Coiled Carbon Nanotubes Research Articles

Strain Engineering of Electronic Band Structure and Optical Absorption Spectra of Helically Coiled Carbon Nanotubes

Detailed theoretical study of the electro-optical properties of helically coiled carbon nanotubes (CNTs) is presented. Electronic band structure and density of states as well as optical absorption spectra are calculated for fully relaxed structures and for the structures subjected to the tensile strain. It is shown that according to the conducting properties helically coiled CNTs can be classified as quasi-metals, semi-metals or semiconductors (with direct or indirect band gap). Under the strain band gap narrowing and ultimate band gap closing is predicted, while no change of the conducting properties of the metallic tubes is expected, according to our calculations. As for the optical absorption the situation is quite the opposite: metallic helically coiled CNTs response substantially in contrast to the semiconducting tubes.

Erratum: Synthesis, Model and Stability of Helically Coiled Carbon Nanotubes [ECS Solid State Lett., 2, M21 (2013)

Erratum: Synthesis, Model and Stability of Helically Coiled Carbon Nanotubes [ECS Solid State Lett., 2, M21 (2013)

Superior electrical and mechanical characteristics observed through the incorporation of coiled carbon nanotubes, in comparison to non-coiled forms, in polymers

It is shown that the addition of coiled carbon nanotubes (CCNTs), to polymer matrices confers a two-fold increase of the relative electrical permittivity, in addition to an improvement in the mechanical characteristics. A four-fold augmentation of the elastic modulus and a two-fold improvement in the ultimate tensile strength (compared to the polymer) at ∼2 vol% filler fractions was also obtained. Such attributes are shown to be superior to those obtained through the use of linear (both single-walled and multi-walled) CNTs.

High Energy Density, High Operating Frequency and Energy Efficient On-Chip Inductors based on Coiled Carbon Nanotubes (CCNTs)

ABSTRACTWe demonstrate the superior inductive properties of coiled carbon nanotubes (CCNTs) through numerical computation and analytical modeling, for the next generation of nanoscale, on-chip inductors. Taking advantage of the kinetic inductance (Lk), particularly evident at the nanoscale we find that the inductance can be increased by three orders of magnitude through changing the tube radius as well as the coil radius while the device footprint of the CCNTs can be reduced by 60%. By varying the geometric parameters of the coiled structure, the external magnetic inductance (LM,ext) can be as high as 20% of the Lk. We also report that the self resonant frequency (fSR) of CCNTs can be as much of the order of THz whereas the fSR of conventional copper(Cu) spiral inductors are limited to around 40GHz. Moreover when the material volume is considered, CCNTs have the potential to achieve Quality Factor (Q) eight times as Cu and when the footprint volume is considered Q can be twice as Cu All these promising properties of CCNTs make them a potential candidate for the entire frequency spectrum.

Flame spray pyrolysis generated transition metal oxide nanoparticles as catalysts for the growth of carbon nanotubes

Herein, we investigate the growth of multi-walled carbon nanotubes (CNT) using three transition metal oxide nanoparticles; namely hematite (Fe2O3), cobalt oxide (Co3O4) and nickel oxide (NiO). The nanoparticles were synthesised using flame spray pyrolysis (FSP). As the nanoparticle and CNT syntheses are identical for all materials, a direct comparison between the products is possible and a link between catalyst and morphology of the resultant nanostructures can be elucidated. Conventional CNT were grown on Fe2O3 nanoparticles, no discernible nanotubes were observed on the Co3O4 catalysts whilst a mixture of conventional and coiled CNT (CCNT) were synthesised on the NiO nanoparticles. We investigated the effect of temperature, time and acetylene/hydrogen gas mixtures on the morphology, yield and purity of the CNT produced. By regulating the acetylene pyrolysis temperature for NiO, the CCNT yield can be increased to approximately 70% of the CNT yield.

Synthesis, Model and Stability of Helically Coiled Carbon Nanotubes

Synthesis, Model and Stability of Helically Coiled Carbon Nanotubes

Compressive response of vertically aligned carbon nanotube films gleaned from in situ flat-punch indentations

Abstract

Structure and stability of coiled carbon nanotubes

AbstractHelically coiled carbon nanotubes are modeled using topological coordinate method which is based on the toroidal triply connected graphs, containing pentagons, hexagons, and heptagons. Their regular incorporation into the hexagonal carbon net induces transition from the straight to the helical geometry. Relaxation of the structural model is performed in two steps: Firstly, molecular dynamics based on the Brenner potential is applied and then the coil parameters are, once again, optimized within symmetry preserving density functional tight binding (DFTB) method. Model of smooth regularly helically coiled single‐walled nanotube structure is obtained. Correlations between the helical angle, tubular and helical diameter are found. Cohesive energy of the coiled structure is calculated by DFTB method within symmetry based POLSym code. Its dependence on the diameter of the coil is shown. The calculated energies range from 7.5 to 8.0 eV/atom.

CARBON NANOCOILS: STRUCTURE AND STABILITY

We have constructed a model of single-wall helically coiled carbon nanotubes by means of graph theory and topological coordinates method. After obtaining three-dimensional coordinates of the atoms we proceed with the relaxation by successive application of the following methods: 1) harmonic approximation; 2) molecular mechanics based on the Brenner potential; and 3) density functional tight binding (DFTB). Finally, by DFTB and line group symmetry implemented POLSym code, we calculate total and cohesive energy of the obtained fully relaxed structures of CNCs.

Coiled carbon nanotubes combined with ionic liquid: a new soft material for SPE

For the first time a soft material formed from coiled carbon nanotubes and 1-hexyl-3-methylimidazolium hexafluorophosphate has been used as sorbent material. The soft material has high stability as well as a high capacity to adsorb analytes. In this work we propose using a natural cotton fiber impregnated with the soft material to miniaturize the system. The system was tested for the analysis of polycyclic aromatic hydrocarbons in spiked river water samples. The absolute recovery ranged between 97.5 and 105.5%, demonstrating the usefulness of the soft material. The limit of detection ranged from 2.5 to 6.1 μg/L and the precision expressed as the relative standard deviation for the analysis of five consecutive analyses ranged between 2.5 and 5.8%.

(Invited) Structural Model, Catalytic CVD Synthesis and Elasticity of Helically Coiled Carbon Nanotubes

not Available.

Molecular structural mechanics applied to coiled carbon nanotubes

In this paper, mechanical properties of single-walled helically coiled carbon nanotubes are investigated by means of molecular structural mechanics method in ANSYS finite element code. To specify the geometry of coiled carbon nanotubes, a construction procedure is proposed which offers a full control over the morphology of the coiled nanotubes. In this construction approach, first a development map is drawn on a graphene sheet and then this graphene sheet is rolled to form a defected straight carbon nanotube; then, the sides of these defects are stuck together through a nonlinear analysis and finally, the straight carbon nanotube forms into coiled carbon nanotube. Using this construction procedure, several coiled nanotubes are built and their spring constants are calculated. It is shown that the spring constants found are in good agreement with those obtained from density function theory and tight-binding calculations reported in the literature. Moreover, in order to facilitate the simulation of those macroscopic systems which contain coiled carbon nanotubes, an equivalent continuum model is proposed and its mechanical properties are investigated. It is found that, as the tube diameter increases, both spring constant and shear modulus of the coiled carbon nanotube increase.

On the structural rules of helically coiled carbon nanotubes

► We investigate the geometries of helically coiled carbon nanotubes. ► Two schemes, namely horizontal and vertical shifting, are studied. ► A new type of helically coiled carbon nanotubes is proposed. We discuss various possibilities for the geometries of helically coiled carbon nanotubes (HCCNTs), especially those derived from toroidal carbon nanotubes (TCNTs) containing nonhexagonal defects. Two schemes for the derivation of HCCNTs from a particular TCNT are studied, namely horizontal and vertical shifting. For both cases there is a parameter characterizing the skewness of the corresponding HCCNTs. In particular, we found that when the horizontal shift parameter (HSP) is larger than a certain value, depending on the parent TCNT chosen, the resulting HCCNT possesses a peculiar geometry that has not been reported, in which the molecular shape cannot be described by a tube rolling on a cylinder. The pitch angle as a function of HSP can be nicely approximated by simple trigonometry functions of HCCNT parameters. In the case of vertical shifting, the dependence of pitch angle on the shift parameter is relatively simpler and more intuitive.

Predicted mechanical properties of a coiled carbon nanotube

Nanostructured carbon materials continue to attract much interest for use in devices and as fillers in composites. Here, classical molecular dynamics simulations are carried out using many-body empirical potentials to contrast the mechanical properties of straight and coiled carbon nanotubes. The specific properties of a coiled carbon nanotube (CCNT) are investigated under compression, tension, re-compression, re-tension and pullout from a polyethylene (PE) matrix. The stress–strain curves, spring constants, and yielding strains under compression and tension are given for each system, and the corresponding reasons for the differences in their behavior are discussed. They indicate that the interaction between a CCNT and a PE matrix is stronger than the corresponding interactions between CNTs and PE. Thus, the results indicate that CCNTs are good potential candidates for lightweight, tough composites.

Synthesis and characterisation of coiled carbon nanotubes

Recent results from our group and from literature data are summarized. Emphasis is put on the various supported catalysts that can lead to the formation of helical (or coiled) carbon nanotubes. Detailed analysis of transmission electron microscopy images reveals that not all types of nanotubes – having any type of coil pitch and coil diameter – are equally probable: stability islands can be found in the 3D representation of the number of nanotubes as a function of both coil pitch and coil diameter. In most of the cases the coils are formed by introducing pairs of five-membered and seven-membered rings into the nanotubes containing the basic six-membered rings. Possible applications of the helical carbon nanotubes are discussed.

Optical properties of coiled carbon nanotubes: A simple model

AbstractExperimental evidence of regularly coiled carbon nanotubes have been reported in 1994. They are predicted to have excellent electro‐magnetic properties, although their structure, formation mechanism and theoretical aspects are still subjects of scientific discussions. We propose model of hexagonal, helically coiled single wall carbon nanotubes, and determine their line group symmetry. Further, we calculate electronic band structure and optical conductivity of the various configurations of coiled nanotubes by means of fully symmetry adopted density functional tight binding implemented into the POLSym code. Comparison of conducting and optical properties of coiled and straight armchair carbon nanotubes is shown.

Electronic Band Structure of Coiled Carbon Nanotubes

More than fifteen years have passed since the first report of experimental evidence of regularly coiled carbon nanotubes, but, the structure, formation mechanism and theoretical aspects of these nanotubes still remain unresolved. We propose model of hexagonal, helically coiled single wall carbon nanotubes, determine their line group symmetry and calculate electronic band structure of the relaxed configurations by means of fully symmetry adopted density functional tight binding method implemented into the POLSym code. Electrical properties of the straight and coiled carbon nanotubes of dierent chiralities are compared and analyzed. PACS: 61.48.De, 73.22.‐f, 81.07.‐b

The influence of carbon nanotube structure on complex permittivity and determination of filler density by microwave techniques

The influence of carbon nanotube geometry and morphology on complex permittivity (both ɛ′ and ɛ″) was investigated. In a dilute complex system, it was found that single walled carbon nanotubes (SWNTs) composites can obtain a higher relative dielectric permittivity due to the largest length/diameter aspect ratio (A. R.). Although the A. R. did make a difference, the variation of permittivity could be slightly influenced by the structure in microwave frequencies. Motivated by the idea that the permittivity of carbon nanotubes (CNTs) composites is mostly related to the volume fraction, a process which can determine the sequence of CNTs density is proposed. The influence of the functional group on CNTs was investigated based on dielectric measurements of CNTs-paraffin nanocomposites. The experimental results denoted that the variation of both ɛ′ and ɛ″ in the coiled CNTs (CCNTs) composites shown less frequency dependence.

Tailoring the carbon nanostructures grown on the surface of Ni–Al bimetallic nanoparticles in the gas phase

A gas-phase, one-step method for producing various aerosol carbon nanostructures is described. The carbon nanostructures can be selectively tailored with either straight, coiled, or sea urchin-like structures by controlling the size of Ni–Al bimetallic nanoparticles and the reaction temperature. The carbon nanostructures were grown using both conventional spray pyrolysis and thermal chemical vapor deposition. Bimetallic nanoparticles with catalytic Ni (guest) and non-catalytic Al (host) matrix were reacted with acetylene and hydrogen gases. At the processing temperature range of 650–800°C, high concentration straight carbon nanotubes (S-CNTs) with a small amount of coiled carbon nanotubes (C-CNTs) can be grown on the surface of seeded bimetallic nanoparticle size <100nm, resulting from consumption of the melting Al matrix sites; sea urchin-like carbon nanotubes (SU-CNTs) of small diameter (∼10±4nm) can be grown on the bimetallic nanoparticle size >100nm, resulting from the significant size reduction of the available Ni sites due to thermal expansion of molten Al matrix sites without consumption of Al matrix. However, at the processing temperature range of 500–650°C, C-CNTs can be grown on the bimetallic nanoparticle size <100nm due to the presence of Al matrix in the bimetallic nanoparticles; SU-CNTs of large diameter (∼60±13nm) can also be grown on the bimetallic nanoparticle size >100nm due to the isolation of Ni sites in the Al matrix.

Catalyst preparation with ball milling for catalytic synthesis of coiled carbon nanotubes

AbstractThe aim of our experiments was the production of helically coiled carbon nanotubes selectively. The influence of catalytic particles prepared by ball milling (dry and wet method) was investigated on the growth of coiled carbon nanotubes under CVD conditions. For qualitative characterization of carbon deposit on the surface, the products were imaged by transmission and scanning electron microscopy (TEM, SEM). The activity of each catalyst sample was characterized by carbon yield.magnified image HRTEM image of helically coiled carbon nanotube.