Showing papers on "Nanotube published in 2009"
TL;DR: It is reported that vertically aligned nitrogen-containing carbon nanotubes (VA-NCNTs) can act as a metal-free electrode with a much better electrocatalytic activity, long-term operation stability, and tolerance to crossover effect than platinum for oxygen reduction in alkaline fuel cells.
Abstract: The large-scale practical application of fuel cells will be difficult to realize if the expensive platinum-based electrocatalysts for oxygen reduction reactions (ORRs) cannot be replaced by other efficient, low-cost, and stable electrodes. Here, we report that vertically aligned nitrogen-containing carbon nanotubes (VA-NCNTs) can act as a metal-free electrode with a much better electrocatalytic activity, long-term operation stability, and tolerance to crossover effect than platinum for oxygen reduction in alkaline fuel cells. In air-saturated 0.1 molar potassium hydroxide, we observed a steady-state output potential of –80 millivolts and a current density of 4.1 milliamps per square centimeter at –0.22 volts, compared with –85 millivolts and 1.1 milliamps per square centimeter at –0.20 volts for a platinum-carbon electrode. The incorporation of electron-accepting nitrogen atoms in the conjugated nanotube carbon plane appears to impart a relatively high positive charge density on adjacent carbon atoms. This effect, coupled with aligning the NCNTs, provides a four-electron pathway for the ORR on VA-NCNTs with a superb performance.
6,370 citations
TL;DR: The capacity in a Li-ion full cell consisting of a cathode of LiCoO2 and anode of Si nanotubes demonstrates a 10 times higher capacity than commercially available graphite even after 200 cycles.
Abstract: We present Si nanotubes prepared by reductive decomposition of a silicon precursor in an alumina template and etching. These nanotubes show impressive results, which shows very high reversible charge capacity of 3247 mA h/g with Coulombic efficiency of 89%, and also demonstrate superior capacity retention even at 5C rate (=15 A/g). Furthermore, the capacity in a Li-ion full cell consisting of a cathode of LiCoO2 and anode of Si nanotubes demonstrates a 10 times higher capacity than commercially available graphite even after 200 cycles.
1,407 citations
TL;DR: In this paper, a method was proposed to identify and purify all 12 major single-chirality semiconducting species from a synthetic mixture of carbon nanotubes, with sufficient yield for both fundamental studies and application development.
Abstract: Single-walled carbon nanotubes (SWNTs) are a family of molecules that have the same cylindrical shape but different chiralities. Many fundamental studies and technological applications of SWNTs require a population of tubes with identical chirality that current syntheses cannot provide. The SWNT sorting problem-that is, separation of a synthetic mixture of tubes into individual single-chirality components-has attracted considerable attention in recent years. Intense efforts so far have focused largely on, and resulted in solutions for, a weaker version of the sorting problem: metal/semiconductor separation. A systematic and general method to purify each and every single-chirality species of the same electronic type from the synthetic mixture of SWNTs is highly desirable, but the task has proven to be insurmountable to date. Here we report such a method, which allows purification of all 12 major single-chirality semiconducting species from a synthetic mixture, with sufficient yield for both fundamental studies and application development. We have designed an effective search of a DNA library of approximately 10(60) in size, and have identified more than 20 short DNA sequences, each of which recognizes and enables chromatographic purification of a particular nanotube species from the synthetic mixture. Recognition sequences exhibit a periodic purine-pyrimidines pattern, which can undergo hydrogen-bonding to form a two-dimensional sheet, and fold selectively on nanotubes into a well-ordered three-dimensional barrel. We propose that the ordered two-dimensional sheet and three-dimensional barrel provide the structural basis for the observed DNA recognition of SWNTs.
1,031 citations
TL;DR: Efficient solar conversion of carbon dioxide and water vapor to methane and other hydrocarbons is achieved using nitrogen-doped titania nanotube arrays, with a wall thickness low enough to facilitate effective carrier transfer to the adsorbing species, surface-loaded with nanodimensional islands of cocatalysts platinum and/or copper.
Abstract: Efficient solar conversion of carbon dioxide and water vapor to methane and other hydrocarbons is achieved using nitrogen-doped titania nanotube arrays, with a wall thickness low enough to facilitate effective carrier transfer to the adsorbing species, surface-loaded with nanodimensional islands of cocatalysts platinum and/or copper. All experiments are conducted in outdoor sunlight at University Park, PA. Intermediate reaction products, hydrogen and carbon monoxide, are also detected with their relative concentrations underlying hydrocarbon production rates and dependent upon the nature of the cocatalysts on the nanotube array surface. Using outdoor global AM 1.5 sunlight, 100 mW/cm(2), a hydrocarbon production rate of 111 ppm cm(-2) h(-1), or approximately 160 microL/(g h), is obtained when the nanotube array samples are loaded with both Cu and Pt nanoparticles. This rate of CO(2) to hydrocarbon production obtained under outdoor sunlight is at least 20 times higher than previous published reports, which were conducted under laboratory conditions using UV illumination.
982 citations
TL;DR: In this paper, the authors review various aspects of fabrication, characterization, device implementation and operation of carbon nanotube-polymer composites to be used in photonic applications.
Abstract: Polymer composites are one of the most attractive near-term means to exploit the unique properties of carbon nanotubes and graphene. This is particularly true for composites aimed at electronics and photonics, where a number of promising applications have already been demonstrated. One such example is nanotube-based saturable absorbers. These can be used as all-optical switches, optical amplifier noise suppressors, or mode-lockers to generate ultrashort laser pulses. Here, we review various aspects of fabrication, characterization, device implementation and operation of nanotube-polymer composites to be used in photonic applications. We also summarize recent results on graphene-based saturable absorbers for ultrafast lasers.
959 citations
TL;DR: The reversible capacity of the battery was increased by an order compared to template grown MnO2 nanotubes, making them suitable electrodes for advanced Li ion batteries.
Abstract: Coaxial manganese oxide/carbon nanotube (CNT) arrays deposited inside porous alumina templates were used as cathodes in a lithium battery. Excellent cyclic stability and capacity of MnO2/CNT coaxial nanotube electrodes resulted from the hybrid nature of the electrodes with improved electronic conductivity and dual mechanism of lithium storage. The reversible capacity of the battery was increased by an order compared to template grown MnO2 nanotubes, making them suitable electrodes for advanced Li ion batteries.
932 citations
TL;DR: In this article, the properties of anodically formed semiconducting TiO2 nanotubes as well as nanowire arrays as electrodes for oxidative photoelectrochemistry were discussed.
Abstract: In this article, we present recent advances that we have achieved toward improving the properties of anodically formed semiconducting TiO2 nanotubes as well as nanowire arrays as electrodes for oxidative photoelectrochemistry. The morphology, crystallinity, composition, and illumination geometry of nanotube or nanowire arrays are critical factors in their performance as photoelectrodes. We discuss the key aspects relating to each factor and the advances achieved in improving each. With respect to the more fully investigated nanotube arrays, the ability to control the morphological parameters such as pore size, tube length, and wall thickness of the nanotube architecture has enabled high performance in applications such as water photoelectrolysis, photocatalysis, dye-sensitized solar cells, and heterojunction TiO2−polymer hybrid solar cells. We begin by reviewing the photoelectrochemical performance of state-of-the-art nanotube arrays fabricated on planar substrates. We then present more recent results rel...
765 citations
TL;DR: The fabrication of transparent titania nanotube array films on transparent conducting oxide glass with lengths between 0.3 and 33.0 microm using a novel electrochemistry approach is reported.
Abstract: Dye-sensitized solar cells consist of a random network of titania nanoparticles that serve both as a high-surface-area support for dye molecules and as an electron-transporting medium. Despite achieving high power conversion efficiencies, their performance is limited by electron trapping in the nanoparticle film. Electron diffusion lengths can be increased by transporting charge through highly ordered nanostructures such as titania nanotube arrays. Although titania nanotube array films have been shown to enhance the efficiencies of both charge collection and light harvesting, it has not been possible to grow them on transparent conducting oxide glass with the lengths needed for high-efficiency device applications (tens of micrometres). Here, we report the fabrication of transparent titania nanotube array films on transparent conducting oxide glass with lengths between 0.3 and 33.0 µm using a novel electrochemistry approach. Dye-sensitized solar cells containing these arrays yielded a power conversion efficiency of 6.9%. The incident photon-to-current conversion efficiency ranged from 70 to 80% for wavelengths between 450 and 650 nm. Transparent films of titania nanotubes up to 30-μm long are fabricated on transparent conducting oxide glass, and used to make dye-sensitized solar cells.
726 citations
TL;DR: In this article, the use of HNO3, H2SO4 and H2O2 at relatively low concentrations, short treatment times and low sonication power, in an attempt to achieve experimental conditions which efficiently functionalize the surface of multiwalled CNTs minimizing nanotube damage.
540 citations
TL;DR: Large diameter nanotubes, in the approximately 100 nm regime, induced extremely elongated cellular shapes, with an aspect ratio of 11:1, which resulted in substantially enhanced up-regulation of alkaline phosphatase activity, suggesting greater bone-forming ability than nanot tubes with smaller diameters.
539 citations
TL;DR: Carbon nanotube aerogel sheets are the sole component of new artificial muscles that provide giant elongations and elongation rates of 220% and (3.7 × 104)% per second, respectively, at operating temperatures from 80 to 1900 kelvin.
Abstract: Improved electrically powered artificial muscles are needed for generating force, moving objects, and accomplishing work. Carbon nanotube aerogel sheets are the sole component of new artificial muscles that provide giant elongations and elongation rates of 220% and (3.7 x 10(4))% per second, respectively, at operating temperatures from 80 to 1900 kelvin. These solid-state-fabricated sheets are enthalpic rubbers having gaslike density and specific strength in one direction higher than those of steel plate. Actuation decreases nanotube aerogel density and can be permanently frozen for such device applications as transparent electrodes. Poisson's ratios reach 15, a factor of 30 higher than for conventional rubbers. These giant Poisson's ratios explain the observed opposite sign of width and length actuation and result in rare properties: negative linear compressibility and stretch densification.
TL;DR: In this paper, a simple sonoelectrochemical anodization method was proposed to grow smooth and ultrathin (5−7 nm thick) Fe2O3 nanotube arrays (3−4 μm long) on Fe foil in as little as 13 min.
Abstract: One-dimensional nanostructures exhibit quantum confinement that leads to unique electronic properties, making them attractive as the active elements for various applications. Iron oxide (α-Fe2O3 or hematite) nanotubes are of particular interest in catalysis, sensor devices, Li-ion battery, environmental remediation and photocatalysis. Here, we report a simple sonoelectrochemical anodization method to grow smooth and ultrathin (5−7 nm thick) Fe2O3 nanotube arrays (3−4 μm long) on Fe foil in as little as 13 min. The prepared catalyst has shown tremendous potential to split water to generate hydrogen under solar light illumination. A photocurrent density of 1.41 mA/cm2 is observed for hematite nanotube arrays with more than 50% being contributed by the visible light components of the solar spectrum.
TL;DR: This work has achieved solution-based assembly of separated nanotube thin films on complete 3 in.
Abstract: Preseparated, semiconductive enriched carbon nanotubes hold great potential for thin-film transistors and display applications due to their high mobility, high percentage of semiconductive nanotubes, and room-temperature processing compatibility. Here in this paper, we report our progress on wafer-scale processing of separated nanotube thin-film transistors (SN-TFTs) for display applications, including key technology components such as wafer-scale assembly of high-density, uniform separated nanotube networks, high-yield fabrication of devices with superior performance, and demonstration of organic light-emitting diode (OLED) switching controlled by a SN-TFT. On the basis of separated nanotubes with 95% semiconductive nanotubes, we have achieved solution-based assembly of separated nanotube thin films on complete 3 in. Si/SiO2 wafers, and further carried out wafer-scale fabrication to produce transistors with high yield (>98%), small sheet resistance (∼25 kΩ/sq), high current density (∼10 μA/μm), and super...
TL;DR: Amphiphilic TiO(2) nanotube arrays are fabricated by a two-step anodization procedure combined with hydrophobic monolayer modification after the first step to provide an efficient cap against drug leaching to the environment.
Abstract: Amphiphilic TiO(2) nanotube arrays are fabricated by a two-step anodization procedure combined with hydrophobic monolayer modification after the first step. These tubes can be used as biomolecular carriers, where the outer hydrophobic barrier provides an efficient cap against drug leaching to the environment. By utilizing the photocatalytic ability of TiO(2), a precisely controlled removal of the cap and a highly controlled release of the hydrophilic payload (drug) can be achieved.
TL;DR: In this article, the interfacial shear strength of carbon nanotube (CNT) coated carbon fibers in epoxy was studied using the single-fiber composite fragmentation test.
TL;DR: A high-quality mechanical resonator made from a suspended carbon nanotubes driven into motion by applying a periodic radio frequency potential using a nearby antenna was studied, and it was discovered that a direct current through the nanotube spontaneously drives the mechanical resonators, exerting a force that is coherent with the high-frequency resonant mechanical motion.
Abstract: Nanoscale resonators that oscillate at high frequencies are useful in many measurement applications. We studied a high-quality mechanical resonator made from a suspended carbon nanotube driven into motion by applying a periodic radio frequency potential using a nearby antenna. Single-electron charge fluctuations created periodic modulations of the mechanical resonance frequency. A quality factor exceeding 10 5 allows the detection of a shift in resonance frequency caused by the addition of a single-electron charge on the nanotube. Additional evidence for the strong coupling of mechanical motion and electron tunneling is provided by an energy transfer to the electrons causing mechanical damping and unusual nonlinear behavior. We also discovered that a direct current through the nanotube spontaneously drives the mechanical resonator, exerting a force that is coherent with the high-frequency resonant mechanical motion.
TL;DR: It is proposed that neither Hildebrand nor Hansen solubility parameters are fundamental quantities when it comes to nanotube-solvent interactions, and it is confirmed that successful solvents occupy a well-defined range of Hansen parameter space.
Abstract: We have measured the dispersibility of single-walled carbon nanotubes in a range of solvents, observing values as high as 3.5 mg/mL. By plotting the nanotube dispersibility as a function of the Hansen solubility parameters of the solvents, we have confirmed that successful solvents occupy a well-defined range of Hansen parameter space. The level of dispersibility is more sensitive to the dispersive Hansen parameter than the polar or H-bonding Hansen parameter. We estimate the dispersion, polar, and hydrogen bonding Hansen parameter for the nanotubes to be = 17.8 MPa(1/2), = 7.5 MPa(1/2), and = 7.6 MPa(1/2). We find that the nanotube dispersibility in good solvents decays smoothly with the distance in Hansen space from solvent to nanotube solubility parameters. Finally, we propose that neither Hildebrand nor Hansen solubility parameters are fundamental quantities when it comes to nanotube-solvent interactions. We show that the previously calculated dependence of nanotube Hildebrand parameter on nanotube diameter can be reproduced by deriving a simple expression based on the nanotube surface energy. We show that solubility parameters based on surface energy give equivalent results to Hansen solubility parameters. However, we note that, contrary to solubility theory, a number of nonsolvents for nanotubes have both Hansen and surface energy solubility parameters similar to those calculated for nanotubes. The nature of the distinction between solvents and nonsolvents remains to be fully understood.
TL;DR: In this paper, the transversal vibration mode of suspended carbon nanotubes at millikelvin temperatures was observed by measuring the single-electron tunneling current through the nanotube.
Abstract: We have observed the transversal vibration mode of suspended carbon nanotubes at millikelvin temperatures by measuring the singleelectron tunneling current. The suspended nanotubes are actuated contact-free by the radio frequency electric field of a nearby antenna; the mechanical resonance is detected in the time-averaged current through the nanotube. Sharp, gate-tunable resonances due to the bending mode of the nanotube are observed, combining resonance frequencies of up to ν0 ) 350 MHz with quality factors above Q ) 10 5 , much higher than previously reported results on suspended carbon nanotube resonators. The measured magnitude and temperature dependence of the Q factor shows a remarkable agreement with the intrinsic damping predicted for a suspended carbon nanotube. By adjusting the radio frequency power on the antenna, we find that the nanotube resonator can easily be driven into the nonlinear regime.
TL;DR: Sharp, gate-tunable resonances due to the bending mode of the nanotubes are observed, combining resonance frequencies of up to nu(0) = 350 MHz with quality factors above Q = 10(5), much higher than previously reported results on suspended carbon nanotube resonators.
Abstract: We have observed the transversal vibration mode of suspended carbon nanotubes at millikelvin temperatures by measuring the single-electron tunneling current. The suspended nanotubes are actuated contact-free by the radio frequency electric field of a nearby antenna; the mechanical resonance is detected in the time-averaged current through the nanotube. Sharp, gate-tuneable resonances due to the bending mode of the nanotube are observed, combining resonance frequencies of up to
u_0 = 350 MHz with quality factors above Q = 10^5, much higher than previously reported results on suspended carbon nanotube resonators. The measured magnitude and temperature dependence of the Q-factor shows a remarkable agreement with the intrinsic damping predicted for a suspended carbon nanotube. By adjusting the RF power on the antenna, we find that the nanotube resonator can easily be driven into the non-linear regime.
TL;DR: In this article, a comparative study of conductive, free-standing, binder-free flexible films made from three different types of commercial carbon nanotubes (CNTs) was carried out.
TL;DR: TiN nanotube arrays, prepared by the anodization of metallic Ti foil substrate and subsequent simple nitridation in an ammonia atmosphere, were investigated as low-cost counter electrodes in dye-sensitized solar cells for the first time.
TL;DR: In this article, a glucose biosensor is fabricated with immobilization of glucose oxidase onto ZnO nanotube arrays by cross-linking method, which has a wide linear range for the detection of glucose from 50μM to 12mM with 3 s response time.
Abstract: A glucose biosensor is fabricated with immobilization of glucose oxidase onto ZnO nanotube arrays by cross-linking method. The ZnO nanotube arrays are synthesized by chemical etching of ZnO nanorods that are electrochemically deposited on the Au surface. Morphology and structure of ZnO nanotubes are characterized by FESEM, HRTEM and XRD. Fourier-transform infrared spectroscopy reveals that the glucose oxidase immobilized on the ZnO nanotubes retains its native conformation. The biosensor has a wide linear range for the detection of glucose from 50 μM to 12 mM (a correlation coefficient of 0.998) with 3 s response time. The sensitivity of the biosensor is found to be 21.7 μA/mM cm 2 . Moreover, its experimental detection limit is 1 μM (S/N = 3) and the apparent Michaelis–Menten constant is calculated to be 19 mM. The anti-interference ability and long-term stability of the biosensor are also assessed. Compared with the biosensors based on the nanorod and flat structure, the proposed biosensor shows expanded linear range and sensitivity. All these results demonstrate that ZnO nanotube can provide a promising material for the biosensor designs and other biological applications.
TL;DR: Progress towards nanotube electronics for radiofrequency applications is reviewed in terms of device physics, circuit design and the manufacturing challenges.
Abstract: Electronic devices based on carbon nanotubes are among the candidates to eventually replace silicon-based devices for logic applications. Before then, however, nanotube-based radiofrequency transistors could become competitive for high-performance analogue components such as low-noise amplifiers and power amplifiers in wireless systems. Single-walled nanotubes are well suited for use in radiofrequency transistors because they demonstrate near-ballistic electron transport and are expected to have high cut-off frequencies. To achieve the best possible performance it is necessary to use dense arrays of semiconducting nanotubes with good alignment between the nanotubes, but techniques that can economically manufacture such arrays are needed to realize this potential. Here we review progress towards nanotube electronics for radiofrequency applications in terms of device physics, circuit design and the manufacturing challenges. Arrays of semiconducting single-walled carbon nanotubes are well suited for use in radiofrequency transistors. This article reviews progress towards nanotube-based radiofrequency devices in terms of device physics, circuit design and manufacturing challenges.
TL;DR: In this paper, a flexible dielectric polystyrene based composites containing multi-walled carbon nanotubes (MWCNTs) were reported, which were coated with polypyrrole (PPy) by an inverse microemulsion polymerization.
TL;DR: In this article, four types of presynthesized CdTe quantum dots (QDs) of different sizes were deposited into the TiO 2 nanotubes to serve as the sensitizers, and the performance of the QD-sensitized TiO2 nanotube arrays was measured in a PEC solar cell.
Abstract: TiO 2 nanotube array films, formed by anodic oxidation, have been shown to yield high efficiency of charge generation and collection in photoelectrochemical (PEC) devices. However, the wide band gap (3.2 eV) of TiO 2 limits the efficiency of these devices in the visible region. In this work, four types of presynthesized CdTe quantum dots (QDs) of different sizes were deposited into the TiO 2 nanotubes to serve as the sensitizers, and the performance of the CdTe QD-sensitized TiO 2 nanotube arrays was measured in a PEC solar cell. It is found that, with decreasing particle size, the driving force for electron injection increases while the visible light response decreases. Maximum photocurrent was obtained for the QDs that have an absorption peak at 536 nm. Under AM 1.5 G illuminations, a 6 mA/cm 2 short circuit current density is achieved, which presents a 35 times improvement compared to that based on using a plain TiO 2 nanotube film.
TL;DR: Higher nanometer scale roughness, low contact angle and high surface energy in nanoporous surface enhanced the osteoblast-material interactions, and immunochemistry study with alkaline phosphatase showed enhanced osteoblastic phenotype expressions in nanoporus surface.
Abstract: Ti being bioinert shows poor bone cell adhesion with an intervening fibrous capsule. Ti could be made bioactive by several methods including growing in situ TiO2 layer on Ti-surface. TiO2 nanotubes were grown on Ti surface via anodization process and the bone cell-material interactions were evaluated. Human osteoblast cell attachment and growth behavior were studied using an osteoprecursor cell line for 3, 7, and 11 days. An abundant amount of extracellular matrix (ECM) between the neighboring cells was noticed on anodized nanotube surface with filopodia extensions coming out from cells to grasp the nanoporous surface of the nanotube for anchorage. To better understand and compare cell-materials interactions, anodized nanoporous sample surfaces were etched with different patterns. Preferential cell attachment was noticed on nanotube surface compare to almost no cells in etched Ti surface. Cell adhesion with vinculin adhesive protein showed higher intensity, positive contacts on nanoporous surface and thin focal contacts on the Ti-control. Immunochemistry study with alkaline phosphatase showed enhanced osteoblastic phenotype expressions in nanoporous surface. Osteoblast proliferation was significantly higher on anodized nanotube surface. Surface properties changed with the emergence of nanoscale morphology. Higher nanometer scale roughness, low contact angle and high surface energy in nanoporous surface enhanced the osteoblast-material interactions. Mineralization study was done under simulated body fluid (SBF) with ion concentration nearly equal to human blood plasma to understand biomimetic apatite deposition behavior. Although apatite layer formation was noticed on nanotube surface, but it was nonuniform even after 21 days in SBF.
TL;DR: The results reveal that the Fermi level of the free CNT is red-shifted by the adsorption of the amino acids and the degree of shift is consistent with the trend in polarizability of these molecules.
Abstract: In this study we have investigated the interaction of phenylalanine (Phe), histidine (His), tyrosine (Tyr), and tryptophan (Tryp) molecules with graphene and single walled carbon nanotubes (CNTs) with an aim to understand the effect of curvature on the non-covalent interaction. The calculations are performed using density functional theory and the Moller-Plesset second-order perturbation theory (MP2) within linear combination of atomic orbitals-molecular orbital (LCAO-MO) approach. Using these methods, the equilibrium configurations of these complexes were found to be very similar, i.e., the aromatic rings of the amino acids prefer to orient in parallel with respect to the plane of the substrates, which bears the signature of weak pi-pi interactions. The binding strength follows the trend: His
TL;DR: In this article, oxygen-containing groups were introduced onto multiwall carbon nanotubes (MWCNTs) by using microwave-excited Ar/O2 surface-wave plasma (SWP) treatment.
Abstract: In this work, oxygen-containing groups were introduced onto multiwall carbon nanotubes (MWCNTs) by using microwave-excited Ar/O2 surface-wave plasma (SWP) treatment. The changes of the atomic contents and structure properties of MWCNTs as a function of gas flow rate, treatment time, and plasma power were analyzed using X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. A mechanism of MWCNT oxidation was proposed, based on XPS analysis, which showed how oxygen-containing groups, such as C−O, C═O, and O−C═O, were generated on the surfaces of MWCNTs. The surface morphology of MWCNTs was observed by field emission scanning electron microscopy (FE-SEM). The results indicated that Ar/O2 plasma treatment greatly enhanced the content of oxygen, modified structure properties, induced more surface defects, and improved the dispersion of MWCNTs in aqueous solution. The integrity of the nanotube patterns was not damaged.
TL;DR: A film of highly aligned single-walled carbon nanotubes that acts as an excellent terahertz linear polarizer that demonstrates nearly perfect alignment as well as intrinsically anisotropic terAhertz response of single-Walled carbon Nanotubes in the film.
Abstract: We describe a film of highly aligned single-walled carbon nanotubes that acts as an excellent terahertz linear polarizer. There is virtually no attenuation (strong absorption) when the terahertz polarization is perpendicular (parallel) to the nanotube axis. From the data, the reduced linear dichrosim was calculated to be 3, corresponding to a nematic order parameter of 1, which demonstrates nearly perfect alignment as well as intrinsically anisotropic terahertz response of single-walled carbon nanotubes in the film.
TL;DR: An extensive all-atom molecular dynamics study on the morphology of sodium dodecyl sulfate (SDS) surfactant aggregates adsorbed on single walled carbon nanotubes at room conditions reveals that the nanotube diameter is the primary factor that determines the morphologyof the aggregates.
Abstract: Although carbon nanotubes have attracted enormous research interest, their practical application is still hindered, primarily, by the difficulty of separating them into samples monodispersed in diameter, chirality, and length. Recent advances show that ultracentrifugating carbon nanotube dispersions stabilized by surfactants is a promising route for achieving the desired separation. For further perfectioning this procedure it is necessary to know how surfactants adsorb on nanotubes of different diameters, which determines the nanotube-surfactant aggregate effective density and the nanotube-nanotube potential of mean force. Because only limited experimental data are available to elucidate these phenomena, we report here an extensive all-atom molecular dynamics study on the morphology of sodium dodecyl sulfate (SDS) surfactant aggregates adsorbed on (6,6), (12,12), and (20,20) single walled carbon nanotubes at room conditions. Our calculations reveal that the nanotube diameter is the primary factor that determines the morphology of the aggregates because of a competition between the entropic and energetic advantage encountered by the surfactants when they wrap one nanotube, and the enthalpic penalty faced during this process due to bending of the surfactant molecule. The data are in qualitative agreement with the neutron scattering results reported by Yurekli et al. [J. Am. Chem. Soc. 2004, 126, 9902], and for the first time provide an atomic-level description helpful in designing better separation, as well as stabilization techniques for aqueous carbon nanotube dispersions.