Single-walled Carbon Nanotube Bundles Research Articles

Partial dehydration-mediated selective ion-permeation through subnanometer-scale windows in highly crystalline single walled carbon nanotube walls

We propose single-atom catalytic oxidation method for production of subnanometer-scale windows on the graphene layer of single walled carbon nanotubes (SWCNTs) in this study. We used the free-standing SWCNT films which had merits for reliable measurements and applicability to electrochemical measurements for determination of the nanowindow size. Copper(II) 2,3,9,10,16,17,23,24-octakis(octyloxy)-29H,31H-phthalocyanine (CuPc) was adsorbed on SWCNT bundles using liquid-phase adsorption at surface coverage of 0.9. Then, nanowindows were produced by oxidation above 550 K being higher than the decomposition temperature of the bulk CuPc. The oxidation of CuPc-adsorbed SWCNT film markedly increased the surface area from N2 adsorption at 77 K due to access of N2 to the internal tube space through the nanowindows. The nanowindow size was estimated to be the molecular size of N2 through the evident low-pressure adsorption hysteresis of the N2 adsorption isotherm and TEM observation. The selective ion permeability through the nanowindows for H3O+, Li+, Na+, K+, Mg2+, Ca2+, and Ba2+ ions was determined by the inside-capacitance being the capacitance difference of SWCNT between with and without nanowindows. The selective permeation of the hydrated ions depended on the oxidation conditions for production of nanowindows, showing less than 1 nm of the nanowindow size. The relationship between the inside-capacitance and hydrated ion diameter for the selective permeation of hydrated ions indicated partial dehydration of the hydrated ions just only on their permeation through the nanowindows under the accelerated conditions.

Conductivity-based approach to estimate average bundle length in randomly oriented network of single-walled carbon nanotubes

In this paper, we report a method to estimate the average length of bundles in a randomly oriented network of single-walled carbon nanotubes (SWCNTs) by analyzing the dependence of its sheet resistance on the distance between contacts. We propose an analytical model to verify the method and find the model's limitations using Monte Carlo simulations. Then, we apply the proposed approach to experimental results acquired from 95% (at 550 nm wavelength) transparent SWCNT films. The proposed method to estimate the average SWCNT bundle length can be used in situ and does not require any specific sample preparation step that can distort the SWCNT network.

Low-temperature radiation damage studies in single-walled carbon nanotube bundles by hopping conductance

The paper shows the results of studying radiation defects in single-walled carbon nanotube bundles at low temperatures. The data were obtained in a unique experiment that inseparably combines 1 MeV electron irradiation at a temperature of ∼10 K and electrical conductivity measurements over a wide temperature range of 5–300 K. The experiment allowed us to reveal and separate the influence of stable and unstable radiation defects on the electrical properties of SWCNTs. It is shown that the 2D Mott variable range hopping conduction regime exhibits resistance to electron irradiation. The hopping conductivity is the dominant charge transfer mechanism in the temperature range of 5–50 K in both the pristine and irradiated SWCNT samples. It was found that the parameters of hopping transport demonstrate high sensitivity to the introduction and annealing of radiation defects. The low-temperature electron irradiation revealed the possibility of the emergence of an additional conduction channel in the irradiated SWCNTs. This channel demonstrates thermally activated behavior with a low activation energy of ∼0.5 meV at temperatures of 5–50 K. The obtained data indicate that unstable radiation defects create conditions for the possibility of impurity band conduction in SWCNT bundles.

More than the interface: Synergistic engineering of the interfacial and its subjacent layers followed by self-triggering for high efficient bioelectricity harvesting

The practical application of microbial fuel cell (MFC) is severely impeded by its low output power density stemming from the low bacterial loadings and the sluggish extracellular electron transfer (EET) kinetics. Thus, the current collector designed to greatly enhance the electrocatalytic performance of microbial electrodes ought to possess both high hydrophilicity and high conductivity, which are, however, often mutually incompatible. Herein, to resolve this dilemma, a composite bioelectrode consisting of the poly(ionic liquid) functionalized single-walled carbon nanotube bundles (SWCNT-PIL) layer at the biotic-electrode interface and its subjacent hydrophilic graphene oxides (GO) layer is prepared. Bacterial adhesion is significantly enhanced, resulting from the positive charges of SWCNT-PIL and the hydrophilic GO. After self-reduction of GO by attached electricigens, the as-prepared mrGSP bioelectrode exhibits a maximum output power density of 4.808 W m−2, which is more than one order of magnitude larger than that of conventional carbon-based electrode (0.319 W m−2), because the SWCNT-PIL layer is capable of not only accelerating the flavin-based mediated electron transfer (MET), but also upregulating the membrane protein expression from 14.64% to 18.01% induced by the enhanced electric field, promoting the outer membrane c-type cytochromes-based direct electron transfer (DET). This work provides a new concept of synergistic engineering the interfacial and its subjacent layers to solve the dilemma between high hydrophilicity and high conductivity of the current collector surface for microbial electrocatalysis.

Designed Production of Atomic-Scale Nanowindows in Single-Walled Carbon Nanotubes

The controlled production of nanowindows in graphene layers is desirable for the development of ultrathin membranes. Herein, we propose a single-atom catalytic oxidation method for introducing nanowindows into the graphene layers of single-walled carbon nanotubes (SWCNTs). Using liquid-phase adsorption, copper(II) 2,3,9,10,16,17,23,24-octakis(octyloxy)-29H,31H-phthalocyanine (CuPc) was adsorbed on SWCNT bundles at a surface coverage of 0.9. Subsequently, narrow nanowindows with a number density of 0.13 nm-2 were produced by oxidation above 550 K, which is higher than the decomposition temperature of bulk CuPc. In particular, oxidation of the CuPc-adsorbed SWCNTs at 623 K increased the surface area from 280 to 1690 m2 g-1 owing to the efficient production of nanowindows. The nanowindow size was estimated to be similar to the molecular size of N2 based on the pronounced low-pressure adsorption hysteresis in the N2 adsorption isotherm. In addition, the enthalpy change for the nanowindow-formation equilibrium decreased by 4 kJ mol-1 when CuPc was present, further evidencing the catalytic effect of the Cu atoms supplied by the adsorbed CuPc molecules.

Sb2Te3 nanoparticle-containing single-walled carbon nanotube films coated with Sb2Te3 electrodeposited layers for thermoelectric applications

Single-walled carbon nanotubes (SWCNTs) are promising thermoelectric materials owing to their flexibility and excellent durability when exposed to heat and chemicals. Thus, they are expected to be used in power supplies for various sensors. However, their thermoelectric performances are inferior to those of inorganic thermoelectric materials. To improve the thermoelectric performance while maintaining the excellent characteristics of SWCNTs, a novel approach to form inorganic thermoelectric layers on the SWCNT bundle surfaces using electrodeposition is proposed. We synthesized Sb2Te3 nanoparticle-containing SWCNT films and coated them with electrodeposited Sb2Te3 layers. The Sb2Te3 nanoparticles were synthesized via a spontaneous redox reaction, which were then added to a SWCNT dispersion solution, and films were produced via vacuum filtration. At higher nanoparticle contents in the films, the Sb2Te3 electrodeposited layers completely covered the SWCNT bundles owing to the increase in the concentration of precursor ions near the SWCNT bundle surface, which in turn was the result of melted nanoparticles. The thermoelectric performance improved, and the maximum power factor at approximately 25 °C was 59.5 µW/(m K2), which was 4.7 times higher than that of the normal SWCNT film. These findings provide valuable insights for designing and fabricating high-performance flexible thermoelectric materials.

Enhanced toughness of boron carbide by single-wall carbon nanotube bundles

Breaking the contradictory of hardness and toughness in B4C is still a challenge to fabricate robust materials. Although compositing B4C with carbon nanotubes (CNTs) is an effective way to improve the toughness, the toughness has the limitation about 6 MPa·m1/2 or hardness below 30 GPa. The limitation of toughness in B4C-CNTs composites is caused by the weak interaction between B4C and CNTs, which impair the strength of composite. So, in this work, the inner compressive stress is introduced in B4C composite with the single-walled carbon nanotube bundles (B4C-SWNTb) by high pressure and high temperature (HPHT). The optimal hardness and fracture toughness are 30 GPa and 8.27 MPa·m1/2 in B4C-2 vol% SWNTb composites, which is 3.3 times higher than that of pure B4C. The high hardness and excellent toughness of B4C-SWNTb composite come from grain refinement of B4C particles, strong combination and inner compressive stress between B4C and SWNTb. This work holds much significance for improving hardness and toughness simultaneously in robust matrix composites.

Delay analysis of mixed CNT bundles as global interconnect for nanotechnology nodes

Abstract This paper presents modeling of high current capability of mixed carbon nanotube (CNT) bundle interconnects depending upon the type of constituent CNT materials and their orientations. With different arrangements, one category of novel mixed CNT bundles formed by the combination of multi-walled/multi-shell CNT and double-shell CNT bundles (MDCB) are proposed and compared with the mixed CNT bundles (MSCB) formed with multi-shell CNT and single-walled CNT bundles. A time-domain analysis is performed for these structures to analyse the effect of delay and power dissipation. It has also been observed that MDCB structures give better performance (≈ 30%) than MSCB structures in terms of power-delay product at the global length of interconnect for nano-regime technology nodes. Also, MDCB structure formed by placing multi-walled CNTs along the periphery and double-walled CNTs in the centre of structure yields the best result against all proposed mixed CNT bundled structures and can be employed for future interconnect applications.

Achieving Both Ultrahigh Electrical Conductivity and Mechanical Modulus of Carbon Films: Templating-Coalescing Behavior of Single-Walled Carbon Nanotube in Polyacrylonitrile.

Promoting the feasibility of carbon films as electrode applications requires sufficient performances in view of both electrical and mechanical properties. Herein, carbon films with ultrahigh electrical conductivity and mechanical modulus are prepared by high temperature carbonization of polyacrylonitrile (PAN)/single-walled carbon nanotube (SWNT) nanocomposites. Achieving both performances is ascribed to remarkable graphitic crystallinity, resulting from the sequential templating-coalescing behavior of concentrated SWNT bundles (B-CNTs). While well-dispersed SWNTs (WD-CNTs) facilitate radial templating according to their tubular geometry, flattened B-CNTs sandwiched between carbonized PAN matrices induce vertical templating, where the former and latter produce concentric and planar crystallizations of the graphitic structure, respectively. After carbonization at 2500 °C with the remaining WD-CNTs as microstructural defects, the flattened B-CNTs coalesce into graphitic crystals by zipping the surrounding matrix, resulting in high crystallinity with the crystal thicknesses of 27.4 and 39.4nm for the (002) and (10) planes, respectively. For comparison, the graphene oxide (GO) containing carbon films produce a less-ordered graphitic phase owing to irregular templating, despite the geometrical consistency. Consequently, PAN/B-CNT carbon films exhibit exceptional electrical conductivity (40.7× 104 S m-1 ) and mechanical modulus (38.2 ± 6.4GPa). Thus, controlling the templating-coalescing behavior of SWNTs is the key for improving final performances of carbon films.

Proportional correlation between heat capacity and thermal expansion of atomic, molecular crystals and carbon nanostructures

Correlation between thermal expansions β(T) and heat capacity C(T) of atomic and molecular crystals, amorphous materials with a structural disorder, carbon nanomaterials (fullerite C60, bundles SWCNTs of single-walled carbon nanotubes) was analyzed. The influence of the contribution to the coefficient of linear thermal expansion αXe(T) of Xe atoms adsorbed on the SWCNTs bundles is considered. The proportional correlation was found between the contribution to the coefficient of linear thermal expansion αXe(T) and the normalized to the gas constant heat capacity C Xe(T)/R of Xe atoms adsorbed on the SWCNTs bundles. The proportional correlation (β/β*) ∼ (CV/R) with the parameter β* for the bulk thermal expansion coefficient for cryocrystals is proposed. In the case of atomic crystals such as Xe and Ar, the proportional correlation (β/β*) ∼ (CV/R) is observed in the temperature range from the lowest experimental to temperatures where CV/R ≈ 2.3. The correlation is not observed in the temperatures where 2.3 < C V/R < 3 (classical Dulong-Petit law). It was found that the universal proportional correlation is also observed for molecular crystals with linear symmetry, such as CO2, CO, and N2O if the normalized heat capacity below the values CV/R ≈ 3 ÷ 3.5. It indicates that the proportional correlation between thermal expansions (β/β*) and heat capacity (CV/R) is related not only to the translational, but also to the rotational degrees of freedom of the molecule in the crystal. In the case of the C0, molecular crystal with translational and rotational degrees of freedom and intramolecular vibrations, the discussed above correlation occurs below the values of normalized heat capacity CV/R ≈ 7.5. In strongly anisotropic systems, such as systems of compacted bundles of single-walled carbon nanotubes and SWCNTs bundles with adsorbed Xe atoms, this universal dependence appears in a limited temperature range that does not include the lowest temperatures. A qualitative explanation of the observed correlation is proposed.

Tuning the Optical Properties and Conductivity of Bundles in Networks of Single-Walled Carbon Nanotubes.

The films of single-walled carbon nanotubes (SWCNTs) are a promising material for flexible transparent electrodes, which performance depends not only on the properties of individual nanotubes but also, foremost, on bundling of individual nanotubes. This work investigates the impact of densification on optical and electronic properties of SWCNT bundles and fabricated films. Our ab initio analysis shows that the optimally densified bundles, consisting of a mixture of quasi-metallic and semiconducting SWCNTs, demonstrate quasi-metallic behavior and can be considered as an effective conducting medium. Our density functional theory calculations indicate the band curving and bandgap narrowing with the reduction of the distance between nanotubes inside bundles. Simulation results are consistent with the observed conductivity improvement and shift of the absorption peaks in SWCNT films densified in isopropyl alcohol. Therefore, not only individual nanotubes but also the bundles should be considered as building blocks for high-performance transparent conductive SWCNT-based films.

Shock loading of carbon nanotube bundle

A single-walled carbon nanotube (CNT) bundle under shock loading in lateral direction is studied by means of the chain model with reduced number of degrees of freedom. One or two compressive shock waves are initiated by a piston moving at a constant speed V0. At lower piston speeds, only the faster wave front resulting in an elliptization of CNTs propagates, while at higher speeds this is followed by the slower wave front resulting in CNT collapse. Time evolution of the CNT bundle structure during compression is investigated in detail. Energy absorption rate W as a function of the piston speed V0 is evaluated for bundles having CNTs of different diameter D. Bundles with smaller CNT diameter demonstrate a higher energy absorption rate scaling as W∼D−3. The rate of energy absorption increases bilinearly with V0, and in the regime of CNT collapse the slope of the line is twice as high as in the case when only elliptization takes place. The obtained results can be useful for the development of new types of elastic dampers.

Frequency response analysis of CNT bundle interconnects

ABSTRACT When carbon nanotubes (CNTs) are used in interconnects, their electrical properties are appealing as they are not affected by surface scattering when the feature size decreases. After almost two decades of research on CNT-based interconnects, it is still a question which type of CNT bundle performs better than the other. There are many contradictory reports in this regard. So, it is very important to study the frequency response of these interconnects to ascertain their actual performance and compare them. HSPICE-based circuit simulations at 20 nm and 14 nm technology nodes are carried out. Furthermore, the analysis for local, semi-global and global interconnect lengths is carried out. Results show that single-walled CNT (SWCNT) bundles have higher voltage gain and higher current gain for all lengths at both the technology nodes. These results are significant in understanding the best choice of interconnects among SWCNT bundle, MWCNT bundle and mixed CNT bundle interconnects.

Development of a home-made experimental set-up for in situ coupling under vacuum of conductivity measurements, x-ray absorption and Raman Spectroscopies on bundles of single-walled carbon nanotubes intercalated with alkali metals

Here, we report the development of a homemade experimental setup to perform under vacuum an in situ study of the physical properties of bundles of single-walled carbon nanotubes intercalated with rubidium ions using electrical conductivity, X-ray absorption and Raman measurements. This set-up was successfully used at the SAMBA beamline at the Soleil synchrotron. The electrical resistance displays an important drop with the stoichiometry (intercalation time). The Raman radial breathing modes and the G-band of the nanotubes clearly indicate an important electron transfer. The G-band behaviour features a transition from semiconducting to metallic nanotubes, confirmed by the electrical resistance measurements as a function of the temperature after rubidium intercalation. This set-up can be used for the study of any type of extremely air sensitive materials.

Space-confined synthesis of SWNT bundles wrapped by MoS2 crystalline layers as flexible sensors and detectors

Single-walled carbon nanotubes (SWNTs) are ideal template for constructing one-dimensional (1D) heterojunctions with intriguing optical and electrical properties, yet it remains challenging to wrap foreign materials around SWNTs due to their very small diameter and large curvature. Here, we present a space-confined method to synthesize SWNT bundles wrapped by MoS2 crystalline layers (SWNT@MoS2) film by embedding a pristine SWNT film within a porous multi-walled nanotube sponge, which acts as a liquid precursor container for hydrothermal reaction. We find that crystalline MoS2 sheets could be formed around the outer surface of SWNT bundles uniformly and continuously, with tailored number of multi-layers (3–17 layers), for bundle sizes ranging from several to hundreds of nanometers. The resulting SWNT@MoS2 network shows much enhanced light response and gas sensitivity, presenting promising applications as flexible photo-detectors and toxic gas sensors. Our scalable synthesis method and SWNT-based coaxial-cables will be useful in future developing innovated 1D van der Waals heterojunctions and flexible nanoelectronic systems.

Ultrasensitive, Transparent, Flexible, and Ecofriendly NO2 Gas Sensors Enabled by Oxidized Single-Walled Carbon Nanotube Bundles on Cellulose with Engineered Surface Roughness

Ultrasensitive, Transparent, Flexible, and Ecofriendly NO₂ Gas Sensors Enabled by Oxidized Single-Walled Carbon Nanotube Bundles on Cellulose with Engineered Surface Roughness

Structural properties of single-walled carbon nanotubes under extreme dynamic pressures

The structural behaviors of single-walled carbon nanotubes (SWNTs) along the radial direction are critical to the cross-sectional phase transition, elastic recovery, and band structure engineering. Previous static pressure studies have established a clear picture on the structural behaviors of SWNTs that governed by the Lévy-Carrier law. But when the pressurization becomes dynamic, there lacks a fundamental understanding of the structural properties of SWNTs along the radial direction. Here, different from static (< 1 GPa/s) and shock compression (> 107 GPa/s), we gain new insights on the phase transition, recovery dynamics and energy dissipation of SWNT bundles with a median diameter of dt ∼1.4 and ∼0.8 nm under modest dynamic pressures in two common pressure mediums (4:1 methanol-ethanol mixture, silicone oil). Upon single ramp compression (ramp rate in an order of magnitude of ∼10–103 GPa/s), the lineshape and intensity changes of Raman spectra induced by the dynamic effect of hydrostatic stress are commonly observed, suggesting different structural behaviors compared with static pressure results. Unexpectedly, the pressure-induced defects are not found in cyclic ramp compressions up to 105 cycles, showing high structural stability to dynamic loading. The corresponding recovery dynamics and energy dissipation mechanism of SWNTs under varying dynamic conditions are also discussed. By analyzing the shear strain potential, distinct dynamic effects of hydrostatic pressure on the SWNTs in two pressure mediums are quantitatively unveiled.

Unfolding the mechanical properties of buckypaper composites: nano- to macro-scale coupled atomistic-continuum simulations

Carbon-based nanostructures are receiving increasing attention over the past two decades due to their unprecedented multi-functional features. However, the macro-scale structural applications of these nanostructures have not yet come to full fruition due to the involvement of complex multi-scale computations and manufacturing. Recently, the research community has started investigating buckypaper, which can be described as a sheet or membrane developed using a network of bundles of single-wall carbon nanotubes, multi-wall carbon nanotubes, or a mixture of both. This article aims to focus on the computational bridging of different length scales involving six levels in the range of nano- to macro-scale behaviour concerning buckypaper composites. The sequential derivatives of carbon at six levels, as analyzed in this paper, involve graphene, CNT, CNT bundle, buckypaper, and buckypaper composite automotive components. Here, we adopt a coupled atomistic-continuum modelling approach for the multi-level simulations. Graphene, CNTs, and CNT bundles are modelled using atomistic simulations, while the buckypaper and its composites are modelled using equivalent beam representations for the bundles and continuum solid representation for resin. At the macro-scale, an industry-relevant multi-material composite automotive component has been investigated, wherein the buckypaper is proposed to be embedded involving sheet moulding compound and carbon prepreg. The current simulations have led to the determination of mechanical properties at each level of the carbon-based materials and their mutual dependence. The numerical results demonstrate that a buckypaper composite can enhance the natural frequency and stiffness up to 25 and 37% with respect to conventional monolithic metallic designs, while reducing the weight by 57%. Such outcomes lead to the realization that carbon-based nanostructural derivative in the form of buckypaper can significantly improve the mechanical properties of advanced lightweight structural components as reinforcements for the next generation of aerospace and automotive structures.Graphical abstract

Selective separation of single-walled carbon nanotubes in aqueous solution by assembling redox nanoclusters.

The selective separation of soluble and individual single-walled carbon nanotubes (SWCNTs) in aqueous solution is a key step for harnessing the extraordinary properties of these materials. Manipulating the strong van der Waals intertube interactions between the SWCNT bundles is very important in selective separation, which is a long-standing challenge. Here we reported the ability of redox polyoxometalate clusters to modulate the intertube π-π stacking interaction through electron transfer and achieved the diameter-selective separation of SWCNTs in a surfactant aqueous solution. The large-diameter SWCNTs concentrated at ∼1.3-1.4 nm were selectively separated when ∼1 nm clusters encapsulated within the tube cavity, and the dispersion of subnanometer ∼0.7-0.9 nm SWCNTs was boosted when clusters were adsorbed on the outer surface of small-diameter nanotubes. The mechanism of diameter-selective separation of SWCNTs associated with the size-dependent interaction between cluster-tubes and the steric hindrance effect of clusters was revealed by optical absorption and Raman spectroscopy. This simple method thus enables the selective separation of individual high-quality SWCNTs in aqueous solutions without harsh sonication with the potential for other separation applications.

Армированные одностенными углеродными нанотрубками композиты на основе ZrO2, полученные свободным вакуумным спеканием

The results of a study of sintered composites based on yttria-stabilized zirconia (ZrO2) reinforced with single-walled carbon nanotubes (SWCNTs) are presented in this paper. Mixing of ZrO2 nanopowder with SWCNTs was carried out in ethanol using an ultrasonic bath and a magnetic stirrer. Composite powders with 0.1, 0.5 and 1 wt.% SWCNTs and ZrO2 nanopowder were pressed into compacts at a pressure of 100 MPa, and then they were sintered in a high temperature vacuum furnace for 2 h at a temperature of 1500°C with a heating rate of 300°C / h. Changes in the microstructure, phase composition, and mechanical properties were investigated depending on the SWCNT content in the samples. It was found that in the selected sintering mode, high density samples (99.2 – 97.5 %) were obtained. It was found by scanning electron microscopy that undivided, entangled SWCNT bundles / aggregates and individual nanotubes, which together formed a continuous reinforcing structure, were observed in the microstructure of the composites. Moreover, SWCNTs led to the refinement of the microstructure of composites; the average grain size of composites was 16 % lower than that of ZrO2 ceramics. It was found by X-Ray diffraction that only high temperature modifications of zirconia (cubic and tetragonal) were present in ZrO2 ceramics and composites, and SWCNTs led to a slight decrease in the size of coherent scattering domain. It was found by the Vickers indentation method that the composite based on ZrO2 with 0.5 wt.% SWCNT was optimal in terms of mechanical properties, since it had the highest microhardness (13.6 GPa, which was 6 % higher than that of ZrO2 ceramics) and had a 12 % higher fracture toughness.