Tubes Of Carbon Nanotubes Research Articles

Investigation of the Pulsing Characteristic of a Carbon Nanotube Emitter.

The carbon nanotube (CNT) field emitter is suitable for the high frequency pulsing of X-ray. Pulsing reduces 49% of the dose in grid-controlled fluoroscopy and improves the image of moving objects. Various structures and manufacturing processes are being studied. However, more studies on the dynamic characteristic of a pulsing CNT and its application are needed. In this study, the combined dynamics including the field emission, MOSFET, and modified gate driver for MOSFET have been analyzed. In this configuration, between the cathode of the tube and ground, there is a MOSFET switch that turns the tube current on/off and a shunt resistor that measures the tube current. Due to the high impedance of the vacuum between the gate and cathode of the tube, about 85% of the gate voltage is still exerted between the Gate and cathode of the tube during the off-state of the MOSFET. Therefore, space charges are built during the off-state and then released at the beginning of the on-state of the MOSFET. The modified gate driver structure for MOSFET that we propose in this paper can limit the amount of current flow through the cathode. Tube current (boosted current) can be accurately controlled through a modified gate driver structure. Combining the boosted current and pulse control of MOSFET, the dynamic current performance of a CNT tube can be enhanced and the average tube current or dose can be accurately controlled. Experiments, simulation, and analysis have been conducted to study the combined dynamics and its applications.

Optimization of CNT and TFT Parameters for Maximum Transconductance and Safe Temperature Operation of Carbon Nanotube Thin-Film Transistors (CNT-TFTs) Employed in Flat Panel Displays

Thin Film Transistors (TFTs) have lived to see its significant technological improvement for various display applications in recent years. Carbon nanotube (CNT) based TFT technologies have been found to be a promising component for next generation flexible electronics and flat panel displays in view of CNTs high carrier mobility, device stability and mechanical flexibility. However, the design of CNT-TFT is still not well established, especially with a view to achieve the best performance still protecting thermal stability. In this study, the authors had analysed the device structure and operation of transistor in which carbon nanotubes act as active channel region. CNT-TFT with different device geometrics and CNT physical parameters such as channel length, channel width, CNT tube length, network density and its orientation have been extensively studied using NanoNet simulation tool. This study has thrown new insight into the device performance characteristics of CNT-TFTs. The results show that it is essential to fix the length of the channel more than 5 µm for restricting the device temperature at 300 K and it can be brought down as low as 3 µm if the maximum operating temperature can be 400 K. Comparison with already reported experimental results show that the TFT parameters returned by the simulation experiments and presented in this paper match closely.

Effects of proton irradiation on structures and photo-catalytic property of nano-TiO2/CNTs films

Thin nano-TiO2 films were prepared using aqueous SILAR (successive ionic layer adsorption and reaction) technique on the carbon nanotubes (CNTs) films using titanium trichloride and water as precursors. TiO2-deposited carbon nanotubes (TiO2/CNTs) films were irradiated with 120 keV proton beam, and then analyzed using Raman spectroscopy (Raman), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and photocatalytic degradation tests. The results indicate that irradiation could transfer the amorphous deposited TiO2 films to a crystalline state, while the CNTs substrate would also be damaged, namely CNT tube diameter shrinkage and the Raman peak ratio of ID/IG decreases with increasing proton fluences. It was also found that the TiO2 modification could result in more damage to the CNTs substrate as the proton fluence is lower. This is largely due to the fact that the process of activation before deposition could cause damage to the CNTs to some degree. It is interested to be noted that proton irradiation would induce the nano-TiO2/CNTs films to show the remarkable photocatalytic degradation behaviors using methylene blue as the test additive. Moreover, the case with thinner TiO2 on CNTs appears relatively better photocatalytic degradation behaviors. The reasons for the change of photocatalytic behaviors may be due to both crystallization of TiO2 layers and carrier trapping effect of CNTs.

Effect of Carbon Nanotubes on Direct Electron Transfer and Electrocatalytic Activity of Immobilized Glucose Oxidase.

Carbon nanotubes (CNTs) are excellent supports for electrocatalysts because of their large surface area, excellent electronic conductivity, and high chemical and structural stability. In the present study, the activity of CNTs on direct electron transfer (DET) and on immobilized glucose oxidase (GOX) is studied as a function of number of walls of CNTs. The results indicate that the GOX immobilized by the CNTs maintains its electrocatalytic activity toward glucose; however, the DET and electrocatalytic activity of GOX depend strongly on the number of inner tubes of CNTs. The GOX immobilized on triple-walled CNTs (TWNTs) has the highest electron-transfer rate constant, 1.22 s–1, for DET, the highest sensitivity toward glucose detection, 66.11 ± 5.06 μA mM–1 cm–2, and the lowest apparent Michaelis–Menten constant, 6.53 ± 0.58 mM, as compared to GOX immobilized on single-walled and multiwalled CNTs. The promotion effect of CNTs on the GOX electrocatalytic activity and DET is most likely due to the electron-tunneling effect between the outer wall and inner tubes of TWNTs. The results of this study have general implications for the fundamental understanding of the role of CNT supports in DET processes and can be used for the better design of more effective electrocatalysts for biological processes including biofuel cells and biosensors.

1D-2D carbon heterostructure with low Pt loading as a superior cathode electrode for dye-sensitized solar cell

Cost-effective counter electrode (CE) with high electrocatalytic performance is very much essential for the wide application of dye-sensitized solar cells (DSSC). The 1D-2D carbon heterostructure (Pt/GR@CNT) with low platinum (Pt) loading has been synthesized by a facile in situ microwave-assisted polyol-reduction method. The excellent electrocatalytic activity as well as photovoltaic performance was achieved due to the combination of 2D graphene nanoribbons (GR) and 1D multi-walled carbon nanotubes (CNT) with high catalytically active Pt nanoparticles. Microwave-assisted longitudinal unzipping of few outer layers of CNTs along with co-reduction of Pt nanoparticles is an effective method to create electrochemically active defective edge sites, which have a crucial role in enhancing electrochemical performance. Synergistic effect of ultra-fine Pt nanoparticles, partially unzipped graphene nanoribbons and inner core tubes of CNTs modulates the power conversion efficiency of solar cell to 5.57% ± 0.03 as compared with 4.73% ± 0.13 of CNTs. Pt/GR@CNT CE even with low Pt loading of 14 μg cm−2 showcases equivalent performance with that of pure Pt counter electrode.

Influence of Carbon Nanotubes on Morphology of Asphalts Modified with Styrene–Butadiene–Styrene

The main challenge of asphalt modified with styrene–butadiene–styrene (SBS) during storage and application is the phase separation of SBS-rich phases and asphaltene-rich phases. These phases have a close relationship with the morphology of SBS-modified asphalt [SBS–polymer-modified binders (PMBs)]. Carbon nanotubes (CNTs) were selected in this paper to provide different morphology of SBS-PMBs with CNTs. The morphology was composed of SBS-rich phases, asphaltene-rich phases, and their interphase, captured from fluorescence microscopy (FM), atomic force microscopy (AFM), and scanning electron microscopy (SEM). The components and morphologies of the interface on a molecular scale were obtained by molecular dynamic simulation. The results from FM images showed an increase in the relative content of SBS-rich phases as the amount of CNTs increased, highlighting CNTs’ positive role in the compatibility of SBS and asphalt. Mixing CNTs with a mechanical stirrer provided a larger size of SBS-rich phases than that of SBS-PMBs in AFM images using an ultrasound performed on an interpenetration network of AFM and FM images, whereas mixing with an extruding machine resulted in an orange-skin morphology in FM images. The results from SEM demonstrated that CNTs changed the interface of SBS-PMBs by pullout behaviors. The results from the molecular dynamic simulation showed that SBS intertwined or surrounded CNTs to improve their interaction. Saturate, aromatic, and resin were absorbed into the tube of CNTs. Therefore, CNTs had a positive action on the interaction between SBS and asphalt because they acted as a bridge to link the different phases, finally reinforcing the interface of SBS-PMBs.

Characterization of Doubled Walled Carbon Nanotubes using Finite Element Method

composites will be developed using carbon nanotubes (CNTs). When compared with the conventional carbon fibers, CNTs in polymer matrices enhance the stiffness and strength of composites. The work is focused on the Double walled carbon nanotubes (DWCNTs) to investigate the mechanical properties. Modulus of elasticity is considered to analyze the behavior of CNTs by adopting the Finite element model (FEM). The experiments conducted on both armchair and zig- zag Nanotubes. By considering the length and radius of the inner and outer tubes of CNTs, the developed stress with the applied load, strain and young's modulus and its response to the load applied is estimated using FEM. The influence of external vibrations on the CNTs considerably minimized with significant stiffness constant (K) of the CNTs. The results obtained are supportive to analyze the behavior of CNTs. KeywordsDWCNTs, FEM, Stress, strain, young's modulus.

Elucidating the local interfacial structure of highly photoresponsive carbon nanotubes/PbS-QDs based nanohybrids grown by pulsed laser deposition

Carbon nanotubes (CNTs)/lead sulfide (PbS) quantum dots (QDs) nanohybrids have been synthesized through the controlled decoration of CNTs by PbS-QDs by means of the pulsed laser deposition technique. The size of the PbS-QDs and their surface coverage of the CNTs' surface are monitored through the number of laser ablation pulses. Here, while comparing both single-walled (SW) and double-walled (DW) CNTs based nanohybrids, focus is put on the investigation of their interfacial structure and the effect of inner tube. Anchoring PbS through direct sulfur-carbon chemical bonding between CNTs' outer wall and PbS-QDs, which are thought to be profitable for efficient charge transfer but not for charge transport along CNT's tube axis, are confirmed by Raman spectroscopy and X-ray photoelectron spectroscopy. In the case of double-walled CNTs (DWCNTs), inner tube remains unaffected by ablated PbS species, then it serves efficient conduction way for transferred photo-generated charges. This unique feature of the DWCNTs based nanohybrid, where the photocharges are generated by the chemically bonded PbS-QDs to the outer tube and then efficiently conveyed by the inner tube of the nanotubes, is highly likely at the origin of their significantly higher photo-activity (several hundred times than in SWCNTs-based nanohybrids).

Carbon-Nanotubes-Supported Pd Nanoparticles for Alcohol Oxidations in Fuel Cells: Effect of Number of Nanotube Walls on Activity.

Carbon nanotubes (CNTs) are well known electrocatalyst supports due to their high electrical conductivity, structural stability, and high surface area. Here, we demonstrate that the number of inner tubes or walls of CNTs also have a significant promotion effect on the activity of supported Pd nanoparticles (NPs) for alcohol oxidation reactions of direct alcohol fuel cells (DAFCs). Pd NPs with similar particle size (2.1-2.8 nm) were uniformly assembled on CNTs with different number of walls. The results indicate that Pd NPs supported on triple-walled CNTs (TWNTs) have the highest mass activity and stability for methanol, ethanol, and ethylene glycol oxidation reactions, as compared to Pd NPs supported on single-walled and multi-walled CNTs. Such a specific promotion effect of TWNTs on the electrocatalytic activity of Pd NPs is not related to the contribution of metal impurities in CNTs, oxygen-functional groups of CNTs or surface area of CNTs and Pd NPs. A facile charge transfer mechanism via electron tunneling between the outer wall and inner tubes of CNTs under electrochemical driving force is proposed for the significant promotion effect of TWNTs for the alcohol oxidation reactions in alkaline solutions.

Sheet resistance, transmittance, and chromatic property of CNTs coated with PEDOT:PSS films for transparent electrodes of touch screen panels

This study demonstrates hybrid-type transparent electrodes based on carbon nanotubes (CNTs) that possess characteristics desirable for touch screen panels. This has been accomplished by depositing CNTs via spray-coating and then depositing thin conductive polymer (such as PEDOT:PSS) films on the CNTs via spin-coating. For all of the samples such as CNTs, PEDOT:PSS, and hybrid (i.e., PEDOT:PSS-coated CNTs), their surface morphologies, sheet resistances, visible transmittances, and chromatic properties are characterized as functions of their preparation conditions. In the PEDOT:PSS-coated CNTs, the PEDOT:PSS particles fill up the voids between tubes in CNTs, forming a conduction bridge for electron transfer and eventually decreasing the sheet resistance of the hybrid electrode. Also, the hybrid electrode reveals a superior color property compared with that of CNTs or the PEDOT:PSS single electrode due to the complementary color relation between CNTs and PEDOT:PSS. Experimental results show that the fabricated hybrid-type electrodes can simultaneously satisfy the requirements necessary for transparent electrodes of touch screen panels such as the sheet resistance requiring to be lower than 100Ω/sq, visible transmittance higher than 80%, and yellowness approaching to zero.

Rectangular Fixed-Gantry CT Prototype: Combining CNT X-Ray Sources and Accelerated Compressed Sensing-Based Reconstruction

Carbon nanotube (CNT)-based multibeam X-ray tubes provide an array of individually controllable X-ray focal spots. The CNT tube allows for flexible placement and distribution of X-ray focal spots in a system. Using a CNT tube, a computed tomography (CT) system with a noncircular geometry and a nonrotating gantry can be created. The noncircular CT geometry can be optimized around a specific imaging problem, utilizing the flexibility of CNT multibeam X-ray tubes to achieve the optimal focal spot distribution for the design constraints of the problem. Iterative reconstruction algorithms provide flexible CT reconstruction to accommodate the noncircular geometry. Compressed sensing-based iterative reconstruction algorithms apply a sparsity constraint to the reconstructed images that can partially account for missing angular coverage due to the noncircular geometry. In this paper, we present a laboratory prototype CT system that uses CNT multibeam X-ray tubes; a rectangular, nonrotating imaging geometry; and an accelerated compressed sensing-based iterative reconstruction algorithm. We apply a total variation minimization as our sparsity constraint. We present the advanced CNT multibeam tubes and show the stability and flexibility of these new tubes. We also present the unique imaging geometry and discuss the design constraints that influenced the specific system design. The reconstruction method is presented along with an overview of the acceleration of the algorithm to near real-time reconstruction. We demonstrate that the prototype reconstructed images have image quality comparable with a conventional CT system. The prototype is optimized for airport checkpoint baggage screening, but the concepts developed may apply to other application-specific CT imaging systems.

Symmetries and fuzzy symmetries of Carbon nanotubes

Carbon nanotubes (CNTs) possess the fuzzy cylinder group characteristic. Comparing with the linear and planer molecules, there are included the fuzzy symmetry of the cylinder screw rotation (CSR) in relation to some higher ( $$>$$ 2) fold rotation axis. The CSR may be noted as the product of translation (T) and rotation (C). The CSR symmetry will be imperfect owing to the introduction of T. As the extent of whole translation is more than 10-fold than every time, the membership function of CNT in relation to CSR will be more than about 0.9, and such CNT may be seems as provided with the perfect CSR symmetry. For analyse the CNT we may using the cylindrical orthogonal curvilinear coordinate system. The MO ought to be provided with a pure irreducible representation, but the component of symmetry adapted atomic orbital (SA-AO) set may be not sole, and it is difficult to get and analyse the ‘pure’ $$\uppi $$ -MO. There are some various AO (1S-, 2S-, 2Pz-, 2Pr-, 2Pt of carbon and 1S- for hydrogen)-set components in a certain MO. For the CNT with the same diameter and different length, the MO energy and the SA-AO component versus the relative serial number will be with the similar distribution. The MOs of CNT with higher fold C symmetry may be provided with two-dimensional irreducible representation. For the molecular skeleton and the MO which belong to one-dimensional irreduable representation, their membership functions in relation to the CSR with the product of the same T and different C would be equality. However, for the single MO which belong to two-dimensional irreducible representation that may be somewhat difference. The torus carbon nanotube (TCNT) may be provided the symmetry with the torus group and torus screw rotation (TSR), such symmetry would be or near be not rare in nature. Similar as the planer rectangle (called as the MH rectangle) may composed the Huckel- or Mobius-strip band, the more MH rectangles in the cylinder CNT may be composed the more Huckel- or Mobius-strip bands, such strip bands set may be called strip tube, meanwhile the fuzzy CSR symmetry will be transform to the perfect TSR symmetry. The intersecting line (Z-axis) of the MH rectangles will be transform to the common basic circle of these strip bands. When the CNT to form a TCNT, as one of the MH rectangle form a Huckel-strip band or an $$n(t)$$ -twisted Mobius-strip band itself, the other MH rectangle will be form the strip band with the same topological structure synchronously, and the set of these strip bands may be called the strip tube. The boundary closed curves of the strip band may reflect the torus group symmetrical characteristic of the relative strip bands. The closed curve may correspond to a cyclical group or subgroup. The number of carbon atomic pairs on the closed curve denoted the order of such group or subgroup. As the CNT to form the TCNT, it is different as the single MH rectangle, they may be to form the fractal-twisted Mobius-strip tube synchronously, in which the single Mobius-strip band may be formed from more one MH rectangle, however, single MH rectangle may enter into only one Mobius-strip band. As the hetero-CNT with the helical-structure distribution, such hetero-CNT may form the relative torus hetero-CNT, but according to the continuity of CNT tube side, a certain twisted to form Mobius-strip tube may often be required. There is some interaction between the distributional helical-structure and twisting way, such interaction may touch to the degree of tightness of the helical-structure distribution in torus hetero-CNT.

Pronounced field emission from vertically aligned carbon nanotube blocks and bundles

Field emission from aligned carbon nanotube (CNT) blocks and bundles grown by two different chemical vapor deposition (CVD) methods were investigated. A single CNT block consists of about 1600 double-walled nanotubes per μm2 of area with an intertube distance in the range 15–20 nm, while a bundle consists of a few multiwalled CNTs, which contact each other in the tip region. Hydrogen/water assisted catalytic CVD on a silicon wafer resulted in ultrahigh aspect ratios for the CNT blocks with extremely high field enhancement coefficients >11 000, a turn-on field of 0.36 V/μm, and good field emission stability. The water and hydrogen concentration ratio were found to be a critical parameter for establishing high quality, ultralong (up to 2 mm) CNT growth. The second CVD growth method used was a noncatalytic template assisted technique for bundle generation. Special self-organized anodic alumina films controlled the synthesis of highly aligned carbon nanotube arrays with the desired tube geometry and adjustable intertube distances. The CNT bundle generation was adjusted by the CNT tube diameter, wall thickness, and length-controlled growth. Subsequent etching of the Al2O3 template resulted in substrateless flexible CNT bundles permitting simple gate electrode integration process. Field emission tests showed that the field enhancement factor, turn-on field, and field emission current density of the CNT cathode arrays could be optimized by adjusting the block or bundle distance. The authors obtained, for the block emitter, a smaller turn-on field and better stability. The block emitter with the better performance was additionally coated with CVD grown ZnO nanoparticles to obtain further improvement. The ZnO nanoparticle diameter was in the range of 15–20 nm. First results showed partial clustering of the ZnO particles suggesting the need for further optimization of the deposition.

Molecular mechanics investigations of carbon nanotube and graphene sheet interaction

The interaction between a carbon nanotube (CNT) and a graphene sheet is investigated to describe the contact properties between a CNT atomic force microscope (AFM) tip and a graphite surface. The energy of the whole system is calculated using $\text{MM}+$ molecular mechanical modeling. With the numerical calculations, one explores the sliding motion of the CNT on the graphene sheet either at the CNT apex or with a given CNT length contacting the surface. The aim is to mimic the AFM CNT tip scanning a graphite surface. To do so we calculate the energy barriers, the tips have to overcome to achieve a full translation. The results show that the barrier heights markedly depend on the contact length between the CNT and the graphene but show a weak dependence, if any, on the CNT tube diameter.

A Paradigm of Carbon Nanotube Interconnects in Microelectronic Packaging

Carbon nanotube (CNT) arrays/films were transferred onto copper substrates via eutectic tin/lead (SnPb) solder pastes. The morphologies, thermal stabilities, adhesion to substrates, and electrical properties of the as-transferred CNT arrays were studied. The CNT arrays generated negligible expansion or contraction below 250°C. The adhesion of CNT arrays to the substrate was significantly improved by the transfer process. An ohmic contact was formed between the transferred CNT arrays and the Sn-Pb solder. Four-probe electrical measurements yielded the resistance of the as-transferred CNT films under the electrode to be around 0.0056 Ω, from which the resistivity of each individual CNT tube was calculated to be 2.44 × 10−4 Ω cm.

Microwave-assisted acid digestion of alumina-supported carbon nanotubes

Microwave-assisted acid digestion was assessed for the purification of carbon nanotubes (CNTs), synthesised in a fluidised-bed by chemical vapour deposition (CVD) on alumina-supported catalysts. The effects of (i) digestion time (10, 20 or 30 min), (ii) temperature (120, 180 or 230 °C) and (iii) acid type (HNO 3, 12.8 mol/L or H 2SO 4, 4.4 mol/L) were investigated. Thermogravimetric analysis (TGA) results show that CNT purity increases with increasing digestion time and temperature, from 2.6 wt% in the as-synthesised bed material to 67.9 wt% for samples treated at 230 °C in H 2SO 4 for 30 min. Raman spectra show bands corresponding to disordered and sp 2-bonded crystalline graphitic carbon at approximately 1350 and 1580 cm −1 respectively. These Raman results further suggest that microwave-assisted purification is effective at removing amorphous carbon and defects from the outer CNT tube walls. TEM and HRTEM images suggest that CNTs are able to exist in contact with strong oxidizing acids at high temperatures in a microwave, and in particular, that it causes no damage to the CNT walls. Microwave-assisted acid digestion is able to achieve comparatively high purity from low-quality feedstocks in less than 30 min.

Adsorption of microcystins by carbon nanotubes

The production of cyanobacterial toxins microcystins (MCs) by cyanobacterial bloom which may promote the growth of tumor in human liver is a growing environmental problem worldwide. In this paper, the adsorption of MC-RR and LR, which were extracted from cyanobacterial cells in Dianchi Lake in China, by carbon nanotubes (CNTs), wood-based activated carbon (ACs) and clays were investigated. Compared with ACs and clay materials of sepiolite, kaolinite and talc tested, CNTs were found to have a strong ability in the adsorption of MCs. At the concentrations of 21.5 mg l −1 MC-RR and 9.6 mg l −1 MC-LR in 50 mmol phosphate buffer solution (pH 7.0), the adsorption amounts of MCs by CNTs with the range of outside diameter from 2 to 10 nm were 14.8 and 5.9 mg g −1, which were about four times higher than those by other adsorbents tested. It was shown that with the decrease of CNTs outside diameters from 60 to 2 nm, the adsorption amount of MCs was apparently increased, however the size of CNTs particles formed in solution declined. This result implies that the size of CNTs tube pore that is fit for the molecular dimension of MCs plays a dominant role. Furthermore the specific surface area of CNTs was also found to be a factor in the adsorption of MCs. The results suggested that the selection of suitable size of CNTs as a kind of adsorbent is very important in the efficient eliminating MCs from drinking water in future.