Diameter Of Single-walled Carbon Nanotubes Research Articles

Chirality-dependent mechanical response of empty and water-filled single-wall carbon nanotubes at high pressure

The mechanical stability of single-wall carbon nanotubes (SWCNTs) at high pressure was studied by high-resolution resonant Raman and wavelength-dependent fluorescence-excitation (PLE) spectroscopy resolving the vibrational and electronic resonances of 18 individual chiralities and furthermore even resolving the different behaviour of empty (closed, pristine) and water-filled (opened) SWCNTs (diameter range = 0.6–1.42 nm). We find that water-filling exerts a stabilizing counter-pressure on the SWCNT walls, leading to an increasing difference between the radial breathing mode frequencies of water-filled and empty SWCNTs at elevated pressures. For small diameter SWCNTs (d < 1 nm) with a chiral angle of ∼12°, in particular for the (7,2) chirality, an anomalous behaviour is observed, revealing an increased mechanical instability for these SWCNTs. We furthermore ascribe the longstanding contradiction between experiments and theory on the collapse pressure of SWCNTs to the presence of filling in most experiments to date, while empty SWCNTs follow the theoretically predicted collapse behaviour.

The origin of nondispersive Raman lines in the D-band region for ferrocene@HiPco SWCNTs transformed at high temperatures

Small diameter single-walled carbon nanotubes can be filled with carbon-rich molecules if the latter are small enough. For HiPco tubes ferrocene turned out to be appropriate. After filling and high temperature treatment (transformation) new Raman lines are observed. Here we show that these lines appear also for small diameter DIPS tubes after similar temperature treatment and that all new lines originate from one special molecule. This molecule has a C=C stretch vibration at 1597 cm observed on top of the G-line components of the tubes. Mass spectra from the transformed tube material revealed compounds with masses of the order of 500–750 Da which are typical for large organic molecules. Experiments with isotope labeled ferrocene showed characteristic changes of the Raman response which extend beyond the consequences of a simple change of atomic masses. DFT calculations using B3LYP functionals revealed that narrow width and short length carbon nanoribbons such as quaterrylene or dimeric PTCDA are possible candidates for the new molecules.

Controlling the Diameter of Single-Walled Carbon Nanotubes by Improving the Dispersion of the Uniform Catalyst Nanoparticles on Substrate.

To have uniform nanoparticles individually dispersed on substrate before single-walled carbon nanotubes (SWNTs) growth at high temperature is the key for controlling the diameter of the SWNTs. In this letter, a facile approach to control the diameter and distribution of the SWNTs by improving the dispersion of the uniform Fe/Mo nanoparticles on silicon wafers with silica layer chemically modified by 1,1,1,3,3,3-hexamethyldisilazane under different conditions is reported. It is found that the dispersion of the catalyst nanoparticles on Si wafer surface can be improved greatly from hydrophilic to hydrophobic, and the diameter and distribution of the SWNTs depend strongly on the dispersion of the catalyst on the substrate surface. Well dispersion of the catalyst results in relatively smaller diameter and narrower distribution of the SWNTs due to the decrease of aggregation and enhancement of dispersion of the catalyst nanoparticles before growth. It is also found that the diameter of the superlong aligned SWNTs is smaller with more narrow distribution than that of random nanotubes.

Resonant Raman Scattering Studies of SWCNT Templated Extreme Nanowires of Hgte and Pbi

By filling the central pore of a single walled carbon nanotube (SWCNT) it is possible to form nanowires of a wide range of inorganic materials that are one unit cell in diameter. These are extreme nanowires, i.e. at the limit of miniaturisation of nanowires. Nanowires of these diameters show extreme quantum confinement effects and in some cases have crystal structures which cannot be stabilised as 3D crystals. Wide ranges of scientifically and technologically interesting materials have already been used to produce such nanowires. These include ferromagnetic materials, e.g. Fe and Co, phase change materials, e.g. GeTe, ferroelectric materials, e.g. SbSeI, and semiconductors, e.g. HgTe. It is likely that extreme nanowires will have entirely new properties, not just modified versions of the properties of the materials from which they are formed. Such properties would be interesting both fundamentally and technologically. However, as yet there has only been very limited characterisation of the properties of nanowires formed inside single walled carbon nanotubes and the fundamental physics is not yet really understood. We will present a comprehensive study of the Raman spectra of the vibrational modes of HgTe extreme nanowires inside single walled carbon nanotubes alongside atomic resolution TEM of the samples. Both TEM and the vibrational spectra clearly indicate that HgTe forms nanowires with an entirely new crystal structure when infiltrated into 1.3-1.4nm diameter SWCNTs. The strength of the Raman scattering is strongly dependent on incoming photon energy, with a strong resonance centred at 1.77eV which tails off more slowly to low energy than to high. Whilst all of the fundamental and combination modes are resonant at the same basic energy, the shape of the resonance varies for different features. It is clear that the form of the resonance has a lot to tell us about the electron-phonon coupling in these 1-Dimensional structures. We will present the dependence of the Raman scattering on excitation and scattered polarisation, which is entirely in line with what would be expected for nanowires. However the temperature dependence of the Raman scattering is anomalous, showing a decrease in scattering intensity by a factor of ten with increasing temperature from 4K to 300K. We will also present results of electrochemically gated Raman scattering from HgTe nanowires which allow us to determine the band alignment of the template tubes and extreme nanowire. In addition to a comprehensive discussion of Raman scattering from HgTe nanowires, we will also present Raman scattering from PbI2 and CoI2 nanowires formed in SWCNTs and prove that the physics demonstrated by the HgTe nanowires is more generally applicable. Figure 1

Gas phase synthesis of non-bundled, small diameter single-walled carbon nanotubes with near-armchair chiralities

We present a floating catalyst synthesis route for individual, i.e., non-bundled, small diameter single-walled carbon nanotubes (SWCNTs) with a narrow chiral angle distribution peaking at high chiralities near the armchair species. An ex situ spark discharge generator was used to form iron particles with geometric number mean diameters of 3–4 nm and fed into a laminar flow chemical vapour deposition reactor for the continuous synthesis of long and high-quality SWCNTs from ambient pressure carbon monoxide. The intensity ratio of G/D peaks in Raman spectra up to 48 and mean tube lengths up to 4 μm were observed. The chiral distributions, as directly determined by electron diffraction in the transmission electron microscope, clustered around the (n,m) indices (7,6), (8,6), (8,7), and (9,6), with up to 70% of tubes having chiral angles over 20°. The mean diameter of SWCNTs was reduced from 1.10 to 1.04 nm by decreasing the growth temperature from 880 to 750 °C, which simultaneously increased the fraction of semiconducting tubes from 67% to 80%. Limiting the nanotube gas phase number concentration to ∼105 cm−3 prevented nanotube bundle formation that is due to collisions induced by Brownian diffusion. Up to 80% of 500 as-deposited tubes observed by atomic force and transmission electron microscopy were individual. Transparent conducting films deposited from these SWCNTs exhibited record low sheet resistances of 63 Ω/□ at 90% transparency for 550 nm light.

Synthesis of Fe&lt;sub&gt;3&lt;/sub&gt;O&lt;sub&gt;4&lt;/sub&gt; Nanoparticles to Synthesize Bundles of Single-Walled Carbon Nanotubes

Magnetite (Fe3O4) nanoparticles were synthesized in aqueous solutions without any surfactants. The Fe3O4 nanoparticles are nearly spherical and have an average diameter of 10.33nm and a narrow size distribution. Bundles of single-walled carbon nanotube (SWCNT) were synthesized using these Fe3O4 nanoparticles supported by MgO. Transmission electron microscopy (TEM) images show that tremendous amount of bundles SWCNT with uniform diameters were produced. The average diameter of bundles SWCNT is 1.22nm. Raman spectrum shows that well graphitized SWCNTs were formed based on the low ratio of ID/IG. Fe3O4 nanoparticles could be an effective active metal to synthesize large quantity bundles of SWCNT.

Experimental and theoretical studies on the electronic properties of praseodymium chloride-filled single-walled carbon nanotubes

Praseodymium chloride (PrCl3) was encapsulated into channels of 1.4 nm diameter single-walled carbon nanotubes (SWCNTs) by a capillary filling method. The high-resolution transmission electron microscopy data demonstrated a high filling factor of the nanotubes and the formation of one-dimensional (1D) PrCl3 nanocrystals. The optical absorption, Raman spectroscopy, and X-ray photoelectron spectroscopy data testified to the filling-induced lowering of the Fermi level of the nanotubes as a result of the electron transfer from the SWCNTs to the embedded PrCl3. The density functional theory modeling showed the absence of local chemical interactions between the nanotubes and the 1D crystals. It was found that the incorporated PrCl3 has stronger influence on the electronic properties of metallic nanotubes than semiconducting SWCNTs.

Synthesis of uniform single-wall carbon nanotubes using Mn12 clusters as the catalyst precursor

Structure-selective synthesis of single-walled carbon nanotubes (SWCNTs) is of critical importance while an elaborative choice of catalysts is one of the feasible strategies toward such a purpose. Consequently, an investigation of how to synthesize uniform single-walled carbon nanotubes (SWCNTs) using Mn12 clusters as the catalyst precursor by means of mist flow chemical vapor deposition (CVD) has been implemented. As a result, according to Raman mapping and calculated diameter distribution, the diameter of as-grown SWCNTs is homogeneously around 1.51±0.31nm even though Mn is rarely used as the catalyst for the synthesis of SWCNTs individually. The promising results may enlighten us with new experimental information for understanding the growth mechanism of SWCNTs, which is beneficial for their controllable synthesis in the future.

Isolation of >1 nm Diameter Single-Wall Carbon Nanotube Species Using Aqueous Two-Phase Extraction.

In this contribution we demonstrate the effective separation of single-wall carbon nanotube (SWCNT) species with diameters larger than 1 nm through multistage aqueous two-phase extraction (ATPE), including isolation at the near-monochiral species level up to at least the diameter range of SWCNTs synthesized by electric arc synthesis (1.3-1.6 nm). We also demonstrate that refined species are readily obtained from both the metallic and semiconducting subpopulations of SWCNTs and that this methodology is effective for multiple SWCNT raw materials. Using these data, we report an empirical function for the necessary surfactant concentrations in the ATPE method for separating different SWCNTs into either the lower or upper phase as a function of SWCNT diameter. This empirical correlation enables predictive separation design and identifies a subset of SWCNTs that behave unusually as compared to other species. These results not only dramatically increase the range of SWCNT diameters to which species selective separation can be achieved but also demonstrate that aqueous two-phase separations can be designed across experimentally accessible ranges of surfactant concentrations to controllably separate SWCNT populations of very small (∼0.62 nm) to very large diameters (>1.7 nm). Together, the results reported here indicate that total separation of all SWCNT species is likely feasible by the ATPE method, especially given future development of multistage automated extraction techniques.

Mist Flow Chemical Vapor Deposition Growth of Thin Single-Wall Carbon Nanotubes Using Fe18 Clusters as the Catalyst Precursor

An investigation about the fabrication of thin single-walled carbon nanotubes (SWCNTs) using Fe 18 clusters as the catalyst precursor by means of mist flow chemical vapor deposition (CVD) has been carried out. The advantage of Fe 18 clusters is the uniform and small particle size. As a result, choosing the acetonitrile (MeCN), the original solvent for preparing Fe 18 clusters, as the carbon source can lead to the mean diameter of as-grown SWCNTs around 0.81 nm and thinner than some published results (zeolite-supported CVD and HiPco). In addition, according to the measured diameter distribution of as-grown SWCNTs, we are aware that thin SWCNTs less than 1.0 nm are dominant within the as-grown products corresponding to photoluminescence (PL) map indicating that mist flow CVD could be another option for the fabrication of thin SWCNTs in a floating CVD system and beneficial for the application of SWCNTs and development of CNT-based semiconducting electronic devices.

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.

Deformation of single-walled carbon nanotubes by interaction with graphene: a first-principles study.

The interaction between single-walled carbon nanotubes (SWNTs) and graphene were studied with first-principles calculations. Both SWNTs and single-layer graphene (SLG) or double-layer graphene (DLG) display more remarkable deformations with the increase of SWNT diameter, which implies a stronger interaction between SWNTs and graphene. Besides, in DLG, deformation of the upper-layer graphene is less than in SLG. Zigzag SWNTs show stronger interactions with SLG than armchair SWNTs, whereas the order is reversed for DLG, which can be interpreted by the mechanical properties of SWNTs and graphene. Density of states and band structures were also studied, and it was found that the interaction between a SWNT and graphene is not strong enough to bring about obvious influence on the electronic structures of SWNTs.

Phonon scattering at SWCNT–SWCNT junctions in branched carbon nanotube networks

In this research article, we analyze phonon scattering in branched single-walled carbon nanotube (SWCNT) networks with SWCNT–SWCNT T- and X- junctions using the wave packet method. Five phonon branches including the longitudinal acoustic, twisting, transverse acoustic, radial breathing, and flexural optical modes are selected to study energy reflection, ramification, and transmission through T- and X-junctions with (6,6) and (4,4) SWCNTs. The results of the simulations indicate that the diameter of SWCNTs affects phonon scattering at carbon nanotube junctions; T-junctions of (6,6) SWCNTs transmit energy more efficiently when compared to T-junctions with (4,4) SWCNTs. In addition, T-junctions of both (6,6) and (4,4) SWCNTs transmit vibrational energy more efficiently when compared to X-junctions in the same phonon frequency range—for example, in the case of the longitudinal acoustic branch, the average energy transmission at T-junctions for low-frequency phonons (lower than 6 THz) was found to be 1.8–2.4 times higher [for the case of (6.6) and (4,4) SWCNTs, respectively] when compared to the X-junctions. It is also observed that energy transmission at the T-junctions shows a dependency on the phonon group velocity with the higher group velocity phonons showing higher energy transmission; however, for the case of the X-junctions, there is little or no correlation observed between the group velocity and energy transmission indicating a complete energy redistribution of the incoming phonons at the junction. Moreover, for the SWCNT–SWCNT branched networks, the energy ramification at the T-junctions was found to be very similar to that at the X-junctions for both (6,6) and (4,4) SWCNTs indicating transverse thermal transport at the X-junctions to be as efficient as the T-junctions.

Water-assisted growth of uniform 100 mm diameter SWCNT arrays.

We report a simple method for growing high-quality single-walled carbon nanotube (SWCNT) arrays on 100 mm wafers via the addition of water vapor to highly purified gases during the CNT growth step. We show that adding a small amount of water during growth helps to create a uniform catalyst distribution and yields high-quality (Raman G/D of 26 ± 3), high-density (up to 6 × 10(11) cm(-2)) and uniform SWCNT arrays on 100 mm large wafers. We rationalize our finding by suggesting that the addition of water decreases catalyst mobility, preventing its coarsening at higher temperatures. We also report a new mechanism of catalyst inactivation in wafer-scale growth using ultrapurified gas sources by the formation of large, 5 ± 3 μm iron particles. We found such formations to be common for substrates with large temperature gradients, such as for wafers processed in a typical cold-wall chemical vapor deposition reactor.

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.

Diameter dependence of the optoelectronic properties of single walled carbon nanotubes determined by ellipsometry

We report ellipsometric measurement on single walled carbon nanotube (SWCNT) films performed in a large spectral range from 0.07 to 4.97eV. The complex dielectric functions of SWCNTs are correlated to their diameter distribution extracted from transmission electron microscopy. Here we show that the transition energies between Van Hove singularities are directly related to the strong one dimensional confinement. In the infrared spectral range, the real part of the dielectric function becomes negative. The electronic properties of SWCNTs are extracted from ellipsometry by using a Drude model. The mobility and the mean free path of charge carriers are limited by the high number of SWCNT contacts. In accordance with tight binding simulation, the conductivity and the charge carrier concentration increase with the SWCNT diameter. Finally, we demonstrate that the π-plasmon energy depends on the charge carrier concentration.

Intraexciton Transitions Observed in High Stability Doped Single-Wall Carbon Nanotube Films and Solutions

Normally hidden excited state transitions were observed in large diameter single-walled carbon nanotubes for the first time by controlling the degree of doping. With increased doping, the normally observed photoinduced bleach (PB) signal associated with the creation of excitons switched to a photoinduced absorption (PA). A delay in the onset of the PA signal made it clear that the absorption was due to an intraexcitonic transition. The study was afforded by the development of novel methods that allowed samples to be reproducibly and stably prepared in specific states. Our results further the understanding of the photophysics of large diameter single-walled carbon nanotube materials, which are promising for a variety of optoelectronic applications.

ChemInform Abstract: State of the Art of Single‐Walled Carbon Nanotube Synthesis on Surfaces

AbstractReview: 187 refs.

Diameter control of single wall carbon nanotubes synthesized using chemical vapor deposition

Lack of control on the chirality or diameter of single-wall carbon nanotubes (SWCNTs) during synthesis is a major impediment in the path of their widespread commercialization. We demonstrate that the humble technique of catalytic chemical vapor deposition of methane, without any sophisticated catalyst preparation, can provide significant control on the diameter of the synthesized SWCNTs. The catalyst used is a solid solution of the bimetals Fe-Mo or Co-Mo in MgO. The radial breathing modes (RBMs) in the Raman spectra of SWCNTs were used to find out the diameters. Kataura plot along with RBMs was used to study the chirality of the tubes. High concentration of the catalysts (Co:Mo:MgO=1:0.5:15 and Fe:Mo:MgO=1:0.5:30) resulted in high yields. However, most of these carbonaceous materials were impurities. Reducing the concentration not only improved the purity and crystallinity (ID/IG ratio ∼0.1), but most importantly reduced the diameter spread of the SWCNTs. Majority of the SWCNTs grown using the low concentration catalysts (Co:Mo:MgO=1:0.5:300 and Fe:Mo:MgO=1:0.5:200) were estimated to have diameters lying between 1.13 and 1.65nm. This narrowing of diameter spread happened for both Fe and Co catalyst systems and depended only on the concentration of the catalyst.

Intrinsic diameter dependent degradation of single-wall carbon nanotubes from ion irradiation

The structural response of single-wall carbon nanotube (SWCNT) thin-films to ion irradiation has been systematically studied with increasing fluence between 5×1012 and 1×1015 (150keV11B+)/cm2 as a function of SWCNT diameter distribution. SEM analysis reveals that the SWCNT morphology remains intact after radiation exposure. The optical absorbance intensity decreases with increasing fluence, and near complete suppression is observed at approximately 2.5×1014(11B+)/cm2, resulting in an equivalent reduction in signal intensity for resonant Raman spectroscopy. Changes observed in the optical response with increasing fluence demonstrate that defective SWCNTs behave similarly to other strongly doped or physically shortened SWCNTs. The Raman D/G′ increases with fluence for all samples, yet the magnitude of increase is strongly dependent on the SWCNT diameter distribution. The diameter dependence stems from differences in the SWCNT mass per unit length, which is incorporated into an inter-vacancy length (Lv) model that describes the radiation-induced changes. Ultimately, all SWCNT data converge to show an equivalent change in D/G′ at a corresponding Lv, even though the fluence required to achieve a particular Lv varies with SWCNT diameter. Thus, the radiation-induced changes in SWCNTs are intrinsically linked to their diameter, representing a fundamental property unique to this class of nanomaterials.