Length Of Single-walled Carbon Nanotubes Research Articles

Chirality-independent characteristic crystal length in carbon nanotube textiles measured by Raman spectroscopy

Raman spectroscopy's D:G ratio is a well-known indicator of graphitic crystallinity in single-wall carbon nanotubes (SWCNTs) with widespread qualitative application to macroscopic CNT assemblies. Here, we show how the D:G ratio yields quantitative characteristic crystal length features that is remarkably independent of SWCNT chirality when purified SWCNTs are in a high density, heavily bundled textile form. Purified, unaligned, SWCNT films of enriched length distributions and controlled chirality responded in ways consistent with power law behaviour, where the D:G ratio is proportional to the fourth power of excitation wavelength, inversely proportional to SWCNT length, and fits to a master curve independent of electronic species concentration. This behaviour, matching the established response of graphite and graphene, unexpectedly persists despite complications from chirality-dependent resonances unique to SWCNTs. We also show that textiles comprising of aligned, long length CNTs defy these simple power laws until defective multiwall CNTs and impurities are removed post-process, and only if sample heating under the Raman laser is minimized. Adjusting the Raman laser beam diameter up to 6 mm, which is well beyond the average CNT length, we propose that the CNT textile's characteristic crystal length is the CNT length or, with point defects, the distance between point defects.

Perturbation of the pulmonary surfactant monolayer by single-walled carbon nanotubes: a molecular dynamics study.

Single-walled carbon nanotubes (SWCNTs) are at present synthesized on a large scale with a variety of applications. The increasing likelihood of exposure to SWCNTs, however, puts human health at a high risk. As the front line of the innate host defense system, the pulmonary surfactant monolayer (PSM) at the air-water interface of the lungs interacts with the inhaled SWCNTs, which in turn inevitably perturb the ultrastructure of the PSM and affect its biophysical functions. Here, using molecular dynamics simulations, we demonstrate how the diameter and length of SWCNTs critically regulate their interactions with the PSM. Compared to their diameters, the inhalation toxicity of SWCNTs was found to be largely affected by their lengths. Short SWCNTs with lengths comparable to the monolayer thickness are found to vertically insert into the PSM with no indication of translocation, possibly leading to accumulation of SWCNTs in the PSM with prolonged retention and increased inflammation potentials. The perturbation also comes from the forming water pores across the PSM. Longer SWCNTs are found to horizontally insert into the PSM during inspiration, and they can be wrapped by the PSM during deep expiration via a tube diameter-dependent self-rotation. The potential toxicity of longer SWCNTs comes from severe lipid depletion and the PSM-rigidifying effect. Our findings could help reveal the inhalation toxicity of SWCNTs, and pave the way for the safe use of SWCNTs as vehicles for pulmonary drug delivery.

Length effects of single-walled carbon nanotubes on pulmonary toxicity after intratracheal instillation in rats.

We aimed to evaluate the effects of the length of single-walled carbon nanotubes (SWCNTs) on pulmonary toxicity in rats. Each rat received a single intratracheal instillation of short (S-) (average length of 0.40 μm) or long (L-) (average length of 2.77 μm) SWCNTs at a dose of 1 mg/kg and was observed for the next 6 months. Neither S- nor L-SWCNTs affected clinical signs, body weight, or autopsy findings. An increase in lung weight was observed after instillation of S- or L-SWCNTs; however, lung weights were slightly higher in the rats that were administered the S-SWCNTs. Distinct differences in bronchoalveolar lavage fluid (BALF) composition were observed between the S- and L-SWCNT-treated rats as early as 7 days after the intratracheal instillations of the SWCNTs. The S-SWCNTs caused persistent lung injury and inflammation during the 6-month observational period. However, the L-SWCNTs induced minimal lung injury and inflammation. Although the S- and L-SWCNTs changed BALF parameters and histopathological features of the lung, the magnitudes of the changes observed after the S-SWCNT treatment were greater than the respective changes observed after the L-SWCNT treatment. These findings indicate that the severity of the pulmonary toxicity caused after intratracheal instillation of SWCNT depends on the length of the SWCNTs. It appears that shorter SWCNTs induce greater pulmonary toxicity than longer SWCNTs do.

Linking growth mode to lengths of single-walled carbon nanotubes

Elucidating the key factors that determine the lengths of single-walled carbon nanotubes (SWCNTs) is of great importance for understanding the origin of chiral selectivity. We use transmission electron microscopy to thoroughly investigate as-grown SWCNTs. The lengths and growth modes of SWCNTs were decided by bright-field imaging. Their respective chiral angles were calculated on the basis of nanobeam diffraction patterns. Systematic investigations reveal that there is no correlation between the SWCNT length and its chiral angle. Instead, it shows that SWCNT lengths depend more on their growth mode, i.e. the link between SWCNT and its seeding catalyst particle. Atomistic computer simulations demonstrate that low carbon fractions in the catalyst lead to so-called tangential growth, with a partial wetting of the metal in the tube, where metal catalyst tends to be deactivated by graphite layer encapsulation and results in short SWCNTs. In contrast, a high carbon concentration inside metal particle favors perpendicular growth modes, where only the tube lip is in contact with the catalyst. Catalysts adopting perpendicular mode could have a longer lifetime, thus catalyze the growth of long SWCNTs. Finally, the carbon concentration related growth mode was applied to interpret diverse SWCNT growth results.

Length separation of single-walled carbon nanotubes and its impact on structural and electrical properties of wafer-level fabricated carbon nanotube–field-effect transistors

For an industrial realization of devices based on single-walled carbon nanotube (SWCNTs) such as field-effect transistors (FETs) it becomes increasingly important to consider technological aspects such as intrinsic device structure, integration process controllability as well as yield. From the perspective of a wafer-level integration technology, the influence of SWCNT length on the performance of short-channel CNT–FETs is demonstrated by means of a statistical and comparative study. Therefore, a methodological development of a length separation process based on size-exclusion chromatography was conducted in order to extract well-separated SWCNT dispersions with narrowed length distribution. It could be shown that short SWCNTs adversely affect integrability and reproducibility, underlined by a 25% decline of the integration yield with respect to long SWCNTs. Furthermore, it turns out that the significant changes in electrical performance are directly linked to a SWCNT chain formation in the transistor channel. In particular, CNT–FETs with long SWCNTs outperform reference and short SWCNTs with respect to hole mobility and subthreshold controllability by up to 300% and up to 140%, respectively. As a whole, this study provides a statistical and comparative analysis towards chain-less CNT–FETs fabricated with a wafer-level technology.

Chiral-index resolved length mapping of carbon nanotubes in solution using electric-field induced differential absorption spectroscopy

The length of single-walled carbon nanotubes (SWCNTs) is an important metric for the integration of SWCNTs into devices and for the performance of SWCNT-based electronic or optoelectronic applications. In this work we propose a rather simple method based on electric-field induced differential absorption spectroscopy to measure the chiral-index-resolved average length of SWCNTs in dispersions. The method takes advantage of the electric-field induced length-dependent dipole moment of nanotubes and has been verified and calibrated by atomic force microscopy. This method not only provides a low cost, in situ approach for length measurements of SWCNTs in dispersion, but due to the sensitivity of the method to the SWCNT chiral index, the chiral index dependent average length of fractions obtained by chromatographic sorting can also be derived. Also, the determination of the chiral-index resolved length distribution seems to be possible using this method.

Sorting centimetre-long single-walled carbon nanotubes.

While several approaches have been developed for sorting metallic (m) or semiconducting (s) single-walled carbon nanotubes (SWCNTs), the length of SWCNTs is limited within a micrometer, which restricts excellent electrical performances of SWCNTs for macro-scale applications. Here, we demonstrate a simple sorting method of centimetre-long aligned m- and s-SWCNTs. Ni particles were selectively and uniformly coated along the 1-cm-long m-SWCNTs by applying positive gate bias during electrochemical deposition with continuous electrolyte injection. To sort s-SWCNTs, the Ni coating was oxidized to form insulator outer for blocking of current flow through inner m-SWCNTs. Sorting of m-SWCNTs were demonstrated by selective etching of s-SWCNTs via oxygen plasma, while the protected m-SWCNTs by Ni coating remained intact. The series of source-drain pairs were patterned along the 1-cm-long sorted SWCNTs, which confirmed high on/off ratio of 104–108 for s-SWCNTs and nearly 1 for m-SWCNTs.

Effect of CNT length and structural density on viscoelasticity of buckypaper: A coarse-grained molecular dynamics study

Carbon nanotube (CNT) buckypapers, having exceptional mechanical and electrical properties, have been reported to demonstrate frequency-invariant and temperature-invariant viscoelastic properties. In an attempt to provide an in-depth insight into the viscoelasticity of buckypapers with (5, 5) single-walled CNTs (SWCNTs), we perform coarse-grained non-equilibrium molecular dynamics simulations to investigate the effects of oscillatory shear strain amplitude, buckypaper's density, and length of individual SWCNTs on the viscoelastic properties. SWCNT buckypapers exhibit linear viscoelasticity over shear strain amplitude from 0.03 to 0.05. Higher density SWCNT buckypapers can result in larger dynamic stiffness and a higher loss factor of up to ∼0.29. In the frequency-independent regime (≤1 GHz), increasing the length of individual SWCNTs causes a very slight decrease of elastic properties and has minor influence on the viscous mode. Thus, this study provides deep insight into the viscoelasticity of (5, 5) SWCNT buckypapers and demonstrates controllability of the excellent energy dissipation potential of buckypapers, and can thus help us design new energy dissipation devices from carbon nanomaterials.

Differential conductance of armchair single-wall carbon nanotubes due to presence of electron–phonon interaction

We have theoretically investigated the first correction to conductance of armchair single wall carbon nanotubes (SWCNTs) with finite length, embedded between two electrodes, due to the presence of electron–transversal phonon interaction. The perturbative scheme has been used with finite length real space nearest neighbors tight binding method. Both radial breathing and tangential modes are investigated separately. It is found that not only the conductance correction crucially depends on source-drain voltage but also it strongly depends on the length and diameter of SWCNT. So, this work opens up opportunities to control the electrical conductance of SWCNT and increases yield of micro or nanodevices based on carbon nanotube.

Mitigation of bactericidal effect of carbon nanotubes by cell entrapment

This study investigated the effects of the alginate and polyvinyl alcohol (PVA) entrapment on the viability of Escherichia coli cells exposed to single wall carbon nanotubes (SWCNTs) with a diameter of 1–2nm. Viability was examined using a galactosidase enzyme assay, LIVE/DEAD BacLight assay, and total ribonucleic acid quantity. Variables studied included SWCNT concentration (5, 10, 20, 50, 100, 200, 500, and 1000μg/ml), SWCNT length (0.5–2μm for short SWCNTs and 5–30μm for long SWCNTs), and initial bacterial concentration (6.5 log10 CFU and 9 log10 CFU per test). Results showed that both alginate and PVA entrapments mitigate the bactericidal effect of SWCNTs. At the highest SWCNT concentration tested (1000μg/ml), the viability of the cells relative to controls (systems with only E. coli, no SWCNTs), was 0–60% for free cells and 60–90% for alginate and PVA entrapped cells. The bactericidal effect depended on SWCNT type and concentration, and bacterial concentration. In general, long SWCNTs (5–30μm) caused significantly greater reductions in the viability of entrapped cells than the short SWCNTs except for the two highest SWCNT concentrations studied, 500 and 1000μg/ml. Microscopy showed that the entrapment matrices prevented SWCNTs from entering the beads. This study shows that bacterial entrapment is effective at limiting the bactericidal effect of SWCNTs.

Angular Emission Properties of Single-Wall Carbon Nanotubes and Individual Covalent Dopant Sites

Controlled low-level covalent functionalization of single-wall carbon nanotubes (SWCNTs) has refocused the attention of the nanophotonics community on the use of SWCNTs as promising building blocks in photonic circuits due to their recently discovered property of room temperature single photon emission.1 Further, these new emitting states introduced through chemically stable oxygen2 and aryl diazonium dopants3 exhibit a significant increase in photoluminescence (PL) quantum yield and sensitivity to their dielectric environment, which enables their use in imaging and sensor applications.4 However, successful integration into waveguide structures and other photonic circuits requires a comprehensive understanding of the angular emission behavior of these dopant sites. One powerful microscopy technique to study the angular emission properties of emitters is Back focal plane (BFP) imaging, which enables to distinguish different radiation channels5, to reveal emitter orientations6 and magnetic light properties7, amongst others. We present a refinement of the covalent doping procedure2,3 to achieve the control of the doping level and type of dopant down to the introduction of individual dopant sites in a short timescale. At the same time this procedure is compatible with protocols for isolating chirality sorted and rather long SWCNTs8, which enables us to study the length dependence of the angular emission as a function of SWCNT length. In contrast, we also investigate the spatially localized emission from individual dopant sites along the SWCNTs to learn in which angles the emission occurs and to be able to design waveguides tailored specifically to the emission properties. Further we show the significant redirection of emission when placing doped SWCNTs on plasmonic gold thin films. Both, the pristine E 11 and the dopant E 11 *emission can launch different propagating surface plasmons along the metal interface. These plasmons can be coupled into propagating light via leakage radiation and observed in the BFP. 1 X. Ma, et. al., Nat. Nanotechnol. 2015, 10, 671. 2 S. Ghosh, et al., Science, 2010, 330, 1656. 3 Y. Piao, et al., Nat. Chem., 2013, 5, 840. 4 H. Kwon, et. al., J. Phys. Chem. C 2015, 119, 3733. 5 N. F. Hartmann, et. al., ACS Nano 2013, 7, 10257. 6 A. Lieb, et. al., J. Opt. Soc. Am. B 2004, 21, 1210. 7 T. H. Taminiau et. al., Nat. Commun. 2012, 3, 979. 8 N. F. Hartmann, et. al., Nanoscale 2015, 7, 20521.

Highly individual SWCNTs for high performance thin film electronics

We report a continuous floating catalyst chemical vapor deposition synthesis of highly individual single-walled carbon nanotubes (SWCNT) for high performance transparent conducting films (TCF). Active feedback dilution of ferrocene-based catalyst vapor leads to an almost complete elimination of SWCNT bundling and a substantial increase in SWCNT lengths via the suppression of bundling-induced growth termination. The fabricated uniform TCFs exhibit sheet resistances of 89 Ω/sq. at 90% transmittance. This was further improved by micro-patterning, resulting in a sheet resistance of 69 Ω/sq. at 97% transmittance – the highest reported for any carbon nanotube TCF – and highly competitive with commercial indium-tin-oxide-TCFs. Furthermore, we demonstrate that thin film transistors fabricated from these highly individual SWCNTs reach charge carrier mobilities up to 100 cm2 V−1s−1 and ON/OFF-ratios up to 106.

Length dependent performance of single-wall carbon nanotube thin film transistors

The effects of the length of single-wall carbon nanotubes (SWCNTs) on their thin film transistors (TFTs) were investigated by using SWCNTs sorted in length using size exclusion chromatography. Higher device performances were obtained in longer SWCNTs and it was found that the average length of the SWCNTs is an important factor to determine the device performance. Detailed analyses, in which the SWCNT density was normalized using percolation threshold, confirmed that the dependence of on-current on the normalized density approximately follows percolation theory, independently of the SWCNT length. On the other hand, the behaviors of off-current and on/off ratio showed the considerably different dependence among SWCNT lengths.

Role of surfactant structure in aqueous dispersions of carbon nanotubes

Gemini surfactants typically consist of two single-chain surfactant schemically connected by a spacer chain. Recently, it has been shown experimentally that they are able to effectively disperse and stabilize carbon nanotubes (CNTs) in aqueous solutions at very low surfactant concentration. To aid elucidate the role of surfactant structure in the CNT dispersion process, we report herein the results of fully atomistic molecular dynamics (MD) simulations of the adsorption and surface self-assembly of a cationic single-chain surfactant, dodecyltrimethyl-ammonium bromide (C12TAB), and its related Gemini surfactant dimethylene-α,β-bis (dodecyldimethylammonium bromide) [12-2-12]Br2, on (5,7), and (10,14) single-walled carbon nanotubes (SWNTs) in aqueous solution at ambient conditions. We find that the morphology of surfactant aggregates on the SWNT is influenced by the surfactant structure. The same number of [12-2-12]Br2 Gemini surfactants adsorbed are able to cover a larger surface area of SWNT and their head-groups are protruded more extensively toward the aqueous phase, preventing water molecules from accessing the nanotube surface. These morphological results propose that [12-2-12]Br2 should be more effective than C12TAB at stabilizing aqueous dispersions of carbon nanotubes. Furthermore, the influence of SWNT diameter and length of the Gemini surfactant spacer on the structure of aggregates formed onto nanotubes are investigated. These simulation results advance our understanding of the mechanism of CNT solubilization via Gemini surfactants.

Vibration analysis of initially curved single walled carbon nanotube with vacancy defect for ultrahigh frequency nanoresonators

Single walled carbon nanotubes (SWCNTs) are ideal choices for resonators due to its ultrahigh natural frequency. Fundamental frequency of resonators significantly affects their functionality and performance; therefore, an accurate prediction of SWCNTs' natural frequency is vital for designing and developing such devices. In reality, CNTs are not straight and perfect; indeed, they have some degree of vacancy defect and waviness, which occurs during growth and manipulation processes. This research investigates for the first time the combination effects of both initial curvature and vacancy defects on vibrational behaviour of SWCNTs in order to make the simulation closer to the "real world". In this study, an efficient method based on the molecular dynamics model and the finite element method is used to simulate wavy SWCNTs with vacancy defects. Zigzag carbon nanotube with chirality indices (5, 0) is considered. Accuracy of our modelling method is verified by comparing our results with the results obtained from previous studies in simulating ideal SWCNT natural frequency. The effects of vacancy, vacancy location, curvature and aspect ratio on natural vibration of the defected wavy SWCNTs have been investigated, and a parameter of critical waviness ratio has been defined for the first time to emphasize the combination effect of vacancies and waviness on the natural frequency of SWCNTs. Our results show that critical waviness is sensitive to the aspect ratio and indicate that by increasing the length of SWCNTs, the critical waviness ratio increases.

Chirality analysis of horizontally aligned single-walled carbon nanotubes: decoupling populations and lengths

Populations and lengths of single-walled carbon nanotubes with different chiralities (n,m) were evaluated by Raman mapping together with scanning electron microscopy.

The effect of single-walled carbon nanotubes on Escherichia coli: multiple indicators of viability

The impact of single-walled carbon nanotubes (SWCNTs) on Escherichia coli ATCC 8739 was investigated using four indicators of viability: enzyme activity, membrane integrity, plate count, and total RNA. The study examined the effects of SWCNT concentration (5, 10, 20, 50, 100, 200, 500, and 1,000 μg/ml), SWCNT length (0.5–2 and 5–30 μm), and bacterial density (6.5 log10 CFU and 9 log10 CFU per treatment) on E. coli ATCC 8739 viability. Results show that anti-bacterial activity is dependent on both the length and concentration of SWCNTs. Long SWCNTs (5–30 µm) were more toxic for E. coli than short SWCNTs (0.5–2 µm). The susceptibility of E. coli to SWCNTs was dependent on the initial density of cells in the treatment, with cells at the higher density being more resistant. Estimates of viability reductions were generally similar for the four assays examined; however, the beta galactosidase and LIVE/DEAD assays were more conservative than the plate count as indicators of viability reductions.

Forced Transverse Vibration of a Closed Double Single-Walled Carbon Nanotube System Containing a Fluid with Effect of Compressive Axial Load

Based on the Rayleigh beam theory, the forced transverse vibrations of a closed double single-walled carbon nanotube (SWCNT) system containing a fluid with a Pasternak layer in-between are investigated. It is assumed that the two single-walled carbon nanotubes of the system are continuously joined by a Pasternak layer and both sides of SWCNTs containing a fluid are closed. The dynamic responses of the system caused by arbitrarily distributed continuous loads are obtained. The effect of compressive axial load on the forced vibrations of the double single-walled carbon nanotube system is discussed for one case of particular excitation loading. The properties of the forced transverse vibrations of the system are found to be significantly dependent on the compressive axial load. The steady-state vibration amplitudes of the SWCNT decrease with increasing of length of SWCNT. Vibrations caused by the harmonic exciting forces are discussed, and conditions of resonance and dynamic vibration absorption are formulated. The SWCNT-type dynamic absorber is a new concept of a dynamic vibration absorber (DVA), which can be applied to suppress excessive vibrations of corresponding SWCNT systems.

Controlled functionalisation of single-walled carbon nanotube network electrodes for the enhanced voltammetric detection of dopamine

Voltammetric studies of dopamine (DA) oxidation on pristine and acid-treated single-walled carbon nanotube (SWNT) network electrodes were undertaken in order to investigate both the effect of network density and acid treatment times on the voltammetric characteristics for DA oxidation and the susceptibility of the electrodes to fouling. Through careful control of catalysed chemical vapour deposition growth parameters, multiply interconnected and randomly oriented SWNT networks of two significantly different densities were grown (high density, HD, coverage ≫10 μm length of SWNT per μm(-2) and low density, LD, coverage = 5 (±1) μmSWNTμm(-2)). Acid treatment was performed to provide materials with different electrochemical properties and SWNT coverage, as determined by field emission-scanning electron microscopy, atomic force microscopy and micro-Raman spectroscopy. A high concentration of DA (100 μM) was deliberately employed to accelerate the fouling phenomenon associated with DA oxidation in order to evaluate the lifetime of the electrodes. HD pristine SWNT networks were found to promote more facile electron transfer (ET) and were less susceptible to blocking, compared to LD pristine SWNT networks. Acid treatment resulted in both a further enhancement of the ET rate and a reduction in susceptibility towards electrode fouling. However, lengthy acid treatment detrimentally affected ET, due to a decrease in network density and significant damage to the SWNT network structure. These studies highlight the subtle interplay between SWNT coverage and degree of acid functionalisation when seeking to achieve the optimal SWNT electrode for the voltammetric detection of DA.

Molecular dynamics study on heat transport from single-walled carbon nanotubes to Si substrate

Abstract In this paper, non-equilibrium molecular dynamics simulations were performed to investigate the heat transport between a vertically aligned single-walled carbon nanotube (SWNT) and Si substrate, to find out the influence of temperature and system sizes, including diameter and length of SWNT and measurements of substrate. Results revealed that high temperature hindered heat transport in SWNT itself but was a beneficial stimulus for heat transport at interface of SWNT and Si. Furthermore, the system sizes strongly affected the peaks in vibrational density of states of Si, which led to interfacial thermal conductance dependent on system sizes.