Single nanotube Raman spectroscopy

A review is presented on the observation of the resonant Raman spectra from one isolated single wall carbon nanotube, focusing on the important structural information that is provided by single nanotube spectroscopy including the (n, m) determination of the individual tubes. The special sensitivity of the radial breathing mode to the (n, m) determination is emphasized, and the corroboration of this (n, m) assignment by diameter- and chirality-dependent phenomena in other Raman modes, such as the G-band, D-band, and G'-band features is also discussed. The significance of single nanotube spectroscopy for future nanotube research in general is briefly reviewed.     

Liquid crystal behavior of single wall carbon nanotubes

Single wall carbon nanotubes are dispersed in water with the water-soluble polymer polyvinylpyrrolidone and the surfactant sodium dodecylbenzene sulfonate, and then deposited by evaporative deposition onto degeneratively-doped silicon wafer substrates. These deposits were examined by scanning electron microscopy, which revealed highly-ordered arrays of large single wall carbon nanotube bundles. Various solution concentrations were prepared and deposition conditions were varied to determine their affect on the single wall carbon nanotube arrays. These observations were related to existing lyotropic liquid crystal theory and theories explaining the behavior of carbon nanotubes in solution, which allowed for further development and interpretation of the phase diagram which describes the behavior of single wall carbon nanotubes in lyotropic liquid crystal systems, and how competing liquid crystal systems in the same solution directly affect the ordering of the single wall carbon nanotube arrays.     

Modeling of interfacial modification effects on thermal conductivity of carbon nanotube composites

The effect of functionalization of carbon nanotubes on the thermal conductivity of nanocomposites has been studied using a multi-scale modeling approach. These results predict that grafting linear hydrocarbon chains to the surface of a single wall carbon nanotube with covalent chemical bonds should result in a significant increase in the thermal conductivity of these nanocomposites. This is due to the decrease in the interfacial thermal (Kapitza) resistance between the single wall carbon nanotube and the surrounding polymer matrix upon chemical functionalization. The nanocomposites studied here consist of single wall carbon nanotubes in a bulk poly(ethylene vinyl acetate) matrix. The nanotubes are functionalized by end-grafting linear hydrocarbon chains of varying length to the surface of the nanotube. The effect which this functionalization has on the interfacial thermal resistance is studied by molecular dynamics simulation. Interfacial thermal resistance values are calculated for a range of chemical grafting densities and with several chain lengths. These results are subsequently used in an analytical model to predict the resulting effect on the bulk thermal conductivity of the nanocomposite.     

Electrochemical properties of double wall carbon nanotube electrodes

Electrochemical properties of double wall carbon nanotubes (DWNT) were assessed and compared to their single wall (SWNT) counterparts. The double and single wall carbon nanotube materials were characterized by Raman spectroscopy, scanning and transmission electron microscopy and electrochemistry. The electrochemical behavior of DWNT film electrodes was characterized by using cyclic voltammetry of ferricyanide and NADH. It is shown that while both DWNT and SWNT were significantly functionalized with oxygen containing groups, double wall carbon nanotube film electrodes show a fast electron transfer and substantial decrease of overpotential of NADH when compared to the same way treated single wall carbon nanotubes. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Ejection of DNA molecules from carbon nanotubes

Ejection of DNA molecule from carbon nanotubes subjected to torsion is investigated with molecular dynamics simulations. The wall of a carbon nanotube undergoes a collapse and a corresponding propagation of the collapse when a torsion loading applied to the tube is beyond a critical value. The van der Waals force between the encapsulated DNA molecule and the collapsed wall of the nanotube on one hand is a driving force to push the molecule out of the tube, while may also prevent the ejection when the onset of the collapsed wall is in front of the molecule. To ensure a complete DNA ejection, a design of a stopper, a small fixed portion on the carbon nanotube to prevent the collapsed wall from propagating in front of the DNA molecule, is developed. The effects of the environmental temperature, the torsion loading, and the size of the nanotube on the delivering process of the DNA molecule are also examined. Simulation results demonstrate the feasibility of ejection of DNA molecules from carbon nanotubes subjected to torsion and provide guidance on designs of the DNA delivery in biology and medical applications.     

Studies on near infrared optical absorption, Raman scattering, and corresponding thermal properties of single- and double-walled carbon nanotubes for possible cancer targeting and laser-based ablation

We report the photo-thermal properties of single and double wall carbon nanotubes (CNT) dispersed in various solvents with different concentrations when exposed to near infrared nm laser irradiations. All these studies were correlated to the dispersivity of CNT in various solvents. The observed temperature increase of the various nanotube solutions was found to be determined by the concentration of the optically active nanotubes, as determined from their Raman scattering spectra, which are resonant in the spectral range of the laser excitation. Such findings could significantly improve the understanding of the optically active CNT species, their overall laser induced-heating levels, and thus reducing the amount of the CNT required for bio-medical photothermal applications to limit the possible undesired cytotoxic effects that occur at high nanotube concentrations. Our studies open up the possibility of using selective species of CNT as effective low-toxic photo thermal agents for cancer targeting and ablation.     

Quantitative assessment of carbon nanotube dispersions by Raman spectroscopy

Aqueous dispersions of single wall carbon nanotubes (C-SWNTs), prepared using different dispersing agents, have been analysed by Raman spectroscopy. Normalising the spectra with respect to the area of the water O-H stretching transition eliminates the effects of photon scattering and absorption on the way through the dispersion, and the dispersions can be assessed quantitatively by comparison of the areas of the carbon nanotube G-band. The normalised G-band areas show linear concentration dependence according to Beer’s law. The influences of different dispersing agents and excitation wavelengths are discussed and the results are compared to the commonly used UV-Visible spectroscopic analysis. The method presented here is semi-quantitative and it is proposed to use the most effective dispersing agent found in this study, sodium dodecylbenzene sulfonate (SDBS), as a benchmark for future dispersion experiments.     

Molecular mechanics simulation of the sliding behavior between nested walls in a multi-walled carbon nanotube

The clarification of the sliding behavior between nested walls in a multi-walled carbon nanotube (MWCNT) is crucial for its applications in nano-electro-mechanical systems. The pull-out processes of some outer walls against other inner walls in MWCNTs are studied by molecular mechanics simulations to investigate this sliding behavior between nested walls. The pull-out force for both double-walled carbon nanotube (DWCNT) and MWCNT with more than two walls is found to be proportional to the diameter of the critical wall (i.e., the immediate outer wall at the sliding surface), and independent of nanotube length and chirality. The underlined mechanism for this phenomenon is systematically explored by investigating the interfacial shear stress during the pull-out and the corresponding surface energy density. The importance and necessity of considering MWCNTs with more than two walls are indicated from their higher surface energy densities than that of DWCNT. Furthermore, the obtained result demonstrates that the conventional definition of the interfacial shear strength is inappropriate for the sliding behavior between nested walls in MWCNTs. Finally, a simple universal theory is proposed for the first time to predict the pull-out force for an arbitrary sliding in a given MWCNT, directly from the diameter of the critical wall.     

Origin of radial breathing mode in multiwall carbon nanotubes synthesized by catalytic chemical vapor deposition

The origin of radial breathing mode (RBM) in the Raman spectra of multiwall carbon nanotubes (MWNCTs) is discussed. In general, RBM is characteristics of single wall carbon nanotube (SWCNT). With the help of transmission electron microscope (TEM) and Raman spectroscopic studies, it is established that the presence of SWCNT in the cavity of MWCNT is responsible for the appearance of RBM in MWCNT (synthesized by low temperature catalytic chemical vapor deposition technique). The estimated diameter of 8.2 Å (from Raman study) of SWCNT is almost same as that observed (∼8.3 Å) in TEM studies.     

High temperature rearrangement of disordered nanoporous carbon at the interface with single wall carbon nanotubes

Composites of nanoporous carbon and single wall carbon nanotubes were heat treated in vacuum at temperatures ranging from 1200 to 2000 °C. The resultant interface between the two allotropes of carbon was characterized using high resolution transmission electron microscopy and Raman spectroscopy. At the interface between the nanoporous carbon and the nanotube, the nanotube served as a template for ordering and orientation of the normally disordered nanoporous carbon along the nanotube axis during high temperature treatment. When annealed at 2000 °C, the nanoporous carbon transformed to graphitic nanoribbon which in turn crushed the nanotube to form a nanoscale carbon “bulb”. This result is interesting since at these temperatures, the native nanoporous carbon is well known to resist ordering and is therefore referred to as being a “non-graphitizing” carbon. That the nanotube should act as a template for the incipient graphitization suggests that bonding and strength for load transfer may be developed at these interfaces.     

Channeling of protons in single-walled carbon nanotubes based on kinetic and molecular-dynamics treatment

A semi-classical kinetic model for the electronic response of a single-walled carbon nanotube (SWCNT) is combined with the Molecular Dynamics (MD) method to simulate propagation of fast protons through the nanotube, with the initial kinetic energies between 1 and 100 keV. Instead of the continuum potential based on the Thomas–Fermi–Moliere model that was used in our previous work, we introduce here a MD simulation with the reactive empirical bond order potential to describe the atomic interaction between the incident ion and the carbon atoms on the nanotube wall by considering the exact carbon atom array near the impact position. The electronic polarization of the nanotube surface is described by the kinetic model in which the electron band structure dependent on the nanotube geometry is embodied. With the use of both the forces from carbon atoms and the dynamic image force due to the electronic polarization, the proton channeling trajectories that result from a sequence of consecutive reflections off the wall are discussed by solving Newton’s equations of motion. We find that, if the incident ion speed is not too high, the ion may be channeled in the SWCNT along helical trajectories that are established after several reflections from the wall.     

Electronic and magnetic properties of deformed and defective single wall carbon nanotubes

The combined effect of radial deformation and defects on the properties of semiconducting single wall carbon nanotubes are studied using density functional theory. A Stone-Thrower-Wales defect, a substitutional nitrogen impurity, and a mono-vacancy at the highest curvature side of a radially strained nanotube are considered. The energies characterizing the deformation and defect formation, the band gap energies, and various bond lengths are calculated. We find that there is magneto-mechanical coupling behavior in the nanotube properties which can be tailored by the degree of radial deformation and the type of defect. The carbon nanotube energetics and magnetism are also explained in terms of electronic structure changes as a function of deformation and types of defects present in the structure.     

Optimization of methane cold wall chemical vapor deposition for the production of single walled carbon nanotubes and devices

Carbon nanotubes are synthesized by cold wall chemical vapor deposition (CVD) using methane as the carbon source and iron thin film catalyst. The yield of thin nanotubes as determined by scanning electron microscopy (SEM) is strongly dependent on the precise CVD process and the preparation of the substrate. The effects of pressure (5–80 kPa), temperature (700–950 °C), substrate conditioning (air preheat) and metallization (Fe, Al, Mo) on thin nanotube yield are reported. High yields of thin nanotubes are obtained under optimum conditions. These thin nanotubes are candidates to be single walled carbon nanotubes (SWNTs) and Raman spectroscopy, photoluminescence spectroscopy and electrical transport provide evidence that, at least at optimum conditions, many, and perhaps all of the thin nanotubes are single walled. Single nanotube field effect transistors are fabricated and factors affecting device yield are reported. Optimum single nanotube device yield does not necessarily coincide with the optimum nanotube yield.     

Electronic transport in composites of graphite oxide with carbon nanotubes

We show that the presence of electrically insulating graphite oxide (GO) within a single wall carbon nanotube (SWCNT) network strongly enhances electrical conductivity, whereas reduced graphite oxide, even though electrically conductive, suppresses electrical conductivity within a composite network with SWCNTs. Measurements of Young’s modulus and of Raman spectra strongly support our interpretation of the “indirect” role of the oxide groups, present in GO within the SWCNT-GO composite, through electronic doping of metallic SWCNTs.     

Effect of high‐shear mixing by twin‐screw extruder on the dispersion and homogeneity of polyacrylonitrile/carbon nanotube composite solution

High‐shear mixing experiments using twin‐screw extruder were conducted to study the effect of shearing on carbon nanotube (CNT) dispersion in polyacrylonitrile (PAN) polymer solution. Different types of CNTs (few‐wall carbon nanotube and single‐wall carbon nanotube) were used to prepare composite solution at 0.5 wt% with respect to the PAN polymer through various preparation conditions. The resulting PAN/CNT composite solution was characterized using various techniques including dynamic light scattering, preparative ultracentrifuge method, optical microscopy, solution rheology, and high‐resolution transmission electron microscopy. With increasing the number of extrusion cycle, it was observed that the CNT bundle size was moderately reduced, while solution homogeneity and macroscopic CNT dispersion was significantly improved. POLYM. COMPOS., 38:719–726, 2017. © 2015 Society of Plastics Engineers     

Femtosecond Dynamics in Single Wall Carbon Nanotube/Poly(3-Hexylthiophene) Composites

Femtosecond transient absorption measurements on single wall carbon nanotube/poly(3-hexylthiophene) composites are used to investigate the relaxation dynamics of this blended material. The influence of the addition of nanotubes in polymer matrix on the ultrashort relaxation dynamics is examined in detail. The introduction of nanotube/polymer heterojunctions enhances the exciton dissociation and quenches the radiative recombination of composites. The relaxation dynamics of these composites are compared with the fullerene derivative-polymer composites with the same matrix. These results provide explanation to the observed photovoltaic performance of two types of composites.     

Single wall carbon nanotube templated oriented crystallization of poly(vinyl alcohol)

Shearing of poly(vinyl alcohol) (PVA)/single wall carbon nanotube (SWNT) dispersions result in the formation of self-assembled oriented PVA/SWNT fibers or ribbons, while PVA solution results in the formation of unoriented fibers. Diameter/width and length of these self-assembled fibers was 5-45 μm and 0.5-3 mm, respectively. High-resolution transmission electron micrographs showed well resolved PVA (200) lattice with molecules oriented parallel to the nanotube axis. Nanotube orientation in the self-assembled fibers was also determined from Raman spectroscopy. PVA fibers exhibited about 48% crystallinity, while crystallinity in PVA/SWNT fibers was 84% as determined by wide angle X-ray diffraction. PVA and carbon nanotubes were at an angle of 25-40° to the self-assembled fiber axis. In comparison to PVA, PVA/SWNT samples exhibited significantly enhanced electron beam radiation resistance. This study shows that single wall carbon nanotubes not only nucleate polymer crystallization, but also act as a template for polymer orientation.     

Solutions for Clamped Adhesively Bonded Single Lap Joint With Movement of Support End and Its Application to a Carbon Nanotube Junction in Tension

This article presents analytical solutions for a clamped-clamped adhesively bonded single lap joint with movement of supports and its application to studying the failure mechanism of carbon nanotube junctions in a tensile test. In the analytical model, the interface shear and normal stresses, movement of one support end, geometric nonlinearity, and the contact stresses between two cylinders are considered. Analytical solutions are derived for a clamped-clamped single lap joint with movement of one support end first, and then geometrically nonlinear finite element analysis is conducted to verify the present analytical solutions. An equivalent two-dimensional model is presented for a junction self-assembled by two carbon nanotubes, and the failure mechanism of the carbon nanotube junction is then studied by using the present analytical solutions. Structural performance of single lap joints with movement of support ends as boundary conditions is also investigated.     

Methane cracking on single-wall carbon nanotubes studied by semi-empirical tight binding simulations

The catalytic properties of thermally distorted single wall carbon nanotubes for the methane dissociation reaction have been investigated in the framework of semi-empirical tight-binding molecular dynamics, electronic structure and total energy calculations. It is shown that, if methane molecules and the nanotube are allowed to get closer than the equilibrium physi-sorption distance, the next dissociation reaction step is characterized by a small enthalpy change. Moreover the reactivity hierarchy of the various carbon nanotubes considered is related to the electronic density of states originating from the axial components of the atomic orbitals.     

Production of controlled architectures of aligned carbon nanotubes by an injection chemical vapour deposition method

High purity, aligned multi-wall carbon nanotube films were grown on quartz substrates by injecting a solution of ferrocene in toluene into a suitable reaction furnace. The injection CVD method allows excellent control of the catalyst to carbon ratio. The detailed study presented here demonstrates how such a system can be used to control the nanotube diameter, length, alignment and yield by manipulating the experimental parameters. Primary growth was found to occur via a base growth mechanism, although overgrowths of single wall carbon nanotubes were obtained under certain conditions. Such a method also allows nanotubes of various packing densities to be produced which may be useful for specific applications such as electrodes.