Properties Of Single-walled Carbon Nanotubes Research Articles

Performance Evaluation of CNTFETs Fabricated with Carbon Nanotubes of Different Synthesis Methods

Single walled carbon nanotubes (SWCNTs) exhibit extraordinary electronic properties that render it as an exciting candidate to be applied as the active channel of high-performance carbon nanotube field effect transistors (CNTFETs). The electronic properties of SWCNTs have been demonstrated to be dependent on the tube intrinsic properties that includes structural defects, chirality and diameter. Structural tube defects can be affected by the synthesis method and therefore the latter should also affect the device performance. Hence, this paper aims to present the influence of SWCNTs source synthesis method towards the resulting CNTFET device characteristics. A total of four SWCNT samples were sourced from different synthesis methods in fabricating CNTFETs. The synthesis methods are arc-discharge and three different variation of chemical vapor deposition (CVD) processes, which are DIPS, HiPco and CoMoCAT, respectively. Prior to fabrication, the SWCNT samples were characterized via Raman spectroscopy to quantifythe tube defect levels of each sample, which are directly proportional to the G-peak to D-peak height ratio, G/D. Electrical characterization was carried out via 3-terminal field effect I-Vmeasurement to evaluate key device performance parameters such ason-off current ratio, ION/IOFF, transconductance, gm,subthreshold slope, Spand field effect mobility, μFE.Analysis shows that G/Daffects the IOFFmore significantly relative to ION, resulting in increasing ION/IOFF, and hence switching performance, when G/Dincreases. It is shown an increase of ~50% to the G/Dof the SWCNT source resulted in ~ 860% increase in μFE. Based on the correlation between the optical analysis and electrical measurement, weconclude that theSWCNT growth method cansignificantly affectthe CNTFET device performance.

Influence of defects on the static and dynamic buckling behavior of single-wall carbon nanotubes via molecular dynamics method

Carbon nanotubes (CNTs) exhibit often various defects during the preparation process. Thus, a detailed understanding of the impact of defects on the mechanical properties of CNTs is essential for the design of both CNTs devices and composites. Along these lines, in this work, the effects of two common defects (vacancy and Stone-Wales) on static buckling and dynamic vibration properties of single-walled carbon nanotubes (SWCNTs) are investigated. Firstly, the formation energies of single vacancy defects and Stone-Wales (S-W) defects are studied by molecular dynamics (MD), while the impact of these two defects on the compression performance and natural frequency properties of SWCNTs are explored. Secondly, the axial vibration properties of SWCNTs are studied by using the nonlocal elastic theory and the influence of defects on the dynamic axial displacement of SWCNTs under different aspect ratio is also studied. Moreover, through the change of axial displacement, the change trend of SWCNTs natural frequency with the change of aspect ratio is predicted. The results show that SWCNTs with larger aspect ratios are more prone to defects and its natural frequency will decreases. The study also found that the existence of defects will reduce the buckling properties and vibration characteristics of SWCNTs, and the impact of the S-W defect on the axial mechanical properties of SWCNTs are greater than that of the vacancy defect.

Functionalization of Pristine, Metallic, and Semiconducting-SWCNTs by ZnO for Efficient Charge Carrier Transfer: Analysis through Critical Coagulation Concentration.

Noncovalent functionalization of single-walled carbon nanotubes (SWCNT) by semiconducting oxides is a majorly sought technique to retain individual properties while creating a synergetic effect for an efficient heterostructure charge transfer. Three types of electronically and optically different SWCNTs: metallic (m), semiconducting (s), and pristine (p) are functionalized by ZnO using a facile sonication method. The physicochemical and morphological properties of the ZnO-functionalized SWCNTs, m-SWCNT+ZnO, s-SWCNT+ZnO, and p-SWCNT+ZnO, are analyzed by advanced characterization techniques. Evidence of charge transfer between SWCNT and ZnO is observed with an increase in charge carrier lifetime from 3.31 ns (ZnO) to 4.76 ns (s-SWCNT+ZnO). To investigate the optimum interaction between SWCNTs and ZnO, critical coagulation concentrations (CCC) are determined using UV–vis absorption spectroscopy for m-SWCNT, s-SWCNT, and p-SWCNT using different molar concentrations of ZnO as the coagulant. The interaction and coagulation mechanisms are described by the modified DLVO theory. Due to the variation in dielectric values and electronic properties of SWCNTs, the CCC values obtained have differed: m-SWCNT (1.9 × 10–4), s-SWCNT (3.4 × 10–4), and p-SWCNT (2 × 10–4). An additional analysis of the aggregates and supernatants of the CCC experiments is also shown to give an insight into the interaction and coagulation processes, explaining the absence of influence exerted by sedimentation and centrifugation.

First-principles study on electronic and optical properties of single-walled carbon nanotube under an external electric field.

In this study, the electronic and optical properties of one-dimensional (1D) single-walled carbon nanotube (SWCNT) nanostructures, and under the external electric field [Formula: see text] applied in the z-direction, are investigated using density functional theory (DFT) calculations. The applied [Formula: see text] leads to significant modulation of the bandgap and changes the total density of states (TDOS), partial density of states (PDOS), absorption coefficient, dielectric function, optical conductivity, refractive index, and the loss function. The application of the [Formula: see text] on the SWCNT/Carboxyl structure leads to tighten its bandgap. The peaks of TDOS around the Fermi level are very weak. The absorption coefficient increases in visible range and decreases in ultraviolet (UV) domain proportionally with the [Formula: see text]. It is found that electronic structures and optical properties of the SWCNT/Carboxyl could be affected by the [Formula: see text]. All these results provide the important information for understanding and controlling the electronic and optical properties of 1D crystals by the [Formula: see text]. This study establishes a theoretical foundation for our future experimental work regarding optoelectronic properties of the SWCNT/Carboxyl material.

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.

Influence of Gamma Irradiation on the Properties of Single-Walled Carbon Nanotubes Obtained by CVD Synthesis

Influence of Gamma Irradiation on the Properties of Single-Walled Carbon Nanotubes Obtained by CVD Synthesis

Quantification and removal of carbonaceous impurities in a surfactant-assisted carbon nanotube dispersion and its implication on electronic properties.

Carbonaceous impurities (CIs) affect the optoelectronic properties as well as the ability to use absorption spectroscopy to estimate the metallic content of a single-walled carbon nanotube (SWNT) dispersion. Therefore, a method for the accurate quantification and removal of CIs is required. We have devised methods to characterize and quantify CIs present in SWNT batches and to determine the effects of CIs on the optical and electrical properties of SWNT. Quantitative determination of CIs stems from the finding that chloroform selectively disperses CIs present in SWNT batches. CIs separated by dispersing the as-purchased SWNT batch in chloroform have the morphology of defective and agglomerated few-layered graphenes, whose sizes and locations depend on SWNT batches. Moreover, CIs exhibit a featureless UV-vis-mid-wavelength IR (MWIR) absorption curve and an extinction coefficient comparable to graphenes and show difference with carbon black, which is frequently used as the CI reference. The MWIR region that shows least absorptions caused by the transition of various SWNT types was utilized to assess the significant contribution made by CIs present in a surfactant-assisted SWNT dispersion, showing about 12–19 wt% of CIs in various SWNT dispersions. In addition, the extraction of CIs with chloroform results in a highly purified SWNT batch without any diameter distribution change originating from oxidative damage as compared to the commercially available purified SWNT batch. Finally, we found that increasing the weight of CIs present in a SWNT dispersion strongly lowers the thermal conductivity of a SWNT film when compared with the electrical conductivity. This study provides a way to understand the negative effects that CI has on the optoelectronic properties of SWNTs as well as the beneficial effects of excluding ubiquitous CIs in SWNTs batches.

Amperometric sensor for the detection of hydrogen stable isotopes based on Pt nanoparticles confined within single-walled carbon nanotubes (SWNTs)

The development of hydrogen-based energy and nuclear energy requires new sensing material and high-performance gas sensor for hydrogen stable isotopes, hydrogen (H2) and deuterium (D2). Amperometric gas sensors based on SWNT-filled Pt composite material (Pt-SWNT-in) to combine the good electronic properties of SWNTs and space-confined effect of Pt catalyst have been investigated for detecting H2 and D2. The Pt-SWNT-in electrode shows an excellent linear response in a wide range of 160–8000 ppm hydrogen in N2 atmosphere with the correlation coefficient of 0.9993, and compared to the electrode with Pt nanoparticles supported outside of SWNTs, its sensitivity per Pt loading is 3 times, moreover, it gives larger response current for detection of H2 in air and D2 in N2 atmosphere. Additionally, the Pt-SWNT-in electrode provides a response current to deuterium 0.9 times that to hydrogen in N2. The results present the Pt-SWNT-in electrode with superior sensitivity, selectivity, stability and a response variation for detection of hydrogen and deuterium, which would take advantage of the space-confined effect of SWNTs on Pt catalysts to enhance the sensor performance for detecting hydrogen stable isotopes, and provide an approach to discriminate between hydrogen and deuterium.

N-doped direction-dependent electronic and mechanical properties of single-walled carbon nanotube (SWCNT) from a first-principles density functional theory (DFT) and MD-simulation

In this paper, the electronic and mechanical properties of Nitrogen (N) doped (6,1) single walled carbon nanotube (SWCNT) is analysed based on the first principles density functional theory (DFT) and Molecular dynamic (MD) calculation. A systematic N-doping on SWCNT was performed along zigzag (zz) and armchair (ac) direction, where the armchair doping is parallel to tube axis while zigzag is along the cross-section perpendicular to tube axis. The zz and ac doping resulted in variations in the electronic properties of the even and odd number of N-dopant atoms. To evaluate the mechanical properties, ab − initio MD-simulations was carried out. We found a dependence of the tensile response of the tube on the dopant concentration and doping pattern. Single N-doped system show enhanced tensile stress by 55% as compared to the pristine SWCNT with marginal changes in the young's modulus for all N-doped systems.

Aqueous two-phase extraction of single-walled carbon nanotubes using nonionic surfactant Tween 60

<p indent="0mm">Due to its excellent electronic and optical properties, single-walled carbon nanotubes (SWNTs) have attracted extensive attention. Since the property of SWNTs is determined by their structures, applications like high-performance devices require SWNTs with identical structures and uniform properties. Therefore, the sorting of SWNTs is of great significance. Aqueous two-phase (ATP) extraction is an emerging method that can be utilized to realize the structure sorting of SWNTs. ATP extraction is a repeatable and reliable technique that does not require state-of-the-art equipment. It is efficient and easy to scale up. In this article, by adjusting the concentration of sodium deoxycholate (DOC) and nonionic surfactant Tween 60, the diameter sorting of SWNTs and the separation of high purity (6,5) tubes were achieved. The sorting can be carried out at a higher DOC concentration, which could improve the competitive coating between DOC and Tween 60 on the surface of SWNTs, and further improve the sorting efficiency of the co-surfactant system. The comparison of the separation results between the Tween 60-DOC surfactant system and the SDS-DOC surfactant system shows that the introduction of nonionic surfactant Tween 60 is beneficial to the separation of higher purity (6,5) tubes.

Finite element framework for static analysis of temperature dependent IHSDT based functionally graded CNT reinforced plates

In this study, a finite element model is presented to investigate the effect of temperature dependent material properties of single-walled carbon nanotube (SWCNT) and PMPV on the static response of functionally graded carbon-nano tube reinforced (FG-CNTR) plate with four different boundary conditions. The governing equations are developed on the basis of inverse hyperbolic shear deformation theory (IHSDT) and Hamilton’s principle. The effective material properties are evaluated using the extended rule of mixture. The pattern of CNTs distribution in the plate is assumed to be uniformly distributed (UD) and functionally graded (FG-V, FG-Λ, FG-O, and FG-X) along the thickness direction. The governing equations are solved using a C0 isoparametric finite element method (FEM) and discretized with an isoparametric eight noded element with seven degrees of freedom per node. The authors have performed various parametric studies to observe the effect of plate span to thickness ratio, volume fraction, CNTs distribution on the static response of FG-CNTR plate subjected to sinusoidal (SSL) and uniformly distributed (UDL) loading conditions. The numerical solutions for the deflection and stresses are obtained and compared with known results in the literature. The study concludes that IHSDT accurately predicts the behavior of the FG-CNTR plate, also temperature dependent material properties have significantly influenced the static behavior of the FG-CNTR plate.

The role of topological defects on the mechanical properties of single-walled carbon nanotubes

ABSTRACT Carbon nanotubes (CNTs) are among the most employed nanomaterials in developing new technologies. Their applicability requires a fundamental understanding of the chirality and defect effects on the mechanical properties. In this study, molecular dynamics (MD) simulations were performed to investigate the mechanical response of defective single-walled carbon nanotubes (SWCNTs) under tension loading. The Stones-Wales, monovacancy, and the divacancy reconstructions (585, 555777, and 555567777) defects were considered. In addition, we investigated the influence of the adaptive intermolecular reactive bond order (AIREBO) potential cut-off radii on the defect formation energy of SWCNTs. Our results reveal that the tensile strength properties are notably dependent on the chirality and defect configurations at strains over 8%. Energetically favourable defects have a high impact on the mechanical response of SWCNTs. A combination of certain defects may lead the control on the fracture pattern of the SWCNTs, which can significantly contribute to the designing of innovative nanostructures with tailored properties.

Development of Quality Control Methods for Dispersibility and Stability of Single-Wall Carbon Nanotubes in an Aqueous Medium.

The attractive properties of single-wall carbon nanotubes (SWCNT) such as mechanical strength and high electrical and thermal conductivity are often undercut by their agglomeration and re-agglomeration tendencies. As a result, the application of SWCNT as additives in advanced composite materials remain far from their potential, with proper dispersion being the major inhibitor. This work presents a dispersion quality control approach for water-based SWCNT dispersions (dispersed by a unique combination of physical and chemical methods), using complementary and easily scalable, characterization methods. UV-Vis spectroscopy, rheological measurements, and precipitant sheet resistance were used to understand the properties of the initial solution through processing and application. From an industrial perspective, these methods are fast and easy to measure while giving a repetitive and quick indication of dispersion quality and stability. The methods were correlated with microscopy and Raman spectroscopy to validate dispersion and SWCNT quality under various dispersing energies. The protocol was then applied to estimate the stability of SWCNT solutions, as well as the effectiveness of different surfactants in aiding dispersion. The simple, fast, and scalable combination of different characterizations provides good SWCNT dispersion and can be used as a quality control system for industrial production and usage.

Nickelocene-Filled Purely Metallic Single-Walled Carbon Nanotubes: Sorting and Tuning the Electronic Properties.

We conducted the filling of single-walled carbon nanotubes (SWCNTs) with nickelocene molecules and separation of the filled SWCNTs by conductivity type by density-gradient ultracentrifugation. We tailored the electronic properties of nickelocene-filled purely metallic SWCNTs by thermal treatment in high vacuum. Our results demonstrated that annealing at low temperatures (360–600 °C) leads to n-doping of SWCNTs, whereas annealing at high temperatures (680–1200 °C) results in p-doping of SWCNTs. We found a correlation between the chemical state of the incorporated substances at different annealing temperatures and its influence on the electronic properties of SWCNTs.

The Effects of Hydrogen Annealing on Carbon Nanotube Field-Effect Transistors.

We have systematically investigated the effects of hydrogen annealing on Ni- and Al-contacted carbon nanotube field-effect transistors (CNTFETs), whose work functions have not been affected by hydrogen annealing. Measured results show that the electronic properties of single-walled carbon nanotubes are modified by hydrogen adsorption. The Ni-contacted CNTFETs, which initially showed metallic behavior, changed their p-FET behavior with a high on-current over 10 µA after hydrogen annealing. The on-current of the as-made p-FETs is much improved after hydrogen annealing. The Al-contacted CNTFETs, which initially showed metallic behavior, showed unipolar p-FET behavior after hydrogen annealing. We analyzed the energy band diagrams of the CNTFETs to explain experimental results, finding that the electron affinity and the bandgap of single-walled carbon nanotubes changed after hydrogen annealing. These results are consistent with previously reported ab initio calculations.

On the role of surface oxygen during nascent single-walled carbon nanotube cap spreading and tube nucleation on iron catalysts

Single-walled carbon nanotubes (SWCNTs) are commonly grown in oxygen-rich environments. The precursor used as input for the SWCNT synthesis reaction typically provides oxygen atoms either as a pure gas or as an oxygen-containing compound. Similarly, metal oxide substrates are used to support the catalysts or as reactor wall materials and can transfer oxygen atoms while in contact with the catalytic particles. It has been proposed and experimentally observed that the interaction of the metal catalyst with specific promoters (e.g., oxygen, sulfur, hydrogen) triggers significant changes in the SWCNT properties during spreading, nucleation and growth. However, very few studies address the carbon-catalyst surface interactions in rich oxygen environments. Here we show that an increased surface oxygen concentration in the neighborhood of a spreading nascent carbon shell reduces the strength of interaction of the carbon shell with the iron catalyst's surface and increases the probability of carbon nucleation and SWCNT lift-off. The evolution of the carbon-surface interaction during the spreading and nucleation phases suggests that closed pentagons at the rim are preferentially formed in oxidized iron surfaces, and they exhibit the strongest and most stable interaction with the iron surface.

Band structure dependent electronic localization in macroscopic films of single-chirality single-wall carbon nanotubes

Significant understanding has been achieved over the last few decades regarding chirality-dependent properties of single-wall carbon nanotubes (SWCNTs), primarily through single-tube studies. However, macroscopic manifestations of chirality dependence have been limited, especially in electronic transport, despite the fact that such distinct behaviors are needed for many applications of SWCNT-based devices. In addition, developing reliable transport theory is challenging since a description of localization phenomena in an assembly of nanoobjects requires precise knowledge of disorder on multiple spatial scales, particularly if the ensemble is heterogeneous. Here, we report an observation of pronounced chirality-dependent electronic localization in temperature and magnetic field dependent conductivity measurements on macroscopic films of single-chirality SWCNTs. The samples included large-gap semiconducting (6,5) and (10,3) films, narrow-gap semiconducting (7,4) and (8,5) films, and armchair metallic (6,6) films. Experimental data and theoretical calculations revealed Mott variable-range-hopping dominated transport in all samples, while localization lengths fall into three distinct categories depending on their band gaps. Armchair films have the largest localization length. Our detailed analyses on electronic transport properties of single-chirality SWCNT films provide significant new insight into electronic transport in ensembles of nanoobjects, offering foundations for designing and deploying macroscopic SWCNT solid-state devices.

Sensing Organophosphorus Compounds with SWCNT Films.

Promising electrical properties of single-walled carbon nanotubes (SWCNTs) open a spectrum of applications for this material. As the SWCNT electronic characteristics respond well to the presence of various analytes, this makes them highly sensitive sensors. In this contribution, selected organophosphorus compounds were detected by studying their impact on the electronic properties of the nanocarbon network. The goal was to untangle the n-doping mechanism behind the beneficial effect of organic phosphine derivatives on the electrical conductivity of SWCNT networks. The highest sensitivity was obtained in the case of the application of 1,6-Bis(diphenylphoshpino)hexane. Consequently, free-standing SWCNT films experienced a four-fold improvement to the electrical conductivity from 272 ± 21 to 1010 ± 44 S/cm and an order of magnitude increase in the power factor. This was ascribed to the beneficial action of electron-rich phenyl moieties linked with a long alkyl chain, making the dopant interact well with SWCNTs.

High‐Performance ITO‐Free Perovskite Solar Cells Enabled by Single‐Walled Carbon Nanotube Films

AbstractThe unprecedented advancement in power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) has rendered them a promising game‐changer in photovoltaics. However, unsatisfactory environmental stability and high manufacturing cost of window electrodes are bottlenecks impeding their commercialization. Here, a strategy is introduced to address these bottlenecks by replacing the costly indium tin oxide (ITO) window electrodes via a simple transfer technique with single‐walled carbon nanotubes (SWCNTs) films, which are made of earth‐abundant elements with superior chemical and environmental stability. The resultant devices exhibit PCEs of ≈19% on rigid substrates, which is the highest value reported to date for ITO‐free PSCs. The facile approach for SWCNTs also enables application in flexible PSCs (f‐PSCs), delivering a PCE of ≈18% with superior mechanical robustness over their ITO‐based counterparts due to the excellent mechanical properties of SWCNTs. The SWCNT‐based PSCs also deliver satisfactory performances on large‐area (1 cm2 active area in this work). Furthermore, these SWCNT‐based PSCs can retain over 80% of original PCEs after exposure to air over 700 h while ITO‐based devices only sustain ≈60% of initial PCEs. This work paves a promising way to accelerate the commercialization of ITO‐free PSCs with reduced material cost and prolonged lifetimes.

Stability, rheology, and thermophysical properties of surfactant free aqueous single-walled carbon nanotubes and graphene nanoplatelets nanofluids: a comparative study

A comparative study, for the first time, was conducted on thermophysical and rheological properties of single-walled carbon nanotubes (SWCNT) and graphene nanoplatelets (GNP) nanofluids. Highly stable aqueous 0.5, 1.0, and 2.0 wt% SWCNT and GNP nanofluids were successfully prepared with no surfactant, through ultrasound technology. The preparation was explained in detail, adjusting pH to around 8 where nanofluids would be expected to be stable. The highest zeta potential of −60.5 mV was obtained for 2.0 wt% SWCNT nanofluids. Shear thinning was observed for all nanofluids at low shear rates. Unlike shear thickening of GNP, Newtonian behavior of SWCNT nanofluids was detected at high shear rate region. The effect of ultrasound technology was directly verified by scanning electron microscopy (SEM), resulting in GNP size reduction and separation of bundles for SWCNT. The results revealed that SWCNT nanofluids showed a remarkable zeta potential value for heat transfer systems compared to GNP nanofluids.