Defective Nanotubes Research Articles

Tuning band structure and electronic transport properties of ZrN nanotube – A first-principles investigation

The band structure and electronic transport properties of pristine ZrN nanotube, oxygen, fluorine and niobium substituted ZrN are successfully optimized using density functional theory. The transport properties of ZrN nanotube are studied in terms of band structure, density of states, electron density and transmission spectrum of ZrN nanotube. The band structure reveals that the nanostructures show metallic nature due to orbital overlapping of zirconium and nitrogen atoms. The density of states gives the information of localization of charges in energy intervals. The major contribution in density of states arises from p and d orbitals of zirconium and nitrogen atoms. The electron density is observed more in nitrogen sites for pristine and impurity substituted ZrN nanotube. The electrons near the Fermi level contributes more to the transmission, the impact in the transmission is seen due to substitution impurity and position of the defect in the ZrN nanotube. The results of the present work focus light to tailor ZrN nanotube with enhanced electronic properties in nanoelectronics applications.

Synthesis of carbon nanotubes using Cu-Cr-O as catalyst by chemical vapor deposition

A novel powder catalyst Cu-Cr-O applied to the synthesis of carbon nanotubes (CNTs) was developed, which was prepared via ammonia precipitation method. Techniques of thermo-gravimetric/differential scanning calorimeter (TG-DSC), X-ray diffraction (XRD) as well as scanning electron microscopy (SEM) and transmission electron microscopy (TEM) have been employed to characterize the thermal decomposition procedure, crystal phase and micro structural morphologies of the as-synthesized materials, respectively. The results show that carbon nanotubes are successfully synthesized using Cu-Cr-O as catalyst when the precursors are calcined at 400, 500, 600, and 700 °C. The results indicate that the calcination of the Cu-Cr-O catalyst at 600 °C is an effective method to get MWCNT with few nano-tube defects or amorphous carbons.

First-principles insights on tuning band structure and transport property of GaN nanotube

The band structure and transport properties of GaN nanotube are explored using density functional theory with substitution impurity and defect in GaN nanostructure. The band structure varies with oxygen substitution and defect in the GaN nanotube. The density of states spectrum provides the insight for the localization of charges in different energy intervals. The electron density is found to be more in nitrogen site than in gallium site across GaN nanotube. The substitution impurity has the influence over electron density along GaN nanotube. The transport properties are discussed in terms of transmission spectrum. The orbital delocalization gives rise to peak maximum in different energy intervals. The substitution effect of oxygen and defect in the structure has much impact in the transmission along the valence band and conduction band. The finding of present work gives the insight to tailor the band structure and enhance the transport property of GaN nanotube with substitution impurity and defect structure.

Invited: In Situ Characterization of Plasma Assisted Hydrogenation/Fluorination of Graphene and CFx Battery Applications

Monolayer graphene synthesized by chemical vapor deposition was subjected to controlled and sequential hydrogenation using RF plasma while monitoring its electrical properties in-situ. Low temperature transport properties, viz., electrical resistance (R), thermopower (S), Hall mobility (m), and magneto-resistance (MR) were measured for each sample and correlated with ex-situ Raman scattering and X-ray photoemission (XPS) characteristics. For weak-hydrogenation, the transport is seen to be governed by electron diffusion and low temperature transport properties show metallic behavior (conductance G remains non-zero as 0). For strong-hydrogenation, the transport is found to be describable by variable range hopping (VRH) and the low T conductance shows insulating behavior (0 as 0). Weak localization (WL) behavior is seen with a negative MR for weakly-hydrogenated graphene and this WL effects are seen to diminish as the hydrogenation progresses. A clear transition to strong localization (SL) is evident with the emergence of pronounced negative MR for strongly-hydrogenated graphene. Multi-walled carbon nanotubes synthesized using fluidized bed chemical vapor deposition technique were fluorinated sequentially to prepare a series of CFx battery electrodes. Primary battery performance was tested using CFx as a cathode against Li. Fully fluorinated MWNTs showed capacity exceeding 815 mAh/g while partially fluorinated samples showed systematically lowered capacity with decreasing x (in CFx). However, fully fluorinated MWCNTs showed distinctly low rechargeable capacity compared to the subfluorinated samples when used as an anode against Li. Mildly fluorinated MWNTs show high capacity and better stability during charge/discharge cycles. High concentrations of fluorine seem to affect capacity retention due to the increased defect densities and reduced electronic conduction. These defects of nanotubes will provide additional pathways for lithium ions to diffuse within the core of the fluorinated structure and to access the electrochemically active C-F sites. XRD, XPS, and Raman spectroscopy were utilized to characterize the samples. Finally the electrochemical performance of fluorinated MWNTs was compared with that of Natural Chinese Graphite (NCG).

Buckling Behavior and Atomic Elastic Stiffness in Defective Multi-Walled Carbon Nanotube under Axial Compression

Axial compressive simulations are performed on defective and non-defective multiwalledcarbon nanotubes (MWCNTs) using the molecular dynamics method, and the effectof defects upon the buckling behavior is discussed. In our previous study, changes in atomicstresses in MWCNTs with three layers were evaluated until buckling occurred. That studysuggested that the transition from homogeneous stress distributions to inhomogeneous onesplays an important role in the occurrence of buckling in MWCNTs, though the critical stressesor strains relating to buckling are dependent upon the structure and location of defects. In thepresent study, the atomic elastic stiffness of each atom, Bij , is evaluated to discuss the onsetof local buckling in MWCNTs with five layers. The det(Bij) of all atoms is found to change toa negative value long before buckling occurs, while the second smallest eigenvalues of Bij forsome atoms change to a negative value just prior to buckling. The existence of dense regions ofatoms that have two negative eigenvalues of Bij are found to vary as a function of the defectlocation, and to correspond with onset points of local buckling.

Titanate nanotubes produced from microwave-assisted hydrothermal synthesis: Photocatalytic and structural properties

Titanate nanotubes were successfully synthesized using the microwave-assisted hydrothermal method from commercial TiO2-anatase powder. Several samples were obtained at varying temperatures and time. Powder samples containing titanate nanotube (Na2Ti6O13) single phase were obtained at 130°C for 4h and 150°C for 2h, demonstrating the kinetics dependence of reaction temperature. Through XRD analysis and electron diffraction pattern, the nanotube structures were found to be composed of a short range ordering, thus giving rise to a broad XRD peak profile. The higher time and temperature (150°C for 4h) led to the formation of more organized structures. The nanotubes UV–vis spectra showed a band gap of 3.90eV and a shoulder on the curve which led to another band gap value 3.25eV. The photoluminescence spectrum emission peak presented a significant decrease, indicating the reduction of surface or structural defects of titanate nanotubes due to longer hydrothermal treatment duration. All structural, electronics and morphologics transformation led to an improvement on photocatalytic activities for nanotubes, especially the sample obtained at 150°C for 1h that rate of decolorization is 0.01879min−1, 2.25 times faster than TiO2-anatase (starting phase).

Erratum to: “Aqueous Suspensions of Single Wall Carbon Nanotubes: Degree of Aggregation into Bundles and Optical Properties”

Aqueous suspensions of nanotubes, as well as the structure and optical properties of their aggregates (bundles), are studied by spectroscopy and high-resolution electron microscopy. The structure of nanoparticles is controlled by varying the ultrasonication time during preparation of suspensions. It is found that the defectiveness of nanotubes increases with decreasing bundle size. A correlation is shown to take place between the suspension preparation regime, the structure of nanoparticles, and the relaxation of the photoexcitation energy of their electronic shells. It is found that the efficiency of photoexcitation energy conversion into heat increases with increasing degree of aggregation of nanotubes into bundles.

An improved understanding of the dispersion of multi-walled carbon nanotubes in non-aqueous solvents

The homogeneous and stable dispersion of carbon nanotubes (CNTs) in solvents is often a prerequisite for their use in advanced materials. Dispersion procedures, reagent concentration as well as the interactions among reagent, defective CNTs and near-perfect CNTs will affect the resulting CNT dispersion properties. This study, for the first time, presents a detailed comparison between two different approaches for dispersing CNTs. The results enhance our understanding of the interactions between surfactant, defective CNTs and near-perfect CNTs and thus provide insight into the mechanism of CNT dispersion. Dispersions of “as-produced” short multi-walled carbon nanotubes (MWCNTs) in N,N-dimethylformamide were prepared by two different surfactant (Triton X-100) assisted methods: ultrasonication and ultrasonication followed by centrifugation, decanting the supernatant and redispersing the precipitate. Visual observation and UV–visible spectroscopy results showed that the latter method produce a more stable dispersion with higher MWCNT content compared to dispersions produced by ultrasonication alone. Transmission electron microscopy and Raman spectroscopic investigations revealed that the centrifugation/decanting step removed highly defective nanotubes, amorphous carbon and excess surfactant from the readily re-dispersible near-perfect CNT precipitate. This is contrary to other published findings where the dispersed MWCNTs were found in the supernatant. Thermogravimetric analysis showed that 95 % of Triton X-100 was removed by centrifugation/decanting step, and the remainder of the Triton X-100 molecules is likely randomly adsorbed onto the MWCNT surface. Infrared spectral analysis suggests that the methylene groups of the polyoxyethylene (aliphatic ether) chains of the residual Triton X-100 molecules are interacting with the MWCNTs.

Adsorption and dissociation of nitrous oxide on pristine and defective BeO and ZnO nanotubes: DFT studies

Adsorption of N2O on pristine and oxygen vacancy defect ZnO and BeO nanotubes was studied at the B3LYP and M06-2X levels of theory. It was found that this molecule can be used to repair the oxygen vacancy defects of these tubes. Adsorption energies of the dissociation of N2O on the defective BeO and ZnO nanotubes were calculated to be about 786.2 and 506.1 kJ/mol at the B3LYP level of theory, respectively. Molecular adsorption is barrierless, while the dissociative adsorptions have to overcome a small activation energy.

Study of atomic and molecular oxygen chemisorption on BC3 nanotubes with Stone–Wales defects using density functional theory

Density functional theory calculations are used to study the adsorption of chemical species including oxygen atom and oxygen molecule on the perfect and defective BC3 nanotubes. Stone–Wales topological defects with four different bond rotations have been examined. The adsorption of atomic oxygen is exothermic in all cases, while for the molecular oxygen, some sites showed endothermic adsorption. Comparative studies on the adsorption of these chemical species shows the maintenance of semiconductive behavior of nanotubes, except for one of the systems, the defected nanotube with a circumferential C–C bond rotation. In this system, the adsorption of molecular oxygen generates a half-metallic antiferromagnet. The results obtained in this paper are relevant for chemical sensing and spintronics applications.

Multi-walled Carbon Nanotube Conductivity Enhancement and Band Gap Widening via Rapid Pulsed Thermal Annealing

Herein we report on the transport characteristics of rapid pulsed vacuum-arc thermally annealed, individual and network multi-walled carbon nanotubes. Substantially reduced defect densities (by at least an order of magnitude), measured by micro-Raman spectroscopy, and were achieved by partial reconstruction of the bamboo-type defects during thermal pulsing compared with more traditional single-pulse thermal annealing. Rapid pulsed annealed processed networks and individual multi-walled nanotubes showed a consistent increase in conductivity (of over a factor of five at room temperature), attributed to the reduced number density of resistive axial interfaces and, in the case of network samples, the possible formation of structural bonds between crossed nanotubes. Compared to the highly defective as-grown nanotubes, the pulsed annealed samples exhibited reduced temperature sensitivity in their transport characteristics signifying the dominance of scattering events from structural defects. Transport measurements in the annealed multi-walled nanotubes deviated from linear Ohmic, typically metallic, behavior to an increasingly semiconducting-like behavior attributed to thermally induced axial strains. Rapid pulsed annealed networks had an estimated band gap of 11.26 meV (as-grown; 6.17 meV), and this observed band gap enhancement was inherently more pronounced for individual nanotubes compared with the networks most likely attributed to mechanical pinning effect of the probing electrodes which possibly amplifies the strain induced band gap. In all instances the estimated room temperature band gaps increased by a factor of two. The gating performance of back-gated thin-film transistor structures verified that the observed weak semiconductivity (p-type) inferred from the transport characteristic at room temperature.

Multi-Walled Carbon Nanotubes Synthesized by Methane Pyrolysis: Structure and Magnetic Properties

The structure and magnetic properties of multi-walled carbon nanotubes produced by catalytic pyrolysis of methane have been investigated by means of mutually complementary physical methods. The average sizes and number of carbon layers forming nanotubes, smearing of the density of states near the Fermi level, degeneracy temperature of gas of extrinsic current carriers, concentrations of localized spins and extrinsic two-dimensional current carriers have been determined. The conclusion has been drawn that ferromagnetic nanoparticles are present in the inner regions of nanotubes, including their tubular cavities. The difference in electronic structure near the Fermi level for carbon nanotubes and ordered graphite has been revealed. The possible reason is that the electronic states near zigzag-type sites of ends as well as edges of linear structural defects in nanotubes make greater contribution to the spectrum than that from similar sites of graphite.

Features of radiation impact on nanostructured materials

Features of formation and migration of radiation-induced defects in carbon nanotubes (CNT) and nanostructured materials are examined. The main methods and software tools used for the simulating nanomaterial structure and space factors are described. The results of mathematical simulation are presented.

Dynamics of Topological Defects in Single-Walled Carbon Nanotubes during Catalytic Growth

Nucleation and healing of structural defects in single-walled carbon nanotubes (SWCNTs) studied through reactive molecular dynamics simulations (RMD) and RMD trajectories reveal formation and healing mechanisms of various topological defects on the catalyst surface. A quality percentage of nanotubes is measured by calculating the amount of hexagons per carbon atom relative to the same quantity for a perfect nanotube of the same length. Following this approach, the concentration of defects is estimated for nanotubes grown on catalysts with different sizes and morphologies and for various temperatures and gas-phase densities. From this analysis, we identify specific catalyst morphologies that favor the growth of SWCNTs with low defect concentration. Vacancies, 5–7, and Stone–Wales defects are observed to nucleate distinctly in the tubes depending on the catalyst morphology. We find that a strong interaction between the catalyst surface and the graphitic lattice of the nanotube is absolutely necessary for he...

Carbon monoxide adsorption on carbon atom doped perfect and Stone–Wales defect single-walled boron nitride nanotubes: a DFT investigation

The CO adsorption on the perfect and defective boron nitride nanotubes (BNNTs) was investigated using the density functional theory at the B3LYP/LanL2DZ theoretical level. The 7-layered armchair (5,5) BNNT doping with C atom on B and N sites was selected for the doped BNNT models, in which the ends of the BNNTs were saturated by hydrogen atoms. The structural and electronic properties of BNNTs and their adsorption configurations with CO were obtained. The binding energies of carbon atom doping on BNNT and adsorption energies of CO molecules on BNNTs were also calculated. The adsorption strength of the CO on BNNT was significantly improved by defective and doped structural creation. The CO adsorption on carbon atom doping on the nitrogen site of Stone–Wales defect BNNT displayed the strongest adsorption with a binding energy of −2.46 kJ/mol.

Elucidation of the origin of grown-in defects in carbon nanotubes

The origin of grown-in defects in carbon nanotubes (CNTs) is elucidated by in situ atomic-scale environmental transmission electron microscope (ETEM) observations of the chemical vapor deposition growth of CNTs. Our high-resolution ETEM observations clearly demonstrate that the deformation of nanoparticle catalysts (NPCs) during the growth of CNTs triggers the formation of various defects in CNTs. The small deformation of NPCs at the interface with CNTs gives rise to the formation of bends and disorder of the interlayer spacing in CNTs. The changes in the diameter and number of graphitic layers in CNTs are caused by the large protrusion on and shrink deformations of NPCs. This study provides insightful strategies to control the grown-in defects of CNTs.

Divacancies in carbon nanotubes and their influence on electron scattering

First-principles calculations are applied to study the formation energies of various divacancy defects in armchair and zigzag carbon nanotubes of varying diameter, and the transport properties for the corresponding structures. Our explicit ab initio calculations confirm that the lateral 585 divacancy is the most stable defect in small diameter tubes, with the 555 777 divacancy becoming more stable in armchair tubes larger than (30, 30). Evaluating the electron transmission as a function of diameter and chirality for a range of defects, the strongest scattering is found for the 555 777 divacancy configuration, which is observable in electrical spectroscopy experiments. Finally, validation of an approximation relating contributions from independent scattering sites enables the study of the characteristic localization length in large diameter tubes. Despite the fixed number of channels, localization lengths increase with increasing diameter and can exceed 100 nm for typical defect densities.

The investigation of field emission properties of defective graphene-carbon nanotube composite

To improve the field emission properties of graphene-carbon nanotube composite, a defective model of graphene-carbon nanotube composite has been established in this study, for exploring the field emission properties of this composite, some efforts have been set on calculating binding energy, then energy level, local electron density distributions, Mulliken charge of the defective graphene-carbon nanotube composite have been analysed, work functions and ionisation potentials are calculated by first principles based on density functional theory (DFT) calculations. When the electric field is applied, the numerical value of band gap keeps in a limited scope, local electron density distribution also shows positive changes, Mulliken charge moves regularly and effectively, work functions and ionisation potentials descend significantly, all of these results we obtained show that the defective graphene-carbon nanotube composite can be used as a good candidate for field emission electron sources.

Spectroscopic signatures of topological and diatom-vacancy defects in single-walled carbon nanotubes

The optical properties, including UV-vis spectra and resonance Raman profiles, of pristine and defected single-walled carbon nanotubes (SWCNTs) are computed using state-of-the-art time-dependent density functional theory (TDDFT) as implemented using the Liouville-Lanczos approach to linear-response TDDFT. The CNT defects were of the form of Stone-Wales and diatom-vacancies. Our results are in very good agreement with experimental results where defects were introduced into a part of defect-free CNTs. In particular, we show that the first and second π-π* excitation energies are barely shifted due to the defects and associated with a relatively small reduction in the maxima of the absorption bands. In contrast, the resonance Raman spectra show close to an order of magnitude reduction in intensities, offering a means to distinguish between pristine and defected SWCNTs even at low defect concentrations.

Effect of the initial state of carbon nanotubes on their ability to be dispersed in polar solvents upon liquid-phase oxidative treatments

Effect of the structural defectiveness of carbon nanotubes on the influence exerted on these nanotubes by their liquid-phase treatments with oxidizing agents (hydrogen peroxide, concentrated nitric acid, and its mixture with sulfuric acid) was studied. It was found that this factor affects changes in the structure of oxidized carbon nanotubes, their hydrophilicity, high-quality arrays of these tubes, and their ability to form stable dispersions in water, ethanol, isopropanol, and acetone.