Number Of Single-walled Carbon Nanotubes Research Articles

Mechanism and Mitigation of Irreversible Material Loss within Gel-Based Single-Walled Carbon Nanotube Purification Schemes

Sephacryl-based separation of single-walled carbon nanotubes (SWCNTs) has afforded the enrichment of samples according to both type (metal/semiconducting) and band structure (chirality). However, Sephacryl-based procedures suffer from low process efficiency, in that some of the purified SWCNTs remain irreversibly bound on the gel. This work focuses on the elucidation of mechanistic aspects relating to the irreversible retention of SWCNT by Sephacryl S200 and identification of strategies to reduce material loss. By probing system parameters such as SWCNT or sodium dodecyl sulfate (SDS) concentration during adsorption, loading ratio (number of SWCNTs vs. number of gel binding sites), and the effect of kosmotropic additives on process elution efficiency, this work identifies inhomogeneous features belonging to SWCNTs as the primary factor which promotes their irreversible retention. Process elution efficiency is found to be negatively correlated with increased SDS surfactant concentration and increased SWNT loading, and methods are identified to mitigate material losses in Sephacryl-based SWCNT separation schemes. Application of NaF, a strong kosmotropic agent, to elute SWCNTs from Sephacryl is found to increase process elution efficiency from 54% to 88% compared to SDS surfactant alone. Collectively, this work both improves upon and provides valuable insight into the purification of SWNT with Sephacryl.

Fast Ion Diffusion in Carbon Nanotube Channels

Many simulations and experiments have investigated pressure-driven fluid flow in carbon nanotubes (CNTs) and demonstrated enormous transport rates through these channels. Comparatively little attention has been given so far to concentration-driven transport1,2 in CNTs despite its importance in a large variety of fields. While several studies assumed bulk/hindered diffusion for small molecules through nm-wide CNTs, other simulations have predicted self-diffusion coefficients several times larger than in the bulk. These large uncertainties in the magnitude of the diffusion rates through CNTs have hampered their full exploitation in nanofluidic devices.3 To obtain a precise quantification of the diffusive flow in CNTs, we have fabricated membranes with a large but known number of single-walled carbon nanotubes (SWCNT) as fluid transport pathways. Contrary to previous membrane systems, this platform enables us to minimize uncertainties in the calculation of the per-pore flow rate. A series of stringent control experiments confirms that these membranes are defect free and that transport occurs only through SWCNTs. Once corrected for the boundary layer resistance at the membrane/fluid interface, our measurements reveal that the transport diffusivity of small ions in single-walled carbon nanotubes is one order of magnitude faster than in the bulk.4 The dependence of the flow enhancement on the ion chemico-physical properties is also discussed. Together with indicating that CNT membranes could enable dialysis processes with unprecedented efficiency, these results have important implications for a broad range of applications, such as energy storage/harvesting and chemical separation/detection, where ion permeation through nanoporous carbon materials is key.

Large magnetic moment at sheared ends of single-walled carbon nanotubes**Project supported by the National Key Research and Development Program of China (Grant Nos. 2018YFA0208403 and 2016YFA0200403), the National Natural Science Foundation of China (Grant Nos. 51472057, 11874129, 91323304, and 11674387), the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDA09040101), and the Baotou Rare Earth Research

In this work we report that after single-walled carbon nanotubes (SWNTs) are sheared with a pair of titanium scissors, the magnetization becomes larger than that of the corresponding pristine ones. The magnetization increases proportionally with the number of SWNTs with sheared ends, suggesting that there exist magnetic moments at the sheared ends of SWNTs. By using the coefficient of this linear relation, the average magnetic moment is estimated to be 41.5 ± 9.8 μB (Bohr magneton) per carbon atom in the edge state at temperature of 300.0 K, suggesting that ultrahigh magnetic fields can be produced. The dangling sigma and pi bonds of the carbon atoms at sheared ends play important roles in determining the unexpectedly high magnetic moments, which may have great potential applications.

Release of Retained Single-Walled Carbon Nanotubes in Gels

The separation of single-chirality, even-enantiomeric single-walled carbon nanotubes (SWCNTs) has been well established using gel permeation chromatography. Successful SWCNTs separation has been considered to be the selective adsorption and desorption of specific SWCNTs on the porous sites of Sephacryl gels. This work reports two nonspecific releases of SWCNTs retained on Sephacryl gels: (1) a considerable number of SWCNTs were eluted using a low-concentration SDS condition solution (0.5 wt %) from the gels exclusively eluted with a high-concentration SDS eluting solution (5 wt %) after being stocked overnight and (2) the retained SWCNTs in Sephacryl gels can be eluted using a low-concentration SDS condition solution (0.5 wt %) after being stocked overnight without any treatments. Inspired by extracellular matrix systems, these releases are attributed to the strain-induced gel relaxation. The roles of surfactants, especially SDS, in the retention and release of SWCNTs on Sephacryl gels were discussed on the basis of spectral dilution and titration experiments using single-chirality (6,5) SWCNT as the probe.

Quantitative study of bundle size effect on thermal conductivity of single-walled carbon nanotubes

Compared with isolated single-walled carbon nanotubes (SWNTs), thermal conductivity is greatly impeded in SWNT bundles; however, the measurement of the bundle size effect is difficult. In this study, the number of SWNTs in a bundle was determined based on the transferred horizontally aligned SWNTs on a suspended micro-thermometer to quantitatively study the effect of the bundle size on thermal conductivity. Increasing the bundle size significantly degraded the thermal conductivity. For isolated SWNTs, thermal conductivity was approximately 5000 ± 1000 W m–1 K–1 at room temperature, three times larger than that of the four-SWNT bundle. The logarithmical deterioration of thermal conductivity resulting from the increased bundle size can be attributed to the increased scattering rate with neighboring SWNTs based on the kinetic theory.

Controlling conducting channels of single-walled carbon nanotube array with atomic force microscopy

In this paper, we report a technique of controlling the number of single-walled carbon nanotubes (SWNTs) between two electrodes. The SWNT devices consist of an array of SWNTs between two silver/palladium electrodes, which are fabricated with electron beam lithography and silver. Using the tip-sample interaction in contact mode of atomic force microscopy (AFM), the number of individual SWNTs can be controllably decreased. The current–voltage measurements indicate that the resistance increases when the conducting channels of SWNTs are reduced. This simple and controllable approach could be useful for the assembly of high performance devices with a desired number of channels for future electronic investigations.

Plasmonic Crystals for Strong Light-Matter Coupling in Carbon Nanotubes.

Their high oscillator strength and large exciton binding energies make single-walled carbon nanotubes (SWCNTs) highly promising materials for the investigation of strong light–matter interactions in the near infrared and at room temperature. To explore their full potential, high-quality cavities—possibly with nanoscale field localization—are required. Here, we demonstrate the room temperature formation of plasmon–exciton polaritons in monochiral (6,5) SWCNTs coupled to the subdiffraction nanocavities of a plasmonic crystal created by a periodic gold nanodisk array. The interaction strength is easily tuned by the number of SWCNTs that collectively couple to the plasmonic crystal. Angle- and polarization resolved reflectivity and photoluminescence measurements combined with the coupled-oscillator model confirm strong coupling (coupling strength ∼120 meV). The combination of plasmon–exciton polaritons with the exceptional charge transport properties of SWCNTs should enable practical polariton devices at room temperature and at telecommunication wavelengths.

Free vibration of in-plane-aligned membranes of single-walled carbon nanotubes in the presence of in-plane-unidirectional magnetic fields

Free in-plane and out-of-plane vibrations of two-dimensional magnetically affected ensembles of single-walled carbon nanotubes (MAESWCNTs) are of concern. Using Maxwell’s equations, nonlocal Rayleigh, Timoshenko, and higher-order beam theories, and Hamilton’s principle, the discrete equations of motion of both in-plane and out-of-plane vibrations for the proposed models are constructed. When the number of single-walled carbon nanotubes (SWCNTs) within the ensemble is large enough, evaluation of the frequencies of the nanostructure would not be an easy task. To overcome such a dilemma, some useful nonlocal continuous models are proposed. Through various numerical studies, the accuracy of such models is validated. The obtained results display that the in-plane and out-of-plane frequencies rely on the strength of the longitudinal magnetic field, small-scale parameter, number of SWCNTs with the ensemble, intertube distance, and the geometrical properties of the constitutive SWCNTs of the ensemble. The roles of these crucial factors in the fundamental frequencies of the MAESWCNTs are comprehensively examined via many numerical studies. The capabilities of the proposed nonlocal continuous models in predicting the bending frequencies are also discussed.

Microchip based electrochemical-piezoelectric integrated multi-mode sensing system for continuous glucose monitoring

We presented a MEMS multi-mode sensing system by integrating electrochemical working electrode and solid-mounted thin-film piezoelectric resonator (SMR) on a single micro-sized chip, which is capable of detecting three sensing modes of electrochemistry, gravimetry and viscometry. As a model test sample, glucose concentration was successfully monitored using this integrated sensor. The electrochemical sensor amperometrically detected glucose concentration change, and SMR tracked the concentration variation through impedance response to viscosity. Optimized number of single-walled carbon nanotubes (SWCNTs) – poly (dimethyldiallylammonium chloride) (PDDA) / glucose oxidase (GOD) modification layers was also determined with the help of SMR by monitoring the mass-sensitive frequency shift. SMR proved to be a suitable support for chip-integrated electrochemical sensor for glucose detection. This integrated chip sensor can be conveniently fabricated with high throughput, shows significant potential for chemical and biological sensing applications.

Inter-Carbon Nanotube Contact and Thermal Resistances in Heat Transport of Three-Phase Composites

Single-walled carbon nanotubes (SWNTs) tend to aggregate into bundles due to van der Waals forces during the fabrication of the composite. A computational model using an off-lattice Monte Carlo method is developed to systematically investigate the effects of SWNT bundles, the number of SWNTs per bundle and the thermal boundary resistance (TBR) at the SWNT–SWNT interfaces on the effective thermal conductivity (Keff) of three-phase composites. It is found that the aggregation of the SWNTs in bundles can reduce significantly the Keff of the composites with SWNTs oriented parallel or randomly to the heat flux direction, but it enhances slightly the Keff of those with SWNTs perpendicular to the heat flux direction. The Keff of the composites also decreases when more individual SWNTs aggregate in each bundle and with larger SWNT–SWNT TBR values. The thermal transport mechanism within the composites is dominated by a critical SWNT–SWNT TBR of 0.155 × 10–8 m2K/W.

Axial buckling analysis of vertically aligned ensembles of single-walled carbon nanotubes using nonlocal discrete and continuous models

Several novel models, based on the nonlocal stress theory, on the lateral buckling of two- and three-dimensional (2D and 3D) ensembles of vertically aligned single-walled carbon nanotubes (SWCNTs) are developed. The existing van der Waals forces between the constitutive atoms of the neighboring SWCNTs are modeled by an elastic layer, and each individual SWCNT is modeled using the nonlocal Rayleigh beam theory. The governing equations for lateral buckling of both 2D and 3D SWCNTs ensembles due to axial compressive loads are derived. These are called discrete models since the lateral deformations of each SWCNT only express in terms of the longitudinal coordinate of the SWCNT. It will be revealed that the lateral deformation of SWCNTs can be also stated in terms of two and three coordinates for 2D and 3D ensembles of SWCNTs, respectively. The resulting models are called continuous models. Based on both discrete and continuous models, the critical axial buckling loads for both 2D and 3D ensembles of SWCNTs for a special case, when the outer SWCNTs are prohibited from any lateral movement, are obtained. A reasonably good agreement between the results of the discrete model and those of the continuous model is reported. Subsequently, the roles of small-scale parameter, intertube distance, and number of SWCNTs on the critical buckling loads are examined. The obtained results and the proposed models in the present work would be very helpful in design and fabrication of 2D and 3D groups of vertically aligned SWCNTs, particularly those whose main duties are to transfer securely the applied axial forces.

Surface-Enhanced Raman Scattering from small numbers of single-walled carbon nanotubes and oxidised single-walled carbon nanotubes

Temporal fluctuations of surface-enhanced Raman scattering spectra of purified and oxidised single walled carbon nanotubes have been observed. SERRS spectra were recorded that possessed fluctuating spectral profiles, these profiles possessed randomly fluctuation peak intensities and positions. Observation of bands in the 1000 to 1200 cm-1 frequency window was observed. A series of peaks in this window were observed to coincide with peak positions that have been assigned to arise from Stone-Thrower-Wales and heptagonal-pentagonal intramolecular junction defects on the nanotubes surface. We find that these peaks also occur for chemically treated SWCNTS.

Fabrication of flat capped carbon nanotubes using an arc-discharge method assisted with a Sm-Co catalyst

In this study, carbon nanotubes (CNTs) were fabricated using an arc-discharge method assisted with samarium-cobalt (Sm-Co) chloride as a catalyst. The optimal fabrication condition was determined through a series of experiments on various ambient conditions. Observations were completed using scanning electron microscopy (SEM), Raman spectroscopy, and tunneling electron microscopy (TEM); the main products we observed are well-structured multi-walled carbon nanotubes. By identifying the radial breathing modes (RBMs) of the Raman spectra with a TEM micrograph, we also observed a small number of single-walled carbon nanotubes. With the assistance of the Sm-Co chloride catalyst, the RBMs of the Raman spectra were measured in the ambient pressure of 760 torr. The TEM observations revealed that our nanotubes have good graphitic structures and almost no bamboo defects, which agrees with their Raman measurements with a high IG/ID ratio (~88). A perfect graphitic flat cap was found to be attached at the end of the nanotube. Simulation shows that by incorporating 5 carbon pentagons, it is possible to construct a flat capped carbon nanotube. The results of our experiment offer a unique approach to growing high quality CNTs. Such a flat capped structure may useful for further advanced application in nano-electronics and nano-optics.

Dependence of pore size on catalyst concentration used in synthesis carbon nanotubes

Single-walled carbon nanotubes using chemical vapor deposition with two different concentrations of catalyst were synthesized. Characterization of samples with electron microscopy and Raman spectra has shown that there are a large number of single-walled carbon nanotubes distributed evenly in samples with the range of distribution diameters ranging between 1.10 and 1.45 nm. Nitrogen adsorption at 77 K and pressure up to 1 bar were measured in both samples. Results shows that the surface area depends on the concentration of iron catalyst used for making the nanotube. Calculation of pore size distribution in micropore and mesopore range of samples shows that the shape of isotherm and also size of pores in the samples depend on the catalyst concentration. Sample with more catalyst has a wider pore

An investigation into the interaction between carbon-based nanomaterials and Escherichia coli cells using atomic force microscopy

Using atomic force microscopy (AFM), the nature of the contact between a wide range of carbonbased nanomaterials (CBNs) and Escherichia coli cells is described and the consequences of such an interaction are estimated. It is shown that the contact of multiwall and a number of single-wall carbon nanotubes with the surface of a model microorganism carries a probabilistic nature and is not accompanied by changes in the morphology and viability of bacterial cells. The damage of the surface structures and the consequent destruction of Escherichia coli are observed upon contact with single-wall carbon nanotubes with low degrees of purification, which is presumably determined by the presence of technological impurities in CBNs. A significant enhancement of the affinity of C60 fullerenes functionalized by amine groups to the surface of model microorganisms, which also leads to the development of a bactericidal effect, is shown.

Fabrication of Carbon Nanotube Field-Effect Transistors by Fluidic Alignment Technique

With a fluidic alignment technique for aligning single-walled carbon nanotubes (SWNTs) over a large area on solid substrates, we can assemble SWNTs into parallel arrays with desired average separation. The number of SWNTs in the aligned arrays is controlled by the size of the microfluidic channels and the concentration of SWNTs in suspension. Most of the SWNTs are found to be aligned parallel to the orientation of the microfluidic channels. The performance of carbon nanotube field-effect transistors (CNTFETs) fabricated by this technique and the influences of impurities on the transistor characteristics are discussed.

Intrinsic current gain cutoff frequency of 30GHz with carbon nanotube transistors

High frequency capabilities of carbon nanotube field-effect transistors (CNTFETs) are investigated. Structures with a large number of single-walled carbon nanotubes were fabricated using dielecrophoresis to increase the density of nanotubes in the device channel. The authors obtained an intrinsic current gain cutoff frequency of 30GHz establishing state-of-the-art high frequency (hf) potentialities of CNTFETs. The device also showed a maximum stable gain above 10dB at 20GHz. Finally, the parameters of an equivalent circuit model of multitube CNTFET at 20GHz are determined, which open the route to the modeling of nanotubes-based hf electronics.

An 8-GHz f/sub t/ carbon nanotube field-effect transistor for gigahertz range applications

In this letter, the authors report on the high-frequency (HF) performance of self-assembled carbon nanotube field-effect transistors. HF device structures including a large number of single-wall carbon nanotubes have been designed and optimized in order to establish a new state of the art. The device exhibits a current gain (|H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> | <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) cutoff frequency (f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> ) of 8 GHz and a maximum stable gain value of 10 dB at 1 GHz, after de-embedding the access pads. Considering such results, nanotube-based circuits with gigahertz performance are now conceivable

Curvature effect on the radial breathing modes of single-walled carbon nanotubes

Based on the energy of a relaxed carbon nanotube relative to the graphite sheet (graphene), we construct an analytical correction to the carbon-carbon force constants. Then, the radial breathing modes (RBM) of a number of single-walled carbon nanotubes (SWNTs) are calculated. It is found that for small diameter SWNTs, the curvature effect becomes significant and chirality dependent. Our calculated RBMs are in very good agreement with experimental measurements, especially for ultrasmall diameter SWNTs.

Cluster Origin of the Solubility of Single-Wall Carbon Nanotubes

The possibility of the existence of single-wall carbon nanotubes (SWNT) in organic solvents, in the form of clusters containing a number of SWNTs, is discussed. A theory is developed based on a bundletmodel for clusters, which enables describing the distribution function of clusters by size. Comparison of the calculated values of solubility with experimental data would permit obtaining energetic parameters characterizing the interaction of an SWNT with its surrounding in a solid phase or solution. Fullerenes and SWNTs are unique objects, whose behavior in many physical situations is characterized by remarkable peculiarities. Peculiarities in solutions show up in that fullerenes and SWNTs represent the only soluble forms of carbon, what is primary related to the originality in the molecular structure of fullerenes and SWNTs. The fullerene molecule is a virtually uniform closed spherical or spheroidal surface, having no sharp ridges or dents. Similarly, an SWNT is a smooth cylindrical unit. Both structures give rise to the relatively weak interaction between the neighbouring molecules in a crystal, and promote effective interaction of the molecules with those of a solvent. Another peculiarity in solutions is related to their tendency to form clusters, consisting of a number of fullerene molecules or SWNTs. The energy of interaction of a fullerene molecule or SWNT with solvent molecules is proportional to the surface of the former molecule, and roughly independent of the relative orientation of solvent molecules. A unified treatment is proposed in the framework of the bundlet model of a cluster, in accordance with which the free energy of an SWNT involved in a cluster consists of two components: a volume one proportional to the number of molecules n in a cluster and a surface one proportional to n1/2.