Single-walled Nanotube Bundles Research Articles

Emergence of carbon nanoscrolls from single walled carbon nanotubes: an oxidative route.

Carbon nanoscrolls (CNS), a one dimensional (1D) helical form of carbon, have received enormous attention recently due to their unique structure, superior properties and potential applications. In this work, radial merging of HiPCO single walled nanotube (SWNT) bundles and emergence of CNS are reported following a reflux action involving wet oxidation, HCl washing and annealing at 900 °C. We observe macroscopic quantities of graphene sheets (GS) in the post-treated sample and beautiful manifestation of curling and folding of the GS into CNS. Here, a simple solution based oxidative route for successful merging and exfoliation of SWNT bundles and subsequent formation of CNS are demonstrated and discussed in view of Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) studies. Direct evidence of emergence of CNS from SWNTs via synthesis of GS through a simple oxidative method is reported for the first time.

A bridging cell multiscale modeling of carbon nanotube-reinforced aluminum nanocomposites

In this paper, the Young’s modulus and failure mechanics of nanotube-reinforced aluminum nanocomposites has been investigated using the Bridging Cell Method (BCM). The advantage of the BCM for multiscale modeling of CNT-Al nanocomposites is in its quasi-static formulations in concurrent multiscale environment with specialized local quasi-harmonic approximations for thermal contributions. The model has been initially verified by coupling the atomistic-continuum domains in a representative volume element of the nanocomposite. The multiscale method sets the nanotubes as part of the atomistic domain, while the rest of the domain is kept in the continuum domain and modeled using the finite element method. The types of nanotube reinforcements considered in this study are single-walled nanotubes (SWNTs), multi-walled nanotubes (MWNTs) and a bundle of SWNTs. It was found that the overall strength of the nanocomposite was similar between the different reinforcements, but the toughening mechanisms differed significantly between the three. The model has been tested for two different crystalline planes in the aluminum crystal to observe the degree of toughening on different atomic planes where it was found that the essential plane and the cleavage plane had similar ultimate tensile strength, however the role of toughening was less prevalent in the cleavage plane case.

Simulation of mechanical performance limits and failure of carbon nanotube composites

The mechanical properties of carbon nanotube (CNT) fiber composites are steadily approaching those of traditional carbon fiber composites. This work is focused on establishing a plausible upper bound on these properties by modeling the elastic deformations, yield, and fracture of idealized CNT composites using reactive molecular dynamics. Amorphous carbon (AC) was used for the matrix material because of its structural simplicity and physical compatibility with the CNT fillers. Three different arrangements of CNTs in the simulation cell were investigated: a single-wall nanotube (SWNT) array, a multi-wall nanotube (MWNT) array, and a SWNT bundle system. The SWNT and MWNT array systems are clearly idealizations, but the SWNT bundle system is a step closer to real systems in which individual tubes aggregate into large assemblies. Chemical crosslinking was modeled by adding bonds between the CNTs and AC to explore the balance between weakening the CNTs and improving fiber-matrix load transfer. The simulation results reported here clarify the impact of CNT dispersion, the extent of crosslinking, and CNT-templated matrix structuring on the mechanical properties of CNT composites.

Graphitization of single-wall nanotube bundles at extreme conditions: Collapse or coalescence route

We determine the reaction phase diagram and the transformation mechanism of (5,5) and (10,10) single-walled carbon nanotube bundles up to 20 GPa and 4000 K. We use Monte Carlo simulations, based on the state-of-the-art reactive potential LCBOPII, that incorporates both covalent and van der Waals interactions among the tubes. At low temperature, upon increasing pressure, large (10,10) nanotubes first collapse and then coalesce, yielding almost perfect graphitic structures. In contrast, small (5,5) nanotubes do not collapse, but coalesce and transform to graphite via a mixed graphite-tube structure. At high temperature (above $\ensuremath{\sim}2000$ K), for both (10,10) and (5,5) nanotubes, coalescence dominates the transformation to graphitic structures. We argue that the $s{p}^{3}$-interlinking defects appearing at coalescence can act as seed and facilitate the transformation to diamond structures.

Novel carbon materials: New tunneling systems (Review Article)

This review covers recent achievements in the studies of quantum properties of the novel carbon materials (fullerite C60 and bundles of single-walled nanotubes (SWNT)) saturated with such light-mass species as helium isotopes, the homonuclear molecular hydrogens, and neon. It is shown that even some heavy dopants demonstrate kinetic phenomena, in which coherent effects play an essential role. Two theoretical concepts are surveyed which have been suggested for the explanation of the anomalous phenomena in saturation kinetics and linear thermal expansion of doped C60. Most unusual effects have been also observed in the low-temperature radial expansion of bundles of single-walled carbon nanotubes saturated with the helium isotopes. First, it was shown that low-temperature radial expansion of pure SWNT is negative, i.e., a nanotube shrinks with warming. Second, saturation of SWNT bundles with the helium isotopes entails a huge increase of the negative expansion effect, when the dopant is He. So far, no detailed physical picture has been put forward. It is worth mentioning that the dynamics of a single helium atom on an isolated nanotube corresponds to that of a tight-bound quasiparticle with a band width of about 10 K.

Methane Adsorption on Graphitic Nanostructures: Every Molecule Counts

Bundles of single-walled nanotubes are promising candidates for storage of hydrogen, methane, and other hydrogen-rich molecules, but experiments are hindered by nonuniformity of the tubes. We overcome the problem by investigating methane adsorption on aggregates of fullerenes containing up to six C60; the systems feature adsorption sites similar to those of nanotube bundles. Four different types of adsorption sites are distinguished, namely, registered sites above the carbon hexagons and pentagons, groove sites between adjacent fullerenes, dimple sites between three adjacent fullerenes, and exterior sites. The nature and adsorption energies of the sites in C60 aggregates are determined by density functional theory and molecular dynamics (MD) simulations. Excellent agreement between experiment and theory is obtained for the adsorption capacity in these sites.

Self-heating of metallic carbon nanotube bundles in the regime of the Luttinger-liquid conductivity

The conductivity of bundles of carbon single-walled nanotubes with metallic conductivity (metallic nanotubes) is investigated over the wide temperature range 4.2–330 K and electrical fields up to 50 V. The usage of short electrical pulses of the duration of 10 ns allowed to avoid an influence of a self-heating of the investigated structures on current-voltage characteristics. It is shown that the temperature dependence of conductivity is described by the power function G∝Tα. At helium temperatures the asymptotic dependence of current on applied voltage is close to J∝V1+α with α = 0.45. From comparison of the obtained results of measurements with calculations, it is shown that the conductivity of nanotube bundles is well described within the theory of the Luttinger-liquid conductivity for one-dimensional conductors. The self-heating of the carbon nanotube bundles was observed in the case of measurements in the regime of dc current. A method for determination of the self-heating temperature of nanotube bundles as a function of an applied electrical field is proposed. The power dependence of the self-heating temperature on voltage T∝Vp with the exponent p = 2.1 was observed above some threshold voltage in the temperature range 4.2–200 K. Above 200 K the exponent decreased down to p = 1.35.

Hydrogen sorption and radial thermal expansion of bundles of single-walled nanotubes irradiated by γ-rays in hydrogen atmosphere

The influence of radiation exposure in hydrogen atmosphere on the radial thermal expansion of single-walled carbon nanotubes and on their sorption of hydrogen is studied. The irradiation was carried out with cobalt-60 γ-rays (with an energy of 1.2 MeV and an irradiation dose of 1.5·107 rad) in the normal hydrogen atmosphere under pressure 1 atm and at temperature of 300 K. The sorption and desorption of hydrogen by samples of nanotubes were investigated over the temperature range 15–1170 K before and after irradiation. It was found that the irradiation of carbon nanotubes (CNTs) in hydrogen atmosphere leads to considerable increasing an amount of hydrogen sorbed by the sample. The irradiation in hydrogen atmosphere resulted in increasing absolute values of radial thermal expansion of CNTs bundles over the temperature range investigated (2–120 K). The effects of hydrogen physically and chemically sorbed in bundles of CNTs on the radial thermal expansion of the irradiated samples were distinguished.

Unusual Melting Transition of Nitrogen Physisorbed on Carbon Nanotube Bundles

The melting transition of nitrogen physisorbed on close-ended single-wall nanotube bundles was investigated using synchrotron X-ray diffraction measurements. The beta-nitrogen solid diffraction peak was observed above the coverage that corresponded to the monolayer and the average size of the nitrogen solid was approximately 30 A. The diffraction peak was surprisingly maintained above the triple point of the bulk nitrogen solid. The crystal structure of N2 changed from cubic N2 (beta-phase) to hexagonal N2 (beta-phase) at 35.61 K. The melting temperature of the nano-scale solid nitrogen in the experiment was between 80 K and 90 K, however, which is about 20 K higher than the melting temperature of normal bulk nitrogen. The observed extraordinary melting behavior of nitrogen might originate from a combination of two factors, i.e., the substrate field effect of the carbon nanotube surface (the interaction between the single walled carbon nanotubes and the adsorbates) and the capillary condensation. If the substrate field effect is especially prominent, the nitrogen molecules that were adsorbed mainly in the groove region would be under 1,100-Torr pressure from the nanotube bundles, compared to the corresponding melting temperature of the bulk beta-nitrogen solid under a high pressure.

Osmotic ensemble methods for predicting adsorption-induced structural transitions in nanoporous materials using molecular simulations

Osmotic framework adsorbed solution theory is a useful molecular simulation method to predict the evolution of structural transitions upon adsorption of guest molecules in flexible nanoporous solids. One challenge with previous uses of this approach has been the estimation of free energy differences between the solid phases of interest in the absence of adsorbed molecules. Here we demonstrate that these free energy differences can be calculated without reference to experimental data via the vibrational density of states of each phase, a quantity that can be obtained from molecular dynamics simulations. We show the applicability of this method through case studies of the swelling behaviors of two representative systems in which swelling upon adsorption of water is of importance: single-walled aluminosilicate nanotube bundles and cesium montmorillonite. The resulting predictions show that the aluminosilicate nanotube bundles swell significantly with increasing interstitial adsorption and that the layer spacing of cesium montmorillonite expands up to about 12.5 Å, giving good agreement with experiments. The method is applicable to a wide range of flexible nanoporous materials, such as zeolites, metal-organic frameworks, and layered oxide materials, when candidate structures can be defined and a force field to describe the material is available.

The effect of O2impurities on the low-temperature radial thermal expansion of bundles of closed single-walled carbon nanotubes

The effect of oxygen impurities upon the radial thermal expansion (ar) of bundles of closed single-walled carbon nanotubes has been investigated in the temperature interval 2.2-48 K by the dilatometric method. Saturation of bundles of nanotubes with oxygen caused an increase in the positive ar-values in the whole interval of temperatures used. Also, several peaks appeared in the temperature dependence ar(T) above 20 K. The low temperature desorption of oxygen from powders consisting of bundles of single-walled nanotubes with open and closed ends has been investigated

Explosive percolation in a nanotube-based system

Using the percolation theory, we study the underlying mechanism in the formation of single-walled nanotube bundles with uniform diameter. By applying the cluster repulsion process to stick percolation, we find that the transition becomes explosive. To understand the transition nature, we first investigate the scaling behavior of transition interval Δ. By comparing the results with loopless and loop-allowed bond percolations, we find that the loops crucially affect the scaling behavior of Δ, and Δ is not universal. Moreover, the scaling behavior of Δ for the present nanostick systems is the same as that for loopless bond percolation. For more systematic studies on the transition nature, we also measure the changes in order parameter during the stick removal process and show that there exists a hysteresis. The results more clearly show that the transition of the stick system with cluster repulsion is discontinuous.

Ab initio density functional theory investigation of Li-intercalated zinc oxide nanotube bundles

We have investigated the energetic, and geometric and electronic structure of Li-intercalated (5,5) zinc oxide nanotube (ZnONT) bundles via density functional theory as implemented in the code WIEN2k. Our results showed that the most prominent effect of Li intercalation on the electronic band structure is a shift of the Fermi energy which occurs as a result of charge transfer from lithium to the ZnONTs. All the Li-intercalated (5,5) ZnONT bundles are predicted to be metallic representing a substantial change in electronic properties relative to the undoped bundle, which is a wide band gap semiconductor. Both inside of the nanotube and the interstitial spaces are susceptible for intercalation. The present calculations suggest that the single-walled zinc oxide nanotube (SwZnONT) bundle is a promising candidate for the anode material in battery applications.

Development of Carbon Nanotube Based Through-Silicon Vias

The design and development of reliable 3D integrated systems require high performance interconnects, which in turn are largely dependent on the choice of filler materials used in through-silicon vias (TSVs). Copper, tungsten, and poly-silicon have been explored as filler materials; however, issues such as thermal incompatibility, electromigration, and high resistivity are still a bottleneck. In this paper, we investigate single-walled carbon nanotube (CNT) bundles as a prospective filler material for TSVs and have provided an analysis of CNT based TSVs for package and chip interconnects. The interconnects are fundamental bottlenecks to achieving high performance and reliability. We have provided electrical modeling and performed simulations on TSVs with copper and carbon nanotubes. The results from the CNT based TSVs were greatly superior to those from the conventional vias with copper.

Electrical transport in small bundles of single-walled carbon nanotubes: Intertube interaction and effects of tube deformation

We report a combined electronic transport and structural characterization study of small carbon nanotube bundles in field-effect transistors (FETs). The atomic structures of the bundles are determined by electron diffraction using an observation window built in the FET. The electrical transport of single-walled nanotube bundles depends on the structure of individual tubes, deformation due to intertube interaction, and the orientation with respect to the electric field. Ab initio simulations show that tube deformation in the bundle induces a band gap opening in a metallic tube. These results show the importance of intertube interaction in electrical transport of bundled carbon nanotubes.

Strength and Electrical Conductivity of Carbon Nanotube Yarns

AbstractThe strength and electrical conductivity of Carbon Nanotube (CNT) yarns is dramatically affected by the handling of the material after the nanotubes are produced. Our nanotube production process involving Chemical Vapor Deposition (CVD) using the floating catalyst method produces a mass of entangled bundles of single-walled nanotubes in a gas suspension. Simply collecting and spinning this material produces a yarn with strength and electrical conductivity far less than the properties of the individual nanotubes due to the poor alignment of the bundles on the microscopic scale. We have developed methods of aligning the CNT material that are analogous to the techniques used in the textile industry for spinning staple yarns, but modified to be appropriate for nano-scale material. The result is a dramatic improvement in strength and electrical conductivity of our CNT yarns.

Nanotube bundle oscillators: Carbon and boron nitride nanostructures

Abstract In this paper, we investigate the oscillation of a fullerene that is moving within the centre of a bundle of nanotubes. In particular, certain fullerene–nanotube bundle oscillators, namely C 60 -carbon nanotube bundle, C 60 -boron nitride nanotube bundle, B 36 N 36 -carbon nanotube bundle and B 36 N 36 -boron nitride nanotube bundle are studied using the Lennard–Jones potential and the continuum approach which assumes a uniform distribution of atoms on the surface of each molecule. We address issues regarding the maximal suction energies of the fullerenes which lead to the generation of the maximum oscillation frequency. Since bundles are also found to comprise double-walled nanotubes, this paper also examines the oscillation of a fullerene inside a double-walled nanotube bundle. Our results show that the frequencies obtained for the oscillation within double-walled nanotube bundles are slightly higher compared to those of single-walled nanotube bundle oscillators. Our primary purpose here is to extend a number of established results for carbon to the boron nitride nanostructures.

Radial thermal expansion of single-walled carbon nanotube bundles at low temperatures

For the first time, the linear coefficient of radial thermal expansion is measured on a system of carbon single-walled nanotube (SWNT) bundles at low temperatures (2.2–120K). The measurements are performed using a dilatometer with a sensitivity of 2×10−9cm. A cylindrical sample 7mm high and 10mm in diameter was obtained by compressing powder. The resulting bundles of nanotubes are oriented perpendicular to the sample axis. The starting powder consisted of over 90% SWNTs with outer diameter 1.1nm, the length varying in the range 5–30μm. A change of sign of the radial thermal expansion coefficient at 5.5K is observed.

Ar beam modification of nanotube based composites using molecular dynamics simulations

Ion-beam irradiation of polymers is a common approach to modify their mechanical properties. Here, Ar deposition on polystyrene-carbon nanotube composites is examined. The goals are to determine how subjecting these composites to Ar irradiation influences their surface structure and mechanical properties. The approach is classical molecular dynamics simulations using the reactive empirical bond-order potential to determine the short-ranged forces, and a Lennard–Jones potential to determine the long-ranged forces. Three different composites are considered that consist of a polystyrene matrix with a single-walled nanotube, a double-walled nanotube, or a single-walled nanotube bundle as the reinforcing fiber(s). The composites are irradiated with a beam of 100 Ar atoms with incident energies of 80 eV. The simulations predict that the Ar beam induces cross-linking between the nanotube(s) and polymer and/or between neighboring nanotubes. The results for the composite are contrasted with the results for stand-alone bundles of single-walled and double-walled nanotubes that are also irradiated with Ar. To assess the effect of the cross-linking and irradiation-induced polymer etching on the mechanical properties of the composite, the nanotubes are then pulled axially with respect to the polystyrene. The results indicate that the pull-out forces and interfacial strength increase significantly as a result of irradiation-induced cross-linking.

First-principles study of crystalline bundles of single-walled boron nanotubes with smalldiameter

First-principles calculations based on density functional theory are performedto study structural and electronic properties of crystalline bundles of(n,0) zigzagand (0,n) armchair-type single-walled boron nanotubes (SWBNT) with small diameter, about 4–6 Å.The results predict a modification in the properties of SWBNT bundles relative to thoseof isolated nanotubes with small diameter. The predicted modification can beattributed to a significant interplay between intra- and inter-tubular bonds indetermining the stability of bundles of small diameter SWBNT, analogous to therole played by intra- and inter-icosahedral bonds in the boron crystalline solids.