Single-walled Carbon Nanotube Bundles Research Articles

Molecular simulation of adsorption and separation of pure noble gases and noble gas mixtures on single wall carbon nanotubes

Grand Canonical Monte Carlo simulations were performed to systematically study the adsorption and separation of noble gases on single wall carbon nanotube (SWCNT) bundles. Pure noble gases, as well as binary and ternary mixtures, were simulated in carbon nanotube systems under various conditions. Adsorption data was collected at 100K and 300K over a wide range of pressures. Carbon nanotube bundles present distinct adsorption capacities towards different noble gases. In particular, larger and heavier noble gases are easier to be adsorbed at low pressure, while lighter atoms with smaller sizes can be better stored at high pressure. For noble gas mixtures with equal molar loadings, selective adsorption was observed and the selectivity inverted at different pressure ranges according to the choice of mixtures. Furthermore, the influence of loading proportion of the components on the adsorption behavior was investigated by varying the loading partial pressure in binary mixtures from 1% to 99%. The results suggest gas–CNT interactions dominate the adsorption selectivity at low loading conditions, whereas the entropic effect plays a more important role at high loadings.

Metal nanoparticles reveal the organization of single-walled carbon nanotubes in bundles

Single-walled carbon nanotubes (SWCNTs) were decorated with Ag and Au nanoparticles. The smaller SWCNTs in bundles are preferentially affected by the presence of metal nanoparticles. We postulate that smaller diameter SWCNTs surround larger ones.

Theoretical and experimental investigations of the Li storage capacity in single-walled carbon nanotube bundles

Lithium stored in interstitial sites reflects the actual low capacity observed from the 2nd cycle and beyond.

The influence of geometric heterogeneity of closed carbon nanotube bundles on benzene adsorption from the gaseous phase-Monte Carlo simulations

Benzene adsorption from the gaseous phase at 298 K and the thermodynamics of this process using Monte Carlo methods is studied. A series of closed single-walled carbon nanotube (SWCNT) bundles (triangular packing arrangement) with various distance between nanotubes is investigated. Isolated closed nanotube is treated as the reference system. Benzene is considered as a model compound to represent aromatics. Simulation results show the significant effect of the geometric heterogeneity on benzene adsorption as well as the enthalpy and entropy at low surface coverages. For insignificantly separated nanotubes and at low benzene uptakes, the entropy of the adsorbed phase is close to the entropy of solid benzene. Therefore, C6H6 molecules strongly interacting with walls are ordered in quasi-solid structures. At higher surface coverages, the ordering and packing of benzene molecules is liquid-like. The geometry of bundles (mutual position of SWCNTs) significantly influences the position and orientation of adsorbed molecules against the wall.

Defect-Free Carbon Nanotube Coils.

Carbon nanotubes are promising building blocks for various nanoelectronic components. A highly desirable geometry for such applications is a coil. However, coiled nanotube structures reported so far were inherently defective or had no free ends accessible for contacting. Here we demonstrate the spontaneous self-coiling of single-wall carbon nanotubes into defect-free coils of up to more than 70 turns with identical diameter and chirality, and free ends. We characterize the structure, formation mechanism, and electrical properties of these coils by different microscopies, molecular dynamics simulations, Raman spectroscopy, and electrical and magnetic measurements. The coils are highly conductive, as expected for defect-free carbon nanotubes, but adjacent nanotube segments in the coil are more highly coupled than in regular bundles of single-wall carbon nanotubes, owing to their perfect crystal momentum matching, which enables tunneling between the turns. Although this behavior does not yet enable the performance of these nanotube coils as inductive devices, it does point a clear path for their realization. Hence, this study represents a major step toward the production of many different nanotube coil devices, including inductors, electromagnets, transformers, and dynamos.

Concentration of lysozyme/single-walled carbon nanotube dispersions

The dispersion of single-walled carbon nanotubes (SWNT) in aqueous solutions of biological materials enables the production of bulk films and fibers that combine natural biological activity with SWNT’s intrinsic mechanical, thermal, and electrical properties. In this work, we report the rheology and phase behavior of concentrated lysozyme (LSZ)/SWNT dispersions. Even at low concentration, the LSZ’s globular structure causes a deviation from the rheological behavior expected of rigid rods such as SWNT. With increasing concentration, stabilized SWNT typically form lyotropic liquid crystalline phases. However, in this case, the LSZ results in depletion attraction and the formation of large dense SWNT aggregates surrounded by a LSZ network. At intermediate concentrations, the microstructure and rheological properties are a complex function of the initial dispersion state, the absolute concentrations, and the LSZ to SWNT ratio. The rheological effects of concentrating mixtures comprised of aggregates, a range of bundle sizes, and individual SWNT were compared to the effects of concentrating supernatants comprised solely of individual SWNT and small bundles. In general, lysozyme concentration has the greatest impact on dispersion viscoelasticity. However, the inherent viscosity was a function of SWNT concentration; data from both initial mixtures and supernatants spanning two orders of magnitude in concentration could be collapsed onto a single master curve. This work provides a foundation for exploring the behavior of other globular protein–SWNT dispersions.

Molecular dynamics simulation of doxorubicin adsorption on a bundle of functionalized CNT

In this study, molecular dynamics simulation is used to investigate the adsorption of an anticancer drug, doxorubicin, on bundles of functionalized single-walled carbon nanotubes (SWNTs) in an aqueous solution. Carboxylic group has been selected as the functional group. Molecular dynamics (MD) simulations are performed for both separated systems containing a SWNT bundle and a functionalized carbon nanotube bundle, and results are compared with existing experimental data. MD results show that doxorubicin can be adsorbed on CNTs using different methods such as entrapment within CNT bundle, attachment to the side wall of the CNT, and adsorption on the CNT inner cavity. For functionalized CNT, the adsorption of drugs on the functional groups is essential for predicting the enhancement of drug loading on the functionalized nanotubes. Furthermore, the adsorption behavior of doxorubicin on CNTs is fitted with Langmuir and Freundlich isotherm models. The results show that Langmuir model can predict the adsorption behavior of doxorubicin on CNTs more accurately than Freundlich model does. As predicted by this isotherm model, the adsorption process of doxorubicin on CNTs is relatively difficult, but it can be improved by increasing the functional groups on the CNTs surface.

Growth of micro-crystals in solution by in-situ heating via continuous wave infrared laser light and an absorber

We report on growth of micro-crystals such as sodium chloride (NaCl), copper sulphate (CuSO4), potassium di-hydrogen phosphate (KDP) and glycine (NH2CH2COOH) in solution by in-situ heating using continuous wave Nd:YVO4 laser light. Crystals are grown by adding single walled carbon nanotubes (SWNT). The SWNTs absorb 1064nm light and act as an in-situ heat source that vaporizes the solvent producing microcrystals. The temporal dynamics of micro-crystal growth is investigated by varying experimental parameters such as SWNT bundle size and incident laser power. We also report crystal growth without SWNT in an absorbing medium: copper sulphate in water. Even though the growth dynamics with SWNT and copper sulphate are significantly different, our results indicate that bubble formation is necessary for nucleation. Our simple method may open up new vistas for rapid growth of seed crystals especially for examining the crystallizability of inorganic and organic materials.

Uncovering the ultimate performance of single-walled carbon nanotube films as transparent conductors

The ultimate performance—ratio of electrical conductivity to optical absorbance—of single-walled carbon nanotube (SWCNT) transparent conductive films (TCFs) is an issue of considerable application relevance. Here, we present direct experimental evidence that SWCNT bundling is detrimental for their performance. We combine floating catalyst synthesis of non-bundled, high-quality SWCNTs with an aggregation chamber, in which bundles with mean diameters ranging from 1.38 to 2.90 nm are formed from identical 3 μm long SWCNTs. The as-deposited TCFs from 1.38 nm bundles showed sheet resistances of 310 Ω/□ at 90% transparency, while those from larger bundles of 1.80 and 2.90 nm only reached values of 475 and 670 Ω/□, respectively. Based on these observations, we elucidate how networks formed by smaller bundles perform better due to their greater interconnectivity at a given optical density. Finally, we present a semi-empirical model for TCF performance as a function of SWCNT mean length and bundle diameter. This gives an estimate for the ultimate performance of non-doped, random network mixed-metallicity SWCNT TCFs at ∼80 Ω/□ and 90% transparency.

Design of n-Tier Multilevel Interconnect Architectures by Using Carbon Nanotube Interconnects

In this paper, n-tier methodology is developed to design multilevel interconnect architecture of macrocells using single-wall carbon nanotube (SWCNT) bundles. Upper limit of low-bias voltage of SWCNT bundle interconnects is derived and its dependence on temperature, SWCNTs’ diameter, and interconnect length is studied. Possibility of using SWCNT bundles as local interconnects at 7.5-nm technology node is discussed, and it is shown that SWCNT bundles with 1 nm diameter cannot be used at the first interconnect metal level. Using Cu and SWCNT bundles, multilevel interconnect architecture of a 7.5-nm ASIC macrocell is designed which reduces the number of metal levels by 27% and power dissipation by 25% compared with the multilevel interconnect architecture designed with only Cu. The effect of aspect ratio (AR) on the n-tier design is studied. It is shown that decreasing AR of SWCNT bundle interconnects, decreases total power dissipation of the ASIC macrocell by 41%. The impact of temperature variation on the design of multilevel interconnect architecture is also investigated.

Temperature-Dependent Modeling and Performance Evaluation of Multi-Walled CNT and Single-Walled CNT as Global Interconnects

The influence of temperature on multi-walled carbon nanotube (MWCNT) interconnects have been studied. A temperature-dependent equivalent circuit model is presented for the impedance parameters of MWCNT bundle interconnects that captures various electron–phonon scattering mechanisms as a function of temperature. To estimate the performance of MWCNT bundle interconnects, the signal delay, power dissipation and power delay product (PDP) were simulated based on a temperature-dependent model that results in improvement in the delay, power and PDP estimation accuracy compared to the temperature-independent model. The results revealed that the power delay product of MWCNT bundle interconnects increases with increasing temperature from 200 K to 450 K for three different technology nodes, i.e., 32 nm, 22 nm and 16 nm, based upon a 1000-μm interconnect length. A similar analysis was performed for single-walled carbon nanotube (SWCNT) bundle interconnects and the results are compared with MWCNT bundle interconnects, indicating that the delay, power and power delay product (PDP) also increased with increasing temperature from 200 K to 450 K. The interconnects of the MWCNT bundle interconnects gave a better performance in terms of delay, power and PDP as compared to the SWCNT bundle interconnects.

Electrochemical design of plasmonic nanoantennas for tip-enhanced optical spectroscopy and imaging performance

Optical nanoantennas play a crucial role in controlling near-fields on the nanoscale and being counterparts of commonly used conventional optical components such as lens, prisms, gratings, etc. for shaping the wavefront of light in the far-field. In this paper we highlight a dc-pulsed voltage electrochemical etching method with a self-tuneable duty cycle for highly reproducible design of plasmonic (metallic) nanoantennas. With the method, we introduce such concepts as design, optimization and figure-of-merit for evaluating fabrication efficiency. The ability of the nanoantennas to enhance and localize the optical fields beyond the diffraction limit is statistically studied with Rayleigh scattering from the tip apex and tip-enhanced Raman spectroscopy of a single walled carbon nanotubes bundle.

In Situ Synchrotron X-ray Diffraction Studies of Single-walled Carbon Nanotubes for Electric Double-layer Capacitors

In situ synchrotron X-ray diffraction experiments of SWCNT (single-walled carbon nanotube) electrode in alkali halide aqueous electrolyte at several applied potentials were performed, and the change in the diffraction pattern of SWCNTs was observed. It was found that the position of the 100 diffraction peak does not change with applied potential while the peak intensity decreases with anion adsorption. It was concluded that the space inside the tube would be the important ion adsorption site for the well-grown SWCNT bundles.

Polyazines and Polyazomethines with Didodecylthiophene Units for Selective Dispersion of Semiconducting Single‐Walled Carbon Nanotubes

Polymer wrapped single‐walled carbon nanotubes (SWNTs) have been demonstrated to be a very efficient technique to obtain high purity semiconducting SWNT solutions. However, the extraction yield of this technique is low compared to other techniques. Poly‐alkyl‐thiophenes have been reported to show higher extraction yield compare to polyfluorene derivatives. Here, the affinity for semiconducting SWNTs of two polymers with a backbone containing didodecylthiophene units interspersed with N atoms is reported. It is demonstrated that one of the polymers, namely, poly(2,5‐dimethylidynenitrilo‐3,4‐didodecylthienylene) (PAMDD), has very high semiconducting SWNT extraction yield compared to the poly(3,4‐didodecylthienylene)azine (PAZDD). The dissimilar wrapping efficiency of these two polymers for semiconducting SWNTs is attributed to the interplay between the affinity for the nitrogen atoms of the highly polarizable walls of SWNTs and the mechanical flexibility of the polymer backbones. Photoluminescence (PL) measurements demonstrate the presence of metallic tubes and SWNT bundles in the sample selected with PAZDD and higher purity of SWNT‐PAMDD samples. The high purity of the semiconducting SWNTs selected by PAMDD is further demonstrated by the high performance of the solution‐processed field‐effect transistors (FETs) fabricated using a blade coating technique, which exhibit hole mobilities up to 33.3 cm2 V−1 s−1 with on/off ratios of 106.

Observation of impedance oscillations in single-walled carbon nanotube bundles excited by high-frequency signals

We report experimental observation of impedance oscillations in single-walled carbon nanotube bundles measured from 10 MHz to 65 GHz on coplanar waveguides and a power law dependence of the differential conductance with bias voltage. From the crossover of the real and imaginary parts of the complex impedance observed in the range of 10 GHz, we estimate a long lifetime of 15 ps that can support the claim of ballistic transport. By measuring the scattering parameters at high frequencies at low temperatures we show that this observation is strongly influenced by the number of aligned nanotube bundles present in the devices.

Fabrication of Copper / Single-Walled Carbon Nanotube Composite Plating Films By Electrodeposition

Introduction Copper has many excellent properties such as high electrical conductivity and good thermal conductivity and ductility, resulting in the wide use of copper plating in the electronics industry. Single-walled carbon nanotubes (SWCNTs) also exhibit attractive characteristics such as stable electrical resistance in the presence of high currents and good thermal conductivity and field emission properties, resulting in their application in a wide range of fields. Cu/SWCNT composites would therefore be expected to have excellent electrical and thermal conductivity properties.Our laboratory previously reported the fabrication of electroless Cu/SWCNT composite plating films, 1)but the fabrication of Cu/SWCNT composite plating films by electrodeposition has not been reported.Here we describe an attempt to fabricate Cu/SWCNT composite plating films with homogeneously distributed SWCNTs using electrodeposition. Experimental The Cu/SWCNT composite plating bath comprised 0.1 M CuSO4･5H2O, 0.2 M EDTA･2Na, SWCNTs (Super-growth SWCNTs, Zeon Co.) and dispersants. EDTA･Na was used as a copper chelating agent. A magnetic stirrer, an ultrasonic homogenizer and a mechanical atomizer (Star Burst Labo, SUGINO MACHINE Co.) were used to fragment the SWCNT bundles. The dispersibility of the SWCNTs was evaluated using a particle size distribution analyzer. Electrodeposition was conducted under galvanostatic conditions. A pure copper plate and a phosphorus-containing copper plate were used as cathode and anode, respectively. The morphologies of the composite films were observed by field emission scanning electron microscopy (FE-SEM) and the phase structures of the films were analyzed by X-ray diffraction. The thermal and electrical conductivities of the composite films were also evaluated. In addition, the SWCNTs were quantitatively analyzed. Results and Discussion The results demonstrated that fragmentation of the SWCNTs was improved significantly by using a mechanical atomizer. The content of SWCNTs in the films increased with increasing SWCNT concentration in the plating bath. Fig. 1 shows a surface SEM image of a prepared Cu/SWCNT composite plating film and indicates that the SWCNTs are incorporated relatively uniformly into the Cu film. The diameter of the SWCNTs is ca. 15 nm or less, indicating that the bundles of SWCNTs are highly fragmented. References 1) T. Osaki, S. Arai, of ADMETAPlus 2013 Asian Session (2013) 86 Figure 1

Microstructure and impedance spectroscopy of 3YTZP/SWNT ceramic nanocomposites

This work provides new insights on microstructure and electrical properties of 3mol% Y2O3–ZrO2 (3YTZP) composites with 0.5, 1, and 1.5vol% single walled carbon nanotubes (SWNTs). The composites were spark plasma sintered (SPS) in identical conditions at 1250°C from powder prepared by two different processing routines, with the aim of optimizing the SWNTs dispersion throughout the ceramic matrix. High densification and submicrometric grain size were achieved in all the composites. Electrical properties of the composites were characterized in a wide temperature range, and modeling of the impedance properties was approached by means of an equivalent circuit that allows separation of the individual SWNT bundles contribution to resistance from the resistance due to junctions between bundles. Effects of the homogeneous distribution of SWNTs at the ceramic grain boundaries on the crystalline phases, percolation threshold, total conductivity and evolution of junctions׳ resistivity with temperature were analyzed and discussed.

Aggregates of single-walled carbon nanotube bundles in a surfactant solution

We have carried out small angle X-ray scattering (SAXS), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and 1H NMR studies as a function of temperature on 0.1wt.% single-walled carbon nanotubes (SWCNTs) dispersed aqueous (D2O) cetyl trimethylammonium bromide (CTAB) solution. We find that the single-walled carbon nanotubes in this system aggregate to form bundles and depending on the temperature of the system, the bundles aggregate and exhibit four different structures namely, Y-shaped structures, net-like structures, domains of small spherical structures and sheet-like structures. Our DSC thermogram also showed peaks at these structural transition temperatures of the CNT aggregates. Our SEM and 1H NMR studies reveal that the CTAB micelles are adsorbed on the CNT aggregates and the adsorption depends on the temperature and structure of the CNT aggregates.

Structural Analysis of Encapsulated Single-Walled Carbon Nanotubes

Tip-enhanced Raman spectroscopy revealed the nanoscale chemical properties of organic molecules encapsulated in single walled carbon nanotubes (SWNTs). Our approach is based on an enhanced electric field near a laser-irradiated metal tip functioning as a Raman excitation source. The enhanced field can successfully act on encapsulated molecules through the walls of the SWNTs to extract molecular vibrational information -carotene, which exhibits several active Raman modes under visible light illumination, was used as the encapsulated molecule. Tip-enhanced Raman spectra measured at seven different positions on SWNT bundles showed that carotene molecules inside the tubes were not uniformly distributed. It is also found that the filling rate and peak position of the radial breathing mode of the SWNTs are linearly correlated.

Synthesis of Fe<sub>3</sub>O<sub>4</sub> Nanoparticles to Synthesize Bundles of Single-Walled Carbon Nanotubes

Magnetite (Fe3O4) nanoparticles were synthesized in aqueous solutions without any surfactants. The Fe3O4 nanoparticles are nearly spherical and have an average diameter of 10.33nm and a narrow size distribution. Bundles of single-walled carbon nanotube (SWCNT) were synthesized using these Fe3O4 nanoparticles supported by MgO. Transmission electron microscopy (TEM) images show that tremendous amount of bundles SWCNT with uniform diameters were produced. The average diameter of bundles SWCNT is 1.22nm. Raman spectrum shows that well graphitized SWCNTs were formed based on the low ratio of ID/IG. Fe3O4 nanoparticles could be an effective active metal to synthesize large quantity bundles of SWCNT.