Diameter Of Single-walled Carbon Nanotubes Research Articles

Broadening of van Hove Singularities Measured by Photoemission Spectroscopy of Single- and Mixed-Chirality Single-Walled Carbon Nanotubes

The occupied valence electronic states of single-walled carbon nanotubes (SWCNTs) are responsible for their optoelectronic properties and are unique for each SWCNT chirality. Photoemission spectroscopy (PES) is one of the few methods capable of directly measuring the electron density in the valence states of materials, but there are only a few reports which have observed the valence states of SWCNTs and no examples for single-chirality SWCNTs. Here, we prepare single- and mixed-chirality SWCNT films and characterize their valence states using PES. Chirality-pure SWCNTs were isolated using both gel permeation chromatography and single-stranded DNA-facilitated aqueous two-phase extraction from starting materials consisting of mixed-chirality species. Chirality separation and purity was confirmed with UV-vis-NIR absorption spectroscopy. SWCNT films were prepared for the single-chirality species (10,3), (7,6), (7,3), (6,5), (8,3), (9,1) along with SWCNT chirality mixture of metallic and semiconducting SWCNTs, and as-synthesized mixtures possessing a range of SWCNT diameter. PES using synchrotron radiation was completed for all samples with survey and C 1s core-level spectra obtained to confirm SWCNT coverage, defect level, and purity. Valence band PES was obtained to characterize the valence electronic states and showed significant broadening of the signal, in comparison to calculated density of states, which could not be accounted for by instrument resolution. An inverse diameter dependence of the broadening was observed with greater broadening for smaller-diameter SWCNTs. The broadening is hypothesized to be related to the photohole lifetime, which was found to be significantly longer for wide-diameter SWCNTs. The diameter dependence of the broadening and photohole lifetimes is discussed in terms of both Tomonaga-Luttinger and Landau theories of Fermi liquids.

Single-walled carbon nanotubes–polyaniline composites: Synthesis and field-emission analysis

In this article, we report a facile synthesis and comparative analysis of field emission behavior of polyaniline (PANI)-coated as-received and annealed single-walled carbon nanotube (SWCNT) films by in-situ polymerization and ex-situ synthesis routes, respectively. Amongst all the samples, the sample prepared by in-situ polymerization method with more fraction of annealed SWCNTs in the composite gave an enhanced field emission characteristics with E to = 3 V/μm and β = 1.2 × 104 probably because of good formation of pi-pi non-covalent bonds between the SWCNTs and PANI represented by pi-pi interaction between the quinoid rings of PANI and π bond of the SWCNTs lattice. A significant increase in the threshold field is observed after annealing and doping of nanocomposite films. Field emission behavior of as-prepared nanocomposite samples are also analyzed and discussed with two PANI forms: micro-PANI particles and PANI nanofibers. It is also speculated that PANI may have helped in lowering the overall work function of the composite structure which gave an enhanced field emission. The stability of all the samples are also presented and it is analyzed that nanocomposite sample films synthesized by in-situ polymerization method showed a stability for at least 8 h. The surface morphology analysis by field emission scanning electron microscopy of nanocomposite sample films reveal an increase in SWCNTs diameter upon PANI wrapping. The high-resolution transmission electron microscopy and Raman spectra and X-ray diffraction analysis are also presented.

VQS (Vapor-Quasiliquid-Solid, Vapor-Quasisolid-Solid) Mechanism for Realizing Narrow Distributions of Chirality and Diameters of Single-Walled Carbon Nanotubes (SWCNTs).

Diameter-selective and chiral-selective single-walled carbon nanotubes (SWCNTs), all on a single wafer, have vast technological promise. An investigation has been carried out to study the role of the physicochemical state of the nanoparticle surface, and of the growth parameters and growth mechanism, on the relatively-low-temperature control of SWCNT diameter and chirality. For this, amorphicity, porosity, coarsening, high energy states, etc. resulting from controlled surface disturbance, disorder and/or restructuring of nanoparticle have been considered. Possible relationship between growth rate, chiral angle, diameter, and monodispersity of SWCNTs has been explored. The influence of the nanoparticle's peripheral hill on the diameter selectivity has been examined. Surface segregation and formation of shell have been described. The impact of charge redistribution, creation of contour of charges, and dipole moment in shell in creating chiral-selective SWCNTs has been discussed. The diffusion of the carbon species through the nanopores of the shell via Knudsen dynamics has been elucidated. The role of growth parameters in the growth process has been studied. The fundamental understanding of chiral selectivity and diameter selectivity of SWCNTs has been tried. Possible strategies for realizing narrow diameter and chirality distributions have been presented. The optimized chemical state of nanoparticle surface and the degree of ease and spontaneity, with which SWCNTs are grown on this surface, have been found to govern the chiral-selectivity, diameter-selectivity and high growth rates of SWCNTs. Good agreements of the calculated results with available experiments attest to the validity of the present study.

Tracing chirality, diameter dependence, and temperature-controlling of single-walled carbon nanotube non-covalent functionalization by biologically compatible peptide: insights from molecular dynamics simulations.

Biological applications of single-walled carbon nanotubes (SWCNTs), including drug delivery, require their functionalization with various functional groups such as peptides. Recently, a biologically compatible peptide (named PW3 with the sequence of NH2-Trp-Val-Trp-Val-Trp-Val-Lys-Lys-COOH) has been introduced as a good candidate for modification of carbon nanotubes due to its high affinity toward the exterior surface of these nano-carriers. In order to optimize the process of SWCNT peptide functionalization, the effects of chirality and diameter of SWCNTs as well as the temperature on PW3 adsorption were systematically investigated using molecular dynamics (MD) simulation. It was found that modification of chiral/zigzag SWCNT by PW3 peptide was more suitable compared with the armchair system due to the strong peptide-nanotube interactions and more water solubility at 310K which can be well explained by microscopic structural investigations. Regarding the enhanced peptide-chiral nanotube interactions at the low temperature of 277K, chiral nanotubes can be effective structures for SWCNT functionalization process at reduced temperatures. Our analysis indicated that disrupted PW3 and SWCNT hydration patterns and fewer internal interactions within the peptide could be responsible for the stronger peptide modification of SWCNT at higher temperatures. Additionally, "PW3/SWCNT" systems containing larger tube diameters formed more stable complexes owing to their effective surface area increment.

Thermoelectric properties of single-wall carbon nanotube networks

The Seebeck coefficient S and power factor P of single-wall carbon nanotube (SWCNT) networks were systematically investigated as a function of chemical potential μ, based on theoretical simulations employing non-equilibrium Green’s function theory. The results focused on the gap regions of semiconducting (s-)SWCNTs. The thermoelectric properties of individual SWCNTs were classified into three groups: s-SWCNTs, metallic (m-)SWCNTs, and pseudo-metallic SWCNTs. The maximum values of P for individual s-SWCNTs was independent of SWCNT diameter. In parallel and serial networks of SWCNTs, S and P were found to be very sensitive to the amount of m-SWCNTs, as well as the SWCNT diameter distributions. A comparison with experimental results suggested that an SWCNT bundle can be modeled as a “rope” with an equivalent S calculated for parallel circuits. The presence of SWCNT junctions in the films substantially reduced the P value from those of the composing SWCNTs while S was almost unvaried.

Electron‐Beam Manipulation of Silicon Impurities in Single‐Walled Carbon Nanotubes

AbstractThe recent discovery that impurity atoms in crystals can be manipulated with focused electron irradiation has opened novel perspectives for top‐down atomic engineering. These achievements have been enabled by advances not only in electron optics and microscope stability but also in the preparation of suitable materials with impurity elements incorporated via ion and electron‐beam irradiation or chemical means. Here it is shown that silicon heteroatoms introduced via plasma irradiation into the lattice of single‐walled carbon nanotubes (SWCNTs) can be manipulated using a focused 55–60 keV electron probe aimed at neighboring carbon sites. Moving the silicon atom mainly along the longitudinal axis of large 2.7 nm diameter tubes, more than 90 controlled lattice jumps are recorded and the relevant displacement cross sections are estimated. Molecular dynamics simulations show that even in 2 nm diameter SWCNTs, the threshold energies for out‐of‐plane dynamics are different than in graphene, and depend on the orientation of the silicon‐carbon bond with respect to the electron beam as well as the local bonding of the displaced carbon atom and its neighbors. Atomic‐level engineering of SWCNTs where the electron wave functions are more strictly confined than in 2D materials may enable the fabrication of tunable electronic resonators and other devices.

Diameter dependence of single-walled carbon nanotubes with flavin adenine dinucleotide glucose dehydrogenase for direct electron transfer bioanodes

The diameter dependence of single-walled carbon nanotubes (SWCNTs) with flavin adenine dinucleotide glucose dehydrogenase (FAD-GDH) for direct electron transfer (DET) type bioanodes is presented for the first time. In order to address the issue, we use SWCNTs having different diameters fabricated by direct-injection pyrolytic synthesis, which can control the diameter in a wide range with the other parameters fixed. Three different diameters of SWCNTs are examined: average diameter dm = 1.0, 1.5, and 2.0 nm. In order to achieve DET, a debundled, individual SWCNT has to be placed at the FAD position in the GDH protein pocket. The bioanodes with dm = 1.0 and 1.5 nm SWCNTs show better performance than that with dm = 2.0 nm SWCNTs. The diameter dependence of SWCNTs for bioanode performance is thought to be related to the distance between the SWCNTs and FAD positioned in the reaction center of the GDH protein shell.

(Invited) Separation of Small Diameter Swcnts in 1 – 3 Steps with Aqueous Two-Phase Extraction

An aqueous two-phase extraction (ATPE) technique capable of separating small diameter single walled carbon nanotubes in 1, 2 or at the most 3 steps will be presented. Separation is performed in the well-studied two-phase system containing polyethylene glycol (PEG) and dextran but it is achieved without changing the initial concentration or ratio of co-surfactants. Instead, the technique is reliant upon the unique surfactant shell around each nanotube diameter at a fixed surfactant concentration. The methodology to optimize the surfactant to a single set of conditions for the diameter range (0.69 - 0.91 nm) is provided and 11 different chiralities with a purity of 73 – 97% are isolated. These include semiconducting and both armchair and non-armchair metallic nanotube species. Titration of co-surfactant suspensions reveal separation to be driven by the pH of the suspension with each (n,m) species partitioning over a unique pH range. This allows for an (n,m) separation approach to be presented that is as simple as pipetting known volumes of acid into the ATPE system.

One Dimensional Van Der Waals Heterostructures Wrapped Around Single-Walled Carbon Nanotubes

We have synthesized a new coaxial nanotube structure, in which mono- or few-layer hexagonal boron nitride nanotube (BNNT) seamlessly wrap around a single-walled carbon nanotube (SWCNT), and result in an atomically smooth coaxial tube consisting two different materials, as shown in Fig. 1(a). TEM-EELS clearly demonstrated the BNNT-SWCNT coaxial structure. We have tried various morphologies of SWCNTs as starting material, e.g. vertically aligned array, horizontally aligned array, suspended SWCNTs, and dry-deposited random network films. We can clearly observe the coaxial structure from originally isolated SWCNTs. We found no correlation between chiral angle of inner SWCNT and outer BNNT for ‘double-walled’ SWCNT-BNNT shown in Fig. 1(b). We concluded that these are one-dimensional van der Waals heterostructure. We have further developed the 1D coating CVD for transition metal dichalcogenide nanotubes, such as MoS2 nanotube as shown in Fig. 1 (c). We can grow MoS2 nanotubes around relatively large diameter SWCNT or SWCNT@BNNT [1]. We will discuss properties of the 1D heterostructures though optical absorption, Raman scattering, photoluminescence, FT-IR, and cathode luminance. Reference: [1] Rong Xiang et al., arXiv:1807.06154 (2018). Figure 1

Manufacture of Networks from Large Diameter Single-Walled Carbon Nanotubes of Particular Electrical Character.

We have demonstrated that the aqueous two-phase extraction (ATPE) can differentiate between large diameter single-walled carbon nanotubes (CNTs) by electrical character. Introduction of “hydration modulators” to the ATPE machinery has enabled us to isolate metallic and semiconducting CNTs with ease. We have also shown that often there is a trade-off between the purity of the obtained fractions and the ability to separate both metallic and semiconducting CNTs at the same time. To isolate the separated CNTs from the matrices, we have proposed a method based on precipitation and hydrolysis, which can eliminate the need to use lengthy dialysis routines. In the final step, we prepared thin free-standing films from the sorted material and probed how electrical charge is transported through such macroscopic ensembles.

Systematic investigation of the catalyst composition effects on single-walled carbon nanotubes synthesis in floating-catalyst CVD

Enormous technological promise of single-walled carbon nanotubes (SWCNTs) can only be harnessed with the premise of controllable synthesis of SWCNTs, where catalyst composition thermodynamically plays a vital role. Herein, we have systematically investigated the effects of catalyst composition on SWCNTs synthesis, using a novel floating-catalyst chemical vapor deposition (FCCVD) system, consisting of catalyst synthesis via spark generator, FCCVD reactor and a real-time monitor of catalysts and SWCNTs. We synthesized SWCNTs from both monometallic (Fe, Co, Ni), bimetallic (Co-Ni, Co-Fe) catalyst particles and kinetically optimized yield and performance of SWCNTs films. We found that the highest yield of SWCNTs from Fe is 15 times as that of Ni SWCNTs and the Co-Ni SWCNTs film possesses best opto-electronic performance. Interestingly, the mean diameter of SWCNTs was found related to the catalyst particle size distributions, but not composition. Moreover, detailed atomic structures determination revealed that SWCNTs from Fe and Co have a wide chirality distribution spanning from zig-zag to armchair edges. However, Co-Ni SWCNTs have comparatively narrower chirality distribution having 71% SWCNTs in the chiral angle of 15–30°. Our results indicate that catalyst composition can efficiently tune yield and characteristics of SWCNTs, but it does not dramatically shift chirality of FCCVD SWCNTs.

Unprecedented New Crystalline Forms of SnSe in Narrow to Medium Diameter Carbon Nanotubes.

We report the observation of four unprecedented new crystalline forms of SnSe, obtained as a result of encapsulation in narrow to medium diameter single-walled carbon nanotubes. Aberration-corrected scanning transmission electron microscopy at 80 kV revealed linear, zigzag, helical (i.e., 2 × 1) atomic chains and a new form of encapsulated SnSe. This new form is apparentlyisostructural to free-standing MoS, MoSe, and WSe extreme nanowires etched from the corresponding monolayer dichalcogenidesand also recently observed encapsulated MoTe. A structural model has been attained from annular dark-field (ADF) images. The experimental imaging agrees well with image simulations produced from models anticipated for the new structural forms.

How does acetonitrile modulate single-walled carbon nanotube diameter during CVD growth?

There is a commercial demand for single-walled carbon nanotubes (SWCNTs) with uniform diameters and (n, m) chiralities. However, controlling these structural parameters in practice remains a challenge. Recent studies have shown that acetonitrile reversibly modulates SWCNT diameter during chemical vapour deposition (CVD) growth. Here we propose a mechanism to explain this phenomenon using non-equilibrium quantum chemical molecular dynamics simulations. We reveal that acetonitrile-derived radicals actively abstract hydrogen from surface hydrocarbon species as the SWCNT nucleates. This forms hydrogen (iso)-cyanide as a principal chemical product, and decreases the overall surface carbon density during nucleation. By liberating hydrogen, the number of dangling bonds present at the interface of the nucleating carbon structure is increased, which in turn accelerates SWCNT nucleation kinetics. Critically, the number of pentagon rings formed in the SWCNT precursor cap structure increases. Because the nucleation kinetics are much faster than the kinetics of ring defect healing, the pentagons become ‘trapped’ in the growing SWCNT cap structure, and this leads to more highly-curved SWCNT caps. These more highly-curved caps, combined with the lower surface carbon density and the faster kinetics of nucleation and growth, will ultimately yield narrower-diameter SWCNTs in the presence of acetonitrile.

Confinement Effect of Sub-nanometer Difference on Melting Point of Ice-Nanotubes Measured by Photoluminescence Spectroscopy.

Melting point is independent of size and shape in bulk materials, but it exhibits a size dependence when the material size is extremely small. In this study, we measured the melting point of water confined in single-walled carbon nanotubes (SWCNTs) with 16 different chiralities, which ranged from 0.95 to 1.26 nm in diameter, and revealed the details of the SWCNT diameter dependence on the melting points. The melting points were probed by utilizing the change of photoluminescence (PL) emission wavelength of SWCNTs, which encapsulated water, and the relation between the emission wavelength, and the water phase was confirmed by first-principles calculations. The periodicity of the melting point variation with SWCNT diameter came from the discrete change of ice-nanotube (ice-NT) diameter, and in addition, even ice-NT with an identical diameter exhibited different melting points due to the slight difference of the inner space size of the encapsulating SWCNTs. The present results agreed with those of the molecular dynamics simulation (Takaiwa, D.; et al., Proc. Natl. Acad. Sci. U.S.A. 2008, 105, 39-43). It was elucidated that the melting point of the nanomaterial changed sensitively to the atomic structure and the confinement space size.

Catalyst effect on the preparation of single-walled carbon nanotubes by a modified arc discharge

Single-walled carbon nanotubes (SWCNTs) were prepared by a modified arc discharge furnace using 500 Torr helium as buffer gas at 600 °C. The effect of the catalyst type on the production of SWCNTs was studied by transmission electron microscopy, X-ray diffraction and Raman spectroscopy. The experimental results indicated that the catalyst composition plays an important role in the production rate and purity of the SWCNTs product. Fe-Ni-Mg and Co-Ni powder catalysts demonstrated excellent catalytic effect at a catalyst content of 3 wt%. The soot production rate was up to 15 g/hr and the mean diameter of SWCNTs was about 1.3 nm.

Structural and Thermoelectric Properties of Optically Transparent Thin Films Based on Single-Walled Carbon Nanotubes

Thin films have been produced via a spray method from commercially available single-walled carbon nanotubes (SWCNTs). A SWCNT film thickness has ranged from ~10 to ~80 nm. The SWCNT diameter has accepted values of 1.6–1.8 nm. The existence of SWCNTs longer than 10 μm is established. The optimal thickness of a SWCNT thin film is found to be ~15 nm at which the transmittance exceeds 85%. The specific resistance of SWCNT thin films goes from ~1.5 × 10–3 to ~3 × 10–3 Ohm cm at room temperature. The pioneering study of the temperature dependences of the Seebeck coefficient and surface resistance is performed for this type of SWCNT. A surface resistance is found to increase with rising temperature. Furthermore, the Seebeck coefficient of SWCNT thin films weakly depends on temperature. Its value for all samples is evaluated to be ~40 μV/K. According to the sign of the Seebeck coefficient, thin films exhibit hole-type conductivity. Moreover, the power factor of a 15-nm thin SWCNT-film decreases with a temperature increase to 140◦C from the value of approximately ~120 to ~60 μW m–1 K–2. A further rise in temperature has led to a gain in the power factor.

Carbon and Core Shell like Molecular Nanostructures in Cancer diagnosis and Therapy

During the past years, carbon nanotubes (CNTs) have attracted considerable interest since their first discovery. Great progress has been made in the field of nanomaterials given their great potential in biomedical applications. Carbon nanotubes (CNTs), due to their unique physicochemical properties, have become a popular tool in cancer diagnosis and therapy. They are considered one of the most promising nanomaterials with the capability of both detecting the cancerous cells and delivering drugs or small therapeutic molecules to these cells because of the unique structure, extremely high specific surface area to-volume ratio enable them to use in an intense real time applications such as detection and treatment of cancerous cells, nervous disorders, tissue repair. and excellent electrical and mechanical properties carbon nanotubes composed of excellent mechanical strength, electrical and thermal conductivities makes them a suitable substance toward developing medical devices., CNTs have been explored in almost every single cancer treatment modality, including drug delivery with small nanomolecules, lymphatic targeted chemotherapy, thermal therapy, photodynamic therapy, and gene therapy and demonstrate a great promise in their use in targeted drug delivery systems, diagnostic techniques and in bio-analytical applications. Majority of the biomedical applications of CNTs must be used after successful functionalization for more potential applications than pristine CNTs. There are several approaches to modify pristine CNTs to potentially active. CNTs poised into the human life and exploited in medical context. Here in, we reviewed the following topics (i) Functionalization of CNTs (ii) CNTs in real time applications such as drug delivery, gene therapy, biosensors and bio imaging; (iii) CNTs 3D printed scaffolds for medicine and (iv) Biocompatability and Biodegradability. Single-walled carbon nanotubes (SWCNTs) were synthesized using the high-pressure carbon monoxide disproportionation process (HiPCO). The SWCNT diameter, diameter distribution and yield can be varied depending on the process parameters. The obtained HiPCO product present an iron nanoparticle encapsulated heteronanocarbon (core-shell nanoparticles) at low pressure (1 bar) after removing of iron metal catalyst nanoparticle and amorphous carbon by acid immersion and oxidation. The resulting therapeutic molecule in the form of coreshell nanoparticles and single walled carbon nanotubes after functionalization by filling of iron can be use as therapeutic nanomaterials in nanomedicine in diagnosis and treatment of cancer tumor. This paper describes the synthesis method and role of multifunctional nanoparticle in diagnosis and treatment of cancer. Therefore, the aim of this review is to provide basic information on nanoparticles, describe previously developed methods to functionalize nanoparticles and discuss their potential applications in nanobiomedical and mention the therapeutic nanoparticle large scale production and commercialization challenges. In the final part of the review, emphasis is given on the pharmacokinetic aspects of carbon nanotubes including administration routes, absorption mechanisms, distribution and elimination of carbon nanotubes based systems. Lastly, a comprehensive account about the potential biomedical applications has been given followed by insights into the future carbon nanotubes from synthesis to in vivo biomedical applications.

Polyiodide structures in thin single-walled carbon nanotubes: A large-scale density-functional study

Using automatic structure generation algorithms and large-scale density functional computations we study polyiodide structures encapsulated within a 1 nm diameter single-walled carbon nanotube. The most energetically preferable confined iodine structures are the I3−, I5− and I82− molecular anions and periodic single, double and triple chain systems. The formation energy drops with increasing number of iodine atoms, reaching a minimum for a single iodine chain. Double and triple chains are metastable but have higher formation energies due to spatial confinement within the thin carbon nanotube. The calculated electron transfer from the nanotube to the molecular structures is close to the integer charge values of the molecular anions. The corresponding Fermi energy shift depends on the iodine concentration. For the single, double and triple chains the calculated Fermi shift is ∼0.13, ∼0.23 and ∼0.19 eV below the top of the nanotube valence band, respectively. The computational approaches presented here require minimal a priori knowledge of the system under study, yet are able to predict stable iodine structures observed in experiment.

Selective dispersion of arc-discharged single-walled carbon nanotubes with polymethyl(crylic acidyl)silane

ABSTRACTA water soluble polysilane derivative, polymethyl(crylic acidyl)silane, has been synthesized by the hydrosilylation of crylic acid with polymethylsilane using 2,2′-azobisisbutyronitrile as initiator. After heating in air at a temperature of 673 K and treatment with two-step concentrated acids, arc discharged single-walled carbon nanotubes (SWNTs) are ultrasonically dispersed in the aqueous solution of polymethyl(crylic acidyl)silane, and then subjected to ultracentrifugation to get rid of those insoluble species. Optical absorption spectra show that polymethyl(crylic acidyl)silane has very good dispersing ability toward arc-discharged SWNTs, and metallic SWNTs are preferentially extracted over semiconducting ones in the supernatants. Moreover, Raman spectra evidence that metallic SWNTs with chiral indexes of (15,3) and semiconducting ones with chiral indexes of (12,2) and (11,1) are selectively dispersed in the aqueous solution of polymethyl(crylic acidyl)silane, indicating that polymethyl(crylic acidyl)silane could simultaneously discriminate the metallicity, helical angle, and diameter of SWNTs.

Probing the mechanics of aqueous two-phase extraction using large diameter single-walled carbon nanotubes

We have demonstrated that large diameter (1.8 ± 0.4 nm) carbon nanotubes (CNTs) can be separated by means of the aqueous two-phase extraction (ATPE). This rapid and convenient tool has enabled us to isolate fractions of particular CNT diameter distribution. We have shown how a range of parameters can be used to fine tune the characteristics of the isolated material. Interestingly, by varying the pH of the medium, we have suppressed the extraction of low diameter CNTs and only large diameter CNTs were obtained. A number of other factors such as selected surfactant concentration steps, temperature or amount of starting CNT material have been found to have a significant effect on the end result of the CNT differentiation. The findings have provided us with more insight regarding the underlying mechanics of ATPE for processing polydisperse CNT mixtures.