric (TE) materials due to their potential application in flexible electronics. Non-conventional charge and heat transport in these nanocomposites, presents the possibility to enhance the TE conversion efficiency, given by ZT. However, the highly non-linear and complex association of structure and composition with the overall TE properties have hindered the development of any general strategy to develop high ZT nanocomposites. Here, we implement artificial neural network (ANN) and genetic algorithm (GA) to develop data driven models followed by optimization to design high efficiency nanocomposites based on CNT dispersed in polyaniline (PANI) matrix. Our models suggest that CNT concentration plays the most crucial role in determining ZT. Non-dominated Pareto optimal solutions consisting of different combinations of design variables are obtained by multi-objective optimization. Although a range of optimal solutions span over different regions of the search space, in general we note that longer CNTs boost Seebeck coefficient (S) and electrical conductivity (σ), and smaller length lowers thermal conductivity (k), while higher diameter of CNTs increase S and lowers σ and k. The results provide a general guideline for developing CNT-PANI nanocomposites with enhanced TE figure of merit.

Pragmatic structure optimization: Achieving optimal crosstalk delay and gate oxide reliability of randomly mixed CNT bundle interconnects

This study explores the potential of randomly mixed carbon nanotube bundle (RMCB) as a viable on-chip interconnect. Achieving high-quality carbon nanotubes (CNTs) with uniform diameters is challenging for the current framework of enhanced fabrication techniques. The Stoyan and Yaskov technique is employed to optimize CNT arrangement within a specified rectangular area. This method accounts for statistical variation in CNT diameters, offering a more realistic and fabrication-focused approach to designing CNT bundle interconnects. Eight such practical RMCB structures (RMCB-50 to RMCB-350) are selected using this technique, each characterized by distinct CNT counts and variable diameters. Comprehensive average crosstalk-delay and reliability assessments are conducted by comparing different CNT bundle interconnects with the best-optimized RMCB (O-RMCB) interconnect, placed on various dielectric substrates such as SiO2, SiC, BN. The study unequivocally indicates that O-RMCB produces highly favorable results and stands as the most suitable future solution for VLSI circuits. Additionally, the thickness optimization of O-RMCB interconnect is explored, yielding in improvements in both performance and reliability compared to other well-known CNT bundled interconnects.

Molecular Dynamics Simulation of Effect of Carbon Nanotube Diameter on Properties of Crosslinked Epichlorohydrin Rubbers.

Molecular dynamics simulation (MD) technology can be used to simulate and study the physicochemical properties of polymer materials on the basis of material data obtained in traditional experiments. In this study, we use MD to construct models of crosslinked carbon nanotubes/epichlorohydrin rubber composites with different carbon nanotube diameters and study the effect of CNT tube diameter on crosslinked ECO. The results show that with the increase in CNT tube diameter, the contact area between the CNTs and rubber matrix increases, the interaction force is enhanced, the free volume fraction of rubber matrix decreases by 21.36%, the glass transition temperature increases by 6.5%, the mean square displacement decreases, the radius of gyration decreases by 3.18 Å, and the radial distribution function of the C-atom group and the H-atom group in the system gradually decreases. The binding energy between the two is elevated, which in turn verifies the enhancement of the interaction force.

Simulation of Novel Nano Low-Dimensional FETs at the Scaling Limit.

The scaling of bulk Si-based transistors has reached its limits, while novel architectures such as FinFETs and GAAFETs face challenges in sub-10 nm nodes due to complex fabrication processes and severe drain-induced barrier lowering (DIBL) effects. An effective strategy to avoid short-channel effects (SCEs) is the integration of low-dimensional materials into novel device architectures, leveraging the coupling between multiple gates to achieve efficient electrostatic control of the channel. We employed TCAD simulations to model multi-gate FETs based on various dimensional systems and comprehensively investigated electric fields, potentials, current densities, and electron densities within the devices. Through continuous parameter scaling and extracting the sub-threshold swing (SS) and DIBL from the electrical outputs, we offered optimal MoS2 layer numbers and single-walled carbon nanotube (SWCNT) diameters, as well as designed structures for multi-gate FETs based on monolayer MoS2, identifying dual-gate transistors as suitable for high-speed switching applications. Comparing the switching performance of two device types at the same node revealed CNT's advantages as a channel material in mitigating SCEs at sub-3 nm nodes. We validated the performance enhancement of 2D materials in the novel device architecture and reduced the complexity of the related experimental processes. Consequently, our research provides crucial insights for designing next-generation high-performance transistors based on low-dimensional materials at the scaling limit.

Electrochemically-Tunable Intersubband Plasmon Absorption in Carbon Nanotube Films

Owing to their unique photophysics and highly tunable electronic properties, carbon nanotubes (CNTs) are promising materials for next-generation electrochromic devices. Here, we present recent work on ionic liquid-gated carbon nanotube devices that show reversible, bistable, and tunable absorption of near-infrared (NIR) radiation. Gating of the CNTs enables reversible changes in the optical transmittance of up to 40% in the wavelength range of 1.7 – 2.2 µm. Additionally, these devices exhibit bistability in an open-circuit configuration that persists for hundreds of seconds. We explore—both experimentally and with numerical modelling—the impact of CNT diameter on the absorption spectrum and the electrochemical properties of the devices. Our results have implications for the use of CNTs in electrochromic, charge storage, and chemical sensing applications.

Mobility of dislocations in carbon nanotube bundles

Horizontally aligned carbon nanotubes (CNTs) have a unique combination of mechanical and physical properties and find numerous applications. The shear deformation of a horizontally aligned CNT bundle is studied under plane-strain conditions using the method of molecular dynamics. The CNTs in the bundle are not perfectly packed, and it is important to see how defects alter the mechanisms of their deformation under applied load. The defects in the form of edge dislocations are introduced into the bundle. It is found that the dislocation core structure depends on the CNT diameter, as the deformability of the CNT cross section increases with the diameter. Different deformation mechanisms (dislocation sliding or cracking) are revealed in the bundles with CNTs of different diameters. The results presented describe how the dislocation core structure affects the dislocation mobility in CNT bundles and the mechanisms of their deformation.

Simultaneous Effect of Diameter and Concentration of Multi-Walled Carbon Nanotubes on Mechanical and Electrical Properties of Cement Mortars: With and without Biosilica.

In this work, the effect of multi-walled carbon nanotubes (MWCNT1, MWCNT2, and MWCNT3) with different outer diameters and specific surface areas on the mechanical and electrical properties of cement mortar have been investigated. Various concentrations of MWCNTs were used (0.05, 0.10, and 0.15%), the effective dispersion of which was carried out by an Ultrasonic machine (for 40 min with 160 W power and a 24 kHz frequency) using a surfactant. Composites have been processed with a biosilica content of 10% by weight of cement and without it. Compressive strength tests were carried out on days 7 and 28 of curing. The 7-day compressive strength of samples prepared without biosilica increased compared to the result of the control sample (6.4% for MWCNT1, 7.4% for MWCNT2, and 10.8% for MWCNT3), as did those using biosilica (6.7% in the case of MWCNT1, 29.2% for MWCNT2, and 2.1% for MWCNT3). Compressive strength tests of 28-day specimens yielded the following results: 21.7% for MWCNT1, 3.8% for MWCNT2, and 4.2% for MWCNT3 in the absence of biosilica and 8.5%, 12.6%, and 6.3% with biosilica, respectively. The maximum increase in compressive strength was observed in the composites treated with a 0.1% MWCNT concentration, while in the case of 0.05 and 0.15% concentrations, the compressive strengths were relatively low. The MWCNT-reinforced cement matrix obtained electrical properties due to the high electrical conductivity of these particles. The effect of MWCNT concentrations of 0.05, 0.10, and 0.15 wt% on the electrical properties of cement mortar, especially the bulk electrical resistivity and piezoresistive characteristics of cement mortar, was studied in this work. At a concentration of 0.05%, the lowest value of resistivity was obtained, and then it started to increase. The obtained results show that all investigated specimens have piezoresistive properties and that the measurements led to a deviation in fractional change in resistivity.

Impact of diameter and temperature on domain suppression by hot electrons in zigzag carbon nanotubes under constant electric field

The impact of the diameter of zigzag carbon nanotubes (CNTs) and temperature on domain suppression by injection of hot electrons at a strong rate along the axis of the tubes are investigated. The semiclassical Boltzmann kinetic equation was utilized in the theoretical work to derive the current density when hot electrons are available. First, the study was carried on by changing the value of the zigzag carbon nanotube's diameter at a fixed temperature. Second, we vary the temperature while keeping the diameter constant. For the semiconducting zigzag CNTs, increasing both the diameter and temperature enhances the suppression of the electric field domain required for a higher potential of terahertz radiation generation. However, in the metallic zigzag CNTs, we observed an enhancement of domain suppression when the diameter and temperature were decreased. These observations suggest that larger-diameter semiconducting zigzag CNTs at higher temperatures and smaller-diameter metallic zigzag CNTs at lower temperatures are better candidates for the generation of terahertz radiation.

Dynamics of confined water inside carbon nanotubes based on studying tetrahedral order parameters

Water dynamics inside hydrophobic confinement, such as carbon nanotubes (CNTs), has garnered significant attention, focusing on water diffusion. However, a crucial aspect remains unexplored - the influence of confinement size on water ordering and intrinsic hydrogen bond dynamics. To address this gap, we conducted extensive molecular dynamics simulations to investigate local ordering and intrinsic hydrogen bond dynamics of water molecules within CNTs of various sizes (length:20 nm, diameters: 1.0 nm to 5.0 nm) over a wide range of temperatures (260K, 280K, 300K, and 320K). A striking observation emerged: in smaller CNTs, water molecules adopt an icy structure near tube walls while maintaining liquid state towards the center. Notably, water behavior within a 2.0 nm CNT stands out as an anomaly, distinct from other CNT sizes considered in this study. This anomaly was explained through the formation of water layers inside CNTs. The hydrogen bond correlation function of water within CNTs decayed more slowly than bulk water, with an increasing rate as CNT diameter increased. In smaller CNTs, water molecules hold onto their hydrogen bond longer than larger ones. Interestingly, in larger CNTs, the innermost layer’s hydrogen bond lasts a shorter time compared to the other layers, and this changes with temperature.

Improved energy method and agglomeration influence of carbon nanotubes on polymer composites

In this paper, the geometric analysis of carbon nanotubes (CNTs) without external loading is carried out by energy method. Based on the theory of molecular mechanics, an improved mechanical model is proposed to predict the energy of armchair carbon nanotubes under stress-free conditions, and the diameter of CNTs is estimated according to the principle of minimum energy. The results show that the diameter obtained by the improved model is larger, but basically consistent with that obtained by conformal mapping. The inversion energy term is added to the modified model, and the inversion energy term related to atomic curvature is characterized by the conization angle. It can be seen from the error that the inversion energy of carbon nanotubes can not be neglected in the stress-free state, especially in the case of small diameter. The agglomeration of nanotubes is one of the important factors, which affects the effective elastic modulus of nanocomposites. Here, a new micro-mechanics model consisting of both agglomeration of CNTs and pure matrix is also presented to analyze its effect on the effective elastic modulus. It is noted from the results that the stiffness of nanocomposites is very sensitive to the CNTs agglomeration.

Review of Carbon Nanotube Field Effect Transistor for Nanoscale Regime

Background: The need for high performance, small size, low delay, low power consumption, and long battery backup of portable systems is increasing with the advancement of technology. Many features of portable systems can be improved using scaling methods. In the scaling process, reducing the size of devices causes serious difficulties, including the short channel effect (SCE) and leakage current, which degenerates the characteristics of the systems. Objective: In this review paper, a trending carbon nanotube field effect transistor (CNTFET) technology is discussed in detail. CNTFET can replace the conventional metal oxide semiconductor field effect transistor (MOSFET) technology to overcome the SCE problems in the nanoscale regime and also meet the requirements of portable systems. Methods: The CNTFET is an extremely good nanoscale technology due to its one-dimension band structure, high transconductance, high electron mobility, superior control over channel formation, and better threshold voltage. This technology is used to construct high-performance and low-power circuits by replacing the MOSFET technology. CNTFET in comparison to MOSFET takes the carbon nanotube (CNT) as a channel region. Results: The value of threshold voltage in CNTFET changes with the diameter of CNT. The threshold voltage of the devices controls many parameters at the circuit-level design. Hence, the detailed operation and the characteristics of CNTFET devices are presented in this review paper. The existing CNTFET-based ternary full adder (TFA) circuits are also described in this review paper for the performance evaluation of different parameters. Conclusion: CNTFET technology is the possible solution for the SCE in the nanoscale regime and is capable to design efficient logic circuits. The circuits using the CNTFET technology can provide better performance and various advantages, including fast speed, small area, and low power consumption, in comparison to the MOSFET circuits. Thus, CNTFET technology is the best choice for circuit designs at the nanoscale.

Purification of carbon nanotubes for dissolution in chlorosulfonic acid

Carbon nanotubes (CNTs) can be scalably processed into high-performance fiber with a low environmental footprint by solution spinning from chlorosulfonic acid (CSA). CNTs are produced by numerous manufacturers, but CNTs typically need to undergo purification to improve solubility in CSA. For over two decades, oxidative techniques have been used to remove amorphous carbon species to improve CNT dissolution in acid. However, more recent work has attributed the improved solubility after single-walled carbon nanotube (SWCNT) oxidation to the inclusion of oxygen groups in the sidewall of the SWCNT. Here, we refute the recent claim that oxidation incorporates oxygen into the sidewall of CNTs to improve CNT dissolution to CSA. Instead, we provide experimental evidence in support of classical purification literature: at the appropriate time and temperature, oxidation removes amorphous carbon shells and defective SWCNTs without oxidizing the SWCNT sidewall. Once these amorphous carbon shells are removed, CSA can access and protonate the sp2-bonded carbon sites, which results in SWCNT dissolution. Additionally, we explore how oxidation conditions impact SWCNT aspect ratio (length of CNT divided by CNT diameter), which directly controls macroscale fiber properties.

Encapsulation and Evolution of Polyynes Inside Single-Walled Carbon Nanotubes.

Polyyne is an sp-hybridized linear carbon chain (LCC) with alternating single and triple carbon-carbon bonds. Polyyne is very reactive; thus, its structure can be easily damaged through a cross-linking reaction between the molecules. The longer the polyyne is, the more unstable it becomes. Therefore, it is difficult to directly synthesize long polyynes in a solvent. The encapsulation of polyynes inside carbon nanotubes not only stabilizes the molecules to avoid cross-linking reactions, but also allows a restriction reaction to occur solely at the ends of the polyynes, resulting in long LCCs. Here, by controlling the diameter of single-walled carbon nanotubes (SWCNTs), polyynes were filled with high yield below room temperature. Subsequent annealing of the filled samples promoted the reaction between the polyynes, leading to the formation of long LCCs. More importantly, single chiral (6,5) SWCNTs with high purity were used for the successful encapsulation of polyynes for the first time, and LCCs were synthesized by coalescing the polyynes in the (6,5) SWCNTs. This method holds promise for further exploration of the synthesis of property-tailored LCCs through encapsulation inside different chiral SWCNTs.

Molecular insights into strengthening of biomineral apatite with carbon nanofillers: A simulation study

Biomineral apatite (Ap) has been widely utilized in clinical bone graft procedures for over 25 years. However, its lower tensile strength and fracture toughness compared to natural bone limit its application in large load-bearing systems. This approach aims to enhance the mechanical performance of Ap while preserving its bioactivity, thereby expanding its potential clinical applications. In this study, the creation and processing of carbon nanofiller-based Ap nanocomposites, including pristine and vacancy-defective carbon nanofillers, are investigated using molecular dynamics simulations. The mechanical behaviour of Ap nanocomposites reinforced with three types of carbon nanofillers (CNF) is examined: (i) three-dimensional metallic carbon nanostructure with interlocking hexagons T6B (beam-like), (ii) carbon nanotubes (CNT), and (iii) three-dimensional metallic carbon nanostructure with interlocking hexagons T6P (plate-like). The analysis encompasses detailing the methodology utilized for modelling the equilibrated structures of CNF/Ap nanocomposites, along with the characterization of their elastic parameters. Computational findings reveal the significant impact of CNT chirality, Aspect Ratio (AR) of T6B and orientation of T6P on the mechanical properties of the nanocomposites and observed inclusion of CNF enhances the mechanical properties compared with those of pure Ap. The findings indicate that the lower diameter CNT and smaller cross-sectional area of T6B exhibit higher tensile strength compared to the larger CNT diameter and larger cross-sectional area of T6B of the same length. Further, the analysis highlights the substantial influence of vacancy defects concentration on CNF on the mechanical behaviour of nanocomposites, with an increase in defects correlating to a decrease in the mechanical strength of both CNF and CNF-based nanocomposites.

Optimized Design of Carbon Nanotube Field-Effect Transistor Using Taguchi Method for Enhanced Current Ratio Performance

Abstract Presently, the integrated circuit (IC) industry grapples with obstacles in downsizing MOSFET technology further, hindered by its inherent physical constraints. Therefore, the substitution of silicon with carbon nanotubes (CNTs) holds promise for paving a novel path in semiconductor industries, driven by their diminutive dimensions and superior electrical properties. Hence, this project employed SILVACO ATLAS software in conjunction with the Taguchi method to refine a CNTFET design for optimal performance. In this work, response variables consists of on-current (Ion), current ratio (Ion/Ioff) and threshold voltage (Vth) are extracted. In this particular design, the Taguchi method was employed to ascertain the most effective combination of design parameters and materials to achieve optimal CNTFET performance, as assessed by the three key response variables. The design parameter and material that had been chosen were the diameter of carbon nanotube (Dcnt), dielectric material (K) and oxide thickness (tox). Each of the design parameters and material had three different values. For K, the values are 3.9 (SiO2), 25 (ZrO2) and 80 (TiO2). While for Dcnt and tox, the values are 4.0 nm, 6.0 nm, 8.0 nm and 2.0 nm, 4.0 nm, 6.0 nm respectively. According to the Taguchi optimization findings, the ideal combination of parameters comprises a CNT diameter of 4.0 nm, an oxide thickness of 2.0 nm, and the use of TiO2 (80) as the dielectric material. The ANOVA analysis underscores the significance of prioritizing optimization efforts towards the CNT diameter parameter. This is attributed to its substantial contribution, accounting for 93.55% of the variation in the Ion/Ioff value, surpassing the influence of dielectric materials and oxide thickness.

A subbands study on the resistivity of field-effect CNT-based piezoresistive nanocomposites

In this paper, an analytical model based on the percolation theory has been developed to predict the subbands effect on the effective electrical resistivity of carbon nanotubes (CNT)-based polymer nanocomposites. The CNTs are considered as randomly distributed or aligned channel material in the polymer transmitting electrons through tunneling. The tunneling effect takes into account the electron transmission between each connected pair of CNTs to evaluate electrical resistivity. The modeling approach contains two steps of primary prediction of resistivity and further calculation of CNTs’ displacements and subsequent change of the resistance. A good agreement is found between the analytical model predictions and experimental data when the tunneling behavior was considered in the percolation transition region. The effect of CNT diameter, orientation state, and subbands on the resistivity has been investigated. The results depict that subbands increment is a collateral benefit to the aspect ratio in decreasing the resistivity. The analytical results demonstrate that a random CNT dispersion leads to a decreased piezoresistivity, while an increased strain range depicts a more non-linear behavior.

Effect of Crystallinity on the Field Emission Characteristics of Carbon Nanotube Grown on W-Co Bimetallic Catalyst.

Carbon nanotube (CNT) is an excellent field emission material. However, uniformity and stability are the key issues hampering its device application. In this work, a bimetallic W-Co alloy was adopted as the catalyst of CNT in chemical vapor deposition process. The high melting point and stable crystal structure of W-Co helps to increase the grown CNT diameter uniformity and homogeneous crystal structure. High-crystallinity CNTs were grown on the W-Co bimetallic catalyst. Its field emission characteristics demonstrated a low turn-on field, high current density, stable current stability, and uniform emission distribution. The Fowler-Nordheim (FN) and Seppen-Katamuki (SK) analyses revealed that the CNT grown on the W-Co catalyst has a relatively low work function and high field enhancement factor. The high crystallinity and homogeneous crystal structure of CNT also reduce the body resistance and increase the emission current stability and maximum current. The result provides a way to synthesis a high-quality CNT field emitter, which will accelerate the development of cold cathode vacuum electronic device application.

Effects of CaCO3/MgO on Fe-Co-Mo catalyst in the reprocessing of recycled polypropylene to carbon nanotubes

In recent times, there has been a global discourse on the menace of plastic waste (PW) materials on the ecosystem and ways for effective management of PW. This has resulted in the utilization of PW in the research arena in the synthesis of smart nanomaterials of high value as a sustainable solution. In this study, the catalytic-pyrolysis procedure was used to develop carbon nanotubes (CNTs) from recycled polypropylene (PP) plastic in a one-step chemical vapour deposition (CVD) reactor. The impacts of CaCO3 and MgO as supports for Fe-Co-Mo catalysts in the production of CNTs were studied. Kinetic and thermodynamic parameters were determined from the thermal profile of the catalysts to establish the nature of the reaction in CNTs synthesis. Transmission electron microscopy (TEM), energy Dispersive X-ray (EDX), selected area electron diffraction pattern, particle size distribution (PSD), thermogravimetric analysis (TGA), Raman spectroscopy, Fourier transforms infrared (FTIR) and X-ray diffraction (XRD) were employed to characterize the catalysts and CNTs. The results obtained showed the impact of the supports on the yield, quality, and morphology of the synthesized CNTs. The CNTs yield from catalysts supported with CaCO3 and MgO were 35.12 % and 37.24% respectively. The average outer diameters of CNTs produced over the catalyst with CaCO3 and MgO supports were 36 and 29 nm respectively. The ID/IG ratio for CaCO3 and MgO supports were 0.6724 and 0.8401 respectively. The change in entropy for all phases were −274.41 and −1032.97 J/mol/K and −213.0, −318.48 and −1022.13 J/mol/K for CaCO3 and MgO supported catalyst respectively which confirmed non-spontaneous endothermic reaction. It was observed that MgO support showed better catalytic activity toward CNTs growth in terms of yield while those with CaCO3 support showed higher graphitization.

A molecular simulation study on the adsorption and separation performance of carbon nanotubes for SO2 in flue gas

To control the emission of SO2 from flue gas into the atmosphere while considering the capture and collection of greenhouse gas CO2, the adsorption behavior of a binary mixture of SO2 and other gases in flue gas (O2/N2/H2O/CO[Formula: see text] in (10, 10) carbon nanotube (CNT) was simulated using grand canonical Monte Carlo (GCMC) simulation. The adsorption and separation performance of SO2 in CNTs with a diameter range of 0.81–1.63 nm for the five-component mixture gas was also analyzed. The findings suggest that the adsorption and separation of SO2 are primarily influenced by CO2 (reduction of adsorption capacity by about 50%, separation coefficient of SO2/CO2 is lowest) with this effect being more pronounced under high pressure. Meanwhile, it was observed that CNTs with larger pipe diameters exhibit higher SO2 adsorption capacity, but relatively lower SO2/CO2 selectivity and lower stability. On the other hand, CNTs with smaller diameters have relatively lower adsorption capacity for SO2, but exhibit good selectivity and stability (under different pressure) for SO2/CO2. Based on the statistical analysis of SO2 adsorption capacity and SO2/CO2 selectivity, it was determined that (6, 6) CNT with a diameter of 0.81[Formula: see text]nm can exhibit excellent SO2 adsorption and separation performance at atmospheric pressure, while appropriate large diameter CNTs should be selected for flue gas treatment under high pressure.

Multiple graphdiyne‐like chains self‐assemble into carbon nanotubes

The formation process of core–shell structure from multiple graphdiyne‐like chains and carbon nanotube is investigated by a molecular dynamics simulation. Multiple graphdiyne‐like chains self‐curl into helical structures located inside carbon nanotubes. The entire process involves two steps: sliding and twisting. A detailed analysis is conducted on the formation mechanism. Both the van der Waals potential well and the π–π stacking interaction between carbon nanotube and graphdiyne‐like chains play a major role in the self‐assemble process. Furthermore, the influence factors such as the number of graphdiyne‐like chains, the diameter of carbon nanotube, the length of carbon nanotube, the length of graphdiyne‐like chains, and the simulation temperature is also investigated. The research results are an important theoretical basis for manufacturing high‐quality carbon nanomaterials and other novel nanostructures.