Properties Of Double-walled Carbon Nanotubes Research Articles

Study on electrochemical effects of carbon nanotube material defects

The study and implementation of clean, efficient, and long-lasting forms of new energy are currently the focal point of scientific inquiry all over the globe. Carbon nanotubes are excellent hydrogen storage materials, catalyst carriers, and electronic device components due to their outstanding electrochemical properties and near-ideal one-dimensional nanospace. The periodic structure of the crystal and the surrounding charge distribution can be effectively altered by constructing defects in electrode materials or electrocatalysts, as has been demonstrated in a large number of recent studies. This paper provides a summary of the interaction of carbon-carbon double bonds, an analysis of the electrochemical properties of single-wall carbon nanotubes with various chiral graphene defects, and an investigation of the electrochemical properties of double-walled carbon nanotubes with blade dislocation, spiral dislocation, and their composite structures, all based on molecular dynamics simulation.

Enhanced mechanical properties of double-walled carbon nanotubes reinforced silica aerogels: An all-atom simulation study

To enhance the mechanical properties of highly porous low strength and stiffness silica aerogel, we proposed double-walled carbon nanotubes (DWCNTs) of different length to diameter ratios as reinforcement material for the silica aerogel matrix using molecular dynamics (MD) simulations. It is found that a small amount of DWCNTs (2.06%) in the silica aerogel resulted in a significant improvement in the tensile strength and elastic modulus, which is mainly due to random distribution of strong and stiff DWCNT fibers. Moreover, the elastic modulus values of nanocomposites increase quadratically with respect to the weight percentage (wt %) of DWCNT fibers. Furthermore, in compression simulations, as the wt % of DWCNT fibers increases, the initial stiffness also increases, and early densification occurs. The presented work helps to design a new composite material for a specific application.

Temperature-related study on buckling properties of double-walled carbon nanotubes

In this paper, the influence of finite temperature on the axial buckling of double walled carbon nanotubes (DWCNTs) is investigated based on the non-local Timoshenko beam model. The double walled carbon nanotube with different nonlocal effects is considered as an elastic structure model of mechanics, which is composed of the Van der Waals' force between the two-layers/two walls of carbon nanotubes. Molecular structure mechanics model incorporating thermal temperature is developed to study the relation between Young's modulus and temperature. The temperature dependent Young's modulus is applied to study the mechanical property of double walled carbon nanotubes. It is found that the axial buckling properties of DWCNTs decrease with the increase of the finite temperature at high temperature, however, the axial buckling properties of DWCNTs increase with the increase of the finite temperature at low or room temperature. Moreover, it is noted that the continuous temperature has litter effect on the axial buckling property of DWCNTs at the low temperature. However, the influence of continuous temperature on the mechanical properties of DWCNTs can not be neglected at the high temperature.

Transport and mechanical properties of double-walled carbon nanotubes as a function of interwall distance

ABSTRACTWe present an accurate theoretical technique to investigate electronic, electrical, mechanical and optical characteristic of metal@semiconductor ((4,0)@(8,0)) and metal@metal ((6,0)@(12,0)) double-walled carbon nanotubes. The simulation was conducted in the framework of a combination of DFT and Non-Equilibrium Green's Function (NEGF). The outputs reinforced that by decreasing interwall distance the π-conjugate delocalized electrons movement and the transmission characteristics of these sort of nanotubes are affected. Moreover, the obtained results showed the stability of double-walled CNTs with small interlayer distance due to the compatibility of the rotational symmetry of inner and outer tubes. Nevertheless, the electrical conductivity of (4,0)@(8,0)DWCNTs is extraordinary less than (6,0)@(12,0) DWCNTs and those of their internal and external SWCNTs separately. However, Young's modulus of DWCNTs (4,0)@(8,0) remained in Tetra Pascal range.

Structural Properties of Double-Walled Carbon Nanotubes Driven by Mechanical Interlayer Coupling.

Structural identification of double-walled carbon nanotubes (DWNTs) is presented through a robust procedure based on the latest generation of transmission electron microscope, making possible a statistical analysis based on numerous nano-objects. This approach reveals that inner and outer tubes of DWNTs are not randomly oriented, suggesting the existence of a mechanical coupling between the two concentric walls. With the support of atomic-scale modeling, we attribute it to the presence of incommensurate domains whose structures depend on the diameters and helicities of both tubes and where inner tubes try to achieve a local stacking orientation to reduce strain effects.

Intrinsic phonon properties of double-walled carbon nanotubes**Invited talk at 8th International Workshop on Advanced Materials Science and Nanotechnology (IWAMSN2016), 8–12 November 2016, Ha Long City, Vietnam.

Double-walled carbon nanotubes (DWNT) are made of two concentric and weakly van der Waals coupled single-walled carbon nanotubes (SWNT). DWNTs are the simplest systems for studying the mechanical and electronic interactions between concentric carbon layers. In this paper we review recent results concerning the intrinsic features of phonons of DWNTs obtained from Raman experiments performed on index-identified DWNTs. The effect of the interlayer distance on the strength of the mechanical and electronic coupling between the layers, and thus on the frequencies of the Raman-active modes, namely the radial breathing-like modes (RBLMs) and G-modes, are evidenced and discussed.

Transport properties of double-walled carbon nanotubes and carbon boronitride heteronanotubes

Using the density functional theory combined with the nonequilibrium Green's function, the transport properties of double-walled carbon nanotubes (DWCNTs) and carbon boronitride (CBN) heteronanotubes were investigated. As the hopping length increases, the conductance of DWCNTs shows a dramatic variation that is independent of the intertube space. The transport of the CBN heterojunctions also displays abnormal behavior when the hopping length is changed, which is very different from the behavior of DWCNTs. The currents of the forward in the CBN heterojunctions are about 3–15 times as large as those of the back under lower bias voltages. The negative differential resistance (NDR) effect occurs in the CBN heterojunctions, and the peak-to-valley ratio in the additional NDR regions is about 2–4 for the current–voltage relationship. The hopping length and BN parts have a great influence on the transport of the double-walled nanodevices.

Multi-wall effects on the thermal transport properties of nanotube structures

Understanding the role of inter-layer interactions in multi-walled carbon nanotubes is one of the challenges in the design of potential materials because of their large impact on the physical properties of carbon nanotubes. We focused on the thermal properties of double-walled carbon nanotubes (DWCNTs), which are promising materials due to their high durability and thermal efficiency. We investigated the thermal conductance of DWCNTs by using the nonequilibrium Green’s function method, and found that the quadratic temperature dependence of the thermal conductance at low temperatures consisted of three regions with different tendencies. Based on analysis of the transmission coefficients and the distribution of the normal modes, the three nonuniform regions were attributed to the energy shifts of the normal modes at the low-energy region. We examined the mechanism of these energy shifts using the coupled vibration model with the parameters from our simulations, and elucidated the multi-wall effects on the thermal transport properties of the nanotube structures. The effects we found demonstrated the significance of tailoring thermal properties to obtain the desired applications.

Electronic and Quantum Transport Properties of Substitutionally Doped Double-Walled Carbon Nanotubes

A first-principles investigation of the electronic and quantum transport properties of double-walled carbon nanotubes doped with nitrogen and boron atoms is presented. Concentric nanotube sidewalls separated by the typical graphitic van der Waals bond distance are found to strongly interact upon incorporation of doping atoms in the hexagonal networks. The local perturbation caused by the doping atoms extends over both shells due to a hybridization of their electronic states, yielding a reduction of the backscattering efficiency as compared with two independent single-walled nanotubes. A multiscale approach for the study of transport properties of micrometer-long double-walled carbon nanotubes demonstrates that transitions from the ballistic to the localized regime can occur depending on the type of doping and the energy of the charge carrier. These results shed light on the quantum mechanism by which B and N doping represent an efficient method to create mobility gaps in metallic concentric carbon nanotubes.

Synthesis of a DWNTs/PAni composite and its supercapacitive behavior compared to the SWNTs/PAni and MWNTs/PAni composites

Double walled carbon nanotubes (DWNTs) have unique coaxial structures and corresponding physical and chemical properties, making them good candidates for supercapacitor materials. However, there are almost no reports on DWNT based composites for supercapacitor applications. In this study, a DWNTs/PAni composite was synthesized by in situ chemical polymerization of aniline onto DWNTs, and its electrochemical performance as the electrode material in a supercapacitor was studied and compared to single-walled carbon nanotubes (SWNTs)/PAni and multi-walled carbon nanotubes (MWNTs)/PAni composites synthesized by the same method. TEM and SEM observations show that the PAni is uniformly coated on the DWNTs to form DWNTs/PAni bundles with diameters of about 100 nm. Raman characterization further indicates the strong interactions between the DWNT and PAni components in the DWNTs/PAni composite. Electrochemical analyses demonstrate that the DWNTs/PAni composite has not only significantly higher specific capacitance (576 F g−1) but also better cycling stability than the SWNTs/PAni and MWNTs/PAni composites. The excellent electrochemical performance of the DWNTs/PAni composite as the electrode material in a supercapacitor is attributed to the good charge transfer ability between the PAni and DWNT components, the comparatively large specific surface area of the DWNTs/PAni composite and the good stress and load transfer properties of DWNT due to its coaxial structure.

Buckling of double-walled carbon nanotubes under compression and bending: Influence of vacancy defects and effect of high-temperature annealing

We study by molecular dynamics simulations the effect of vacancy defects on mechanical properties of double-walled carbon nanotubes (DWCNTs) under compression and bending. Our results show that the critical buckling strain under compression and critical buckling angle under bending generally decrease with increasing defect density, but the detailed buckling behavior is sensitive to defect distribution patterns (e.g., whether vacancies are on the inner or outer wall, at separate sites or clustered together). Interestingly, upon high-temperature annealing, vacancy defects undergo structural reconstructions and, in particular, form interlayer bonds that significantly improve the load carrying capability of the DWCNTs under compressive and bending deformation. These results provide new insights into the role of vacancy defects in determining the buckling behavior of multi-walled carbon nanotubes (MWCNTs); they also suggest that high-temperature annealing is an effective tool for defect engineering to improve mechanical properties of MWCNTs. The present study reveals trends and underlying mechanisms with regard to the buckling of DWCNTs under different loading conditions, and the obtained results may provide a useful guide for post-synthesis treatment and application of MWCNTs.

Nonlocal effects on thermal buckling properties of double-walled carbon nanotubes

The thermal buckling properties of double-walled carbon nanotubes (DWCNTs) are studied using nonlocal Timoshenko beam model, including the effects of transverse shear deformation and rotary inertia. The DWCNTs are considered as two nanotube shells coupled through the van der Waals interaction between them. The geometric nonlinearity is taken into account, which arises from the mid-plane stretching. Considering the small-scale effects, the governing equilibrium equations are derived and the critical buckling temperatures under uniform temperature rise are obtained. The results show that the critical buckling temperature can be overestimated by the local beam model if the nonlocal effect is overlooked for long nanotubes. In addition, the effect of shear deformation and rotary inertia on the buckling temperature is more obvious for the higher-order modes. The investigation of the thermal buckling properties of DWCNTs may be used as a useful reference for the application and the design of nanostructures in which DWCNTs act as basic elements.

On the influence of van der Waals coefficient on the transverse vibration of double walled carbon nanotubes

The influence of van der Waals interaction coefficient on the vibrational properties of double-walled carbon nanotubes (DWCNTs) is studied. A high order continuum beam model is used, which can be applied to study the transverse vibrations of MWCNTs, including those that could have initial deformations due to defects or external actions. A numerical study was carried out and it was found that the non-coaxial intertube frequencies are strongly influenced by the coefficient used. The importance of this result can be valued considering that the concentric structure of DWCNTs is a crucial geometrical characteristic and a non-coaxial vibration would affect their electronic and optical properties.

Interwall screening and excitons in double-wall carbon nanotubes

Exciton properties of double-wall carbon nanotubes are studied in the static screened Hartree-Fock approximation within a k ·p scheme. The intrawall electron-hole interaction is largely suppressed by interwall screening effects. The suppression is sensitive to the effective interwall distance between the inner and outer tubes and reduces the exciton binding energy as well as the band gap. As a result, the exciton energy levels are redshifted from those in the single-wall tube with the same diameter. The energy shift of the ground exciton has little dependence on the tube diameter, in contrast to that of the excited excitons. In the case of a metallic outer and inner tube, excited exciton states in the semiconducting tube disappear due to strong screening.

Molecular insight into the high selectivity of double-walled carbon nanotubes

Combining experimental knowledge with molecular simulations, we investigated the adsorption and separation properties of double-walled carbon nanotubes (DWNTs) against flue/synthetic gas mixture components (e.g. CO(2), CO, N(2), H(2), O(2), and CH(4)) at 300 K. Except molecular H(2), all studied nonpolar adsorbates assemble into single-file chain structures inside DWNTs at operating pressures below 1 MPa. Molecular wires of adsorbed molecules are stabilized by the strong solid-fluid potential generated from the cylindrical carbon walls. CO(2) assembly is formed at very low operating pressures in comparison to all other studied nonpolar adsorbates. The adsorption lock-and-key mechanism results from perfect fitting of rod-shaped CO(2) molecules into the cylindrical carbon pores. The enthalpy of CO(2) adsorption in DWNTs is very high and reaches 50 kJ mol(-1) at 300 K and low pore concentrations. In contrast, adsorption enthalpy at zero coverage is significantly lower for all other studied nonpolar adsorbates, for instance: 35 kJ mol(-1) for CH(4), and 14 kJ mol(-1) for H(2). Applying the ideal adsorption solution theory, we predicted that the internal pores of DWNTs have unusual ability to differentiate CO(2) molecules from other flue/synthetic gas mixture components (e.g. CO, N(2), H(2), O(2), and CH(4)) at ambient operating conditions. Computed equilibrium selectivity for equimolar CO(2)-X binary mixtures (where X: CO, N(2), H(2), O(2), and CH(4)) is very high at low mixture pressures. With an increase in binary mixture pressure, we predicted a decrease in equilibrium separation factor because of the competitive adsorption of the X binary mixture component. We showed that at 300 K and equimolar mixture pressures up to 1 MPa, the CO(2)-X equilibrium separation factor is higher than 10 for all studied binary mixtures, indicating strong preference for CO(2) adsorption. The overall selective properties of DWNTs seem to be superior, which may be beneficial for potential industrial applications of these novel carbon nanostructures.

Tuning the electrical transport properties of double-walled carbon nanotubes by semiconductor and semi-metal filling

Manipulating the electrical properties of carbon nanotubes through semi-metal or semiconductor filling is of paramount importance in the realization of nano-electronic devices based on one dimensional composite materials. From low temperature electrical conductivity measurements of a network, of empty and filled double-walled carbon nanotubes (DWNT’s), we report a transition in electrical transport features from hopping to weakly activated conduction by HgTe filling and also semi-metallic conduction in selenium (Se) filled DWNT’s. Magneto-resistance (MR) studies of the filled DWNT’s show suppression of the hopping conduction and a signature of 3D weak localization for Se@DWNT’s at low temperatures and high magnetic fields. These results are discussed on the basis of strength of interaction between the filler material and the inner-walls of the host DWNT’s, which enhances the electronic density of states (DOS) in the material as well as the change in the property of the filler material due to constrained encapsulation.

Electronic transport properties of double-wall carbon nanotubes

We studied the discretized electronic spectra of double-wall carbon nanotube (DWCNT) quantum dots (QDs) in the Coulomb-blockade regime. At low temperatures, the stability diagrams show a clear and regular eight-electron periodicity, which is due to the nonzero intershell couplings. Furthermore, the electronic charging energy, the energy level spacing, and the intershell coupling strengths of the measured DWCNT QDs were determined.

Pressure-Induced Collapse in Double-Walled Carbon Nanotubes: Chemical and Mechanical Screening Effects

The vibrational properties of double-walled carbon nanotubes (DWNTs) is investigated by high-pressure resonance Raman scattering up to 30 GPa in two different pressure-transmitting media (PTM): paraffin oil and NaCl. The protection effect on the outer tube during compression is verified .The collapse of DWNTs is experimentally observed for the first time, showing to be two-step: the onset of the outer 1.56 nm diameter tube collapse at ∼21 GPa is followed by the collapse of the inner 0.86 nm diameter tube at a higher pressure of ∼25 GPa. This observation is supported by calculations. We show that filling a tube with another tube leads to a pressure stabilization against collapse, in strong opposition to what is observed when filling a tube with fullerenes or iodine. The collapse pressure in DWNTs appears to follow a 1/dtav3 law, where dtav is the average diameter from the inner and outer tubes, in agreement with predictions [Yang, X.;Appl. Phys. Lett. 2006, 89, 113101]. Contrary to SWNTs and peapods, for DWNTs, the observed collapse pressure is independent of the PTM nature. Those differences are discussed in terms of tube filling homogeneity and of the separate roles of inner and outer tubes: the outer tube offers chemical screening to the inner tube, whereas the inner tube guarantees mechanical support to the outer one. This leads to high collapse pressure independent of the DWNT environnment: a characteristic that makes DWNTs ideal fillers for composite nanomaterials for high load mechanical support.

Electrical Transport Properties of C59N Azafullerene Encapsulated Double-Walled Carbon Nanotube

Electrical transport properties of double-walled carbon nanotubes (DWNTs) are modulated by encapsulating the azafullerene C59N which is synthesized via a plasma ion-irradiation method. The encapsulation of C59N molecules inside DWNTs has been confirmed by both transmission electron microscopy and Raman spectroscopy. The pristine DWNTs with outer diameter 4 - 5 nm are found to exhibit an ambipolar semiconducting behavior due to their small band gap. It is found that C60 fullerene encapsulated DWNTs exhibit a unipolar p-type semiconducting behavior. By comparison, C59N encapsulated DWNTs display an n-type semiconducting behavior. Our findings demonstrate that C59N operates as an electron donor compared with the acceptor behavior of C60, which is further clarified by photoelectron emission spectroscopy.

Covalent Synthesis and Optical Characterization of Double-Walled Carbon Nanotube−Nanocrystal Heterostructures

The unique electronic structure and optical properties of double-walled carbon nanotubes (DWNTs) have made them a key focus material of research in recent years. However, the incorporation of DWNTs with quantum dots (QDs) into nanocomposites via a covalent chemical approach as well as the optical properties of the composites have rarely been explored. In particular, we have been interested in this model system to investigate whether nanomaterial heterostructures can provide efficient pathways for charge separation relative to loss mechanisms such as recombination. In this specific work, the synthesis of DWNT-CdSe QD heterostructures obtained by using a conventional covalent protocol has been demonstrated. CdSe QDs with terminal amino groups have been conjugated onto the surfaces of oxidized DWNTs by the formation of amide bonds. The observed trap emission of CdSe is thought to arise from the presence of 2-aminoethanethiol capping ligands and is effectively quenched upon conjugation with the DWNT surface b...