Tubes Of Double-walled Carbon Nanotubes Research Articles

A discrete-continuum mosaic model for the buckling of inner tubes of double-walled carbon nanotubes under compression

In this paper, the discrete-continuum mosaic (DCM) method is applied for predicting buckling of inner tubes of double-walled carbon nanotubes (DWNTs). The moving least squares (MLS) approximation is used for linking discrete atomic model and the corresponding continuum counterpart. Actual atomic positions are used as interaction points for the interlayer van der Waals (vdW) force of DWNTs, which can accurately capture the discreteness of non-bonded interactions, and a DCM contact model is constructed. A variationally consistent meshless computational scheme based on the DCM contact model is developed for simulating the buckling of inner tubes of DWNTs upon compression. Results show that both the lengths and radii of outer tubes can influence the buckling patterns of the corresponding inner tubes. The inner tubes of DWNTs with the interlayer spacing of 0.2034 nm have strongest buckling resistance for the case that the outer tubes are not extremely short. The local critical axial compression ratio of the inner tube increases with the lengths of the inner and outer tube increasing given that the interlayer spacing of a DWNT is less than 0.34 nm.

(Invited) Intertube Coupling in Double-Walled Carbon Nanotubes Beyond Mechanical Interaction

Double walled carbon nanotubes (DWCNTs) are an intriguing example of a one-dimensional Moiré system, because they differ in diameter and chirality of the inner and outer tubes. For many years, DWCNTs have been described as two weakly coupled single walled carbon nanotubes (SWCNTs) without much electronic interaction. Advances in theoretical modeling, however, predicted diverse coupling possibilities when considering the electronic interactions between twisted layers of low dimensional materials. This coupling can induce the formation flat bands and strongly perturb the electronic states. Experimentally, this should manifest in a reduced bandgap in DWCNTs and a red-shift of the optical transition energies. Chasing this coupling effect, we used resonant Raman spectroscopy to measure the transition energies of semiconducting inner tubes in DWCNTs. The transition energies are indeed reduced, with varying red-shifts for the same inner wall chirality (50 and 150 meV). The shift depends on the electronic type of the host tube that we assign from based on the Radial breathing mode frequencies. The coupling increases from weak to strong by tightening intratube spacing in agreement with theoretical predictions. We discuss our observations in light of joint and localized vibrational and optical excitations in the two tubes making up the DWCNT.

Spectrum of Temperature-Dependent Rotational Frequency of the Rotor in a Thermally Diven Rotary Nanomotor

By fixing of the outer tube of double-walled carbon nanotubes, a thermally driven rotary nanomotor can be obtained one or more carbon atoms at the end of the stator have an obvious inward radial deviation. Due to the asymmetry of the potential field of the stator, a collision between two tubes leads to the axial component of angular momentum that drives the rotation of the rotor. Relative sliding between the two tubes is resisted due to the roughness of the potential field of stators. Hence, the rotational frequency of the rotor has a maximal value in the balanced state. The spectrum of rotational frequency with respect to temperatures from 8 to 2000 K is presented by means of molecular dynamics simulation. The temperature interval is divided into five zones on the basis of the characteristics of the spectrum. In the robust zone, the nanomotor exhibits stationary rotation. In the controllable zone, the rotational frequency of rotor can be adjusted by varying the temperature. In particular, if a rotating r...

Double-walled carbon nanotubes: synthesis, structural characterization, and application

Double walled carbon nanotubes (DWCNTs) are considered an ideal model for studying the coupling interactions between different concentric shells in multi-walled CNTs. Due to their intrinsic coaxial structures they are mechanically, thermally, and structurally more stable than single walled CNTs. Geometrically, owing to the buffer-like function of the outer tubes in DWCNTs, the inner tubes exhibit exciting transport and optical properties that lend them promise in the fabrication of field-effect transistors, stable field emitters, and lithium ion batteries. In addition, by utilizing the outer tube chemistry, DWCNTs can be useful for anchoring semiconducting quantum dots and also as effective multifunctional fillers in producing tough, conductive transparent polymer films. The inner tubes meanwhile preserve their excitonic transitions. This article reviews the synthesis of DWCNTs, their electronic structure, transport, and mechanical properties, and their potential uses.

Purification, separation and extraction of inner tubes from double-walled carbon nanotubes by tailoring density gradient ultracentrifugation using optical probes

We studied the effect of varying sonication and centrifugation parameters on double-walled carbon nanotubes (DWCNT) by measuring optical absorption and photoluminescence (PL) of the samples. We found that by using a low sonication intensity before applying density gradient ultracentrifugation (DGU), only inner tube species with a diameter ⩽0.8nm can be identified in absorption measurements. This is in stark contrast to the result after sonicating at higher intensities, where also bigger inner tubes can be found. Furthermore, by comparing PL properties of samples centrifugated either with or without a gradient medium, we found that applying DGU greatly enhances the PL intensity, whereas centrifugation at even higher speeds but without a gradient medium results in lower intensities. This can be explained by extraction of inner tubes from their host outer tubes in a two-stage process: the different shearing forces from the sonication treatments result in some DWCNT to be opened, whereas others stay uncut. A subsequent application of DGU leads to the extraction of the inner tubes or not if the host nanotube stayed uncut or no gradient medium was used. This work shows a pathway to avoid this phenomenon to unravel the intrinsic PL from inner tubes of DWCNT.

Determination of the inner diameter of a double-walled carbon nanotube from its Raman spectra

In this paper, an exact formula is obtained for the inner diameter of double-walled carbon nanotube (DWCNT) as a function of its higher radial breathing mode (RBM) frequency, using the symbolic package of maple software. Its outer diameter is obtained from the inner diameter formula by considering the constant interlayer spacing between two tubes of DWCNT. For this purpose, DWCNT is considered as double concentric elastic thin cylindrical shells, which are coupled through the van der Waals (vdW) forces between two tubes. Lennard-Jones potential is used to calculate the vdW forces between tubes. The advantage of this analytical approach is that in the double concentric elastic shell model all degrees of freedom in the vibrational analysis of DWCNTs are considered. To demonstrate the accuracy of this work, the relationship between RBM frequency of a single-walled carbon nanotube and its radius is deduced from the DWCNT formula that is well consistent with other publications. To illustrate the application of this approach, the diameters of DWCNTs are obtained from their known RBM frequencies which show an excellent agreement with the available experimental results. Also, the influence of changing the geometrical and mechanical parameters of a DWCNT on its RBM frequencies has been investigated.

Stone–Wales Transformation in Double-Walled Carbon Nanotubes and the Role of Inner Tube

The Stone-Wales (SW) transformations in outer and inner tubes of double-walled carbon nanotubes (DWCNTs) have been studied using density functional theory (DFT)-based Becke’s three parameter hybrid exchange functional and Lee–Yang–Parr correlation functional (B3LYP) method. A comparative analysis of the SW transformation in DWCNT has been made with that in single-walled carbon nanotubes (SWCNTs) of similar chirality. Results reveal that both kinetic and thermodynamic feasibilities of SW transformation in SWCNTs dwindle down with a decrease in the curvature of the tubes. However, the feasibility of the same transformation in DWCNT initially increases and then decreases with a reduction in the curvature of the tube. Both π...π interactions between the two concentric tubes and the intertube distance play a vital role in SW transformation of outer tube of DWCNT. The important findings from this study are as follows: (i) the inner-tube can act as a catalyst in the SW transformation of the outer tube, (ii) the ...

Thermal transport in double-wall carbon nanotubes using heat pulse

Multi-wall carbon nanotubes (MWCNTs) are outstanding materials for diverse applications such as electrodes, interconnects, or thermal management. Deep understanding of the underlying thermal transport mechanism in MWCNTs is crucial to engineer their thermal properties for a specific application. This paper investigates the interfacial thermal interaction in double-wall carbon nanotubes (DWCNTs) using molecular dynamics simulation and compares the transport in DWCNT with that in single-wall carbon nanotubes (SWCNTs). The present study is based on the application of intense heat pulse in the middle of the CNTs and analysis of wavelike responses of energy propagation as well as the kinetic energy corresponding to the velocity components in the radial, tangential, and longitudinal directions of CNTs. The analysis shows that the leading wave packets corresponding to the tangential and longitudinal components propagate ballistically along the tube, while the radial components show diffusive behavior with slow propagation speed. However, the radial components can efficiently transfer energy between tubes of DWCNTs while the fast moving longitudinal components and tangential components are weak in the interfacial energy transfer. An appropriate understanding of the energy exchange between different layers of tubes will pave the path of the future design of MWCNT based pellets and composites.

Probing Charge Transfer between Shells of Double‐Walled Carbon Nanotubes Sorted by Outer‐Wall Electronic Type

Double-walled carbon nanotubes (DWCNTs) with outer metallic (M) or semiconducting (S) shells were sorted by density-gradient ultracentrifugation and examined by Raman spectroscopy and in situ Raman spectroelectrochemistry. The combination of sorting and the selection of appropriate laser excitation energies allowed the disentanglement of the effects of different variations of the electronic type (M or S) of the inner and outer tubes in DWCNTs on the doping behavior and charge transfer between the inner and outer walls. Charge transfer from the outer tube to the inner tube occurs only if the electronic states of the outer tube are filled with electrons or holes, and if these filled states are higher in energy than those of the inner tube. Therefore, each combination of inner and outer tube (i.e., inner@outer: M@M, M@S, S@M, and S@S) exhibits a distinct behavior. The potential needed to observe the effects of charge transfer between the inner and outer tubes is found to increase in the following order: M@M < S@M < M@S < S@S.

Raman and Fluorescence Spectroscopic Studies of a DNA-Dispersed Double-Walled Carbon Nanotube Solution

We performed resonant Raman/fluorescence spectroscopic studies on double-walled carbon nanotubes (DWNTs) that were dispersed in an aqueous single stranded DNA solution. The luminescence signals from the inner tubes of DWNTs are intensified in the isolated state of each individual DWNT. The completely depressed radial breathing modes (RBMs) associated with the outer tubes (whether semiconducting or metallic) via the mechanical wrapping and the strong charge transfer between DNA and the outer tubes support our interpretation that the bright luminescence and sharp absorption spectra come from only the inner tubes, and not from isolated SWNTs. The circumferentially wrapped DNA on the outer tubes of individually isolated DWNTs in an aqueous solution gives rise to strong charge transfer to the semiconducting and metallic outer tubes as well as to generating physical strain in the outer tubes.

Bright Photoluminescence from the Inner Tubes of “Peapod”‐Derived Double‐Walled Carbon Nanotubes

The first observation of bright photoluminescence (PL) corresponding to the inner tubes of double-walled carbon nanotubes (DWNTs) prepared by thermal treatment of fullerene-encapsulated nanotubes at temperatures of 1700–2000°C is reported (see image). The results suggest that DWNTs could replace single-walled NTs in biomarker and optoelectronics applications due to their strong and stable luminescence properties.

Optical studies of the inner tubes in double-walled carbon nanotubes

Optical studies of the inner tubes in double-walled carbon nanotubes

High Pressure Raman Spectroscopy in Carbon Nanotubes

This work focuses on the high pressure Raman study of carbon nanostuctures comprising of singleor double-wall carbon nanotubes. The detailed examination of the Raman peaks, especially those attributed to the radial breathing modes of the carbon nanotubes, as a function of pressure provides a wealth of information concerning the pressure response of individual nanotubes as well as the internal-external tube (intratube) interactions. The radial breathing modes of both the internal and the external tubes in double-wall carbon nanotubes show reduced pressure slope values as compared to the corresponding in single-wall carbon nanotubes. The reduced slopes for the internal tubes reflect the pressure screening effect inside the external tubes, while those for the external tubes their structural reinforcement due to the encapsulation of smaller diameter tubes in their interior. Moreover, the magnitude of the pressure screening effect depends strongly on the intratube spacing and thus on the intratube interaction. All the experimental observations are well reproduced qualitatively by means of theoretical calculations based on a simple phenomenological model.

Third-order nonlinear optical response in double-walled carbon nanotubes

Resonant behavior and magnitudes of third-order nonlinear optical susceptibilities in double-walled carbon nanotubes (DWNTs) have been investigated by means of femtosecond pump-probe spectroscopy with different pump-photon energies. With the selective excitation of the E 22 exciton transition of the inner tubes labeled by the chiral vector indices (7,5) and (7,6), the imaginary part of nonlinear susceptibility Im χ (3) has shown the resonant enhancement compared with the case of the nonresonant excitation of the specific tube. The nonlinear response signal at the E 22 transition energy of the (8,7) tube has been also enhanced for the excitation of the G-band phonon sideband of its E 22 transition. This result is consistent with the phonon-mediated nonlinear optical process observed for the E 22 transitions in single-walled carbon nanotubes (SWNTs). It has been also found that the values of the figure of merit Im χ (3)/ α ( α: absorption coefficient) of the inner tubes in DWNTs are smaller than those of the corresponding SWNTs, which is interpreted in terms of decay time shortening due to the energy relaxation between the inner and outer tubes.

Structural support of the external tubes in double-wall carbon nanotubes

High-pressure Raman studies of double-wall carbon nanotubes (DWCNTs) and their parent single-wall carbon nanotubes provide experimental evidence of the structural support of carbon nanotubes due to the encapsulation of smaller diameter tubes in their interior. The structural support is manifested by the reduced slope of the radial breathing mode frequency of the external tubes in DWCNTs, which further decreases at higher pressures as the inner–outer tube (intratube) interaction increases.

Exciton energy transfer between the inner and outer tubes in double-walled carbon nanotubes

Exciton energy transfer between the inner and outer tubes in double-walled carbon nanotubes

RamanGband in double-wall carbon nanotubes combiningpdoping and high pressure

We use sulfuric acid as pressure medium to extrapolate the $G$-band position of the inner and outer tubes of double-wall carbon nanotubes. Keeping the $G$-band position of the inner and outer tubes constant, we can determine the fraction of double-wall and single-wall tubes in samples containing a mixture of the two. $A$-band-related electronic interwall interaction at $1560\text{ }{\text{cm}}^{\ensuremath{-}1}$ is observed, which is associated with the outer tube walls. This band is observed to shift with pressure at the same rate as the $G$ band of outer tubes and is not suppressed with chemical doping. Differences in the interwall interaction is discussed for double-wall carbon nanotubes grown by the catalytic chemical-vapor method and double-wall carbon nanotubes obtained through transformation of peapods.

Controlled doping of double walled carbon nanotubes and conducting polymers in a composite: An in situ Raman spectroelectrochemical study

The interaction of double wall carbon nanotubes (DWCNTs) and the conducting polymer poly(3,4-ethylenedioxythiphene)/polystyrenesulfonate (PEDOT/PSS) was studied by in-situ Raman spectroelectrochemistry. The mixing of DWCNTs with PEDOT/PSS caused a partial doping of the outer tube of DWCNTs, which was indicated by the relative change of the Raman intensity of the DWCNTs features. On the other hand, the bands corresponding to inner tubes of DWCNTs and to the polymer were almost untouched by assembling both species into a composite. The in-situ Raman spectroelectrochemical experiments have shown that the changes in electronic structure of inner tubes of DWCNTs embedded in PEDOT/PSS matrix are dependent on the doping level. While at the low doping level of the composite, the Raman features of inner tubes of DWCNTs do not change significantly, at high doping level they reflect the changes caused by the applied electrochemical potential similar to those observed in the polymer-free DWCNTs.

Selective Optical Property Modification of Double-Walled Carbon Nanotubes by Fluorination

We found that by fluorination of double-walled carbon nanotubes (DWNTs), it is possible to suppress only the Raman radial breathing mode and absorption peaks from the outer (large diameter) tubes of DWNTs. In contrast, Raman signals from the inner shells showed no difference from the pristine DWNTs. The stability of the inner shells of fluorinated DWNTs was also confirmed from the photoluminescence (PL) map and the optical absorption spectra, which only showed the signals from the inner shells of DWNTs, with no distinct change in the optical properties of the inner tubes after fluorination. Our results indicate that once fluorinated, there exists only a weak, if not none, interaction between the inner tube and the outer fluorinated tube, proving that fluorination can be used to suppress the optical properties of carbon nanotubes without interfering the properties of inner tubes. The present finding can be important in electronic and sensor applications, keeping the inner tube from having unwanted contact with other substances that may distract from the inner tube's own characteristics.

In Situ Raman Spectroelectrochemistry as a Tool for the Differentiation of Inner Tubes of Double-Wall Carbon Nanotubes and Thin Single-Wall Carbon Nanotubes

In situ Raman spectroelectrochemistry has been used to distinguish between thin single-wall carbon nanotubes (SWCNT) and the inner tubes of double-wall carbon nanotubes (DWCNT). The spectroelectrochemical method is based on the different change of the electronic structure of the inner tube in DWCNT and that of SWCNT during electrochemical charging, which is reflected in the Raman spectra. During electrochemical charging the inner tubes of DWCNT exhibit a delayed attenuation of the intensities of their Raman modes as referred to the behavior of SWCNT of similar diameter. The changes are pronounced for the radial breathing mode (RBM), and thus, these modes are diagnostic for the distinction of inner tubes of DWCNT from the thin SWCNT. The different sensitivities of inner and outer tubes to the applied electrochemical charging is a simple analytical tool for differentiation of SWCNT and DWCNT in a mixture. The significance of the proposed method is demonstrated on a commercial DWCNT sample.