Double-walled Carbon Nanotube Bundles Research Articles

Impact of functional crosstalk on mixed CNT bundles for future VLSI nodes

This paper focuses on a novel class of interconnect material employed in integrated circuits at nanotechnology nodes called as mixed CNT (carbon nanotube) bundle structures. These mixed bundle structures are formed by changing different positions of multi-wall and double-wall CNTs. The impact of temperature on the performance of global interconnects and the effect of undesirable functional crosstalk is also presented in detail. Crosstalk has been studied by performing transient analysis of MDCB (multi-walled CNT and double-walled CNT bundles) structures to evaluate their performance in relation with signal functionality.

Stability- and Crosstalk-Based Performance of Multi- and Double-walled Mixed CNT Bundles as Interconnect for Next-Generation Technology Nodes

The temperature-dependent modeling technique (in the temperature range of 200–500[Formula: see text]K) for a mixed class of carbon nanotube (CNT) bundle interconnects is proposed. The equivalent single conductor (ESC) transmission line models of multi-walled carbon nanotube (MWCNT) and double-walled carbon nanotube (DWCNT) are combined to develop multiple single conductor (MSC) model of mixed CNT interconnects. Various possible arrangements of densely packed MWCNT and DWCNT bundles (MDCB) are considered to form different types of mixed CNT bundle structures (MDCB-1, MDCB-2, MDCB-3 and MDCB-4). The integrated circuit emphasis simulation is performed and the performances of these mixed CNT bundle interconnects are investigated in terms of propagation delay (with and without crosstalk), power dissipation, power-delay product (PDP). Switching times, overshoot voltages and Nyquist plots are analyzed to check the stability of these mixed CNT structures for global interconnect length for 32-nm, 22-nm and 16-nm technology nodes. It is observed that the MDCB-1 structure yields the most promising result in all aspects for interconnect applications in the near future.

Nitrogen-doped graphene nanosheet-double-walled carbon nanotube hybrid nanostructures for high-performance supercapacitors

A hybrid nitrogen-doped graphene nanosheet-grafted double-walled carbon nanotube (NG-DWCNT) was synthesized by chemical vapor deposition (CVD). Double-walled carbon nanotube (DWCNT) was synthesized by floating catalytic CVD using ferrocene and thiophene dissolved in ethanol. NG was directly grafted onto the DWCNT bundles by thermal CVD using mixed ethanol-urea solution. The NG possess sharp-edged petal-like structure on one-dimensional DWCNT bundle. The NG-DWCNT showed the nitrogen content of approximately 1.93 at%. The NG-DWCNT hybrid nanostructures exhibited a higher specific capacitance of 563 F g−1 than that of the DWCNT and un-doped G-DWCNT. The improvement of capacitance value is attributed to the synergic effect of the nitrogen doping together with the sharp-edged petal-like structure of the NG. The facile technique by CVD method provides a promising approach for simple and low-cost technique to synthesize the NG-DWCNT hybrid nanostructures. A hybrid carbon nanostructure of NG-DWCNT has a potential application in electrochemical conversion and energy storage devices.

Impacts from the stacking morphology on the tensile performance of double-walled carbon nanotube bundles

Carbon nanotube (CNT) based fibers/films are envisioned as the building blocks for next generation high-performance composite materials. However, the mechanical performance of the as-synthesized or as-prepared CNT bundles are still well below their constituent CNTs. Here, we systematically assessed the influence from the stacking morphology on the tensile properties of double-walled CNTs (DWNTs)-based bundles through molecular dynamics simulations. We found that the bundles containing zigzag DWNTs exhibit higher Young’s modulus, but lower yielding strength (and yielding strain) compared with that of the pure armchair DWNT-based bundles. In particular, an initial off-axial angle perturbation in one of the constituent DWNTs induces evident misalignments in other constituent DWNTs, which remarkably degrades the yielding strength and yielding strain of the bundle structures. Following the Hooke’s law, the impacts from the stacking morphology on the overall tensile properties of DWNT bundles can be quantitatively predicted by approximating each DWNT as an elastic column approximation. Overall, this work establishes a comprehensive understanding of the influence from the stacking morphology, which not only provides a perspective explanation of the unexpected low performance of as-synthesized CNT bundles, but also shed light on the design of high-performance CNT based bundles.

Graphene nanosheet-grafted double-walled carbon nanotube hybrid nanostructures by two-step chemical vapor deposition and their application for ethanol detection

Here, we present a facile technique for synthesis of graphene nanosheet (GNS)-grafted double-walled carbon nanotube (DWCNT) hybrid carbon nanostructures (here after referred to as G-DWCNTs) by directly growing GNSs along the sidewalls of DWCNTs using a two-step chemical vapor deposition (CVD). DWCNTs were synthesized by floating catalyst CVD at 1300 °C using ferrocene and thiophene dissolved in ethanol. Then, GNSs were grafted onto the synthesized DWCNT bundles by thermal CVD at 1300 °C using ethanol. The sharp-edged petal-like structure of GNSs were grown along the sidewalls of DWCNT bundles while maintaining the one-dimensional structure of DWCNT. Next, DWCNTs and G-DWCNTs were dispersed in ethanol, then deposited on the paper using vacuum filtration method and used for ethanol detection. G-DWCNTs sensor exhibited a 3-fold improvement in the response to ethanol vapor compared to the DWCNTs sensor. The sensing mechanism of DWCNTs and G-DWCNTs can be described in terms of charge transfer between the gas molecules and sensing material. These results demonstrate that the facile technique by two-step CVD method provides a promising approach for simple and low-cost technique to synthesize the hybrid nanostructure of GNSs and DWCNTs. The new hybrid carbon nanostructures are attractive for gas sensing application.

Adsorptive Separation of CO2 from Multicomponent Mixtures of Flue Gas in Carbon Nanotube Arrays: A Grand Canonical Monte Carlo Study

Grand canonical Monte Carlo (GCMC) simulations have been performed to investigate the adsorption and separation behavior of ternary and quaternary gaseous mixtures of CO2, along with H2S, SO2, and N2, in bundles of aligned double-walled carbon nanotubes with a diameter of 3 nm and an intertube distance of 0.5 nm. All of the simulations are performed at 303 K and at pressures varying between 0 and 3 bar. The GCMC results are then compared to the ideal adsorbed solution theory (IAST) predictions. For the ternary mixture H2S–CO2–N2, the results show that CO2 has the highest adsorption among the three components. The IAST predictions agree reasonably well with the GCMC data for the ternary mixture, except for H2S. For the quaternary mixture H2S–SO2–CO2–N2, it is observed that initially CO2 has the highest adsorption up until around 2 bar, whereafter there is a crossover by SO2 to have the highest adsorption. IAST fails to predict the adsorption behavior of the quaternary mixture involving SO2.

Pressure Tuning of Bromine Ionic States in Double-Walled Carbon Nanotubes

The energetic, vibrational, and electronic properties of bromine polyanions intercalated in double-walled carbon nanotubes (DWCNTs) were investigated by resonance Raman and X-ray absorption spectroscopies under high pressure conditions up to values close to 25 GPa. The mechanical resistance of the bromine intercalated DWCNTs is known to be affected by the presence of bromine polyanions, which induces uniaxial constraints in the interstitial regions of DWCNT bundles, thus leading to lower collapse pressure as compared with pristine DWCNTs. An upshift of bromine Raman frequencies concomitant to changes in the local structure of bromine atoms takes place at about 15 GPa, which is the pressure where the studied DWCNT intercalated bundles collapse. This suggests a differentiation of bromine polyanions interaction depending on the local curvature and the arrangement of the collapsed carbon structures. Supported by atomistic calculations, we suggest that those chains of Br2– and Br5– tend to dissociate to form B...

Nonlinear dynamics of bi-layered graphene sheet, double-walled carbon nanotube and nanotube bundle

Due to strong van der Waals (vdW) interactions, the graphene sheets and nanotubes stick to each other and form clusters of these corresponding nanostructures, viz. bi-layered graphene sheet (BLGS), double-walled carbon nanotube (DWCNT) and nanotube bundle (NB) or ropes. This research work is concerned with the study of nonlinear dynamics of BLGS, DWCNT and NB due to nonlinear interlayer vdW forces using multiscale atomistic finite element method. The energy between two adjacent carbon atoms is represented by the multibody interatomic Tersoff–Brenner potential, whereas the nonlinear interlayer vdW forces are represented by Lennard-Jones 6–12 potential function. The equivalent nonlinear material model of carbon–carbon bond is used to model it based on its force–deflection relation. Newmark’s algorithm is used to solve the nonlinear matrix equation governing the motion of the BLGS, DWCNT and NB. An impulse and harmonic excitations are used to excite these nanostructures under cantilevered, bridged and clamped boundary conditions. The frequency responses of these nanostructures are computed, and the dominant resonant frequencies are identified. Along with the forced vibration of these structures, the eigenvalue extraction problem of armchair and zigzag NB is also considered. The natural frequencies and corresponding mode shapes are extracted for the different length and boundary conditions of the nanotube bundle.

Double-walled carbon nanotube array for CO2 and SO2 adsorption.

Grand-canonical Monte Carlo simulations and adsorption experiments are combined to find the optimized carbon nanotube (CNT) arrays for gas adsorption at low pressures and 303 K. Bundles of 3D aligned double-walled carbon nanotube (DWCNT) with inner diameter of 8 nm and different intertube distances were made experimentally. The experimental results show that decreasing intertube distance leads to a significant enhancement in carbon-dioxide (CO2) adsorption capacity at 1 bar. The molecular simulation study on CO2 adsorption onto bundles of 3D aligned DWCNT with inner diameters of 1, 3, and 8 nm and intertube distance of 0-15 nm shows that the intertube distance plays a more important role than the CNT diameter. The simulation results show that decreasing the intertube distance up to 1 nm increases the excess adsorption generally in all the studied systems at pressures 0 < p < 14 bars (the increase can be up to ∼40% depending on the system and pressure). This is in agreement with the experimental result. Further reduction in intertube distance leads to a decrease in the excess adsorption in the pressure range 9 < p < 14 bars. However, at lower pressure, 0 < p < 9 bars, intertube distance of 0.5 nm is found to have the highest excess adsorption. This result is indifferent to tube diameter. Furthermore, molecular simulations are conducted to obtain the optimal parameters, for the DWCNT bundle, for SO2 adsorption, which are similar to those observed for CO2 in the pressure range 0 < p < 3 bars.

Preparation of WO3 nanorods with high specific surface area using double-walled carbon nanotubes as template

The preparation of WO3 nanorods by double-walled carbon nanotube (DWCNT) template was investigated in this study. Owing to that the prepared H2WO4 can be isolated by the homogenously dispersed DWCNT bundles and secondary accumulation can be avoided effectively, the growth of H2WO4 can be restrained, and H2WO4 nanorods with diameter of 10–50 nm can be prepared. After calcination of the prepared DWCNT/H2WO4 composite in oxygen, WO3 nanorods with diameter of 10–100 nm and high specific surface area of 16.4 m2·g−1 can be obtained. It is concluded that the DWCNTs play an important role in the effective mediation of the morphology and size of nano-WO3.

Statistical shear lag model – Unraveling the size effect in hierarchical composites

Numerous experimental and computational studies have established that the hierarchical structures encountered in natural materials, such as the brick-and-mortar structure observed in sea shells, are essential for achieving defect tolerance. Due to this hierarchy, the mechanical properties of natural materials have a different size dependence compared to that of typical engineered materials. This study aimed to explore size effects on the strength of bio-inspired staggered hierarchical composites and to define the influence of the geometry of constituents in their outstanding defect tolerance capability. A statistical shear lag model is derived by extending the classical shear lag model to account for the statistics of the constituents’ strength. A general solution emerges from rigorous mathematical derivations, unifying the various empirical formulations for the fundamental link length used in previous statistical models. The model shows that the staggered arrangement of constituents grants composites a unique size effect on mechanical strength in contrast to homogenous continuous materials. The model is applied to hierarchical yarns consisting of double-walled carbon nanotube bundles to assess its predictive capabilities for novel synthetic materials. Interestingly, the model predicts that yarn gauge length does not significantly influence the yarn strength, in close agreement with experimental observations.

Performance modeling and analysis of carbon nanotube bundles for future VLSI circuit applications

In this work, we have presented a comprehensive analysis of the performance of copper (Cu) and existing carbon nano tube (CNT) bundle structures (i.e. SWCNT, DWCNT and MWCNT) across nanometer technology nodes like 45, 32, 22 and 16 nm at local, intermediate and global level interconnects. Double walled carbon nano tubes (DWCNTs) and multi walled carbon nano tubes (MWCNTs) are modeled like simple single walled carbon nano tube (SWCNT) equivalent model with high accuracy. The analytical closed form delay expressions for SWCNT, DWCNT and MWCNT bundles have been found out. It has been observed that sparse SWCNT bundle interconnects show about 50 % performance improvement for 20 $$\upmu $$ μ m long local level interconnects over Cu in 16 nm technology node, whereas the performance advantage numbers for MWCNT and sparse DWCNT bundles are 50 and 35 % respectively. For 200 $$\upmu $$ μ m long intermediate level interconnects, the performance advantage numbers are 85, 80 and 75 % for dense SWCNT, MWCNT and dense DWCNT bundles respectively in 16 nm node. For 10 mm long global level interconnects, the performance advantage numbers are 85, 85 and 75 % for dense SWCNT, MWCNT and dense DWCNT bundles respectively in 16 nm node. It is also observed that the performance numbers improve with scaling for all levels of interconnects. It is also shown that the ratio of delay of CNT bundles and Cu for various levels of interconnects agree well with the existing work.

Understanding Carbon Dioxide Adsorption in Carbon Nanotube Arrays: Molecular Simulation and Adsorption Measurements

Grand-canonical Monte Carlo simulations and adsorption experiments are conducted to understand the adsorption of CO2 onto bundles of 3D aligned double-walled carbon-nanotubes of diameter 5 nm at 303 K. The simulation of partial adsorption isotherms, i.e., only inner tube volume, only interstices between tubes, and unrestricted, allows a breakdown of the experimental adsorption isotherms into contributions of different regions. The results are compatible with microscopic observations of the majority of the inner tube volumes being accessible for CO2. Further, the unrestricted adsorption isotherm is quantitatively equivalent to the sum of inner and outer adsorption for the pressure range considered in this work, p < 40 bar, indicating no significant interference between inner and outer regions. The intertube distance, which is varied from 0 to 15 nm, dramatically affects the isosteric heat of adsorption and adsorption capacity. Excess adsorption is found to display a nonlinear behavior with d, for unrestric...

Bio-Inspired Carbon Nanotube–Polymer Composite Yarns with Hydrogen Bond-Mediated Lateral Interactions

Polymer composite yarns containing a high loading of double-walled carbon nanotubes (DWNTs) have been developed in which the inherent acrylate-based organic coating on the surface of the DWNT bundles interacts strongly with poly(vinyl alcohol) (PVA) through an extensive hydrogen-bond network. This design takes advantage of a toughening mechanism seen in spider silk and collagen, which contain an abundance of hydrogen bonds that can break and reform, allowing for large deformation while maintaining structural stability. Similar to that observed in natural materials, unfolding of the polymeric matrix at large deformations increases ductility without sacrificing stiffness. As the PVA content in the composite increases, the stiffness and energy to failure of the composite also increases up to an optimal point, beyond which mechanical performance in tension decreases. Molecular dynamics (MD) simulations confirm this trend, showing the dominance of nonproductive hydrogen bonding between PVA molecules at high PVA contents, which lubricates the interface between DWNTs.

Significantly enhanced thermoelectric properties of ultralong double-walled carbon nanotube bundle

A T-type method is developed to comprehensively evaluate the thermoelectric properties of materials. The thermoelectric properties, including thermal conductivity, thermopower, and electrical conductivity of an ultralong double-walled carbon nanotube bundle are studied from 240 K to 340 K by applying the T-type method. The determined figure of merit achieves 10−3 which is significantly larger than that reported for carbon nanotubes samples. The bundle consists of thousands of nanotubes aligned along the long axis with low levels of impurities, and the thermal conductivity is significantly reduced compared to that of individual double-walled nanotube, while the electrical conductivity is superior to most of the carbon nanotubes samples.

Carbon nanotube and graphene multiple-thread yarns

Carbon nanotubes (CNTs) and graphene (GNS) hybrid multiple-thread yarns were fabricated by chemical vapor deposition followed by a posted-stretching processing. The as-prepared CNTs and GNS multiple-thread yarns consisted of tens of single-thread fibers with diameters of around 20 μm. The single-thread fibers are composed of double-walled carbon nanotube (DWNT) bundles and GNS tablets. DWNT bundles in the single-thread fiber are highly disordered and are rounded by GNS. The content and dimensions of GNS are changeable along the fiber axial direction. The as-obtained CNT and GNS hybrid multiple-thread yarns can be twisted, forming one fiber. The mechanical measurement of the twisted yarn gave a strength of 300 MPa and the electrical conductivity is 10(5) S m(-1). These unique structures, possessing various promising properties, can be readily and directly applied in different fields. Here, the hybrid yarns of CNTs and GNS were applied as a lamp thread and woven macroscopic body, as demonstrated.

Stabilization of carbon nanotubes by filling with inner tubes: An optical spectroscopy study on double-walled carbon nanotubes under hydrostatic pressure

The stabilization of carbon nanotubes via the filling with inner tubes is demonstrated by probing the optical transitions in double-walled carbon nanotube bundles under hydrostatic pressure with optical spectroscopy. Double-walled carbon nanotube films were prepared from fullerene peapods and characterized by high-resolution transmission electron microscopy and optical spectroscopy. In comparison to single-walled carbon nanotubes, the pressure-induced redshifts of the optical transitions in the outer tubes are significantly smaller below $\ensuremath{\sim}$10 GPa, demonstrating the enhanced mechanical stability due to the inner tube already at low pressures. Anomalies at the critical pressure $P$${}_{d}\ensuremath{\approx}12$ GPa signal the onset of the pressure-induced deformation of the tubular cross sections. The value of $P$${}_{d}$ is in very good agreement with theoretical predictions of the pressure-induced structural transitions in double-walled carbon nanotube bundles with similar average diameters.

Effect of surface “groove” structure of carbon nanotube bundles on the formation of nanohybrid shish kebab

Abstract

Effect of compression on the enhancement of friction and strengthen of double-walled carbon nanotube bundles: A molecular dynamics study

Interfacial friction plays a crucial role in the mechanical properties of carbon nanotube (CNT) based fibers, composites, and devices. With the molecular dynamics simulation, we investigate the compression effect on the friction within the 16×(10,10) @ (5,5) double-walled CNTs. Our results show that the double-walled CNTs has perfect compression and recovery qualities, and its variation in sliding velocity also has good accordance with the single-walled CNTs. The structure transition varies during the three different deformation stages, which can be denoted by before the structure deformation, during the structure deformation, and after the structure deformation, of double-walled CNT under increasing pressure. And we find that, after deformation, the CNT collapse and the friction forces within the double-walled CNTs have at least 1.6 times larger than its beginning. Finally, in order to make comparisons with the same type double-walled CNT bundles, we constructed the 16×(10,10) @ (6,6) bundles in theory and studied its sliding velocity, which shows that larger diameter inner CNTs have higher friction after deformation. This may provide an effective way to reinforce the strengthen of CNT fibers.

Nanohybrid shish kebab structure and its effect on mechanical properties in poly(L‐lactide)/carbon nanotube nanocomposite fibers

AbstractIn our previous work, the formation of a nanohybrid shish kebab (NHSK) structure was successfully achieved in helical polymer systems promoted by using single‐walled carbon nanotube (CNT) bundles with a unique ‘groove structure’, which is of great crystallographic interest. To further investigate the effect of surface groove structure of CNT bundles on the formation of NHSK structure in helical polymer systems, in the work reported here double‐walled carbon nanotube (DWNT) fibers with bundle structure were used as nucleating agents and orientation templates for poly(L‐lactide) (PLLA) crystallization. A fine NHSK structure with controlled lateral size and period of kebabs was successfully obtained under various experimental conditions by using DWNT bundles. This could be due to the geometric confinement effect of the surface groove structure of the DWNT bundles, which could facilitate the orientation of PLLA chains along the DWNT axis and the lateral formation of a stable nucleus. Our work suggests an efficient method for the functionalization of CNTs with biocompatible PLLA, which may have some potential applications in biomedical areas. In addition, it is demonstrated that the formation of NHSK structure can effectively improve the physical bonding between PLLA and nanotubes, thus significantly improving the mechanical properties of PLLA/CNT nanocomposite fibers. Copyright © 2012 Society of Chemical Industry