Vertically Aligned Carbon Nanotube Electrodes for Lithium-Ion Batteries

DTIC Science & Technology

2011-01-01

wpafb.af.mil (M.F. Durstock). [11] nanowires, and iron oxide/copper [12] and tin/copper [13] nanorods. Carbon nanotubes ( CNTs ) have also been examined as...negative electrodes [14–17]. Although CNTs and other nega- tive electrode nanomaterials have been shown to exhibit similar or greater capacities...rate capability [18]. Studies suggest that aligned CNTs could allow for better contact with the current collector and increased ion diffu- sivity to

Highly efficient growth of vertically aligned carbon nanotubes on Fe-Ni based metal alloy foils for supercapacitors

NASA Astrophysics Data System (ADS)

Amalina Raja Seman, Raja Noor; Asyadi Azam, Mohd; Ambri Mohamed, Mohd

2016-12-01

Supercapacitors are highly promising energy devices with superior charge storage performance and a long lifecycle. Construction of the supercapacitor cell, especially electrode fabrication, is critical to ensure good performance in applications. This work demonstrates direct growth of vertically aligned carbon nanotubes (CNTs) on Fe-Ni based metal alloy foils, namely SUS 310S, Inconel 600 and YEF 50, and their use in symmetric vertically aligned CNT supercapacitor electrodes. Alumina and cobalt thin film catalysts were deposited onto the foils, and then CNT growth was performed using alcohol catalytic chemical vapour deposition. By this method, vertically aligned CNTs were successfully grown and used directly as a binder-free supercapacitor electrode to deliver excellent electrochemical performance. The device showed relatively good specific capacitance, a superior rate capability and excellent cycle stability, maintaining about 96% capacitance up to 1000 cycles.

Continuous high-yield production of vertically aligned carbon nanotubes on 2D and 3D substrates.

PubMed

Guzmán de Villoria, Roberto; Hart, A John; Wardle, Brian L

2011-06-28

Vertically aligned carbon nanotubes (VACNTs) have certain advantages over bulk CNT powders and randomly oriented CNT mats for applications in flexible electronic devices, filtration membranes, biosensors and multifunctional aerospace materials. Here, a machine and a process to synthesize VACNTs in a continuous manner are presented showing uniform growth on 2D and 3D substrates, including alumina fibers, silicon wafer pieces, and stainless steel foils. Aligned multiwalled carbon nanotubes (MWNT) are synthesized at substrate feed rates of up to 6.8 cm/min, and the CNTs reach up to 60 μm in length depending on residence time in the reactor. In addition to the aligned morphology indicative of high yield growth, transmission electron microscopy and Raman spectroscopy reveal that the CNTs are of comparable quality to CNTs grown via a similar batch process. A significant reduction in time, reaction products, gases, and energy is demonstrated relative to batch processing, paving the way for industrial production of VACNTs.

Failure mechanism of the polymer infiltration of carbon nanotube forests

NASA Astrophysics Data System (ADS)

Buchheim, Jakob; Park, Hyung Gyu

2016-11-01

Polymer melt infiltration is one of the feasible methods for manufacturing filter membranes out of carbon nanotubes (CNTs) on large scales. Practically, however, its process suffers from low yields, and the mechanism behind this failure is rather poorly understood. Here, we investigate a failure mechanism of polymer melt infiltration of vertical aligned (VA-) CNTs. In penetrating the VA-CNT interstices, polymer melts exert a capillarity-induced attractive force laterally on CNTs at the moving meniscus, leading to locally agglomerated macroscale bunches. Such a large configurational change can deform and distort individual CNTs so much as to cause buckling or breakdown of the alignment. In view of membrane manufacturing, this irreversible distortion of nanotubes is detrimental, as it could block the transport path of the membranes. The failure mechanism of the polymer melt infiltration is largely attributed to steric hindrance and an energy penalty of confined polymer chains. Euler beam theory and scaling analysis affirm that CNTs with low aspect ratio, thick walls and sparse distribution can maintain their vertical alignment. Our results can enrich a mechanistic understanding of the polymer melt infiltration process and offer guidelines to the facile large-scale manufacturing of the CNT-polymer filter membranes.

The Surface Interface Characteristics of Vertically Aligned Carbon Nanotube and Graphitic Carbon Fiber Arrays Grown by Thermal and Plasma Enhanced Chemical Vapor Deposition

NASA Technical Reports Server (NTRS)

Delzeit, Lance; Nguyen, Cattien; Li, Jun; Han, Jie; Meyyappan, M.

2002-01-01

The development of nano-arrays for sensors and devices requires the growth of arrays with the proper characteristics. One such application is the growth of vertically aligned carbon nanotubes (CNTs) and graphitic carbon fibers (GCFs) for the chemical attachment of probe molecules. The effectiveness of such an array is dependent not only upon the effectiveness of the probe and the interface between that probe and the array, but also the array and the underlaying substrate. If that array is a growth of vertically aligned CNTs or GCFs then the attachment of that array to the surface is of the utmost importance. This attachment provides the mechanical stability and durability of the array, as well as, the electrical properties of that array. If the detection is to be acquired through an electrical measurement, then the appropriate resistance between the array and the surface need to be fabricated into the device. I will present data on CNTs and GCFs grown from both thermal and plasma enhanced chemical vapor deposition. The focus will be on the characteristics of the metal film from which the CNTs and GCFs are grown and the changes that occur due to changes within the growth process.

Ultra-high density aligned Carbon-nanotube with controled nano-morphology for supercapacitors

NASA Astrophysics Data System (ADS)

Ghaffari, Mehdi; Zhao, Ran; Liu, Yang; Zhou, Yue; Cheng, Jiping; Guzman de Villoria, Roberto; Wardle, B. L.; Zhang, Q. M.

2012-02-01

Recent advances in fabricating controlled-morphology vertically aligned carbon nanotubes (VA-CNTs) with ultrahigh volume fractioncreate unique opportunities for developing unconventional supercapacitors with ultra-high energy density, power density, and long charge/discharge cycle life.Continuous paths through inter-VA-CNT channels allow fast ion transport, and high electrical conduction of the aligned CNTs in the composite electrodes lead to fast discharge speed. We investigate the charge-discharge characteristics of VA-CNTs with >20 vol% of CNT and ionic liquids as electrolytes. By employing both the electric and electromechanical spectroscopes, as well as nanostructured materials characterization, the ion transport and storage behaviors in porous electrodes are studied. The results suggest pathways for optimizing the electrode morphology in supercapacitorsusing ultra-high volume fraction VA-CNTs to further enhance performance.

New Three-Dimensional Porous Electrode Concept: Vertically-Aligned Carbon Nanotubes Directly Grown on Embroidered Copper Structures.

PubMed

Aguiló-Aguayo, Noemí; Amade, Roger; Hussain, Shahzad; Bertran, Enric; Bechtold, Thomas

2017-12-11

New three-dimensional (3D) porous electrode concepts are required to overcome limitations in Li-ion batteries in terms of morphology (e.g., shapes, dimensions), mechanical stability (e.g., flexibility, high electroactive mass loadings), and electrochemical performance (e.g., low volumetric energy densities and rate capabilities). Here a new electrode concept is introduced based on the direct growth of vertically-aligned carbon nanotubes (VA-CNTs) on embroidered Cu current collectors. The direct growth of VA-CNTs was achieved by plasma-enhanced chemical vapor deposition (PECVD), and there was no application of any post-treatment or cleaning procedure. The electrochemical behavior of the as-grown VA-CNTs was analyzed by charge/discharge cycles at different specific currents and with electrochemical impedance spectroscopy (EIS) measurements. The results were compared with values found in the literature. The as-grown VA-CNTs exhibit higher specific capacities than graphite and pristine VA-CNTs found in the literature. This together with the possibilities that the Cu embroidered structures offer in terms of specific surface area, total surface area, and designs provide a breakthrough in new 3D electrode concepts.

Film fabrication of Fe or Fe3O4 nanoparticles mixed with palmitic acid for vertically aligned carbon nanotube growth using Langmuir-Blodgett technique

NASA Astrophysics Data System (ADS)

Nakamura, Kentaro; Kuriyama, Naoki; Takagiwa, Shota; Sato, Taiga; Kushida, Masahito

2016-03-01

Vertically aligned carbon nanotubes (VA-CNTs) were studied as a new catalyst support for polymer electrolyte fuel cells (PEFCs). Controlling the number density and the diameter of VA-CNTs may be necessary to optimize PEFC performance. As the catalyst for CNT growth, we fabricated Fe or Fe3O4 nanoparticle (NP) films by the Langmuir-Blodgett (LB) technique. The catalyst Fe or Fe3O4 NPs were widely separated by mixing with filler molecules [palmitic acid (C16)]. The number density of VA-CNTs was controlled by varying the ratio of catalyst NPs to C16 filler molecules. The VA-CNTs were synthesized from the catalyst NP-C16 LB films by thermal chemical vapor deposition (CVD) using acetylene gas as the carbon source. The developing solvents used in the LB technique and the hydrogen reduction conditions of CVD were optimized to improve the VA-CNT growth rate. We demonstrate that the proposed method can independently control both the density and the diameter of VA-CNTs.

Determination of the electrical resistivity of vertically aligned carbon nanotubes by scanning probe microscopy

NASA Astrophysics Data System (ADS)

Ageev, O. A.; Il'in, O. I.; Rubashkina, M. V.; Smirnov, V. A.; Fedotov, A. A.; Tsukanova, O. G.

2015-07-01

Techniques are developed to determine the resistance per unit length and the electrical resistivity of vertically aligned carbon nanotubes (VA CNTs) using atomic force microscopy (AFM) and scanning tunneling microscopy (STM). These techniques are used to study the resistance of VA CNTs. The resistance of an individual VA CNT calculated with the AFM-based technique is shown to be higher than the resistance of VA CNTs determined by the STM-based technique by a factor of 200, which is related to the influence of the resistance of the contact of an AFM probe to VA CNTs. The resistance per unit length and the electrical resistivity of an individual VA CNT 118 ± 39 nm in diameter and 2.23 ± 0.37 μm in height that are determined by the STM-based technique are 19.28 ± 3.08 kΩ/μm and 8.32 ± 3.18 × 10-4 Ω m, respectively. The STM-based technique developed to determine the resistance per unit length and the electrical resistivity of VA CNTs can be used to diagnose the electrical parameters of VA CNTs and to create VA CNT-based nanoelectronic elements.

Effects of Conformal Nanoscale Coatings on Thermal Performance of Vertically Aligned Carbon Nanotubes.

PubMed

Silvestri, Cinzia; Riccio, Michele; Poelma, René H; Jovic, Aleksandar; Morana, Bruno; Vollebregt, Sten; Irace, Andrea; Zhang, Guo Qi; Sarro, Pasqualina M

2018-04-17

The high aspect ratio and the porous nature of spatially oriented forest-like carbon nanotube (CNT) structures represent a unique opportunity to engineer a novel class of nanoscale assemblies. By combining CNTs and conformal coatings, a 3D lightweight scaffold with tailored behavior can be achieved. The effect of nanoscale coatings, aluminum oxide (Al 2 O 3 ) and nonstoichiometric amorphous silicon carbide (a-SiC), on the thermal transport efficiency of high aspect ratio vertically aligned CNTs, is reported herein. The thermal performance of the CNT-based nanostructure strongly depends on the achieved porosity, the coating material and its infiltration within the nanotube network. An unprecedented enhancement in terms of effective thermal conductivity in a-SiC coated CNTs has been obtained: 181% compared to the as-grown CNTs and Al 2 O 3 coated CNTs. Furthermore, the integration of coated high aspect ratio CNTs in an epoxy molding compound demonstrates that, next to the required thermal conductivity, the mechanical compliance for thermal interface applications can also be achieved through coating infiltration into foam-like CNT forests. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Highly Anisotropic Adhesive Film Made from Upside-Down, Flat, and Uniform Vertically Aligned CNTs.

PubMed

Hong, Sanghyun; Lundstrom, Troy; Ghosh, Ranajay; Abdi, Hamed; Hao, Ji; Jeoung, Sun Kyoung; Su, Paul; Suhr, Jonghwan; Vaziri, Ashkan; Jalili, Nader; Jung, Yung Joon

2016-12-14

We have created a multifunctional dry adhesive film with transferred vertically aligned carbon nanotubes (VA-CNTs). This unique VA-CNT film was fabricated by a multistep transfer process, converting the flat and uniform bottom of VA-CNTs grown on atomically flat silicon wafer substrates into the top surface of an adhesive layer. Unlike as-grown VA-CNTs, which have a nonuniform surface, randomly entangled CNT arrays, and a weak interface between the CNTs and substrates, this transferred VA-CNT film shows an extremely high coefficient of static friction (COF) of up to 60 and a shear adhesion force 30 times higher (12 N/cm 2 ) than that of the as-grown VA-CNTs under a very small preloading of 0.2 N/cm 2 . Moreover, a near-zero normal adhesion force was observed with 20 mN/cm 2 preloading and a maximum 100-μm displacement in a piezo scanner, demonstrating ideal properties for an artificial gecko foot. Using this unique structural feature and anisotropic adhesion properties, we also demonstrate effective removal and assembly of nanoparticles into organized micrometer-scale circular and line patterns by a single brushing of this flat and uniform VA-CNT film.

Effects of vertically aligned carbon nanotubes on shear performance of laminated nanocomposite bonded joints.

PubMed

Askari, Davood; Ghasemi-Nejhad, Mehrdad N

2012-08-01

The main objective is to improve the most commonly addressed weakness of the laminated composites (i.e. delamination due to poor interlaminar strength) using carbon nanotubes (CNTs) as reinforcement between the laminae and in the transverse direction. In this work, a chemical vapor deposition technique has been used to grow dense vertically aligned arrays of CNTs over the surface of chemically treated two-dimensionally woven cloth and fiber tows. The nanoforest-like fabrics can be used to fabricate three-dimensionally reinforced laminated nanocomposites. The presence of CNTs aligned normal to the layers and in-between the layers of laminated composites is expected to considerably enhance the properties of the laminates. To demonstrate the effectiveness of our approach, composite single lap-joint specimens were fabricated for interlaminar shear strength testing. It was observed that the single lap-joints with through-the-thickness CNT reinforcement can carry considerably higher shear stresses and strains. Close examination of the test specimens showed that the failure of samples with CNT nanoforests was completely cohesive, while the samples without CNT reinforcement failed adhesively. This concludes that the adhesion of adjacent carbon fabric layers can be considerably improved owing to the presence of vertically aligned arrays of CNT nanoforests.

Effects of vertically aligned carbon nanotubes on shear performance of laminated nanocomposite bonded joints

PubMed Central

Askari, Davood; Ghasemi-Nejhad, Mehrdad N

2012-01-01

The main objective is to improve the most commonly addressed weakness of the laminated composites (i.e. delamination due to poor interlaminar strength) using carbon nanotubes (CNTs) as reinforcement between the laminae and in the transverse direction. In this work, a chemical vapor deposition technique has been used to grow dense vertically aligned arrays of CNTs over the surface of chemically treated two-dimensionally woven cloth and fiber tows. The nanoforest-like fabrics can be used to fabricate three-dimensionally reinforced laminated nanocomposites. The presence of CNTs aligned normal to the layers and in-between the layers of laminated composites is expected to considerably enhance the properties of the laminates. To demonstrate the effectiveness of our approach, composite single lap-joint specimens were fabricated for interlaminar shear strength testing. It was observed that the single lap-joints with through-the-thickness CNT reinforcement can carry considerably higher shear stresses and strains. Close examination of the test specimens showed that the failure of samples with CNT nanoforests was completely cohesive, while the samples without CNT reinforcement failed adhesively. This concludes that the adhesion of adjacent carbon fabric layers can be considerably improved owing to the presence of vertically aligned arrays of CNT nanoforests. PMID:27877502

WC Nanocrystals Grown on Vertically Aligned Carbon Nanotubes: An Efficient and Stable Electrocatalyst for Hydrogen Evolution Reaction.

PubMed

Fan, Xiujun; Zhou, Haiqing; Guo, Xia

2015-05-26

Single nanocrystalline tungsten carbide (WC) was first synthesized on the tips of vertically aligned carbon nanotubes (VA-CNTs) with a hot filament chemical vapor deposition (HF-CVD) method through the directly reaction of tungsten metal with carbon source. The VA-CNTs with preservation of vertical structure integrity and alignment play an important role to support the nanocrystalline WC growth. With the high crystallinity, small size, and uniform distribution of WC particles on the carbon support, the formed WC-CNTs material exhibited an excellent catalytic activity for hydrogen evolution reaction (HER), giving a η10 (the overpotential for driving a current of 10 mA cm(-2)) of 145 mV, onset potential of 15 mV, exchange current density@ 300 mV of 117.6 mV and Tafel slope values of 72 mV dec(-1) in acid solution, and η10 of 137 mV, onset potential of 16 mV, exchange current density@ 300 mV of 33.1 mV and Tafel slope values of 106 mV dec(-1) in alkaline media, respectively. Electrochemical stability test further confirms the long-term operation of the catalyst in both acidic and alkaline media.

Crystallization Behavior of Poly(ethylene oxide) in Vertically Aligned Carbon Nanotube Array.

PubMed

Sheng, Jiadong; Zhou, Shenglin; Yang, Zhaohui; Zhang, Xiaohua

2018-03-27

We investigate the effect of the presence of vertically aligned multiwalled carbon nanotubes (CNTs) on the orientation of poly(ethylene oxide) (PEO) lamellae and PEO crystallinity. The high alignment of carbon nanotubes acting as templates probably governs the orientation of PEO lamellae. This templating effect might result in the lamella planes of PEO crystals oriented along a direction parallel to the long axis of the nanotubes. The presence of aligned carbon nanotubes also gives rise to the decreases in PEO crystallinity, crystallization temperature, and melting temperature due to the perturbation of carbon nanotubes to the crystallization of PEO. These effects have significant implications for controlling the orientation of PEO lamellae and decreasing the crystallinity of PEO and thickness of PEO lamellae, which have significant impacts on ion transport in PEO/CNT composite and the capacitive performance of PEO/CNT composite. Both the decreased PEO crystallinity and the orientation of PEO lamellae along the long axes of vertically aligned CNTs give rise to the decrease in the charge transfer resistance, which is associated with the improvements in the ion transport and capacitive performance of PEO/CNT composite.

High Electromechanical Response of Ionic Polymer Actuators with Controlled-Morphology Aligned Carbon Nanotube/Nafion Nanocomposite Electrodes

PubMed Central

Liu, Sheng; Liu, Yang; Cebeci, Hülya; de Villoria, Roberto Guzmán; Lin, Jun-Hong

2011-01-01

Recent advances in fabricating controlled-morphology vertically aligned carbon nanotubes (VA-CNTs) with ultrahigh volume fraction create unique opportunities for markedly improving the electromechanical performance of ionic polymer conductor network composite (IPCNC) actuators. Continuous paths through inter-VA-CNT channels allow fast ion transport, and high electrical conduction of the aligned CNTs in the composite electrodes lead to fast device actuation speed (>10% strain/second). One critical issue in developing advanced actuator materials is how to suppress the strain that does not contribute to the actuation (unwanted strain) thereby reducing actuation efficiency. Here our experiments demonstrate that the VA-CNTs give an anisotropic elastic response in the composite electrodes, which suppresses the unwanted strain and markedly enhances the actuation strain (>8% strain under 4 volts). The results reported here suggest pathways for optimizing the electrode morphology in IPCNCs using ultra-high volume fraction VA-CNTs to further enhanced performance. PMID:21765822

Diameter control of vertically aligned carbon nanotubes using CoFe2O4 nanoparticle Langmuir-Blodgett films

NASA Astrophysics Data System (ADS)

Tamiya, Shuhei; Sato, Taiga; Kushida, Masahito

2018-03-01

Vertically aligned carbon nanotubes (VA-CNTs) are suggested for utilization as a new catalyst support of polymer electrolyte fuel cells (PEFCs). The independent control of the diameter and number density of VA-CNTs is essential for application in PEFCs. As the catalyst for VA-CNT growth, we fabricated CoFe2O4 nanoparticle (NP) films using the Langmuir-Blodgett (LB) technique. Using the LB technique, we were able to separately control the diameter and number density of VA-CNTs. The number density of VA-CNTs was changed by mixing with the filler moleculer, palmitic acid (C16). The VA-CNT diameter was changed by the adjusting the CoFe2O4 NP diameter. However, the heat-induced aggregation of CoFe2O4 NPs occurred in thermal chemical vapor deposition to synthesize VA-CNTs. Therefore, we examined how to minimize the effect of heat-induced aggregation of CoFe2O4 NPs. As a result, selection of the appropriate number density and diameter of CoFe2O4 NPs was found to be important for the control of VA-CNT diameter.

New Three-Dimensional Porous Electrode Concept: Vertically-Aligned Carbon Nanotubes Directly Grown on Embroidered Copper Structures

PubMed Central

Amade, Roger; Hussain, Shahzad; Bertran, Enric; Bechtold, Thomas

2017-01-01

New three-dimensional (3D) porous electrode concepts are required to overcome limitations in Li-ion batteries in terms of morphology (e.g., shapes, dimensions), mechanical stability (e.g., flexibility, high electroactive mass loadings), and electrochemical performance (e.g., low volumetric energy densities and rate capabilities). Here a new electrode concept is introduced based on the direct growth of vertically-aligned carbon nanotubes (VA-CNTs) on embroidered Cu current collectors. The direct growth of VA-CNTs was achieved by plasma-enhanced chemical vapor deposition (PECVD), and there was no application of any post-treatment or cleaning procedure. The electrochemical behavior of the as-grown VA-CNTs was analyzed by charge/discharge cycles at different specific currents and with electrochemical impedance spectroscopy (EIS) measurements. The results were compared with values found in the literature. The as-grown VA-CNTs exhibit higher specific capacities than graphite and pristine VA-CNTs found in the literature. This together with the possibilities that the Cu embroidered structures offer in terms of specific surface area, total surface area, and designs provide a breakthrough in new 3D electrode concepts. PMID:29232892

Liquid-phase synthesis of vertically aligned carbon nanotubes and related nanomaterials on preheated alloy substrates

NASA Astrophysics Data System (ADS)

Yamagiwa, Kiyofumi

2018-02-01

Carbon nanotubes (CNTs) and related nanocarbons were selectively synthesized on commercially available alloy substrates by a simple liquid-phase technique. Fe- and Ni-rich stainless-steel (JIS SUS316L and Inconel®600, respectively) and Ni-Cu alloy (Monel®400) substrates were used for the synthesis, and each substrate was preheated in air to promote the self-formation of catalyst nanolayers on the surface. The substrates were resistance heated in ethanol without any addition of catalysts to grow CNTs. The yield of the CNTs effectively increased when the preheating process was employed. Highly aligned CNT arrays grew on the SUS316L substrate, while non-aligned CNTs and distinctive twisted fibers were observed on the other substrates. An Fe oxide layer was selectively formed on the preheated SUS316L substrate promoting the growth of the CNT arrays. Characterizations including cyclic voltammetry for the arrays revealed that the CNTs possess a comparatively defect-rich surface, which is a desirable characteristic for its application such as electrode materials for capacitors.

Carbon nanotubes for thermal interface materials in microelectronic packaging

NASA Astrophysics Data System (ADS)

Lin, Wei

As the integration scale of transistors/devices in a chip/system keeps increasing, effective cooling has become more and more important in microelectronics. To address the thermal dissipation issue, one important solution is to develop thermal interface materials with higher performance. Carbon nanotubes, given their high intrinsic thermal and mechanical properties, and their high thermal and chemical stabilities, have received extensive attention from both academia and industry as a candidate for high-performance thermal interface materials. The thesis is devoted to addressing some challenges related to the potential application of carbon nanotubes as thermal interface materials in microelectronics. These challenges include: 1) controlled synthesis of vertically aligned carbon nanotubes on various bulk substrates via chemical vapor deposition and the fundamental understanding involved; 2) development of a scalable annealing process to improve the intrinsic properties of synthesized carbon nanotubes; 3) development of a state-of-art assembling process to effectively implement high-quality vertically aligned carbon nanotubes into a flip-chip assembly; 4) a reliable thermal measurement of intrinsic thermal transport property of vertically aligned carbon nanotube films; 5) improvement of interfacial thermal transport between carbon nanotubes and other materials. The major achievements are summarized. 1. Based on the fundamental understanding of catalytic chemical vapor deposition processes and the growth mechanism of carbon nanotube, fast synthesis of high-quality vertically aligned carbon nanotubes on various bulk substrates (e.g., copper, quartz, silicon, aluminum oxide, etc.) has been successfully achieved. The synthesis of vertically aligned carbon nanotubes on the bulk copper substrate by the thermal chemical vapor deposition process has set a world record. In order to functionalize the synthesized carbon nanotubes while maintaining their good vertical alignment, an in situ functionalization process has for the first time been demonstrated. The in situ functionalization renders the vertically aligned carbon nanotubes a proper chemical reactivity for forming chemical bonding with other substrate materials such as gold and silicon. 2. An ultrafast microwave annealing process has been developed to reduce the defect density in vertically aligned carbon nanotubes. Raman and thermogravimetric analyses have shown a distinct defect reduction in the CNTs annealed in microwave for 3 min. Fibers spun from the as-annealed CNTs, in comparison with those from the pristine CNTs, show increases of ˜35% and ˜65%, respectively, in tensile strength (˜0.8 GPa) and modulus (˜90 GPa) during tensile testing; an ˜20% improvement in electrical conductivity (˜80000 S m-1) was also reported. The mechanism of the microwave response of CNTs was discussed. Such a microwave annealing process has been extended to the preparation of reduced graphene oxide. 3. Based on the fundamental understanding of interfacial thermal transport and surface chemistry of metals and carbon nanotubes, two major transfer/assembling processes have been developed: molecular bonding and metal bonding. Effective improvement of the interfacial thermal transport has been achieved by the interfacial bonding. 4. The thermal diffusivity of vertically aligned carbon nanotube (VACNT, multi-walled) films was measured by a laser flash technique, and shown to be ˜30 mm2 s-1 along the tube-alignment direction. The calculated thermal conductivities of the VACNT film and the individual CNTs are ˜27 and ˜540 W m-1 K-1, respectively. The technique was verified to be reliable although a proper sampling procedure is critical. A systematic parametric study of the effects of defects, buckling, tip-to-tip contacts, packing density, and tube-tube interaction on the thermal diffusivity was carried out. Defects and buckling decreased the thermal diffusivity dramatically. An increased packing density was beneficial in increasing the collective thermal conductivity of the VACNT film; however, the increased tube-tube interaction in dense VACNT films decreased the thermal conductivity of the individual CNTs. The tip-to-tip contact resistance was shown to be ˜1x10-7 m2 K W -1. The study will shed light on the potential application of VACNTs as thermal interface materials in microelectronic packaging. 5. A combined process of in situ functionalization and microwave curing has been developed to effective enhance the interface between carbon nanotubes and the epoxy matrix. Effective medium theory has been used to analyze the interfacial thermal resistance between carbon nanotubes and polymer matrix, and that between graphite nanoplatlets and polymer matrix.

High-performance Supercapacitors Based on Electrochemical-induced Vertical-aligned Carbon Nanotubes and Polyaniline Nanocomposite Electrodes

NASA Astrophysics Data System (ADS)

Wu, Guan; Tan, Pengfeng; Wang, Dongxing; Li, Zhe; Peng, Lu; Hu, Ying; Wang, Caifeng; Zhu, Wei; Chen, Su; Chen, Wei

2017-03-01

Supercapacitors, which store electrical energy through reversible ion on the surface of conductive electrodes have gained enormous attention for variously portable energy storage devices. Since the capacitive performance is mainly determined by the structural and electrochemical properties of electrodes, the electrodes become more crucial to higher performance. However, due to the disordered microstructure and low electrochemical activity of electrode for ion tortuous migration and accumulation, the supercapacitors present relatively low capacitance and energy density. Here we report a high-performance supercapacitor based on polyaniline/vertical-aligned carbon nanotubes (PANI/VA-CNTs) nanocomposite electrodes where the vertical-aligned-structure is formed by the electrochemical-induction (0.75 V). The supercapacitor displays large specific capacitance of 403.3 F g-1, which is 6 times higher than disordered CNTs in HClO4 electrolyte. Additionally, the supercapacitor can also present high specific capacitance (314.6 F g-1), excellent cycling stability (90.2% retention after 3000 cycles at 4 A g-1) and high energy density (98.1 Wh kg-1) in EMIBF4 organic electrolyte. The key to high-performance lies in the vertical-aligned-structure providing direct path channel for ion faster diffusion and high electrochemical capacitance of polyaniline for ion more accommodation.

High-performance Supercapacitors Based on Electrochemical-induced Vertical-aligned Carbon Nanotubes and Polyaniline Nanocomposite Electrodes.

PubMed

Wu, Guan; Tan, Pengfeng; Wang, Dongxing; Li, Zhe; Peng, Lu; Hu, Ying; Wang, Caifeng; Zhu, Wei; Chen, Su; Chen, Wei

2017-03-08

Supercapacitors, which store electrical energy through reversible ion on the surface of conductive electrodes have gained enormous attention for variously portable energy storage devices. Since the capacitive performance is mainly determined by the structural and electrochemical properties of electrodes, the electrodes become more crucial to higher performance. However, due to the disordered microstructure and low electrochemical activity of electrode for ion tortuous migration and accumulation, the supercapacitors present relatively low capacitance and energy density. Here we report a high-performance supercapacitor based on polyaniline/vertical-aligned carbon nanotubes (PANI/VA-CNTs) nanocomposite electrodes where the vertical-aligned-structure is formed by the electrochemical-induction (0.75 V). The supercapacitor displays large specific capacitance of 403.3 F g -1 , which is 6 times higher than disordered CNTs in HClO 4 electrolyte. Additionally, the supercapacitor can also present high specific capacitance (314.6 F g -1 ), excellent cycling stability (90.2% retention after 3000 cycles at 4 A g -1 ) and high energy density (98.1 Wh kg -1 ) in EMIBF 4 organic electrolyte. The key to high-performance lies in the vertical-aligned-structure providing direct path channel for ion faster diffusion and high electrochemical capacitance of polyaniline for ion more accommodation.

High-performance Supercapacitors Based on Electrochemical-induced Vertical-aligned Carbon Nanotubes and Polyaniline Nanocomposite Electrodes

PubMed Central

Wu, Guan; Tan, Pengfeng; Wang, Dongxing; Li, Zhe; Peng, Lu; Hu, Ying; Wang, Caifeng; Zhu, Wei; Chen, Su; Chen, Wei

2017-01-01

Supercapacitors, which store electrical energy through reversible ion on the surface of conductive electrodes have gained enormous attention for variously portable energy storage devices. Since the capacitive performance is mainly determined by the structural and electrochemical properties of electrodes, the electrodes become more crucial to higher performance. However, due to the disordered microstructure and low electrochemical activity of electrode for ion tortuous migration and accumulation, the supercapacitors present relatively low capacitance and energy density. Here we report a high-performance supercapacitor based on polyaniline/vertical-aligned carbon nanotubes (PANI/VA-CNTs) nanocomposite electrodes where the vertical-aligned-structure is formed by the electrochemical-induction (0.75 V). The supercapacitor displays large specific capacitance of 403.3 F g−1, which is 6 times higher than disordered CNTs in HClO4 electrolyte. Additionally, the supercapacitor can also present high specific capacitance (314.6 F g−1), excellent cycling stability (90.2% retention after 3000 cycles at 4 A g−1) and high energy density (98.1 Wh kg−1) in EMIBF4 organic electrolyte. The key to high-performance lies in the vertical-aligned-structure providing direct path channel for ion faster diffusion and high electrochemical capacitance of polyaniline for ion more accommodation. PMID:28272474

En route to controlled catalytic CVD synthesis of densely packed and vertically aligned nitrogen-doped carbon nanotube arrays.

PubMed

Boncel, Slawomir; Pattinson, Sebastian W; Geiser, Valérie; Shaffer, Milo S P; Koziol, Krzysztof K K

2014-01-01

The catalytic chemical vapour deposition (c-CVD) technique was applied in the synthesis of vertically aligned arrays of nitrogen-doped carbon nanotubes (N-CNTs). A mixture of toluene (main carbon source), pyrazine (1,4-diazine, nitrogen source) and ferrocene (catalyst precursor) was used as the injection feedstock. To optimize conditions for growing the most dense and aligned N-CNT arrays, we investigated the influence of key parameters, i.e., growth temperature (660, 760 and 860 °C), composition of the feedstock and time of growth, on morphology and properties of N-CNTs. The presence of nitrogen species in the hot zone of the quartz reactor decreased the growth rate of N-CNTs down to about one twentieth compared to the growth rate of multi-wall CNTs (MWCNTs). As revealed by electron microscopy studies (SEM, TEM), the individual N-CNTs (half as thick as MWCNTs) grown under the optimal conditions were characterized by a superior straightness of the outer walls, which translated into a high alignment of dense nanotube arrays, i.e., 5 × 10(8) nanotubes per mm(2) (100 times more than for MWCNTs grown in the absence of nitrogen precursor). In turn, the internal crystallographic order of the N-CNTs was found to be of a 'bamboo'-like or 'membrane'-like (multi-compartmental structure) morphology. The nitrogen content in the nanotube products, which ranged from 0.0 to 3.0 wt %, was controlled through the concentration of pyrazine in the feedstock. Moreover, as revealed by Raman/FT-IR spectroscopy, the incorporation of nitrogen atoms into the nanotube walls was found to be proportional to the number of deviations from the sp(2)-hybridisation of graphene C-atoms. As studied by XRD, the temperature and the [pyrazine]/[ferrocene] ratio in the feedstock affected the composition of the catalyst particles, and hence changed the growth mechanism of individual N-CNTs into a 'mixed base-and-tip' (primarily of the base-type) type as compared to the purely 'base'-type for undoped MWCNTs.

Synthesis and interface characterization of CNTs on graphene

NASA Astrophysics Data System (ADS)

Zhou, Changjian; Senegor, Richard; Baron, Zachary; Chen, Yihan; Raju, Salahuddin; Vyas, Anshul A.; Chan, Mansun; Chai, Yang; Yang, Cary Y.

2017-02-01

Carbon nanotubes (CNTs) and graphene are potential candidates for future interconnect materials. CNTs are promising on-chip via interconnect materials due to their readily formed vertical structures, their current-carrying capacity, which is much larger than existing on-chip interconnect materials such as copper and tungsten, and their demonstrated ability to grow in patterned vias with sub-50 nm widths; meanwhile, graphene is suitable for horizontal interconnects. However, they both present the challenge of having high-resistance contacts with other conductors. An all-carbon structure is proposed in this paper, which can be formed using the same chemical vapor deposition method for both CNTs and graphene. Vertically aligned CNTs are grown directly on graphene with an Fe or Ni catalyst. The structural characteristics of the graphene and the grown CNTs are analyzed using Raman spectroscopy and electron microscopy techniques. The CNT-graphene interface is studied in detail using transmission electron microscopic analysis of the CNT-graphene heterostructure, which suggests C-C bonding between the two materials. Electrical measurement results confirm the existence of both a lateral conduction path within graphene and a vertical conduction path in the CNT-graphene heterostructure, giving further support to the C-C bonding at the CNT-graphene interface and resulting in potential applications for all-carbon interconnects.

Synthesis and interface characterization of CNTs on graphene.

PubMed

Zhou, Changjian; Senegor, Richard; Baron, Zachary; Chen, Yihan; Raju, Salahuddin; Vyas, Anshul A; Chan, Mansun; Chai, Yang; Yang, Cary Y

2017-02-03

Carbon nanotubes (CNTs) and graphene are potential candidates for future interconnect materials. CNTs are promising on-chip via interconnect materials due to their readily formed vertical structures, their current-carrying capacity, which is much larger than existing on-chip interconnect materials such as copper and tungsten, and their demonstrated ability to grow in patterned vias with sub-50 nm widths; meanwhile, graphene is suitable for horizontal interconnects. However, they both present the challenge of having high-resistance contacts with other conductors. An all-carbon structure is proposed in this paper, which can be formed using the same chemical vapor deposition method for both CNTs and graphene. Vertically aligned CNTs are grown directly on graphene with an Fe or Ni catalyst. The structural characteristics of the graphene and the grown CNTs are analyzed using Raman spectroscopy and electron microscopy techniques. The CNT-graphene interface is studied in detail using transmission electron microscopic analysis of the CNT-graphene heterostructure, which suggests C-C bonding between the two materials. Electrical measurement results confirm the existence of both a lateral conduction path within graphene and a vertical conduction path in the CNT-graphene heterostructure, giving further support to the C-C bonding at the CNT-graphene interface and resulting in potential applications for all-carbon interconnects.

Water Plasma Functionalized CNTs/MnO2 Composites for Supercapacitors

PubMed Central

Hussain, Shahzad; Jover, Eric; Bertran, Enric

2013-01-01

A water plasma treatment applied to vertically-aligned multiwall carbon nanotubes (CNTs) synthesized by plasma enhanced chemical vapour deposition gives rise to surface functionalization and purification of the CNTs, along with an improvement of their electrochemical properties. Additional increase of their charge storage capability is achieved by anodic deposition of manganese dioxide lining the surface of plasma-treated nanotubes. The morphology (nanoflower, layer, or needle-like structure) and oxidation state of manganese oxide depend on the voltage window applied during charge-discharge measurements and are found to be key points for improved efficiency of capacitor devices. MnO2/CNTs nanocomposites exhibit an increase in their specific capacitance from 678 Fg−1, for untreated CNTs, up to 750 Fg−1, for water plasma-treated CNTs. PMID:24348189

Water plasma functionalized CNTs/MnO2 composites for supercapacitors.

PubMed

Hussain, Shahzad; Amade, Roger; Jover, Eric; Bertran, Enric

2013-01-01

A water plasma treatment applied to vertically-aligned multiwall carbon nanotubes (CNTs) synthesized by plasma enhanced chemical vapour deposition gives rise to surface functionalization and purification of the CNTs, along with an improvement of their electrochemical properties. Additional increase of their charge storage capability is achieved by anodic deposition of manganese dioxide lining the surface of plasma-treated nanotubes. The morphology (nanoflower, layer, or needle-like structure) and oxidation state of manganese oxide depend on the voltage window applied during charge-discharge measurements and are found to be key points for improved efficiency of capacitor devices. MnO2/CNTs nanocomposites exhibit an increase in their specific capacitance from 678 Fg(-1), for untreated CNTs, up to 750 Fg(-1), for water plasma-treated CNTs.

Gas adsorption capacity in an all carbon nanomaterial composed of carbon nanohorns and vertically aligned carbon nanotubes.

PubMed

Puthusseri, Divya; Babu, Deepu J; Okeil, Sherif; Schneider, Jörg J

2017-10-04

Whereas vertically aligned carbon nanotubes (VACNTs) typically show a promising adsorption behavior at high pressures, carbon nanohorns (CNHs) exhibit superior gas adsorption properties in the low pressure regime due to their inherent microporosity. These adsorption characteristics are further enhanced when both materials are opened at their tips. The so prepared composite material allows one to investigate the effect of physical entrapment of CO 2 molecules within the specific adsorption sites of VACNTs composed of opened double walled carbon nanotubes (CNTs) and in specific adsorption sites created by spherically aggregated opened single walled carbon nanohorns. Combining 50 wt% of tip opened CNTs with tip opened CNHs increases the CO 2 adsorption capacity of this material by ∼24% at 30 bar and 298 K compared to opened CNHs alone.

Wet catalyst-support films for production of vertically aligned carbon nanotubes.

PubMed

Alvarez, Noe T; Hamilton, Christopher E; Pint, Cary L; Orbaek, Alvin; Yao, Jun; Frosinini, Aldo L; Barron, Andrew R; Tour, James M; Hauge, Robert H

2010-07-01

A procedure for vertically aligned carbon nanotube (VA-CNT) production has been developed through liquid-phase deposition of alumoxanes (aluminum oxide hydroxides, boehmite) as a catalyst support. Through a simple spin-coating of alumoxane nanoparticles, uniform centimer-square thin film surfaces were coated and used as supports for subsequent deposition of metal catalyst. Uniform VA-CNTs are observed to grow from this film following deposition of both conventional evaporated Fe catalyst, as well as premade Fe nanoparticles drop-dried from the liquid phase. The quality and uniformity of the VA-CNTs are comparable to growth from conventional evaporated layers of Al(2)O(3). The combined use of alumoxane and Fe nanoparticles to coat surfaces represents an inexpensive and scalable approach to large-scale VA-CNT production that makes chemical vapor deposition significantly more competitive when compared to other CNT production techniques.

The rapid growth of vertically aligned carbon nanotubes using laser heating.

PubMed

Park, J B; Jeong, S H; Jeong, M S; Lim, S C; Lee, I H; Lee, Y H

2009-05-06

Growth of densely packed vertically aligned carbon nanotubes (VA-CNTs) using laser-induced chemical vapor deposition with visible laser (lambda = 532 nm) irradiation at room temperature is reported. Using a multiple-catalyst layer (Fe/Al/Cr) on quartz as the substrate and an acetylene-hydrogen mixture as the precursor gas, VA-CNT pillars with 60 microm height and 4 microm diameter were grown at a high rate of around 1 microm s(-1) with good reproducibility. It is demonstrated that the fabrication of uniform pillar arrays of VA-CNTs can be achieved with a single irradiation for each pillar using LCVD with no annealing or preprocessing of the substrate. Here, laser fast heating is considered the primary mechanism facilitating the growth of VA-CNT pillars. Field emission characteristics of an array of VA-CNT pillars were then examined to investigate their potential application in vacuum electronic devices.

Enhancing Thermal Conductive Performance of Vertically Aligned Carbon Nanotube Array Composite by Pre-Annealing Treatment.

PubMed

Wang, Miao; Chen, Hong-Yuan; Xing, Ya-Juan; Wei, Han-Xing; Li, Qiang; Chen, Ming-Hai; Li, Qing-Wen; Xuan, Yi-Min

2015-04-01

Vertically aligned carbon nanotube (VACNT) array/polymer composite has already been recognized as a promising candidate for advanced thermal pad in thermal management of high-power electronic devices. However, the thermal conductive performance of this composite was limited by the quality of CNTs arrays. In this study, pre-annealing treatment was used to purify CNT arrays and improve thermal conductive performance of VACNT arrays/silicone composite. The thermal conductivity of the composite was enhanced by 34.52% and the thermal interface resistance was also reduced by 65.94% at a pre-annealing temperature of 490 °C for 5 min. The annealing process could remove some amorphous carbon and open the tips of CNTs. As a result, the interfacial compatibility in composite between carbon nanotube and polymer matrix was improved. The cyclic compression and tension performance of VACNT/S160 composite was investigated for further application.

CVD Growth of Carbon Nanotubes: Structure, Catalyst, and Growth

NASA Technical Reports Server (NTRS)

Delzeit, Lance

2003-01-01

Carbon nanotubes (CNTs) exhibit extraordinary mechanical and unique electronic properties and hence have been receiving much attention in recent years for their potential in nanoelectronics, field emission devices, scanning probes, high strength composites and many more applications. Catalytic decomposition of hydrocarbon feedstock with the aid of supported transition metal catalysts - also known as chemical vapor deposition (CVD) - has become popular to produce single-walled and multi-walled nanotubes (SWNTs, MWNTs) and multiwalled nanofibers (MWNFs). The ability to grow CNTs on patterned substrates and in vertically aligned arrays, and the simplicity of the process, has made CVD growth of CNTs an attractive approach.

Synthesis of highly aligned carbon nanotubes by one-step liquid-phase process: Effects of carbon sources on morphology of carbon nanotubes

NASA Astrophysics Data System (ADS)

Yamagiwa, Kiyofumi; Kuwano, Jun

2017-06-01

This paper describes a unique and innovative synthesis technique for carbon nanotubes (CNTs) by a one-step liquid-phase process under ambient pressure. Vertically aligned multi-walled CNT arrays with a maximum height of 100 µm are prepared on stainless steel substrates, which are submerged and electrically heated in straight-chain primary alcohols with n C = 1-4 (n C: number of C atoms in the molecule) containing an appropriate amount of cobalt-based organometallic complex as a catalyst precursor. Structural isomers of butanol were also used for the synthesis to examine the effects of structural factors on the morphology of the deposited products. Notably, 2-methyl-2-propanol, which is a tertiary alcohol, produced only a small amount of low-crystallinity carbonaceous deposits, whereas vertically aligned CNTs were grown from the other isomers of butanol. These results suggest that the presence or absence of β-hydrogen in the molecular structure is a key factor for understanding the dissociation behavior of the carbon source molecules on the catalyst.

In situ SEM Observation of Column-like and Foam-like CNT Array Nanoindentation

DTIC Science & Technology

2011-03-02

frompyrolization of iron(II) phthalocyanine , producing vertically aligned CNTs with a nominal outer diameter of 50 nm.11,12 The array was indented using a 40 40 μm...www.acsami.org In situ SEM Observation of Column-like and Foam-like CNT Array Nanoindentation Matthew R. Maschmann,†,‡Qiuhong Zhang,†,§ Robert Wheeler...multiple length scales. Their behavior is expected to rely heavily on the properties of individual constituent CNTs , interactions and load distribution

Vertical Alignment of Single-Walled Carbon Nanotubes on Nanostructure Fabricated by Atomic Force Microscope

DTIC Science & Technology

2007-02-16

SWNT films by Langmuir - Blodgett methods,8 and chemical assembly of SWNTs on a large substrate.9 Al- though these methods provide a good way to control... Langmuir - Blodgett to Self-Assembly. Academic: New York, (1991). [10] Moon, J.H., Shin, J.W., Kim, S.Y., Park, J.W. Langmuir , 12, 4621, (1996...aligning CNTs in solu- tion by applying an electric field5 or a magnetic field,6 align- ing SWNTs by blending them with liquid crystal,7 assem- bling

Femtosecond laser modification of an array of vertically aligned carbon nanotubes intercalated with Fe phase nanoparticles

PubMed Central

2013-01-01

Femtosecond lasers (FSL) are playing an increasingly important role in materials research, characterization, and modification. Due to an extremely short pulse width, interactions of FSL irradiation with solid surfaces attract special interest, and a number of unusual phenomena resulted in the formation of new materials are expected. Here, we report on a new nanostructure observed after the interaction of FSL irradiation with arrays of vertically aligned carbon nanotubes (CNTs) intercalated with iron phase catalyst nanoparticles. It was revealed that the FSL laser ablation transforms the topmost layer of CNT array into iron phase nanospheres (40 to 680 nm in diameter) located at the tip of the CNT bundles of conical shape. Besides, the smaller nanospheres (10 to 30 nm in diameter) are found to be beaded at the sides of these bundles. Some of the larger nanospheres are encapsulated into carbon shells, which sometime are found to contain CNTs. The mechanism of creation of such nanostructures is proposed. PMID:24004518

Femtosecond laser modification of an array of vertically aligned carbon nanotubes intercalated with Fe phase nanoparticles.

PubMed

Labunov, Vladimir; Prudnikava, Alena; Bushuk, Serguei; Filatov, Serguei; Shulitski, Boris; Tay, Beng Kang; Shaman, Yury; Basaev, Alexander

2013-09-03

Femtosecond lasers (FSL) are playing an increasingly important role in materials research, characterization, and modification. Due to an extremely short pulse width, interactions of FSL irradiation with solid surfaces attract special interest, and a number of unusual phenomena resulted in the formation of new materials are expected. Here, we report on a new nanostructure observed after the interaction of FSL irradiation with arrays of vertically aligned carbon nanotubes (CNTs) intercalated with iron phase catalyst nanoparticles. It was revealed that the FSL laser ablation transforms the topmost layer of CNT array into iron phase nanospheres (40 to 680 nm in diameter) located at the tip of the CNT bundles of conical shape. Besides, the smaller nanospheres (10 to 30 nm in diameter) are found to be beaded at the sides of these bundles. Some of the larger nanospheres are encapsulated into carbon shells, which sometime are found to contain CNTs. The mechanism of creation of such nanostructures is proposed.

Porosimetry and packing morphology of vertically-aligned carbon nanotube arrays via impedance spectroscopy.

PubMed

Mutha, Heena K; Lu, Yuan; Stein, Itai; Cho, H Jeremy; Suss, Matthew; Laoui, Tahar; Thompson, Carl; Wardle, Brian; Wang, Evelyn

2016-12-13

Vertically aligned one-dimensional nanostructure arrays are promising in many applications such as electrochemical systems, solar cells, and electronics, taking advantage of high surface area per unit volume, nanometer length scale packing, and alignment leading to high conductivity. However, many devices need to optimize arrays for device performance by selecting an appropriate morphology. Developing a simple, non-invasive tool for understanding the role of pore volume distribution and interspacing would aid in the optimization of nanostructure morphologies in electrodes. In this work, we combined electrochemical impedance spectroscopy (EIS) with capacitance measurements and porous electrode theory to conduct in situ porosimetry of vertically-aligned carbon nanotubes (VA-CNTs) non-destructively. We utilized the EIS measurements with a pore size distribution model to quantify the average and dispersion of inter-CNT spacing (Γ), stochastically, in carpets that were mechanically densified from 1.7 × 10¹⁰ tubes/cm² to 4.5 × 10¹¹ tubes/cm². Our analysis predicts that the inter-CNT spacing ranges from over 100 ± 50 nm in sparse carpets to sub 10 ± 5 nm in packed carpets. Our results suggest that waviness of CNTs leads to variations in the inter-CNT spacing, which can be significant in sparse carpets. This methodology can be used to predict the performance of many nanostructured devices, including supercapacitors, batteries, solar cells, and semiconductor electronics. Copyright 2016 IOP Publishing Ltd.

Pressure sensor based on pristine multi-walled carbon nanotubes forest

NASA Astrophysics Data System (ADS)

Yasar, M.; Mohamed, N. M.; Hamid, N. H.; Shuaib, M.

2016-11-01

In the course of the most recent decade, carbon nanotubes (CNTs) have been developed as alternate material for many sensing applications because of their interesting properties. Their outstanding electromechanical properties make them suitable for pressure/strain sensing application. Other than in view of their structure and number of walls (i.e. Single-Walled CNTs and MultiWalled CNTs), carbon nanotubes can likewise be classified based on their orientation and combined arrangement. One such classification is vertically aligned Multi-Walled Carbon Nanotubes (VA-MWCNTs), regularly termed as CNTs arrays, foam or forest which is macro scale form of CNTs. Elastic behavior alongside exceptional electromechanical (high gauge factor) make it suitable for pressure sensing applications. This paper presents pressure sensor based on such carbon nanotubes forest in pristine form which enables it to perform over wider temperature range as compared to pressure sensors based on conventional materials such as Silicon.

Modeling and experimental study of resistive switching in vertically aligned carbon nanotubes

NASA Astrophysics Data System (ADS)

Ageev, O. A.; Blinov, Yu F.; Ilina, M. V.; Ilin, O. I.; Smirnov, V. A.

2016-08-01

Model of the resistive switching in vertically aligned carbon nanotube (VA CNT) taking into account the processes of deformation, polarization and piezoelectric charge accumulation have been developed. Origin of hysteresis in VA CNT-based structure is described. Based on modeling results the VACNTs-based structure has been created. The ration resistance of high-resistance to low-resistance states of the VACNTs-based structure amounts 48. The correlation the modeling results with experimental studies is shown. The results can be used in the development nanoelectronics devices based on VA CNTs, including the nonvolatile resistive random-access memory.

Multilevel, Multicomponent Microarchitectures of Vertically-Aligned Carbon Nanotubes for Diverse Applications

DTIC Science & Technology

2011-01-31

Oxide from Synthesis to Proper- ties and to Novel Devices. J. Mater. Chem. 2007, 17, 711– 720. 29. Wang, Z. L. The New Field of Nanopiezotronics...regard, wehave reportedpreviously thepreparation of multicomponent micropatterns of VA- MWNTs interposed with nanoparticles ,17 nonaligned CNTs,18 or VA...aligned arrays on growth substrates, which enabled us to fabricate the CNT nanoelectrode *Address correspondence to lqu@bit.edu.cn, liming.dai

Nonhomogeneous morphology and the elastic modulus of aligned carbon nanotube films

NASA Astrophysics Data System (ADS)

Won, Yoonjin; Gao, Yuan; Guzman de Villoria, Roberto; Wardle, Brian L.; Xiang, Rong; Maruyama, Shigeo; Kenny, Thomas W.; Goodson, Kenneth E.

2015-11-01

Carbon nanotube (CNT) arrays offer the potential to develop nanostructured materials that leverage their outstanding physical properties. Vertically aligned carbon nanotubes (VACNTs), also named CNT forests, CNT arrays, or CNT turfs, can provide high heat conductivity and sufficient mechanical compliance to accommodate thermal expansion mismatch for use as thermal interface materials (TIMs). This paper reports measurements of the in-plane moduli of vertically aligned, single-walled CNT (SWCNT) and multi-walled CNT (MWCNT) films. The mechanical response of these films is related to the nonhomogeneous morphology of the grown nanotubes, such as entangled nanotubes of a top crust layer, aligned CNTs in the middle region, and CNTs in the bottom layer. To investigate how the entanglements govern the overall mechanical moduli of CNT films, we remove the crust layer consisting of CNT entanglements by etching the CNT films from the top. A microfabricated cantilever technique shows that crust removal reduces the resulting moduli of the etched SWCNT films by as much as 40%, whereas the moduli of the etched MWCNT films do not change significantly, suggesting a minimal crust effect on the film modulus for thick MWCNT films (>90 μm). This improved understanding will allow us to engineer the mechanical moduli of CNT films for TIMs or packaging applications.

Optical anisotropy in micromechanically rolled carbon nanotube forest

NASA Astrophysics Data System (ADS)

Razib, Mohd Asyraf bin Mohd; Rana, Masud; Saleh, Tanveer; Fan, Harrison; Koch, Andrew; Nojeh, Alireza; Takahata, Kenichi; Muthalif, Asan Gani Bin Abdul

2017-09-01

The bulk appearance of arrays of vertically aligned carbon nanotubes (VACNT arrays or CNT forests) is dark as they absorb most of the incident light. In this paper, two postprocessing techniques have been described where the CNT forest can be patterned by selective bending of the tips of the nanotubes using a rigid cylindrical tool. A tungsten tool was used to bend the vertical structure of CNTs with predefined parameters in two different ways as stated above: bending using the bottom surface of the tool (micromechanical bending (M2B)) and rolling using the side of the tool (micromechanical rolling (M2R)). The processed zone was investigated using a Field Emission Scanning Electron Microscope (FESEM) and optical setup to reveal the surface morphology and optical characteristics of the patterned CNTs on the substrate. Interestingly, the polarized optical reflection from the micromechanical rolled (M2R) sample was found to be significantly influenced by the rotation of the sample. It was observed that, if the polarization of the light is parallel to the alignment of the CNTs, the reflectance is at least 2 x higher than for the perpendicular direction. Furthermore, the reflectance varied almost linearly with good repeatability ( 10%) as the processed CNT forest sample was rotated from 0° to 90°. [Figure not available: see fulltext.

A Forest of Sub-1.5-nm-wide Single-Walled Carbon Nanotubes over an Engineered Alumina Support

NASA Astrophysics Data System (ADS)

Yang, Ning; Li, Meng; Patscheider, Jörg; Youn, Seul Ki; Park, Hyung Gyu

2017-04-01

A precise control of the dimension of carbon nanotubes (CNTs) in their vertical array could enable many promising applications in various fields. Here, we demonstrate the growth of vertically aligned, single-walled CNTs (VA-SWCNTs) with diameters in the sub-1.5-nm range (0.98 ± 0.24 nm), by engineering a catalyst support layer of alumina via thermal annealing followed by ion beam treatment. We find out that the ion beam bombardment on the alumina allows the growth of ultra-narrow nanotubes, whereas the thermal annealing promotes the vertical alignment at the expense of enlarged diameters; in an optimal combination, these two effects can cooperate to produce the ultra-narrow VA-SWCNTs. According to micro- and spectroscopic characterizations, ion beam bombardment amorphizes the alumina surface to increase the porosity, defects, and oxygen-laden functional groups on it to inhibit Ostwald ripening of catalytic Fe nanoparticles effectively, while thermal annealing can densify bulk alumina to prevent subsurface diffusion of the catalyst particles. Our findings contribute to the current efforts of precise diameter control of VA-SWCNTs, essential for applications such as membranes and energy storage devices.

Hierarchically structured carbon nanotubes for energy conversion and storage

NASA Astrophysics Data System (ADS)

Du, Feng

As the world population continues to increase, large amounts of energy are consumed. Reality pushes us to find new energy or use our current energy more efficiently. Researches on energy conversion and storage have become increasingly important and essential. This grand challenge research has led to a recent focus on nanostructured materials. Carbon nanomaterials such as carbon nanotubes (CNTs) play a critical role in all of these nanotechnology challenges. CNTs have a very large surface area, a high electrochemical accessibility, high electronic conductivity and strong mechanical properties. This combination of properties makes them promising materials for energy device applications, such as FETs, supercapacitors, fuel cells, and lithium batteries. This study focuses on exploring the possibility of using vertically aligned carbon nanotubes (VA-CNTs) as the electrode materials in these energy applications. For the application of electrode materials, electrical conductive, vertically aligned CNTs with controllable length and diameter were synthesized. Several CVD methods for VA-CNT growth have been explored, although the iron / aluminum pre-coated catalyst CVD system was the main focus. A systematic study of several factors, including growth time, temperature, gas ratio, catalyst coating was conducted. The mechanism of VA-CNTs was discussed and a model for VA-CNT length / time was proposed to explain the CNT growth rate. Furthermore, the preferential growth of semiconducting (up to 96 atom% carbon) VA-SWNTs by using a plasma enhanced CVD process combined with fast heating was also explored, and these semiconducting materials have been directly used for making FETs using simple dispersion in organic solvent, without any separation and purification. Also, by inserting electron-accepting nitrogen atoms into the conjugated VA-CNT structure during the growth process, we synthesized vertically aligned nitrogen containing carbon nanotubes (VA-NCNTs). After purification of the metal catalyst, these metal-free VA-NCNTs have shown even better oxidation reduction reaction (ORR) performance than commercially available platinum based electrodes in many aspects, including electrocatalytic activity, long-term operation stability, and tolerance to fuel-molecule crossover. Quantum mechanics calculations and electrochemical experimental results indicate that the charge-deficient carbon atoms around the electron-rich nitrogen atoms improve the ORR reaction and the action of the electrochemical cycling. Finally, by growing vertically aligned carbon nanotubes between graphitic layers in thermally-expanded HOPG, we developed a novel, controlled orientation 3D VA-CNT-graphene architecture, which could allow free transport of electrons and ions. These 3D architectures with a tunable pillar length were demonstrated to be excellent electrode materials for energy related devices. Further, these 3D structures were functionalized with nickel hydroxide by electrodeposition, and the resultant hybrid materials could deliver a high energy density (e.g., ~35 Wh/kg) at a high power density (e.g., ~8 kW/kg), which would significantly outperform many currently available electrode materials.

Synthesis of an ultradense forest of vertically aligned triple-walled carbon nanotubes of uniform diameter and length using hollow catalytic nanoparticles.

PubMed

Baliyan, Ankur; Nakajima, Yoshikata; Fukuda, Takahiro; Uchida, Takashi; Hanajiri, Tatsuro; Maekawa, Toru

2014-01-22

It still remains a crucial challenge to actively control carbon nanotube (CNT) structure such as the alignment, area density, diameter, length, chirality, and number of walls. Here, we synthesize an ultradense forest of CNTs of a uniform internal diameter by the plasma-enhanced chemical vapor deposition (PECVD) method using hollow nanoparticles (HNPs) modified with ligand as a catalyst. The diameters of the HNPs and internal cavities in the HNPs are uniform. A monolayer of densely packed HNPs is self-assembled on a silicon substrate by spin coating. HNPs shrink via the collapse of the internal cavities and phase transition from iron oxide to metallic iron in hydrogen plasma during the PECVD process. Agglomeration of catalytic NPs is avoided on account of the shrinkage of the NPs and ligand attached to the NPs. Diffusion of NPs into the substrate, which would inactivate the growth of CNTs, is also avoided on account of the ligand. As a result, an ultradense forest of triple-walled CNTs of a uniform internal diameter is successfully synthesized. The area density of the grown CNTs is as high as 0.6 × 10(12) cm(-2). Finally, the activity of the catalytic NPs and the NP/carbon interactions during the growth process of CNTs are investigated and discussed. We believe that the present approach may make a great contribution to the development of an innovative synthetic method for CNTs with selective properties.

Filament Winding Multifunctional Carbon Nanotube Composites of Various Dimensionality

NASA Astrophysics Data System (ADS)

Wells, Brian David

Carbon nanotubes (CNT) have been long considered an optimal material for composites due to their high strength, high modulus, and electrical/thermal conductivity. These composite materials have the potential to be used in the aerospace, computer, automotive, medical industry as well as many others. The nano dimensions of these structures make controlled alignment and distribution difficult using many production techniques. An area that shows promise for controlled alignment is the formation of CNT yarns. Different approaches have been used to create yarns with various winding angles and diameters. CNTs resemble traditional textile fiber structures due to their one-dimensional dimensions, axial strength and radial flexibility. One difference is, depending on the length, CNTs can have aspect ratios that far exceed those of traditional textile fibers. This can complicate processing techniques and cause agglomeration which prevents optimal structures from being created. However, with specific aspect ratios and spatial distributions a specific type of CNT, vertically aligned spinnable carbon nanotubes (VASCNTs), have interesting properties that allow carbon nanotubes to be drawn from an array in a continuous aligned web. This dissertation examines the feasibility of combining VASCNTs with another textile manufacturing process, filament winding, to create structures with various levels of dimensionality. While yarn formation with CNTs has been largely studied, there has not been significant work studying the use of VASCNTs to create composite materials. The studies that have been produces revolve around mixing CNTs into epoxy or creating uni-directional wound structures. In this dissertation VASCNTs are used to create filament wound materials with various degrees of alignment. These structures include 1 dimensional coatings applied to non-conductive polymer monofilaments, two dimensional multifunctional adhesive films, and three dimensional hybrid-nano composites. The angle of alignment between the individual CNTs relative to the overall structure was used to affect the electrical properties in all of these structures and the mechanical properties of the adhesive films and hybrid-nano composites. Varying the concentration of CNT was also found to have a significant effect on the electrical and mechanical properties. The variable properties that can be created with these production techniques allow users to engineer the structure to match the desired property.

Filtration-wet transferred transparent conducting films of mm long carbon nanotubes grown using water-assisted chemical vapor deposition.

PubMed

Patole, Shashikant P; Shin, Dong Wook; Fugetsu, Bunshi; Yoo, Ji-Beom

2013-11-01

Transparent conducting films (TCF) made up from carbon nanotubes (CNTs) have a tremendous potential in replacing the indium tin oxide films. Compare to single wall CNTs multiwall CNTs are more metallic and are more suitable candidate for the TCF. In this letter we report the use of selectively grown mm-scale, few-wall, vertically aligned CNTs for the fabrication of TCF. Water-assisted chemical vapor deposition was used to grow the mm-scale CNTs within short growth time. A special post-growth water-vapor treatment allowed us to remove the catalyst-free CNT forest very easily from the substrate and use it for the further process. A filtration-wet transfer process was used to form the TCF. The TCF shows sheet resistance of 228 omega/sq. at 72% transparency (at 550 nm). The ratio of optical conductivity to dc conductivity was observed in between 0.21 to 0.25 for below 80% transmission.

Electrical and Raman spectroscopic studies of vertically aligned multi-walled carbon nanotubes.

PubMed

Mathur, Ashish; Tweedie, Mark; Roy, Susanta Sinha; Maguire, P D; McLaughlin, James A

2009-07-01

Microwave plasma enhanced chemical vapour deposition (MPECVD) was used for the production of carbon nanotubes. Vertically aligned multi-walled carbon nanotubes (MWCNTs) were grown on silicon substrates coated with cobalt thin films of thickness ranging from 0.5 nm to 3 nm. Prior to the nanotube growth the catalyst were treated with N2 plasma for 5-10 minutes that break the films into small nanoparticles which favour the growth of nanotubes. The CNTs were grown at a substrate temperature of 700 degrees C for 5, 10 and 15 minutes. The height of the CNT films ranging from 10 microm-30 microm indicating that the initial growth rate of the CNTs are very high at a rate of approximately 100 nm/sec. Electrical resistivity of the above samples was evaluated from I-V measurements. The activation energy (E(a)) was also calculated from the temperature dependent studies and it was found that the E(a) lies in the range of 15-35 meV. Raman spectroscopy was used to identify the quality of the nanotubes.

Systematic periodicity in waviness of vertically aligned carbon nanotubes explained by helical buckling

NASA Astrophysics Data System (ADS)

Jahangiri, Mehdi

2017-09-01

A hypothesis is proposed in this work to account for the geometry of individual vertically aligned carbon nanotubes (VACNTs) that not only justifies the directionality of their growth, but also explains the origin of the waviness frequently reported for these nanotube forests. Such waviness has fundamental effects on the transport/conduction properties of VACNTs, either through or along them, regarding phenomena such as mass, stress, heat and electricity. Despite the general opinion about randomness of carbon nanotubes (CNTs) tortuosity, we demonstrate here that rules of helical buckling of tubular strings is applicable to VACNTs, based on which a regular 3D helical geometry is proposed for VACNTs, with a 2D sine wave shape side-profile. In this framework, gradual increase of the total free surface energy by growth of CNTs ensues their partial cohesion, driven by van der Waals interactions, to reduce the excess surface energy. On the other hand, their cohesion is accompanied by their deformation and loss of straightness, which in turn, translates to buildup of an elastic strain energy in the system. The balance of the two energies along with the spatial constraints on each CNT at its contact points with neighboring CNTs, is manifested in its helical buckling, that is systematically influenced by nanostructural characteristics of VACNTs, such as their diameter, wall thickness and inter-CNT spacing.

Systematic periodicity in waviness of vertically aligned carbon nanotubes explained by helical buckling.

PubMed

Jahangiri, Mehdi

2017-09-15

A hypothesis is proposed in this work to account for the geometry of individual vertically aligned carbon nanotubes (VACNTs) that not only justifies the directionality of their growth, but also explains the origin of the waviness frequently reported for these nanotube forests. Such waviness has fundamental effects on the transport/conduction properties of VACNTs, either through or along them, regarding phenomena such as mass, stress, heat and electricity. Despite the general opinion about randomness of carbon nanotubes (CNTs) tortuosity, we demonstrate here that rules of helical buckling of tubular strings is applicable to VACNTs, based on which a regular 3D helical geometry is proposed for VACNTs, with a 2D sine wave shape side-profile. In this framework, gradual increase of the total free surface energy by growth of CNTs ensues their partial cohesion, driven by van der Waals interactions, to reduce the excess surface energy. On the other hand, their cohesion is accompanied by their deformation and loss of straightness, which in turn, translates to buildup of an elastic strain energy in the system. The balance of the two energies along with the spatial constraints on each CNT at its contact points with neighboring CNTs, is manifested in its helical buckling, that is systematically influenced by nanostructural characteristics of VACNTs, such as their diameter, wall thickness and inter-CNT spacing.

Development of end-selective functionalized carbon nanotubes for biomedical applications

NASA Astrophysics Data System (ADS)

Lee, Seung Ho; Kim, Wan Sun; Lee, Ha Rim; Park, Kyu Chang; Lee, Chang Hoon; Park, Hun Kuk; Kim, Kyung Sook

2015-12-01

Carbon nanotube (CNT) is a type of carbon allotrope with excellent physical and electrical properties, including high thermal conductivity, mechanical strength, and thermal stability. Therefore, applications of CNT have been considered for a variety of fields, including biosensors, molecular electronics, X-ray, and fuel cells. However, the application of CNT to biomedicine is limited because this material is cytotoxic and inhomogeneous. In particular, the irregularity in the structural properties of paste or bundle-type CNTs causes an uncontrolled modification in biomolecules. Therefore, using CNT as biosensors to obtain quantitative analyses is difficult. In this study, we developed a new method to perform end-selective functionalization of CNT in order to enable quantitative analysis for biomedical applications. The process was as follows: (1) etching the tip of vertically-aligned CNTs under optimum conditions, (2) oxidation of exposed CNTs, and (3) end-selective linkage of functionalized CNTs with biomolecules (dsDNA).

One pot electrochemical synthesis of polymer/CNT/metal nanoparticles for fuel cell applications

NASA Astrophysics Data System (ADS)

Ventrapragada, Lakshman; Zhu, Jingyi; Karakaya, Mehmet; Podila, Ramakrishna; Rao, Apparao; Clemson Nanomaterials center Team

Carbon nanotubes (CNTs) have become a key player in the design of materials for energy applications. They gained their popularity in industrial and scientific research due to their unique properties like excellent conductivity, high surface area, etc. Here we used chemical vapor deposition (CVD) to synthesize two types of CNTs namely, helically coiled CNTs and vertically aligned CNTs. These CNTs were subsequently used to make composites with conducting polymers and metal nanoparticles. One pot electrochemical synthesis was designed to electropolymerize aniline, pyrrole etc. on the surface of the electrode with simultaneous deposition of platinum and gold metal nanoparticles, and CNTs in the polymer matrix. The as synthesized composite materials were characterized with scanning electron microscope for surface morphology and spectroscopic techniques like Raman, UV-Vis for functionality. These were used to study electrocatalytic oxidation of methanol and ethanol for alkaline fuel cell applications. Electrodes fabricated from these composites not only showed good kinetics but also exhibited excellent stability. Uniqueness of this composite lies in its simple two step synthesis and it doesn't involve any surfactants unlike conventional chemical synthesis routes.

Synthesis of Patterned Vertically Aligned Carbon Nanotubes by PECVD Using Different Growth Techniques: A Review.

PubMed

Gangele, Aparna; Sharma, Chandra Shekhar; Pandey, Ashok Kumar

2017-04-01

Immense development has been taken place not only to increase the bulk production, repeatability and yield of carbon nanotubes (CNTs) in last 25 years but preference is also given to acknowledge the basic concepts of nucleation and growth methods. Vertically aligned carbon nanotubes (VAC-NTs) are forest of CNTs accommodated perpendicular on a substrate. Their exceptional chemical and physical properties along with sequential arrangement and dense structure make them suitable in various fields. The effect of different type of selected substrate, carbon precursor, catalyst and their physical and chemical status, reaction conditions and many other key parameters have been thoroughly studied and analysed. The aim of this paper is to specify the trend and summarize the effect of key parameters instead of only presenting all the experiments reported till date. The identified trends will be compared with the recent observations on the growth of different types of patterned VACNTs. In this review article, we have presented a comprehensive analysis of different techniques to precisely determine the role of different parameters responsible for the growth of patterned vertical aligned carbon nanotubes. We have covered various techniques proposed in the span of more than two decades to fabricate the different structures and configurations of carbon nanotubes on different types of substrates. Apart from a detailed discussion of each technique along with their specific process and implementation, we have also provided a critical analysis of the associated constraints, benefits and shortcomings. To sum it all for easy reference for researchers, we have tabulated all the techniques based on certain main key factors. This review article comprises of an exhaustive discussion and a handy reference for researchers who are new in the field of synthesis of CNTs or who wants to get abreast with the techniques of determining the growth of VACNTs arrays.

Thermally Resilient, Broadband Optical Absorber from UV to IR Derived from Carbon Nanostructures

NASA Technical Reports Server (NTRS)

Kaul, Anupama B.; Coles, James B.

2012-01-01

Optical absorber coatings have been developed from carbon-based paints, metal blacks, or glassy carbon. However, such materials are not truly black and have poor absorption characteristics at longer wavelengths. The blackness of such coatings is important to increase the accuracy of calibration targets used in radiometric imaging spectrometers since blackbody cavities are prohibitively large in size. Such coatings are also useful potentially for thermal detectors, where a broadband absorber is desired. Au-black has been a commonly used broadband optical absorber, but it is very fragile and can easily be damaged by heat and mechanical vibration. An optically efficient, thermally rugged absorber could also be beneficial for thermal solar cell applications for energy harnessing, particularly in the 350-2,500 nm spectral window. It has been demonstrated that arrays of vertically oriented carbon nanotubes (CNTs), specifically multi-walled-carbon- nanotubes (MWCNTs), are an exceptional optical absorber over a broad range of wavelengths well into the infrared (IR). The reflectance of such arrays is 100x lower compared to conventional black materials, such as Au black in the spectral window of 350-2,500 nm. Total hemispherical measurements revealed a reflectance of approximately equal to 1.7% at lambda approximately equal to 1 micrometer, and at longer wavelengths into the infrared (IR), the specular reflectance was approximately equal to 2.4% at lambda approximately equal to 7 micrometers. The previously synthesized CNTs for optical absorber applications were formed using water-assisted thermal chemical vapor deposition (CVD), which yields CNT lengths in excess of 100's of microns. Vertical alignment, deemed to be a critical feature in enabling the high optical absorption from CNT arrays, occurs primarily via the crowding effect with thermal CVD synthesized CNTs, which is generally not effective in aligning CNTs with lengths less than 10 m. Here it has been shown that the electric field inherent in a plasma yields vertically aligned CNTs at small length scales (less than 10 m), which still exhibit broadband, and high-efficiency optical absorption characteristics from the ultraviolet (UV) to IR. A thin and yet highly absorbing coating is extremely valuable for detector applications for radiometry in order to enhance sensitivity. A plasma-based process also increases the potential of forming the optical absorbers at lower synthesis temperatures in the future, increasing the prospects of integrating the absorbers with flexible substrates for low-cost solar cell applications, for example.

Aligned carbon nanotubes patterned photolithographically by silver

NASA Astrophysics Data System (ADS)

Huang, Shaoming; Mau, Albert H. W.

2003-02-01

Selective growth of aligned carbon nanotubes (CNTs) by pyrolysis of iron (II) phthalocyanine (FePc) on quartz substrate patterned photolithographically by metallic silver has been demonstrated. Micro/nanopattern of aligned CNTs can be achieved by using a photomask with features on a microscale. With convenient use of simple high-contract black and white films as a photomask, aligned nanotubes patterned with 20 μm resolution in large scale can be fabricated. This practical fabrication of aligned CNTs on patterned conducting substrate could be applied to various device applications of CNTs.

Plasma-assisted nitrogen doping of VACNTs for efficiently enhancing the supercapacitor performance

NASA Astrophysics Data System (ADS)

Mashayekhi, Alireza; Hosseini, Seyed Mahmoud; Hassanpour Amiri, Morteza; Namdar, Naser; Sanaee, Zeinab

2016-06-01

Nitrogen doping of vertically aligned carbon nanotubes (VACNTs) using plasma-enhanced chemical vapour deposition has been investigated to improve the supercapacitance performance of CNTs. Incorporating electrochemical measurements on the open-ended nitrogen-doped CNTs, showed the achievement of 6 times improvement in the capacitance value. For nitrogen-doped CNTs on silicon substrate, specific capacitance of 60 F g-1 was obtained in 0.5 M KCl solution, with capacity retention ratio above 90 % after cycled at 0.1 A g-1 for 5000 cycles. Using this sample, a symmetric supercapacitance was fabricated which showed the power density of 37.5 kW kg-1. The facile fabrication approach and its excellent capacitance improvement, propose it as an efficient technique for enhancing the supercapacitance performance of the carbon-based electrodes.

Vertically aligned BCN nanotubes with high capacitance.

PubMed

Iyyamperumal, Eswaramoorthi; Wang, Shuangyin; Dai, Liming

2012-06-26

Using a chemical vapor deposition method, we have synthesized vertically aligned BCN nanotubes (VA-BCNs) on a Ni-Fe-coated SiO(2)/Si substrate from a melamine diborate precursor. The effects of pyrolysis conditions on the morphology and thermal property of grown nanotubes, as well as the nanostructure and composition of an individual BCN nanotube, were systematically studied. It was found that nitrogen atoms are bonded to carbons in both graphitic and pyridinic forms and that the resultant VA-BCNs grown at 1000 °C show the highest specific capacitance (321.0 F/g) with an excellent rate capability and high durability with respect to nonaligned BCN (167.3 F/g) and undoped multiwalled carbon nanotubes (117.3 F/g) due to synergetic effects arising from the combined co-doping of B and N in CNTs and the well-aligned nanotube structure.

Fabrication of a novel carbon nanotube & graphene based device for gas detection

NASA Astrophysics Data System (ADS)

Khosravi, Yusef; Abdi, Yaser; Arzi, Ezatollah

2018-06-01

We present a novel, simple method for gas detection using a nano-device fabricated on a silicon substrate. The proposed method is based on changing the density of state (DOS) of a graphene sheet during the gas absorption. Fabrication of the carbon nanotube (CNT) and graphene based device for gas detection includes silicon micro machining and the growth of vertically aligned CNTs. Field emission between the as-grown CNTs and the graphene sheet which is placed on top of the CNTs is measured at a liquid nitrogen temperature to obtain the DOS of the structure in different gas environments. The measured local DOS of the structure using the fabricated device showed that each gas had its own signatory spectrum. We believe that this method will open up a new and simple way of fabricating a portable gas spectroscope.

Large-scale synthesis of high-purity well-aligned carbon nanotubes using pyrolysis of iron(II) phthalocyanine and acetylene

NASA Astrophysics Data System (ADS)

Liu, B. C.; Lee, T. J.; Lee, S. H.; Park, C. Y.; Lee, C. J.

2003-08-01

Well-aligned carbon nanotubes (CNTs) with high purity have been produced by pyrolysis of iron(II) phthalocyanine and acetylene at 800 °C. The synthesized CNTs have a length of 75 μm and diameters ranging from 20 to 60 nm. The CNTs have a bamboo-like structure and exhibit good crystallinity of graphite sheets. The growth rate of the CNTs was rapidly increased with adding C 2H 2. Our results demonstrate that the proposed growth method is suitable to large-scale synthesis of high-purity well-aligned CNTs on various substrates.

Separation of methane-nitrogen mixtures using synthesis vertically aligned carbon nanotube membranes

NASA Astrophysics Data System (ADS)

Gilani, Neda; Daryan, Jafar Towfighi; Rashidi, Alimorad; Omidkhah, Mohammad Reza

2012-03-01

In this paper, capabilities of carbon nanotube (CNT) membranes fabricated in cylindrical pores of anodic aluminum oxide (AAO) substrate to separate the binary mixtures of CH4/N2 are studied experimentally. For this purpose, the permeability and selectivity of three CNT/AAO membranes with different growth time as 6 h, 12 h and 18 h are investigated. CNTs are grown vertically through holes of AAO with average pore diameter of 45 nm by chemical vapor deposition (CVD) of acetylene gas. CNT/AAO membranes with the same CNTs' outer diameters and different inner diameters are synthesized. The AAO are characterized by SEM analysis. In addition, SEM, TEM, BET N2 adsorption analysis and Raman spectroscopy are employed to characterize aligned CNTs. Study on permeability and selectivity of membranes for three binary mixtures of CH4/N2 showed that when the CNT inner diameters are 34 nm and 24 nm, viscous flow is the governing mechanism and insignificant selectivities of 1.2-1.24 are achieved. However, the membrane with CNT inner diameter and wall thickness of 8 nm and 16 nm respectively is considerably selective for CH4 over N2. It was also found that CH4 mole fraction in the feed and upstream feed pressure have major effect on permeability and selectivity. The membrane with 18 h synthesis time showed the selectivity is in the range of 1.8-3.85. The enhancement factor for N2 single gas diffusivity was also found to be about three times larger than that predicted by Knudsen diffusion model.

Superaligned carbon nanotube arrays, films, and yarns: a road to applications.

PubMed

Jiang, Kaili; Wang, Jiaping; Li, Qunqing; Liu, Liang; Li, Changhong; Fan, Shoushan

2011-03-04

A superaligned carbon nanotube (CNT) array is a special kind of vertically aligned CNT array with the capability of being converted into continuous fi lms and yarns. The as-produced CNT fi lms are transparent and highly conductive, with aligned CNTs parallel to the direction of drawing. After passing through volatile solutions or being twisted, CNT fi lms can be further condensed into shrunk yarns. These shrunk yarns possess high tensile strengths and Young’s moduli, and are good conductors. Many applications of CNT fi lms and shrunk yarns have been demonstrated, such as TEM grids, loudspeakers, touch screens, etc.

Synthesis of Vertically-Aligned Carbon Nanotubes from Langmuir-Blodgett Films Deposited Fe Nanoparticles on Al2O3/Al/SiO2/Si Substrate.

PubMed

Takagiwa, Shota; Kanasugi, Osamu; Nakamura, Kentaro; Kushida, Masahito

2016-04-01

In order to apply vertically-aligned carbon nanotubes (VA-CNTs) to a new Pt supporting material of polymer electrolyte fuel cell (PEFC), number density and outer diameter of CNTs must be controlled independently. So, we employed Langmuir-Blodgett (LB) technique for depositing CNT growth catalysts. A Fe nanoparticle (NP) was used as a CNT growth catalyst. In this study, we tried to thicken VA-CNT carpet height and inhibit thermal aggregation of Fe NPs by using Al2O3/Al/SiO2/Si substrate. Fe NP LB films were deposited on three typed of substrates, SiO2/Si, as-deposited Al2O3/Al/SiO2/Si and annealed Al2O3/Al/SiO2/Si at 923 K in Ar atmosphere of 16 Pa. It is known that Al2O3/Al catalyzes hydrocarbon reforming, inhibits thermal aggregation of CNT growth catalysts and reduces CNT growth catalysts. It was found that annealed Al2O3/Al/SiO2/Si exerted three effects more strongly than as-deposited Al2O3/Al/SiO2/Si. VA-CNTs were synthesized from Fe NPs-C16 LB films by thermal chemical vapor deposition (CVD) method. As a result, at the distance between two nearest CNTs 28 nm or less, VA-CNT carpet height on annealed Al2O3/Al/SiO2/Si was about twice and ten times thicker than that on SiO2/Si and that on as-deposited Al2O3/Al/SiO2/Si, respectively. Moreover, distribution of CNT outer diameter on annealed Al2O3/Al/SiO2/Si was inhibited compared to that on SiO2/Si. These results suggest that since thermal aggregation of Fe NPs is inhibited, catalyst activity increases and distribution of Fe NP size is inhibited.

Multifunctional Structural-Energy Storage Nanocomposites for Ultra Lightweight Micro Autonomous Systems (First-year Report)

DTIC Science & Technology

2012-02-01

SUBJECT TERMS Carbon nanotubes , CNTs, supercapacitor, multifunctional, energy, structural-Energy 16. SECURITY CLASSIFICATION OF: 17. LIMITATION...Pulickel M. Ajayan of Rice University for providing us with the vertically aligned carbon nanotube (CNT) forests used in this project and for helpful...10–18) and man-portable unmanned vehicles (19). In related research, ARL has also investigated using carbon nanotube (CNT)-based electrodes for

Growth of vertically aligned multiwalled carbon nanotubes forests on metal alloy Ni-Nb-N with low content of catalyst

NASA Astrophysics Data System (ADS)

Dubkov, S.; Trifonov, A.; Shaman, Yu; Pavlov, A.; Shulyat'ev, A.; Skorik, S.; Kirilenko, E. P.; Rygalin, B.

2016-08-01

This research shows the possibility of carbon nanotubes (CNTs) formation on the surface of low nickel (∼ 10 at.%) Ni-Nb-N amorphous metal alloy film by CVD method at 550 °C of the gas mixture based on acetylene. The structure of CNT were studied by transmission and scanning-electron microscopy, energy-dispersive X-ray and the Raman spectroscopy.

Maskless localized patterning of biomolecules on carbon nanotube microarray functionalized by ultrafine atmospheric pressure plasma jet using biotin-avidin system

NASA Astrophysics Data System (ADS)

Abuzairi, Tomy; Okada, Mitsuru; Purnamaningsih, Retno Wigajatri; Poespawati, Nji Raden; Iwata, Futoshi; Nagatsu, Masaaki

2016-07-01

Ultrafine plasma jet is a promising technology with great potential for nano- or micro-scale surface modification. In this letter, we demonstrated the use of ultrafine atmospheric pressure plasma jet (APPJ) for patterning bio-immobilization on vertically aligned carbon nanotube (CNT) microarray platform without a physical mask. The biotin-avidin system was utilized to demonstrate localized biomolecule patterning on the biosensor devices. Using ±7.5 kV square-wave pulses, the optimum condition of plasma jet with He/NH3 gas mixture and 2.5 s treatment period has been obtained to functionalize CNTs. The functionalized CNTs were covalently linked to biotin, bovine serum albumin (BSA), and avidin-(fluorescein isothiocyanate) FITC, sequentially. BSA was necessary as a blocking agent to protect the untreated CNTs from avidin adsorption. The localized patterning results have been evaluated from avidin-FITC fluorescence signals analyzed using a fluorescence microscope. The patterning of biomolecules on the CNT microarray platform using ultrafine APPJ provides a means for potential application of microarray biosensors based on CNTs.

Octahedral Tin Dioxide Nanocrystals Anchored on Vertically Aligned Carbon Aerogels as High Capacity Anode Materials for Lithium-Ion Batteries.

PubMed

Liu, Mingkai; Liu, Yuqing; Zhang, Yuting; Li, Yiliao; Zhang, Peng; Yan, Yan; Liu, Tianxi

2016-08-11

A novel binder-free graphene - carbon nanotubes - SnO2 (GCNT-SnO2) aerogel with vertically aligned pores was prepared via a simple and efficient directional freezing method. SnO2 octahedrons exposed of {221} high energy facets were uniformly distributed and tightly anchored on multidimensional graphene/carbon nanotube (GCNT) composites. Vertically aligned pores can effectively prevent the emersion of "closed" pores which cannot load the active SnO2 nanoparticles, further ensure quick immersion of electrolyte throughout the aerogel, and can largely shorten the transport distance between lithium ions and active sites of SnO2. Especially, excellent electrical conductivity of GCNT-SnO2 aerogel was achieved as a result of good interconnected networks of graphene and CNTs. Furthermore, meso- and macroporous structures with large surface area created by the vertically aligned pores can provide great benefit to the favorable transport kinetics for both lithium ion and electrons and afford sufficient space for volume expansion of SnO2. Due to the well-designed architecture of GCNT-SnO2 aerogel, a high specific capacity of 1190 mAh/g with good long-term cycling stability up to 1000 times was achieved. This work provides a promising strategy for preparing free-standing and binder-free active electrode materials with high performance for lithium ion batteries and other energy storage devices.

Octahedral Tin Dioxide Nanocrystals Anchored on Vertically Aligned Carbon Aerogels as High Capacity Anode Materials for Lithium-Ion Batteries

NASA Astrophysics Data System (ADS)

Liu, Mingkai; Liu, Yuqing; Zhang, Yuting; Li, Yiliao; Zhang, Peng; Yan, Yan; Liu, Tianxi

2016-08-01

A novel binder-free graphene - carbon nanotubes - SnO2 (GCNT-SnO2) aerogel with vertically aligned pores was prepared via a simple and efficient directional freezing method. SnO2 octahedrons exposed of {221} high energy facets were uniformly distributed and tightly anchored on multidimensional graphene/carbon nanotube (GCNT) composites. Vertically aligned pores can effectively prevent the emersion of “closed” pores which cannot load the active SnO2 nanoparticles, further ensure quick immersion of electrolyte throughout the aerogel, and can largely shorten the transport distance between lithium ions and active sites of SnO2. Especially, excellent electrical conductivity of GCNT-SnO2 aerogel was achieved as a result of good interconnected networks of graphene and CNTs. Furthermore, meso- and macroporous structures with large surface area created by the vertically aligned pores can provide great benefit to the favorable transport kinetics for both lithium ion and electrons and afford sufficient space for volume expansion of SnO2. Due to the well-designed architecture of GCNT-SnO2 aerogel, a high specific capacity of 1190 mAh/g with good long-term cycling stability up to 1000 times was achieved. This work provides a promising strategy for preparing free-standing and binder-free active electrode materials with high performance for lithium ion batteries and other energy storage devices.

Multilevel, multicomponent microarchitectures of vertically-aligned carbon nanotubes for diverse applications.

PubMed

Qu, Liangti; Vaia, Rich A; Dai, Liming

2011-02-22

A simple multiple contact transfer technique has been developed for controllable fabrication of multilevel, multicomponent microarchitectures of vertically aligned carbon nanotubes (VA-CNTs). Three dimensional (3-D) multicomponent micropatterns of aligned single-walled carbon nanotubes (SWNTs) and multiwalled carbon nanotubes (MWNTs) have been fabricated, which can be used to develop a newly designed touch sensor with reversible electrical responses for potential applications in electronic devices, as demonstrated in this study. The demonstrated dependence of light diffraction on structural transfiguration of the resultant CNT micropattern also indicates their potential for optical devices. Further introduction of various components with specific properties (e.g., ZnO nanorods) into the CNT micropatterns enabled us to tailor such surface characteristics as wettability and light response. Owing to the highly generic nature of the multiple contact transfer strategy, the methodology developed here could provide a general approach for interposing a large variety of multicomponent elements (e.g., nanotubes, nanorods/wires, photonic crystals, etc.) onto a single chip for multifunctional device applications.

Three-dimensional machining of carbon nanotube forests using water-assisted scanning electron microscope processing

NASA Astrophysics Data System (ADS)

Rajabifar, Bahram; Kim, Sanha; Slinker, Keith; Ehlert, Gregory J.; Hart, A. John; Maschmann, Matthew R.

2015-10-01

We demonstrate that vertically aligned carbon nanotubes (CNTs) can be precisely machined in a low pressure water vapor ambient using the electron beam of an environmental scanning electron microscope. The electron beam locally damages the irradiated regions of the CNT forest and also dissociates the water vapor molecules into reactive species including hydroxyl radicals. These species then locally oxidize the damaged region of the CNTs. The technique offers material removal capabilities ranging from selected CNTs to hundreds of cubic microns. We study how the material removal rate is influenced by the acceleration voltage, beam current, dwell time, operating pressure, and CNT orientation. Milled cuts with depths between 0-100 microns are generated, corresponding to a material removal rate of up to 20.1 μm3/min. The technique produces little carbon residue and does not disturb the native morphology of the CNT network. Finally, we demonstrate direct machining of pyramidal surfaces and re-entrant cuts to create freestanding geometries.

Three-dimensional machining of carbon nanotube forests using water-assisted scanning electron microscope processing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rajabifar, Bahram; Maschmann, Matthew R., E-mail: MaschmannM@missouri.edu; Kim, Sanha

2015-10-05

We demonstrate that vertically aligned carbon nanotubes (CNTs) can be precisely machined in a low pressure water vapor ambient using the electron beam of an environmental scanning electron microscope. The electron beam locally damages the irradiated regions of the CNT forest and also dissociates the water vapor molecules into reactive species including hydroxyl radicals. These species then locally oxidize the damaged region of the CNTs. The technique offers material removal capabilities ranging from selected CNTs to hundreds of cubic microns. We study how the material removal rate is influenced by the acceleration voltage, beam current, dwell time, operating pressure, andmore » CNT orientation. Milled cuts with depths between 0–100 microns are generated, corresponding to a material removal rate of up to 20.1 μm{sup 3}/min. The technique produces little carbon residue and does not disturb the native morphology of the CNT network. Finally, we demonstrate direct machining of pyramidal surfaces and re-entrant cuts to create freestanding geometries.« less

Ethanol flame synthesis of carbon nanotubes in deficient oxygen environments

NASA Astrophysics Data System (ADS)

Hu, Wei-Chieh; Lin, Ta-Hui

2016-04-01

In this study, carbon nanotubes (CNTs) were synthesized using ethanol diffusion flames in a stagnation-flow system composed of an upper oxidizer duct and a lower liquid pool. In the experiments, a gaseous mixture of oxygen and nitrogen flowed from the upper oxidizer duct, and then impinged onto the vertically aligned ethanol pool to generate a planar and steady diffusion flame in a deficient oxygen environment. A nascent nickel mesh was used as the catalytic metal substrate to collect deposited materials. The effect of low oxygen concentration on the formation of CNTs was explored. The oxygen concentration significantly influenced the flame environment and thus the synthesized carbon products. Lowering the oxygen concentration increased the yield, diameter, and uniformity of CNTs. The optimal operating conditions for CNT synthesis were an oxygen concentration in the range of 15%-19%, a flame temperature in the range of 460 °C-870 °C, and a sampling position of 0.5-1 mm below the upper edge of the blue flame front. It is noteworthy that the concentration gradient of C2 species and CO governed the CNT growth directly. CNTs were successfully fabricated in regions with uniform C2 species and CO distributions.

Metal-modified and vertically aligned carbon nanotube sensors array for landfill gas monitoring applications.

PubMed

Penza, M; Rossi, R; Alvisi, M; Serra, E

2010-03-12

Vertically aligned carbon nanotube (CNT) layers were synthesized on Fe-coated low-cost alumina substrates using radio-frequency plasma enhanced chemical vapour deposition (RF-PECVD) technology. A miniaturized CNT-based gas sensor array was developed for monitoring landfill gas (LFG) at a temperature of 150 degrees C. The sensor array was composed of 4 sensing elements with unmodified CNT, and CNT loaded with 5 nm nominally thick sputtered nanoclusters of platinum (Pt), ruthenium (Ru) and silver (Ag). Chemical analysis of multicomponent gas mixtures constituted of CO(2), CH(4), H(2), NH(3), CO and NO(2) has been performed by the array sensor responses and pattern recognition based on principal component analysis (PCA). The PCA results demonstrate that the metal-decorated and vertically aligned CNT sensor array is able to discriminate the NO(2) presence in the multicomponent mixture LFG. The NO(2) gas detection in the mixture LFG was proved to be very sensitive, e.g.: the CNT:Ru sensor shows a relative change in the resistance of 1.50% and 0.55% for NO(2) concentrations of 3.3 ppm and 330 ppb dispersed in the LFG, respectively, with a wide NO(2) gas concentration range measured from 0.33 to 3.3 ppm, at the sensor temperature of 150 degrees C. The morphology and structure of the CNT networks have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. A forest-like nanostructure of vertically aligned CNT bundles in the multi-walled form appeared with a height of about 10 microm and a single-tube diameter varying in the range of 5-35 nm. The intensity ratio of the Raman spectroscopy D-peak and G-peak indicates the presence of disorder and defects in the CNT networks. The size of the metal (Pt, Ru, Ag) nanoclusters decorating the CNT top surface varies in the range of 5-50 nm. Functional characterization based on electrical charge transfer sensing mechanisms in the metal-modified CNT-chemoresistor array demonstrates high sensitivity by providing minimal sub-ppm level detection, e.g., download up to 100 ppb NO(2), at the sensor temperature of 150 degrees C. The gas sensitivity of the CNT sensor array depends on operating temperature, showing a lower optimal temperature of maximum sensitivity for the metal-decorated CNT sensors compared to unmodified CNT sensors. Results indicate that the recovery mechanisms in the CNT chemiresistors can be altered by a rapid heating pulse from room temperature to about 110 degrees C. A comparison of the NO(2) gas sensitivity for the chemiresistors based on disorderly networked CNTs and vertically aligned CNTs is also reported. Cross-sensitivity towards relative humidity of the CNT sensors array is investigated. Finally, the sensing properties of the metal-decorated and vertically aligned CNT sensor arrays are promising to monitor gas events in the LFG for practical applications with low power consumption and moderate sensor temperature.

High performance carbon nanotube-Si core-shell wires with a rationally structured core for lithium ion battery anodes.

PubMed

Fan, Yu; Zhang, Qing; Lu, Congxiang; Xiao, Qizhen; Wang, Xinghui; Tay, Beng Kang

2013-02-21

Core-shell Si nanowires are very promising anode materials. Here, we synthesize vertically aligned carbon nanotubes (CNTs) with relatively large diameters and large inter-wire spacing as core wires and demonstrate a CNT-Si core-shell wire composite as a lithium ion battery (LIB) anode. Owing to the rationally engineered core structure, the composite shows good capacity retention and rate performance. The excellent performance is superior to most core-shell nanowires previously reported.

Optical properties of ordered vertical arrays of multi-walled carbon nanotubes from FDTD simulations.

PubMed

Bao, Hua; Ruan, Xiulin; Fisher, Timothy S

2010-03-15

A finite-difference time-domain (FDTD) method is used to model thermal radiative properties of vertical arrays of multi-walled carbon nanotubes (MWCNT). Individual CNTs are treated as solid circular cylinders with an effective dielectric tensor. Consistent with experiments, the results confirm that CNT arrays are highly absorptive. Compared with the commonly used Maxwell-Garnett theory, the FDTD calculations generally predict larger reflectance and absorbance, and smaller transmittance, which are attributed to the diffraction and scattering within the cylinder array structure. The effects of volume fraction, tube length, tube distance, and incident angle on radiative properties are investigated systematically. Low volume fraction and long tubes are more favorable to achieve low reflectance and high absorbance. For a fixed volume fraction and finite tube length, larger periodicity results in larger reflectance and absorbance. The angular dependence studies reveal an optimum incident angle at which the reflectance can be minimized. The results also suggest that an even darker material could be achieved by using CNTs with good alignment on the top surface.

Competing mechanisms and scaling laws for carbon nanotube scission by ultrasonication.

PubMed

Pagani, Guido; Green, Micah J; Poulin, Philippe; Pasquali, Matteo

2012-07-17

Dispersion of carbon nanotubes (CNTs) into liquids typically requires ultrasonication to exfoliate individuals CNTs from bundles. Experiments show that CNT length drops with sonication time (or energy) as a power law t(-m). Yet the breakage mechanism is not well understood, and the experimentally reported power law exponent m ranges from approximately 0.2 to 0.5. Here we simulate the motion of CNTs around cavitating bubbles by coupling brownian dynamics with the Rayleigh-Plesset equation. We observe that, during bubble growth, CNTs align tangentially to the bubble surface. Surprisingly, we find two dynamical regimes during the collapse: shorter CNTs align radially, longer ones buckle. We compute the phase diagram for CNT collapse dynamics as a function of CNT length, stiffness, and initial distance from the bubble nuclei and determine the transition from aligning to buckling. We conclude that, depending on their length, CNTs can break due to either buckling or stretching. These two mechanisms yield different power laws for the length decay (0.25 and 0.5, respectively), reconciling the apparent discrepancy in the experimental data.

Carbon nanotubes based vacuum gauge

NASA Astrophysics Data System (ADS)

Rudyk, N. N.; Il'in, O. I.; Il'ina, M. V.; Fedotov, A. A.; Klimin, V. S.; Ageev, O. A.

2017-11-01

We have created an ionization type Vacuum gauge with sensor element based on an array of vertically aligned carbon nanotubes. Obtained asymmetrical current-voltage characteristics at different voltage polarity on the electrode with the CNTs. It was found that when applying a negative potential on an electrode with the CNTs, the current in the gap is higher than at a positive potential. In the pressure range of 1 ÷ 103 Torr vacuum gauge sensitivity was 6 mV/Torr (at a current of 4.5·10-5 A) and in the range of 10-5 ÷ 1 Torr was 10 mV/Torr (at a current of 1.3·10-5 A). It is shown that the energy efficiency of vacuum gauge can be increased in the case where electrode with CNT operates as an emitter of electrons.

Highly selective electrodeposition of sub-10 nm crystalline noble metallic nanorods inside vertically aligned multiwall carbon nanotubes.

PubMed

Wang, Xuyang; Wang, Ranran; Wu, Qiang; Zhang, Xiaohua; Yang, Zhaohui; Guo, Jun; Chen, Muzi; Tang, Minghua; Cheng, Yajun; Chu, Haibin

2016-07-08

In this paper crystalline noble metallic nanorods including Au and Ag with sub-10 nm diameter, are encapsulated within prealigned and open-ended multiwall carbon nanotubes (MWCNTs) through an electrodeposition method. As the external surface of CNTs has been insulated by the epoxy the CNT channel becomes the only path for the mass transport as well as the nanoreactor for the metal deposition. Highly crystallized Au and Ag2O nanorods parallel to the radial direction of CNTs are confirmed by high-resolution transmission electron microscopy, energy dispersive x-ray spectroscopy and x-ray powder diffraction spectroscopy. The Ag2O nanorods are formed by air oxidation on the Ag metals and show a single crystalline structure with (111) planes. The Au nanorods exhibit a complex crystalline structure including twin-crystal and lattice dislocation with (111) and (200) planes. These crystalline noble metallic nanostructures may have important applications for nanocatalysts for fuel cells as well as nanoelectronic and nanophotonic devices. This method is deemed to benefit the precise deposition of other crystalline nanostructures inside CNTs with a small diameter.

Highly selective electrodeposition of sub-10 nm crystalline noble metallic nanorods inside vertically aligned multiwall carbon nanotubes

NASA Astrophysics Data System (ADS)

Wang, Xuyang; Wang, Ranran; Wu, Qiang; Zhang, Xiaohua; Yang, Zhaohui; Guo, Jun; Chen, Muzi; Tang, Minghua; Cheng, Yajun; Chu, Haibin

2016-07-01

In this paper crystalline noble metallic nanorods including Au and Ag with sub-10 nm diameter, are encapsulated within prealigned and open-ended multiwall carbon nanotubes (MWCNTs) through an electrodeposition method. As the external surface of CNTs has been insulated by the epoxy the CNT channel becomes the only path for the mass transport as well as the nanoreactor for the metal deposition. Highly crystallized Au and Ag2O nanorods parallel to the radial direction of CNTs are confirmed by high-resolution transmission electron microscopy, energy dispersive x-ray spectroscopy and x-ray powder diffraction spectroscopy. The Ag2O nanorods are formed by air oxidation on the Ag metals and show a single crystalline structure with (111) planes. The Au nanorods exhibit a complex crystalline structure including twin-crystal and lattice dislocation with (111) and (200) planes. These crystalline noble metallic nanostructures may have important applications for nanocatalysts for fuel cells as well as nanoelectronic and nanophotonic devices. This method is deemed to benefit the precise deposition of other crystalline nanostructures inside CNTs with a small diameter.

Sensing Properties of Multiwalled Carbon Nanotubes Grown in MW Plasma Torch: Electronic and Electrochemical Behavior, Gas Sensing, Field Emission, IR Absorption

PubMed Central

Majzlíková, Petra; Sedláček, Jiří; Prášek, Jan; Pekárek, Jan; Svatoš, Vojtěch; Bannov, Alexander G.; Jašek, Ondřej; Synek, Petr; Eliáš, Marek; Zajíčková, Lenka; Hubálek, Jaromír

2015-01-01

Vertically aligned multi-walled carbon nanotubes (VA-MWCNTs) with an average diameter below 80 nm and a thickness of the uniform VA-MWCNT layer of about 16 μm were grown in microwave plasma torch and tested for selected functional properties. IR absorption important for a construction of bolometers was studied by Fourier transform infrared spectroscopy. Basic electrochemical characterization was performed by cyclic voltammetry. Comparing the obtained results with the standard or MWCNT‐modified screen-printed electrodes, the prepared VA-MWCNT electrodes indicated their high potential for the construction of electrochemical sensors. Resistive CNT gas sensor revealed a good sensitivity to ammonia taking into account room temperature operation. Field emission detected from CNTs was suitable for the pressure sensing application based on the measurement of emission current in the diode structure with bending diaphragm. The advantages of microwave plasma torch growth of CNTs, i.e., fast processing and versatility of the process, can be therefore fully exploited for the integration of surface-bound grown CNTs into various sensing structures. PMID:25629702

Investigation of H2S separation from H2S/CH4 mixtures using functionalized and non-functionalized vertically aligned carbon nanotube membranes

NASA Astrophysics Data System (ADS)

Gilani, Neda; Towfighi, Jafar; Rashidi, Alimorad; Mohammadi, Toraj; Omidkhah, Mohammad Reza; Sadeghian, Ahmad

2013-04-01

Separation of H2S from binary mixtures of H2S/CH4 using vertically aligned carbon nanotube membranes fabricated in anodic aluminum oxide (AAO) template was studied experimentally. Carbon nanotubes (CNTs) were grown in five AAO templates with different pore diameters using chemical vapor deposition, and CNT/AAO membranes with tubular carbon nanotube structure and open caps were selected for separation of H2S. For this, two tubular CNT/AAO membranes were fabricated with the CNT inner diameters of 23 and 8 nm. It was found that permeability and selectivity of the membrane with inner diameter of 23 nm for CNT were independent of upstream feed pressure and H2S feed concentration unlike that of CNT having an inner diameter of 8 nm. Selectivity of these membranes for separation of H2S was obtained in the ranges of 1.36-1.58 and 2.11-2.86, for CNTs with internal diameters of 23 and 8 nm, respectively. In order to enhance the separation of H2S from H2S/CH4 mixtures, dodecylamine was used to functionalize the CNT/AAO membrane with higher selectivity. The results showed that for amido-functionalized membrane, both upstream feed pressure and H2S partial pressure in the feed significantly increased H2S permeability, and selectivity for H2S being in the range of 3.0-5.57 respectively.

Promotion of Water Channels for Enhanced Ion Transport in 14 nm Diameter Carbon Nanotubes.

PubMed

Sheng, Jiadong; Zhu, Qi; Zeng, Xian; Yang, Zhaohui; Zhang, Xiaohua

2017-03-29

Ion transport plays an important role in solar-to-electricity conversion, drug delivery, and a variety of biological processes. Carbon nanotube (CNT) is a promising material as an ion transporter in the applications of the mimicking of natural ion channels, desalination, and energy harvesting. Here, we demonstrate a unique, enhanced ion transport through a vertically aligned multiwall CNT membrane after the application of an electric potential across CNT membranes. Interestingly, electrowetting arising from the application of an electric potential is critical for the enhancement of overall ion transport rate through CNT membranes. The wettability of a liquid with high surface tension on the interior channel walls of CNTs increases during an electric potential treatment and promotes the formation of water channels in CNTs. The formation of water channels in CNTs induces an increase in overall ion diffusion through CNT membranes. This phenomenon is also related to a decrease in the charge transfer resistance of CNTs (R ct ) after an electric potential is applied. Correspondingly, the enhanced ion flow rate gives rise to an enhancement in the capacitive performance of CNT based membranes. Our observations might have profound impact on the development of CNT based energy storage devices as well as artificial ion channels.

Effect of distribution, interface property and density of hydrogel-embedded vertically aligned carbon nanotube arrays on the properties of a flexible solid state supercapacitor

NASA Astrophysics Data System (ADS)

Zhu, Qi; Yuan, Xietao; Zhu, Yihao; Ni, Jiangfeng; Zhang, Xiaohua; Yang, Zhaohui

2018-05-01

In this paper we fabricate a robust flexible solid-state supercapacitor (FSC) device by embedding a conductive poly(vinyl alcohol) hydrogel into aligned carbon nanotube (CNT) arrays. We carefully investigate the effect of distribution, interface properties and densification of CNTs in the gel matrix on the electrochemical properties of an FSC. The total electrochemical capacitance of the device is measured to be 227 mF cm‑3 with a maximum energy density of 0.02 mWh cm‑3, which is dramatically enhanced compared with a similar device composed of non-parallel CNTs. Additionally, controllable in situ electrochemical oxidation greatly improved the compatibility between the hydrophobic CNTs and the hydrophilic hydrogel, which decreased the resistance of the device and introduced extra pseudocapacitance. After such oxidation treatment the energy storage ability further doubled to 430 mF cm‑3 with a maximum energy density of 0.04 mWh cm‑3 . The FSCs based on densified CNT arrays exhibited a much higher volumetric capacitance of 1140 mF cm‑3 and a larger energy density of 0.1 mWh cm‑3, with a large power density of 14 mW cm‑3. All devices show excellent stability of capacitance after at least 10 000 charge–discharge cycles with a loss of less than 2%. These easy-to-assemble hybrid arrays thus potentially provide a new method for manufacturing wearable devices and implantable medical devices.

Effect of distribution, interface property and density of hydrogel-embedded vertically aligned carbon nanotube arrays on the properties of a flexible solid state supercapacitor.

PubMed

Zhu, Qi; Yuan, Xietao; Zhu, Yihao; Ni, Jiangfeng; Zhang, Xiaohua; Yang, Zhaohui

2018-05-11

In this paper we fabricate a robust flexible solid-state supercapacitor (FSC) device by embedding a conductive poly(vinyl alcohol) hydrogel into aligned carbon nanotube (CNT) arrays. We carefully investigate the effect of distribution, interface properties and densification of CNTs in the gel matrix on the electrochemical properties of an FSC. The total electrochemical capacitance of the device is measured to be 227 mF cm -3 with a maximum energy density of 0.02 mWh cm -3 , which is dramatically enhanced compared with a similar device composed of non-parallel CNTs. Additionally, controllable in situ electrochemical oxidation greatly improved the compatibility between the hydrophobic CNTs and the hydrophilic hydrogel, which decreased the resistance of the device and introduced extra pseudocapacitance. After such oxidation treatment the energy storage ability further doubled to 430 mF cm -3 with a maximum energy density of 0.04 mWh cm -3 . The FSCs based on densified CNT arrays exhibited a much higher volumetric capacitance of 1140 mF cm -3 and a larger energy density of 0.1 mWh cm -3 , with a large power density of 14 mW cm -3 . All devices show excellent stability of capacitance after at least 10 000 charge-discharge cycles with a loss of less than 2%. These easy-to-assemble hybrid arrays thus potentially provide a new method for manufacturing wearable devices and implantable medical devices.

Analytical, numerical, and experimental investigations on effective mechanical properties and performances of carbon nanotubes and nanotube based nanocomposites with novel three dimensional nanostructures

NASA Astrophysics Data System (ADS)

Askari, Davood

The theoretical objectives and accomplishment of this work are the analytical and numerical investigation of material properties and mechanical behavior of carbon nanotubes (CNTs) and nanotube nanocomposites when they are subjected to various loading conditions. First, the finite element method is employed to investigate numerically the effective Young's modulus and Poisson's ratio of a single-walled CNT. Next, the effects of chirality on the effective Young's modulus and Poisson's ratio are investigated and then variations of their effective coefficient of thermal expansions and effective thermal conductivities are studied for CNTs with different structural configurations. To study the influence of small vacancy defects on mechanical properties of CNTs, finite element analyses are performed and the behavior of CNTs with various structural configurations having different types of vacancy defects is studied. It is frequently reported that nano-materials are excellent candidates as reinforcements in nanocomposites to change or enhance material properties of polymers and their nanocomposites. Second, the inclusion of nano-materials can considerably improve electrical, thermal, and mechanical properties of the bonding agent, i.e., resin. Note that, materials atomic and molecular level do not usually show isotropic behaviour, rather they have orthotropic properties. Therefore, two-phase and three-phase cylindrically orthotropic composite models consisting of different constituents with orthotropic properties are developed and introduced in this work to analytically predict the effective mechanical properties and mechanical behavior of such structures when they are subjected to various external loading conditions. To verify the analytically obtained exact solutions, finite element analyses of identical cylindrical structures are also performed and then results are compared with those obtained analytically, and excellent agreement is achieved. The third part of this dissertation investigates the growth of vertically aligned, long, and high density arrays of CNTs and novel 3-D carbon nanotube nano-forests. A Chemical vapor deposition technique is used to grow radially aligned CNTs on various types of fibrous materials such as silicon carbide, carbon, Kevlar, and glass fibers and clothes that can be used for the fabrication of multifunctional high performing laminated nanocomposite structures. Using the CNTs nano-forest clothes, nanocomposite samples are prepared and tested giving promising results for the improvement of mechanical properties and performance of composites structures.

Controlled Deposition and Alignment of Carbon Nanotubes

NASA Technical Reports Server (NTRS)

Smits, Jan M. (Inventor); Wincheski, Russell A. (Inventor); Ingram, JoAnne L. (Inventor); Watkins, Anthony Neal (Inventor); Jordan, Jeffrey D. (Inventor)

2009-01-01

A carbon nanotube (CNT) attraction material is deposited on a substrate in the gap region between two electrodes on the . substrate. An electric potential is applied to the two electrodes. The CNT attraction material is wetted with a solution defined by a carver liquid having carbon nanotubes (CNTs) suspended therein. A portion of the CNTs align with the electric field and adhere to The CNT attraction material. The carrier liquid and any CNTs not adhered to the CNT attraction material are then removed.

Controlled Deposition and Alignment of Carbon Nanotubes

NASA Technical Reports Server (NTRS)

Patry, JoAnne L. (Inventor); Smits, Jan M. (Inventor); Watkins, Anthony Neal (Inventor); Jordan, Jeffrey D. (Inventor); Wincheski, Russell A. (Inventor)

2012-01-01

A carbon nanotube (CNT) attraction material is deposited on a substrate in the gap region between two electrodes on the substrate. An electric potential is applied to the two electrodes. The CNT attraction material is wetted with a solution defined by a carrier liquid having carbon nanotubes (CNTs) suspended therein. A portion of the CNTs align with the electric field and adhere to the CNT attraction material. The carrier liquid and any CNTs not adhered to the CNT attraction material are then removed.

Field emission luminescence of nanodiamonds deposited on the aligned carbon nanotube array

NASA Astrophysics Data System (ADS)

Fedoseeva, Yu. V.; Bulusheva, L. G.; Okotrub, A. V.; Kanygin, M. A.; Gorodetskiy, D. V.; Asanov, I. P.; Vyalikh, D. V.; Puzyr, A. P.; Bondar, V. S.

2015-03-01

Detonation nanodiamonds (NDs) were deposited on the surface of aligned carbon nanotubes (CNTs) by immersing a CNT array in an aqueous suspension of NDs in dimethylsulfoxide (DMSO). The structure and electronic state of the obtained CNT-ND hybrid material were studied using optical and electron microscopy and Infrared, Raman, X-ray photoelectron and near-edge X-ray absorption fine structure spectroscopy. A non-covalent interaction between NDs and CNT and preservation of vertical orientation of CNTs in the hybrid were revealed. We showed that current-voltage characteristics of the CNT-ND cathode are changed depending on the applied field; below ~3 V/µm they are similar to those of the initial CNT array and at the higher field they are close to the ND behavior. Involvement of the NDs in field emission process resulted in blue luminescence of the hybrid surface at an electric field higher than 3.5 V/µm. Photoluminescence measurements showed that the NDs emit blue-green light, while blue luminescence prevails in the CNT-ND hybrid. The quenching of green luminescence was attributed to a partial removal of oxygen-containing groups from the ND surface as the result of the hybrid synthesis.

Growth kinetics of vertically aligned carbon nanotube arrays in clean oxygen-free conditions.

PubMed

In, Jung Bin; Grigoropoulos, Costas P; Chernov, Alexander A; Noy, Aleksandr

2011-12-27

Vertically aligned carbon nanotubes (CNTs) are an important technological system, as well as a fascinating system for studying basic principles of nanomaterials synthesis; yet despite continuing efforts for the past decade many important questions about this process remain largely unexplained. We present a series of parametric ethylene chemical vapor deposition growth studies in a "hot-wall" reactor using ultrapure process gases that reveal the fundamental kinetics of the CNT growth. Our data show that the growth rate is proportional to the concentration of the carbon feedstock and monotonically decreases with the concentration of hydrogen gas and that the most important parameter determining the rate of the CNT growth is the production rate of active carbon precursor in the gas phase reaction. The growth termination times obtained with the purified gas mixtures were strikingly insensitive to variations in both hydrogen and ethylene pressures ruling out the carbon encapsulation of the catalyst as the main process termination cause.

Peeling off effects in vertically aligned Fe3C filled carbon nanotubes films grown by pyrolysis of ferrocene

NASA Astrophysics Data System (ADS)

Boi, Filippo S.; Medranda, Daniel; Ivaturi, Sameera; Wang, Jiayu; Guo, Jian; Lan, Mu; Wen, Jiqiu; Wang, Shanling; He, Yi; Mountjoy, Gavin; Willis, Maureen A. C.; Xiang, Gang

2017-06-01

We report the observation of an unusual self-peeling effect which allows the synthesis of free standing vertically aligned carbon nanotube films filled with large quantities of Fe3C and small quantities of γ-Fe crystals. We demonstrate that this effect depends on the interplay of three main factors: (1) the physical interactions between the chosen substrate surface and grown carbon nanotubes (CNTs), which is fixed by the composition of the used substrate (111 SiO2/Si or quartz), (2) the CNT-CNT Van der Waals interactions, and (3) the differential thermal contraction between the grown CNT film and the used substrate, which is fixed by the cooling rate differences between the grown film and the used quartz or Si/SiO2 substrates. The width and stability of these films are then further increased to cm-scale by addition of small quantities of toluene to the ferrocene precursor.

High Current Emission from Patterned Aligned Carbon Nanotubes Fabricated by Plasma-Enhanced Chemical Vapor Deposition

NASA Astrophysics Data System (ADS)

Cui, Linfan; Chen, Jiangtao; Yang, Bingjun; Jiao, Tifeng

2015-12-01

Vertically, carbon nanotube (CNT) arrays were successfully fabricated on hexagon patterned Si substrates through radio frequency plasma-enhanced chemical vapor deposition using gas mixtures of acetylene (C2H2) and hydrogen (H2) with Fe/Al2O3 catalysts. The CNTs were found to be graphitized with multi-walled structures. Different H2/C2H2 gas flow rate ratio was used to investigate the effect on CNT growth, and the field emission properties were optimized. The CNT emitters exhibited excellent field emission performance (the turn-on and threshold fields were 2.1 and 2.4 V/μm, respectively). The largest emission current could reach 70 mA/cm2. The emission current was stable, and no obvious deterioration was observed during the long-term stability test of 50 h. The results were relevant for practical applications based on CNTs.

Growth of primary motor neurons on horizontally aligned carbon nanotube thin films and striped patterns

NASA Astrophysics Data System (ADS)

Roberts, Megan J.; Leach, Michelle K.; Bedewy, Mostafa; Meshot, Eric R.; Copic, Davor; Corey, Joseph M.; Hart, A. John

2014-06-01

Objective. Carbon nanotubes (CNTs) are attractive for use in peripheral nerve interfaces because of their unique combination of strength, flexibility, electrical conductivity and nanoscale surface texture. Here we investigated the growth of motor neurons on thin films of horizontally aligned CNTs (HACNTs). Approach. We cultured primary embryonic rat motor neurons on HACNTs and performed statistical analysis of the length and orientation of neurites. We next presented motor neurons with substrates of alternating stripes of HACNTs and SiO2. Main results. The neurons survived on HACNT substrates for up to eight days, which was the full duration of our experiments. Statistical analysis of the length and orientation of neurites indicated that the longest neurites on HACNTs tended to align with the CNT direction, although the average neurite length was similar between HACNTs and glass control substrates. We observed that when motor neurons were presented with alternating stripes of HACNTs and SiO2, the proportion of neurons on HACNTs increases over time, suggesting that neurons selectively migrate toward and adhere to the HACNT surface. Significance. The behavior of motor neurons on CNTs has not been previously investigated, and we show that aligned CNTs could provide a viable interface material to motor neurons. Combined with emerging techniques to build complex hierarchical structures of CNTs, our results suggest that organised CNTs could be incorporated into nerve grafts that use physical and electrical cues to guide regenerating axons.

Growth of carbon nanotubes at low powers by impedance-matched microwave plasma enhanced chemical vapor deposition method.

PubMed

Chen, S Y; Chang, L W; Peng, C W; Miao, H Y; Lue, Juh-Tzeng

2005-11-01

A solo carbon nanotube (CNT) was successfully grown on nickel electrodes by a microwave plasma enhanced chemical vapor deposition (MPECVD) method equipped with an impedance-matched substrate holder with the reaction gases composed of hydrogen (H2), carbon dioxide (CO2), and methane (CH4) mixtures. An introduction of carbon dioxide gas before CNTs growth, the substrate temperature can easily be reached above 610 degrees C even heated at a low microwave power. This can be enunciated from fact that carbon dioxide inherits with higher bond energy for molecular dissociation, lower thermal conductivity, and higher heat capacity in comparing to other gases. The electron field emissions for randomly aligned CNTs and well-aligned CNTs grown by MPECVD and by radio frequency assisted hot-filament methods, respectively, are measured and compared. The higher field emission characteristic of the randomly aligned CNTs is presumed to be due to the protruded CNTs, which inheriting with less screening effect and manifesting with defects are crucial to play the effective emission sites.

Oxygen-promoted catalyst sintering influences number density, alignment, and wall number of vertically aligned carbon nanotubes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shi, Wenbo; Li, Jinjing; Polsen, Erik S.

A lack of synthetic control and reproducibility during vertically aligned carbon nanotube (CNT) synthesis has stifled many promising applications of organic nanomaterials. Oxygen-containing species are particularly precarious in that they have both beneficial and deleterious effects and are notoriously difficult to control. In this paper, we demonstrated diatomic oxygen's ability, independent of water, to tune oxide-supported catalyst thin film dewetting and influence nanoscale (diameter and wall number) and macro-scale (alignment and density) properties for as-grown vertically aligned CNTs. In particular, single- or few-walled CNT forests were achieved at very low oxygen loading, with single-to-multi-walled CNT diameters ranging from 4.8 ±more » 1.3 nm to 6.4 ± 1.1 nm over 0–800 ppm O 2, and an expected variation in alignment, where both were related to the annealed catalyst morphology. Morphological differences were not the result of subsurface diffusion, but instead occurred via Ostwald ripening under several hundred ppm O 2, and this effect was mitigated by high H 2 concentrations and not due to water vapor (as confirmed in O 2-free water addition experiments), supporting the importance of O 2 specifically. Further characterization of the interface between the Fe catalyst and Al 2O 3 support revealed that either oxygen-deficit metal oxide or oxygen-adsorption on metals could be functional mechanisms for the observed catalyst nanoparticle evolution. Finally, taken as a whole, our results suggest that the impacts of O 2 and H 2 on the catalyst evolution have been underappreciated and underleveraged in CNT synthesis, and these could present a route toward facile manipulation of CNT forest morphology through control of the reactive gaseous atmosphere alone.« less

Oxygen-promoted catalyst sintering influences number density, alignment, and wall number of vertically aligned carbon nanotubes.

PubMed

Shi, Wenbo; Li, Jinjing; Polsen, Erik S; Oliver, C Ryan; Zhao, Yikun; Meshot, Eric R; Barclay, Michael; Fairbrother, D Howard; Hart, A John; Plata, Desiree L

2017-04-20

A lack of synthetic control and reproducibility during vertically aligned carbon nanotube (CNT) synthesis has stifled many promising applications of organic nanomaterials. Oxygen-containing species are particularly precarious in that they have both beneficial and deleterious effects and are notoriously difficult to control. Here, we demonstrated diatomic oxygen's ability, independent of water, to tune oxide-supported catalyst thin film dewetting and influence nanoscale (diameter and wall number) and macro-scale (alignment and density) properties for as-grown vertically aligned CNTs. In particular, single- or few-walled CNT forests were achieved at very low oxygen loading, with single-to-multi-walled CNT diameters ranging from 4.8 ± 1.3 nm to 6.4 ± 1.1 nm over 0-800 ppm O 2 , and an expected variation in alignment, where both were related to the annealed catalyst morphology. Morphological differences were not the result of subsurface diffusion, but instead occurred via Ostwald ripening under several hundred ppm O 2 , and this effect was mitigated by high H 2 concentrations and not due to water vapor (as confirmed in O 2 -free water addition experiments), supporting the importance of O 2 specifically. Further characterization of the interface between the Fe catalyst and Al 2 O 3 support revealed that either oxygen-deficit metal oxide or oxygen-adsorption on metals could be functional mechanisms for the observed catalyst nanoparticle evolution. Taken as a whole, our results suggest that the impacts of O 2 and H 2 on the catalyst evolution have been underappreciated and underleveraged in CNT synthesis, and these could present a route toward facile manipulation of CNT forest morphology through control of the reactive gaseous atmosphere alone.

Oxygen-promoted catalyst sintering influences number density, alignment, and wall number of vertically aligned carbon nanotubes

DOE PAGES

Shi, Wenbo; Li, Jinjing; Polsen, Erik S.; ...

2017-04-11

A lack of synthetic control and reproducibility during vertically aligned carbon nanotube (CNT) synthesis has stifled many promising applications of organic nanomaterials. Oxygen-containing species are particularly precarious in that they have both beneficial and deleterious effects and are notoriously difficult to control. In this paper, we demonstrated diatomic oxygen's ability, independent of water, to tune oxide-supported catalyst thin film dewetting and influence nanoscale (diameter and wall number) and macro-scale (alignment and density) properties for as-grown vertically aligned CNTs. In particular, single- or few-walled CNT forests were achieved at very low oxygen loading, with single-to-multi-walled CNT diameters ranging from 4.8 ±more » 1.3 nm to 6.4 ± 1.1 nm over 0–800 ppm O 2, and an expected variation in alignment, where both were related to the annealed catalyst morphology. Morphological differences were not the result of subsurface diffusion, but instead occurred via Ostwald ripening under several hundred ppm O 2, and this effect was mitigated by high H 2 concentrations and not due to water vapor (as confirmed in O 2-free water addition experiments), supporting the importance of O 2 specifically. Further characterization of the interface between the Fe catalyst and Al 2O 3 support revealed that either oxygen-deficit metal oxide or oxygen-adsorption on metals could be functional mechanisms for the observed catalyst nanoparticle evolution. Finally, taken as a whole, our results suggest that the impacts of O 2 and H 2 on the catalyst evolution have been underappreciated and underleveraged in CNT synthesis, and these could present a route toward facile manipulation of CNT forest morphology through control of the reactive gaseous atmosphere alone.« less

Engineering of oriented carbon nanotubes in composite materials

PubMed Central

Beigmoradi, Razieh; Mohebbi-Kalhori, Davod

2018-01-01

The orientation and arrangement engineering of carbon nanotubes (CNTs) in composite structures is considered a challenging issue. In this regard, two groups of in situ and ex situ techniques have been developed. In the first, the arrangement is achieved during CNT growth, while in the latter, the CNTs are initially grown in random orientation and the arrangement is then achieved during the device integration process. As the ex situ techniques are free from growth restrictions and more flexible in terms of controlling the alignment and sorting of the CNTs, they are considered by some as the preferred technique for engineering of oriented CNTs. This review focuses on recent progress in the improvement of the orientation and alignment of CNTs in composite materials. Moreover, the advantages and disadvantages of the processes are discussed as well as their future outlook. PMID:29515955

Fabrication, Densification, and Replica Molding of 3D Carbon Nanotube Microstructures

PubMed Central

Copic, Davor; Park, Sei Jin; Tawfick, Sameh; De Volder, Michael; Hart, A. John

2012-01-01

The introduction of new materials and processes to microfabrication has, in large part, enabled many important advances in microsystems, lab-on-a-chip devices, and their applications. In particular, capabilities for cost-effective fabrication of polymer microstructures were transformed by the advent of soft lithography and other micromolding techniques 1, 2, and this led a revolution in applications of microfabrication to biomedical engineering and biology. Nevertheless, it remains challenging to fabricate microstructures with well-defined nanoscale surface textures, and to fabricate arbitrary 3D shapes at the micro-scale. Robustness of master molds and maintenance of shape integrity is especially important to achieve high fidelity replication of complex structures and preserving their nanoscale surface texture. The combination of hierarchical textures, and heterogeneous shapes, is a profound challenge to existing microfabrication methods that largely rely upon top-down etching using fixed mask templates. On the other hand, the bottom-up synthesis of nanostructures such as nanotubes and nanowires can offer new capabilities to microfabrication, in particular by taking advantage of the collective self-organization of nanostructures, and local control of their growth behavior with respect to microfabricated patterns. Our goal is to introduce vertically aligned carbon nanotubes (CNTs), which we refer to as CNT "forests", as a new microfabrication material. We present details of a suite of related methods recently developed by our group: fabrication of CNT forest microstructures by thermal CVD from lithographically patterned catalyst thin films; self-directed elastocapillary densification of CNT microstructures; and replica molding of polymer microstructures using CNT composite master molds. In particular, our work shows that self-directed capillary densification ("capillary forming"), which is performed by condensation of a solvent onto the substrate with CNT microstructures, significantly increases the packing density of CNTs. This process enables directed transformation of vertical CNT microstructures into straight, inclined, and twisted shapes, which have robust mechanical properties exceeding those of typical microfabrication polymers. This in turn enables formation of nanocomposite CNT master molds by capillary-driven infiltration of polymers. The replica structures exhibit the anisotropic nanoscale texture of the aligned CNTs, and can have walls with sub-micron thickness and aspect ratios exceeding 50:1. Integration of CNT microstructures in fabrication offers further opportunity to exploit the electrical and thermal properties of CNTs, and diverse capabilities for chemical and biochemical functionalization 3. PMID:22806089

Fabrication, densification, and replica molding of 3D carbon nanotube microstructures.

PubMed

Copic, Davor; Park, Sei Jin; Tawfick, Sameh; De Volder, Michael; Hart, A John

2012-07-02

The introduction of new materials and processes to microfabrication has, in large part, enabled many important advances in microsystems, lab-on-a-chip devices, and their applications. In particular, capabilities for cost-effective fabrication of polymer microstructures were transformed by the advent of soft lithography and other micromolding techniques (1, 2), and this led a revolution in applications of microfabrication to biomedical engineering and biology. Nevertheless, it remains challenging to fabricate microstructures with well-defined nanoscale surface textures, and to fabricate arbitrary 3D shapes at the micro-scale. Robustness of master molds and maintenance of shape integrity is especially important to achieve high fidelity replication of complex structures and preserving their nanoscale surface texture. The combination of hierarchical textures, and heterogeneous shapes, is a profound challenge to existing microfabrication methods that largely rely upon top-down etching using fixed mask templates. On the other hand, the bottom-up synthesis of nanostructures such as nanotubes and nanowires can offer new capabilities to microfabrication, in particular by taking advantage of the collective self-organization of nanostructures, and local control of their growth behavior with respect to microfabricated patterns. Our goal is to introduce vertically aligned carbon nanotubes (CNTs), which we refer to as CNT "forests", as a new microfabrication material. We present details of a suite of related methods recently developed by our group: fabrication of CNT forest microstructures by thermal CVD from lithographically patterned catalyst thin films; self-directed elastocapillary densification of CNT microstructures; and replica molding of polymer microstructures using CNT composite master molds. In particular, our work shows that self-directed capillary densification ("capillary forming"), which is performed by condensation of a solvent onto the substrate with CNT microstructures, significantly increases the packing density of CNTs. This process enables directed transformation of vertical CNT microstructures into straight, inclined, and twisted shapes, which have robust mechanical properties exceeding those of typical microfabrication polymers. This in turn enables formation of nanocomposite CNT master molds by capillary-driven infiltration of polymers. The replica structures exhibit the anisotropic nanoscale texture of the aligned CNTs, and can have walls with sub-micron thickness and aspect ratios exceeding 50:1. Integration of CNT microstructures in fabrication offers further opportunity to exploit the electrical and thermal properties of CNTs, and diverse capabilities for chemical and biochemical functionalization (3).

Synthesis and Investigation of Millimeter-Scale Vertically Aligned Boron Nitride Nanotube Arrays

NASA Astrophysics Data System (ADS)

Tay, Roland; Li, Hongling; Tsang, Siu Hon; Jing, Lin; Tan, Dunlin; Teo, Edwin Hang Tong

Boron nitride nanotubes (BNNTs) have shown potential in a wide range of applications due to their superior properties such as exceptionally high mechanical strength, excellent chemical and thermal stabilities. However, previously reported methods to date only produced BNNTs with limited length/density and insufficient yield at high temperatures. Here we present a facile and effective two-step synthesis route involving template-assisted chemical vapor deposition at a relatively low temperature of 900 degree C and subsequent annealing process to fabricate vertically aligned (VA) BN coated carbon nanotube (VA-BN/CNT) and VA-BNNT arrays. By using this method, we achieve the longest VA-BN/CNTs and VA-BNNTs to date with lengths of over millimeters (exceeding two orders of magnitude longer than the previously reported length of VA-BNNTs). In addition, the morphology, chemical composition and microstructure of the resulting products, as well as the mechanism of coating process are systematically investigated. This versatile BN coating technique and the synthesis of millimeter-scale BN/CNT and BNNT arrays pave a way for new applications especially where the aligned geometry of the NTs is essential such as for field-emission, interconnects and thermal management.

Versatile transfer of aligned carbon nanotubes with polydimethylsiloxane as the intermediate

NASA Astrophysics Data System (ADS)

Zhu, Yanwu; Lim, Xiaodai; Chea Sim, Mong; Teck Lim, Chwee; Haur Sow, Chorng

2008-08-01

A simple technique to transfer aligned multi-walled carbon nanotubes (MWCNTs) is demonstrated in this work. With polydimethylsiloxane (PDMS) as the transfer medium, as-grown or patterned MWCNT arrays are directly transferred onto a wide variety of Pt-coated substrates such as glossy paper, cloth, polymers, glass slides, and metal foils at low temperatures. The surface of the transferred CNTs is cleaner with better alignment, compared with the as-grown one. Furthermore, the transferred CNTs show strong adhesion and good electric contact with the target substrates. A maximal current density of ~104 A cm-2 has been achieved from the CNT interconnects prepared with this technique. Because of the lower density and open-ended structures, improved field emission performance has been obtained from CNTs transferred on polymers, based on which flexible emitter devices can be fabricated. In addition, the surface of transferred CNTs becomes more hydrophilic, with an averaged contact angle of 93.4 ± 5.8°, in contrast to the super-hydrophobic as-grown CNT surface (contact angle 151.6 ± 5.5°). With versatile properties and flexible applications, the technique provides a simple and cost-effective way towards future nanodevices based on CNTs.

Carbon nanotube-incorporated collagen hydrogels improve cell alignment and the performance of cardiac constructs

PubMed Central

Sun, Hongyu; Zhou, Jing; Huang, Zhu; Qu, Linlin; Lin, Ning; Liang, Chengxiao; Dai, Ruiwu; Tang, Lijun; Tian, Fuzhou

2017-01-01

Carbon nanotubes (CNTs) provide an essential 2-D microenvironment for cardiomyocyte growth and function. However, it remains to be elucidated whether CNT nanostructures can promote cell–cell integrity and facilitate the formation of functional tissues in 3-D hydrogels. Here, single-walled CNTs were incorporated into collagen hydrogels to fabricate (CNT/Col) hydrogels, which improved mechanical and electrical properties. The incorporation of CNTs (up to 1 wt%) exhibited no toxicity to cardiomyocytes and enhanced cell adhesion and elongation. Through the use of immunohistochemical staining, transmission electron microscopy, and intracellular calcium-transient measurement, the incorporation of CNTs was found to improve cell alignment and assembly remarkably, which led to the formation of engineered cardiac tissues with stronger contraction potential. Importantly, cardiac tissues based on CNT/Col hydrogels were noted to have better functionality. Collectively, the incorporation of CNTs into the Col hydrogels improved cell alignment and the performance of cardiac constructs. Our study suggests that CNT/Col hydrogels offer a promising tissue scaffold for cardiac constructs, and might serve as injectable biomaterials to deliver cell or drug molecules for cardiac regeneration following myocardial infarction in the near future. PMID:28450785

Fabrication of Single, Vertically Aligned Carbon Nanotubes in 3D Nanoscale Architectures

NASA Technical Reports Server (NTRS)

Kaul, Anupama B.; Megerian, Krikor G.; Von Allmen, Paul A.; Baron, Richard L.

2010-01-01

Plasma-enhanced chemical vapor deposition (PECVD) and high-throughput manufacturing techniques for integrating single, aligned carbon nanotubes (CNTs) into novel 3D nanoscale architectures have been developed. First, the PECVD growth technique ensures excellent alignment of the tubes, since the tubes align in the direction of the electric field in the plasma as they are growing. Second, the tubes generated with this technique are all metallic, so their chirality is predetermined, which is important for electronic applications. Third, a wafer-scale manufacturing process was developed that is high-throughput and low-cost, and yet enables the integration of just single, aligned tubes with nanoscale 3D architectures with unprecedented placement accuracy and does not rely on e-beam lithography. Such techniques should lend themselves to the integration of PECVD grown tubes for applications ranging from interconnects, nanoelectromechanical systems (NEMS), sensors, bioprobes, or other 3D electronic devices. Chemically amplified polyhydroxystyrene-resin-based deep UV resists were used in conjunction with excimer laser-based (lambda = 248 nm) step-and-repeat lithography to form Ni catalyst dots = 300 nm in diameter that nucleated single, vertically aligned tubes with high yield using dc PECVD growth. This is the first time such chemically amplified resists have been used, resulting in the nucleation of single, vertically aligned tubes. In addition, novel 3D nanoscale architectures have been created using topdown techniques that integrate single, vertically aligned tubes. These were enabled by implementing techniques that use deep-UV chemically amplified resists for small-feature-size resolution; optical lithography units that allow unprecedented control over layer-to-layer registration; and ICP (inductively coupled plasma) etching techniques that result in near-vertical, high-aspect-ratio, 3D nanoscale architectures, in conjunction with the use of materials that are structurally and chemically compatible with the high-temperature synthesis of the PECVD-grown tubes. The techniques offer a wafer-scale process solution for integrating single PECVD-grown nanotubes into novel architectures that should accelerate their integration in 3D electronics in general. NASA can directly benefit from this technology for its extreme-environment planetary missions. Current Si transistors are inherently more susceptible to high radiation, and do not tolerate extremes in temperature. These novel 3D nanoscale architectures can form the basis for NEMS switches that are inherently less susceptible to radiation or to thermal extremes.

Carbon Nanotube-Based Structural Health Monitoring Sensors

NASA Technical Reports Server (NTRS)

Wincheski, Russell; Jordan, Jeffrey; Oglesby, Donald; Watkins, Anthony; Patry, JoAnne; Smits, Jan; Williams, Phillip

2011-01-01

Carbon nanotube (CNT)-based sensors for structural health monitoring (SHM) can be embedded in structures of all geometries to monitor conditions both inside and at the surface of the structure to continuously sense changes. These CNTs can be manipulated into specific orientations to create small, powerful, and flexible sensors. One of the sensors is a highly flexible sensor for crack growth detection and strain field mapping that features a very dense and highly ordered array of single-walled CNTs. CNT structural health sensors can be mass-produced, are inexpensive, can be packaged in small sizes (0.5 micron(sup 2)), require less power than electronic or piezoelectric transducers, and produce less waste heat per square centimeter than electronic or piezoelectric transducers. Chemically functionalized lithographic patterns are used to deposit and align the CNTs onto metallic electrodes. This method consistently produces aligned CNTs in the defined locations. Using photo- and electron-beam lithography, simple Cr/Au thin-film circuits are patterned onto oxidized silicon substrates. The samples are then re-patterned with a CNT-attracting, self-assembled monolayer of 3-aminopropyltriethoxysilane (APTES) to delineate the desired CNT locations between electrodes. During the deposition of the solution-suspended single- wall CNTs, the application of an electric field to the metallic contacts causes alignment of the CNTs along the field direction. This innovation is a prime candidate for smart skin technologies with applications ranging from military, to aerospace, to private industry.

Real-Time Imaging of Self-Organization and Mechanical Competition in Carbon Nanotube Forest Growth.

PubMed

Balakrishnan, Viswanath; Bedewy, Mostafa; Meshot, Eric R; Pattinson, Sebastian W; Polsen, Erik S; Laye, Fabrice; Zakharov, Dmitri N; Stach, Eric A; Hart, A John

2016-12-27

The properties of carbon nanotube (CNT) networks and analogous materials comprising filamentary nanostructures are governed by the intrinsic filament properties and their hierarchical organization and interconnection. As a result, direct knowledge of the collective dynamics of CNT synthesis and self-organization is essential to engineering improved CNT materials for applications such as membranes and thermal interfaces. Here, we use real-time environmental transmission electron microscopy (E-TEM) to observe nucleation and self-organization of CNTs into vertically aligned forests. Upon introduction of the carbon source, we observe a large scatter in the onset of nucleation of individual CNTs and the ensuing growth rates. Experiments performed at different temperatures and catalyst particle densities show the critical role of CNT density on the dynamics of self-organization; low-density CNT nucleation results in the CNTs becoming pinned to the substrate and forming random networks, whereas higher density CNT nucleation results in self-organization of the CNTs into bundles that are oriented perpendicular to the substrate. We also find that mechanical coupling between growing CNTs alters their growth trajectory and shape, causing significant deformations, buckling, and defects in the CNT walls. Therefore, it appears that CNT-CNT coupling not only is critical for self-organization but also directly influences CNT quality and likely the resulting properties of the forest. Our findings show that control of the time-distributed kinetics of CNT nucleation and bundle formation are critical to manufacturing well-organized CNT assemblies and that E-TEM can be a powerful tool to investigate the mesoscale dynamics of CNT networks.

Enhanced graphitization of carbon around carbon nanotubes during the formation of carbon nanotube/graphite composites by pyrolysis of carbon nanotube/polyaniline composites.

PubMed

Nam, Dong Hoon; Cha, Seung Il; Jeong, Yong Jin; Hong, Soon Hyung

2013-11-01

The carbon nanotubes (CNTs) are actively applied to the reinforcements for composite materials during last decade. One of the attempts is development of CNT/Carbon composites. Although there are some reports on the enhancement of mechanical properties by addition of CNTs in carbon or carbon fiber, it is far below the expectation. Considering the microstructure of carbon materials such as carbon fiber, the properties of them can be modified and enhanced by control of graphitization and alignment of graphene planes. In this study, enhanced graphitization of carbon has been observed the vicinity of CNTs during the pyrolysis of CNT/Polyaniline composites. As a result, novel types of composite, consisting of treading CNTs and coated graphite, can be fabricated. High-resolution transmission electron microscopy revealed a specific orientation relationship between the graphene layers and the CNTs, with an angle of 110 degrees between the layers and the CNT axis. The possibility of graphene alignment control in the carbon by the addition of CNTs is demonstrated.

Controlled growth of well-aligned carbon nanotubes with large diameters

NASA Astrophysics Data System (ADS)

Wang, Xianbao; Liu, Yunqi; Zhu, Daoben

2001-06-01

Well-aligned carbon nanotubes (CNTs) with large diameters (25-200 nm) were synthesized by pyrolysis of iron(II) phthalocyanine. The outer diameter up to 218.5 nm and the length of the well-aligned CNTs can be systematically controlled by varying the growth time. A tube-in-tube nano-structure with large and small diameters of 176 and 16.7 nm, respectively, was found. The grain sizes of the iron catalyst play an important role in controlling the CNT diameters. These results are of great importance to design new aligned CNT-based electron field emitters in the potential application of panel displays.

Modifying the morphology and properties of aligned CNT foams through secondary CNT growth.

PubMed

Faraji, Shaghayegh; Stano, Kelly; Akyildiz, Halil; Yildiz, Ozkan; Jur, Jesse S; Bradford, Philip D

2018-07-20

In this work, we report for the first time, growth of secondary carbon nanotubes (CNTs) throughout a three-dimensional assembly of CNTs. The assembly of nanotubes was in the form of aligned CNT/carbon (ACNT/C) foams. These low-density CNT foams were conformally coated with an alumina buffer layer using atomic layer deposition. Chemical vapor deposition was further used to grow new CNTs. The CNT foam's extremely high porosity allowed for growth of secondary CNTs inside the bulk of the foams. Due to the heavy growth of new nanotubes, density of the foams increased more than 2.5 times. Secondary nanotubes had the same graphitic quality as the primary CNTs. Microscopy and chemical analysis revealed that the thickness of the buffer layer affected the diameter, nucleation density as well as growth uniformity across the thickness of the foams. The effects of secondary nanotubes on the compressive mechanical properties of the foams was also investigated.

Modifying the morphology and properties of aligned CNT foams through secondary CNT growth

NASA Astrophysics Data System (ADS)

Faraji, Shaghayegh; Stano, Kelly; Akyildiz, Halil; Yildiz, Ozkan; Jur, Jesse S.; Bradford, Philip D.

2018-07-01

In this work, we report for the first time, growth of secondary carbon nanotubes (CNTs) throughout a three-dimensional assembly of CNTs. The assembly of nanotubes was in the form of aligned CNT/carbon (ACNT/C) foams. These low-density CNT foams were conformally coated with an alumina buffer layer using atomic layer deposition. Chemical vapor deposition was further used to grow new CNTs. The CNT foam’s extremely high porosity allowed for growth of secondary CNTs inside the bulk of the foams. Due to the heavy growth of new nanotubes, density of the foams increased more than 2.5 times. Secondary nanotubes had the same graphitic quality as the primary CNTs. Microscopy and chemical analysis revealed that the thickness of the buffer layer affected the diameter, nucleation density as well as growth uniformity across the thickness of the foams. The effects of secondary nanotubes on the compressive mechanical properties of the foams was also investigated.

Controllable 3D architectures of aligned carbon nanotube arrays by multi-step processes

NASA Astrophysics Data System (ADS)

Huang, Shaoming

2003-06-01

An effective way to fabricate large area three-dimensional (3D) aligned CNTs pattern based on pyrolysis of iron(II) phthalocyanine (FePc) by two-step processes is reported. The controllable generation of different lengths and selective growth of the aligned CNT arrays on metal-patterned (e.g., Ag and Au) substrate are the bases for generating such 3D aligned CNTs architectures. By controlling experimental conditions 3D aligned CNT arrays with different lengths/densities and morphologies/structures as well as multi-layered architectures can be fabricated in large scale by multi-step pyrolysis of FePc. These 3D architectures could have interesting properties and be applied for developing novel nanotube-based devices.

Liquid spreading on ceramic-coated carbon nanotube films and patterned microstructures

NASA Astrophysics Data System (ADS)

Zhao, Hangbo; Hart, A. John

2015-11-01

We study the capillary-driven liquid spreading behavior on films and microstructures of ceramic-coated vertically aligned carbon nanotubes (CNTs) fabricated on quartz substrates. The nanoscale porosity and micro-scale dimensions of the CNT structures, which can be precisely varied by the fabrication process, enable quantitative measurements that can be related to analytical models of the spreading behavior. Moreover, the conformal alumina coating by atomic layer deposition (ALD) prevents capillary-induced deformation of the CNTs upon meniscus recession, which has complicated previous studies of this topic. Washburn-like liquid spreading behavior is observed on non-patterned CNT surfaces, and is explained using a scaling model based on the balance of capillary driving force and the viscous drag force. Using these insights, we design patterned surfaces with controllable spreading rates and study the contact line pinning-depinning behavior. The nanoscale porosity, controllable surface chemistry, and mechanical stability of coated CNTs provide significantly enhanced liquid-solid interfacial area compared to solid microstructures. As a result, these surface designs may be useful for applications such as phase-change heat transfer and electrochemical energy storage. Funding for this project is provided by the National Institutes of Health and the MIT Center for Clean Water and Clean Energy supported by the King Fahd University of Petroleum and Minerals.

Real-time imaging of self-organization and mechanical competition in carbon nanotube forest growth [Real-time environmental TEM investigation of self-organization and mechanical competition in carbon nanotube forest growth

DOE Office of Scientific and Technical Information (OSTI.GOV)

Balakrishnan, Viswanath; Bedewy, Mostafa; Meshot, Eric R.

Here, the properties of carbon nanotube (CNT) networks and analogous materials comprising filamentary nanostructures are governed by the intrinsic filament properties and their hierarchical organization and interconnection. As a result, direct knowledge of the collective dynamics of CNT synthesis and self-organization is essential to engineering improved CNT materials for applications such as membranes and thermal interfaces. Here, we use real-time environmental transmission electron microscopy (E-TEM) to observe nucleation and self-organization of CNTs into vertically aligned forests. Upon introduction of the carbon source, we observe a large scatter in the onset of nucleation of individual CNTs and the ensuing growth rates.more » Experiments performed at different temperatures and catalyst particle densities show the critical role of CNT density on the dynamics of self-organization; low-density CNT nucleation results in the CNTs becoming pinned to the substrate and forming random networks, whereas higher density CNT nucleation results in self-organization of the CNTs into bundles that are oriented perpendicular to the substrate. We also find that mechanical coupling between growing CNTs alters their growth trajectory and shape, causing significant deformations, buckling, and defects in the CNT walls. Therefore, it appears that CNT–CNT coupling not only is critical for self-organization but also directly influences CNT quality and likely the resulting properties of the forest. As a result, our findings show that control of the time-distributed kinetics of CNT nucleation and bundle formation are critical to manufacturing well-organized CNT assemblies and that E-TEM can be a powerful tool to investigate the mesoscale dynamics of CNT networks.« less

Real-time imaging of self-organization and mechanical competition in carbon nanotube forest growth [Real-time environmental TEM investigation of self-organization and mechanical competition in carbon nanotube forest growth

DOE PAGES

Balakrishnan, Viswanath; Bedewy, Mostafa; Meshot, Eric R.; ...

2016-11-23

Here, the properties of carbon nanotube (CNT) networks and analogous materials comprising filamentary nanostructures are governed by the intrinsic filament properties and their hierarchical organization and interconnection. As a result, direct knowledge of the collective dynamics of CNT synthesis and self-organization is essential to engineering improved CNT materials for applications such as membranes and thermal interfaces. Here, we use real-time environmental transmission electron microscopy (E-TEM) to observe nucleation and self-organization of CNTs into vertically aligned forests. Upon introduction of the carbon source, we observe a large scatter in the onset of nucleation of individual CNTs and the ensuing growth rates.more » Experiments performed at different temperatures and catalyst particle densities show the critical role of CNT density on the dynamics of self-organization; low-density CNT nucleation results in the CNTs becoming pinned to the substrate and forming random networks, whereas higher density CNT nucleation results in self-organization of the CNTs into bundles that are oriented perpendicular to the substrate. We also find that mechanical coupling between growing CNTs alters their growth trajectory and shape, causing significant deformations, buckling, and defects in the CNT walls. Therefore, it appears that CNT–CNT coupling not only is critical for self-organization but also directly influences CNT quality and likely the resulting properties of the forest. As a result, our findings show that control of the time-distributed kinetics of CNT nucleation and bundle formation are critical to manufacturing well-organized CNT assemblies and that E-TEM can be a powerful tool to investigate the mesoscale dynamics of CNT networks.« less

Aligned Carbon Nanotube to Enhance Through Thickness Thermal Conductivity in Adhesive Joints (Preprint)

DTIC Science & Technology

2006-12-01

aligned CNT films were prepared by pyrolyzing iron (II) phthalocyanine under Ar/H2 at 900°C as described in details elsewhere16. The average diameter...zone. Keywords: thermal conductivity, carbon nanotubes The unique properties of carbon nanotubes ( CNTs ) have generated interest amongst many...structure and high aspect ratio. These 2 unique properties make CNTs the material of choice for numerous applications like sensors5, actuators6, energy

Mechanical coupling limits the density and quality of self-organized carbon nanotube growth

NASA Astrophysics Data System (ADS)

Bedewy, Mostafa; Hart, A. John

2013-03-01

Aligned carbon nanotube (CNT) structures are promising for many applications; however, as-grown CNT "forests" synthesized by chemical vapor deposition (CVD) are typically low-density and mostly comprise tortuous defective CNTs. Here, we present evidence that the density and alignment of self-organized CNT growth is limited by mechanical coupling among CNTs in contact, in combination with their diameter-dependent growth rates. This study is enabled by comprehensive X-ray characterization of the spatially and temporally-varying internal morphology of CNT forests. Based on this data, we model the time evolution and diameter-dependent scaling of the ensuing mechanical forces on catalyst nanoparticles during CNT growth, which arise from the mismatch between the collective lengthening rate of the forest and the diameter-dependent growth rates of individual CNTs. In addition to enabling self-organization of CNTs into forests, time-varying forces between CNTs in contact dictate the hierarchical tortuous morphology of CNT forests, and may be sufficient to influence the structural quality of CNTs. These forces reach a maximum that is coincident with the maximum density observed in our growth process, and are proportional to CNT diameter. Therefore, we propose that improved manufacturing strategies for self-organized CNTs should consider both chemical and mechanical effects. This may be especially necessary to achieve high density CNT forests with low defect density, such as for improved thermal interfaces and high-permeability membranes.Aligned carbon nanotube (CNT) structures are promising for many applications; however, as-grown CNT "forests" synthesized by chemical vapor deposition (CVD) are typically low-density and mostly comprise tortuous defective CNTs. Here, we present evidence that the density and alignment of self-organized CNT growth is limited by mechanical coupling among CNTs in contact, in combination with their diameter-dependent growth rates. This study is enabled by comprehensive X-ray characterization of the spatially and temporally-varying internal morphology of CNT forests. Based on this data, we model the time evolution and diameter-dependent scaling of the ensuing mechanical forces on catalyst nanoparticles during CNT growth, which arise from the mismatch between the collective lengthening rate of the forest and the diameter-dependent growth rates of individual CNTs. In addition to enabling self-organization of CNTs into forests, time-varying forces between CNTs in contact dictate the hierarchical tortuous morphology of CNT forests, and may be sufficient to influence the structural quality of CNTs. These forces reach a maximum that is coincident with the maximum density observed in our growth process, and are proportional to CNT diameter. Therefore, we propose that improved manufacturing strategies for self-organized CNTs should consider both chemical and mechanical effects. This may be especially necessary to achieve high density CNT forests with low defect density, such as for improved thermal interfaces and high-permeability membranes. Electronic supplementary information (ESI) available: Detailed description of the cold-wall CVD reactor used for growing CNTs; fitting the diameter-dependent model-predicted CNT growth kinetics; time evolution of compressive stresses as a function of CNT diameter; time evolution of the diameter dependent variations in CNT number density; cumulative forest mass kinetics normalized to the number of CNTs. See DOI: 10.1039/c3nr34067h

Hierarchical multifunctional composites by conformally coating aligned carbon nanotube arrays with conducting polymer.

PubMed

Vaddiraju, Sreeram; Cebeci, Hülya; Gleason, Karen K; Wardle, Brian L

2009-11-01

A novel method for the fabrication of carbon nanotube (CNT)-conducting polymer composites is demonstrated by conformally coating extremely high aspect ratio vertically aligned-CNT (A-CNT) arrays with conducting polymer via oxidative chemical vapor deposition (oCVD). A mechanical densification technique is employed that allows the spacing of the A-CNTs to be controlled, yielding a range of inter-CNT distances between 20 and 70 nm. Using this morphology control, oCVD is shown to conformally coat 8-nm-diameter CNTs having array heights up to 1 mm (an aspect ratio of 10(5)) at all inter-CNT spacings. Three phase CNT-conducting polymer nanocomposites are then fabricated by introducing an insulating epoxy via capillary-driven wetting. CNT morphology is maintained during processing, allowing quantification of direction-dependent (nonisotropic) composite properties. Electrical conductivity occurs primarily along the CNT axial direction, such that the conformal conducting polymer has little effect on the activation energy required for charge conduction. In contrast, the conducting polymer coating enhanced the conductivity in the radial direction by lowering the activation energy required for the creation of mobile charge carriers, in agreement with variable-range-hopping models. The fabrication strategy introduced here can be used to create many multifunctional materials and devices (e.g., direction-tailorable hydrophobic and highly conducting materials), including a new four-phase advanced fiber composite architecture.

Fabrication and flow characterization of vertically aligned carbon-nanotube/polymer membranes

NASA Astrophysics Data System (ADS)

Castellano, Richard; Meshot, Eric; Fornasiero, Francesco; Shan, Jerry

2017-11-01

Membranes with well-controlled nanopores are of interest for applications as diverse as chemical separations, water purification, and ``green'' power generation. In particular, membranes incorporating carbon nanotubes (CNTs) as through-pores have been shown to pass fluids at rates orders-of-magnitude faster than predicted by continuum theory. However, cost-effective and scalable solutions for fabricating such membranes are still an area of research. We describe a solution-based fabrication technique for creating polymer composite membranes from bulk nanotubes using electric-field alignment and electrophoretic concentration. We then focus on flow characterization of membranes with single-wall nanotube (SWNT) pores. We demonstrate membrane quality by size-exclusion testing and showing that the flowrate of different gasses scales as the square root of molecular weight. The gas flowrates and moisture-vapor-transmission rates are compared with theoretical predictions and with composite membranes -fabricated from CVD-grown SWNT arrays. Funded by DTRA Grant BA12PHM123.

Synthesis and metrology of conducting carbon nanotube assemblies

NASA Astrophysics Data System (ADS)

Longson, Timothy Jay

Since its discovery, the carbon nanotube (CNT) has been proposed as one of the ultimate materials for its electrical, thermal and mechanical properties due to its incredibly strong sp2 bonds, low defect density, and large aspect ratio. Many experimental results on individual CNTs have confirmed these outstanding theoretically predicted properties. However, scaling these properties to the macroscopic regime has proved to be challenging. This work focused on the synthesis and measurement of highly conducting, macroscopic, CNT assemblies. Scaling up the synthesis of vertically aligned multiwalled CNT (MWNT) forests was investigated through the development of a large, 100mm, wafer scale, cold wall chemical vapor deposition chamber. In addition to the synthesis, two distinct CNT assemblies have been investigated. A linear morphology where CNTs are strung in series for electrical transport (CNT wires) and a massively parallel 2D array of vertically aligned CNTs for Thermal Interface Material (TIM) applications. Poymer-CNT wire composites have been fabricated by developing a coaxial CNT core-polymer shell electrospinning technique. The core-shell interactions in this system have been studied by way of Hansen's solubility parameters. The most well defined CNT core was achieved using a core solvent that is semi-immiscible with the shell solution, yet still a solvent of the shell polymer. Electrical characterization of the resulting CNT core has shown a two orders of magnitude increase in conductivity over traditional, homogeneously mixed, electrospun CNT wires. A number of vertically aligned MWNT assemblies were studied for their thermal interface properties. Double-sided Silicon substrate (MWNT-Si-MWNT) TIM assemblies were characterized using a DC, 1D reference bar, thermal measurement technique. While attempts to control MWNT density via a micelle template technique produced only 'spaghetti like' CNTs, sputter deposited catalyst provided stark variations in array density. Relevant array morphologies such as density, height, and crystallinity were studied in conjunction with their thermal performance. A Euler buckling model was used to identify the transition between increasing and decreasing resistance with density over array height, these two regimes are explained by way of contact analysis. Self catalyzing Fecralloy substrate MWNT TIMs were studied in a similar vein to the Silicon based assemblies. This substrate was investigated because of its malleability, ease of CNT synthesis and increased CNT adhesion. The growth behavior was studied with respect to the array morphologies, i.e. array height, density, crystallinity, and diameter, while the contact resistance was evaluated using a DC, 1D reference bar technique. The best performing samples were found to have a factor of two increase over their Si counterparts. Temperature dependent thermal measurements offer insight into the interfacial phonon conduction physics and are found to agree with other temperature dependent studies, suggesting inelastic scattering at the MWNT-Cu interface. Due to the challenges associated with deliberately controlling a single array morphology, a statistical approach was used for identifying the influences of the multivariate array morphology on contact resistance. Showing the strongest correlation with array height, following a R ~ L-0.5. Several models were investigated to help explain this behavior, although little insight is gained over the empirical relations. To better characterize these MWNT TIM assemblies two experimental techniques were developed. A transient 3o thermal measurement technique was adapted to characterize the thermal performance of CNT TIMs, offering insight into the limiting resistance in a mulilayer material stack. The MWNT-growth substrate interface was found to dominate in the Si samples while the MWNT-opposing substrate interface dominated in the Fecralloy samples. These measurements strongly supported the DC thermal measurements and the qualitative observations of substrate adhesion. Additionally, a new technique for observing nano sized contacts was established by viewing contact loading through an electron transparent membrane, imaged under an SEM. The contrast mechanism is explained by a voltage contrast phenomenon developed by trapped charges at the interface. The resolution limits have been studied by way of electron beam interactions and the use of Monte Carlo simulations, showing nanometer resolution with appropriate experimental conditions. The real MWNT contact area was found to be less than 1/100th the apparent contact area even at moderate pressures and the number of contacting CNTs is approximately 1/10th the total number of CNTs. These results confirm experimental measurement values for van der Waals adhesion strengths and thermal interface resistance.

Chemical vapour deposition growth of carbon nanotube forests: kinetics, morphology, composition, and their mechanisms

NASA Astrophysics Data System (ADS)

Vinten, Phillip

This thesis analyzes the chemical vapour deposition (CVD) growth of vertically aligned carbon nanotube (CNT) forests in order to understand how CNT forests grow, why they stop growing, and how to control the properties of the synthesized CNTs. in situ kinetics data of the growth of CNT forests are gathered by in situ optical microscopy. The overall morphology of the forests and the characteristics of the individual CNTs in the forests are investigated using scanning electron microscopy and Raman spectroscopy. The in situ data show that forest growth and termination are activated processes (with activation energies on the order of 1 eV), suggesting a possible chemical origin. The activation energy changes at a critical temperature for ethanol CVD (approximately 870°C). These activation energies and critical temperature are also seen in the temperature dependence of several important characteristics of the CNTs, including the defect density as determined by Raman spectroscopy. This observation is seen across several CVD processes and suggests a mechanism of defect healing. The CNT diameter also depends on the growth temperature. In this thesis, a thermodynamic model is proposed. This model predicts a temperature and pressure dependence of the CNT diameter from the thermodynamics of the synthesis reaction and the effect of strain on the enthalpy of formation of CNTs. The forest morphology suggests significant interaction between the constituent CNTs. These interactions may play a role in termination. The morphology, in particular a microscale rippling feature that is capable of diffracting light, suggest a non-uniform growth rate across the forest. A gas phase diffusion model predicts a non-uniform distribution of the source gas. This gas phase diffusion is suggested as a possible explanation for the non-uniform growth rate. The gas phase diffusion is important because growth by acetylene CVD is found to be very efficient (approximately 30% of the acetylene is converted to CNTs). It is seen that multiple mechanisms are active during CNT growth. The results of this thesis provide insight into both the basic understanding of the microscopic processes involved in CVD growth and how to control the properties of the synthesized CNTs.

Vertically aligned CNT-Cu nano-composite material for stacked through-silicon-via interconnects.

PubMed

Sun, Shuangxi; Mu, Wei; Edwards, Michael; Mencarelli, Davide; Pierantoni, Luca; Fu, Yifeng; Jeppson, Kjell; Liu, Johan

2016-08-19

For future miniaturization of electronic systems using 3D chip stacking, new fine-pitch materials for through-silicon-via (TSV) applications are likely required. In this paper, we propose a novel carbon nanotube (CNT)/copper nanocomposite material consisting of high aspect ratio, vertically aligned CNT bundles coated with copper. These bundles, consisting of hundreds of tiny CNTs, were uniformly coated by copper through electroplating, and aspect ratios as high as 300:1 were obtained. The resistivity of this nanomaterial was found to be as low as ∼10(-8) Ω m, which is of the same order of magnitude as the resistivity of copper, and its temperature coefficient was found to be only half of that of pure copper. The main advantage of the composite TSV nanomaterial is that its coefficient of thermal expansion (CTE) is similar to that of silicon, a key reliability factor. A finite element model was set up to demonstrate the reliability of this composite material and thermal cycle simulations predicted very promising results. In conclusion, this composite nanomaterial appears to be a very promising material for future 3D TSV applications offering both a low resistivity and a low CTE similar to that of silicon.

Synergistic fusion of vertical graphene nanosheets and carbon nanotubes for high-performance supercapacitor electrodes.

PubMed

Seo, Dong Han; Yick, Samuel; Han, Zhao Jun; Fang, Jing Hua; Ostrikov, Kostya Ken

2014-08-01

Graphene and carbon nanotubes (CNTs) are attractive electrode materials for supercapacitors. However, challenges such as the substrate-limited growth of CNTs, nanotube bundling in liquid electrolytes, under-utilized basal planes, and stacking of graphene sheets have so far impeded their widespread application. Here we present a hybrid structure formed by the direct growth of CNTs onto vertical graphene nanosheets (VGNS). VGNS are fabricated by a green plasma-assisted method to break down and reconstruct a natural precursor into an ordered graphitic structure. The synergistic combination of CNTs and VGNS overcomes the challenges intrinsic to both materials. The resulting VGNS/CNTs hybrids show a high specific capacitance with good cycling stability. The charge storage is based mainly on the non-Faradaic mechanism. In addition, a series of optimization experiments were conducted to reveal the critical factors that are required to achieve the demonstrated high supercapacitor performance. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Electrophoretic deposition of multi-walled carbon nanotubes on porous anodic aluminum oxide using ionic liquid as a dispersing agent

NASA Astrophysics Data System (ADS)

Hekmat, F.; Sohrabi, B.; Rahmanifar, M. S.; Jalali, A.

2015-06-01

Multi-wall carbon nanotubes (MW-CNTs) have been arranged in nanochannels of anodic aluminum oxide template (AAO) by electrophoretic deposition (EPD) to make a vertically-aligned carbon nanotube (VA-CNT) based electrode. Well ordered AAO templates were prepared by a two-step anodizing process by applying a constant voltage of 45 V in oxalic acid solution. The stabilized CNTs in a water-soluble room temperature ionic liquid (1-methyl-3-octadecylimidazolium bromide), were deposited in the pores of AAO templates which were conductive by deposition of Ni nanoparticles in the bottom of pores. In order to obtain ideal results, different EPD parameters, such as concentration of MWCNTs and ionic liquid on stability of MWCNT suspensions, deposition time and voltage which are applied in EPD process and also optimal conditions for anodizing of template were investigated. The capacitive performance of prepared electrodes was analyzed by measuring the specific capacitance from cyclic voltammograms and the charge-discharge curves. A maximum value of 50 Fg-1 at the scan rate of 20 mV s-1was achieved for the specific capacitance.

Growth behavior of carbon nanotubes on multilayered metal catalyst film in chemical vapor deposition

NASA Astrophysics Data System (ADS)

Cui, H.; Eres, G.; Howe, J. Y.; Puretkzy, A.; Varela, M.; Geohegan, D. B.; Lowndes, D. H.

2003-06-01

The temperature and time dependences of carbon nanotube (CNT) growth by chemical vapor deposition are studied using a multilayered Al/Fe/Mo catalyst on silicon substrates. Within the 600-1100 °C temperature range of these studies, narrower temperature ranges were determined for the growth of distinct types of aligned multi-walled CNTs and single-walled CNTs by using high-resolution transmission electron microscopy and Raman spectroscopy. At 900 °C, in contrast to earlier work, double-walled CNTs are found more abundant than single-walled CNTs. Defects also are found to accumulate faster than the ordered graphitic structure if the growth of CNTs is extended to long durations.

Electrostatically Induced Carbon Nanotube Alignment for Polymer Composite Applications

NASA Astrophysics Data System (ADS)

Chapkin, Wesley Aaron

We have developed a non-invasive technique utilizing polarized Raman spectroscopy to measure changes in carbon nanotube (CNT) alignment in situ and in real time in a polymer matrix. With this technique, we have confirmed the prediction of faster alignment for CNTs in higher electric fields. Real-time polarized Raman spectroscopy also allows us to demonstrate the loss of CNT alignment that occurs after the electric field is removed, which reveals the need for fast polymerization steps or the continued application of the aligning force during polymerization to lock in CNT alignment. Through a study on the effect of polymer viscosity on the rate of CNT alignment, we have determined that shear viscosity serves as the controlling mechanism for CNT rotation. This finding matches literature modeling of rigid rod mobility in a polymer melt and demonstrates that the rotational mobility of CNTs can be explained by a continuum model even though the diameters of single-walled CNTs are 1-2 nm. The viscosity dependence indicates that the manipulation of temperature (and indirectly viscosity) will have a direct effect on the rate of CNT alignment, which could prove useful in expediting the manufacturing of CNT-reinforced composites cured at elevated temperatures. Using real-time polarized Raman spectroscopy, we also demonstrate that electric fields of various strengths lead not only to different speeds of CNT rotation but also to different degrees of alignment. We hypothesize that this difference in achievable alignment results from discrete populations of nanotubes based on their length. The results are then explained by balancing the alignment energy for a given electric field strength with the randomizing thermal energy of the system. By studying the alignment dynamics of different CNT length distributions, we show that different degrees of alignment achieved as a function of the applied electric field strength are directly related to the square of the nanotube length. This finding matches an electrostatic potential energy model for CNT rotation. Lastly, we investigate the effects of conductive carbon fibers on electrostatically induced alignment of CNTs within carbon fiber composites. The relative electric field strength throughout the composite is modeled using COMSOL Multiphysics. We show the ability to generate enhanced electric field gradients within the gaps between carbon fibers for various fiber orientations. Using polarized Raman spectroscopy, increased levels of CNT alignment are observed between carbon fiber tows, which is consistent with the modeled higher electric field strengths in these regions. These findings could potentially lead to the development of carbon fiber composites with CNT additions that selectively enhance the composite properties outside the carbon fiber interphase in the neat epoxy.

Self aligned hysteresis free carbon nanotube field-effect transistors

NASA Astrophysics Data System (ADS)

Shlafman, M.; Tabachnik, T.; Shtempluk, O.; Razin, A.; Kochetkov, V.; Yaish, Y. E.

2016-04-01

Hysteresis phenomenon in the transfer characteristics of carbon nanotube field effect transistor (CNT FET) is being considered as the main obstacle for successful realization of electronic devices based on CNTs. In this study, we prepare four kinds of CNTFETs and explore their hysteretic behavior. Two kinds of devices comprise on-surface CNTs (type I) and suspended CNTs (type II) with thin insulating layer underneath and a single global gate which modulates the CNT conductance. The third and fourth types (types III and IV) consist of suspended CNT over a metallic local gate underneath, where for type IV the local gate was patterned self aligned with the source and drain electrodes. The first two types of devices, i.e., type I and II, exhibit substantial hysteresis which increases with scanning range and sweeping time. Under high vacuum conditions and moderate electric fields ( |E |>4 ×106 V /cm ), the hysteresis for on-surface devices cannot be eliminated, as opposed to suspended devices. Interestingly, type IV devices exhibit no hysteresis at all at ambient conditions, and from the different roles which the global and local gates play for the four types of devices, we could learn about the hysteresis mechanism of this system. We believe that these self aligned hysteresis free FETs will enable the realization of different electronic devices and sensors based on CNTs.

Surface analysis and mechanical behaviour mapping of vertically aligned CNT forest array through nanoindentation

NASA Astrophysics Data System (ADS)

Koumoulos, Elias P.; Charitidis, C. A.

2017-02-01

Carbon nanotube (CNT) based architectures have increased the scientific interest owning to their exceptional performance rendering them promising candidates for advanced industrial applications in the nanotechnology field. Despite individual CNTs being considered as one of the most known strong materials, much less is known about other CNT forms, such as CNT arrays, in terms of their mechanical performance (integrity). In this work, thermal chemical vapor deposition (CVD) method is employed to produce vertically aligned multiwall (VA-MW) CNT carpets. Their structural properties were studied by means of scanning electron microscopy (SEM), X-Ray diffraction (XRD) and Raman spectroscopy, while their hydrophobic behavior was investigated via contact angle measurements. The resistance to indentation deformation of VA-MWCNT carpets was investigated through nanoindentation technique. The synthesized VA-MWCNTs carpets consisted of well-aligned MWCNTs. Static contact angle measurements were performed with water and glycerol, revealing a rather super-hydrophobic behavior. The structural analysis, hydrophobic behavior and indentation response of VA-MWCNTs carpets synthesized via CVD method are clearly demonstrated. Additionally, cycle indentation load-depth curve was applied and hysteresis loops were observed in the indenter loading-unloading cycle due to the local stress distribution. Hardness (as resistance to applied load) and modulus mapping, at 200 nm of displacement for a grid of 70 μm2 is presented. Through trajection, the resistance is clearly divided in 2 regions, namely the MWCNT probing and the in-between area MWCNT - MWCNT interface.

Coated carbon nanotube array electrodes

DOEpatents

Ren, Zhifeng; Wen, Jian; Chen, Jinghua; Huang, Zhongping; Wang, Dezhi

2006-12-12

The present invention provides conductive carbon nanotube (CNT) electrode materials comprising aligned CNT substrates coated with an electrically conducting polymer, and the fabrication of electrodes for use in high performance electrical energy storage devices. In particular, the present invention provides conductive CNTs electrode material whose electrical properties render them especially suitable for use in high efficiency rechargeable batteries. The present invention also provides methods for obtaining surface modified conductive CNT electrode materials comprising an array of individual linear, aligned CNTs having a uniform surface coating of an electrically conductive polymer such as polypyrrole, and their use in electrical energy storage devices.

Coated carbon nanotube array electrodes

DOEpatents

Ren, Zhifeng [Newton, MA; Wen, Jian [Newton, MA; Chen, Jinghua [Chestnut Hill, MA; Huang, Zhongping [Belmont, MA; Wang, Dezhi [Wellesley, MA

2008-10-28

The present invention provides conductive carbon nanotube (CNT) electrode materials comprising aligned CNT substrates coated with an electrically conducting polymer, and the fabrication of electrodes for use in high performance electrical energy storage devices. In particular, the present invention provides conductive CNTs electrode material whose electrical properties render them especially suitable for use in high efficiency rechargeable batteries. The present invention also provides methods for obtaining surface modified conductive CNT electrode materials comprising an array of individual linear, aligned CNTs having a uniform surface coating of an electrically conductive polymer such as polypyrrole, and their use in electrical energy storage devices.

Influence of synthesis parameters on CCVD growth of vertically aligned carbon nanotubes over aluminum substrate.

PubMed

Szabó, Anna; Kecsenovity, Egon; Pápa, Zsuzsanna; Gyulavári, Tamás; Németh, Krisztián; Horvath, Endre; Hernadi, Klara

2017-08-25

In the past two decades, important results have been achieved in the field of carbon nanotube (CNT) research, which revealed that carbon nanotubes have extremely good electrical and mechanical properties The range of applications widens more, if CNTs form a forest-like, vertically aligned structure (VACNT) Although, VACNT-conductive substrate structure could be very advantageous for various applications, to produce proper system without barrier films i.e. with good electrical contact is still a challenge. The aim of the current work is to develop a cheap and easy method for growing carbon nanotubes forests on conductive substrate with the CCVD (Catalytic Chemical Vapor Deposition) technique at 640 °C. The applied catalyst contained Fe and Co and was deposited via dip coating onto an aluminum substrate. In order to control the height of CNT forest several parameters were varied during the both catalyst layer fabrication (e.g. ink concentration, ink composition, dipping speed) and the CCVD synthesis (e.g. gas feeds, reaction time). As-prepared CNT forests were investigated with various methods such as scanning electron microscopy, Raman spectroscopy, and cyclic voltammetry. With such an easy process it was possible to tune both the height and the quality of carbon nanotube forests.

Extremely Black Vertically Aligned Carbon Nanotube Arrays for Solar Steam Generation.

PubMed

Yin, Zhe; Wang, Huimin; Jian, Muqiang; Li, Yanshen; Xia, Kailun; Zhang, Mingchao; Wang, Chunya; Wang, Qi; Ma, Ming; Zheng, Quan-Shui; Zhang, Yingying

2017-08-30

The unique structure of a vertically aligned carbon nanotube (VACNT) array makes it behave most similarly to a blackbody. It is reported that the optical absorptivity of an extremely black VACNT array is about 0.98-0.99 over a large spectral range of 200 nm-200 μm, inspiring us to explore the performance of VACNT arrays in solar energy harvesting. In this work, we report the highly efficient steam generation simply by laminating a layer of VACNT array on the surface of water to harvest solar energy. It is found that under solar illumination the temperature of upper water can significantly increase with obvious water steam generated, indicating the efficient solar energy harvesting and local temperature rise by the thin layer of VACNTs. We found that the evaporation rate of water assisted by VACNT arrays is 10 times that of bare water, which is the highest ratio for solar-thermal-steam generation ever reported. Remarkably, the solar thermal conversion efficiency reached 90%. The excellent performance could be ascribed to the strong optical absorption and local temperature rise induced by the VACNT layer, as well as the ultrafast water transport through the VACNT layer due to the frictionless wall of CNTs. Based on the above, we further demonstrated the application of VACNT arrays in solar-driven desalination.

A novel approach for the fabrication of a flexible glucose biosensor: The combination of vertically aligned CNTs and a conjugated polymer.

PubMed

Gokoglan, Tugba Ceren; Soylemez, Saniye; Kesik, Melis; Dogru, Itir Bakis; Turel, Onur; Yuksel, Recep; Unalan, Husnu Emrah; Toppare, Levent

2017-04-01

A novel flexible glucose biosensor using vertically aligned carbon nanotubes (VACNT) and a conjugated polymer (CP) was fabricated. A scaffold based on VACNT grown on aluminum foil (VACNT-Al foil) with poly (9,9-di-(2-ethylhexyl)-fluorenyl-2,7-diyl)-end capped with 2,5-diphenyl-1,2,4-oxadiazole (PFLO) was used as the immobilization matrix for the glucose biosensor. Glucose oxidase (GOx) was immobilized on a modified indium tin oxide (ITO) coated polyethylene terephthalate (PET) electrode surface. The biosensor response at a potential of -0.7V versus Ag wire was followed by the decrease in oxygen level as a result of enzymatic reaction. The biosensor exhibited a linear range between 0.02mM and 0.5mM glucose and kinetic parameters (K M app , I max , limit of detection (LOD) and sensitivity) were estimated as 0.193mM, 8.170μA, 7.035×10 -3 mM and 65.816μA/mMcm 2 , respectively. Scanning electron microscopy (SEM) was used for surface characterization. The constructed biosensor was applied to determine the glucose content in several beverages. Copyright © 2016 Elsevier Ltd. All rights reserved.

Photonic Sorting of Aligned, Crystalline Carbon Nanotube Textiles.

PubMed

Bulmer, John S; Gspann, Thurid S; Orozco, Francisco; Sparkes, Martin; Koerner, Hilmar; Di Bernardo, A; Niemiec, Arkadiusz; Robinson, J W A; Koziol, Krzysztof K; Elliott, James A; O'Neill, William

2017-10-11

Floating catalyst chemical vapor deposition uniquely generates aligned carbon nanotube (CNT) textiles with individual CNT lengths magnitudes longer than competing processes, though hindered by impurities and intrinsic/extrinsic defects. We present a photonic-based post-process, particularly suited for these textiles, that selectively removes defective CNTs and other carbons not forming a threshold thermal pathway. In this method, a large diameter laser beam rasters across the surface of a partly aligned CNT textile in air, suspended from its ends. This results in brilliant, localized oxidation, where remaining material is an optically transparent film comprised of few-walled CNTs with profound and unique improvement in microstructure alignment and crystallinity. Raman spectroscopy shows substantial D peak suppression while preserving radial breathing modes. This increases the undoped, specific electrical conductivity at least an order of magnitude to beyond that of single-crystal graphite. Cryogenic conductivity measurements indicate intrinsic transport enhancement, opposed to simply removing nonconductive carbons/residual catalyst.

Tunable and label-free virus enrichment for ultrasensitive virus detection using carbon nanotube arrays

PubMed Central

Yeh, Yin-Ting; Tang, Yi; Sebastian, Aswathy; Dasgupta, Archi; Perea-Lopez, Nestor; Albert, Istvan; Lu, Huaguang; Terrones, Mauricio; Zheng, Si-Yang

2016-01-01

Viral infectious diseases can erupt unpredictably, spread rapidly, and ravage mass populations. Although established methods, such as polymerase chain reaction, virus isolation, and next-generation sequencing have been used to detect viruses, field samples with low virus count pose major challenges in virus surveillance and discovery. We report a unique carbon nanotube size-tunable enrichment microdevice (CNT-STEM) that efficiently enriches and concentrates viruses collected from field samples. The channel sidewall in the microdevice was made by growing arrays of vertically aligned nitrogen-doped multiwalled CNTs, where the intertubular distance between CNTs could be engineered in the range of 17 to 325 nm to accurately match the size of different viruses. The CNT-STEM significantly improves detection limits and virus isolation rates by at least 100 times. Using this device, we successfully identified an emerging avian influenza virus strain [A/duck/PA/02099/2012(H11N9)] and a novel virus strain (IBDV/turkey/PA/00924/14). Our unique method demonstrates the early detection of emerging viruses and the discovery of new viruses directly from field samples, thus creating a universal platform for effectively remediating viral infectious diseases. PMID:27730213

Fast synthesis of multilayer carbon nanotubes from camphor oil as an energy storage material.

PubMed

TermehYousefi, Amin; Bagheri, Samira; Shinji, Kawasaki; Rouhi, Jalal; Rusop Mahmood, Mohamad; Ikeda, Shoichiro

2014-01-01

Among the wide range of renewable energy sources, the ever-increasing demand for electricity storage represents an emerging challenge. Utilizing carbon nanotubes (CNTs) for energy storage is closely being scrutinized due to the promising performance on top of their extraordinary features. In this work, well-aligned multilayer carbon nanotubes were successfully synthesized on a porous silicon (PSi) substrate in a fast process using renewable natural essential oil via chemical vapor deposition (CVD). Considering the influx of vaporized multilayer vertical carbon nanotubes (MVCNTs) to the PSi, the diameter distribution increased as the flow rate decreased in the reactor. Raman spectroscopy results indicated that the crystalline quality of the carbon nanotubes structure exhibits no major variation despite changes in the flow rate. Fourier transform infrared (FT-IR) spectra confirmed the hexagonal structure of the carbon nanotubes because of the presence of a peak corresponding to the carbon double bond. Field emission scanning electron microscopy (FESEM) images showed multilayer nanotubes, each with different diameters with long and straight multiwall tubes. Moreover, the temperature programmed desorption (TPD) method has been used to analyze the hydrogen storage properties of MVCNTs, which indicates that hydrogen adsorption sites exist on the synthesized multilayer CNTs.

Fast Synthesis of Multilayer Carbon Nanotubes from Camphor Oil as an Energy Storage Material

PubMed Central

TermehYousefi, Amin; Bagheri, Samira; Shinji, Kawasaki; Rouhi, Jalal; Rusop Mahmood, Mohamad; Ikeda, Shoichiro

2014-01-01

Among the wide range of renewable energy sources, the ever-increasing demand for electricity storage represents an emerging challenge. Utilizing carbon nanotubes (CNTs) for energy storage is closely being scrutinized due to the promising performance on top of their extraordinary features. In this work, well-aligned multilayer carbon nanotubes were successfully synthesized on a porous silicon (PSi) substrate in a fast process using renewable natural essential oil via chemical vapor deposition (CVD). Considering the influx of vaporized multilayer vertical carbon nanotubes (MVCNTs) to the PSi, the diameter distribution increased as the flow rate decreased in the reactor. Raman spectroscopy results indicated that the crystalline quality of the carbon nanotubes structure exhibits no major variation despite changes in the flow rate. Fourier transform infrared (FT-IR) spectra confirmed the hexagonal structure of the carbon nanotubes because of the presence of a peak corresponding to the carbon double bond. Field emission scanning electron microscopy (FESEM) images showed multilayer nanotubes, each with different diameters with long and straight multiwall tubes. Moreover, the temperature programmed desorption (TPD) method has been used to analyze the hydrogen storage properties of MVCNTs, which indicates that hydrogen adsorption sites exist on the synthesized multilayer CNTs. PMID:25258714

Nanoengineered thermal materials based on carbon nanotube array composites

NASA Technical Reports Server (NTRS)

Li, Jun (Inventor); Meyyappan, Meyya (Inventor); Dangelo, Carlos (Inventor)

2010-01-01

A method for providing for thermal conduction using an array of carbon nanotubes (CNTs). An array of vertically oriented CNTs is grown on a substrate having high thermal conductivity, and interstitial regions between adjacent CNTs in the array are partly or wholly filled with a filler material having a high thermal conductivity so that at least one end of each CNT is exposed. The exposed end of each CNT is pressed against a surface of an object from which heat is to be removed. The CNT-filler composite adjacent to the substrate provides improved mechanical strength to anchor CNTs in place and also serves as a heat spreader to improve diffusion of heat flux from the smaller volume (CNTs) to a larger heat sink.

Nanoengineered thermal materials based on carbon nanotube array composites

NASA Technical Reports Server (NTRS)

Li, Jun (Inventor); Meyyappan, Meyya (Inventor)

2007-01-01

A method for providing for thermal conduction using an array of carbon nanotubes (CNTs). An array of vertically oriented CNTs is grown on a substrate having high thermal conductivity, and interstitial regions between adjacent CNTs in the array are partly or wholly filled with a filler material having a high thermal conductivity so that at least one end of each CNT is exposed. The exposed end of each CNT is pressed against a surface of an object from which heat is to be removed. The CNT-filler composite adjacent to the substrate provides improved mechanical strength to anchor CNTs in place and also serves as a heat spreader to improve diffusion of heat flux from the smaller volume (CNTs) to a larger heat sink.

Nanoengineered Thermal Materials Based on Carbon Nanotube Array Composites

NASA Technical Reports Server (NTRS)

Li, Jun (Inventor); Meyyappan, Meyya (Inventor)

2007-01-01

A method for providing for thermal conduction using an array of carbon nanotubes (CNTs). An array of vertically oriented CNTs is grown on a substrate having high thermal conductivity, and interstitial regions between adjacent CNTs in the array are partly or wholly filled with a filler material having a high thermal conductivity so that at least one end of each CNT is exposed. The exposed end of each CNT is pressed against a surface of an object from which heat is to be removed. The CNT-filler composite adjacent to the substrate provides improved mechanical strength to anchor CNTs in place and also serves as a heat spreader to improve diffusion of heat flux from the smaller volume (CNTs) to a larger heat sink.

Noble Metal Decoration and Alignment of Carbon Nanotubes in Carboxymethyl Cellulose

EPA Science Inventory

A facile microwave (MW) method is described that accomplishes alignment and decoration of noble metals on carbon nanotubes wrapped with carboxymethyl cellulose (CMC). Carbon nanotubes (CNTs) such as single-wall (SWNT), multi-wall (MWNT) and Buckminsterfullerene (C-60) were well ...

Aligned Carbon Nanotubes for High-Performance Films and Composites

NASA Astrophysics Data System (ADS)

Zhang, Liwen

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Behavior of oxidized platinum nanoparticles on an aligned carbon nanotube forest

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matsuda, Keita, E-mail: matsuda.keita@c.mbox.nagoya-u.ac.jp; Norimatsu, Wataru; Arai, Shigeo

2016-10-14

We observed and analyzed the behavior of platinum nanoparticles (PtNPs) supported on aligned-carbon nanotubes (CNTs) at high temperatures by X-ray photoelectron spectroscopy and high-resolution transmission electron microscope observations. We found that the PtNPs moved toward the inner-side along each CNT on which they were deposited. The mechanism of this behavior is related to the redox reaction of Pt with the carbon atoms in the CNT. We also performed in-situ observation of this process at a high temperature using an environmental transmission electron microscope under an oxygen atmosphere. We found that the PtNPs penetrated down into a high-density aligned CNT forestmore » along the tube axis and that the PtNPs changed their shape to fit the structure of the CNTs during their movement.« less

A critical evaluation of the enhancement of mechanical properties of epoxy modified using CNTs

NASA Astrophysics Data System (ADS)

Bedsole, Robert W.; Park, Cheol; Bogert, Philip B.; Tippur, Hareesh V.

2015-09-01

Carbon nanotubes (CNTs) have been widely shown in the literature to improve mechanical properties of epoxy, such as tensile strength, elastic modulus, strain to failure, and fracture toughness. These improvements in nanocomposite properties have been attributed to the extraordinary properties of the nanotubes, as well as the quality of their dispersion within and adhesion to the epoxy matrix. However, many authors have also struggled to show significant mechanical improvements using similar methodologies and despite, in some cases, showing qualitative improvements in dispersion with optical microscopy. These authors have frequently resorted to other methods for improving the mechanical properties of CNT/epoxy, such as electrically aligning CNTs, using different types of CNTs, or modifying the stoichiometry. The current work examines many different dispersion techniques, types of CNTs, types of epoxies, curing cycles, and other variables in an attempt to improve the mechanical properties of neat epoxy with CNTs. Despite seeing significant changes in the microscopy, no significant improvements in tensile or fracture properties have been attributed to CNTs in this work.

Carbon Nanotubes (CNTs) for the Development of Electrochemical Biosensors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Yuehe; Yantasee, Wassana; Wang, Joseph

2005-01-01

Carbon nanotube (CNT) is a very attractive material for the development of biosensors because of its capability to provide strong electrocatalytic activity and minimize surface fouling of the sensors. This article reviews our recent developments of oxidase- and dehydrogenase-amperometric biosensors based on the immobilization of CNTs, the co-immobilization of enzymes on the CNTs/Nafion or the CNT/Teflon composite materials, or the attachment of enzymes on the controlled-density aligned CNT-nanoelectrode arrays. The excellent electrocatalytic activities of the CNTs on the redox reactions of hydrogen peroxide, nicotinamide adenine dinucleotide (NADH), and homocysteine have been demonstrated. Successful applications of the CNT-based biosensors reviewed hereinmore » include the low-potential detections of glucose, organophosphorus compounds, and alcohol.« less

Directly measuring of thermal pulse transfer in one-dimensional highly aligned carbon nanotubes

PubMed Central

Zhang, Guang; Liu, Changhong; Fan, Shoushan

2013-01-01

Using a simple and precise instrument system, we directly measured the thermo-physical properties of one-dimensional highly aligned carbon nanotubes (CNTs). A kind of CNT-based macroscopic materials named super aligned carbon nanotube (SACNT) buckypapers was measured in our experiment. We defined a new one-dimensional parameter, the “thermal transfer speed” to characterize the thermal damping mechanisms in the SACNT buckypapers. Our results indicated that the SACNT buckypapers with different densities have obviously different thermal transfer speeds. Furthermore, we found that the thermal transfer speed of high-density SACNT buckypapers may have an obvious damping factor along the CNTs aligned direction. The anisotropic thermal diffusivities of SACNT buckypapers could be calculated by the thermal transfer speeds. The thermal diffusivities obviously increase as the buckypaper-density increases. For parallel SACNT buckypapers, the thermal diffusivity could be as high as 562.2 ± 55.4 mm2/s. The thermal conductivities of these SACNT buckypapers were also calculated by the equation k = Cpαρ. PMID:23989589

Directly measuring of thermal pulse transfer in one-dimensional highly aligned carbon nanotubes.

PubMed

Zhang, Guang; Liu, Changhong; Fan, Shoushan

2013-01-01

Using a simple and precise instrument system, we directly measured the thermo-physical properties of one-dimensional highly aligned carbon nanotubes (CNTs). A kind of CNT-based macroscopic materials named super aligned carbon nanotube (SACNT) buckypapers was measured in our experiment. We defined a new one-dimensional parameter, the "thermal transfer speed" to characterize the thermal damping mechanisms in the SACNT buckypapers. Our results indicated that the SACNT buckypapers with different densities have obviously different thermal transfer speeds. Furthermore, we found that the thermal transfer speed of high-density SACNT buckypapers may have an obvious damping factor along the CNTs aligned direction. The anisotropic thermal diffusivities of SACNT buckypapers could be calculated by the thermal transfer speeds. The thermal diffusivities obviously increase as the buckypaper-density increases. For parallel SACNT buckypapers, the thermal diffusivity could be as high as 562.2 ± 55.4 mm(2)/s. The thermal conductivities of these SACNT buckypapers were also calculated by the equation k = Cpαρ.

Enhanced vapor transport in membrane distillation via functionalized carbon nanotubes anchored into electrospun nanofibres

PubMed Central

Kyoungjin An, Alicia; Lee, Eui-Jong; Guo, Jiaxin; Jeong, Sanghyun; Lee, Jung-Gil; Ghaffour, Noreddine

2017-01-01

To ascertain membrane distillation (MD) as an emerging desalination technology to meet the global water challenge, development of membranes with ideal material properties is crucial. Functionalized carbon nanotubes (CNTs) were anchored to nanofibres of electrospun membranes. Covalent modification and fluorination of CNTs improved their dispersibility and interfacial interaction with the polymer membrane, resulting in well-aligned CNTs inside crystalline fibres with superhydrophobicity. Consideration for the chemical/physical properties of the CNT composite membranes and calculation of their theoretical fluxes revealed the mechanism of MD: CNTs facilitated the repulsive force for Knudsen and molecular diffusions, reduced the boundary-layer effect in viscous flow, and assisted surface diffusion, allowing for fast vapor transport with anti-wetting. This study shows that the role of CNTs and an optimal composite ratio can be used to reduce the gap between theoretical and experimental approaches to desalination. PMID:28134288

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shukrullah, S., E-mail: zshukrullah@gmail.com, E-mail: noranimuti-mohamed@petronas.com.my, E-mail: maizats@petronas.com.my; Mohamed, N. M., E-mail: zshukrullah@gmail.com, E-mail: noranimuti-mohamed@petronas.com.my, E-mail: maizats@petronas.com.my; Shaharun, M. S., E-mail: zshukrullah@gmail.com, E-mail: noranimuti-mohamed@petronas.com.my, E-mail: maizats@petronas.com.my

In this research work, Multiwalled Carbon Nanotubes (MWCNTs) have been synthesized successfully by using floating catalytic chemical vapor deposition (FCCVD) method. Different ferrocene amounts (0.1, 0.125 and 0.15 g) were used as catalyst and ethylene was used as a carbon precursor at reaction temperature of 800°C. Characterization of the grown MWCNTs was carried out by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The obtained data showed that the catalyst weight affects the nanotubes diameter, alignment, crystallinity and growth significantly, whereas negligible influence was noticed on CNTs forest length. The dense, uniform and meadow like patterns of grownmore » CNTs were observed for 0.15 g ferrocene. The average diameter of the grown CNTs was found in the range of 32 to 75 nm. Close inspection of the TEM images also confirmed the defects in some of the grown CNTs, where few black spots were evident in CNTs structure.« less

Enhanced vapor transport in membrane distillation via functionalized carbon nanotubes anchored into electrospun nanofibres

NASA Astrophysics Data System (ADS)

Kyoungjin An, Alicia; Lee, Eui-Jong; Guo, Jiaxin; Jeong, Sanghyun; Lee, Jung-Gil; Ghaffour, Noreddine

2017-01-01

To ascertain membrane distillation (MD) as an emerging desalination technology to meet the global water challenge, development of membranes with ideal material properties is crucial. Functionalized carbon nanotubes (CNTs) were anchored to nanofibres of electrospun membranes. Covalent modification and fluorination of CNTs improved their dispersibility and interfacial interaction with the polymer membrane, resulting in well-aligned CNTs inside crystalline fibres with superhydrophobicity. Consideration for the chemical/physical properties of the CNT composite membranes and calculation of their theoretical fluxes revealed the mechanism of MD: CNTs facilitated the repulsive force for Knudsen and molecular diffusions, reduced the boundary-layer effect in viscous flow, and assisted surface diffusion, allowing for fast vapor transport with anti-wetting. This study shows that the role of CNTs and an optimal composite ratio can be used to reduce the gap between theoretical and experimental approaches to desalination.

Improved field emission properties of carbon nanotubes grown on stainless steel substrate and its application in ionization gauge

NASA Astrophysics Data System (ADS)

Li, Detian; Cheng, Yongjun; Wang, Yongjun; Zhang, Huzhong; Dong, Changkun; Li, Da

2016-03-01

Vertically aligned carbon nanotube (CNT) arrays were fabricated by chemical vapor deposition (CVD) technique on different substrates. Microstructures and field emission characteristics of the as-grown CNT arrays were investigated systematically, and its application in ionization gauge was also evaluated preliminarily. The results indicate that the as-grown CNT arrays are vertically well-aligned relating to the substrate surfaces, but the CNTs grown on stainless steel substrate are longer and more crystalline than the ones grown on silicon wafer substrate. The field emission behaviors of the as-grown CNT arrays are strongly dependent upon substrate properties. Namely, the CNT array grown on stainless steel substrate has better field emission properties, including lower turn on and threshold fields, better emission stability and repeatability, compared with the one grown on silicon wafer substrate. The superior field emission properties of the CNT array grown on stainless steel substrate are mainly attributed to low contact resistance, high thermal conductivity, good adhesion strength, etc. In addition, the metrological behaviors of ionization gauge with the CNT array grown on stainless steel substrate as an electron source were investigated, and this novel cathode ionization gauge extends the lower limit of linear pressure measurement to 10-8 Pa, which is one order of magnitude lower than the result reported for the same of gauge with CNT cathode.

Immobilization of glucose oxidase into a nanoporous TiO₂ film layered on metallophthalocyanine modified vertically-aligned carbon nanotubes for efficient direct electron transfer.

PubMed

Cui, Hui-Fang; Zhang, Kuan; Zhang, Yong-Fang; Sun, Yu-Long; Wang, Jia; Zhang, Wei-De; Luong, John H T

2013-08-15

Glucose oxidase (GOD) was adsorbed into a nanoporous TiO₂ film layered on the surface of an iron phthalocyanine (FePc) vertically-aligned carbon nanotube (CNT) modified electrode. A Nafion film was then dropcast on the electrode's surface to improve operational and storage stabilities of the GOD-based electrode. Scanning electron microscopy (SEM) micrographs revealed the formation of FePc and nanoporous TiO₂ nanoparticles along the sidewall and the tip of CNTs. Cyclic voltammograms of the GOD electrode in neutral PBS exhibited a pair of well-defined redox peaks, attesting the direct electron transfer of GOD (FAD/FADH₂) with the underlying electrode. The potential of glucose electro-oxidation under nitrogen was ∼+0.12 V with an oxidation current density of 65.3 μA cm(-2) at +0.77 V. Voltammetric and amperometric responses were virtually unaffected by oxygen, illustrating an efficient and fast direct electron transfer. The modification of the CNT surface with FePc resulted in a biosensor with remarkable detection sensitivity with an oxygen-independent bioelectrocatalysis. In deaerated PBS, the biosensor displayed average response time of 12 s, linearity from 50 μM to 4 mM, and a detection limit of 30 μM (S/N=3) for glucose. Copyright © 2013 Elsevier B.V. All rights reserved.

Anisotropic piezoresistivity characteristics of aligned carbon nanotube-polymer nanocomposites

NASA Astrophysics Data System (ADS)

Sengezer, Engin C.; Seidel, Gary D.; Bodnar, Robert J.

2017-09-01

Dielectrophoresis under the application of AC electric fields is one of the primary fabrication techniques for obtaining aligned carbon nanotube (CNT)-polymer nanocomposites, and is used here to generate long range alignment of CNTs at the structural level. The degree of alignment of CNTs within this long range architecture is observed via polarized Raman spectroscopy so that its influence on the electrical conductivity and piezoresistive response in both the alignment and transverse to alignment directions can be assessed. Nanocomposite samples consisting of randomly oriented, well dispersed single-wall carbon nanotubes (SWCNTs) and of long range electric field aligned SWCNTs in a photopolymerizable monomer blend (urethane dimethacrylate and 1,6-hexanediol dimethacrylate) are quantitatively and qualitatively evaluated. Piezoresistive sensitivities in form of gauge factors were measured for randomly oriented, well dispersed specimens with 0.03, 0.1 and 0.5 wt% SWCNTs and compared with gauge factors in both the axial and transverse to SWCNT alignment directions for electric field aligned 0.03 wt% specimens under both quasi-static monotonic and cyclic tensile loading. Gauge factors in the axial direction were observed to be on the order of 2, while gauge factors in the transverse direction demonstrated a 5 fold increase with values on the order of 10 for aligned specimens. Based on Raman analysis, it is believed the higher sensitivity of the transverse direction is related to architectural evolution of misaligned bridging structures which connect alignment structures under load due to Poisson’s contraction.

Growth of carbon nanotubes on fully processed silicon-on-insulator CMOS substrates.

PubMed

Haque, M Samiul; Ali, S Zeeshan; Guha, P K; Oei, S P; Park, J; Maeng, S; Teo, K B K; Udrea, F; Milne, W I

2008-11-01

This paper describes the growth of Carbon Nanotubes (CNTs) both aligned and non-aligned on fully processed CMOS substrates containing high temperature tungsten metallization. While the growth method has been demonstrated in fabricating CNT gas sensitive layers for high temperatures SOI CMOS sensors, it can be employed in a variety of applications which require the use of CNTs or other nanomaterials with CMOS electronics. In our experiments we have grown CNTs both on SOI CMOS substrates and SOI CMOS microhotplates (suspended on membranes formed by post-CMOS deep RIE etching). The fully processed SOI substrates contain CMOS devices and circuits and additionally, some wafers contained high current LDMOSFETs and bipolar structures such as Lateral Insulated Gate Bipolar Transistors. All these devices were used as test structures to investigate the effect of additional post-CMOS processing such as CNT growth, membrane formation, high temperature annealing, etc. Electrical characterisation of the devices with CNTs were performed along with SEM and Raman spectroscopy. The CNTs were grown both at low and high temperatures, the former being compatible with Aluminium metallization while the latter being possible through the use of the high temperature CMOS metallization (Tungsten). In both cases we have found that there is no change in the electrical behaviour of the CMOS devices, circuits or the high current devices. A slight degradation of the thermal performance of the CMOS microhotplates was observed due to the extra heat dissipation path created by the CNT layers, but this is expected as CNTs exhibit a high thermal conductance. In addition we also observed that in the case of high temperature CNT growth a slight degradation in the manufacturing yield was observed. This is especially the case where large area membranes with a diameter in excess of 500 microns are used.

Structure-Property Relations in Carbon Nanotube Fibers by Downscaling Solution Processing.

PubMed

Headrick, Robert J; Tsentalovich, Dmitri E; Berdegué, Julián; Bengio, Elie Amram; Liberman, Lucy; Kleinerman, Olga; Lucas, Matthew S; Talmon, Yeshayahu; Pasquali, Matteo

2018-03-01

At the microscopic scale, carbon nanotubes (CNTs) combine impressive tensile strength and electrical conductivity; however, their macroscopic counterparts have not met expectations. The reasons are variously attributed to inherent CNT sample properties (diameter and helicity polydispersity, high defect density, insufficient length) and manufacturing shortcomings (inadequate ordering and packing), which can lead to poor transmission of stress and current. To efficiently investigate the disparity between microscopic and macroscopic properties, a new method is introduced for processing microgram quantities of CNTs into highly oriented and well-packed fibers. CNTs are dissolved into chlorosulfonic acid and processed into aligned films; each film can be peeled and twisted into multiple discrete fibers. Fibers fabricated by this method and solution-spinning are directly compared to determine the impact of alignment, twist, packing density, and length. Surprisingly, these discrete fibers can be twice as strong as their solution-spun counterparts despite a lower degree of alignment. Strength appears to be more sensitive to internal twist and packing density, while fiber conductivity is essentially equivalent among the two sets of samples. Importantly, this rapid fiber manufacturing method uses three orders of magnitude less material than solution spinning, expanding the experimental parameter space and enabling the exploration of unique CNT sources. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ionization Gas Sensor using Aligned Multiwalled Carbon Nanotubes Array

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kermany, A. R.; Mohamed, N. M.; Singh, B. S. M.

2011-05-25

The challenge with current conventional gas sensors which are operating using semiconducting oxides is their size. After the introduction of nanotechnology and in order to reduce the dimension and consequently the power consumption and cost, new materials such as carbon nanotubes (CNTs) are being introduced. From previous works and characterization results, it was proven that the CNTs based gas sensor has better sensitivity, selectivity and faster response time in compared with semiconducting oxides based gas sensors. As in this work, a fabrication and successful testing of an ionization-based gas sensor using aligned Multiwalled CNTs (MWCNTs) as sensing element is discussed,more » in which MWCNTs array and Al film are used as anode and cathode plates respectively with electrode separation ranging from 80 {mu}m to 140 {mu}m. Aligned MWCNTs array was incorporated into a sensor configuration in the gas chamber for testing of gases such as argon, air, and mixed gas of 2%H{sub 2} in air. Obtained results show that among the three gases, argon has the lowest breakdown voltage whilst air has the highest value and the breakdown voltage was found to decrease as the electrode spacing was reduced from 140 {mu}m to 80 {mu}m for all three gases.« less

Highly Efficient Organic Photovoltaic Cells from Polymer-Aligned Carbon Nanotube Dispersed Heterojunctions

DTIC Science & Technology

2009-09-01

semiconducting VA-SWNTs, and muiltcomponent micropatterns of VA- CNTs . We also designed and synthesized several classes of novel low bandgap...photovoltaic active polymers, and polymer-/TiO2–coated VA- CNTs , critical to developing high efficient polymer photovoltaic cells and dye-sensitized solar...an efficient solar absorption and charge separation/collection. Besides, novel N-doped CNT fuel cells, polymer/quantum dot light-emitting diodes, and

Laser-directed 3D assembly of carbon nanotubes using two-photon polymerization (Conference Presentation)

NASA Astrophysics Data System (ADS)

Liu, Ying; Xiong, Wei; Jiang, Li Jia; Zhou, Yunshen; Li, Dawei; Jiang, Lan; Silvain, Jean-Francois; Lu, Yongfeng

2017-02-01

Precise assembly of carbon nanotubes (CNTs) in arbitrary 3D space with proper alignment is critically important and desirable for CNT applications but still remains as a long-standing challenge. Using the two-photon polymerization (TPP) technique, it is possible to fabricate 3D micro/nanoscale CNT/polymer architectures with proper CNT alignments in desired directions, which is expected to enable a broad range of applications of CNTs in functional devices. To unleash the full potential of CNTs, it is strategically important to develop TPP-compatible resins with high CNT concentrations for precise assembly of CNTs into 3D micro/nanostructures for functional device applications. We investigated a thiol grafting method in functionalizing multiwalled carbon nanotubes (MWNTs) to develop TPP-compatible MWNT-thiol-acrylate (MTA) composite resins. The composite resins developed had high MWNT concentrations up to 0.2 wt%, over one order of magnitude higher than previously published work. Significantly enhanced electrical and mechanical properties of the 3D micro/nanostructures were achieved. Precisely controlled MWNT assembly and strong anisotropic effects were confirmed. Microelectronic devices made of the MTA composite polymer were demonstrated. The nanofabrication method can achieve controlled assembly of MWNTs in 3D micro/nanostructures, enabling a broad range of CNT applications, including 3D electronics, integrated photonics, and micro/nanoelectromechanical systems (MEMS/NEMS).

Growth of hybrid carbon nanostructures on iron-decorated ZnO nanorods

NASA Astrophysics Data System (ADS)

Mbuyisa, Puleng N.; Rigoni, Federica; Sangaletti, Luigi; Ponzoni, Stefano; Pagliara, Stefania; Goldoni, Andrea; Ndwandwe, Muzi; Cepek, Cinzia

2016-04-01

A novel carbon-based nanostructured material, which includes carbon nanotubes (CNTs), porous carbon, nanostructured ZnO and Fe nanoparticles, has been synthetized using catalytic chemical vapour deposition (CVD) of acetylene on vertically aligned ZnO nanorods (NRs). The deposition of Fe before the CVD process induces the presence of dense CNTs in addition to the variety of nanostructures already observed on the process done on the bare NRs, which range from amorphous graphitic carbon up to nanostructured dendritic carbon films, where the NRs are partially or completely etched. The combination of scanning electron microscopy and in situ photoemission spectroscopy indicate that Fe enhances the ZnO etching, and that the CNT synthesis is favoured by the reduced Fe mobility due to the strong interaction between Fe and the NRs, and to the presence of many defects, formed during the CVD process. Our results demonstrate that the resulting new hybrid shows a higher sensitivity to ammonia gas at ambient conditions (∼60 ppb) than the carbon nanostructures obtained without the aid of Fe, the bare ZnO NRs, or other one-dimensional carbon nanostructures, making this system of potential interest for environmental ammonia monitoring. Finally, in view of the possible application in nanoscale optoelectronics, the photoexcited carrier behaviour in these hybrid systems has been characterized by time-resolved reflectivity measurements.

Investigation of Electron Transport Across Vertically Grown CNTs Using Combination of Proximity Field Emission Microscopy and Scanning Probe Image Processing Techniques

NASA Astrophysics Data System (ADS)

Kolekar, Sadhu; Patole, Shashikant P.; Yoo, Ji-Beom; Dharmadhikari, Chandrakant V.

2018-03-01

Field emission from nanostructured films is known to be dominated by only small number of localized spots which varies with the voltage, electric field and heat treatment. It is important to develop processing methods which will produce stable and uniform emitting sites. In this paper we report a novel approach which involves analysis of Proximity Field Emission Microscopic (PFEM) images using Scanning Probe Image Processing technique. Vertically aligned carbon nanotube emitters have been deposited on tungsten foil by water assisted chemical vapor deposition. Prior to the field electron emission studies, these films were characterized by scanning electron microscopy, transmission electron microscopy, and Atomic Force Microscopy (AFM). AFM images of the samples show bristle like structure, the size of bristle varying from 80 to 300 nm. The topography images were found to exhibit strong correlation with current images. Current-Voltage (I-V) measurements both from Scanning Tunneling Microscopy and Conducting-AFM mode suggest that electron transport mechanism in imaging vertically grown CNTs is ballistic rather than usual tunneling or field emission with a junction resistance of 10 kΩ. It was found that I-V curves for field emission mode in PFEM geometry vary initially with number of I-V cycles until reproducible I-V curves are obtained. Even for reasonably stable I-V behavior the number of spots was found to increase with the voltage leading to a modified Fowler-Nordheim (F-N) behavior. A plot of ln(I/V3) versus 1/V was found to be linear. Current versus time data exhibit large fluctuation with the power spectral density obeying 1/f2 law. It is suggested that an analogue of F-N equation of the form ln(I/Vα) versus 1/V may be used for the analysis of field emission data, where α may depend on nanostructure configuration and can be determined from the dependence of emitting spots on the voltage.

Structures of water molecules in carbon nanotubes under electric fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Winarto,; Takaiwa, Daisuke; Yamamoto, Eiji

2015-03-28

Carbon nanotubes (CNTs) are promising for water transport through membranes and for use as nano-pumps. The development of CNT-based nanofluidic devices, however, requires a better understanding of the properties of water molecules in CNTs because they can be very different from those in the bulk. Using all-atom molecular dynamics simulations, we investigate the effect of axial electric fields on the structure of water molecules in CNTs having diameters ranging from (7,7) to (10,10). The water dipole moments were aligned parallel to the electric field, which increases the density of water inside the CNTs and forms ordered ice-like structures. The electricmore » field induces the transition from liquid to ice nanotubes in a wide range of CNT diameters. Moreover, we found an increase in the lifetime of hydrogen bonds for water structures in the CNTs. Fast librational motion breaks some hydrogen bonds, but the molecular pairs do not separate and the hydrogen bonds reform. Thus, hydrogen bonds maintain the water structure in the CNTs, and the water molecules move collectively, decreasing the axial diffusion coefficient and permeation rate.« less

Remarkably enhanced thermal transport based on a flexible horizontally-aligned carbon nanotube array film

PubMed Central

Qiu, Lin; Wang, Xiaotian; Su, Guoping; Tang, Dawei; Zheng, Xinghua; Zhu, Jie; Wang, Zhiguo; Norris, Pamela M.; Bradford, Philip D.; Zhu, Yuntian

2016-01-01

It has been more than a decade since the thermal conductivity of vertically aligned carbon nanotube (VACNT) arrays was reported possible to exceed that of the best thermal greases or phase change materials by an order of magnitude. Despite tremendous prospects as a thermal interface material (TIM), results were discouraging for practical applications. The primary reason is the large thermal contact resistance between the CNT tips and the heat sink. Here we report a simultaneous sevenfold increase in in-plane thermal conductivity and a fourfold reduction in the thermal contact resistance at the flexible CNT-SiO2 coated heat sink interface by coupling the CNTs with orderly physical overlapping along the horizontal direction through an engineering approach (shear pressing). The removal of empty space rapidly increases the density of transport channels, and the replacement of the fine CNT tips with their cylindrical surface insures intimate contact at CNT-SiO2 interface. Our results suggest horizontally aligned CNT arrays exhibit remarkably enhanced in-plane thermal conductivity and reduced out-of-plane thermal conductivity and thermal contact resistance. This novel structure makes CNT film promising for applications in chip-level heat dissipation. Besides TIM, it also provides for a solution to anisotropic heat spreader which is significant for eliminating hot spots. PMID:26880221

Patterned growth of carbon nanotubes on Si substrates without predeposition of metal catalysts

NASA Astrophysics Data System (ADS)

Chen, Y.; Yu, J.

2005-07-01

Aligned carbon nanotubes (CNTs) can be readily synthesized on quartz or silicon-oxide-coated Si substrates using a chemical vapor deposition method, but it is difficult to grow them on pure Si substrates without predeposition of metal catalysts. We report that aligned CNTs were grown by pyrolysis of iron phthalocyanine at 1000°C on the templates created on Si substrates with simple mechanical scratching. Scanning electron microscopy and x-ray energy spectroscopy analysis revealed that the trenches and patterns created on the surface of Si substrates were preferred nucleation sites for nanotube growth due to a high surface energy, metastable surface structure, and possible capillarity effect. A two-step pyrolysis process maintained Fe as an active catalyst.

Positioning and aligning CNTs by external magnetic field to assist localised epoxy cure

NASA Astrophysics Data System (ADS)

Ariu, G.; Hamerton, I.; Ivanov, D.

2016-01-01

This work focuses on the generation of conductive networks through the localised alignment of nano fillers, such as multi-walled carbon nanotubes (MWCNTs). The feasibility of alignment and positioning of functionalised MWCNTs by external DC magnetic fields was investigated. The aim of this manipulation is to enhance resin curing through AC induction heating due to hysteresis losses from the nanotubes. Experimental analyses focused on in-depth assessment of the nanotube functionalisation, processing and characterisation of magnetic, rheological and cure kinetics properties of the MWCNT solution. The study has shown that an external magnetic field has great potential for positioning and alignment of CNTs. The study demonstrated potential for creating well-ordered architectures with an unprecedented level of control of network geometry. Magnetic characterisation indicated cobalt-plated nanotubes to be the most suitable candidate for magnetic alignment due to their high magnetic sensitivity. Epoxy/metal-plated CNT nanocomposite systems were validated by thermal analysis as induction heating mediums. The curing process could therefore be optimised by the use of dielectric resins. This study offers a first step towards the proof of concept of this technique as a novel repair technology.

Technical feasibility and economical viability of remote hybrid power systems in Northern Ontario

NASA Astrophysics Data System (ADS)

Gubbels, Jason Matthew

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Evaluation of remotely sensed wetland mapping

NASA Astrophysics Data System (ADS)

Gluck, Michael J.

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Effects of propagational factors on quantum wires in close parallel proximity

NASA Astrophysics Data System (ADS)

Wilson, David A.

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Tectonic magnetic fabrics in pure and simple shear: Experimental investigations

NASA Astrophysics Data System (ADS)

Alford, Craig Steven

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Use of a single epiphyte lichen species Hypogymnia physodes as an indicator of air quality in northern Ontario

NASA Astrophysics Data System (ADS)

Pfeiffer, Helmut Nickolaus

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Gravity study of an Archaen crustal segment near Thunder Bay, Ontario

NASA Astrophysics Data System (ADS)

Cheadle, Scott Philip

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Northern lights: A history of Thunder Bay Hydro

NASA Astrophysics Data System (ADS)

Black, David Leo

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Static dielectric properties of an ensemble of restricted one-dimensional oscillators

NASA Astrophysics Data System (ADS)

Tjipto Margo, Broto

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Photoluminescence and Raman characterization of PLEE and MBE grown semiconductor epilayers

NASA Astrophysics Data System (ADS)

Harrison, Dale A.

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Development of nonlinear 3-D, and novel 2-D optical microscope imaging systems for time-lapse imaging

NASA Astrophysics Data System (ADS)

Girardin, Robert Joseph

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Simple route to new palladium-carbonyl-bis(diphenylphosphino)methane complexes

NASA Astrophysics Data System (ADS)

Krysa, Elizabeth

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Impurity band conduction in reduced samples of bismuth iron molybdate

NASA Astrophysics Data System (ADS)

McIntyre, Shawn M.

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Photon number density operator

NASA Astrophysics Data System (ADS)

Melde, Thomas

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Dielectric and infrared studies of radio frequency processes in some alcohols

NASA Astrophysics Data System (ADS)

Mandal, Humayun

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Real-time implementation of some attitude estimation algorithms on a quadrotor UAV

NASA Astrophysics Data System (ADS)

Nayak, Siddhant

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Ordered supramolecular oligothiophene structures on passivated silicon surfaces

NASA Astrophysics Data System (ADS)

Liu, Renjie

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Synthesis and electrochemical study of PtIr and PtRu nanomaterials

NASA Astrophysics Data System (ADS)

Alammari, Walaa S.

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

P-type gallium nitride semiconductor development and characterization for LEDs and other devices

NASA Astrophysics Data System (ADS)

Togtema, Gregorey L.

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Tuning carbon nanotube assembly for flexible, strong and conductive films

NASA Astrophysics Data System (ADS)

Wang, Yanjie; Li, Min; Gu, Yizhuo; Zhang, Xiaohua; Wang, Shaokai; Li, Qingwen; Zhang, Zuoguang

2015-02-01

Carbon nanotubes are ideal scaffolds for designing and architecting flexible graphite films with tunable mechanical, electrical and thermal properties. Herein, we demonstrate that the assembly of aligned carbon nanotubes with different aggregation density and morphology leads to different mechanical properties and anisotropic electrical conduction along the films. Using drying evaporation under tension treatment, the carbon nanotubes can be assembled into strong films with tensile strength and Young's modulus as high as 3.2 GPa and 124 GPa, respectively, leading to a remarkable toughness of 54.38 J g-1, greatly outperforming conventional graphite films, spider webs and even Kevlar fiber films. Different types of solvents may result in the assembly of CNTs with different aggregation morphology and therefore different modulus. In addition, we reveal that the high density assembly of aligned CNTs correlates with better electric conduction along the axial direction, enabling these flexible graphite films to be both strong and conductive.Carbon nanotubes are ideal scaffolds for designing and architecting flexible graphite films with tunable mechanical, electrical and thermal properties. Herein, we demonstrate that the assembly of aligned carbon nanotubes with different aggregation density and morphology leads to different mechanical properties and anisotropic electrical conduction along the films. Using drying evaporation under tension treatment, the carbon nanotubes can be assembled into strong films with tensile strength and Young's modulus as high as 3.2 GPa and 124 GPa, respectively, leading to a remarkable toughness of 54.38 J g-1, greatly outperforming conventional graphite films, spider webs and even Kevlar fiber films. Different types of solvents may result in the assembly of CNTs with different aggregation morphology and therefore different modulus. In addition, we reveal that the high density assembly of aligned CNTs correlates with better electric conduction along the axial direction, enabling these flexible graphite films to be both strong and conductive. Electronic supplementary information (ESI) available: The TEM image of array CNTs. The surface height curves of x-z cross-section of the films. A comparison of the mechanical properties of the pure CNT films described in this work with other CNT films/fibers spun from CNT array reported in the literature. The measured evaporation rates of ethanol and acetone. See DOI: 10.1039/c4nr06401a

Aligning Solution-Derived Carbon Nanotube Film with Full Surface Coverage for High-Performance Electronics Applications.

PubMed

Zhu, Ma-Guang; Si, Jia; Zhang, Zhiyong; Peng, Lian-Mao

2018-06-01

The main challenge for application of solution-derived carbon nanotubes (CNTs) in high performance field-effect transistor (FET) is how to align CNTs into an array with high density and full surface coverage. A directional shrinking transfer method is developed to realize high density aligned array based on randomly orientated CNT network film. Through transferring a solution-derived CNT network film onto a stretched retractable film followed by a shrinking process, alignment degree and density of CNT film increase with the shrinking multiple. The quadruply shrunk CNT films present well alignment, which is identified by the polarized Raman spectroscopy and electrical transport measurements. Based on the high quality and high density aligned CNT array, the fabricated FETs with channel length of 300 nm present ultrahigh performance including on-state current I on of 290 µA µm -1 (V ds = -1.5 V and V gs = -2 V) and peak transconductance g m of 150 µS µm -1 , which are, respectively, among the highest corresponding values in the reported CNT array FETs. High quality and high semiconducting purity CNT arrays with high density and full coverage obtained through this method promote the development of high performance CNT-based electronics. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Wafer-scale, massively parallel carbon nanotube arrays for realizing field effect transistors with current density exceeding silicon and gallium arsenide

NASA Astrophysics Data System (ADS)

Arnold, Michael

Calculations have indicated that aligned arrays of semiconducting carbon nanotubes (CNTs) promise to outperform conventional semiconducting materials in short-channel, aggressively scaled field effect transistors (FETs) like those used in semiconductor logic and high frequency amplifier technologies. These calculations have been based on extrapolation of measurements of FETs based on one CNT, in which ballistic transport approaching the quantum conductance limit of 2Go = 4e2/h has been achieved. However, constraints in CNT sorting, processing, alignment, and contacts give rise to non-idealities when CNTs are implemented in densely-packed parallel arrays, which has resulted in a conductance per CNT far from 2Go. The consequence has been that it has been very difficult to create high performance CNT array FETs, and CNT array FETs have not outperformed but rather underperformed channel materials such as Si by 6 x or more. Here, we report nearly ballistic CNT array FETs at a density of 50 CNTs um-1, created via CNT sorting, wafer-scale alignment and assembly, and treatment. The on-state conductance in the arrays is as high as 0.46 Go per CNT, and the conductance of the arrays reaches 1.7 mS um-1, which is 7 x higher than previous state-of-the-art CNT array FETs made by other methods. The saturated on-state current density reaches 900 uA um-1 and is similar to or exceeds that of Si FETs when compared at equivalent gate oxide thickness, off-state current density, and channel length. The on-state current density exceeds that of GaAs FETs, as well. This leap in CNT FET array performance is a significant advance towards the exploitation of CNTs in high-performance semiconductor electronics technologies.

Alignment of SWNTs by protein-ligand interaction of functionalized magnetic particles under low magnetic fields.

PubMed

Park, Tae Jung; Park, Jong Pil; Lee, Seok Jae; Jung, Dae-Hwan; Ko, Young Koan; Jung, Hee-Tae; Lee, Sang Yup

2011-05-01

Carbon nanotubes (CNTs) have attracted considerable attention for applications using their superior mechanical, thermal and electrical properties. A simple method to controllably align single-walled CNTs (SWNTs) by using magnetic particles embedded with superparamagnetic iron oxide as an accelerator under the magnetic field was developed. The functionalization of SWNTs using biotin, interacted with streptavidin-coupled magnetic particles (micro-to-nano in diameter), and layer-by-layer assembly were performed for the alignment of a particular direction onto the clean silicon and the gold substrate at very low magnetic forces (0.02-0.89 T) at room temperature. The successful alignment of the SWNTs with multi-layer film was observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). By changing the orientation and location of the substrates, crossed-networks of SWNTs-magnetic particle complex could easily be fabricated. We suggest that this approach, which consists of a combination of biological interaction among streptavidin-biotin and magnetite particles, should be useful for lateral orientation of individual SWNTs with controllable direction.

Carbon nanotubes within polymer matrix can synergistically enhance mechanical energy dissipation

NASA Astrophysics Data System (ADS)

Ashraf, Taimoor; Ranaiefar, Meelad; Khatri, Sumit; Kavosi, Jamshid; Gardea, Frank; Glaz, Bryan; Naraghi, Mohammad

2018-03-01

Safe operation and health of structures relies on their ability to effectively dissipate undesired vibrations, which could otherwise significantly reduce the life-time of a structure due to fatigue loads or large deformations. To address this issue, nanoscale fillers, such as carbon nanotubes (CNTs), have been utilized to dissipate mechanical energy in polymer-based nanocomposites through filler-matrix interfacial friction by benefitting from their large interface area with the matrix. In this manuscript, for the first time, we experimentally investigate the effect of CNT alignment with respect to reach other and their orientation with respect to the loading direction on vibrational damping in nanocomposites. The matrix was polystyrene (PS). A new technique was developed to fabricate PS-CNT nanocomposites which allows for controlling the angle of CNTs with respect to the far-field loading direction (misalignment angle). Samples were subjected to dynamic mechanical analysis, and the damping of the samples were measured as the ratio of the loss to storage moduli versus CNT misalignment angle. Our results defied a notion that randomly oriented CNT nanocomposites can be approximated as a combination of matrix-CNT representative volume elements with randomly aligned CNTs. Instead, our results points to major contributions of stress concentration induced by each CNT in the matrix in proximity of other CNTs on vibrational damping. The stress fields around CNTs in PS-CNT nanocomposites were studied via finite element analysis. Our findings provide significant new insights not only on vibrational damping nanocomposites, but also on their failure modes and toughness, in relation to interface phenomena.

Scalable synthesis of aligned carbon nanotubes bundles using green natural precursor: neem oil

NASA Astrophysics Data System (ADS)

Kumar, Rajesh; Tiwari, Radhey Shyam; Srivastava, Onkar Nath

2011-12-01

Practical application of aligned carbon nanotubes (ACNTs) would have to be determined by a matter of its economical and large-scale preparation. In this study, neem oil (also named Margoaa oil, extracted from the seeds of the neem-- Azadirachta indica) was used as carbon source to fabricate the bundles of ACNTs. ACNTs have been synthesized by spray pyrolysis of neem oil and ferrocene mixture at 825°C. The major components of neem oil are hydrocarbon with less amount of oxygen, which provided the precursor species in spray pyrolysis growth of CNTs. The bundles of ACNTs have been grown directly inside the quartz tube. The as-grown ACNTs have been characterized through Raman spectroscopy, scanning and transmission electron microscopic (SEM/TEM) techniques. SEM images reveal that the bundles of ACNTs are densely packed and are of several microns in length. High-resolution TEM analysis reveals these nanotubes to be multi-walled CNTs. These multi-walled CNTs were found to have inner diameter between 15 and 30 nm. It was found that present technique gives high yield with high density of bundles of ACNTs.

Scalable synthesis of aligned carbon nanotubes bundles using green natural precursor: neem oil.

PubMed

Kumar, Rajesh; Tiwari, Radhey Shyam; Srivastava, Onkar Nath

2011-01-18

Practical application of aligned carbon nanotubes (ACNTs) would have to be determined by a matter of its economical and large-scale preparation. In this study, neem oil (also named Margoaa oil, extracted from the seeds of the neem--Azadirachta indica) was used as carbon source to fabricate the bundles of ACNTs. ACNTs have been synthesized by spray pyrolysis of neem oil and ferrocene mixture at 825°C. The major components of neem oil are hydrocarbon with less amount of oxygen, which provided the precursor species in spray pyrolysis growth of CNTs. The bundles of ACNTs have been grown directly inside the quartz tube. The as-grown ACNTs have been characterized through Raman spectroscopy, scanning and transmission electron microscopic (SEM/TEM) techniques. SEM images reveal that the bundles of ACNTs are densely packed and are of several microns in length. High-resolution TEM analysis reveals these nanotubes to be multi-walled CNTs. These multi-walled CNTs were found to have inner diameter between 15 and 30 nm. It was found that present technique gives high yield with high density of bundles of ACNTs.

A smart temperature and magnetic-responsive gating carbon nanotube membrane for ion and protein transportation

PubMed Central

Cong, Hailin; Xu, Xiaodan; Yu, Bing; Yang, Zhaohui; Zhang, Xiaoyan

2016-01-01

Carbon nanotube (CNT) nanoporous membranes based on pre-aligned CNTs have superior nano-transportation properties in biological science. Herein, we report a smart temperature- and temperature-magnetic-responsive CNT nanoporous membrane (CNM) by grafting thermal-sensitive poly(N-isopropylacrylamide) (PNIPAM) and Fe3O4 nanoparticles (Fe3O4-NPs) on the open ends of pre-aligned CNTs with a diameter around 15 nm via surface-initiated atom transfer radical polymerization (SI-ATRP) method. The inner cavity of the modified CNTs in the membrane is designed to be the only path for ion and protein transportation, and its effective diameter with a variation from ~5.7 nm to ~12.4 nm can be reversible tuned by temperature and magnetic field. The PNIPAM modified CNM (PNIPAM-CNM) and PNIPAM magnetic nanoparticles modified CNM (PNIPAM-MAG-CNM) exhibit excellent temperature- or temperature-magnetic-responsive gating property to separate proteins of different sizes. The PNIPAM-CNMs and PNIPAM-MAG-CNMs have potential applications in making artificial cells, biosensors, bioseparation and purification filters. PMID:27535103

Preparation of CNTs rope by electrostatic and airflow field carding with high speed rotor spinning

NASA Astrophysics Data System (ADS)

Dai, J. F.; Liu, J. F.; Zou, J. T.; Dai, Y. L.

2015-12-01

The large-scale preparation of disorderly CNTs with a length larger than 3 mm using CVD method were aligned in polymer monomer airflow fields in a quartz tube with an internal diameter of 200 μm and a length of 1.5 m. The airflow aligned CNTs at the output end of the pipe connects to a copper nozzle with an electrostatic field of applied voltage 5x105 V/m and space length of 0.03 m, which were further realigned using via electrostatic spinning. End to end spray into the high speed rotor twisted single-stranded carbon nanotubes threads via rotor spinning technology. The essential component of this technique was the use of carbon nanotubes at a high rotory speed (200000 r/min) combined with the double twisting of filaments that were twisted together to increase the radial friction of the entire section. SEM micrography showed that carbon nanotube thread has a uniform diameter of approximately 200 μm. Its tensile strength was tested up to 2.7 Gpa, with a length of several meters.

Multi-Scale CNT-Based Reinforcing Polymer Matrix Composites for Lightweight Structures

NASA Technical Reports Server (NTRS)

Eberly, Daniel; Ou, Runqing; Karcz, Adam; Skandan, Ganesh; Mather, Patrick; Rodriguez, Erika

2013-01-01

Reinforcing critical areas in carbon polymer matrix composites (PMCs), also known as fiber reinforced composites (FRCs), is advantageous for structural durability. Since carbon nanotubes (CNTs) have extremely high tensile strength, they can be used as a functional additive to enhance the mechanical properties of FRCs. However, CNTs are not readily dispersible in the polymer matrix, which leads to lower than theoretically predicted improvement in mechanical, thermal, and electrical properties of CNT composites. The inability to align CNTs in a polymer matrix is also a known issue. The feasibility of incorporating aligned CNTs into an FRC was demonstrated using a novel, yet commercially viable nanofiber approach, termed NRMs (nanofiber-reinforcing mats). The NRM concept of reinforcement allows for a convenient and safe means of incorporating CNTs into FRC structural components specifically where they are needed during the fabrication process. NRMs, fabricated through a novel and scalable process, were incorporated into FRC test panels using layup and vacuum bagging techniques, where alternating layers of the NRM and carbon prepreg were used to form the reinforced FRC structure. Control FRC test panel coupons were also fabricated in the same manner, but comprised of only carbon prepreg. The FRC coupons were machined to size and tested for flexural, tensile, and compression properties. This effort demonstrated that FRC structures can be fabricated using the NRM concept, with an increased average load at break during flexural testing versus that of the control. The NASA applications for the developed technologies are for lightweight structures for in-space and launch vehicles. In addition, the developed technologies would find use in NASA aerospace applications such as rockets, aircraft, aircraft/spacecraft propulsion systems, and supporting facilities. The reinforcing aspect of the technology will allow for more efficient joining of fiber composite parts, thus offering additional weight savings. More robust structures capable of withstanding micrometeoroid and space debris impacts will be possible with the enhanced mechanical properties imparted by the aligned CNTs incorporated into the fiber composite structure, as well as the potential for improved electrical and thermal properties. The materials fabrication approach developed in the present effort is a platform for customer applications where additional reinforcement is required or would be beneficial, especially in FRC structures and component parts. Depending upon the specific customer application, the NRM could be tailored to the specific matrix resin and desired property enhancement.

Realization of high temperature superconductivity in carbon nanotubes and its low powerapplications

DTIC Science & Technology

radial breathing phonon mode and hybrid orbital electrons. Previously, I tried to realize high-Tc SC in thin films consisting of randomly placed CNTs...based on such advantages. Moreover, I applied ionic-gel (liquid) gating to the CNT thin films in order to cause extremely high EDOS on the surface and...bromide (CTAB)) to chemically modify CNT surface and create thin films consisting of highly oriented (aligned) CNTs with flat and homogeneous surface

Carbon nanotube mass production: principles and processes.

PubMed

Zhang, Qiang; Huang, Jia-Qi; Zhao, Meng-Qiang; Qian, Wei-Zhong; Wei, Fei

2011-07-18

Our society requires new materials for a sustainable future, and carbon nanotubes (CNTs) are among the most important advanced materials. This Review describes the state-of-the-art of CNT synthesis, with a focus on their mass-production in industry. At the nanoscale, the production of CNTs involves the self-assembly of carbon atoms into a one-dimensional tubular structure. We describe how this synthesis can be achieved on the macroscopic scale in processes akin to the continuous tonne-scale mass production of chemical products in the modern chemical industry. Our overview includes discussions on processing methods for high-purity CNTs, and the handling of heat and mass transfer problems. Manufacturing strategies for agglomerated and aligned single-/multiwalled CNTs are used as examples of the engineering science of CNT production, which includes an understanding of their growth mechanism, agglomeration mechanism, reactor design, and process intensification. We aim to provide guidelines for the production and commercialization of CNTs. Although CNTs can now be produced on the tonne scale, knowledge of the growth mechanism at the atomic scale, the relationship between CNT structure and application, and scale-up of the production of CNTs with specific chirality are still inadequate. A multidisciplinary approach is a prerequisite for the sustainable development of the CNT industry. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Graphene—vertically aligned carbon nanotube hybrid on PDMS as stretchable electrodes

NASA Astrophysics Data System (ADS)

Ding, Junjun; Fu, Shichen; Zhang, Runzhi; Boon, Eric; Lee, Woo; Fisher, Frank T.; Yang, Eui-Hyeok

2017-11-01

Stretchable electrodes are a critical component for flexible electronics such as displays, energy devices, and wearable sensors. Carbon nanotubes (CNTs) and graphene have been considered for flexible electrode applications, due to their mechanical strength, high carrier mobility, and excellent thermal conductivity. Vertically aligned carbon nanotubes (VACNTs) provide the possibility to serve as interconnects to graphene sheets as stretchable electrodes that could maintain high electrical conductivity under large tensile strain. In this work, a graphene oxide (GO)-VACNT hybrid on a PDMS substrate was demonstrated. Here, 50 μm long VACNTs were grown on a Si/SiO2 wafer substrate via atmospheric pressure chemical vapor deposition. VACNTs were directly transferred by delamination from the Si/SiO2 to a semi-cured PDMS substrate, ensuring strong adhesion between VACNTs and PDMS upon full curing of the PDMS. GO ink was then printed on the surface of the VACNT carpet and thermally reduced to reduced graphene oxide (rGO). The sheet resistance of the rGO-VACNT hybrid was measured under uniaxial tensile strains up to 300% applied to the substrate. Under applied strain, the rGO-VACNT hybrid maintained a sheet resistant of 386 ± 55 Ω/sq. Cyclic stretching of the rGO-VACNT hybrid was performed with up to 50 cycles at 100% maximum tensile strain, showing no increase in sheet resistance. These results demonstrate promising performance of the rGO-VACNT hybrid for flexible electronics applications.

Graphene-Vertically Aligned Carbon Nanotube Hybrid on PDMS as Stretchable Electrodes.

PubMed

Ding, Junjun; Fu, Shichen; Zhang, Runzhi; Boon, Eric Peter; Lee, Woo; Fisher, Frank T; Yang, Eui-Hyeok

2017-09-11

Stretchable electrodes are a critical component for flexible electronics such as displays, energy devices, and wearable sensors. Carbon nanotubes (CNTs) and graphene have been considered for flexible electrode applications, due to their mechanical strength, high carrier mobility, and excellent thermal conductivity. Vertically aligned carbon nanotubes (VACNTs) provide the possibility to serve as interconnects to graphene sheets as stretchable electrodes that could maintain high electrical conductivity under large tensile strain. In this work, a graphene oxide (GO) -VACNT hybrid on a PDMS substrate was demonstrated. Here, 50 μm long VACNTs were grown on a Si/SiO2 wafer substrate via atmospheric pressure chemical vapor deposition (APCVD). VACNTs were directly transferred by delamination from the Si/SiO2 to a semi-cured PDMS substrate, ensuring strong adhesion between VACNTs and PDMS upon full curing of the PDMS. GO ink was then printed on the surface of the VACNT carpet and thermally reduced to reduced graphene oxide (rGO). The sheet resistance of the rGO-VACNT hybrid was measured under uniaxial tensile strains up to 300% applied to the substrate. Under applied strain, the rGO-VACNT hybrid maintained a sheet resistant of 386±55 Ω/sq. Cyclic stretching of the rGO-VACNT hybrid was performed with up to 50 cycles at 100% maximum tensile strain, showing no increase in sheet resistance. These results demonstrate promising performance of the rGO-VACNT hybrid for flexible electronics applications. © 2017 IOP Publishing Ltd.

Vertically aligned carbon nanotube-sheathed carbon fibers as pristine microelectrodes for selective monitoring of ascorbate in vivo.

PubMed

Xiang, Ling; Yu, Ping; Hao, Jie; Zhang, Meining; Zhu, Lin; Dai, Liming; Mao, Lanqun

2014-04-15

Using as-synthesized vertically aligned carbon nanotube-sheathed carbon fibers (VACNT-CFs) as microelectrodes without any postsynthesis functionalization, we have developed in this study a new method for in vivo monitoring of ascorbate with high selectivity and reproducibility. The VACNT-CFs are formed via pyrolysis of iron phthalocyanine (FePc) on the carbon fiber support. After electrochemical pretreatment in 1.0 M NaOH solution, the pristine VACNT-CF microelectrodes exhibit typical microelectrode behavior with fast electron transfer kinetics for electrochemical oxidation of ascorbate and are useful for selective ascorbate monitoring even with other electroactive species (e.g., dopamine, uric acid, and 5-hydroxytryptamine) coexisting in rat brain. Pristine VACNT-CFs are further demonstrated to be a reliable and stable microelectrode for in vivo recording of the dynamic increase of ascorbate evoked by intracerebral infusion of glutamate. Use of a pristine VACNT-CF microelectrode can effectively avoid any manual electrode modification and is free from person-to-person and/or electrode-to-electrode deviations intrinsically associated with conventional CF electrode fabrication, which often involves electrode surface modification with randomly distributed CNTs or other pretreatments, and hence allows easy fabrication of highly selective, reproducible, and stable microelectrodes even by nonelectrochemists. Thus, this study offers a new and reliable platform for in vivo monitoring of neurochemicals (e.g., ascorbate) to largely facilitate future studies on the neurochemical processes involved in various physiological events.

Multiple thermal transitions and anisotropic thermal expansions of vertically aligned carbon nanotubes

NASA Astrophysics Data System (ADS)

Ya'akobovitz, Assaf

2016-10-01

Vertically aligned carbon nanotubes (VA-CNTs) hold the potential to play an instrumental role in a wide variety of applications in micro- and nano-devices and composites. However, their successful large-scale implementation in engineering systems requires a thorough understanding of their material properties, including their thermal behavior, which was the focus of the current study. Thus, the thermal expansion of as-grown VA-CNT microstructures was investigated while increasing the temperature from room temperature to 800 °C and then cooling it down. First thermal transition was observed at 191 ± 68 °C during heating, and an additional thermal transition was observed at 523 ± 138 °C during heating and at similar temperatures during cooling. Each thermal transition was characterized by a significant change in the coefficient of thermal expansion (CTE), which can be related to a morphological change in the VA-CNT microstructures. Measurements of the CTEs in the lateral directions revealed differences in the lateral thermal behaviors of the top, middle, and bottom portions of the VA-CNT microstructures, again indicating that their morphology dominates their thermal characteristics. A hysteretic behavior was observed, as the measured values of CTEs were altered due to the applied thermal loads and the height of the microstructures was slightly higher compared to its initial value. These findings provide an insight into the anisotropic thermal behavior of VA-CNT microstructures and shed light on the relationship between their morphology and thermal behavior.

Controlled Synthesis of Ultralong Carbon Nanotubes with Perfect Structures and Extraordinary Properties.

PubMed

Zhang, Rufan; Zhang, Yingying; Wei, Fei

2017-02-21

Carbon nanotubes (CNTs) have drawn intensive research interest in the past 25 years due to their excellent properties and wide applications. Ultralong CNTs refers to the horizontally aligned CNT arrays which are usually grown on flat substrates, parallel with each other with large intertube distances. They usually have perfect structures, excellent properties, and lengths up to centimeters, even decimeters. Ultralong CNTs are promising candidates as building blocks for transparent displays, nanoelectronics, superstrong tethers, aeronautics and aerospace materials, etc. The controlled synthesis of ultralong CNTs with perfect structures is the key to fully exploit the extraordinary properties of CNTs. CNTs are typical one-dimensional single-crystal nanomaterials. It has always been a great challenge how to grow macroscale single-crystals with no defects. Thus, the synthesis of ultralong CNTs with no defect is of significant importance from both fundamental and industrial aspects. In this Account, we focus on our progress on the controlled synthesis of ultralong CNTs with perfect structures and excellent properties. A deep understanding of the CNT growth mechanism is the first step for the controlled synthesis of ultralong CNTs with high quality. We first introduce the growth mechanism for ultralong CNTs and the main factor affecting their structures. We then discuss the strategies to control the defects in the as-grown ultralong CNTs. With these approaches, ultralong high-quality CNTs with different structures can be obtained. By completely eliminating the factors which may induce defects in the CNT walls, ultralong CNTs with perfect structures can be obtained. Their chiral indices keep unchanged for several centimeters long along the axial direction of the CNTs. The defect-free structures render the ultralong CNTs with excellent electrical, mechanical and thermal properties. The as-grown ultralong CNTs exhibit superhigh mechanical strength (>100 GPa) and their breaking strain (>17.5%) reach the theoretical limits. They also show excellent electrical and thermal properties. In addition, centimeters long CNTs showed macroscale interwall superlubricious properties due to their defect-free structures. Ultralong, defect-free CNTs with controlled structures are highly desirable for many high-end applications. We hope that this Account will shed light on the controlled synthesis of ultralong CNTs with perfect structures and excellent properties. Moreover, the growth mechanism and controlled synthesis of ultralong CNTs with perfect structures also offers a good model for other one-dimensional nanomaterials.

Magnetic field effect on Poiseuille flow and heat transfer of carbon nanotubes along a vertical channel filled with Casson fluid

NASA Astrophysics Data System (ADS)

Aman, Sidra; Khan, Ilyas; Ismail, Zulkhibri; Salleh, Mohd Zuki; Alshomrani, Ali Saleh; Alghamdi, Metib Said

2017-01-01

Applications of carbon nanotubes, single walls carbon nanotubes (SWCNTs) and multiple walls carbon nanotubes (MWCNTs) in thermal engineering have recently attracted significant attention. However, most of the studies on CNTs are either experimental or numerical and the lack of analytical studies limits further developments in CNTs research particularly in channel flows. In this work, an analytical investigation is performed on heat transfer analysis of SWCNTs and MWCNTs for mixed convection Poiseuille flow of a Casson fluid along a vertical channel. These CNTs are suspended in three different types of base fluids (Water, Kerosene and engine Oil). Xue [Phys. B Condens. Matter 368, 302-307 (2005)] model has been used for effective thermal conductivity of CNTs. A uniform magnetic field is applied in a transverse direction to the flow as magnetic field induces enhancement in the thermal conductivity of nanofluid. The problem is modelled by using the constitutive equations of Casson fluid in order to characterize the non-Newtonian fluid behavior. Using appropriate non-dimensional variables, the governing equations are transformed into the non-dimensional form, and the perturbation method is utilized to solve the governing equations with some physical conditions. Velocity and temperature solutions are obtained and discussed graphically. Expressions for skin friction and Nusselt number are also evaluated in tabular form. Effects of different parameters such as Casson parameter, radiation parameter and volume fraction are observed on the velocity and temperature profiles. It is found that velocity is reduced under influence of the exterior magnetic field. The temperature of single wall CNTs is found greater than MWCNTs for all the three base fluids. Increase in volume fraction leads to a decrease in velocity of the fluid as the nanofluid become more viscous by adding CNTs.

Handspinning Enabled Highly Concentrated Carbon Nanotubes with Controlled Orientation in Nanofibers

PubMed Central

Lee, Hoik; Watanabe, Kei; Kim, Myungwoong; Gopiraman, Mayakrishnan; Song, Kyung-Hun; Lee, Jung Soon; Kim, Ick Soo

2016-01-01

The novel method, handspinning (HS), was invented by mimicking commonly observed methods in our daily lives. The use of HS allows us to fabricate carbon nanotube-reinforced nanofibers (CNT-reinforced nanofibers) by addressing three significant challenges: (i) the difficulty of forming nanofibers at high concentrations of CNTs, (ii) aggregation of the CNTs, and (iii) control of the orientation of the CNTs. The handspun nanofibers showed better physical properties than fibers fabricated by conventional methods, such as electrospinning. Handspun nanofibers retain a larger amount of CNTs than electrospun nanofibers, and the CNTs are easily aligned uniaxially. We attributed these improvements provided by the HS process to simple mechanical stretching force, which allows for orienting the nanofillers along with the force direction without agglomeration, leading to increased contact area between the CNTs and the polymer matrix, thereby providing enhanced interactions. HS is a simple and straightforward method as it does not require an electric field, and, hence, any kinds of polymers and solvents can be applicable. Furthermore, it is feasible to retain a large amount of various nanofillers in the fibers to enhance their physical and chemical properties. Therefore, HS provides an effective pathway to create new types of reinforced nanofibers with outstanding properties. PMID:27876892

Outstanding adsorption performance of high aspect ratio and super-hydrophobic carbon nanotubes for oil removal.

PubMed

Kayvani Fard, Ahmad; Mckay, Gordon; Manawi, Yehia; Malaibari, Zuhair; Hussien, Muataz A

2016-12-01

Oil removal from water is a highly important area due to the large production rate of emulsified oil in water, which is considered one of the major pollutants, having a negative effect on human health, environment and wildlife. In this study, we have reported the application of high quality carbon nanotube bundles produced by an injected vertical chemical vapor deposition (IV-CVD) reactor for oil removal. High quality, bundles, super hydrophobic, and high aspect ratio carbon nanotubes were produced. The average diameters of the produced CNTs ranged from 20 to 50 nm while their lengths ranged from 300 to 500 μm. Two types of CNTs namely, P-CNTs and C-CNTs, (Produced CNTs from the IV-CVD reactor and commercial CNTs) were used for oil removal from water. For the first time, thermogravimetric analysis (TGA) was conducted to measure maximum oil uptake using CNT and it was found that P-CNT can take oil up to 17 times their weight. The effect of adsorbent dosage, contact time, and agitation speed were examined on the oil spill clean-up efficiency using batch sorption experiments. Higher efficiency with almost 97% removal was achieved using P-CNTs compared to 87% removal using C-CNTs. Copyright © 2016 Elsevier Ltd. All rights reserved.

Understanding carbon nanotube channel formation in the lipid membrane

NASA Astrophysics Data System (ADS)

Choi, Moon-ki; Kim, Hyunki; Lee, Byung Ho; Kim, Teayeop; Rho, Junsuk; Kim, Moon Ki; Kim, Kyunghoon

2018-03-01

Carbon nanotubes (CNTs) have been considered a prominent nano-channel in cell membranes because of their prominent ion-conductance and ion-selectivity, offering agents for a biomimetic channel platform. Using a coarse-grained molecular dynamics simulation, we clarify a construction mechanism of vertical CNT nano-channels in a lipid membrane for a long period, which has been difficult to observe in previous CNT-lipid interaction simulations. The result shows that both the lipid coating density and length of CNT affect the suitable fabrication condition for a vertical and stable CNT channel. Also, simulation elucidated that a lipid coating on the surface of the CNT prevents the CNT from burrowing into the lipid membrane and the vertical channel is stabilized by the repulsion force between the lipids in the coating and membrane. Our study provides an essential understanding of how CNTs can form stable and vertical channels in the membrane, which is important for designing new types of artificial channels as biosensors for bio-fluidic studies.

Using Carbon Nanotubes for Nanometer-Scale Energy Transfer Microscopy

NASA Astrophysics Data System (ADS)

Johnston, Jessica; Shafran, Eyal; Mangum, Ben; Mu, Chun; Gerton, Jordan

2009-10-01

We investigate optical energy transfer between fluorophores and carbon nanotubes (CNTs). CNTs are grown on Si-oxide wafers by chemical vapor deposition (CVD), lifted off substrates by atomic force microscope (AFM) tips via Van der Waals forces, then shortened by electrical pulses. The tip-attached CNTs are scanned over fluorescent CdSe-ZnS quantum dots (QDs) with sub-nm precision while recording the fluorescence rate. A novel photon counting technique enables us to produce 3D maps of the QD-CNT coupling, revealing nanoscale lateral and vertical features. All CNTs tested (>50) strongly quenched the QD fluorescence, apparently independent of chirality. In some data, a delay in the recovery of QD fluorescence following CNT-QD contact was observed, suggesting possible charge transfer in this system. In the future, we will perform time-resolved studies to quantify the rate of energy and charge transfer processes and study the possible differences in fluorescence quenching and nanotube-QD energy transfer when comparing single-walled (SW) versus multi-walled (MW) CNTs, attempting to grow substrates consisting primarily of SW or MWCNTs and characterizing the structure of tip-attached CNTs using optical spectroscopy.

Structure and magnetic fabric of the Quetico metasedimentary rocks in the Calm Lake - Perch Lake area, near Atikokan, Northwestern Ontario

NASA Astrophysics Data System (ADS)

Sarvas, Perry

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Fire disturbance mapping in a northern boreal forest using AVHRR/NDVI imagery: Comparing techniques of change detection and substrate correction

NASA Astrophysics Data System (ADS)

Remmel, Tarmo Kaarel

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Aligned coaxial tungsten oxide-carbon nanotube sheet: a flexible and gradient electrochromic film.

PubMed

Yao, Zhaojun; Di, Jiangtao; Yong, Zhenzhong; Zhao, Zhigang; Li, Qingwen

2012-08-25

We develop a simple dry wrapping method to fabricate a tungsten oxide (WO(3))/carbon nanotube (CNT) cable, in which WO(3) layers act as an electrochromic component while aligned CNTs as the core provide mechanical support and an anisotropic, continuous electron transport pathway. Interestingly, the resultant cable material exhibits an obvious gradient electrochromic phenomenon.

Theory of Carbon Nanotube (CNT)-Based Electron Field Emitters

PubMed Central

Bocharov, Grigory S.; Eletskii, Alexander V.

2013-01-01

Theoretical problems arising in connection with development and operation of electron field emitters on the basis of carbon nanotubes are reviewed. The physical aspects of electron field emission that underlie the unique emission properties of carbon nanotubes (CNTs) are considered. Physical effects and phenomena affecting the emission characteristics of CNT cathodes are analyzed. Effects given particular attention include: the electric field amplification near a CNT tip with taking into account the shape of the tip, the deviation from the vertical orientation of nanotubes and electrical field-induced alignment of those; electric field screening by neighboring nanotubes; statistical spread of the parameters of the individual CNTs comprising the cathode; the thermal effects resulting in degradation of nanotubes during emission. Simultaneous consideration of the above-listed effects permitted the development of the optimization procedure for CNT array in terms of the maximum reachable emission current density. In accordance with this procedure, the optimum inter-tube distance in the array depends on the region of the external voltage applied. The phenomenon of self-misalignment of nanotubes in an array has been predicted and analyzed in terms of the recent experiments performed. A mechanism of degradation of CNT-based electron field emitters has been analyzed consisting of the bombardment of the emitters by ions formed as a result of electron impact ionization of the residual gas molecules. PMID:28348342

Use of Nanocomposites for Flexible Pressure Sensors =

NASA Astrophysics Data System (ADS)

Sepulveda, Alexandra Conceicao Teixeira

Polymer nanocomposites (PNCs) are defined as polymers bonded with nanoparticles to create materiais with improved properties. The development of this type of material is rapidly emerging as a multidisciplinary research activity, since their final properties can benefit many different fields of application, namely in the development of electrical devices as studied herein. A fabrication technique to produce conductive PNCs was developed in this work and used to fabricate flexible capacitive pressure sensors. The process is based on vertically aligned-carbon nanotubes (A-CNTs) embedded in a flexible and biocompatible matrix of polydimethylsiloxane (PDMS). Thin A-CNTs/PDMS nanocomposite films ( 400 mum) were produced using wetting of as-grown A-CNTs with uncured PDMS and the resulting nanocomposites were used to fabricate flexible pressure sensors. The sensing capability of this A-CNTs/PDMS nanocomposite is attributed to the distinctive combination of mechanical flexibility and electrical properties. The fabricated nanocomposites were characterized and mechanical and electrical properties evaluated. The PDMS is significantly modified by the reinforcing A-CNT fibers, demonstrating non-isotropic (as opposed to the isotropic neat PDMS) elastic properties ali different than the PDMS (Young's modulus of 0.8 MPa), including an anisotropy ratio of 4.8 and increases in the modulus of A-CNTs/PDMS nanocomposites over PDMS by more than 900 % and 100 %, in the CNTs longitudinal and transverse directions, respectively. Regarding the electrical measurements, A-CNTs/PDMS nanocomposites presented an electrical conductivity of 0.35 Sim. The rather low conductivity does not compromise the developed capacitive sensor, but since passive telemetry is required to measure and power the sensor, solutions to overcome this problem were also studied. The configuration of the developed flexible sensor is similar to typical silicon-based capacitive pressure sensors. It is composed of three thin films, where two of them are A-CNTs/PDMS nanocomposites (defining the diaphragm type electrodes) separated by a film made of neat PDMS (defining the dielectric) and its operating principie is based on the change of the deflection of the nanocomposite layers due to the change of an external pressure. The developed flexible pressure sensors tested for pressures between 0 kPa and 100 kPa (operation required to measure the blood pressure in the aneurysm sac) showed good linearity, mainly in the region near to the atmospheric pressure (pressure inside of dielectric ). To demonstrate feasibility for practical applications, the flexible sensor technology was used in a biomedical application, more specifically in the context of abdominal aortic aneurysms. The proposed implantable flexible pressure sensing system (capacitive sensor plus inductor) consists of a mixed technology that uses A-CNTs/nanocomposites to build the capacitar electrodes and flexible printed circuit board (PCB) technology to build an inductor. The complete system was assessed by applying pressures varying from 0 kPa to 100 kPa. The results showed that the flexible sensors responded to pressure variations with a well-defined characteristic curve and oscillation frequencies centered around 5.3 MHz (the sensor receives energy and reflects back its oscillation frequency by means of inductive coupling). Finally, the developed technology to fabricate flexible pressure sensors based on A-CNTs/PDMS nanocomposites proved successful in sensing applications and due to its biocompatibility and versatility, can be used in other fields of application such as portable medical devices and e-textiles (to monitor the vital signs of an individual, such as heart rate and temperature, by using textile substrates with integrated electronics). (Abstract shortened by ProQuest.).

Corrugated paraffin nanocomposite films as large stroke thermal actuators and self-activating thermal interfaces.

PubMed

Copic, Davor; Hart, A John

2015-04-22

High performance active materials are of rapidly growing interest for applications including soft robotics, microfluidic systems, and morphing composites. In particular, paraffin wax has been used to actuate miniature pumps, solenoid valves, and composite fibers, yet its deployment is typically limited by the need for external volume constraint. We demonstrate that compact, high-performance paraffin actuators can be made by confining paraffin within vertically aligned carbon nanotube (CNT) films. This large-stroke vertical actuation is enabled by strong capillary interaction between paraffin and CNTs and by engineering the CNT morphology by mechanical compression before capillary-driven infiltration of the molten paraffin. The maximum actuation strain of the corrugated CNT-paraffin films (∼0.02-0.2) is comparable to natural muscle, yet the maximum stress is limited to ∼10 kPa by collapse of the CNT network. We also show how a CNT-paraffin film can serve as a self-activating thermal interface that closes a gap when it is heated. These new CNT-paraffin film actuators could be produced by large-area CNT growth, infiltration, and lamination methods, and are attractive for use in miniature systems due to their self-contained design.

Postgrowth Microwave Treatment to Align Carbon Nanotubes

DTIC Science & Technology

2013-03-01

interface material, microwave processing , metal substrate, alignment, contact area, thermal chemical vapor deposition Introduction Since their discovery, CNTs...short forests. The entangled “canopy” of a CNT forest can be removed with additional processing after growth, e.g., plasma etching, to create more...strates for CNT growth at increased manufacturing scale [34]. Studies have shown that CNT forests grown on both sides of metal foils can produce thermal

Dramatic improvement in water retention and proton conductivity in electrically aligned functionalized CNT/SPEEK nanohybrid PEM.

PubMed

Gahlot, Swati; Kulshrestha, Vaibhav

2015-01-14

Nanohybrid membranes of electrically aligned functionalized carbon nanotube f CNT with sulfonated poly ether ether ketone (SPEEK) have been successfully prepared by solution casting. Functionalization of CNTs was done through a carboxylation and sulfonation route. Further, a constant electric field (500 V·cm(-2)) has been applied to align CNTs in the same direction during the membrane drying process. All the membranes are characterized chemically, thermally, and mechanically by the means of FTIR, DSC, DMA, UTM, SEM, TEM, and AFM techniques. Intermolecular interactions between the components in hybrid membranes are established by FTIR. Physicochemical measurements were done to analyze membrane stability. Membranes are evaluated for proton conductivity (30-90 °C) and methanol crossover resistance to reveal their potential for direct methanol fuel cell application. Incorporation of f CNT reasonably increases the ion-exchange capacity, water retention, and proton conductivity while it reduces the methanol permeability. The maximum proton conductivity has been found in the S-sCNT-5 nanohybrid PEM with higher methanol crossover resistance. The prepared membranes can be also used for electrode material for fuel cells and batteries.

Carbon nanotubes grown on metal microelectrodes for the detection of dopamine

DOE PAGES

Yang, Cheng; Jacobs, Christopher B.; Nguyen, Michael; ...

2015-12-07

Microelectrodes modified with carbon nanotubes (CNTs) are useful for the detection of neurotransmitters because the CNTs enhance sensitivity and have electrocatalytic effects. CNTs can be grown on carbon fiber microelectrodes (CFMEs) but the intrinsic electrochemical activity of carbon fibers makes evaluating the effect of CNT enhancement difficult. Metal wires are highly conductive and many metals have no intrinsic electrochemical activity for dopamine, so we investigated CNTs grown on metal wires as microelectrodes for neurotransmitter detection. In this work, we successfully grew CNTs on niobium substrates for the first time. Instead of planar metal surfaces, metal wires with a diameter ofmore » only 25 μm were used as CNT substrates; these have potential in tissue applications due to their minimal tissue damage and high spatial resolution. Scanning electron microscopy shows that aligned CNTs are grown on metal wires after chemical vapor deposition. By use of fast-scan cyclic voltammetry, CNT-coated niobium (CNT-Nb) microelectrodes exhibit higher sensitivity and lower ΔE p value compared to CNTs grown on carbon fibers or other metal wires. The limit of detection for dopamine at CNT-Nb microelectrodes is 11 ± 1 nM, which is approximately 2-fold lower than that of bare CFMEs. Adsorption processes were modeled with a Langmuir isotherm, and detection of other neurochemicals was also characterized, including ascorbic acid, 3,4-dihydroxyphenylacetic acid, serotonin, adenosine, and histamine. CNT-Nb microelectrodes were used to monitor stimulated dopamine release in anesthetized rats with high sensitivity. This research demonstrates that CNT-grown metal microelectrodes, especially CNTs grown on Nb microelectrodes, are useful for monitoring neurotransmitters.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Cheng; Jacobs, Christopher B.; Nguyen, Michael

Microelectrodes modified with carbon nanotubes (CNTs) are useful for the detection of neurotransmitters because the CNTs enhance sensitivity and have electrocatalytic effects. CNTs can be grown on carbon fiber microelectrodes (CFMEs) but the intrinsic electrochemical activity of carbon fibers makes evaluating the effect of CNT enhancement difficult. Metal wires are highly conductive and many metals have no intrinsic electrochemical activity for dopamine, so we investigated CNTs grown on metal wires as microelectrodes for neurotransmitter detection. In this work, we successfully grew CNTs on niobium substrates for the first time. Instead of planar metal surfaces, metal wires with a diameter ofmore » only 25 μm were used as CNT substrates; these have potential in tissue applications due to their minimal tissue damage and high spatial resolution. Scanning electron microscopy shows that aligned CNTs are grown on metal wires after chemical vapor deposition. By use of fast-scan cyclic voltammetry, CNT-coated niobium (CNT-Nb) microelectrodes exhibit higher sensitivity and lower ΔE p value compared to CNTs grown on carbon fibers or other metal wires. The limit of detection for dopamine at CNT-Nb microelectrodes is 11 ± 1 nM, which is approximately 2-fold lower than that of bare CFMEs. Adsorption processes were modeled with a Langmuir isotherm, and detection of other neurochemicals was also characterized, including ascorbic acid, 3,4-dihydroxyphenylacetic acid, serotonin, adenosine, and histamine. CNT-Nb microelectrodes were used to monitor stimulated dopamine release in anesthetized rats with high sensitivity. This research demonstrates that CNT-grown metal microelectrodes, especially CNTs grown on Nb microelectrodes, are useful for monitoring neurotransmitters.« less

Growth behavior of carbon nanotubes on multilayered metal catalyst film (Al/Fe/Mo) in chemical vapor deposition

NASA Astrophysics Data System (ADS)

Cui, H.; Eres, G.; Howe, J. Y.; Puretzky, A.; Varela, M.; Geohegan, D. B.; Lowndes, D. H.

2003-03-01

The temperature- and time- dependences of carbon nanotube (CNT) growth by chemical vapor deposition are studied using a multilayered Al/Fe/Mo catalyst on silicon substrates. Within the 600 - 1100 ^oC temperature range in these studies, narrower temperature ranges were determined for the growth of aligned multi-walled carbon nanotubes (MWCNTs) and single-walled carbon nanotubes (SWCNTs). Aligned MWCNT growth is favored at lower temperatures ( ˜700 ^oC). At 900 ^oC, in contrast to earlier work, double-walled carbon nanotubes (DWCNTs) are found more abundant than SWCNTs. At further elevated temperature, highly defective carbon structures are produced. Defects also are found to accumulate faster than the ordered graphitic structure if the growth of CNTs is extended to long growth durations. Atomic force microscopy, field emission scanning electron microscopy, high resolution transmission electron microscopy, and Raman spectroscopy are used to characterize the catalyst and various types of CNTs.

Tuning carbon nanotube assembly for flexible, strong and conductive films.

PubMed

Wang, Yanjie; Li, Min; Gu, Yizhuo; Zhang, Xiaohua; Wang, Shaokai; Li, Qingwen; Zhang, Zuoguang

2015-02-21

Carbon nanotubes are ideal scaffolds for designing and architecting flexible graphite films with tunable mechanical, electrical and thermal properties. Herein, we demonstrate that the assembly of aligned carbon nanotubes with different aggregation density and morphology leads to different mechanical properties and anisotropic electrical conduction along the films. Using drying evaporation under tension treatment, the carbon nanotubes can be assembled into strong films with tensile strength and Young's modulus as high as 3.2 GPa and 124 GPa, respectively, leading to a remarkable toughness of 54.38 J g(-1), greatly outperforming conventional graphite films, spider webs and even Kevlar fiber films. Different types of solvents may result in the assembly of CNTs with different aggregation morphology and therefore different modulus. In addition, we reveal that the high density assembly of aligned CNTs correlates with better electric conduction along the axial direction, enabling these flexible graphite films to be both strong and conductive.

Aspects of the Fracture Toughness of Carbon Nanotube Modified Epoxy Polymer Composites

NASA Astrophysics Data System (ADS)

Mirjalili, Vahid

Epoxy resins used in fibre reinforced composites exhibit a brittle fracture behaviour, because they show no sign of damage prior to a catastrophic failure. Rubbery materials and micro-particles have been added to epoxy resins to improve their fracture toughness, which reduces strength and elastic properties. In this research, carbon nanotubes (CNTs) are investigated as a potential toughening agent for epoxy resins and carbon fibre reinforced composites, which can also enhance strength and elastic properties. More specifically, the toughening mechanisms of CNTs are investigated theoretically and experimentally. The effect of aligned and randomly oriented carbon nanotubes (CNTs) on the fracture toughness of polymers was modelled using Elastic Plastic Fracture Mechanics. Toughening from CNT pull-out and rupture were considered, depending on the CNTs critical length. The model was used to identify the effect of CNTs geometrical and mechanical properties on the fracture toughness of CNT-modified epoxies. The modelling results showed that a uniform dispersion and alignment of a high volume fraction of CNTs normal to the crack growth plane would lead to the maximum fracture toughness enhancement. To achieve a uniform dispersion, the effect of processing on the dispersion of single walled and multi walled CNTs in epoxy resins was investigated. An instrumented optical microscope with a hot stage was used to quantify the evolution of the CNT dispersion during cure. The results showed that the reduction of the resin viscosity at temperatures greater than 100 °C caused an irreversible re-agglomeration of the CNTs in the matrix. The dispersion quality was then directly correlated to the fracture toughness of the modified resin. It was shown that the fine tuning of the ratio of epoxy resin, curing agent and CNT content was paramount to the improvement of the base resin fracture toughness. For the epoxy resin (MY0510 from Hexcel), an improvement of 38% was achieved with 0.3 wt.% of Single Walled CNT (SWNT). Finally, the CNT-modified epoxy resin was used to manufacture carbon fibre laminates by resin film infusion and prepreg technologies. The Mode I and Mode II delamination properties of the CNT-modified composite increased by 140% and 127%, respectively. In contrast, this improvement was not observed for the base CNT-modified polymers, used to manufacture the composite laminates. A qualitative analysis of the fractured surface using a Scanning Electron Microscope revealed a good dispersion in the composites samples, confirming the importance of processing to harness the full potential of carbon nanotubes for toughening polymer composites.

Tough and flexible CNT-polymeric hybrid scaffolds for engineering cardiac constructs.

PubMed

Kharaziha, Mahshid; Shin, Su Ryon; Nikkhah, Mehdi; Topkaya, Seda Nur; Masoumi, Nafiseh; Annabi, Nasim; Dokmeci, Mehmet R; Khademhosseini, Ali

2014-08-01

In the past few years, a considerable amount of effort has been devoted toward the development of biomimetic scaffolds for cardiac tissue engineering. However, most of the previous scaffolds have been electrically insulating or lacked the structural and mechanical robustness to engineer cardiac tissue constructs with suitable electrophysiological functions. Here, we developed tough and flexible hybrid scaffolds with enhanced electrical properties composed of carbon nanotubes (CNTs) embedded aligned poly(glycerol sebacate):gelatin (PG) electrospun nanofibers. Incorporation of varying concentrations of CNTs from 0 to 1.5% within the PG nanofibrous scaffolds (CNT-PG scaffolds) notably enhanced fiber alignment and improved the electrical conductivity and toughness of the scaffolds while maintaining the viability, retention, alignment, and contractile activities of cardiomyocytes (CMs) seeded on the scaffolds. The resulting CNT-PG scaffolds resulted in stronger spontaneous and synchronous beating behavior (3.5-fold lower excitation threshold and 2.8-fold higher maximum capture rate) compared to those cultured on PG scaffold. Overall, our findings demonstrated that aligned CNT-PG scaffold exhibited superior mechanical properties with enhanced CM beating properties. It is envisioned that the proposed hybrid scaffolds can be useful for generating cardiac tissue constructs with improved organization and maturation. Copyright © 2014 Elsevier Ltd. All rights reserved.

Perspectives on the Growth of High Edge Density Carbon Nanostructures: Transitions from Vertically Oriented Graphene Nanosheets to Graphenated Carbon Nanotubes

PubMed Central

2015-01-01

Insights into the growth of high edge density carbon nanostructures were achieved by a systematic parametric study of plasma-enhanced chemical vapor deposition (PECVD). Such structures are important for electrode performance in a variety of applications such as supercapacitors, neural stimulation, and electrocatalysis. A morphological trend was observed as a function of temperature whereby graphenated carbon nanotubes (g-CNTs) emerged as an intermediate structure between carbon nanotubes (CNTs) at lower temperatures and vertically oriented carbon nanosheets (CNS), composed of few-layered graphene, at higher temperatures. This is the first time that three distinct morphologies and dimensionalities of carbon nanostructures (i.e., 1D CNTs, 2D CNSs, and 3D g-CNTs) have been synthesized in the same reaction chamber by varying only a single parameter (temperature). A design of experiments (DOE) approach was utilized to understand the range of growth permitted in a microwave PECVD reactor, with a focus on identifying graphenated carbon nanotube growth within the process space. Factors studied in the experimental design included temperature, gas ratio, catalyst thickness, pretreatment time, and deposition time. This procedure facilitates predicting and modeling high edge density carbon nanostructure characteristics under a complete range of growth conditions that yields various morphologies of nanoscale carbon. Aside from the morphological trends influenced by temperature, a relationship between deposition temperature and specific capacitance emerged from the DOE study. Transmission electron microscopy was also used to understand the morphology and microstructure of the various high edge density structures. From these results, a new graphene foliate formation mechanism is proposed for synthesis of g-CNTs in a single deposition process. PMID:25089165

Vertically aligned nanostructure scanning probe microscope tips

DOEpatents

Guillorn, Michael A.; Ilic, Bojan; Melechko, Anatoli V.; Merkulov, Vladimir I.; Lowndes, Douglas H.; Simpson, Michael L.

2006-12-19

Methods and apparatus are described for cantilever structures that include a vertically aligned nanostructure, especially vertically aligned carbon nanofiber scanning probe microscope tips. An apparatus includes a cantilever structure including a substrate including a cantilever body, that optionally includes a doped layer, and a vertically aligned nanostructure coupled to the cantilever body.

The Highly Robust Electrical Interconnects and Ultrasensitive Biosensors Based on Embedded Carbon Nanotube Arrays

NASA Technical Reports Server (NTRS)

Li, Jun; Cassell, Alan; Koehne, Jessica; Chen, Hua; Ng, Hou Tee; Ye, Qi; Stevens, Ramsey; Han, Jie; Meyyappan, M.

2003-01-01

We report on our recent breakthroughs in two different applications using well-aligned carbon nanotube (CNT) arrays on Si chips, including (1) a novel processing solution for highly robust electrical interconnects in integrated circuit manufacturing, and (2) the development of ultrasensitive electrochemical DNA sensors. Both of them rely on the invention of a bottom-up fabrication scheme which includes six steps, including: (a) lithographic patterning, (b) depositing bottom conducting contacts, (c) depositing metal catalysts, (d) CNT growth by plasma enhanced chemical vapor deposition (PECVD), (e) dielectric gap-filling, and (f) chemical mechanical polishing (CMP). Such processes produce a stable planarized surface with only the open end of CNTs exposed, whch can be further processed or modified for different applications. By depositing patterned top contacts, the CNT can serve as vertical interconnects between the two conducting layers. This method is fundamentally different fiom current damascene processes and avoids problems associated with etching and filling of high aspect ratio holes at nanoscales. In addition, multiwalled CNTs (MWCNTs) are highly robust and can carry a current density of 10(exp 9) A/square centimeters without degradation. It has great potential to help extending the current Si technology. The embedded MWCNT array without the top contact layer can be also used as a nanoelectrode array in electrochemical biosensors. The cell time-constant and sensitivity can be dramatically improved. By functionalizing the tube ends with specific oligonucleotide probes, specific DNA targets can be detected with electrochemical methods down to subattomoles.

NO2 sensing at room temperature using vertically aligned MoS2 flakes network

NASA Astrophysics Data System (ADS)

Kumar, Rahul; Goel, Neeraj; Kumar, Mahesh

2018-04-01

To exploit the role of alignment of MoS2 flake in chemical sensing, here, we have synthesized the horizontally and vertically aligned MoS2 flake network using conventional chemical vapor deposition technique. The morphology and number of layers were confirmed by SEM and Raman spectroscopy, respectively. The sensing performance of horizontally aligned and vertically aligned flake network was investigated to NO2 at room temperature. Vertically aligned MoS2 based sensor showed higher sensitivity 51.54 % and 63.2 % compared to horizontally aligned MoS2 sensor' sensitivity of 35.32 % and 45.2 % to 50 ppm and 100 ppm NO2, respectively. This high sensitivity attributed to the high aspect ratio and high adsorption energy on the edge site of vertically aligned MoS2.

Carbon nanotubes based methanol sensor for fuel cells application.

PubMed

Kim, D W; Lee, J S; Lee, G S; Overzet, L; Kozlov, M; Aliev, A E; Park, Y W; Yang, D J

2006-11-01

An electrochemical sensor is built using vertically grown multi-walled carbon nanotubes (MWNTs) micro-array to detect methanol concentration in water. This study is done for the potential use of the array as methanol sensor for portable units of direct methanol fuel cells (DMFCs). Platinum (Pt) nanoparticles electro-deposited CNTs (Pt/CNTs) electrode shows high sensitivity in the measurement of methanol concentration in water with cyclic voltammetry (CV) measurement at room temperature. Further investigation has also been undertaken to measure the concentration by changing the amount of the mixture of methanol and formic acid in water. We compared the performance of our micro array sensor built with Pt/CNTs electrodes versus that of Pt wire electrode using CV measurement. We found that our Pt/CNTs array sensor shows high sensitivity and detects methanol concentrations in the range of 0.04 M to 0.10 M. In addition, we found that co-use of formic acid as electrolyte enables us to measure up to 1.0 M methanol concentration.

Highly Enhanced Gas Adsorption Properties in Vertically Aligned MoS2 Layers.

PubMed

Cho, Soo-Yeon; Kim, Seon Joon; Lee, Youhan; Kim, Jong-Seon; Jung, Woo-Bin; Yoo, Hae-Wook; Kim, Jihan; Jung, Hee-Tae

2015-09-22

In this work, we demonstrate that gas adsorption is significantly higher in edge sites of vertically aligned MoS2 compared to that of the conventional basal plane exposed MoS2 films. To compare the effect of the alignment of MoS2 on the gas adsorption properties, we synthesized three distinct MoS2 films with different alignment directions ((1) horizontally aligned MoS2 (basal plane exposed), (2) mixture of horizontally aligned MoS2 and vertically aligned layers (basal and edge exposed), and (3) vertically aligned MoS2 (edge exposed)) by using rapid sulfurization method of CVD process. Vertically aligned MoS2 film shows about 5-fold enhanced sensitivity to NO2 gas molecules compared to horizontally aligned MoS2 film. Vertically aligned MoS2 has superior resistance variation compared to horizontally aligned MoS2 even with same surface area exposed to identical concentration of gas molecules. We found that electrical response to target gas molecules correlates directly with the density of the exposed edge sites of MoS2 due to high adsorption of gas molecules onto edge sites of vertically aligned MoS2. Density functional theory (DFT) calculations corroborate the experimental results as stronger NO2 binding energies are computed for multiple configurations near the edge sites of MoS2, which verifies that electrical response to target gas molecules (NO2) correlates directly with the density of the exposed edge sites of MoS2 due to high adsorption of gas molecules onto edge sites of vertically aligned MoS2. We believe that this observation extends to other 2D TMD materials as well as MoS2 and can be applied to significantly enhance the gas sensor performance in these materials.

Teslaphoresis of Carbon Nanotubes.

PubMed

Bornhoeft, Lindsey R; Castillo, Aida C; Smalley, Preston R; Kittrell, Carter; James, Dustin K; Brinson, Bruce E; Rybolt, Thomas R; Johnson, Bruce R; Cherukuri, Tonya K; Cherukuri, Paul

2016-04-26

This paper introduces Teslaphoresis, the directed motion and self-assembly of matter by a Tesla coil, and studies this electrokinetic phenomenon using single-walled carbon nanotubes (CNTs). Conventional directed self-assembly of matter using electric fields has been restricted to small scale structures, but with Teslaphoresis, we exceed this limitation by using the Tesla coil's antenna to create a gradient high-voltage force field that projects into free space. CNTs placed within the Teslaphoretic (TEP) field polarize and self-assemble into wires that span from the nanoscale to the macroscale, the longest thus far being 15 cm. We show that the TEP field not only directs the self-assembly of long nanotube wires at remote distances (>30 cm) but can also wirelessly power nanotube-based LED circuits. Furthermore, individualized CNTs self-organize to form long parallel arrays with high fidelity alignment to the TEP field. Thus, Teslaphoresis is effective for directed self-assembly from the bottom-up to the macroscale.

Inter-allotropic transformations in the heterogeneous carbon nanotube networks.

PubMed

Jung, Hyun Young; Jung, Sung Mi; Kim, Dong Won; Jung, Yung Joon

2017-01-19

The allotropic transformations of carbon provide an immense technological interest for tailoring the desired molecular structures in the scalable nanoelectronic devices. Herein, we explore the effects of morphology and geometric alignment of the nanotubes for the re-engineering of carbon bonds in the heterogeneous carbon nanotube (CNT) networks. By applying alternating voltage pulses and electrical forces, the single-walled CNTs in networks were predominantly transformed into other predetermined sp 2 carbon structures (multi-walled CNTs and multi-layered graphitic nanoribbons), showing a larger intensity in a coalescence-induced mode of Raman spectra with the increasing channel width. Moreover, the transformed networks have a newly discovered sp 2 -sp 3 hybrid nanostructures in accordance with the alignment. The sp 3 carbon structures at the small channel are controlled, such that they contain up to about 29.4% networks. This study provides a controllable method for specific types of inter-allotropic transformations/hybridizations, which opens up the further possibility for the engineering of nanocarbon allotropes in the robust large-scale network-based devices.

Vertical Carbon Nanotube Device in Nanoporous Templates

NASA Technical Reports Server (NTRS)

Sands, Timothy (Inventor); Fisher, Timothy Scott (Inventor); Bashir, Rashid (Inventor); Maschmann, Matthew Ralph (Inventor)

2014-01-01

A modified porous anodic alumina template (PAA) containing a thin CNT catalyst layer directly embedded into the pore walls. CNT synthesis using the template selectively catalyzes SWNTs and DWNTs from the embedded catalyst layer to the top PAA surface, creating a vertical CNT channel within the pores. Subsequent processing allows for easy contact metallization and adaptable functionalization of the CNTs and template for a myriad of applications.

Study of Charge Transport in Vertically Aligned Nitride Nanowire Based Core Shell P-I-N Junctions

DTIC Science & Technology

2016-07-01

Vertically- Aligned Nitride Nanowire Based Core Shell P-I-N Junctions Distribution Statement A. Approved for public release; distribution is...Study of Charge Transport in Vertically- Aligned Nitride Nanowire Based Core Shell P-I-N Junctions Grant Number: HDTRA1-14-1-0003 Principal...Investigator: Abhishek Motayed University of Maryland DISTRIBUTION A: Public Release Study of Charge Transport in Vertically-Aligned Nitride Nanowire

Electroconductive PET/SWNT Films by Solution Casting

NASA Technical Reports Server (NTRS)

Steinert, Brian W.; Dean, Derrick R.

2008-01-01

The market for electrically conductive polymers is rapidly growing, and an emerging pathway for attaining these materials is via polymer-carbon nanotube (CNT) nanocomposites, because of the superior properties of CNTs. Due to their excellent electrical properties and anisotropic magnetic susceptibility, we expect CNTs could be easily aligned to maximize their effectiveness in imparting electrical conductivity to the polymer matrix. Single-walled carbon nanotubes (SWNT) were dispersed in a polyethylene terephthalate (PET) matrix by solution blending then cast onto a glass substrate to create thin, flexible films. Various SWNT loading concentrations were implemented (0.5, 1.0, and 3.0 wt.%) to study the effect of additive density. The processing method was repeated to produce films in the presence of magnetic fields (3 and 9.4 Tesla). The SWNTs showed a high susceptibility to the magnetic field and were effectively aligned in the PET matrix. The alignment was characterized with Raman spectroscopy. Impedance spectroscopy was utilized to study the electrical behavior of the films. Concentration and dispersion seemed to play very important roles in improving electrical conductivity, while alignment played a secondary and less significant role. The most interesting result proved to be the effect of a magnetic field during processing. It appears that a magnetic field may improve dispersion of unmodified SWNTs, which seems to be more important than alignment. It was concluded that SWNTs offer a good option as conductive, nucleating filler for electroconductive polymer applications, and the utilization of a magnetic field may prove to be a novel method for CNT dispersion that could lead to improved nanocomposite materials.

Pyrolytic Carbon Coatings on Aligned Carbon Nanotube Assemblies and Fabrication of Advanced Carbon Nanotube/Carbon Composites

NASA Astrophysics Data System (ADS)

Faraji, Shaghayegh

Chemical vapor deposition (CVD) is a technique used to create a pyrolytic carbon (PyC) matrix around fibrous preforms in carbon/carbon (C/C) composites. Due to difficulties in producing three-dimensional carbon nanotube (CNT) assemblies, use of nanotubes in CVD fabricated CNT/C composites is limited. This dissertation describes efforts to: 1) Study the microstructure of PyC deposited on CNTs in order to understand the effect of microstructure and morphology of carbon coatings on graphitization behavior of CNT/PyC composites. This understanding helped to suggest a new approach for controlled radial growth of CNTs. 2) Evaluate the properties of CNT/PyC structures as a novel form of CNT assemblies with resilient, anisotropic and tunable properties. PyC was deposited on aligned sheets of nanotubes, drawn from spinnable CNT arras, using CVD of acetylene gas. At longer deposition times, the microstructure of PyC changed from laminar turbostratic carbon to a disordered carbon. For samples with short PyC deposition times (up to 30 minutes), deposited carbon layer rearranged during graphitization treatment and resulted in a crystalline structure where the coating and original tube walls could not be easily differentiated. In contrast, in samples with longer carbon deposition durations, carbon layers close to the surface of the coating remained disordered even after graphitization thermal treatment. Understanding the effect of PyC microstructure transition on graphitization behavior of CNT/PyC composites was used to develop a new method for controlled radial growth of CNTs. Carbon coated aligned CNT sheets were graphitized after each short (20 minutes) carbon deposition cycle. This prevented development of disorder carbon during subsequent PyC deposition cycles. Using cyclic-graphitization method, thick PyC coating layers were successfully graphitized into a crystalline structure that could not be differentiated from the original nanotube walls. This resulted into radial growth of CNTs, from 40 to 100 nm. Infiltration of PyC into stacked layered sheets of aligned CNTs produced resilient foam-like materials that exhibited complete recovery from 90% compressive strain. PyC coated the junctions between nanotubes and also increased their surface roughness. These changes were assumed to be responsible for the resiliency of the, once inelastic, assembly of nanotubes. While nanotubes' alignment resulted in anisotropic properties of the foams, variation in PyC infiltration duration was used to tune the foams' properties. Further investigation into properties of these foams showed promising results for their application as pressure/strain sensor and selective liquid absorbers for oil spill clean ups. Finally, CNT foams were used as novel substrates for growth of secondary nanotube assemblies. In order to achieve that, foams were first coated with alumina buffer layers using atomic layer deposition (ALD) method. New nanotubes were further grown inside the foams by CVD of acetylene over iron nano-particles. Super low density and highly porous structure of the foams allowed for diffusion of catalyst along with growth gasses into their bulk, which resulted in growth of secondary nanotubes throughout the thickness of the foams. The thickness of the alumina buffer layer was shown to influence CNT nucleation density and growth uniformity across the thickness of the foams. Compressive mechanical testing of the foams showed an order of magnitude increase in compression strength after secondary CNT growth.

Confirming the key role of Ar+ ion bombardment in the growth feature of nanostructured carbon materials by PECVD

NASA Astrophysics Data System (ADS)

Liu, Yulin; Lin, Jinghuang; Jia, Henan; Chen, Shulin; Qi, Junlei; Qu, Chaoqun; Cao, Jian; Feng, Jicai; Fei, Weidong

2017-11-01

In order to confirm the key role of Ar+ ion bombardment in the growth feature of nanostructured carbon materials (NCMs), here we report a novel strategy to create different Ar+ ion states in situ in plasma enhanced chemical vapor deposition (PECVD) by separating catalyst film from the substrate. Different bombardment environments on either side of the catalyst film were created simultaneously to achieve multi-layered structural NCMs. Results showed that Ar+ ion bombardment is crucial and complex for the growth of NCMs. Firstly, Ar+ ion bombardment has both positive and negative effects on carbon nanotubes (CNTs). On one hand, Ar+ ions can break up the graphic structure of CNTs and suppress thin CNT nucleation and growth. On the other hand, Ar+ ion bombardment can remove redundant carbon layers on the surface of large catalyst particles which is essential for thick CNTs. As a result, the diameter of the CNTs depends on the Ar+ ion state. As for vertically oriented few-layer graphene (VFG), Ar+ ions are essential and can even convert the CNTs into VFG. Therefore, by combining with the catalyst separation method, specific or multi-layered structural NCMs can be obtained by PECVD only by changing the intensity of Ar+ ion bombardment, and these special NCMs are promising in many fields.

Confirming the key role of Ar+ ion bombardment in the growth feature of nanostructured carbon materials by PECVD.

PubMed

Liu, Yulin; Lin, Jinghuang; Jia, Henan; Chen, Shulin; Qi, Junlei; Qu, Chaoqun; Cao, Jian; Feng, Jicai; Fei, Weidong

2017-11-24

In order to confirm the key role of Ar + ion bombardment in the growth feature of nanostructured carbon materials (NCMs), here we report a novel strategy to create different Ar + ion states in situ in plasma enhanced chemical vapor deposition (PECVD) by separating catalyst film from the substrate. Different bombardment environments on either side of the catalyst film were created simultaneously to achieve multi-layered structural NCMs. Results showed that Ar + ion bombardment is crucial and complex for the growth of NCMs. Firstly, Ar + ion bombardment has both positive and negative effects on carbon nanotubes (CNTs). On one hand, Ar + ions can break up the graphic structure of CNTs and suppress thin CNT nucleation and growth. On the other hand, Ar + ion bombardment can remove redundant carbon layers on the surface of large catalyst particles which is essential for thick CNTs. As a result, the diameter of the CNTs depends on the Ar + ion state. As for vertically oriented few-layer graphene (VFG), Ar + ions are essential and can even convert the CNTs into VFG. Therefore, by combining with the catalyst separation method, specific or multi-layered structural NCMs can be obtained by PECVD only by changing the intensity of Ar + ion bombardment, and these special NCMs are promising in many fields.

Vertically aligned carbon nanopillars with size and spacing control for a transparent field emission display.

PubMed

Lee, Seok Woo; Lee, Chang Hwa; Lee, Jung A; Lee, Seung S

2013-01-18

A top-down fabrication method is presented for vertically aligned carbon nanopillars (CNPs) using photolithography and pyrolysis. The modified backside exposure method of photolithography fabricates vertically aligned polymer (SU-8) nanopillars. The pyrolysis process, which transforms the polymer to amorphous carbon, reliably produces vertically aligned CNPs with widths ranging from 100 to 400 nm. The CNPs can be used as a transparent field emission cathode for a transparent display and light emission is observed.

High yield growth of patterned vertically aligned carbon nanotubes using inkjet-printed catalyst.

PubMed

Beard, James D; Stringer, Jonathan; Ghita, Oana R; Smith, Patrick J

2013-10-09

This study reports on the fabrication of vertically aligned carbon nanotubes localized at specific sites on a growth substrate by deposition of a nanoparticle suspension using inkjet printing. Carbon nanotubes were grown with high yield as vertically aligned forests to a length of approximately 400 μm. The use of inkjet printing for catalyst fabrication considerably improves the production rate of vertically aligned patterned nanotube forests compared with conventional patterning techniques, for example, electron beam lithography or photolithography.

Actuation mechanisms of carbon nanotube-based architectures

NASA Astrophysics Data System (ADS)

Geier, Sebastian; Mahrholz, Thorsten; Wierach, Peter; Sinapius, Michael

2016-04-01

State of the art smart materials such as piezo ceramics or electroactive polymers cannot feature both, mechanical stiffness and high active strain. Moreover, properties like low density, high mechanical stiffness and high strain at the same time driven by low energy play an increasingly important role for their future application. Carbon nanotubes (CNT), show this behavior. Their active behavior was observed 1999 the first time using paper-like mats made of CNT. Therefore the CNT-papers are electrical charged within an electrolyte thus forming a double- layer. The measured deflection of CNT material is based on the interaction between the charged high surface area formed by carbon nanotubes and ions provided by the electrolyte. Although CNT-papers have been extensively analyzed as well at the macro-scale as nano-scale there is still no generally accepted theory for the actuation mechanism. This paper focuses on investigations of the actuation mechanisms of CNT-papers in comparison to vertically aligned CNT-arrays. One reason of divergent results found in literature might be attributed to different types of CNT samples. While CNT-papers represent architectures of short CNTs which need to bridge each other to form the dimensions of the sample, the continuous CNTs of the array feature a length of almost 3 mm, along which the experiments are carried out. Both sample types are tested within an actuated tensile test set-up under different conditions. While the CNT-papers are tested in water-based electrolytes with comparably small redox-windows the hydrophobic CNT-arrays are tested in ionic liquids with comparatively larger redox-ranges. Furthermore an in-situ micro tensile test within an SEM is carried out to prove the optimized orientation of the MWCNTs as result of external load. It was found that the performance of CNT-papers strongly depends on the test conditions. However, the CNT-arrays are almost unaffected by the conditions showing active response at negative and positive voltages. A micro alignment as result of tensile stress can be proven. A comparison of both results point out that the actuation mechanism strongly depends on the weakest bonds of the architectures: Van-der-Waals-bonds vs. covalent C-bonds.

Fabrication of high thermal conductivity arrays of carbon nanotubes and their composites

DOEpatents

Geohegan, David B [Knoxville, TN; Ivanov, Ilya N [Knoxville, TN; Puretzky, Alexander A [Knoxville, TN

2010-07-27

Methods and apparatus are described for fabrication of high thermal conductivity arrays of carbon nanotubes and their composites. A composition includes a vertically aligned nanotube array including a plurality of nanotubes characterized by a property across substantially all of the vertically aligned nanotube array. A method includes depositing a vertically aligned nanotube array that includes a plurality of nanotubes; and controlling a deposition rate of the vertically aligned nanotubes array as a function of an in situ monitored property of the plurality of nanotubes.

Study of modification methods of probes for critical-dimension atomic-force microscopy by the deposition of carbon nanotubes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ageev, O. A., E-mail: ageev@sfedu.ru; Bykov, Al. V.; Kolomiitsev, A. S.

2015-12-15

The results of an experimental study of the modification of probes for critical-dimension atomicforce microscopy (CD-AFM) by the deposition of carbon nanotubes (CNTs) to improve the accuracy with which the surface roughness of vertical walls is determined in submicrometer structures are presented. Methods of the deposition of an individual CNT onto the tip of an AFM probe via mechanical and electrostatic interaction between the probe and an array of vertically aligned carbon nanotubes (VACNTs) are studied. It is shown that, when the distance between the AFM tip and a VACNT array is 1 nm and the applied voltage is withinmore » the range 20–30 V, an individual carbon nanotube is deposited onto the tip. On the basis of the results obtained in the study, a probe with a carbon nanotube on its tip (CNT probe) with a radius of 7 nm and an aspect ratio of 1:15 is formed. Analysis of the CNT probe demonstrates that its use improves the resolution and accuracy of AFM measurements, compared with the commercial probe, and also makes it possible to determine the roughness of the vertical walls of high-aspect structures by CD-AFM. The results obtained can be used to develop technological processes for the fabrication and reconditioning of special AFM probes, including those for CD-AFM, and procedures for the interoperational express monitoring of technological process parameters in the manufacturing of elements for micro- and nanoelectronics and micro- and nanosystem engineering.« less

Fast Response and Spontaneous Alignment in Liquid Crystals Doped with 12-Hydroxystearic Acid Gelators.

PubMed

Lin, Hui-Chi; Wang, Chih-Hung; Wang, Jyun-Kai; Tsai, Sheng-Feng

2018-05-07

The spontaneous vertical alignment of liquid crystals (LCs) in gelator (12-hydroxystearic acid)-doped LC cells was studied. Gelator-induced alignment can be used in both positive and negative LC cells. The electro-optical characteristics of the gelator-doped negative LC cell were similar to those of an LC cell that contained a vertically aligned (VA) host. The rise time of the gelator-doped LC cell was two orders of magnitude shorter than that of the VA host LC cell. The experimental results indicate that the gelator-induced vertical alignment of LC molecules occurred not only on the surface of the indium tin oxide (ITO) but also on the homogeneous alignment layer. Various LC alignments (planar, hybrid, multistable hybrid, and vertical alignments) were achieved by modulating the doped gelator concentrations. The multistable characteristic of LCs doped with the gelator is also presented. The alignment by doping with a gelator reduces the manufacturing costs and provides a means of fabricating fast-responding, flexible LC displays using a low-temperature process.

Quasi-ballistic carbon nanotube array transistors with current density exceeding Si and GaAs

PubMed Central

Brady, Gerald J.; Way, Austin J.; Safron, Nathaniel S.; Evensen, Harold T.; Gopalan, Padma; Arnold, Michael S.

2016-01-01

Carbon nanotubes (CNTs) are tantalizing candidates for semiconductor electronics because of their exceptional charge transport properties and one-dimensional electrostatics. Ballistic transport approaching the quantum conductance limit of 2G0 = 4e2/h has been achieved in field-effect transistors (FETs) containing one CNT. However, constraints in CNT sorting, processing, alignment, and contacts give rise to nonidealities when CNTs are implemented in densely packed parallel arrays such as those needed for technology, resulting in a conductance per CNT far from 2G0. The consequence has been that, whereas CNTs are ultimately expected to yield FETs that are more conductive than conventional semiconductors, CNTs, instead, have underperformed channel materials, such as Si, by sixfold or more. We report quasi-ballistic CNT array FETs at a density of 47 CNTs μm−1, fabricated through a combination of CNT purification, solution-based assembly, and CNT treatment. The conductance is as high as 0.46 G0 per CNT. In parallel, the conductance of the arrays reaches 1.7 mS μm−1, which is seven times higher than the previous state-of-the-art CNT array FETs made by other methods. The saturated on-state current density is as high as 900 μA μm−1 and is similar to or exceeds that of Si FETs when compared at and equivalent gate oxide thickness and at the same off-state current density. The on-state current density exceeds that of GaAs FETs as well. This breakthrough in CNT array performance is a critical advance toward the exploitation of CNTs in logic, high-speed communications, and other semiconductor electronics technologies. PMID:27617293

Quasi-ballistic carbon nanotube array transistors with current density exceeding Si and GaAs.

PubMed

Brady, Gerald J; Way, Austin J; Safron, Nathaniel S; Evensen, Harold T; Gopalan, Padma; Arnold, Michael S

2016-09-01

Carbon nanotubes (CNTs) are tantalizing candidates for semiconductor electronics because of their exceptional charge transport properties and one-dimensional electrostatics. Ballistic transport approaching the quantum conductance limit of 2G 0 = 4e (2)/h has been achieved in field-effect transistors (FETs) containing one CNT. However, constraints in CNT sorting, processing, alignment, and contacts give rise to nonidealities when CNTs are implemented in densely packed parallel arrays such as those needed for technology, resulting in a conductance per CNT far from 2G 0. The consequence has been that, whereas CNTs are ultimately expected to yield FETs that are more conductive than conventional semiconductors, CNTs, instead, have underperformed channel materials, such as Si, by sixfold or more. We report quasi-ballistic CNT array FETs at a density of 47 CNTs μm(-1), fabricated through a combination of CNT purification, solution-based assembly, and CNT treatment. The conductance is as high as 0.46 G 0 per CNT. In parallel, the conductance of the arrays reaches 1.7 mS μm(-1), which is seven times higher than the previous state-of-the-art CNT array FETs made by other methods. The saturated on-state current density is as high as 900 μA μm(-1) and is similar to or exceeds that of Si FETs when compared at and equivalent gate oxide thickness and at the same off-state current density. The on-state current density exceeds that of GaAs FETs as well. This breakthrough in CNT array performance is a critical advance toward the exploitation of CNTs in logic, high-speed communications, and other semiconductor electronics technologies.

Long-term release of antibiotics by carbon nanotube-coated titanium alloy surfaces diminish biofilm formation by Staphylococcus epidermidis.

PubMed

Hirschfeld, Josefine; Akinoglu, Eser M; Wirtz, Dieter C; Hoerauf, Achim; Bekeredjian-Ding, Isabelle; Jepsen, Søren; Haddouti, El-Mustapha; Limmer, Andreas; Giersig, Michael

2017-05-01

Bacterial biofilms cause a considerable amount of prosthetic joint infections every year, resulting in morbidity and expensive revision surgery. To address this problem, surface modifications of implant materials such as carbon nanotube (CNT) coatings have been investigated in the past years. CNTs are biologically compatible and can be utilized as drug delivery systems. In this study, multi-walled carbon nanotube (MWCNT) coated TiAl6V4 titanium alloy discs were fabricated and impregnated with Rifampicin, and tested for their ability to prevent biofilm formation over a period of ten days. Agar plate-based assays were employed to assess the antimicrobial activity of these surfaces against Staphylococcus epidermidis. It was shown that vertically aligned MWCNTs were more stable against attrition on rough surfaces than on polished TiAl6V4 surfaces. Discs with coated surfaces caused a significant inhibition of biofilm formation for up to five days. Therefore, MWCNT-modified surfaces may be effective against pathogenic biofilm formation on endoprostheses. Copyright © 2017 Elsevier Inc. All rights reserved.

Studies of Silicon Nanowires with Different Parameters — By PECVD

NASA Astrophysics Data System (ADS)

Leela, S.; Abirami, T.; Bhattacharya, Sekhar; Ahmed, Nafis; Monika, S.; Priya, R. Nivedha

2016-10-01

One-dimensional nanostructures such as nanowires have a wide range of applications. Silicon is the best competitive material for the carbon nanotubes (CNTs). Carbon and silicon have some similar and peculiar properties. Silicon nanowires (SiNWs) were synthesized using plasma enhanced chemical vapor deposition (PECVD) on p-Si (111) wafer. Gold is used as a catalyst for the growth of the SiNWs. Based on our fundamental understanding of vapor-liquid-solid (VLS) nanowire growth mechanism, different levels of growth controls have been achieved. Gold catalyst deposited and annealed at different temperatures with different thicknesses (450∘C, 500∘C and 550∘C, 600∘C, 650∘C for 4min and 8min and 3nm, 5nm, 30nm Au thickness). SiNW grown by PECVD with different carrier gases varies with flow rate. We observed the different dimensions of Si nanowires by FESEM and optimized the growth parameters to get the vertical aligned and singular Si nanowires. Optical phonon of the Si nanowires and crystallinity nature were identified by Raman spectral studies.

Binder-free carbon nanotube electrode for electrochemical removal of chromium.

PubMed

Wang, Haitao; Na, Chongzheng

2014-11-26

Electrochemical treatment of chromium-containing wastewater has the advantage of simultaneously reducing hexavalent chromium (CrVI) and reversibly adsorbing the trivalent product (CrIII), thereby minimizing the generation of waste for disposal and providing an opportunity for resource reuse. The application of electrochemical treatment of chromium is often limited by the available electrochemical surface area (ESA) of conventional electrodes with flat surfaces. Here, we report the preparation and evaluation of carbon nanotube (CNT) electrodes consisting of vertically aligned CNT arrays directly grown on stainless steel mesh (SSM). We show that the 3-D organization of CNT arrays increases ESA up to 13 times compared to SSM. The increase of ESA is correlated with the length of CNTs, consistent with a mechanism of roughness-induced ESA enhancement. The increase of ESA directly benefits CrVI reduction by proportionally accelerating reduction without compromising the electrode's ability to adsorb CrIII. Our results suggest that the rational design of electrodes with hierarchical structures represents a feasible approach to improve the performance of electrochemical treatment of contaminated water.

Nanoengineered Thermal Materials Based on Carbon Nanotube Array Composites

NASA Technical Reports Server (NTRS)

Li, Jun; Meyyappan, Meyya; Dangelo, Carols

2012-01-01

State-of-the-art integrated circuits (ICs) for microprocessors routinely dissipate power densities on the order of 50 W/cm2. This large power is due to the localized heating of ICs operating at high frequencies and must be managed for future high-frequency microelectronic applications. As the size of components and devices for ICs and other appliances becomes smaller, it becomes more difficult to provide heat dissipation and transport for such components and devices. A thermal conductor for a macro-sized thermal conductor is generally inadequate for use with a microsized component or device, in part due to scaling problems. A method has been developed for providing for thermal conduction using an array of carbon nanotubes (CNTs). An array of vertically oriented CNTs is grown on a substrate having high thermal conductivity, and interstitial regions between adjacent CNTs in the array are partly or wholly filled with a filler material having a high thermal conductivity so that at least one end of each CNT is exposed. The exposed end of each CNT is pressed against a surface of an object from which heat is to be removed. The CNT-filler-composite adjacent to the substrate provides improved mechanical strength to anchor CNTs in place, and also serves as a heat spreader to improve diffusion of heat flux from the smaller volume (CNTs) to a larger heat sink.

Heat transfer enhancement in free convection flow of CNTs Maxwell nanofluids with four different types of molecular liquids.

PubMed

Aman, Sidra; Khan, Ilyas; Ismail, Zulkhibri; Salleh, Mohd Zuki; Al-Mdallal, Qasem M

2017-05-26

This article investigates heat transfer enhancement in free convection flow of Maxwell nanofluids with carbon nanotubes (CNTs) over a vertically static plate with constant wall temperature. Two kinds of CNTs i.e. single walls carbon nanotubes (SWCNTs) and multiple walls carbon nanotubes (MWCNTs) are suspended in four different types of base liquids (Kerosene oil, Engine oil, water and ethylene glycol). Kerosene oil-based nanofluids are given a special consideration due to their higher thermal conductivities, unique properties and applications. The problem is modelled in terms of PDE's with initial and boundary conditions. Some relevant non-dimensional variables are inserted in order to transmute the governing problem into dimensionless form. The resulting problem is solved via Laplace transform technique and exact solutions for velocity, shear stress and temperature are acquired. These solutions are significantly controlled by the variations of parameters including the relaxation time, Prandtl number, Grashof number and nanoparticles volume fraction. Velocity and temperature increases with elevation in Grashof number while Shear stress minimizes with increasing Maxwell parameter. A comparison between SWCNTs and MWCNTs in each case is made. Moreover, a graph showing the comparison amongst four different types of nanofluids for both CNTs is also plotted.

Differences in pediatric vertical ground reaction force between planovalgus and neutrally aligned feet.

PubMed

Pauk, Jolanta; Szymul, Joanna

2014-01-01

Ground reaction forces (GRF) reflect the force history of human body contact with the ground. The purpose of this study was to explore human gait abnormalities due to planovalgus by comparing vertical GRF data between individuals with planovalgus and those with neutrally aligned feet. Second we estimated associations between various measurements and vertical GRF parameters in a pediatric population. Boys and girls between the ages of 4 and 18 years (72 planovalgus feet and 74 neutrally aligned feet) took part in this study. Ground reaction forces were recorded by two Kistler platforms and normalized to body weight. Comparison of vertical GRF between planovalgus and neutrally aligned feet suggests that the first and the second peaks of vertical force (Fz1, Fz2) are most affected by planovalgus. The results also indicate that neutrally aligned feet display a different ground reaction force pattern than planovalgus, and that differences between boys and girls may be observed. The shape of the vertical GRF curve can help in clinical interpretation of abnormal gait.

Crystalline multiwall carbon nanotubes and their application as a field emission electron source.

PubMed

Liu, Peng; Zhou, Duanliang; Zhang, Chunhai; Wei, Haoming; Yang, Xinhe; Wu, Yang; Li, Qingwei; Liu, Changhong; Du, Bingchu; Liu, Liang; Jiang, Kaili; Fan, Shoushan

2018-05-18

Using super-aligned carbon nanotube (CNT) film, we have fabricated van der Waals crystalline multiwall CNTs (MWCNT) by adopting high pressure and high temperature processing. The CNTs keep parallel to each other and are distributed uniformly. X-ray diffraction characterization shows peaks at the small angle range, which can be assigned to the spacing of the MWCNT crystals. The mechanical, electrical and thermal properties are all greatly improved compared with the original CNT film. The field emission properties of van der Waals crystalline MWCNTs are tested and they show a better surface morphology stability for the large emission current. We have further fabricated a field emission x-ray tube and demonstrated a precise resolution imaging ability.

Directed-Assembly of Carbon Nanotubes on Soft Substrates for Flexible Biosensor Array

NASA Astrophysics Data System (ADS)

Lee, Hyoung Woo; Koh, Juntae; Lee, Byung Yang; Kim, Tae Hyun; Lee, Joohyung; Hong, Seunghun; Yi, Mihye; Jhon, Young Min

2009-03-01

We developed a method to selectively assemble and align carbon nanotubes (CNTs) on soft substrates for flexible biosensors. In this strategy, thin oxide layer was deposited on soft substrates via low temperature plasma enhanced chemical vapor deposition, and linker-free assembly process was applied onto the oxide surface where the assembly of carbon nanotubes was guided by methyl-terminated molecular patterns on the oxide surface. The electrical characterization of the fabricated CNT devices exhibited typical p-type gating effect and 1/f noise behavior. The bare oxide regions near CNTs were functionalized with glutamate oxidase to fabricate selective biosensors to detect two forms of glutamate substances existing in different situations: L-glutamic acid, a neuro-transmitting material, and monosodium glutamate, a food additive.

Fast Response and Spontaneous Alignment in Liquid Crystals Doped with 12-Hydroxystearic Acid Gelators

PubMed Central

Lin, Hui-Chi; Wang, Chih-Hung; Wang, Jyun-Kai; Tsai, Sheng-Feng

2018-01-01

The spontaneous vertical alignment of liquid crystals (LCs) in gelator (12-hydroxystearic acid)-doped LC cells was studied. Gelator-induced alignment can be used in both positive and negative LC cells. The electro-optical characteristics of the gelator-doped negative LC cell were similar to those of an LC cell that contained a vertically aligned (VA) host. The rise time of the gelator-doped LC cell was two orders of magnitude shorter than that of the VA host LC cell. The experimental results indicate that the gelator-induced vertical alignment of LC molecules occurred not only on the surface of the indium tin oxide (ITO) but also on the homogeneous alignment layer. Various LC alignments (planar, hybrid, multistable hybrid, and vertical alignments) were achieved by modulating the doped gelator concentrations. The multistable characteristic of LCs doped with the gelator is also presented. The alignment by doping with a gelator reduces the manufacturing costs and provides a means of fabricating fast-responding, flexible LC displays using a low-temperature process. PMID:29735937

Embedded Aligned Carbon Nanotube Sheets for Strain and Damage sensing in Composite Structures

NASA Astrophysics Data System (ADS)

Aly, Karim Aly Abdelomoaty Elsayed

The world demand for fiber reinforced composite materials has been steadily increasing because of the widespread adoption of this class of material in many markets. The automotive, aerospace, marine and energy sectors account for a large percentage of this grow. Outstanding fatigue performance, high specific stiffness and strength, and low density are among the most important properties that fiber reinforced polymer composites offer. Furthermore, their properties can be tailored to meet the specific needs of the final applications. However, this class of material is composed of multiple layers of inhomogeneous and anisotropic constituents, i.e. fibers and matrix. Therefore, this laminated nature make the composite material prone to intrinsic damage including interfacial debonding and delamination and their strength and failure are dependent on the fiber architecture and direction of the applied stresses. Consequently, it is of prime importance to monitor the health of these structures. New and improved methods for early detection of damage and structural health monitoring of composite materials may allow for enhanced reliability, lifetime and performance while minimizing maintenance time during a composite part's service life. Over the last few decades different non-destructive methods and materials have been investigated for use as strain sensors. Since the discovery of carbon nanotubes (CNTs), they have attracted much research interest due to their superior electrical, thermal and mechanical properties as well as their high aspect ratio. In this context, CNTs have been used in the recent years to enable sensing capabilities. In this dissertation, the usage of CNTs for performing strain and damage sensing in composites is evaluated. This was enabled by embedding aligned sheets of two millimeters long, interconnected CNTs into laminated structures that were then subjected to different forms of mechanical loading. The localization of the CNT sheets inside the host structure was done using a novel technique that allowed for carrying out the embedment task conveniently and repeatedly. The real-time electrical resistance change of the CNT sheets in response to the applied mechanical stresses was measured in-situ so that the electromechnical behavior of the CNTs could be linked to the strain change and damage in the host structure. The quasi-static and dynamic flexural, axial tensile and compression loadings of the composite structures revealed that the CNT sheets exhibited sensitivity, stability and repeatability which are vital properties for any successful health monitoring technique. (Abstract shortened by ProQuest.).

Atomic Layer Deposition on Carbon Nanotubes and their Assemblies

NASA Astrophysics Data System (ADS)

Stano, Kelly Lynn

Global issues related to energy and the environment have motivated development of advanced material solutions outside of traditional metals ceramics, and polymers. Taking inspiration from composites, where the combination of two or more materials often yields superior properties, the field of organic-inorganic hybrids has recently emerged. Carbon nanotube (CNT)-inorganic hybrids have drawn widespread and increasing interest in recent years due to their multifunctionality and potential impact across several technologically important application areas. Before the impacts of CNT-inorganic hybrids can be realized however, processing techniques must be developed for their scalable production. Optimization in chemical vapor deposition (CVD) methods for synthesis of CNTs and vertically aligned CNT arrays has created production routes both high throughput and economically feasible. Additionally, control of CVD parameters has allowed for growth of CNT arrays that are able to be drawn into aligned sheets and further processed to form a variety of aligned 1, 2, and 3-dimensional bulk assemblies including ribbons, yarns, and foams. To date, there have only been a few studies on utilizing these bulk assemblies for the production of CNT-inorganic hybrids. Wet chemical methods traditionally used for fabricating CNT-inorganic hybrids are largely incompatible with CNT assemblies, since wetting and drying the delicate structures with solvents can destroy their structure. It is therefore necessary to investigate alternative processing strategies in order to advance the field of CNT-inorganic hybrids. In this dissertation, atomic layer deposition (ALD) is evaluated as a synthetic route for the production of large-scale CNT-metal oxide hybrids as well as pure metal oxide architectures utilizing CNT arrays, ribbons, and ultralow density foams as deposition templates. Nucleation and growth behavior of alumina was evaluated as a function of CNT surface chemistry. While highly graphitic and defect-free CNTs were shown to produce alumina beads on their surfaces, plasma-treated CNTs with a high concentration of oxygen- containing functional groups on their surface promoted conformal film formation. Furthermore, it was determined that ultrahigh aspect ratio CNT assemblies could be uniformly coated throughout the cross-section by orienting the CNT axes parallel to the direction of precursor flow, as well as by removing any barriers to the pump/purge process such as growth substrates or non-porous sample holders. Heat treatment of CNT-alumina hybrids in air not only led to the crystallization of alumina, but also oxidative removal of CNTs from the core-shell structure. In the case of CNT arrays, this resulted in a weak array of alumina nanotubes. When the same process was applied to alumina-coated CNT foams (CNTFs) however, a robust and resilient aerogel-like material remained post-calcination. Further inspection of this novel material revealed that the foam was made up of a three-dimensional network of interconnect alumina nanotubes resulting from the direct templating of alumina on the CNTF structure. With an average density of 1.2 mg cm-3, it is an order of magnitude lower than the lowest density alumina aerogel reported to date, and is among the lowest density for any inorganic aerogel reported to date as well. The structure, and therefore, properties of these novel foams could be easily tuned by varying the thickness of the alumina coating. Evaluation of the compressive behavior of all foams revealed that their mechanical properties exceed those of various foams with similar densities. This was found to be a result of efficient load transfer through the structure due to good connectivity among nanotube ligaments. This connectivity also provided unprecedented elastic recoverability following compression, particularly for thin-walled samples with CNTFs still intact. Structural stability to liquid infiltration and drying increased with the number of ALD cycles, as well as thermal insulation ability.

Specificity Bio-identification of CNT-Based Transistor

NASA Astrophysics Data System (ADS)

Wang, Sheng-Yu; Wu, Hue-Min

2017-12-01

In this research, we report a simple and general approach to π-π stacking functionalization of the sidewalls of CNTs by 1-pyrenebutanoic acid, succinimidyl ester (PSE), and subsequent immobilization of insulin-like growth factor 1 receptor (IGF1R) onto SWNTs with a high degree of control and specificity. The selection of PSE provides visualization and characterization of individual CNTs based on its strong luminescence. In addition, we designed a simple and efficient electrode with a staggered pattern to increase the effect of electrophoresis by using electric field for the macroscopic alignment of CNTs to complete a field-effect device for CNT-based biosensors. Scanning Electron Microscopy (SEM) was used to investigate the morphology of the biosensors. The results of four-point probe method demonstrated high selectivity and sensitivity of detection. The functionalization of SWNTs was investigated by Fourier transform infrared spectroscopy (FTIR). Experimental results imply that specific binding between IGF1R and its specific mAb results in a dramatic change in electrical current of CNT-based devices, and suggest that the devices are very promising biosensor candidates to detect circulating cancer cells.

A nano-microstructured artificial-hair-cell-type sensor based on topologically graded 3D carbon nanotube bundles

NASA Astrophysics Data System (ADS)

Yilmazoglu, O.; Yadav, S.; Cicek, D.; Schneider, J. J.

2016-09-01

A design for a unique artificial-hair-cell-type sensor (AHCTS) based entirely on 3D-structured, vertically aligned carbon nanotube (CNT) bundles is introduced. Standard microfabrication techniques were used for the straightforward micro-nano integration of vertically aligned carbon nanotube arrays composed of low-layer multi-walled CNTs (two to six layers). The mechanical properties of the carbon nanotube bundles were intensively characterized with regard to various substrates and CNT morphology, e.g. bundle height. The CNT bundles display excellent flexibility and mechanical stability for lateral bending, showing high tear resistance. The integrated 3D CNT sensor can detect three-dimensional forces using the deflection or compression of a central CNT bundle which changes the contact resistance to the shorter neighboring bundles. The complete sensor system can be fabricated using a single chemical vapor deposition (CVD) process step. Moreover, sophisticated external contacts to the surroundings are not necessary for signal detection. No additional sensors or external bias for signal detection are required. This simplifies the miniaturization and the integration of these nanostructures for future microsystem set-ups. The new nanostructured sensor system exhibits an average sensitivity of 2100 ppm in the linear regime with the relative resistance change per micron (ppm μm-1) of the individual CNT bundle tip deflection. Furthermore, experiments have shown highly sensitive piezoresistive behavior with an electrical resistance decrease of up to ˜11% at 50 μm mechanical deflection. The detection sensitivity is as low as 1 μm of deflection, and thus highly comparable with the tactile hair sensors of insects, having typical thresholds on the order of 30-50 μm. The AHCTS can easily be adapted and applied as a flow, tactile or acceleration sensor as well as a vibration sensor. Potential applications of the latter might come up in artificial cochlear systems. In particular, the stable mechanical bending of the sensor up to 90° opens up unique application opportunities.

Controlled Synthesis and Functionalization of Vertically-Aligned Carbon Nanotubes for Multifunctional Applications

DTIC Science & Technology

2015-05-07

6 1.6 Lithium - Ion Batteries Based on Vertically-Aligned Carbon Nanotube Electrodes and Ionic...Cl, Br, or I) Prepared by Ball-Milling and Used as Anode Materials for Lithium - Ion Batteries ……………....................23 3.4 Well-Defined Two...9 1.6 Lithium - Ion Batteries Based on Vertically-Aligned Carbon Nanotube Electrodes and Ionic Liquid Electrolytes

Bump Bonding Using Metal-Coated Carbon Nanotubes

NASA Technical Reports Server (NTRS)

Lamb, James L.; Dickie, Matthew R.; Kowalczyk, Robert S.; Liao, Anna; Bronikowski, Michael J.

2012-01-01

Bump bonding hybridization techniques use arrays of indium bumps to electrically and mechanically join two chips together. Surface-tension issues limit bump sizes to roughly as wide as they are high. Pitches are limited to 50 microns with bumps only 8-14 microns high on each wafer. A new process uses oriented carbon nanotubes (CNTs) with a metal (indium) in a wicking process using capillary actions to increase the aspect ratio and pitch density of the connections for bump bonding hybridizations. It merges the properties of the CNTs and the metal bumps, providing enhanced material performance parameters. By merging the bumps with narrow and long CNTs oriented in the vertical direction, higher aspect ratios can be obtained if the metal can be made to wick. Possible aspect ratios increase from 1:1 to 20:1 for most applications, and to 100:1 for some applications. Possible pitch density increases of a factor of 10 are possible. Standard capillary theory would not normally allow indium or most other metals to be drawn into the oriented CNTs, because they are non-wetting. However, capillary action can be induced through the ability to fabricate oriented CNT bundles to desired spacings, and the use of deposition techniques and temperature to control the size and mobility of the liquid metal streams and associated reservoirs. This hybridization of two technologies (indium bumps and CNTs) may also provide for some additional benefits such as improved thermal management and possible current density increases.

Exploring aligned-carbon-nanotubes@polyaniline arrays on household Al as supercapacitors.

PubMed

Huang, Fan; Lou, Fengliu; Chen, De

2012-05-01

Herein, we demonstrate a new approach towards the construction of supercapacitors consisting of carbon nanotubes (CNTs) and conducting polymers (ECPs) with high specific power, high specific energy, and stable cycling performance through a 3D design of a thin film of polyaniline (PANI) on an aligned small carbon nanotube (ACNT) array on household Al foils. The thin-film strategy is used to fully exploit the specific capacitance of PANI, and obtain regular pores, strong interaction between PANI and CNTs, and reduced electrical resistance for the electrodes. A facile process is developed to fabricate a highly flexible supercapacitor using this binder-free composite on household Al foil as the current collector. It exhibits high specific energy of 18.9 Wh kg(-1) , high maximum specific power of 11.3 kW kg(-1) of the active material in an aqueous electrolyte at 1.0 A g(-1) , and excellent rate performance and cycling stability. A high specific energy of 72.4 Wh kg(-1) , a high maximum specific power of 24.9 kW kg(-1) , and a good cycling performance of the active material are obtained in an organic electrolyte. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Directed assembly of carbon nanotubes on soft substrates for use as a flexible biosensor array.

PubMed

Koh, Juntae; Yi, Mihye; Yang Lee, Byung; Kim, Tae Hyun; Lee, Joohyung; Jhon, Young Min; Hong, Seunghun

2008-12-17

We have developed a method to selectively assemble and align carbon nanotubes (CNTs) on soft substrates for use as flexible biosensors. In this strategy, a thin oxide layer was deposited on soft substrates via low temperature plasma enhanced chemical vapor deposition, and a linker-free assembly process was applied on the oxide surface where the assembly of carbon nanotubes was guided by methyl-terminated molecular patterns on the oxide surface. The electrical characterization of the fabricated CNT devices exhibited a typical p-type gating effect and 1/f noise behavior. The bare oxide regions near CNTs were functionalized with glutamate oxidase to fabricate selective biosensors to detect two forms of glutamate substances existing in different situations: L-glutamic acid, a neurotransmitting material, and monosodium glutamate, a food additive.

A critical look at spatial scale choices in satellite-based aerosol indirect effect studies

NASA Astrophysics Data System (ADS)

Grandey, B. S.; Stier, P.

2010-06-01

Analysing satellite datasets over large regions may introduce spurious relationships between aerosol and cloud properties due to spatial variations in aerosol type, cloud regime and synoptic regime climatologies. Using MODerate resolution Imaging Spectroradiometer data, we calculate relationships between aerosol optical depth τa, derived liquid cloud droplet effective number concentration Ne and liquid cloud droplet effective radius re at different spatial scales. Generally, positive values of dlnNe dlnτa are found for ocean regions, whilst negative values occur for many land regions. The spatial distribution of dlnre dlnτa shows approximately the opposite pattern, with generally postive values for land regions and negative values for ocean regions. We find that for region sizes larger than 4°×4°, spurious spatial variations in retrieved cloud and aerosol properties can introduce widespread significant errors to calculations of dlnNe dlnτa and dlnre dlnτa . For regions on the scale of 60°×60°, these methodological errors may lead to an overestimate in global cloud albedo effect radiative forcing of order 80%.

Backward scattering effect of aligned carbon nanotube arrays

NASA Astrophysics Data System (ADS)

Wu, Pengfei; Ren, Zhifeng; Wang, Michael R.

2009-02-01

In terms of operational bandwidth and speed, photonic components are superior to electronic ones. However, it is difficult to control photons on nanoscale structures for data processing and interconnection. Nanophotonic device using surface plasmon (SP) offers an ideal solution to combine the superior technical advantages of both photonics and electronics on the same chip. The SP wavelength is much shorter than that of the exciting light, allowing the use of SP in various techniques that overcome diffraction limits. In this paper, we report an interesting plasmonic effect, enhanced backward scattering, by using a periodically-aligned carbon nanotube (CNT) array. The CNTs are grown on a transparent glass substrate with an average diameter of 50 nm and a length of about 1 μm. To enhance the conductivity, the CNTs are also coated with 10-nm Au layer by using E-beam CVD technique. By shining a laser beam to the CNT array, we found that the scattering intensity is maximally enhanced at the backward incident direction. The enhanced backward incident scattering is observed by using both periodic and nonperiodic CNT samples. The experimental results suggest that the backward scattering effect is due to the SP excitation and coupling. The proposed technique exploiting aligned carbon-nanotube arrays to manipulate surface plasmon will lead to useful optical features such as optical antennae effects, retro-reflection, switching, wavelength add/drop multiplexing, and may be particularly useful for optical sensing, smart target identification and optical wireless secure communication applications.

Extreme Magneto-transport of Bulk Carbon Nanotubes in Sorted Electronic Concentrations and Aligned High Performance Fiber

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bulmer, John S.; Lekawa-Raus, Agnieszka; Rickel, Dwight G.

We explored high-field (60 T) magneto-resistance (MR) with two carbon nanotube (CNT) material classes: (1) unaligned single-wall CNTs (SWCNT) films with controlled metallic SWCNT concentrations and doping degree and (2) CNT fiber with aligned, long-length microstructure. All unaligned SWCNT films showed localized hopping transport where high-field MR saturation definitively supports spin polarization instead of a more prevalent wave function shrinking mechanism. Nitric acid exposure induced an insulator to metal transition and reduced the positive MR component. Aligned CNT fiber, already on the metal side of the insulator to metal transition, had positive MR without saturation and was assigned to classicalmore » MR involving electronic mobility. Subtracting high-field fits from the aligned fiber’s MR yielded an unconfounded negative MR, which was assigned to weak localization. It is concluded that fluctuation induced tunnelling, an extrinsic transport model accounting for most of the aligned fiber’s room temperature resistance, appears to lack MR field dependence.« less

Extreme Magneto-transport of Bulk Carbon Nanotubes in Sorted Electronic Concentrations and Aligned High Performance Fiber.

PubMed

Bulmer, John S; Lekawa-Raus, Agnieszka; Rickel, Dwight G; Balakirev, Fedor F; Koziol, Krzysztof K

2017-09-22

We explored high-field (60 T) magneto-resistance (MR) with two carbon nanotube (CNT) material classes: (1) unaligned single-wall CNTs (SWCNT) films with controlled metallic SWCNT concentrations and doping degree and (2) CNT fiber with aligned, long-length microstructure. All unaligned SWCNT films showed localized hopping transport where high-field MR saturation definitively supports spin polarization instead of a more prevalent wave function shrinking mechanism. Nitric acid exposure induced an insulator to metal transition and reduced the positive MR component. Aligned CNT fiber, already on the metal side of the insulator to metal transition, had positive MR without saturation and was assigned to classical MR involving electronic mobility. Subtracting high-field fits from the aligned fiber's MR yielded an unconfounded negative MR, which was assigned to weak localization. It is concluded that fluctuation induced tunnelling, an extrinsic transport model accounting for most of the aligned fiber's room temperature resistance, appears to lack MR field dependence.

Extreme Magneto-transport of Bulk Carbon Nanotubes in Sorted Electronic Concentrations and Aligned High Performance Fiber

DOE PAGES

Bulmer, John S.; Lekawa-Raus, Agnieszka; Rickel, Dwight G.; ...

2017-09-22

We explored high-field (60 T) magneto-resistance (MR) with two carbon nanotube (CNT) material classes: (1) unaligned single-wall CNTs (SWCNT) films with controlled metallic SWCNT concentrations and doping degree and (2) CNT fiber with aligned, long-length microstructure. All unaligned SWCNT films showed localized hopping transport where high-field MR saturation definitively supports spin polarization instead of a more prevalent wave function shrinking mechanism. Nitric acid exposure induced an insulator to metal transition and reduced the positive MR component. Aligned CNT fiber, already on the metal side of the insulator to metal transition, had positive MR without saturation and was assigned to classicalmore » MR involving electronic mobility. Subtracting high-field fits from the aligned fiber’s MR yielded an unconfounded negative MR, which was assigned to weak localization. It is concluded that fluctuation induced tunnelling, an extrinsic transport model accounting for most of the aligned fiber’s room temperature resistance, appears to lack MR field dependence.« less

Measurement of the Dewetting, Nucleation, and Deactivation Kinetics of Carbon Nanotube Population Growth by Environmental Transmission Electron Microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bedewy, Mostafa; Viswanath, B.; Meshot, Eric R.

In order to understand the collective growth of carbon nanotube (CNT) populations tailoring their properties for many applications is key. During the initial stages of CNT growth by chemical vapor deposition, catalyst nanoparticle formation by thin-film dewetting and the subsequent CNT nucleation processes dictate the CNT diameter distribution, areal density, and alignment. We use in situ environmental transmission electron microscopy (E-TEM) to observe the catalyst annealing, growth, and deactivation stages for a population of CNTs grown from a thin-film catalyst. Complementary in situ electron diffraction and TEM imaging show that, during the annealing step in hydrogen, reduction of the ironmore » oxide catalyst is concomitant with changes in the thin-film morphology; complete dewetting and the formation of a population of nanoparticles is only achieved upon the introduction of the carbon source, acetylene. The dewetting kinetics, i.e., the appearance of distinct nanoparticles, exhibits a sigmoidal (autocatalytic) curve with 95% of all nanoparticles appearing within 6 s. After nanoparticles form, they either nucleate CNTs or remain inactive, with incubation times measured to be as small as 3.5 s. Via E-TEM we also directly observe the crowding and self-alignment of CNTs after dewetting and nucleation. Additionally, in situ electron energy loss spectroscopy reveals that the collective rate of carbon accumulation decays exponentially. We conclude that the kinetics of catalyst formation and CNT nucleation must both be addressed in order to achieve uniform and high CNT density, and their transient behavior may be a primary cause of the well-known nonuniform density of CNT forests.« less

Measurement of the Dewetting, Nucleation, and Deactivation Kinetics of Carbon Nanotube Population Growth by Environmental Transmission Electron Microscopy

DOE PAGES

Bedewy, Mostafa; Viswanath, B.; Meshot, Eric R.; ...

2016-05-23

In order to understand the collective growth of carbon nanotube (CNT) populations tailoring their properties for many applications is key. During the initial stages of CNT growth by chemical vapor deposition, catalyst nanoparticle formation by thin-film dewetting and the subsequent CNT nucleation processes dictate the CNT diameter distribution, areal density, and alignment. We use in situ environmental transmission electron microscopy (E-TEM) to observe the catalyst annealing, growth, and deactivation stages for a population of CNTs grown from a thin-film catalyst. Complementary in situ electron diffraction and TEM imaging show that, during the annealing step in hydrogen, reduction of the ironmore » oxide catalyst is concomitant with changes in the thin-film morphology; complete dewetting and the formation of a population of nanoparticles is only achieved upon the introduction of the carbon source, acetylene. The dewetting kinetics, i.e., the appearance of distinct nanoparticles, exhibits a sigmoidal (autocatalytic) curve with 95% of all nanoparticles appearing within 6 s. After nanoparticles form, they either nucleate CNTs or remain inactive, with incubation times measured to be as small as 3.5 s. Via E-TEM we also directly observe the crowding and self-alignment of CNTs after dewetting and nucleation. Additionally, in situ electron energy loss spectroscopy reveals that the collective rate of carbon accumulation decays exponentially. We conclude that the kinetics of catalyst formation and CNT nucleation must both be addressed in order to achieve uniform and high CNT density, and their transient behavior may be a primary cause of the well-known nonuniform density of CNT forests.« less

Self-assembled ordered carbon-nanotube arrays and membranes.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Overmyer, Donald L.; Siegal, Michael P.; Yelton, William Graham

2004-11-01

Imagine free-standing flexible membranes with highly-aligned arrays of carbon nanotubes (CNTs) running through their thickness. Perhaps with both ends of the CNTs open for highly controlled nanofiltration? Or CNTs at heights uniformly above a polymer membrane for a flexible array of nanoelectrodes or field-emitters? How about CNT films with incredible amounts of accessible surface area for analyte adsorption? These self-assembled crystalline nanotubes consist of multiple layers of graphene sheets rolled into concentric cylinders. Tube diameters (3-300 nm), inner-bore diameters (2-15 nm), and lengths (nanometers - microns) are controlled to tailor physical, mechanical, and chemical properties. We proposed to explore growthmore » and characterize nanotube arrays to help determine their exciting functionality for Sandia applications. Thermal chemical vapor deposition growth in a furnace nucleates from a metal catalyst. Ordered arrays grow using templates from self-assembled hexagonal arrays of nanopores in anodized-aluminum oxide. Polymeric-binders can mechanically hold the CNTs in place for polishing, lift-off, and membrane formation. The stiffness, electrical and thermal conductivities of CNTs make them ideally suited for a wide-variety of possible applications. Large-area, highly-accessible gas-adsorbing carbon surfaces, superb cold-cathode field-emission, and unique nanoscale geometries can lead to advanced microsensors using analyte adsorption, arrays of functionalized nanoelectrodes for enhanced electrochemical detection of biological/explosive compounds, or mass-ionizers for gas-phase detection. Materials studies involving membrane formation may lead to exciting breakthroughs in nanofiltration/nanochromatography for the separation of chemical and biological agents. With controlled nanofilter sizes, ultrafiltration will be viable to separate and preconcentrate viruses and many strains of bacteria for 'down-stream' analysis.« less

Kinesthetic perceptions of earth- and body-fixed axes.

PubMed

Darling, W G; Hondzinski, J M

1999-06-01

The major purpose of this research was to determine whether kinesthetic/proprioceptive perceptions of the earth-fixed vertical axis are more accurate than perceptions of intrinsic axes. In one experiment, accuracy of alignment of the forearm to earth-fixed vertical and head- and trunk-longitudinal axes by seven blindfolded subjects was compared in four tasks: (1) Earth-Arm--arm (humerus) orientation was manipulated by the experimenter; subjects aligned the forearm parallel to the vertical axis, which was also aligned with the head and trunk longitudinal axis; (2) Head--head, trunk, and upper-limb orientations were manipulated by the experimenter, subjects aligned the forearm parallel to the longitudinal axis of the head using only elbow flexion/extension and shoulder internal/external rotation; (3) Trunk--same as (2), except that subjects aligned the forearm parallel to the trunk-longitudinal axis; (4) Earth--same as (2), except that subjects aligned the forearm parallel to the earth-fixed vertical. Head, trunk, and gravitational axes were never parallel in tasks 2, 3, and 4 so that subjects could not simultaneously match their forearm to all three axes. The results showed that the errors for alignment of the forearm with the earth-fixed vertical were lower than for the trunk- and head-longitudinal axes. Furthermore, errors in the Earth condition were less dependent on alterations of the head and trunk orientation than in the Head and Trunk conditions. These data strongly suggest that the earth-fixed vertical is used as one axis for the kinesthetic sensory coordinate system that specifies upper-limb orientation at the perceptual level. We also examined the effects of varying gravitational torques at the elbow and shoulder on the accuracy of forearm alignment to earth-fixed axes. Adding a 450 g load to the forearm to increase gravitational torques when the forearm is not vertical did not improve the accuracy of forearm alignment with the vertical. Furthermore, adding small, variably sized loads (between which the subjects could not distinguish at the perceptual level) to the forearm just proximal to the wrist produced similar errors in aligning the forearm with the vertical and horizontal. Forearm-positioning errors were not correlated with the size of the load, as would be expected if gravitational torques affected forearm-position sense. We conclude that gravitational torques exerted about the shoulder and elbow do not make significant contributions to sensing forearm-orientation relative to earth-fixed axes when the upper-limb segments are not constrained by external supports.

Proposed technique for vertical alignment of a crane's cable

NASA Technical Reports Server (NTRS)

Gera, J., Jr.

1969-01-01

Proposed vertical alignment technique senses the attitude of a cranes cable and displays any deviation from the vertical. The system consists of a detector assembly fixed to the boom and a display scope located in the cabin. It has potential application with either fixed-boom cranes or gantries.

Controllable growth of vertically aligned graphene on C-face SiC

DOE PAGES

Liu, Yu; Chen, Lianlian; Hilliard, Donovan; ...

2016-10-06

We investigated how to control the growth of vertically aligned graphene on C-face SiC by varying the processing conditions. It is found that, the growth rate scales with the annealing temperature and the graphene height is proportional to the annealing time. Temperature gradient and crystalline quality of the SiC substrates influence their vaporization. The partial vapor pressure is crucial as it can interfere with further vaporization. A growth mechanism is proposed in terms of physical vapor transport. The monolayer character of vertically aligned graphene is verified by Raman and X-ray absorption spectroscopy. With the processed samples, d 0 magnetism ismore » realized and negative magnetoresistance is observed after Cu implantation. We also prove that multiple carriers exist in vertically aligned graphene.« less

Controllable growth of vertically aligned graphene on C-face SiC

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Yu; Chen, Lianlian; Hilliard, Donovan

We investigated how to control the growth of vertically aligned graphene on C-face SiC by varying the processing conditions. It is found that, the growth rate scales with the annealing temperature and the graphene height is proportional to the annealing time. Temperature gradient and crystalline quality of the SiC substrates influence their vaporization. The partial vapor pressure is crucial as it can interfere with further vaporization. A growth mechanism is proposed in terms of physical vapor transport. The monolayer character of vertically aligned graphene is verified by Raman and X-ray absorption spectroscopy. With the processed samples, d 0 magnetism ismore » realized and negative magnetoresistance is observed after Cu implantation. We also prove that multiple carriers exist in vertically aligned graphene.« less

Active vacuum brazing of CNT films to metal substrates for superior electron field emission performance

NASA Astrophysics Data System (ADS)

Longtin, Rémi; Sanchez-Valencia, Juan Ramon; Shorubalko, Ivan; Furrer, Roman; Hack, Erwin; Elsener, Hansrudolf; Gröning, Oliver; Greenwood, Paul; Rupesinghe, Nalin; Teo, Kenneth; Leinenbach, Christian; Gröning, Pierangelo

2015-02-01

The joining of macroscopic films of vertically aligned multiwalled carbon nanotubes (CNTs) to titanium substrates is demonstrated by active vacuum brazing at 820 °C with a Ag-Cu-Ti alloy and at 880 °C with a Cu-Sn-Ti-Zr alloy. The brazing methodology was elaborated in order to enable the production of highly electrically and thermally conductive CNT/metal substrate contacts. The interfacial electrical resistances of the joints were measured to be as low as 0.35 Ω. The improved interfacial transport properties in the brazed films lead to superior electron field-emission properties when compared to the as-grown films. An emission current of 150 μA was drawn from the brazed nanotubes at an applied electric field of 0.6 V μm-1. The improvement in electron field-emission is mainly attributed to the reduction of the contact resistance between the nanotubes and the substrate. The joints have high re-melting temperatures up to the solidus temperatures of the alloys; far greater than what is achievable with standard solders, thus expanding the application potential of CNT films to high-current and high-power applications where substantial frictional or resistive heating is expected.

Active vacuum brazing of CNT films to metal substrates for superior electron field emission performance

PubMed Central

Longtin, Rémi; Ramon Sanchez-Valencia, Juan; Shorubalko, Ivan; Furrer, Roman; Hack, Erwin; Elsener, Hansrudolf; Gröning, Oliver; Greenwood, Paul; Rupesinghe, Nalin; Teo, Kenneth; Leinenbach, Christian; Gröning, Pierangelo

2015-01-01

The joining of macroscopic films of vertically aligned multiwalled carbon nanotubes (CNTs) to titanium substrates is demonstrated by active vacuum brazing at 820 °C with a Ag–Cu–Ti alloy and at 880 °C with a Cu–Sn–Ti–Zr alloy. The brazing methodology was elaborated in order to enable the production of highly electrically and thermally conductive CNT/metal substrate contacts. The interfacial electrical resistances of the joints were measured to be as low as 0.35 Ω. The improved interfacial transport properties in the brazed films lead to superior electron field-emission properties when compared to the as-grown films. An emission current of 150 μA was drawn from the brazed nanotubes at an applied electric field of 0.6 V μm−1. The improvement in electron field-emission is mainly attributed to the reduction of the contact resistance between the nanotubes and the substrate. The joints have high re-melting temperatures up to the solidus temperatures of the alloys; far greater than what is achievable with standard solders, thus expanding the application potential of CNT films to high-current and high-power applications where substantial frictional or resistive heating is expected. PMID:27877755

Growth of vertically aligned carbon nanotubes on silicon and quartz substrate by spray pyrolysis of a natural precursor: Turpentine oil

NASA Astrophysics Data System (ADS)

Afre, Rakesh A.; Soga, T.; Jimbo, T.; Kumar, Mukul; Ando, Y.; Sharon, M.

2005-10-01

Vertically aligned carbon nanotubes (VACNTs) were grown by spray pyrolysis of turpentine oil and ferrocene mixture at 700 °C. Using this simple method, we report the successful growth of vertically aligned nanotubes of 300 μm length and diameter in the range of 50-100 nm on Si(1 0 0) substrate. The ferrocene act as an in situ Fe catalyst precursor and forming the nanosize iron particles for formation of VACNTs on Si and quartz substrates. Morphological differences between aligned carbon nanotubes grown on different substrates are studied and discussed by SEM, TEM and Raman spectroscopy characterizations.

A critical look at spatial scale choices in satellite-based aerosol indirect effect studies

NASA Astrophysics Data System (ADS)

Grandey, B. S.; Stier, P.

2010-12-01

Analysing satellite datasets over large regions may introduce spurious relationships between aerosol and cloud properties due to spatial variations in aerosol type, cloud regime and synoptic regime climatologies. Using MODerate resolution Imaging Spectroradiometer data, we calculate relationships between aerosol optical depth τa derived liquid cloud droplet effective number concentration Ne and liquid cloud droplet effective radius re at different spatial scales. Generally, positive values of dlnNedlnτa are found for ocean regions, whilst negative values occur for many land regions. The spatial distribution of dlnredlnτa shows approximately the opposite pattern, with generally postive values for land regions and negative values for ocean regions. We find that for region sizes larger than 4° × 4°, spurious spatial variations in retrieved cloud and aerosol properties can introduce widespread significant errors to calculations of dlnNedlnτa and dlnredlnτa. For regions on the scale of 60° × 60°, these methodological errors may lead to an overestimate in global cloud albedo effect radiative forcing of order 80% relative to that calculated for regions on the scale of 1° × 1°.

Iron encapsulated in 3D N-doped carbon nanotube/porous carbon hybrid from waste biomass for enhanced oxidative activity.

PubMed

Yao, Yunjin; Zhang, Jie; Wu, Guodong; Wang, Shaobin; Hu, Yi; Su, Cong; Xu, Tongwen

2017-03-01

Novel iron encapsulated in nitrogen-doped carbon nanotubes (CNTs) supported on porous carbon (Fe@N-C) 3D structured materials for degrading organic pollutants were fabricated from a renewable, low-cost biomass, melamine, and iron salt as the precursors. SEM and TEM micrographs show that iron encapsulated bamboo shaped CNTs are vertically standing on carbon sheets, and thus, a 3D hybrid was formed. The catalytic activities of the prepared samples were thoroughly evaluated by activation of peroxymonosulfate for catalytic oxidation of Orange II solutions. The influences of some reaction conditions (pH, temperature, and concentrations of reactants, peroxymonosulfate, and dye) were extensively evaluated. It was revealed that the adsorption could enrich the pollutant which was then rapidly degraded by the catalytically generated radicals, accelerating the continuous adsorption of residual pollutant. Remarkable carbon structure, introduction of CNTs, and N/Fe doping result in promoted adsorption capability and catalytic performances. Due to the simple synthetic process and cheap carbon precursor, Fe@N-C 3D hybrid can be easily scaled up and promote the development of Fenton-like catalysts.

Effect of catalyst film thickness on carbon nanotube growth by selective area chemical vapor deposition

NASA Astrophysics Data System (ADS)

Wei, Y. Y.; Eres, Gyula; Merkulov, V. I.; Lowndes, D. H.

2001-03-01

The correlation between prepatterned catalyst film thickness and carbon nanotube (CNT) growth by selective area chemical vapor deposition (CVD) was studied using Fe and Ni as catalyst. To eliminate sample-to-sample variations and create a growth environment in which the film thickness is the sole variable, samples with continuously changing catalyst film thickness from 0 to 60 nm were fabricated by electron-gun evaporation. Using thermal CVD CNTs preferentially grow as a dense mat on the thin regions of the catalyst film. Moreover, beyond a certain critical film thickness no tubes were observed. The critical film thickness for CNT growth was found to increase with substrate temperature. There appears to be no strong correlation between the film thickness and the diameter of the tubes. In contrast, using plasma enhanced CVD with Ni as catalyst, vertically oriented CNTs grow in the entire range of catalyst film thickness. The diameter of these CNTs shows a strong correlation with the catalyst film thickness. The significance of these experimental trends is discussed within the framework of the diffusion model for CNT growth.

A three-dimensional architecture of vertically aligned multilayer graphene facilitates heat dissipation across joint solid surfaces

NASA Astrophysics Data System (ADS)

Liang, Qizhen; Yao, Xuxia; Wang, Wei; Wong, C. P.

2012-02-01

Low operation temperature and efficient heat dissipation are important for device life and speed in current electronic and photonic technologies. Being ultra-high thermally conductive, graphene is a promising material candidate for heat dissipation improvement in devices. In the application, graphene is expected to be vertically stacked between contact solid surfaces in order to facilitate efficient heat dissipation and reduced interfacial thermal resistance across contact solid surfaces. However, as an ultra-thin membrane-like material, graphene is susceptible to Van der Waals forces and usually tends to be recumbent on substrates. Thereby, direct growth of vertically aligned free-standing graphene on solid substrates in large scale is difficult and rarely available in current studies, bringing significant barriers in graphene's application as thermal conductive media between joint solid surfaces. In this work, a three-dimensional vertically aligned multi-layer graphene architecture is constructed between contacted Silicon/Silicon surfaces with pure Indium as a metallic medium. Significantly higher equivalent thermal conductivity and lower contact thermal resistance of vertically aligned multilayer graphene are obtained, compared with those of their recumbent counterpart. This finding provides knowledge of vertically aligned graphene architectures, which may not only facilitate current demanding thermal management but also promote graphene's widespread applications such as electrodes for energy storage devices, polymeric anisotropic conductive adhesives, etc.

Effects of CNT size on the desalination performance of an outer-wall CNT slit membrane.

PubMed

Ang, Elisa Y M; Ng, Teng Yong; Yeo, Jingjie; Lin, Rongming; Liu, Zishun; Geethalakshmi, K R

2018-05-23

We investigate the effect of varying carbon nanotube (CNT) size on the desalination performance through slit confinements formed by horizontally aligned CNTs stacked on top of one another. By increasing the CNT size, the results obtained from this study indicate a corresponding increase in the water flow rate, accompanied by a slight reduction in salt rejection performance. However, due to the increase in the membrane area with CNT size, the permeability performance is observed to reduce as the CNT size increases. Nevertheless, a comparison with nanoporous 2D membranes shows that the permeability of an outer-wall CNT slit membrane remains significantly higher for all CNT sizes considered. This indicates that precise dimensions of the CNTs are not highly crucial for achieving ultra-high permeability performance in such membranes, as long as the critical slit size is maintained. In-depth analytical studies were further conducted to correlate the influence of curvature effects due to increasing CNT size on the flow characteristcis of the outer-wall CNT membrane. These include the analysis of the measured velocity profiles, oxygen density mapping, potential of mean force profile and friction profile. The present numerical results demonstrate the superb desalination performance of the outer-wall CNT slit membrane, regardless of the size of CNTs used. In addition, an extensive analysis conducted provides detailed characterization of how the curvature affects flow across outer-wall CNTs, and can be used to guide future design and fabrication for experimental testing.

Graphene quantum dots-carbon nanotube hybrid arrays for supercapacitors

NASA Astrophysics Data System (ADS)

Hu, Yue; Zhao, Yang; Lu, Gewu; Chen, Nan; Zhang, Zhipan; Li, Hui; Shao, Huibo; Qu, Liangti

2013-05-01

Graphene quantum dots (GQDs) have been successfully deposited onto aligned carbon nanotubes (CNTs) by a benign electrochemical method and the capacitive properties of the as-formed GQD/CNT hybrid arrays were evaluated in symmetrical supercapacitors. It was found that supercapacitors fabricated from GQD/CNT hybrid arrays exhibited a high capacitance of 44 mF cm-2, representing a more than 200% improvement over that of bare CNT electrodes.

Graphene quantum dots-carbon nanotube hybrid arrays for supercapacitors.

PubMed

Hu, Yue; Zhao, Yang; Lu, Gewu; Chen, Nan; Zhang, Zhipan; Li, Hui; Shao, Huibo; Qu, Liangti

2013-05-17

Graphene quantum dots (GQDs) have been successfully deposited onto aligned carbon nanotubes (CNTs) by a benign electrochemical method and the capacitive properties of the as-formed GQD/CNT hybrid arrays were evaluated in symmetrical supercapacitors. It was found that supercapacitors fabricated from GQD/CNT hybrid arrays exhibited a high capacitance of 44 mF cm(-2), representing a more than 200% improvement over that of bare CNT electrodes.

DARPA Perspectives on Multifunctional Materials/Power and Energy

DTIC Science & Technology

2012-08-09

In-situ growth of aligned CNTs Electronics Graphene /Metal oxide CMOS interconnects Erosion Diamond/ZnS LWIR missile domes Tribology TiN/Carbon...application Optoelectronics InGaN LEDs Energy ZnSnN2 Photovoltaics Optoelectronics Indium Tin Oxide/ Polycarbonate Anti-corrosion Paint /Steel...InGaN LEDs Energy ZnSnN2 Photovoltaics Optoelectronics Indium Tin Oxide/ Polycarbonate Anti-corrosion Paint /Steel Tribology TiN/High speed

Plasmonic Properties of Vertically Aligned Nanowire Arrays

DTIC Science & Technology

2012-01-01

scattering (SERS) applications. In this investigation, two types of vertical NW arrays were studied; those of ZnO NWs grown on nanosphere lithography...plasmonic nanowires to investigate this SERS effect. Here we used two types of vertical NWs, ZnO NWs, and Si NWs, respectively, to investigate SERS...successfully grow vertically aligned ZnO nanowires by the well-known VLS process. In this way, the ZnO NWs can be arranged in a repeatable hexagonal pattern

Purification process for vertically aligned carbon nanofibers

NASA Technical Reports Server (NTRS)

Nguyen, Cattien V.; Delziet, Lance; Matthews, Kristopher; Chen, Bin; Meyyappan, M.

2003-01-01

Individual, free-standing, vertically aligned multiwall carbon nanotubes or nanofibers are ideal for sensor and electrode applications. Our plasma-enhanced chemical vapor deposition techniques for producing free-standing and vertically aligned carbon nanofibers use catalyst particles at the tip of the fiber. Here we present a simple purification process for the removal of iron catalyst particles at the tip of vertically aligned carbon nanofibers derived by plasma-enhanced chemical vapor deposition. The first step involves thermal oxidation in air, at temperatures of 200-400 degrees C, resulting in the physical swelling of the iron particles from the formation of iron oxide. Subsequently, the complete removal of the iron oxide particles is achieved with diluted acid (12% HCl). The purification process appears to be very efficient at removing all of the iron catalyst particles. Electron microscopy images and Raman spectroscopy data indicate that the purification process does not damage the graphitic structure of the nanotubes.

Multidirectional flexible force sensors based on confined, self-adjusting carbon nanotube arrays

NASA Astrophysics Data System (ADS)

Lee, J.-I.; Pyo, Soonjae; Kim, Min-Ook; Kim, Jongbaeg

2018-02-01

We demonstrate a highly sensitive force sensor based on self-adjusting carbon nanotube (CNT) arrays. Aligned CNT arrays are directly synthesized on silicon microstructures by a space-confined growth technique which enables a facile self-adjusting contact. To afford flexibility and softness, the patterned microstructures with the integrated CNTs are embedded in polydimethylsiloxane structures. The sensing mechanism is based on variations in the contact resistance between the facing CNT arrays under the applied force. By finite element analysis, proper dimensions and positions for each component are determined. Further, high sensitivities up to 15.05%/mN of the proposed sensors were confirmed experimentally. Multidirectional sensing capability could also be achieved by designing multiple sets of sensing elements in a single sensor. The sensors show long-term operational stability, owing to the unique properties of the constituent CNTs, such as outstanding mechanical durability and elasticity.

Carbon nanotube bundles with tensile strength over 80 GPa.

PubMed

Bai, Yunxiang; Zhang, Rufan; Ye, Xuan; Zhu, Zhenxing; Xie, Huanhuan; Shen, Boyuan; Cai, Dali; Liu, Bofei; Zhang, Chenxi; Jia, Zhao; Zhang, Shenli; Li, Xide; Wei, Fei

2018-05-14

Carbon nanotubes (CNTs) are one of the strongest known materials. When assembled into fibres, however, their strength becomes impaired by defects, impurities, random orientations and discontinuous lengths. Fabricating CNT fibres with strength reaching that of a single CNT has been an enduring challenge. Here, we demonstrate the fabrication of CNT bundles (CNTBs) that are centimetres long with tensile strength over 80 GPa using ultralong defect-free CNTs. The tensile strength of CNTBs is controlled by the Daniels effect owing to the non-uniformity of the initial strains in the components. We propose a synchronous tightening and relaxing strategy to release these non-uniform initial strains. The fabricated CNTBs, consisting of a large number of components with parallel alignment, defect-free structures, continuous lengths and uniform initial strains, exhibit a tensile strength of 80 GPa (corresponding to an engineering tensile strength of 43 GPa), which is far higher than that of any other strong fibre.

Structure and Characterization of Vertically Aligned Single-Walled Carbon Nanotube Bundles

DOE PAGES

Márquez, Francisco; López, Vicente; Morant, Carmen; ...

2010-01-01

Arrmore » ays of vertically aligned single-walled carbon nanotube bundles, SWCNTs, have been synthesized by simple alcohol catalytic chemical vapor deposition process, carried out at 800 ° C . The formed SWCNTs are organized in small groups perpendicularly aligned and attached to the substrate. These small bundles show a constant diameter of ca. 30 nm and are formed by the adhesion of no more than twenty individual SWCNTs perfectly aligned along their length.« less

Highly aligned vertical GaN nanowires using submonolayer metal catalysts

DOEpatents

Wang, George T [Albuquerque, NM; Li, Qiming [Albuquerque, NM; Creighton, J Randall [Albuquerque, NM

2010-06-29

A method for forming vertically oriented, crystallographically aligned nanowires (nanocolumns) using monolayer or submonolayer quantities of metal atoms to form uniformly sized metal islands that serve as catalysts for MOCVD growth of Group III nitride nanowires.

Quasi-Ballistic Carbon Nanotube Array Transistors with Current Density Exceeding Si and GaAs

DTIC Science & Technology

2016-09-02

performance of surfactant- encapsulated and conjugated polymer –wrapped CNTs in aligned arrays prepared by dielectrophoresis (20) and shear-casting (21); how... conjugated polymer poly[(9,9-dioctylfluorenyl- 2,7-diyl)-alt-co-(6,60-(2,20-bipyridine))] (PFO-BPy) in toluene to se- lectively wrap the semiconducting...Malenfant, J. Humes, J. Kroeger, A hybrid enrichment process combining conjugated polymer extraction and silica gel adsorption for high purity

Laser processing for manufacturing nanocarbon materials

NASA Astrophysics Data System (ADS)

Van, Hai Hoang

CNTs have been considered as the excellent candidate to revolutionize a broad range of applications. There have been many method developed to manipulate the chemistry and the structure of CNTs. Laser with non-contact treatment capability exhibits many processing advantages, including solid-state treatment, extremely fast processing rate, and high processing resolution. In addition, the outstanding monochromatic, coherent, and directional beam generates the powerful energy absorption and the resultant extreme processing conditions. In my research, a unique laser scanning method was developed to process CNTs, controlling the oxidation and the graphitization. The achieved controllability of this method was applied to address the important issues of the current CNT processing methods for three applications. The controllable oxidation of CNTs by laser scanning method was applied to cut CNT films to produce high-performance cathodes for FE devices. The production method includes two important self-developed techniques to produce the cold cathodes: the production of highly oriented and uniformly distributed CNT sheets and the precise laser trimming process. Laser cutting is the unique method to produce the cathodes with remarkable features, including ultrathin freestanding structure (~200 nm), greatly high aspect ratio, hybrid CNT-GNR emitter arrays, even emitter separation, and directional emitter alignment. This unique cathode structure was unachievable by other methods. The developed FE devices successfully solved the screening effect issue encounter by current FE devices. The laser-control oxidation method was further developed to sequentially remove graphitic walls of CNTs. The laser oxidation process was directed to occur along the CNT axes by the laser scanning direction. Additionally, the oxidation was further assisted by the curvature stress and the thermal expansion of the graphitic nanotubes, ultimately opening (namely unzipping) the tubular structure to produce GNRs. Therefore the developed laser scanning method optimally exploited the thermal laser-CNT interaction, successfully transforming CNTs into 2D GNRs. The solid-state laser unzipping process effectively addressed the issues of contamination and scalability encountered by the current unzipping methods. Additionally, the produced GNRs were uniquely featured with the freestanding structure and the smooth surfaces. If the scanning process was performed in an inert environment without the appearance of oxygen, the oxidation of CNTs would not happen. Instead, the greatly mobile carbon atoms of the heated CNTs would reorganize the crystal structure, inducing the graphitization process to improve the crystallinity. Many observations showing the structural improvement of CNTs under laser irradiation has been reported, confirming the capability of laser to heal graphitic defects. Laser methods were more time-efficient and energy-efficient than other annealing methods because laser can quickly heat CNTs to generate graphitization in less than one second. This subsecond heating process of laser irradiation was more effective than other heating methods because it avoided the undesired coalescence of CNTs. In my research, the laser scanning method was applied to generate the graphitization, healing the structural defects of CNTs. Different from the reported laser methods, the laser scanning directed the locally annealed areas to move along the CNT axes, migrating and coalescencing the graphitic defects to achieve better healing results. The critical information describing the CNT structural transformation caused by the moving laser irradiation was explored from the successful applications of the developed laser method. This knowledge inspires an important method to modifiy the general graphitic structure for important applications, such as carbon fiber production, CNT self-assembly process and CNT welding. This method will be effective, facile, versatile, and adaptable for laboratory and industrial facilities.

The effects of window shape and reticle presence on performance in a vertical alignment task

NASA Technical Reports Server (NTRS)

Rosenberg, Erika L.; Haines, Richard F.; Jordan, Kevin

1989-01-01

This study was conducted to evaluate the effect of selected interior work-station orientational cuing upon the ability to align a target image with local vertical in the frontal plane. Angular error from gravitational vertical in an alignment task was measured for 20 observers viewing through two window shapes (square, round), two initial orientations of a computer-generated space shuttle image, and the presence or absence of a stabilized optical alignment reticle. In terms of overall accuracy, it was found that observer error was significantly smaller for the square window and reticle-present conditions than for the round window and reticle-absent conditions. Response bias data reflected an overall tendency to undershoot and greater variability of response in the round window/no reticle condition. These results suggest that environmental cuing information, such as that provided by square window frames and alignment reticles, may aid in subjective orientation and increase accuracy of response in a Space Station proximity operations alignment task.

Large-scale fabrication of vertically aligned ZnO nanowire arrays

DOEpatents

Wang, Zhong Lin; Hu, Youfan; Zhang, Yan; Xu, Chen; Zhu, Guang

2014-09-09

A generator includes a substrate, a first electrode layer, a dense plurality of vertically-aligned piezoelectric elongated nanostructures, an insulating layer and a second electrode layer. The substrate has a top surface and the first electrode layer is disposed on the top surface of the substrate. The dense plurality of vertically-aligned piezoelectric elongated nanostructures extends from the first electrode layer. Each of the nanostructures has a top end. The insulating layer is disposed on the top ends of the nanostructures. The second electrode layer is disposed on the non-conductive layer and is spaced apart from the nanostructures.

Direction of balance and perception of the upright are perceptually dissociable

PubMed Central

Panic, Alexander Sacha; DiZio, Paul; Lackner, James R.

2015-01-01

We examined whether the direction of balance rather than an otolith reference determines the perceived upright. Participants seated in a device that rotated around the roll axis used a joystick to control its motion. The direction of balance of the device, the location where it would not be accelerated to either side, could be offset from the gravitational vertical, a technique introduced by Riccio, Martin, and Stoffregen (J Exp Psychol Hum Percept Perform 18: 624–644, 1992). Participants used the joystick to align themselves in different trials with the gravitational vertical, the direction of balance, the upright, or the direction that minimized oscillations. They pressed the joystick trigger whenever they thought they were at the instructed orientation. Achieved angles for the “align with gravity” and “align with the upright” conditions were not different from each other and were significantly displaced past the gravitational vertical opposite from the direction of balance. Mean indicated angles for align with gravity and align with the upright coincided with the gravitational vertical. Both mean achieved and indicated angles for the “minimize oscillations” and “align with the direction of balance” conditions were significantly deviated toward the gravitational vertical. Three control experiments requiring self-settings to instructed orientations only, perceptual judgments only, and perceptual judgments during passive exposure to dynamic roll profiles confirmed that perception of the upright is determined by gravity, not by the direction of balance. PMID:25761954

Synthesis and characterization of carbon nanotube from coconut shells activated carbon

NASA Astrophysics Data System (ADS)

Melati, A.; Hidayati, E.

2016-03-01

Carbon nanotubes (CNTs) have been explored in almost every single cancer treatment modality, including drug delivery, lymphatic targeted chemotherapy, photodynamic therapy, and gene therapy. They are considered as one of the most promising nanomaterial with the capability of both detecting the cancerous cells and delivering drugs or small therapeutic molecules to the cells. CNTs have unique physical and chemical properties such as high aspect ratio, ultralight weight, high mechanical strength, high electrical conductivity, and high thermal conductivity. Coconut Shell was researched as active carbon source on 500 - 600°C. These activated carbon was synthesized becomes carbon nanotube and have been proposed as a promising tool for detecting the expression of indicative biological molecules at early stage of cancer. Clinically, biomarkers cancer can be detected by CNT Biosensor. We are using pyrolysis methods combined with CVD process or Wet Chemical Process on 600°C. Our team has successfully obtained high purity, and aligned MWCNT (Multi Wall Nanotube) bundles on synthesis CNT based on coconut shells raw materials. CNTs can be used to cross the mammalian cell membrane by endocytosis or other mechanisms. SEM characterization of these materials have 179 nm bundles on phase 83° and their materials compound known by using FTIR characterization.

Laser-etch patterning of metal oxide coated carbon nanotube 3D architectures.

PubMed

Aksu, Cemile; Ingram, Wade; Bradford, Philip D; Jur, Jesse S

2018-08-17

This paper describes a way to fabricate novel hybrid low density nanostructures containing both carbon nanotubes (CNTs) and ceramic nanotubes. Using atomic layer deposition, a thin film of aluminum oxide was conformally deposited on aligned multiwall CNT foams in which the CNTs make porous, three-dimensional interconnected networks. A CO 2 laser was used to etch pure alumina nanotube structures by burning out the underlying CNT substrate in discrete locations via the printed laser pattern. Structural and morphological transitions during the calcination process of aluminum oxide coated CNTs were investigated through in situ transmission electron microscopy and high-resolution scanning electron microscopy. Laser parameters were optimized to etch the CNT away (i.e. etching speed, power and focal length) while minimizing damage to the alumina nanotubes due to overheating. This study opens a new route for fabricating very low density three dimensionally patterned materials with areas of dissimilar materials and properties. To demonstrate the attributes of these structures, the etched areas were used toward anisotropic microfluidic liquid flow. The demonstration used the full thickness of the material to make complex pathways for the liquid flow in the structure. Through tuning of processing conditions, the alumina nanotube (etched) regions became hydrophilic while the bulk material remained hydrophobic and electrically conductive.

Cl-Assisted Large Scale Synthesis of Cm-Scale Buckypapers of Fe₃C-Filled Carbon Nanotubes with Pseudo-Capacitor Properties: The Key Role of SBA-16 Catalyst Support as Synthesis Promoter.

PubMed

Boi, Filippo S; He, Yi; Wen, Jiqiu; Wang, Shanling; Yan, Kai; Zhang, Jingdong; Medranda, Daniel; Borowiec, Joanna; Corrias, Anna

2017-10-23

We show a novel chemical vapour deposition (CVD) approach, in which the large-scale fabrication of ferromagnetically-filled cm-scale buckypapers is achieved through the deposition of a mesoporous supported catalyst (SBA-16) on a silicon substrate. We demonstrate that SBA-16 has the crucial role of promoting the growth of carbon nanotubes (CNTs) on a horizontal plane with random orientation rather than in a vertical direction, therefore allowing a facile fabrication of cm-scale CNTs buckypapers free from the onion-crust by-product observed on the buckypaper-surface in previous reports. The morphology and composition of the obtained CNTs-buckypapers are analyzed in detail by scanning electron microscopy (SEM), Energy Dispersive X-ray (EDX), transmission electron microscopy (TEM), high resolution TEM (HRTEM), and thermogravimetric analysis (TGA), while structural analysis is performed by Rietveld Refinement of XRD data. The room temperature magnetic properties of the produced buckypapers are also investigated and reveal the presence of a high coercivity of 650 Oe. Additionally, the electrochemical performances of these buckypapers are demonstrated and reveal a behavior that is compatible with that of a pseudo-capacitor (resistive-capacitor) with better performances than those presented in other previously studied layered-buckypapers of Fe-filled CNTs, obtained by pyrolysis of dichlorobenzene-ferrocene mixtures. These measurements indicate that these materials show promise for applications in energy storage systems as flexible electrodes.

Preparation of the spacer for narrow electrode gap configuration in ionization-based gas sensor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saheed, Mohamed Shuaib Mohamed; Mohamed, Norani Muti; Burhanudin, Zainal Arif

2012-09-26

Carbon nanotubes (CNTs) have started to be developed as the sensing element for ionization-based gas sensors due to the demand for improved sensitivity, selectivity, stability and other sensing properties beyond what can be offered by the conventional ones. Although these limitations have been overcome, the problems still remain with the conventional ionization-based gas sensors in that they are bulky and operating with large breakdown voltage and high temperature. Recent studies have shown that the breakdown voltage can be reduced by using nanostructured electrodes and narrow electrode gap. Nanostructured electrode in the form of aligned CNTs array with evenly distributed nanotipsmore » can enhance the linear electric field significantly. The later is attributed to the shorter conductivity path through narrow electrode gap. The paper presents the study on the design consideration in order to realize ionization based gas sensor using aligned carbon nanotubes array in an optimum sensor configuration with narrow electrode gap. Several deposition techniques were studied to deposit the spacer, the key component that can control the electrode gap. Plasma spray deposition, electron beam deposition and dry oxidation method were employed to obtain minimum film thickness around 32 {mu}m. For plasma spray method, sand blasting process is required in order to produce rough surface for strong bonding of the deposited film onto the surface. Film thickness, typically about 39 {mu}m can be obtained. For the electron beam deposition and dry oxidation, the film thickness is in the range of nanometers and thus unsuitable to produce the spacer. The deposited multilayer film consisting of copper, alumina and ferum on which CNTs array will be grown was found to be removed during the etching process. This is attributed to the high etching rate on the thin film which can be prevented by reducing the rate and having a thicker conductive copper film.« less

Vertically Aligned Carbon Nanotubes at Different Temperatures by Spray Pyrolysis Techniques

NASA Astrophysics Data System (ADS)

Afre, Rakesh A.; Soga, T.; Jimbo, T.; Kumar, Mukul; Ando, Y.; Sharon, M.

Vertically aligned arrays of multi-walled carbon nanotubes (VACNTs) were grown by spray pyrolysis of turpentine oil and ferrocene mixture at temperatures higher than 700°C. Using this simple method, we report the successful growth of vertically aligned nanotubes of ~300μm length and diameter in the range of ?20-80nm on Si(100) substrate. The ferrocene acts as an in situ Fe catalyst precursor, forming the nano-sized metallic iron particles for formation of VACNTs on the Si substrate. The morphological characteristics of VACNTs are confirmed by SEM, TEM and Raman spectroscopy and growth mechanism is discussed in short.

Biosensors and Biofuel Cells based on Vertically Aligned Carbon Nanotubes for Integrated Energy Sensing, Generation, and Storage (SGS) Systems

NASA Astrophysics Data System (ADS)

Pandey, Archana; Prasad, Abhishek; Khin Yap, Yoke

2010-03-01

Diabetes is a growing health issue in the nation. Thus in-situ glucose sensors that can monitor the glucose level in our body are in high demand. Furthermore, it will be exciting if the excessive blood sugar can be converted into usable energy, and be stored in miniature batteries for applications. This will be the basis for an integrated energy sensing, generation, and storage (SGS) system in the future. Here we report the use of functionalized carbon nanotubes arrays as the glucose sensors as well as fuel cells that can convert glucose into energy. In principle, these devices can be integrated to detect excessive blood glucose and then convert the glucose into energy. They are also inline with our efforts on miniature 3D microbatteries using CNTs [1]. All these devices will be the basis for future SGS systems. Details of these results will be discussed in the meeting. [1] Wang et al., in 206^th Meeting of the Electrochemical Society, October 3-8, Honolulu, Hawaii (2004), Symposium Q1, abstract 1492. Y. K. Yap acknowledges supports from DARPA (DAAD17-03-C-0115), USDA (2007-35603-17740), and the Multi-Scale Technologies Institute (MuSTI) at MTU.

Flexible and Lightweight Pressure Sensor Based on Carbon Nanotube/Thermoplastic Polyurethane-Aligned Conductive Foam with Superior Compressibility and Stability.

PubMed

Huang, Wenju; Dai, Kun; Zhai, Yue; Liu, Hu; Zhan, Pengfei; Gao, Jiachen; Zheng, Guoqiang; Liu, Chuntai; Shen, Changyu

2017-12-06

Flexible and lightweight carbon nanotube (CNT)/thermoplastic polyurethane (TPU) conductive foam with a novel aligned porous structure was fabricated. The density of the aligned porous material was as low as 0.123 g·cm -3 . Homogeneous dispersion of CNTs was achieved through the skeleton of the foam, and an ultralow percolation threshold of 0.0023 vol % was obtained. Compared with the disordered foam, mechanical properties of the aligned foam were enhanced and the piezoresistive stability of the flexible foam was improved significantly. The compression strength of the aligned TPU foam increases by 30.7% at the strain of 50%, and the stress of the aligned foam is 22 times that of the disordered foam at the strain of 90%. Importantly, the resistance variation of the aligned foam shows a fascinating linear characteristic under the applied strain until 77%, which would benefit the application of the foam as a desired pressure sensor. During multiple cyclic compression-release measurements, the aligned conductive CNT/TPU foam represents excellent reversibility and reproducibility in terms of resistance. This nice capability benefits from the aligned porous structure composed of ladderlike cells along the orientation direction. Simultaneously, the human motion detections, such as walk, jump, squat, etc. were demonstrated by using our flexible pressure sensor. Because of the lightweight, flexibility, high compressibility, excellent reversibility, and reproducibility of the conductive aligned foam, the present study is capable of providing new insights into the fabrication of a high-performance pressure sensor.

Proton radiation effects on the optical properties of vertically aligned carbon nanotubes

NASA Astrophysics Data System (ADS)

Kuhnhenn, J.; Khavrus, V.; Leonhardt, A.; Eversheim, D.; Noll, C.; Hinderlich, S.; Dahl, A.

2017-11-01

This paper discusses proton-induced radiation effects in vertically aligned carbon nanotubes (VA-CNT). VACNTs exhibit extremely low optical reflectivity which makes them interesting candidates for use in spacecraft stray light suppression. Investigating their behavior in space environment is a precondition for the implementation on a satellite.

Vertically aligned carbon nanotubes as anode and air-cathode in single chamber microbial fuel cells

NASA Astrophysics Data System (ADS)

Amade, R.; Moreno, H. A.; Hussain, S.; Vila-Costa, M.; Bertran, E.

2016-10-01

Electrode optimization in microbial fuel cells is a key issue to improve the power output and cell performance. Vertically aligned carbon nanotubes (VACNTs) grown on low cost stainless-steel mesh present an attractive approach to increase the cell performance while avoiding the use of expensive Pt-based materials. In comparison with non-aligned carbon nanotubes (NACNTs), VACNTs increase the oxygen reduction reaction taking place at the cathode by a factor of two. In addition, vertical alignment also increases the power density up to 2.5 times with respect to NACNTs. VACNTs grown at the anode can further improve the cell performance by increasing the electrode surface area and thus the electron transfer between bacteria and the electrode. The maximum power density obtained using VACNTs was 14 mW/m2 and 160 mV output voltage.

Stacked multilayers of alternating reduced graphene oxide and carbon nanotubes for planar supercapacitors

NASA Astrophysics Data System (ADS)

Moon, Geon Dae; Joo, Ji Bong; Yin, Yadong

2013-11-01

A simple layer-by-layer approach has been developed for constructing 2D planar supercapacitors of multi-stacked reduced graphene oxide and carbon nanotubes. This sandwiched 2D architecture enables the full utilization of the maximum active surface area of rGO nanosheets by using a CNT layer as a porous physical spacer to enhance the permeation of a gel electrolyte inside the structure and reduce the agglomeration of rGO nanosheets along the vertical direction. As a result, the stacked multilayers of rGO and CNTs are capable of offering higher output voltage and current production.A simple layer-by-layer approach has been developed for constructing 2D planar supercapacitors of multi-stacked reduced graphene oxide and carbon nanotubes. This sandwiched 2D architecture enables the full utilization of the maximum active surface area of rGO nanosheets by using a CNT layer as a porous physical spacer to enhance the permeation of a gel electrolyte inside the structure and reduce the agglomeration of rGO nanosheets along the vertical direction. As a result, the stacked multilayers of rGO and CNTs are capable of offering higher output voltage and current production. Electronic supplementary information (ESI) available: Experimental details, SEM and TEM images and additional electrochemical data. See DOI: 10.1039/c3nr04339h

Highly anisotropic magneto-transport and field orientation dependent oscillations in aligned carbon nanotube/epoxy composites

NASA Astrophysics Data System (ADS)

Wells, Brian; Kumar, Raj; Reynolds, C. Lewis; Peters, Kara; Bradford, Philip D.

2017-12-01

Carbon nanotubes (CNTs) have been widely investigated as additive materials for composites with potential applications in electronic devices due to their extremely large electrical conductivity and current density. Here, highly aligned CNT composite films were created using a sequential layering fabrication technique. The degree of CNT alignment leads to anisotropic resistance values which varies >400× in orthogonal directions. Similarly, the magnetoresistance (MR) of the CNT composite differs depending upon the relative direction of current and the applied magnetic field. A suppression of negative to positive MR crossover was also observed. More importantly, an overall positive magnetoresistance behavior with localized +/- oscillations was discovered at low fields which persists up to room temperature when the current (I) and in-plane magnetic field (B) were parallel to the axis of CNT (B∥I∥CNT), which is consistent with Aharonov-Bohm oscillations in our CNT/epoxy composites. When the current, applied magnetic field, and nanotube axis are aligned, the in-plane MR is positive instead of negative as observed for all other field, current, and tube orientations. Here, we provide in-depth analysis of the conduction mechanism and anisotropy in the magneto-transport properties of these aligned CNT-epoxy composites.

Controlled growth of aligned carbon nanotube using pulsed glow barrier discharge

NASA Astrophysics Data System (ADS)

Nozaki, Tomohiro; Kimura, Yoshihito; Okazaki, Ken

2002-10-01

We first achieved a catalytic growth of aligned carbon nanotube (CNT) using atmospheric pressure pulsed glow barrier discharge combined with DC bias (1000 V). Aligned CNT can grow with the directional electric field, and this is a big challenge in barrier discharges since dielectric barrier does not allow DC bias and forces to use AC voltage to maintain stable plasma conditions. To overcome this, we developed a power source generating Gaussian-shape pulses at 20 kpps with 4% duty, and DC bias was applied to the GND electrode where Ni-, Fe-coated substrate existed. With positive pulse, i.e. substrate was the cathode, random growth of CNT was observed at about 10^9 cm-2. Growth rate significantly reduced when applied negative pulse; Negative glow formation near substrate is essential for sufficient supply of radical species to the catalyst. If -DC was biased, aligned CNT with 20 nm was synthesized because negative bias enhanced negative glow formation. Interestingly, 2 to 3 CNTs stuck each other with +DC bias, resulting in 50-70 nm and non-aligned CNT. Atmospheric pressure glow barrier discharges can be highly controlled and be a potential alternative to vacuum plasmas for CVD, micro-scale, nano-scale fabrication.

Effects of alignment layer thickness on the pretilt angle of liquid crystals

NASA Astrophysics Data System (ADS)

Son, Jong-Ho; Zin, Wang-Cheol

2010-12-01

Mixture solutions of vertical- and planar-aligning polyimide precursors were coated on bare glass. The concentrations of the solutions were varied to control the thicknesses of the films. The resulting blend films were baked to induce imidization and then rubbed. The thicknesses (t) of the blend film and of the pure vertical-alignment film affected their surface energies; the pretilt angle can be fully controlled in the range 5.5°≤Θ0≤87° by adjusting t. The surface energy of pure planar-alignment layers was independent of t.

Polymer Composite Using Aligned Carbon Nanotubes for Efficient Heat Transfer

DTIC Science & Technology

2012-01-17

ultrasonic sprayer system (Figs. 2 & 3). We will thermolyze ferrocene -benzylamine solutions at 850 °C under an Ar atmosphere. The material produced...C (center pannel). 1.4 Production of COxHy nanotubes We will use the same ultrasonic sprayer but in this case with solutions of ferrocene (FeCp2...more reactive when compared to standard CNTs. For example, when adding 2.5% by wt. of ethanol in a ferrocene -toluene solution containing 5% by wt. of

Electro-optic characteristics of 4-domain vertical alignment nematic liquid crystal display with interdigital electrode

NASA Astrophysics Data System (ADS)

Hong, S. H.; Jeong, Y. H.; Kim, H. Y.; Cho, H. M.; Lee, W. G.; Lee, S. H.

2000-06-01

We have fabricated a vertically aligned 4-domain nematic liquid crystal display cell with thin film transistor. Unlike the conventional method constructing 4-domain, i.e., protrusion and surrounding electrode which needs additional processes, in this study the pixel design forming 4-domain with interdigital electrodes is suggested. In the device, one pixel is divided into two parts. One part has a horizontal electric field in the vertical direction and the other part has a horizontal one in the horizontal direction. Such fields in the horizontal and vertical direction drive the liquid crystal director to tilt down in four directions. In this article, the electro-optic characteristics of cells with 2 and 4 domain have been studied. The device with 4 domain shows faster response time than normal twisted-nematic and in-plane switching cells, wide viewing angle with optical compensation film, and more stable color characteristics than 2-domain vertical alignment cell with similar structure.

Biodiesel and Integrated STEM: Vertical Alignment of High School Biology/Biochemistry and Chemistry

ERIC Educational Resources Information Center

Burrows, Andrea C.; Breiner, Jonathan M.; Keiner, Jennifer; Behm, Chris

2014-01-01

This article explores the vertical alignment of two high school classes, biology and chemistry, around the core concept of biodiesel fuel production. High school teachers and university faculty members investigated biodiesel as it relates to societal impact through a National Science Foundation Research Experience for Teachers. Using an action…

Fast preparation of hydroxyapatite/superhydrophilic vertically aligned multiwalled carbon nanotube composites for bioactive application.

PubMed

Lobo, Anderson O; Corat, Marcus A F; Ramos, Sandra C; Matsushima, Jorge T; Granato, Alessandro E C; Pacheco-Soares, Cristina; Corat, Evaldo J

2010-12-07

A method for the electrodeposition of hydroxyapatite films on superhydrophilic vertically aligned multiwalled carbon nanotubes is presented. The formation of a thin homogeneous film with high crystallinity was observed without any thermal treatment and with bioactivity properties that accelerate the in vitro biomineralization process and osteoblast adhesion.

Laser-assisted simultaneous transfer and patterning of vertically aligned carbon nanotube arrays on polymer substrates for flexible devices.

PubMed

In, Jung Bin; Lee, Daeho; Fornasiero, Francesco; Noy, Aleksandr; Grigoropoulos, Costas P

2012-09-25

We demonstrate a laser-assisted dry transfer technique for assembling patterns of vertically aligned carbon nanotube arrays on a flexible polymeric substrate. A laser beam is applied to the interface of a nanotube array and a polycarbonate sheet in contact with one another. The absorbed laser heat promotes nanotube adhesion to the polymer in the irradiated regions and enables selective pattern transfer. A combination of the thermal transfer mechanism with rapid direct writing capability of focused laser beam irradiation allows us to achieve simultaneous material transfer and direct micropatterning in a single processing step. Furthermore, we demonstrate that malleability of the nanotube arrays transferred onto a flexible substrate enables post-transfer tailoring of electric conductance by collapsing the aligned nanotubes in different directions. This work suggests that the laser-assisted transfer technique provides an efficient route to using vertically aligned nanotubes as conductive elements in flexible device applications.

Transition of vertically aligned liquid crystal driven by fan-shaped electric field

NASA Astrophysics Data System (ADS)

Tsung, J. W.; Ting, T. L.; Chen, C. Y.; Liang, W. L.; Lai, C. W.; Lin, T. H.; Hsu, W. H.

2017-09-01

Interdigital electrodes are implemented in many commercial and novel liquid crystal devices to align molecules. Although many empirical principles and patents apply to electrode design, only a few numerical simulations of alignment have been conducted. Why and how the molecules align in an ordered manner has never been adequately explained. Hence, this investigation addresses the Fréedericksz transition of vertically aligned liquid crystal that is driven by fishbone electrodes, and thereafter identifies the mechanism of liquid crystal alignment. Theoretical calculations suggest that the periodic deformation that is caused by the fan-shaped fringe field minimizes the free energy in the liquid crystal cell, and the optimal alignment can be obtained when the cell parameters satisfy the relation p /2 d =√{k11/k33 } , where p is the spatial period of the strips of the electrode; d denotes the cell gap; and k11 and k33 are the splay and bend elastic constants of the liquid crystal, respectively. Polymer-stabilized vertical alignment test cells with various p values and spacings between the electrodes were fabricated, and the process of liquid crystal alignment was observed under an optical microscope. The degree of alignment was evaluated by measuring the transmittance of the test cell. The experimental results were consistent with the theoretical predictions. The principle of design, p /2 d =√{k11/k33 } , greatly improves the uniformity and stability of the aligned liquid crystal. The methods that are presented here can be further applied to cholesteric liquid crystal and other self-assembled soft materials.

Installation and assembly device and method of using

DOEpatents

Kolsun, George J.

1997-01-01

An installation and assembly device for aligning a first member such as a pump impeller with a second member such as an inlet nozzle of an impeller pump. The installation and assembly device includes a sleeve slideable within the inlet nozzle and a vertical positioning assembly which has a contact member that is extendable out away from the sleeve so as to vertically position the sleeve on a shoulder of the inlet nozzle and to present an upper contact surface spaced a certain distance from the shoulder to provide the desired vertical spacing with respect to the impeller contacting the upper contact surface. The vertical positioning assembly is retractable so as to allow for removal of the sleeve through the nozzle when installation and assembly are completed. The alignment device also includes a radial alignment assembly supported by the sleeve and adjustable to an expanded state for contacting and spacing the interior surface of the impeller a certain distance from the sleeve and hence a certain distance from the inlet nozzle. The radial alignment device being adjustable from a retracted removal state to an expanded state and also being adjustable to fine tune the spacing of the impeller from the sleeve. The radial alignment device also preferably includes members that can be used to releasably secure the sleeve to the impeller.

Growth control of carbon nanotubes using by anodic aluminum oxide nano templates.

PubMed

Park, Yong Seob; Choi, Won Seek; Yi, Junsin; Lee, Jaehyeong

2014-05-01

Anodic Aluminum Oxide (AAO) template prepared in acid electrolyte possess regular and highly anisotropic porous structure with pore diameter range from five to several hundred nanometers, and with a density of pores ranging from 10(9) to 10(11) cm(-2). AAO can be used as microfilters and templates for the growth of CNTs and metal or semiconductor nanowires. Varying anodizing conditions such as temperature, electrolyte, applied voltage, anodizing and widening time, one can control the diameter, the length, and the density of pores. In this work, we deposited Al thin film by radio frequency magnetron sputtering method to fabricate AAO nano template and synthesized multi-well carbon nanotubes on a glass substrate by microwave plasma-enhanced chemical vapor deposition (MPECVD). AAO nano-porous templates with various pore sizes and depths were introduced to control the dimension and density of CNT arrays. The AAO nano template was synthesize on glass by two-step anodization technique. The average diameter and interpore distance of AAO nano template are about 65 nm and 82 nm. The pore density and AAO nano template thickness are about 2.1 x 10(10) pores/cm2 and 1 microm, respectively. Aligned CNTs on the AAO nano template were synthesized by MPECVD at 650 degrees C with the Ni catalyst layer. The length and diameter of CNTs were grown 2 microm and 50 nm, respectively.

Nanostructured pillars based on vertically aligned carbon nanotubes as the stationary phase in micro-CEC.

PubMed

Wu, Ren-Guei; Yang, Chung-Shi; Wang, Pen-Cheng; Tseng, Fan-Gang

2009-06-01

We present a micro-CEC chip carrying out a highly efficient separation of dsDNA fragments through vertically aligned multi-wall carbon nanotubes (MWCNTs) in a microchannel. The vertically aligned MWCNTs were grown directly in the microchannel to form straight nanopillar arrays as ordered and directional chromatographic supports. 1-Pyrenedodecanoic acid was employed for the surface modification of the MWCNTs' stationary phase to adsorb analytes by hydrophobic interactions. This device was used for separating dsDNA fragments of three different lengths (254, 360, and 572 bp), and fluorescence detection was employed to verify the electrokinetic transport in the MWCNT array. The micro-CEC separation of the three compounds was achieved in less than 300 s at a field strength of 66 V/cm due to superior laminar flow patterns and a lower flow resistance resulting from the vertically aligned MWCNTs being used as the stationary phase medium. In addition, a fivefold reduction of band broadening was obtained when the analyte was separated by the chromatographic MWCNT array channel instead of the CE channel. From all of the results, we suggest that an in situ grown and directional MWCNT array can potentially be useful for preparing more diversified forms of stationary phases for vertically efficient chip-based electrochromatography.

Highly uniform and vertically aligned SnO2 nanochannel arrays for photovoltaic applications

NASA Astrophysics Data System (ADS)

Kim, Jae-Yup; Kang, Jin Soo; Shin, Junyoung; Kim, Jin; Han, Seung-Joo; Park, Jongwoo; Min, Yo-Sep; Ko, Min Jae; Sung, Yung-Eun

2015-04-01

Nanostructured electrodes with vertical alignment have been considered ideal structures for electron transport and interfacial contact with redox electrolytes in photovoltaic devices. Here, we report large-scale vertically aligned SnO2 nanochannel arrays with uniform structures, without lateral cracks fabricated by a modified anodic oxidation process. In the modified process, ultrasonication is utilized to avoid formation of partial compact layers and lateral cracks in the SnO2 nanochannel arrays. Building on this breakthrough, we first demonstrate the photovoltaic application of these vertically aligned SnO2 nanochannel arrays. These vertically aligned arrays were directly and successfully applied in quasi-solid state dye-sensitized solar cells (DSSCs) as photoanodes, yielding reasonable conversion efficiency under back-side illumination. In addition, a significantly short process time (330 s) for achieving the optimal thickness (7.0 μm) and direct utilization of the anodized electrodes enable a simple, rapid and low-cost fabrication process. Furthermore, a TiO2 shell layer was coated on the SnO2 nanochannel arrays by the atomic layer deposition (ALD) process for enhancement of dye-loading and prolonging the electron lifetime in the DSSC. Owing to the presence of the ALD TiO2 layer, the short-circuit photocurrent density (Jsc) and conversion efficiency were increased by 20% and 19%, respectively, compared to those of the DSSC without the ALD TiO2 layer. This study provides valuable insight into the development of efficient SnO2-based photoanodes for photovoltaic application by a simple and rapid fabrication process.Nanostructured electrodes with vertical alignment have been considered ideal structures for electron transport and interfacial contact with redox electrolytes in photovoltaic devices. Here, we report large-scale vertically aligned SnO2 nanochannel arrays with uniform structures, without lateral cracks fabricated by a modified anodic oxidation process. In the modified process, ultrasonication is utilized to avoid formation of partial compact layers and lateral cracks in the SnO2 nanochannel arrays. Building on this breakthrough, we first demonstrate the photovoltaic application of these vertically aligned SnO2 nanochannel arrays. These vertically aligned arrays were directly and successfully applied in quasi-solid state dye-sensitized solar cells (DSSCs) as photoanodes, yielding reasonable conversion efficiency under back-side illumination. In addition, a significantly short process time (330 s) for achieving the optimal thickness (7.0 μm) and direct utilization of the anodized electrodes enable a simple, rapid and low-cost fabrication process. Furthermore, a TiO2 shell layer was coated on the SnO2 nanochannel arrays by the atomic layer deposition (ALD) process for enhancement of dye-loading and prolonging the electron lifetime in the DSSC. Owing to the presence of the ALD TiO2 layer, the short-circuit photocurrent density (Jsc) and conversion efficiency were increased by 20% and 19%, respectively, compared to those of the DSSC without the ALD TiO2 layer. This study provides valuable insight into the development of efficient SnO2-based photoanodes for photovoltaic application by a simple and rapid fabrication process. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr00202h

Dynamic mechanical analysis and high strain-rate energy absorption characteristics of vertically aligned carbon nanotube reinforced woven fiber-glass composites

USDA-ARS?s Scientific Manuscript database

The dynamic mechanical behavior and energy absorption characteristics of nano-enhanced functionally graded composites, consisting of 3 layers of vertically aligned carbon nanotube (VACNT) forests grown on woven fiber-glass (FG) layer and embedded within 10 layers of woven FG, with polyester (PE) and...

A black body absorber from vertically aligned single-walled carbon nanotubes

PubMed Central

Mizuno, Kohei; Ishii, Juntaro; Kishida, Hideo; Hayamizu, Yuhei; Yasuda, Satoshi; Futaba, Don N.; Yumura, Motoo; Hata, Kenji

2009-01-01

Among all known materials, we found that a forest of vertically aligned single-walled carbon nanotubes behaves most similarly to a black body, a theoretical material that absorbs all incident light. A requirement for an object to behave as a black body is to perfectly absorb light of all wavelengths. This important feature has not been observed for real materials because materials intrinsically have specific absorption bands because of their structure and composition. We found a material that can absorb light almost perfectly across a very wide spectral range (0.2–200 μm). We attribute this black body behavior to stem from the sparseness and imperfect alignment of the vertical single-walled carbon nanotubes. PMID:19339498

Designing an optimum pulsed magnetic field by a resistance/self-inductance/capacitance discharge system and alignment of carbon nanotubes embedded in polypyrrole matrix

NASA Astrophysics Data System (ADS)

Kazemikia, Kaveh; Bonabi, Fahimeh; Asadpoorchallo, Ali; Shokrzadeh, Majid

2015-02-01

In this work, an optimized pulsed magnetic field production apparatus is designed based on a RLC (Resistance/Self-inductance/Capacitance) discharge circuit. An algorithm for designing an optimum magnetic coil is presented. The coil is designed to work at room temperature. With a minor physical reinforcement, the magnetic flux density can be set up to 12 Tesla with 2 ms duration time. In our design process, the magnitude and the length of the magnetic pulse are the desired parameters. The magnetic field magnitude in the RLC circuit is maximized on the basis of the optimal design of the coil. The variables which are used in the optimization process are wire diameter and the number of coil layers. The coil design ensures the critically damped response of the RLC circuit. The electrical, mechanical, and thermal constraints are applied to the design process. A locus of probable magnetic flux density values versus wire diameter and coil layer is provided to locate the optimum coil parameters. Another locus of magnetic flux density values versus capacitance and initial voltage of the RLC circuit is extracted to locate the optimum circuit parameters. Finally, the application of high magnetic fields on carbon nanotube-PolyPyrrole (CNT-PPy) nano-composite is presented. Scanning probe microscopy technique is used to observe the orientation of CNTs after exposure to a magnetic field. The result shows alignment of CNTs in a 10.3 Tesla, 1.5 ms magnetic pulse.

Modeling and simulations of carbon nanotube (CNT) dispersion in water/surfactant/polymer systems

NASA Astrophysics Data System (ADS)

Uddin, Nasir Mohammad

An innovative multiscale (atomistic to mesoscale) model capable of predicting carbon nanotube (CNT) interactions and dispersion in water/surfactant/polymer systems was developed. The model was verified qualitatively with available experimental data in the literature. It can be used to computationally screen potential surfactants, solvents, polymers, and CNT with appropriate diameter and length to obtain improved CNT dispersion in aqueous medium. Thus the model would facilitate the reduction of time and cost required to produce CNT dispersed homogeneous solutions and CNT reinforced materials. CNT dispersion in any water/surfactant/polymer system depends on interactions between CNTs and surrounding molecules. Central to the study was the atomistic scale model which used the atomic structure of the surfactant, solvent, polymer, and CNT. The model was capable of predicting the CNT interactions in terms of potential of mean force (PMF) between CNTs under the influence of surrounding molecules in an aqueous solution. On the atomistic scale, molecular dynamics method was used to compute the PMF as a function of CNT separation and CNT alignment. An adaptive biasing force (ABF) method was used to speed up the calculations. Correlations were developed to determine the effective interactions between CNTs as a function of their any inter-atomic distance and orientation angle in water as well as in water/surfactant by fitting the calculated PMF data. On the mesoscale, the fitted PMF correlations were used as input in the Monte Carlo simulations to determine the degree of dispersion of CNTs in water and water/surfactant system. The distribution of CNT cluster size was determined for the CNTs dispersed in water with and without surfactant addition. The entropie and enthalpie contributions to the CNT interactions in water were determined to understand the dispersion mechanism of CNTs in water. The effects of CNT orientation, length, diameter, chirality and surfactant concentrations and structures on CNT interactions in water were investigated at room conditions. CNT interactions in polymer solution were also investigated with polyethylene oxide (PEO) polymer and water as a solvent. In all cases, the atomic arrangement of molecules was discussed in detailed. Simulations revealed that CNT orientation, length, diameter, and addition of surfactant and its structures can significantly affect CNT interactions (i.e., PMFs varied significantly) and in-turn the degree of CNT dispersion in aqueous solution. For all simulation cases, a uniform sampling was achieved by using the ABF method to calculate the governing PMF between CNTs indicating the effectiveness and convergence of the adaptive sampling scheme. The surfactant molecules were shown to adsorb at the CNT surface and contribute to weaker interactions between CNTs which resulted less CNT aggregate size at the mesoscale. Surfactant consisting with a benzene ring contributed much weaker interactions between CNTs as compared with that of without benzene ring. The increase in CNT length contributed the stronger CNT interactions where the increase in CNT diameter caused weaker CNT interactions in water. The interfacial characteristics between the CNT, surfactant and the polymer were also predicted and discussed. The model can be expanded for more solvents, surfactants, and polymers.

Nanoscale Structure-Property Relationships of Polyacrylonitrile/CNT Composites as a Function of Polymer Crystallinity and CNT Diameter.

PubMed

Gissinger, Jacob R; Pramanik, Chandrani; Newcomb, Bradley; Kumar, Satish; Heinz, Hendrik

2018-01-10

Polyacrylonitrile (PAN)/carbon nanotube (CNT) composites are used as precursors for ultrastrong and lightweight carbon fibers. However, insights into the structure at the nanoscale and the relationships to mechanical and thermal properties have remained difficult to obtain. In this study, molecular dynamics simulation with accurate potentials and available experimental data were used to describe the influence of different degrees of PAN preorientation and CNT diameter on the atomic-scale structure and properties of the composites. The inclusion of CNTs in the polymer matrix is favored for an intermediate degree of PAN orientation and small CNT diameter whereas high PAN crystallinity and larger CNT diameter disfavor CNT inclusion. The glass transition at the CNT/PAN interface involves the release of rotational degrees of freedom of the polymer backbone and increased mobility of the protruding nitrile side groups in contact with the carbon nanotubes. The glass-transition temperature of the composite increases in correlation with the amount of CNT/polymer interfacial area per unit volume, i.e., in the presence of CNTs, for higher CNT volume fraction,  and inversely with CNT diameter. The increase in glass-transition temperature upon CNT addition is larger for PAN of lower crystallinity than for PAN of higher crystallinity. Interfacial shear strengths of the composites are higher for CNTs of smaller diameter and for PAN with preorientation, in correlation with more favorable CNT inclusion energies. The lowest interfacial shear strength was observed in amorphous PAN for the same CNT diameter. PAN with ∼75% crystallinity exhibited hexagonal patterns of nitrile groups near and far from the CNT interface which could influence carbonization into regular graphitic structures. The results illustrate the feasibility of near-quantitative insights into macroscale properties of polymer/CNT composites from simulations of nanometer-scale composite domains. Guidance is most effective when key assumptions in experiment and simulation are closely aligned, such as exfoliation versus bundling of CNTs, size, type, potential defects of CNTs, and precise measures for polymer crystallinity.

Motor mechanisms of vertical fusion in individuals with superior oblique paresis.

PubMed

Mudgil, Ananth V; Walker, Mark; Steffen, Heimo; Guyton, David L; Zee, David S

2002-06-01

We wanted to determine the mechanisms of motor vertical fusion in patients with superior oblique paresis and to correlate these mechanisms with surgical outcomes. Ten patients with superior oblique paresis underwent 3-axis, bilateral, scleral search coil eye movement recordings. Eye movements associated with fusion were analyzed. Six patients had decompensated congenital superior oblique paresis and 4 had acquired superior oblique paresis. All patients with acquired superior oblique paresis relied predominantly on the vertical rectus muscles for motor fusion. Patients with congenital superior oblique paresis were less uniform in their mechanisms for motor fusion: 2 patients used predominantly the oblique muscles, 2 patients used predominantly the vertical recti, and 2 patients used predominantly the superior oblique in the hyperdeviated eye and the superior rectus in the hypodeviated eye. The last 2 patients developed the largest changes in torsional eye alignment relative to changes in vertical eye alignment and were the only patients to develop symptomatic surgical overcorrections. There are 3 different mechanisms for vertical fusion in individuals with superior oblique paresis, with the predominant mechanism being the vertical recti. A subset of patients with superior oblique paresis uses predominantly the superior oblique muscle in the hyperdeviated paretic eye and the superior rectus muscle in the fellow eye for fusion. This results in intorsion of both eyes, causing a large change in torsional alignment. The consequent cyclodisparity, in addition to the existing vertical deviation, may make fusion difficult. The differing patterns of vertical fusional vergence may have implications for surgical treatment.

Large-scale horizontally aligned ZnO microrod arrays with controlled orientation, periodic distribution as building blocks for chip-in piezo-phototronic LEDs.

PubMed

Guo, Zhen; Li, Haiwen; Zhou, Lianqun; Zhao, Dongxu; Wu, Yihui; Zhang, Zhiqiang; Zhang, Wei; Li, Chuanyu; Yao, Jia

2015-01-27

A novel method of fabricating large-scale horizontally aligned ZnO microrod arrays with controlled orientation and periodic distribution via combing technology is introduced. Horizontally aligned ZnO microrod arrays with uniform orientation and periodic distribution can be realized based on the conventional bottom-up method prepared vertically aligned ZnO microrod matrix via the combing method. When the combing parameters are changed, the orientation of horizontally aligned ZnO microrod arrays can be adjusted (θ = 90° or 45°) in a plane and a misalignment angle of the microrods (0.3° to 2.3°) with low-growth density can be obtained. To explore the potential applications based on the vertically and horizontally aligned ZnO microrods on p-GaN layer, piezo-phototronic devices such as heterojunction LEDs are built. Electroluminescence (EL) emission patterns can be adjusted for the vertically and horizontally aligned ZnO microrods/p-GaN heterojunction LEDs by applying forward bias. Moreover, the emission color from UV-blue to yellow-green can be tuned by investigating the piezoelectric properties of the materials. The EL emission mechanisms of the LEDs are discussed in terms of band diagrams of the heterojunctions and carrier recombination processes. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Self-assembled vertically aligned Au nanorod arrays for surface-enhanced Raman scattering (SERS) detection of Cannabinol

NASA Astrophysics Data System (ADS)

Milliken, Sarah; Fraser, Jeff; Poirier, Shawn; Hulse, John; Tay, Li-Lin

2018-05-01

Self-assembled multi-layered vertically aligned gold nanorod (AuNR) arrays have been fabricated by a simple preparation process that requires a balance between the particle concentration and the ionic strength of the solvent. An experimentally determined critical AuNR concentration of 2.0 nM and 50 mM NaCl produces well-ordered vertically aligned hexagonally close-packed AuNR arrays. We demonstrate surface treatment via UV Ozone cleaning of such samples to allow introduction of analyte molecules (benzenethiol and cannabinol) for effective surface enhanced Raman scattering detection. This is the first demonstration of the SERS analysis of cannabinol. This approach demonstrates a cost-effective, high-yield and simple fabrication route to SERS sensors with application in the screening for the cannabinoids.

Improvement in device performance from a mixture of a liquid crystal and photosensitive acrylic prepolymer with the photoinduced vertical alignment method

PubMed Central

Ho, Czung-Yu; Lin, Fa-Hsin; Tao, Yu-Tai; Lee, Jiunn-Yih

2011-01-01

In a multicomponent nematic liquid crystal (NLC) mixture of a liquid crystal (negative-type NLC) and a photosensitive acrylic prepolymer, photopolymerization upon UV irradiation induces the separation of the LC and photosensitive acrylic prepolymer layers, thereby leading to a vertical arrangement of LC molecules. In this study, we propose a simple vertical alignment method for LC molecules, by adding a chiral smectic A (SmA∗) liquid crystal having homeotropic texture characteristics to an NLC mixture solution. Measurements of electro-optical properties revealed that the addition of the SmA∗ LC not only strengthened the anchoring force of the copolymer alignment film surface, but also significantly enhanced the contrast ratio (∼73%), response time and grayscale switching performance of the device. PMID:27877462

Effects of cloud condensate vertical alignment on radiative transfer calculations in deep convective regions

NASA Astrophysics Data System (ADS)

Wang, Xiaocong

2017-04-01

Effects of cloud condensate vertical alignment on radiative transfer process were investigated using cloud resolving model explicit simulations, which provide a surrogate for subgrid cloud geometry. Diagnostic results showed that the decorrelation length Lcw varies in the vertical dimension, with larger Lcw occurring in convective clouds and smaller Lcw in cirrus clouds. A new parameterization of Lcw is proposed that takes into account such varying features and gives rise to improvements in simulations of cloud radiative forcing (CRF) and radiative heating, i.e., the peak of bias is respectively reduced by 8 W m- 2 for SWCF and 2 W m- 2 for LWCF in comparison with Lcw = 1 km. The role of Lcw in modulating CRFs is twofold. On the one hand, larger Lcw tends to increase the standard deviation of optical depth στ, as dense and tenuous parts of the clouds would be increasingly aligned in the vertical dimension, thereby broadening the probability distribution. On the other hand, larger στ causes a decrease in the solar albedo and thermal emissivity, as implied in their convex functions on τ. As a result, increasing (decreasing) Lcwleads to decreased (increased) CRFs, as revealed by comparisons among Lcw = 0, Lcw = 1 km andLcw = ∞. It also affects the vertical structure of radiative flux and thus influences the radiative heating. A better representation of στ in the vertical dimension yields an improved simulation of radiative heating. Although the importance of vertical alignment of cloud condensate is found to be less than that of cloud cover in regards to their impacts on CRFs, it still has enough of an effect on modulating the cloud radiative transfer process.

Assisted deposition of nano-hydroxyapatite onto exfoliated carbon nanotube oxide scaffolds.

PubMed

Zanin, H; Rosa, C M R; Eliaz, N; May, P W; Marciano, F R; Lobo, A O

2015-06-14

Electrodeposited nano-hydroxyapatite (nHAp) is more similar to biological apatite in terms of microstructure and dimension than apatites prepared by other processes. Reinforcement with carbon nanotubes (CNTs) enhances its mechanical properties and increases adhesion of osteoblasts. Here, we carefully studied nHAp deposited onto vertically aligned multi-walled CNT (VAMWCNT) scaffolds by electrodeposition and soaking in a simulated body fluid (SBF). VAMWCNTs are porous biocompatible scaffolds with nanometric porosity and exceptional mechanical and chemical properties. The VAMWCNT films were prepared on a Ti substrate by a microwave plasma chemical vapour deposition method, and then oxidized and exfoliated by oxygen plasma etching (OPE) to produce graphene oxide (GO) at the VAMWCNT tips. The attachment of oxygen functional groups was found to be crucial for nHAp nucleation during electrodeposition. A thin layer of plate-like and needle-like nHAp with high crystallinity was formed without any need for thermal treatment. This composite (henceforth referred to as nHAp-VAMWCNT-GO) served as the scaffold for in vitro biomineralization when soaked in the SBF, resulting in the formation of both carbonate-rich and carbonate-poor globular-like nHAp. Different steps in the deposition of biological apatite onto VAMWCNT-GO and during the short-term biomineralization process were analysed. Due to their unique structure and properties, such nano-bio-composites may become useful in accelerating in vivo bone regeneration processes.

Assisted deposition of nano-hydroxyapatite onto exfoliated carbon nanotube oxide scaffolds

NASA Astrophysics Data System (ADS)

Zanin, H.; Rosa, C. M. R.; Eliaz, N.; May, P. W.; Marciano, F. R.; Lobo, A. O.

2015-05-01

Electrodeposited nano-hydroxyapatite (nHAp) is more similar to biological apatite in terms of microstructure and dimension than apatites prepared by other processes. Reinforcement with carbon nanotubes (CNTs) enhances its mechanical properties and increases adhesion of osteoblasts. Here, we carefully studied nHAp deposited onto vertically aligned multi-walled CNT (VAMWCNT) scaffolds by electrodeposition and soaking in a simulated body fluid (SBF). VAMWCNTs are porous biocompatible scaffolds with nanometric porosity and exceptional mechanical and chemical properties. The VAMWCNT films were prepared on a Ti substrate by a microwave plasma chemical vapour deposition method, and then oxidized and exfoliated by oxygen plasma etching (OPE) to produce graphene oxide (GO) at the VAMWCNT tips. The attachment of oxygen functional groups was found to be crucial for nHAp nucleation during electrodeposition. A thin layer of plate-like and needle-like nHAp with high crystallinity was formed without any need for thermal treatment. This composite (henceforth referred to as nHAp-VAMWCNT-GO) served as the scaffold for in vitro biomineralization when soaked in the SBF, resulting in the formation of both carbonate-rich and carbonate-poor globular-like nHAp. Different steps in the deposition of biological apatite onto VAMWCNT-GO and during the short-term biomineralization process were analysed. Due to their unique structure and properties, such nano-bio-composites may become useful in accelerating in vivo bone regeneration processes.

Air-bridged Ohmic contact on vertically aligned si nanowire arrays: application to molecule sensors.

PubMed

Han, Hee; Kim, Jungkil; Shin, Ho Sun; Song, Jae Yong; Lee, Woo

2012-05-02

A simple, cost-effective, and highly reliable method for constructing an air-bridged electrical contact on large arrays of vertically aligned nanowires was developed. The present method may open up new opportunities for developing advanced nanowire-based devices for energy harvest and storage, power generation, and sensing applications. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Superior Thermal Interface via Vertically Aligned Carbon Nanotubes Grown on Graphite Foils

DTIC Science & Technology

2012-01-01

accepted 12 November 2012) In an attempt to study the thermal transport at the interface between nanotubes and graphene, vertically aligned multiwalled...tually increases the thermal barrier in a significant manner. On the other hand, thermal transport properties of thermal tapes and thermally conductive...aforementioned study achieved superior thermal transport properties, the processing and scale-up of the developed process would be prohibitively

Method of fabricating vertically aligned group III-V nanowires

DOEpatents

Wang, George T; Li, Qiming

2014-11-25

A top-down method of fabricating vertically aligned Group III-V micro- and nanowires uses a two-step etch process that adds a selective anisotropic wet etch after an initial plasma etch to remove the dry etch damage while enabling micro/nanowires with straight and smooth faceted sidewalls and controllable diameters independent of pitch. The method enables the fabrication of nanowire lasers, LEDs, and solar cells.

Beyond Scissors and Glue: Staff Developers Guide Teachers in Piecing Together a Vertically Aligned Curriculum and in Creating a Method to Get This Job Done

ERIC Educational Resources Information Center

Phelps, Vickie

2005-01-01

Layers and layers of curricula stuffed into vinyl binders were the norm in this Texas district until teachers sat down with scissors and glue to create a vertically aligned curriculum. They then created standards-based lessons to support the curriculum and put them into a database readily accessible by all.

SU-G-JeP3-02: Comparison of Magnitude and Frequency of Patient Positioning Errors in Breast Irradiation Using AlignRT 3D Optical Surface Imaging and Skin Mark Techniques

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yao, R; Chisela, W; Dorbu, G

2016-06-15

Purpose: To evaluate clinical usefulness of AlignRT (Vision RT Ltd., London, UK) in reducing patient positioning errors in breast irradiation. Methods: 60 patients undergoing whole breast irradiation were selected for this study. Patients were treated to the left or right breast lying on Qfix Access breast board (Qfix, Avondale, PA) in supine position for 28 fractions using tangential fields. 30 patients were aligned using AlignRT by aligning a breast surface region of interest (ROI) to the same area from a reference surface image extracted from planning CT. When the patient’s surface image deviated from the reference by more than 3mmmore » on one or more translational and rotational directions, a new reference was acquired using AlignRT in-room cameras. The other 30 patients were aligned to the skin marks with room lasers. On-Board MV portal images of medial field were taken daily and matched to the DRRs. The magnitude and frequency of positioning errors were determined from measured translational shifts. Kolmogorov-Smirnov test was used to evaluate statistical differences of positional accuracy and precision between AlignRT and non-AlignRT patients. Results: The percentage of port images with no shift required was 46.5% and 27.0% in vertical, 49.8% and 25.8% in longitudinal, 47.6% and 28.5% in lateral for AlignRT and non-AlignRT patients, respectively. The percentage of port images requiring more than 3mm shifts was 18.1% and 35.1% in vertical, 28.6% and 50.8% in longitudinal, 11.3% and 24.2% in lateral for AlignRT and non-AlignRT patients, respectively. Kolmogorov-Smirnov test showed that there were significant differences between the frequency distributions of AlignRT and non-AlignRT in vertical, longitudinal, and lateral shifts. Conclusion: As confirmed by port images, AlignRT-assisted patient positioning can significantly reduce the frequency and magnitude of patient setup errors in breast irradiation compared to the use of lasers and skin marks.« less

Alignment of x-ray tube focal spots for spectral measurement.

PubMed

Nishizawa, K; Maekoshi, H; Kamiya, Y; Kobayashi, Y; Ohara, K; Sakuma, S

1982-01-01

A general method to align a diagnostic x-ray machine for x-ray spectrum measurement purpose was theoretically and experimentally investigated by means of the optical alignment of focal pinhole images. Focal pinhole images were obtained by using a multi-pinholed lead plate. the vertical plane, including the central axis and tube axis, was decided upon by observing the symmetry of focal images. the central axis was designated as a line through the center of focus parallel to the target surface lying in the vertical plane. A method to determine the manipulation of the central axis in any direction is presented.

Fast-switching chiral nematic liquid-crystal mode with polymer-sustained twisted vertical alignment.

PubMed

Chang, Kai-Han; Joshi, Vinay; Chien, Liang-Chy

2017-04-01

We demonstrate a fast-switching liquid-crystal mode with polymer-sustained twisted vertical alignment. By optimizing the polymerization condition, a polymer microstructure with controlled orientation is produced. The polymer microstructure not only synergistically suppresses the optical bounce during field-induced homeotropic-twist transition but also shortens the response time significantly. Theoretical analyses validate that the ground state free energy density is modified by the aligning field of the polymer microstructure, which affects the driving voltage of the device. The outcomes of this paper will enable the development of fast-switching and achromatic electro-optical and photonic devices.

Fast-switching chiral nematic liquid-crystal mode with polymer-sustained twisted vertical alignment

NASA Astrophysics Data System (ADS)

Chang, Kai-Han; Joshi, Vinay; Chien, Liang-Chy

2017-04-01

We demonstrate a fast-switching liquid-crystal mode with polymer-sustained twisted vertical alignment. By optimizing the polymerization condition, a polymer microstructure with controlled orientation is produced. The polymer microstructure not only synergistically suppresses the optical bounce during field-induced homeotropic-twist transition but also shortens the response time significantly. Theoretical analyses validate that the ground state free energy density is modified by the aligning field of the polymer microstructure, which affects the driving voltage of the device. The outcomes of this paper will enable the development of fast-switching and achromatic electro-optical and photonic devices.

Diameter modulation of vertically aligned single-walled carbon nanotubes.

PubMed

Xiang, Rong; Einarsson, Erik; Murakami, Yoichi; Shiomi, Junichiro; Chiashi, Shohei; Tang, Zikang; Maruyama, Shigeo

2012-08-28

We demonstrate wide-range diameter modulation of vertically aligned single-walled carbon nanotubes (SWNTs) using a wet chemistry prepared catalyst. In order to ensure compatibility to electronic applications, the current minimum mean diameter of 2 nm for vertically aligned SWNTs is challenged. The mean diameter is decreased to about 1.4 nm by reducing Co catalyst concentrations to 1/100 or by increasing Mo catalyst concentrations by five times. We also propose a novel spectral analysis method that allows one to distinguish absorbance contributions from the upper, middle, and lower parts of a nanotube array. We use this method to quantitatively characterize the slight diameter change observed along the array height. On the basis of further investigation of the array and catalyst particles, we conclude that catalyst aggregation-rather than Ostwald ripening-dominates the growth of metal particles.

Self-assembled vertically aligned Au nanorod arrays for surface-enhanced Raman scattering (SERS) detection of Cannabinol.

PubMed

Milliken, Sarah; Fraser, Jeff; Poirier, Shawn; Hulse, John; Tay, Li-Lin

2018-05-05

Self-assembled multi-layered vertically aligned gold nanorod (AuNR) arrays have been fabricated by a simple preparation process that requires a balance between the particle concentration and the ionic strength of the solvent. An experimentally determined critical AuNR concentration of 2.0nM and 50mM NaCl produces well-ordered vertically aligned hexagonally close-packed AuNR arrays. We demonstrate surface treatment via UV Ozone cleaning of such samples to allow introduction of analyte molecules (benzenethiol and cannabinol) for effective surface enhanced Raman scattering detection. This is the first demonstration of the SERS analysis of cannabinol. This approach demonstrates a cost-effective, high-yield and simple fabrication route to SERS sensors with application in the screening for the cannabinoids. Copyright © 2018. Published by Elsevier B.V.

Formation of Coaxial Nanocables with Amplified Supramolecular Chirality through an Interaction between Carbon Nanotubes and a Chiral π-Gelator.

PubMed

Vedhanarayanan, Balaraman; Nair, Vishnu S; Nair, Vijayakumar C; Ajayaghosh, Ayyappanpillai

2016-08-22

In an attempt to gather experimental evidence for the influence of carbon allotropes on supramolecular chirality, we found that carbon nanotubes (CNTs) facilitate amplification of the molecular chirality of a π-gelator (MC-OPV) to supramolecular helicity at a concentration much lower than that required for intermolecular interaction. For example, at a concentration 1.8×10(-4)  m, MC-OPV did not exhibit a CD signal; however, the addition of 0-0.6 mg of SWNTs resulted in amplified chirality as evident from the CD spectrum. Surprisingly, AFM analysis revealed the formation of thick helical fibers with a width of more than 100 nm. High-resolution TEM analysis and solid-state UV/Vis/NIR spectroscopy revealed that the thick helical fibers were cylindrical cables composed of individually wrapped and coaxially aligned SWNTs. Such an impressive effect of CNTs on supramolecular chirality and cylindrical-cable formation has not been reported previously. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Carbon nanotube-sensor-integrated microfluidic platform for real-time chemical concentration detection.

PubMed

Yang, Li; Li, Minglin; Qu, Yanli; Dong, Zaili; Li, Wen J

2009-09-01

This paper presents the development of a chemical sensor employing electronic-grade carbon nanotubes (EG-CNTs) as the active sensing element for sodium hypochlorite detection. The sensor, integrated in a PDMS-glass microfluidic chamber, was fabricated by bulk aligning of EG-CNTs between gold microelectrode pairs using dielectrophoretic technique. Upon exposure to sodium hypochlorite solution, the characteristics of the carbon nanotube chemical sensor were investigated at room temperature under constant current mode. The sensor exhibited responsivity, which fits a linear logarithmic dependence on concentration in the range of 1/32 to 8 ppm, a detection limit lower than 5 ppb, while saturating at 16 ppm. The typical response time of the sensor at room temperature is on the order of minutes and the recovery time is a few hours. In particular, the sensor showed an obvious sensitivity to the volume of detected solution. It was found that the activation power of the sensor was extremely low, i.e. in the range of nanowatts. These results indicate great potential of EG-CNT for advanced nanosensors with superior sensitivity, ultra-low power consumption, and less fabrication complexity.

Cornering characteristics of the main-gear tire of the space shuttle orbiter

NASA Technical Reports Server (NTRS)

Daugherty, Robert H.; Stubbs, Sandy M.; Robinson, Martha P.

1988-01-01

An experimental investigation was conducted at the NASA Langley Research Center to study the effects of various vertical load and yaw angle conditions on the cornering behavior of the Space Shuttle Orbiter main gear tire. Measured parameters included side and drag force, side and drag force coefficients, aligning torque, and overturning torque. Side force coefficient was found to increase as yaw angle was increased, but decreased as the vertical load was increased. Drag force was found to increase as vertical load was increased at constant yaw angles. Aligning torque measurements indicated that the tire is stable in yaw.

Vertically-aligned carbon nanotubes on aluminum as a light-weight positive electrode for lithium-polysulfide batteries.

PubMed

Liatard, S; Benhamouda, K; Fournier, A; Ramos, R; Barchasz, C; Dijon, J

2015-05-04

A light-weight, high specific surface current collector made of vertically-aligned carbon nanotubes grown on an aluminum substrate was fabricated and studied as a positive electrode in a semi-liquid lithium/polysulfide battery. This simple system delivered stable capacities over 1000 mA h gS(-1) and 2 mA h cm(-2) with almost no capacity loss over 50 cycles.

Vertically aligned carbon nanotubes for microelectrode arrays applications.

PubMed

Castro Smirnov, J R; Jover, Eric; Amade, Roger; Gabriel, Gemma; Villa, Rosa; Bertran, Enric

2012-09-01

In this work a methodology to fabricate carbon nanotube based electrodes using plasma enhanced chemical vapour deposition has been explored and defined. The final integrated microelectrode based devices should present specific properties that make them suitable for microelectrode arrays applications. The methodology studied has been focused on the preparation of highly regular and dense vertically aligned carbon nanotube (VACNT) mat compatible with the standard lithography used for microelectrode arrays technology.

Topographically induced homeotropic alignment of liquid crystals on self-assembled opal crystals.

PubMed

Kumar, Pankaj; Oh, Su Yeon; Baliyan, Vijay K; Kundu, Sudarshan; Lee, Seung Hee; Kang, Shin-Woong

2018-04-02

The surface of multilayered opal crystals resulted in homeotropic alignment of liquid crystal (LC), originated from the surface topography of opal crystals rather than a chemical nature of the nanoparticles. The polar anchoring energy (5.51 × 10 -5 J/m 2 ) of the crystal surface for nematic LC molecules was in a similar range to the conventional polyimide alignment layer (2.11 × 10 -5 J/m 2 ) used for commercial applications. The critical length scale for anchoring transition was approximately Lw = ~1 μm. If a diameter of particle d < 1 μm for opal crystals, LC molecules preferred to anchor vertically to the surface to minimize elastic free energy of bulk LCs. The LC favored a planar anchoring if d > 1 μm. The results provide crucial insights to understand the homeotropic alignment of LCs on solid surfaces and therefore offer opportunities to develop novel materials for a vertical alignment of LCs.

Experimental and DFT study of thiol-stabilized Pt/CNTs catalysts.

PubMed

Li, L; Chen, S G; Wei, Z D; Qi, X Q; Xia, M R; Wang, Y Q

2012-12-28

Using a combination of experiments and density functional theory (DFT) calculations, we explored the mechanisms of the stabilization effect of the thiolized (-SH) group on the Pt/SH-CNTs catalyst. Pt particles supported on the hydroxyl functionalized CNTs (Pt/OH-CNTs) are synthesized as a baseline for comparison. Experimentally, the platinum on OH-CNTs has a stronger tendency for aggregation than that on SH-CNTs. The differences in the oxidation resistance, migration activation energy, and corrosion resistance between the Pt/SH-CNTs and Pt/OH-CNTs are calculated using DFT. The DFT calculations indicate that the -SH group enhances the oxidation resistance of the Pt cluster and CNTs and restricts Pt migration on the CNTs. DFT calculations also suggest that the enhanced stability of Pt/SH-CNTs originates from the increased interaction between Pt and SH-CNTs and the depressed d-band center of the Pt NPs. Thus, the functional groups on the CNTs used for stabilization of supported Pt NPs should provide a deposit and anchor site for Pt NPs and maintain the perfect structure of CNTs rather than destroying it.

Conformal Fe3O4 sheath on aligned carbon nanotube scaffolds as high-performance anodes for lithium ion batteries.

PubMed

Wu, Yang; Wei, Yang; Wang, Jiaping; Jiang, Kaili; Fan, Shoushan

2013-02-13

A uniform Fe(3)O(4) sheath is magnetron sputtered onto aligned carbon nanotube (CNT) scaffolds that are directly drawn from CNT arrays. The Fe(3)O(4)-CNT composite electrode, with the size of Fe(3)O(4) confined to 5-7 nm, exhibits a high reversible capacity over 800 mAh g(-1) based on the total electrode mass, remarkable capacity retention, as well as high rate capability. The excellent performance is attributable to the superior electrical conductivity of CNTs, the uniform loading of Fe(3)O(4) sheath, and the structural retention of the composite anode on cycling. As Fe(3)O(4) is inexpensive and environmentally friendly, and the synthesis of Fe(3)O(4)-CNT is free of chemical wastes, this composite anode material holds considerable promise for high-performance lithium ion batteries.

Vertically aligned carbon nanotubes black coatings from roll-to-roll deposition process

NASA Astrophysics Data System (ADS)

Goislard de Monsabert, Thomas; Papciak, L.; Sangar, A.; Descarpentries, J.; Vignal, T.; de Longiviere, Xavier; Porterat, D.; Mestre, Q.; Hauf, H.

2017-09-01

Vertically aligned carbon nanotubes (VACNTs) have recently attracted growing interest as a very efficient light absorbing material over a broad spectral range making them a superior coating in space optics applications such as radiometry, optical calibration, and stray light elimination. However, VACNT coatings available to-date most often result from batch-to-batch deposition processes thus potentially limiting the manufacturing repeatability, substrate size and cost efficiency of this material.

Vertically aligned carbon nanotube emitter on metal foil for medical X-ray imaging.

PubMed

Ryu, Je Hwang; Kim, Wan Sun; Lee, Seung Ho; Eom, Young Ju; Park, Hun Kuk; Park, Kyu Chang

2013-10-01

A simple method is proposed for growing vertically aligned carbon nanotubes on metal foil using the triode direct current plasma-enhanced chemical vapor deposition (PECVD). The carbon nanotube (CNT) electron emitter was fabricated using fewer process steps with an acid treated metal substrate. The CNT emitter was used for X-ray generation, and the X-ray image of mouse's joint was obtained with an anode current of 0.5 mA at an anode bias of 60 kV. The simple fabrication of a well-aligned CNT with a protection layer on metal foil, and its X-ray application, were studied.

Uniform, dense arrays of vertically aligned, large-diameter single-walled carbon nanotubes.

PubMed

Han, Zhao Jun; Ostrikov, Kostya

2012-04-04

Precisely controlled reactive chemical vapor synthesis of highly uniform, dense arrays of vertically aligned single-walled carbon nanotubes (SWCNTs) using tailored trilayered Fe/Al(2)O(3)/SiO(2) catalyst is demonstrated. More than 90% population of thick nanotubes (>3 nm in diameter) can be produced by tailoring the thickness and microstructure of the secondary catalyst supporting SiO(2) layer, which is commonly overlooked. The proposed model based on the atomic force microanalysis suggests that this tailoring leads to uniform and dense arrays of relatively large Fe catalyst nanoparticles on which the thick SWCNTs nucleate, while small nanotubes and amorphous carbon are effectively etched away. Our results resolve a persistent issue of selective (while avoiding multiwalled nanotubes and other carbon nanostructures) synthesis of thick vertically aligned SWCNTs whose easily switchable thickness-dependent electronic properties enable advanced applications in nanoelectronic, energy, drug delivery, and membrane technologies.

Thin Polymer Films with Continuous Vertically Aligned 1 nm Pores Fabricated by Soft Confinement

DOE PAGES

Feng, Xunda; Nejati, Siamak; Cowan, Matthew G.; ...

2015-12-03

Membrane separations are critically important in areas ranging from health care and analytical chemistry to bioprocessing and water purification. An ideal nanoporous membrane would consist of a thin film with physically continuous and vertically aligned nanopores and would display a narrow distribution of pore sizes. However, the current state of the art departs considerably from this ideal and is beset by intrinsic trade-offs between permeability and selectivity. We demonstrate an effective and scalable method to fabricate polymer films with ideal membrane morphologies consisting of submicron thickness films with physically continuous and vertically aligned 1 nm pores. The approach is basedmore » on soft confinement to control the orientation of a cross-linkable mesophase in which the pores are produced by self-assembly. The scalability, exceptional ease of fabrication, and potential to create a new class of nanofiltration membranes stand out as compelling aspects.« less

Air-bridge and Vertical CNT Switches for High Performance Switching Applications

NASA Technical Reports Server (NTRS)

Kaul, Anupama B.; Wong, Eric W.; Epp, Larry; Bronikowski, Michael J.; Hunt, BBrian D.

2006-01-01

Carbon nanotubes are attractive for switching applications since electrostatically-actuated CNT switches have low actuation voltages and power requirements, while allowing GHz switching speeds that stem from the inherently high elastic modulus and low mass of the CNT.Our first NEM structure, the air-bridge switch, consists of suspended single-walled nanotubes (SWNTs) that lie above a sputtered Nb base electrode, where contact to the CNTs is made using evaporated Au/Ti. Electrical measurements of these air-bridge devices show well-defined ON and OFF states as a dc bias of a few volts is applied between the CNT and the Nb-base electrode. The CNT air-bridge switches were measured to have switching times down to a few nanoseconds. Our second NEM structure, the vertical CNT switch, consists of nanotubes grown perpendicular to the substrate. Vertical multi-walled nanotubes (MWNTs) are grown directly on a heavily doped Si substrate, from 200 - 300 nm wide, approximately 1 micrometer deep nano-pockets, with Nb metal electrodes to result in the formation of a vertical single-pole-double-throw switch architecture.

Vertically-aligned Mn(OH) 2 nanosheet films for flexible all-solid-state electrochemical supercapacitors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Ziyuan; Gong, Jiangfeng; Tang, Chunmei

We report that the arrangement of the electrode materials is a significant contributor for constructing high performance supercapacitor. Here, vertically-aligned Mn(OH) 2 nanosheet thin films were synthesized by cathodic electrodeposition technique on flexible Au coated polyethylene terephthalate substrates. Morphologies, microstructures, chemical compositions and valence state of the nanosheet films were characterized systematically. It shows that the nanosheets arranged vertically to the substrate, forming a porous nanowall structures and creating large open framework, which greatly facilitate the adsorption or diffusion of electrolyte ions for faradaic redox reaction. Electrochemical tests of the films show the specific capacitance as high as 240.2 Fmore » g -1 at 1.0 A g -1. The films were employed to assemble symmetric all-solid-state supercapacitors with LiCl/PVA gel severed as solid electrolyte. Finally, the solid devices exhibit high volumetric capacitance of 39.3 mF cm -3 at the current density 0.3 mA cm -3 with robust cycling stability. The superior performance is attributed to the vertically-aligned configuration.« less

Vertically-aligned Mn(OH) 2 nanosheet films for flexible all-solid-state electrochemical supercapacitors

DOE PAGES

Yang, Ziyuan; Gong, Jiangfeng; Tang, Chunmei; ...

2017-08-28

We report that the arrangement of the electrode materials is a significant contributor for constructing high performance supercapacitor. Here, vertically-aligned Mn(OH) 2 nanosheet thin films were synthesized by cathodic electrodeposition technique on flexible Au coated polyethylene terephthalate substrates. Morphologies, microstructures, chemical compositions and valence state of the nanosheet films were characterized systematically. It shows that the nanosheets arranged vertically to the substrate, forming a porous nanowall structures and creating large open framework, which greatly facilitate the adsorption or diffusion of electrolyte ions for faradaic redox reaction. Electrochemical tests of the films show the specific capacitance as high as 240.2 Fmore » g -1 at 1.0 A g -1. The films were employed to assemble symmetric all-solid-state supercapacitors with LiCl/PVA gel severed as solid electrolyte. Finally, the solid devices exhibit high volumetric capacitance of 39.3 mF cm -3 at the current density 0.3 mA cm -3 with robust cycling stability. The superior performance is attributed to the vertically-aligned configuration.« less

High voltage electrophoretic deposition for electrochemical energy storage and other applications

NASA Astrophysics Data System (ADS)

Santhanagopalan, Sunand

High voltage electrophoretic deposition (HVEPD) has been developed as a novel technique to obtain vertically aligned forests of one-dimensional nanomaterials for efficient energy storage. The ability to control and manipulate nanomaterials is critical for their effective usage in a variety of applications. Oriented structures of one-dimensional nanomaterials provide a unique opportunity to take full advantage of their excellent mechanical and electrochemical properties. However, it is still a significant challenge to obtain such oriented structures with great process flexibility, ease of processing under mild conditions and the capability to scale up, especially in context of efficient device fabrication and system packaging. This work presents HVEPD as a simple, versatile and generic technique to obtain vertically aligned forests of different one-dimensional nanomaterials on flexible, transparent and scalable substrates. Improvements on material chemistry and reduction of contact resistance have enabled the fabrication of high power supercapacitor electrodes using the HVEPD method. The investigations have also paved the way for further enhancements of performance by employing hybrid material systems and AC/DC pulsed deposition. Multi-walled carbon nanotubes (MWCNTs) were used as the starting material to demonstrate the HVEPD technique. A comprehensive study of the key parameters was conducted to better understand the working mechanism of the HVEPD process. It has been confirmed that HVEPD was enabled by three key factors: high deposition voltage for alignment, low dispersion concentration to avoid aggregation and simultaneous formation of holding layer by electrodeposition for reinforcement of nanoforests. A set of suitable parameters were found to obtain vertically aligned forests of MWCNTs. Compared with their randomly oriented counterparts, the aligned MWCNT forests showed better electrochemical performance, lower electrical resistance and a capability to achieve superhydrophpbicity, indicating their potential in a broad range of applications. The versatile and generic nature of the HVEPD process has been demonstrated by achieving deposition on flexible and transparent substrates, as well as aligned forests of manganese dioxide (MnO2) nanorods. A continuous roll-printing HVEPD approach was then developed to obtain aligned MWCNT forest with low contact resistance on large, flexible substrates. Such large-scale electrodes showed no deterioration in electrochemical performance and paved the way for practical device fabrication. The effect of a holding layer on the contact resistance between aligned MWCNT forests and the substrate was studied to improve electrochemical performance of such electrodes. It was found that a suitable precursor salt like nickel chloride could be used to achieve a conductive holding layer which helped to significantly reduce the contact resistance. This in turn enhanced the electrochemical performance of the electrodes. High-power scalable redox capacitors were then prepared using HVEPD. Very high power/energy densities and excellent cyclability have been achieved by synergistically combining hydrothermally synthesized, highly crystalline α-MnO 2 nanorods, vertically aligned forests and reduced contact resistance. To further improve the performance, hybrid electrodes have been prepared in the form of vertically aligned forest of MWCNTs with branches of α-MnO 2 nanorods on them. Large- scale electrodes with such hybrid structures were manufactured using continuous HVEPD and characterized, showing further improved power and energy densities. The alignment quality and density of MWCNT forests were also improved by using an AC/DC pulsed deposition technique. In this case, AC voltage was first used to align the MWCNTs, followed by immediate DC voltage to deposit the aligned MWCNTs along with the conductive holding layer. Decoupling of alignment from deposition was proven to result in better alignment quality and higher electrochemical performance.

Largely enhanced dielectric properties of carbon nanotubes/polyvinylidene fluoride binary nanocomposites by loading a few boron nitride nanosheets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Minhao; Zhao, Hang; He, Delong

2016-08-15

The ternary nanocomposites of boron nitride nanosheets (BNNSs)/carbon nanotubes (CNTs)/polyvinylidene fluoride (PVDF) are fabricated via a combination of solution casting and extrusion-injection processes. The effects of BNNSs on the electrical conductivity, dielectric behavior, and microstructure changes of CNTs/PVDF binary nanocomposites are systematically investigated. A low percolation value (f{sub c}) for the CNTs/PVDF binary system is obtained due to the integration of solution and melting blending procedures. Two kinds of CNTs/PVDF binary systems with various CNTs contents (f{sub CNTs}) as the matrix are discussed. The results reveal that compared with CNTs/PVDF binary systems at the same f{sub CNTs}, the ternary BNNSs/CNTs/PVDFmore » nanocomposites exhibit largely enhanced dielectric properties due to the improvement of the CNTs dispersion state and the conductive network. The dielectric constant of CNTs/PVDF binary nanocomposite with 6 vol. % CNTs (f{sub CNTs} < f{sub c}) shows a 79.59% enhancement from 49 to 88 after the incorporation of 3 vol. % BNNSs. For the other CNTs/PVDF system with 8 vol. % CNTs (f{sub CNTs} > f{sub c}), it displays a 43.32% improvement from 1325 to 1899 after the addition of 3 vol. % BNNSs. The presence of BNNSs facilitates the formation of the denser conductive network. Meanwhile, the ternary BNNSs/CNTs/PVDF systems exhibit a low dielectric loss. The adjustable dielectric properties could be obtained by employing the ternary systems due to the microstructure changes of nanocomposites.« less

Vertical decomposition with Genetic Algorithm for Multiple Sequence Alignment

PubMed Central

2011-01-01

Background Many Bioinformatics studies begin with a multiple sequence alignment as the foundation for their research. This is because multiple sequence alignment can be a useful technique for studying molecular evolution and analyzing sequence structure relationships. Results In this paper, we have proposed a Vertical Decomposition with Genetic Algorithm (VDGA) for Multiple Sequence Alignment (MSA). In VDGA, we divide the sequences vertically into two or more subsequences, and then solve them individually using a guide tree approach. Finally, we combine all the subsequences to generate a new multiple sequence alignment. This technique is applied on the solutions of the initial generation and of each child generation within VDGA. We have used two mechanisms to generate an initial population in this research: the first mechanism is to generate guide trees with randomly selected sequences and the second is shuffling the sequences inside such trees. Two different genetic operators have been implemented with VDGA. To test the performance of our algorithm, we have compared it with existing well-known methods, namely PRRP, CLUSTALX, DIALIGN, HMMT, SB_PIMA, ML_PIMA, MULTALIGN, and PILEUP8, and also other methods, based on Genetic Algorithms (GA), such as SAGA, MSA-GA and RBT-GA, by solving a number of benchmark datasets from BAliBase 2.0. Conclusions The experimental results showed that the VDGA with three vertical divisions was the most successful variant for most of the test cases in comparison to other divisions considered with VDGA. The experimental results also confirmed that VDGA outperformed the other methods considered in this research. PMID:21867510

Demonstration of high current carbon nanotube enabled vertical organic field effect transistors at industrially relevant voltages

NASA Astrophysics Data System (ADS)

McCarthy, Mitchell

The display market is presently dominated by the active matrix liquid crystal display (LCD). However, the active matrix organic light emitting diode (AMOLED) display is argued to become the successor to the LCD, and is already beginning its way into the market, mainly in small size displays. But, for AMOLED technology to become comparable in market share to LCD, larger size displays must become available at a competitive price with their LCD counterparts. A major issue preventing low-cost large AMOLED displays is the thin-film transistor (TFT) technology. Unlike the voltage driven LCD, the OLEDs in the AMOLED display are current driven. Because of this, the mature amorphous silicon TFT backplane technology used in the LCD must be upgraded to a material possessing a higher mobility. Polycrystalline silicon and transparent oxide TFT technologies are being considered to fill this need. But these technologies bring with them significant manufacturing complexity and cost concerns. Carbon nanotube enabled vertical organic field effect transistors (CN-VFETs) offer a unique solution to this problem (now known as the AMOLED backplane problem). The CN-VFET allows the use of organic semiconductors to be used for the semiconductor layer. Organics are known for their low-cost large area processing compatibility. Although the mobility of the best organics is only comparable to that of amorphous silicon, the CN-VFET makes up for this by orienting the channel vertically, as opposed to horizontally (like in conventional TFTs). This allows the CN-VFET to achieve sub-micron channel lengths without expensive high resolution patterning. Additionally, because the CN-VFET can be easily converted into a light emitting transistor (called the carbon nanotube enabled vertical organic light emitting transistor---CN-VOLET) by essentially stacking an OLED on top of the CN-VFET, more potential benefits can be realized. These potential benefits include, increased aperture ratio, increased OLED lifetime and the potential for an all transparent display. And because carbon nanotubes (CNTs) and organics are used, CN-VFET and CN-VOLET devices are compatible with flexible displays. This dissertation describes the first ever demonstration of CN-VFETs and CN-VOLETs and relates their performance to the specific properties of the CNTs and the new device architecture. In the work that followed, the CN-VFET was systematically optimized overcoming the problems revealed in the demonstration devices. The large undesired hysteresis was decreased by 96%, the on/off ratio was improved three orders of magnitude and the operating voltages were reduced to state of the art values. Additionally, the current output per device area of the CN-VFET was demonstrated to be greater than any other low resolution patterned organic transistor by a factor of 3.9. Moreover, it was demonstrated that the CNTs induce a reorientation of the high mobility plane in small molecule organics like pentacene to coincide with the vertical direction, giving additional explanation for the large currents observed in the CN-VFET. The ability to drive high currents and potentially inexpensive fabrication may provide the solution for the AMOLED backplane problem.

Geometrical appearance and spatial arrangement of structural blocks of the Malan loess in NW China: implications for the formation of loess columns

NASA Astrophysics Data System (ADS)

Li, Yanrong; Zhang, Tao; Zhang, Yongbo; Xu, Qiang

2018-06-01

Loess, as one of the main Quaternary deposits, covers approximately 6% of the land surface of the Earth. Although loess is loose and fragile, loess columns are popular and they can stand stably for hundreds of years, thereby forming a spectacular landform. The formation of such special column-shaped soil structures is puzzling, and the underlying fundamentals remain unclear. The present study focuses on quantifying and examining the geometrical shape and spatial alignment of structural blocks of the Malan loess at different locations in the Loess Plateau of China. The structural blocks under investigation include clay- and silt-sized particles, aggregates, fragments, lumps, and columns, which vary in size from microns to tens of meters. Regardless of their size, the structural blocks of the Malan loess are found to be similar in shape, i.e., elongated with a length-to-width ratio of approximately 2.6. The aggregates, fragments, lumps, columns, and macropores between aggregates exhibit strong concentration in the vertical or subvertical alignment. These phenomena imply that the Malan loess is anisotropic and it is composed of a combination of vertically aligned strong units and vertically aligned weak segments. Based on this, "vertiloess" structure is proposed to denote this combination. The vertiloess structure prevents horizontal erosion, but favors spalling, peeling, toppling, falling and cracking-sliding of vertical loess pieces, thereby forming loess columns.

Decoration of multi-walled carbon nanotubes by polymer wrapping and its application in MWCNT/polyethylene composites.

PubMed

Hsiao, An-En; Tsai, Shu-Ya; Hsu, Mei-Wen; Chang, Shinn-Jen

2012-05-06

We dispersed the non-covalent functionalization of multi-walled carbon nanotubes (CNTs) with a polymer dispersant and obtained a powder of polymer-wrapped CNTs. The UV-vis absorption spectrum was used to investigate the optimal weight ratio of the CNTs and polymer dispersant. The powder of polymer-wrapped CNTs had improved the drawbacks of CNTs of being lightweight and difficult to process, and it can re-disperse in a solvent. Then, we blended the polymer-wrapped CNTs and polyethylene (PE) by melt-mixing and produced a conductive masterbatch and CNT/PE composites. The polymer-wrapped CNTs showed lower surface resistivity in composites than the raw CNTs. The scanning electron microscopy images also showed that the polymer-wrapped CNTs can disperse well in composites than the raw CNTs.

Ultralight anisotropic foams from layered aligned carbon nanotube sheets

NASA Astrophysics Data System (ADS)

Faraji, Shaghayegh; L. Stano, Kelly; Yildiz, Ozkan; Li, Ang; Zhu, Yuntian; Bradford, Philip D.

2015-10-01

In this work, we present large scale, ultralight aligned carbon nanotube (CNT) structures which have densities an order of magnitude lower than CNT arrays, have tunable properties and exhibit resiliency after compression. By stacking aligned sheets of carbon nanotubes and then infiltrating with a pyrolytic carbon (PyC), resilient foam-like materials were produced that exhibited complete recovery from 90% compressive strain. With density as low as 3.8 mg cm-3, the foam structure is over 500 times less dense than bulk graphite. Microscopy revealed that PyC coated the junctions among CNTs, and also increased CNT surface roughness. These changes in the morphology explain the transition from inelastic behavior to foam-like recovery of the layered CNT sheet structure. Mechanical and thermal properties of the foams were tuned for different applications through variation of PyC deposition duration while dynamic mechanical analysis showed no change in mechanical properties over a large temperature range. Observation of a large and linear electrical resistance change during compression of the aligned CNT/carbon (ACNT/C) foams makes strain/pressure sensors a relevant application. The foams have high oil absorption capacities, up to 275 times their own weight, which suggests they may be useful in water treatment and oil spill cleanup. Finally, the ACNT/C foam's high porosity, surface area and stability allow for demonstration of the foams as catalyst support structures.In this work, we present large scale, ultralight aligned carbon nanotube (CNT) structures which have densities an order of magnitude lower than CNT arrays, have tunable properties and exhibit resiliency after compression. By stacking aligned sheets of carbon nanotubes and then infiltrating with a pyrolytic carbon (PyC), resilient foam-like materials were produced that exhibited complete recovery from 90% compressive strain. With density as low as 3.8 mg cm-3, the foam structure is over 500 times less dense than bulk graphite. Microscopy revealed that PyC coated the junctions among CNTs, and also increased CNT surface roughness. These changes in the morphology explain the transition from inelastic behavior to foam-like recovery of the layered CNT sheet structure. Mechanical and thermal properties of the foams were tuned for different applications through variation of PyC deposition duration while dynamic mechanical analysis showed no change in mechanical properties over a large temperature range. Observation of a large and linear electrical resistance change during compression of the aligned CNT/carbon (ACNT/C) foams makes strain/pressure sensors a relevant application. The foams have high oil absorption capacities, up to 275 times their own weight, which suggests they may be useful in water treatment and oil spill cleanup. Finally, the ACNT/C foam's high porosity, surface area and stability allow for demonstration of the foams as catalyst support structures. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr03899e

Annealed Au-assisted epitaxial growth of si nanowires: control of alignment and density.

PubMed

Park, Yi-Seul; Jung, Da Hee; Kim, Hyun Ji; Lee, Jin Seok

2015-04-14

The epitaxial growth of 1D nanostructures is of particular interest for future nanoelectronic devices such as vertical field-effect transistors because it directly influences transistor densities and 3D logic or memory architectures. Silicon nanowires (SiNWs) are a particularly important 1D nanomaterial because they possess excellent electronic and optical properties. What is more, the scalable fabrication of vertically aligned SiNW arrays presents an opportunity for improved device applications if suitable properties can be achieved through controlling the alignment and density of SiNWs, yet this is something that has not been reported in the case of SiNWs synthesized from Au films. This work therefore explores the controllable synthesis of vertically aligned SiNWs through the introduction of an annealing process prior to growth via a Au-catalyzed vapor-liquid-solid mechanism. The epitaxial growth of SiNWs was demonstrated to be achievable using SiCl4 as the Si precursor in chemical vapor deposition, whereas the alignment and density of the SiNWs could be controlled by manipulating the annealing time during the formation of Au nanoparticles (AuNPs) from Au films. During the annealing process, gold silicide was observed to form on the interface of the liquid-phase AuNPs, depending on the size of the AuNPs and the annealing time. This work therefore makes a valuable contribution to improving nanowire-based engineering by controlling its alignment and density as well as providing greater insight into the epitaxial growth of 1D nanostructures.

Decoration of multi-walled carbon nanotubes by polymer wrapping and its application in MWCNT/polyethylene composites

PubMed Central

2012-01-01

We dispersed the non-covalent functionalization of multi-walled carbon nanotubes (CNTs) with a polymer dispersant and obtained a powder of polymer-wrapped CNTs. The UV–vis absorption spectrum was used to investigate the optimal weight ratio of the CNTs and polymer dispersant. The powder of polymer-wrapped CNTs had improved the drawbacks of CNTs of being lightweight and difficult to process, and it can re-disperse in a solvent. Then, we blended the polymer-wrapped CNTs and polyethylene (PE) by melt-mixing and produced a conductive masterbatch and CNT/PE composites. The polymer-wrapped CNTs showed lower surface resistivity in composites than the raw CNTs. The scanning electron microscopy images also showed that the polymer-wrapped CNTs can disperse well in composites than the raw CNTs. PMID:22559082

Combination of small size and carboxyl functionalisation causes cytotoxicity of short carbon nanotubes

PubMed Central

Fröhlich, Eleonore; Meindl, Claudia; Höfler, Anita; Leitinger, Gerd; Roblegg, Eva

2012-01-01

The use of carbon nanotubes (CNTs) could improve medical diagnosis and treatment provided they show no adverse effects in the organism. In this study, short CNTs with different diameters with and without carboxyl surface functionalisation were assessed. After physicochemical characterisation, cytotoxicity in phagocytic and non-phagocytic cells was determined. The role of oxidative stress was evaluated according to the intracellular glutathione levels and protection by N-acetyl cysteine (NAC). In addition to this, the mode of cell death was also investigated. CNTs <8 nm acted more cytotoxic than CNTs ≥20 nm and carboxylated CNTs more than pristine CNTs. Protection by NAC was maximal for large diameter pristine CNTs and minimal for small diameter carboxylated CNTs. Thin (<8 nm) CNTs acted mainly by disruption of membrane integrity and CNTs with larger diameter induced mainly apoptotic changes. It is concluded that cytotoxicity of small carboxylated CNTs occurs by necrosis and cannot be prevented by antioxidants. PMID:22963691

Combined toxicities of copper nanoparticles with carbon nanotubes on marine microalgae Skeletonema costatum.

PubMed

Zhang, Cai; Chen, Xiaohua; Tan, Liju; Wang, Jinagtao

2018-05-01

To investigate the combined toxicities of copper nanoparticles (nano-Cu) with carbon nanotubes (CNTs) on marine microalgae Skeletonema costatum, algal growth inhibition tests were carried out. Toxicities of nano-Cu with CNTs and without CNTs on microalgae were determined, respectively. Chlorophyll content and photosynthetic efficiency (ΦPSII) were determined to compare negative effects of nano-Cu with CNTs and without CNTs on photosynthesis. The concentration of Cu 2+ released by nano-Cu into the medium was determined, and interactions between nano-Cu and CNTs were analyzed to study toxic mechanisms of combined toxicities of nano-Cu with CNTs. It was found that both nano-Cu and CNTs could inhibit the growth of the microalgae; however, the toxicity of CNTs on the microalgae was far lower than that of nano-Cu. The maximum growth inhibition ratio (IR) of nano-Cu on the microalgae was 86% appearing at 96 h under 1.0 mg/L nano-Cu treatment, while the maximum IR of CNTs on the microalgae was 58% at 96 h under 200 mg/L CNT treatment. CNTs could reduce the toxicity of nano-Cu on the microalgae in processes of growth and photosynthesis. Adsorption of Cu 2+ on CNTs and aggregate between Cu and CNTs in the medium were main reasons for attenuation of toxicity of nano-Cu with adding CNTs.

Initial growth of vertically aligned carbon nanofibers

NASA Astrophysics Data System (ADS)

Cui, Hongtao; Yang, Xiaojing; Simpson, Michael L.; Lowndes, Douglas H.; Varela, Maria

2004-05-01

Samples of vertically aligned carbon nanofibers (VACNFs) were viewed transverse to the growth direction and studied using both scanning and transmission electron microscopy. The VACNFs are composed of graphite layers nearly parallel to the substrate at their bottom end, gradually formed graphite "cups" in the main body, and a catalyst particle on the tip. The formation of such structure is due to the corresponding transformation of the shape of the catalyst particle during initial VACNF growth. A model for their initial growth is proposed.

Four-probe charge transport measurements on individual vertically aligned carbon nanofibers

NASA Astrophysics Data System (ADS)

Zhang, Lan; Austin, Derek; Merkulov, Vladimir I.; Meleshko, Anatoli V.; Klein, Kate L.; Guillorn, Michael A.; Lowndes, Douglas H.; Simpson, Michael L.

2004-05-01

We report four-probe I-V measurements on individual vertically aligned carbon nanofibers (VACNFs). These measurements were enabled by the fabrication of multiple Ti/Au ohmic contacts on individual fibers that exhibited resistance of only a few kilohms. These measurements demonstrate that VACNFs exhibit linear I-V behavior at room temperature, with a resistivity of approximately 4.2×10-3 Ω cm. Our measurements are consistent with a dominant transport mechanism of electrons traveling through intergraphitic planes in the VACNFs.

Vertically aligned carbon nanofibers as sacrificial templates for nanofluidic structures

NASA Astrophysics Data System (ADS)

Melechko, A. V.; McKnight, T. E.; Guillorn, M. A.; Merkulov, V. I.; Ilic, B.; Doktycz, M. J.; Lowndes, D. H.; Simpson, M. L.

2003-02-01

We report a method to fabricate nanoscale pipes ("nanopipes") suitable for fluidic transport. Vertically aligned carbon nanofibers grown by plasma-enhanced chemical vapor deposition are used as sacrificial templates for nanopipes with internal diameters as small as 30 nm and lengths up to several micrometers that are oriented perpendicular to the substrate. This method provides a high level of control over the nanopipe location, number, length, and diameter, permitting them to be deterministically positioned on a substrate and arranged into arrays.

Growth of Vertically Aligned ZnO Nanowire Arrays Using Bilayered Metal Catalysts

DTIC Science & Technology

2012-01-01

12] J. P. Liu, C. X. Guo, C. M. Li et al., “Carbon-decorated ZnO nanowire array: a novel platform for direct electrochemistry of enzymes and...cited. Vertically aligned, high-density ZnO nanowires (NWs) were grown for the first time on c-plane sapphire using binary alloys of Ni/Au or Cu/Au as...deleterious to the ZnO NW array growth. Significant improvement of the Au adhesion on the substrate was noted, opening the potential for direct

Does trampoline or hard surface jumping influence lower extremity alignment?

PubMed

Akasaka, Kiyokazu; Tamura, Akihiro; Katsuta, Aoi; Sagawa, Ayako; Otsudo, Takahiro; Okubo, Yu; Sawada, Yutaka; Hall, Toby

2017-12-01

[Purpose] To determine whether repetitive trampoline or hard surface jumping affects lower extremity alignment on jump landing. [Subjects and Methods] Twenty healthy females participated in this study. All subjects performed a drop vertical jump before and after repeated maximum effort trampoline or hard surface jumping. A three-dimensional motion analysis system and two force plates were used to record lower extremity angles, moments, and vertical ground reaction force during drop vertical jumps. [Results] Knee extensor moment after trampoline jumping was greater than that after hard surface jumping. There were no significant differences between trials in vertical ground reaction force and lower extremity joint angles following each form of exercise. Repeated jumping on a trampoline increased peak vertical ground reaction force, hip extensor, knee extensor moments, and hip adduction angle, while decreasing hip flexion angle during drop vertical jumps. In contrast, repeated jumping on a hard surface increased peak vertical ground reaction force, ankle dorsiflexion angle, and hip extensor moment during drop vertical jumps. [Conclusion] Repeated jumping on the trampoline compared to jumping on a hard surface has different effects on lower limb kinetics and kinematics. Knowledge of these effects may be useful in designing exercise programs for different clinical presentations.

Does trampoline or hard surface jumping influence lower extremity alignment?

PubMed Central

Akasaka, Kiyokazu; Tamura, Akihiro; Katsuta, Aoi; Sagawa, Ayako; Otsudo, Takahiro; Okubo, Yu; Sawada, Yutaka; Hall, Toby

2017-01-01

[Purpose] To determine whether repetitive trampoline or hard surface jumping affects lower extremity alignment on jump landing. [Subjects and Methods] Twenty healthy females participated in this study. All subjects performed a drop vertical jump before and after repeated maximum effort trampoline or hard surface jumping. A three-dimensional motion analysis system and two force plates were used to record lower extremity angles, moments, and vertical ground reaction force during drop vertical jumps. [Results] Knee extensor moment after trampoline jumping was greater than that after hard surface jumping. There were no significant differences between trials in vertical ground reaction force and lower extremity joint angles following each form of exercise. Repeated jumping on a trampoline increased peak vertical ground reaction force, hip extensor, knee extensor moments, and hip adduction angle, while decreasing hip flexion angle during drop vertical jumps. In contrast, repeated jumping on a hard surface increased peak vertical ground reaction force, ankle dorsiflexion angle, and hip extensor moment during drop vertical jumps. [Conclusion] Repeated jumping on the trampoline compared to jumping on a hard surface has different effects on lower limb kinetics and kinematics. Knowledge of these effects may be useful in designing exercise programs for different clinical presentations. PMID:29643592

Carbon Nanotubes Reinforced Composites for Biomedical Applications

PubMed Central

Wang, Wei; Zhu, Yuhe; Liao, Susan; Li, Jiajia

2014-01-01

This review paper reported carbon nanotubes reinforced composites for biomedical applications. Several studies have found enhancement in the mechanical properties of CNTs-based reinforced composites by the addition of CNTs. CNTs reinforced composites have been intensively investigated for many aspects of life, especially being made for biomedical applications. The review introduced fabrication of CNTs reinforced composites (CNTs reinforced metal matrix composites, CNTs reinforced polymer matrix composites, and CNTs reinforced ceramic matrix composites), their mechanical properties, cell experiments in vitro, and biocompatibility tests in vivo. PMID:24707488

Carbon nanotubes reinforced composites for biomedical applications.

PubMed

Wang, Wei; Zhu, Yuhe; Liao, Susan; Li, Jiajia

2014-01-01

This review paper reported carbon nanotubes reinforced composites for biomedical applications. Several studies have found enhancement in the mechanical properties of CNTs-based reinforced composites by the addition of CNTs. CNTs reinforced composites have been intensively investigated for many aspects of life, especially being made for biomedical applications. The review introduced fabrication of CNTs reinforced composites (CNTs reinforced metal matrix composites, CNTs reinforced polymer matrix composites, and CNTs reinforced ceramic matrix composites), their mechanical properties, cell experiments in vitro, and biocompatibility tests in vivo.

Micro-miniature gas chromatograph column disposed in silicon wafers

DOEpatents

Yu, Conrad M.

2000-01-01

A micro-miniature gas chromatograph column is fabricated by forming matching halves of a circular cross-section spiral microcapillary in two silicon wafers and then bonding the two wafers together using visual or physical alignment methods. Heating wires are deposited on the outside surfaces of each wafer in a spiral or serpentine pattern large enough in area to cover the whole microcapillary area inside the joined wafers. The visual alignment method includes etching through an alignment window in one wafer and a precision-matching alignment target in the other wafer. The two wafers are then bonded together using the window and target. The physical alignment methods include etching through vertical alignment holes in both wafers and then using pins or posts through corresponding vertical alignment holes to force precision alignment during bonding. The pins or posts may be withdrawn after curing of the bond. Once the wafers are bonded together, a solid phase of very pure silicone is injected in a solution of very pure chloroform into one end of the microcapillary. The chloroform lowers the viscosity of the silicone enough that a high pressure hypodermic needle with a thumbscrew plunger can force the solution into the whole length of the spiral microcapillary. The chloroform is then evaporated out slowly to leave the silicone behind in a deposit.

Functionalization of multi-walled carbon nanotubes by epoxide ring-opening polymerization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jin Fanlong; Rhee, Kyong Yop; Park, Soo-Jin, E-mail: sjpark@inha.ac.kr

2011-12-15

In this study, covalent functionalization of carbon nanotubes (CNTs) was accomplished by surface-initiated epoxide ring-opening polymerization. FT-IR spectra showed that polyether and epoxide group covalently attached to the sidewalls of CNTs. TGA results indicated that the polyether was successfully grown from the CNT surface, with the final products having a polymer weight percentage of ca. 14-74 wt%. The O/C ratio of CNTs increased significantly from 5.1% to 29.8% after surface functionalization of CNTs. SEM and TEM images of functionalized CNTs exhibited that the tubes were enwrapped by polymer chains with thickness of several nanometers, forming core-shell structures with CNTs atmore » the center. - Graphical abstract: Functionalized CNTs were enwrapped by polymer chains with thickness of several nanometers, forming core-shell structures with CNTs at the center. Highlights: Black-Right-Pointing-Pointer CNTs were functionalized by epoxide ring-opening polymerization. Black-Right-Pointing-Pointer Polyether and epoxide group covalently attached to the sidewalls of CNTs. Black-Right-Pointing-Pointer Functionalized CNTs have a polymer weight percentage of ca. 14-74 wt%. Black-Right-Pointing-Pointer Functionalized CNTs were enwrapped by polymer chains with thickness of several nanometers.« less

Vertically Aligned and Continuous Nanoscale Ceramic-Polymer Interfaces in Composite Solid Polymer Electrolytes for Enhanced Ionic Conductivity.

PubMed

Zhang, Xiaokun; Xie, Jin; Shi, Feifei; Lin, Dingchang; Liu, Yayuan; Liu, Wei; Pei, Allen; Gong, Yongji; Wang, Hongxia; Liu, Kai; Xiang, Yong; Cui, Yi

2018-06-13

Among all solid electrolytes, composite solid polymer electrolytes, comprised of polymer matrix and ceramic fillers, garner great interest due to the enhancement of ionic conductivity and mechanical properties derived from ceramic-polymer interactions. Here, we report a composite electrolyte with densely packed, vertically aligned, and continuous nanoscale ceramic-polymer interfaces, using surface-modified anodized aluminum oxide as the ceramic scaffold and poly(ethylene oxide) as the polymer matrix. The fast Li + transport along the ceramic-polymer interfaces was proven experimentally for the first time, and an interfacial ionic conductivity higher than 10 -3 S/cm at 0 °C was predicted. The presented composite solid electrolyte achieved an ionic conductivity as high as 5.82 × 10 -4 S/cm at the electrode level. The vertically aligned interfacial structure in the composite electrolytes enables the viable application of the composite solid electrolyte with superior ionic conductivity and high hardness, allowing Li-Li cells to be cycled at a small polarization without Li dendrite penetration.

Robust forests of vertically aligned carbon nanotubes chemically assembled on carbon substrates.

PubMed

Garrett, David J; Flavel, Benjamin S; Shapter, Joseph G; Baronian, Keith H R; Downard, Alison J

2010-02-02

Forests of vertically aligned carbon nanotubes (VACNTs) have been chemically assembled on carbon surfaces. The structures show excellent stability over a wide potential range and are resistant to degradation from sonication in acid, base, and organic solvent. Acid-treated single-walled carbon nanotubes (SWCNTs) were assembled on amine-terminated tether layers covalently attached to pyrolyzed photoresist films. Tether layers were electrografted to the carbon substrate by reduction of the p-aminobenzenediazonium cation and oxidation of ethylenediamine. The amine-modified surfaces were incubated with cut SWCNTs in the presence of N,N'-dicyclohexylcarbodiimide (DCC), giving forests of vertically aligned carbon nanotubes (VACNTs). The SWCNT assemblies were characterized by scanning electron microscopy, atomic force microscopy, and electrochemistry. Under conditions where the tether layers slow electron transfer between solution-based redox probes and the underlying electrode, the assembly of VACNTs on the tether layer dramatically increases the electron-transfer rate at the surface. The grafting procedure, and hence the preparation of VACNTs, is applicable to a wide range of materials including metals and semiconductors.

Fabrication of Vertically Aligned Carbon Nanotube or Zinc Oxide Nanorod Arrays for Optical Diffraction Gratings.

PubMed

Kim, Jeong; Kim, Sun Il; Cho, Seong-Ho; Hwang, Sungwoo; Lee, Young Hee; Hur, Jaehyun

2015-11-01

We report on new fabrication methods for a transparent, hierarchical, and patterned electrode comprised of either carbon nanotubes or zinc oxide nanorods. Vertically aligned carbon nanotubes or zinc oxide nanorod arrays were fabricated by either chemical vapor deposition or hydrothermal growth, in combination with photolithography. A transparent conductive graphene layer or zinc oxide seed layer was employed as the transparent electrode. On the patterned surface defined using photoresist, the vertically grown carbon nanotubes or zinc oxides could produce a concentrated electric field under applied DC voltage. This periodic electric field was used to align liquid crystal molecules in localized areas within the optical cell, effectively modulating the refractive index. Depending on the material and morphology of these patterned electrodes, the diffraction efficiency presented different behavior. From this study, we established the relationship between the hierarchical structure of the different electrodes and their efficiency for modulating the refractive index. We believe that this study will pave a new path for future optoelectronic applications.

Gas-Phase Functionalization of Macroscopic Carbon Nanotube Fiber Assemblies: Reaction Control, Electrochemical Properties, and Use for Flexible Supercapacitors.

PubMed

Iglesias, Daniel; Senokos, Evgeny; Alemán, Belén; Cabana, Laura; Navío, Cristina; Marcilla, Rebeca; Prato, Maurizio; Vilatela, Juan J; Marchesan, Silvia

2018-02-14

The assembly of aligned carbon nanotubes (CNTs) into fibers (CNTFs) is a convenient approach to exploit and apply the unique physico-chemical properties of CNTs in many fields. CNT functionalization has been extensively used for its implementation into composites and devices. However, CNTF functionalization is still in its infancy because of the challenges associated with preservation of CNTF morphology. Here, we report a thorough study of the gas-phase functionalization of CNTF assemblies using ozone which was generated in situ from a UV source. In contrast with liquid-based oxidation methods, this gas-phase approach preserves CNTF morphology, while notably increasing its hydrophilicity. The functionalized material is thoroughly characterized by Raman spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, and scanning electron microscopy. Its newly acquired hydrophilicity enables CNTF electrochemical characterization in aqueous media, which was not possible for the pristine material. Through comparison of electrochemical measurements in aqueous electrolytes and ionic liquids, we decouple the effects of functionalization on pseudocapacitive reactions and quantum capacitance. The functionalized CNTF assembly is successfully used as an active material and a current collector in all-solid supercapacitor flexible devices with an ionic liquid-based polymer electrolyte.

Visual Servoing-Based Nanorobotic System for Automated Electrical Characterization of Nanotubes inside SEM.

PubMed

Ding, Huiyang; Shi, Chaoyang; Ma, Li; Yang, Zhan; Wang, Mingyu; Wang, Yaqiong; Chen, Tao; Sun, Lining; Toshio, Fukuda

2018-04-08

The maneuvering and electrical characterization of nanotubes inside a scanning electron microscope (SEM) has historically been time-consuming and laborious for operators. Before the development of automated nanomanipulation-enabled techniques for the performance of pick-and-place and characterization of nanoobjects, these functions were still incomplete and largely operated manually. In this paper, a dual-probe nanomanipulation system vision-based feedback was demonstrated to automatically perform 3D nanomanipulation tasks, to investigate the electrical characterization of nanotubes. The XY-position of Atomic Force Microscope (AFM) cantilevers and individual carbon nanotubes (CNTs) were precisely recognized via a series of image processing operations. A coarse-to-fine positioning strategy in the Z-direction was applied through the combination of the sharpness-based depth estimation method and the contact-detection method. The use of nanorobotic magnification-regulated speed aided in improving working efficiency and reliability. Additionally, we proposed automated alignment of manipulator axes by visual tracking the movement trajectory of the end effector. The experimental results indicate the system's capability for automated measurement electrical characterization of CNTs. Furthermore, the automated nanomanipulation system has the potential to be extended to other nanomanipulation tasks.

Visual Servoing-Based Nanorobotic System for Automated Electrical Characterization of Nanotubes inside SEM

PubMed Central

Ding, Huiyang; Shi, Chaoyang; Ma, Li; Yang, Zhan; Wang, Mingyu; Wang, Yaqiong; Chen, Tao; Sun, Lining; Toshio, Fukuda

2018-01-01

The maneuvering and electrical characterization of nanotubes inside a scanning electron microscope (SEM) has historically been time-consuming and laborious for operators. Before the development of automated nanomanipulation-enabled techniques for the performance of pick-and-place and characterization of nanoobjects, these functions were still incomplete and largely operated manually. In this paper, a dual-probe nanomanipulation system vision-based feedback was demonstrated to automatically perform 3D nanomanipulation tasks, to investigate the electrical characterization of nanotubes. The XY-position of Atomic Force Microscope (AFM) cantilevers and individual carbon nanotubes (CNTs) were precisely recognized via a series of image processing operations. A coarse-to-fine positioning strategy in the Z-direction was applied through the combination of the sharpness-based depth estimation method and the contact-detection method. The use of nanorobotic magnification-regulated speed aided in improving working efficiency and reliability. Additionally, we proposed automated alignment of manipulator axes by visual tracking the movement trajectory of the end effector. The experimental results indicate the system’s capability for automated measurement electrical characterization of CNTs. Furthermore, the automated nanomanipulation system has the potential to be extended to other nanomanipulation tasks. PMID:29642495

WIMP detection and slow ion dynamics in carbon nanotube arrays.

PubMed

Cavoto, G; Cirillo, E N M; Cocina, F; Ferretti, J; Polosa, A D

2016-01-01

Large arrays of aligned carbon nanotubes (CNTs), open at one end, could be used as target material for the directional detection of weakly interacting dark matter particles (WIMPs). As a result of a WIMP elastic scattering on a CNT, a carbon ion might be injected in the body of the array and propagate through multiple collisions within the lattice. The ion may eventually emerge from the surface with open end CNTs, provided that its longitudinal momentum is large enough to compensate energy losses and its transverse momentum approaches the channeling conditions in a single CNT. Therefore, the angle formed between the WIMP wind apparent orientation and the direction of parallel carbon nanotube axes must be properly chosen. We focus on very low ion recoil kinetic energies, related to low mass WIMPs ([Formula: see text] GeV) where most of the existing experiments have low sensitivity. Relying on some exact results on two-dimensional lattices of circular obstacles, we study the low energy ion motion in the transverse plane with respect to CNT directions. New constraints are obtained on how to devise the CNT arrays to maximize the target channeling efficiency.

Improved tribological properties of the synthesized copper/carbon nanotube nanocomposites for rapeseed oil-based additives

NASA Astrophysics Data System (ADS)

Wang, Zhiqiang; Ren, Ruirui; Song, Haojie; Jia, Xiaohua

2018-01-01

Carbon nanotubes (CNTs) decorated with uniform copper nanoparticles (Cu NPs) were successfully prepared via a facile approach towards surface modification of CNTs with spontaneous polydopamine (PDA). The structures and morphologies of the nanocomposites were investigated by different kinds of techniques, including X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Cu/PDA/CNTs nanocomposites were fabricated by growing the Cu NPs with an average diameter of 5 nm on the surfaces of PDA-modified CNTs. The CNTs functionalized with PDA layer not only provide an anchoring platform for the Cu NPs immobilization, but also endow Cu/PDA/CNTs with good dispersion stability when Cu/PDA/CNTs nanocomposites were used as lubricant additive. The tribological performance of the nanocomposites as the rapeseed oil lubricant additive, as well as Cu NPs, CNTs, and Cu/CNTs, was also investigated using a MS-T3000 ball-on-disk tribometer. Results show that the 0.2 wt% Cu/PDA/CNTs nanoadditive simultaneously reduce the friction and wear by 33.5% and 23.7%, respectively, outperformed the tribological performance of Cu NPs, CNTs, and Cu/CNTs nanoadditives. In addition, the presence of active sites in Cu/PDA/CNTs was beneficial to reduce the time of running-in period, give rise to the fastest speed to be stable of the friction coefficient curve as compared to the other nanoadditives. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy of the worn surfaces lubricated by the soybean oil with Cu/PDA/CNTs nanocomposites showed that formation of low shear strength tribofilms containing Cu/PDA/CNTs nanocomposites and its self-lubricating property was key factor in reduction of the friction and protection against wear and deformation.

Synthesis of copper coated carbon nanotubes for aluminium matrix composites

NASA Astrophysics Data System (ADS)

Maqbool, Adnan; Khalid, F. Ahmad; Hussain, M. Asif; Bakhsh, Nabi

2014-06-01

In this investigation copper coated carbon nanotubes (CNTs) were prepared to enhance the interfacial bonding between CNTs and aluminum matrix by the molecular-level mixing process. In optimized plating bath of (1:1) by wt. CNT with Cu, thickness of coated CNTs is reduced to 100 nm to promote uniform distribution of Cu nanoparticle on the surface of pretreated CNTs. The mixing of CNTs was accomplished by ultrasonication and ball milling. Scanning electron microscope analysis revealed the homogenous dispersion of Cu-coated CNTs in nanocomposites samples compared to the uncoated CNTs. The samples were pressureless sintered under vacuum. The densification increased with the increase in the CNTs content and is more pronounced in Cu-coated CNT nanocomposites.

Toxicity of carbon nanotubes: A review.

PubMed

Francis, Arul Prakash; Devasena, Thiyagarajan

2018-03-01

Carbon nanotubes (CNTs) are widely used in the aerospace, automotive, and electronics industries because of their stability, enhanced metallic, and electrical properties. CNTs are also being investigated for biomedical applications such as drug delivery systems and biosensors. However, the toxic potential of CNTs was reported in various cell lines and animal models. The toxicity depends on diverse properties of the CNTs, such as length, aspect ratio, surface area, degree of aggregation, purity, concentration, and dose. In addition, CNTs and/or associated contaminants were well known for oxidative stress, inflammation, apoptosis, pulmonary inflammation, fibrosis, and granuloma in lungs. The increased production of CNTs likely enhanced the possibility of its exposure in people. Studies on the toxicity of CNTs are mainly focused on the pulmonary effects after intratracheal administration, and only a few studies are reported about the toxicity of CNTs via other routes of exposure. So, it is essential to consider the chronic toxicity of CNTs before using them for various biomedical applications. This review focuses on the potential toxicities of CNTs.

Effects of Nanowire Length and Surface Roughness on the Electrochemical Sensor Properties of Nafion-Free, Vertically Aligned Pt Nanowire Array Electrodes

PubMed Central

Li, Zhiyang; Leung, Calvin; Gao, Fan; Gu, Zhiyong

2015-01-01

In this paper, vertically aligned Pt nanowire arrays (PtNWA) with different lengths and surface roughnesses were fabricated and their electrochemical performance toward hydrogen peroxide (H2O2) detection was studied. The nanowire arrays were synthesized by electroplating Pt in nanopores of anodic aluminum oxide (AAO) template. Different parameters, such as current density and deposition time, were precisely controlled to synthesize nanowires with different surface roughnesses and various lengths from 3 μm to 12 μm. The PtNWA electrodes showed better performance than the conventional electrodes modified by Pt nanowires randomly dispersed on the electrode surface. The results indicate that both the length and surface roughness can affect the sensing performance of vertically aligned Pt nanowire array electrodes. Generally, longer nanowires with rougher surfaces showed better electrochemical sensing performance. The 12 μm rough surface PtNWA presented the largest sensitivity (654 μA·mM−1·cm−2) among all the nanowires studied, and showed a limit of detection of 2.4 μM. The 12 μm rough surface PtNWA electrode also showed good anti-interference property from chemicals that are typically present in the biological samples such as ascorbic, uric acid, citric acid, and glucose. The sensing performance in real samples (river water) was tested and good recovery was observed. These Nafion-free, vertically aligned Pt nanowires with surface roughness control show great promise as versatile electrochemical sensors and biosensors. PMID:26404303

Microstructure and Properties of Polypropylene/Carbon Nanotube Nanocomposites

PubMed Central

Bikiaris, Dimitrios

2010-01-01

In the last few years, great attention has been paid to the preparation of polypropylene (PP) nanocomposites using carbon nanotubes (CNTs) due to the tremendous enhancement of the mechanical, thermal, electrical, optical and structural properties of the pristine material. This is due to the unique combination of structural, mechanical, electrical, and thermal transport properties of CNTs. However, it is well-known that the properties of polymer-based nanocomposites strongly depend on the dispersion of nanofillers and almost all the discussed properties of PP/CNTs nanocomposites are strongly related to their microstructure. PP/CNTs nanocomposites were, mainly, prepared by melt mixing and in situ polymerization. Young’s modulus, tensile strength and storage modulus of the PP/CNTs nanocomposites can be increased with increasing CNTs content due to the reinforcement effect of CNTs inside the polymer matrix. However, above a certain CNTs content the mechanical properties are reduced due to the CNTs agglomeration. The microstructure of nanocomposites has been studied mainly by SEM and TEM techniques. Furthermore, it was found that CNTs can act as nucleating agents promoting the crystallization rates of PP and the addition of CNTs enhances all other physical properties of PP. The aim of this paper is to provide a comprehensive review of the existing literature related to PP/CNTs nanocomposite preparation methods and properties studies.

Enhanced antibacterial activity through the controlled alignment of graphene oxide nanosheets.

PubMed

Lu, Xinglin; Feng, Xunda; Werber, Jay R; Chu, Chiheng; Zucker, Ines; Kim, Jae-Hong; Osuji, Chinedum O; Elimelech, Menachem

2017-11-14

The cytotoxicity of 2D graphene-based nanomaterials (GBNs) is highly important for engineered applications and environmental health. However, the isotropic orientation of GBNs, most notably graphene oxide (GO), in previous experimental studies obscured the interpretation of cytotoxic contributions of nanosheet edges. Here, we investigate the orientation-dependent interaction of GBNs with bacteria using GO composite films. To produce the films, GO nanosheets are aligned in a magnetic field, immobilized by cross-linking of the surrounding matrix, and exposed on the surface through oxidative etching. Characterization by small-angle X-ray scattering and atomic force microscopy confirms that GO nanosheets align progressively well with increasing magnetic field strength and that the alignment is effectively preserved by cross-linking. When contacted with the model bacterium Escherichia coli , GO nanosheets with vertical orientation exhibit enhanced antibacterial activity compared with random and horizontal orientations. Further characterization is performed to explain the enhanced antibacterial activity of the film with vertically aligned GO. Using phospholipid vesicles as a model system, we observe that GO nanosheets induce physical disruption of the lipid bilayer. Additionally, we find substantial GO-induced oxidation of glutathione, a model intracellular antioxidant, paired with limited generation of reactive oxygen species, suggesting that oxidation occurs through a direct electron-transfer mechanism. These physical and chemical mechanisms both require nanosheet penetration of the cell membrane, suggesting that the enhanced antibacterial activity of the film with vertically aligned GO stems from an increased density of edges with a preferential orientation for membrane disruption. The importance of nanosheet penetration for cytotoxicity has direct implications for the design of engineering surfaces using GBNs.

A rapid quantification of binocular misalignment without recording eye movements: Vertical and torsional alignment nulling.

PubMed

Beaton, Kara H; Shelhamer, Mark J; Roberts, Dale C; Schubert, Michael C

2017-05-01

Small, innate asymmetries between the left and right otolith organs can cause ocular misalignment with symptoms that include double vision and motion sickness. Additionally, ocular misalignment affects nearly 5% of the US population. We have developed a portable, non-invasive technology that uses subjective perception of binocular visual signals to estimate relative binocular alignment. The Vertical Alignment Nulling (VAN) and Torsional Alignment Nulling (TAN) tests ask subjects to view one red and one blue line on a tablet computer while looking through color-matched red and blue filters so that each eye sees only one of the lines. Subjects align the red and blue lines, which are initially vertically offset from one another during VAN or rotated relative to one another during TAN, until they perceive a single continuous line. Ocular misalignments are inferred from actual offsets in the final line positions. During testing, all binocular visual cues are eliminated by employing active-matrix organic light-emitting diode (AMOLED) technology and testing in darkness. VAN and TAN can accurately account for visual offsets induced by prisms, and test-retest reliability is excellent, with resolution better than many current standard clinical tests. VAN and TAN tests are similar to the clinical Lancaster red-green test. However, VAN and TAN employ inexpensive, hand-held hardware that can be self-administered with results that are quickly quantifiable. VAN and TAN provide simple, sensitive, and quantitative measures of binocular positioning alignment that may be useful for detecting subtle abnormalities in ocular positioning. Copyright © 2017 Elsevier B.V. All rights reserved.

49 CFR 572.43 - Lumbar spine and pelvis.

Code of Federal Regulations, 2010 CFR

2010-10-01

... vertical plane which is tangent to the back of the dummy's buttocks. (3) Align the test probe so that at... vertical planes perpendicular to the midsagittal plane passing through the designated impact point. (4) Adjust the dummy so that its midsagittal plane is vertical and the rear surfaces of the thorax and...

Hierarchical composites of sulfonated graphene-supported vertically aligned polyaniline nanorods for high-performance supercapacitors

NASA Astrophysics Data System (ADS)

Ma, Biao; Zhou, Xiao; Bao, Hua; Li, Xingwei; Wang, Gengchao

2012-10-01

Hierarchical composites of sulfonated graphene-supported vertically aligned polyaniline nanorods (sGNS/PANI) are successfully synthesized via interfacial polymerization of aniline monomers in the presence of sulfonated graphene nanosheets (sGNS). The FE-SEM images indicate that the morphologies of sGNS/PANI composites can be controlled by adjusting the concentration of aniline monomers. FTIR and Raman spectra reveal that aligned PANI nanorod arrays for sGNS/PANI exhibit higher degree of conjugation compared with pristine PANI nanorods. The hierarchical composite based on the two-electrode cell possesses higher specific capacitance (497 F g-1 at 0.2 A g-1), better rate capability and cycling stability (5.7% capacitance loss after 2000 cycles) than those of pristine PANI nanorods.

Interface structure and properties of CNTs/Cu composites fabricated by electroless deposition and spark plasma sintering

NASA Astrophysics Data System (ADS)

Wang, Hu; Zhang, Zhao-Hui; Hu, Zheng-Yang; Song, Qi; Yin, Shi-Pan

2018-01-01

In this paper, we fabricated a novel copper matrix composites reinforced by carbon nanotubes (CNTs) using electroless deposition (ED) and spark plasma sintering technique. Microstructure, mechanical, electric conductivity, and thermal properties of the CNTs/Cu composites were investigated. The results show that a favorable interface containing C-O and O-Cu bond was formed between CNTs and matrix when the CNTs were coated with nano-Cu by ED method. Thus, we accomplished the uniformly dispersed CNTs in the CNTs/Cu powders and compacted composites, which eventually leads to the enhancement of the mechanical properties of the CNTs/Cu composites in the macro-scale environment. However, the interface structure can hinder the movement of carriers and free electrons and increase the interface thermal resistance, which leads to modest decrease of electrical and thermal conductivity of the CNTs/Cu composites.

Effect of CNTs dispersion on the thermal and mechanical properties of Cu/CNTs nanocomposites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Muhsan, Ali Samer, E-mail: alisameer2007@gmail.com, E-mail: faizahmad@petronas.com.my; Ahmad, Faiz, E-mail: alisameer2007@gmail.com, E-mail: faizahmad@petronas.com.my; Yusoff, Puteri Sri Melor Megat Bt, E-mail: puteris@petronas.com.my

2014-10-24

Modified technique of metal injection molding (MIM) was used to fabricate multiwalled carbon nanotube (CNT) reinforced Cu nanocomposites. The effect of adding different amount of CNTs (0-10 vol.%) on the thermal and mechanical behaviour of the fabricated nanocomposites is presented. Scanning electron microscope analysis revealed homogenous dispersion of CNTs in Cu matrices at different CNTs contents. The experimentally measured thermal conductivities of Cu/CNTs nanocomposites showed extraordinary increase (76% higher than pure sintered Cu) with addition of 10 vol.% CNTs. As compared to the pure sintered Cu, increase in modulus of elasticity (Young's modulus) of Cu/CNTs nanocomposites sintered at 1050°C formore » 2.5 h was measured to be 48%. However, in case of 7.5 vol.% CNTs, Young's modulus was increased significantly about 51% compared to that of pure sintered Cu.« less

Surface functionalization of carbon nanotubes by direct encapsulation with varying dosages of amphiphilic block copolymers

NASA Astrophysics Data System (ADS)

Yao, Xueping; Li, Jie; Kong, Liang; Wang, Yong

2015-08-01

Encapsulation of carbon nanotubes (CNTs) by amphiphilic block copolymers is an efficient way to stabilize CNTs in solvents. However, the appropriate dosages of copolymers and the assembled structures are difficult to predict and control because of the insufficient understanding on the encapsulation process. We encapsulate multiwalled CNTs with polystyrene-block-poly (4-vinyl pyridine) (PS-b-P4VP) by directly mixing them in acetic acid under sonication. The copolymer forms a lamellar structure along the surface of CNTs with the PS blocks anchoring on the tube wall and the P4VP blocks exposed to the outside. The encapsulated CNTs achieve good dispersibility in polar solvents over long periods. To increase our understanding of the encapsulation process we investigate the assembled structures and stability of copolymer/CNTs mixtures with changing mass ratios. Stable dispersions are obtained at high mass ratios between the copolymer and CNTs, i.e. 2 or 3, with the presence of free spherical micelles. Transmission electron microscopy and thermal gravimetric analysis determine that the threshold for the complete coverage of CNTs by the copolymer occurs at the mass ratio of 1.5. The coated copolymer layer activates the surface of CNTs, enabling further functionalization of CNTs. For instance, atomic layer deposition of TiO2 produces conformal thin layers on the encapsulated CNTs while isolated TiO2 bumps are produced on the pristine, inert CNTs.

Tool post modification allows easy turret lathe cutting-tool alignment

NASA Technical Reports Server (NTRS)

Fouts, L.

1966-01-01

Modified tool holder and tool post permit alignment of turret lathe cutting tools on the center of the spindle. The tool is aligned with the spindle by the holder which is kept in position by a hydraulic lock in feature of the tool post. The tool post is used on horizontal and vertical turret lathes and other engine lathes.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mermigkis, Panagiotis G.; Tsalikis, Dimitrios G.; Institute of Chemical Engineering and High Temperature Chemical Processes, GR 26500 Patras

A kinetic Monte Carlo (kMC) simulation algorithm is developed for computing the effective diffusivity of water molecules in a poly(methyl methacrylate) (PMMA) matrix containing carbon nanotubes (CNTs) at several loadings. The simulations are conducted on a cubic lattice to the bonds of which rate constants are assigned governing the elementary jump events of water molecules from one lattice site to another. Lattice sites belonging to PMMA domains of the membrane are assigned different rates than lattice sites belonging to CNT domains. Values of these two rate constants are extracted from available numerical data for water diffusivity within a PMMA matrixmore » and a CNT pre-computed on the basis of independent atomistic molecular dynamics simulations, which show that water diffusivity in CNTs is 3 orders of magnitude faster than in PMMA. Our discrete-space, continuum-time kMC simulation results for several PMMA-CNT nanocomposite membranes (characterized by different values of CNT length L and diameter D and by different loadings of the matrix in CNTs) demonstrate that the overall or effective diffusivity, D{sub eff}, of water in the entire polymeric membrane is of the same order of magnitude as its diffusivity in PMMA domains and increases only linearly with the concentration C (vol. %) in nanotubes. For a constant value of the concentration C, D{sub eff} is found to vary practically linearly also with the CNT aspect ratio L/D. The kMC data allow us to propose a simple bilinear expression for D{sub eff} as a function of C and L/D that can describe the numerical data for water mobility in the membrane extremely accurately. Additional simulations with two different CNT configurations (completely random versus aligned) show that CNT orientation in the polymeric matrix has only a minor effect on D{sub eff} (as long as CNTs do not fully penetrate the membrane). We have also extensively analyzed and quantified sublinear (anomalous) diffusive phenomena over small to moderate times and correlated them with the time needed for penetrant water molecules to explore the available large, fast-diffusing CNT pores before Fickian diffusion is reached.« less

Determination of the effective diffusivity of water in a poly (methyl methacrylate) membrane containing carbon nanotubes using kinetic Monte Carlo simulations.

PubMed

Mermigkis, Panagiotis G; Tsalikis, Dimitrios G; Mavrantzas, Vlasis G

2015-10-28

A kinetic Monte Carlo (kMC) simulation algorithm is developed for computing the effective diffusivity of water molecules in a poly(methyl methacrylate) (PMMA) matrix containing carbon nanotubes (CNTs) at several loadings. The simulations are conducted on a cubic lattice to the bonds of which rate constants are assigned governing the elementary jump events of water molecules from one lattice site to another. Lattice sites belonging to PMMA domains of the membrane are assigned different rates than lattice sites belonging to CNT domains. Values of these two rate constants are extracted from available numerical data for water diffusivity within a PMMA matrix and a CNT pre-computed on the basis of independent atomistic molecular dynamics simulations, which show that water diffusivity in CNTs is 3 orders of magnitude faster than in PMMA. Our discrete-space, continuum-time kMC simulation results for several PMMA-CNT nanocomposite membranes (characterized by different values of CNT length L and diameter D and by different loadings of the matrix in CNTs) demonstrate that the overall or effective diffusivity, D(eff), of water in the entire polymeric membrane is of the same order of magnitude as its diffusivity in PMMA domains and increases only linearly with the concentration C (vol. %) in nanotubes. For a constant value of the concentration C, D(eff) is found to vary practically linearly also with the CNT aspect ratio L/D. The kMC data allow us to propose a simple bilinear expression for D(eff) as a function of C and L/D that can describe the numerical data for water mobility in the membrane extremely accurately. Additional simulations with two different CNT configurations (completely random versus aligned) show that CNT orientation in the polymeric matrix has only a minor effect on D(eff) (as long as CNTs do not fully penetrate the membrane). We have also extensively analyzed and quantified sublinear (anomalous) diffusive phenomena over small to moderate times and correlated them with the time needed for penetrant water molecules to explore the available large, fast-diffusing CNT pores before Fickian diffusion is reached.

Determination of the effective diffusivity of water in a poly (methyl methacrylate) membrane containing carbon nanotubes using kinetic Monte Carlo simulations

NASA Astrophysics Data System (ADS)

Mermigkis, Panagiotis G.; Tsalikis, Dimitrios G.; Mavrantzas, Vlasis G.

2015-10-01

A kinetic Monte Carlo (kMC) simulation algorithm is developed for computing the effective diffusivity of water molecules in a poly(methyl methacrylate) (PMMA) matrix containing carbon nanotubes (CNTs) at several loadings. The simulations are conducted on a cubic lattice to the bonds of which rate constants are assigned governing the elementary jump events of water molecules from one lattice site to another. Lattice sites belonging to PMMA domains of the membrane are assigned different rates than lattice sites belonging to CNT domains. Values of these two rate constants are extracted from available numerical data for water diffusivity within a PMMA matrix and a CNT pre-computed on the basis of independent atomistic molecular dynamics simulations, which show that water diffusivity in CNTs is 3 orders of magnitude faster than in PMMA. Our discrete-space, continuum-time kMC simulation results for several PMMA-CNT nanocomposite membranes (characterized by different values of CNT length L and diameter D and by different loadings of the matrix in CNTs) demonstrate that the overall or effective diffusivity, Deff, of water in the entire polymeric membrane is of the same order of magnitude as its diffusivity in PMMA domains and increases only linearly with the concentration C (vol. %) in nanotubes. For a constant value of the concentration C, Deff is found to vary practically linearly also with the CNT aspect ratio L/D. The kMC data allow us to propose a simple bilinear expression for Deff as a function of C and L/D that can describe the numerical data for water mobility in the membrane extremely accurately. Additional simulations with two different CNT configurations (completely random versus aligned) show that CNT orientation in the polymeric matrix has only a minor effect on Deff (as long as CNTs do not fully penetrate the membrane). We have also extensively analyzed and quantified sublinear (anomalous) diffusive phenomena over small to moderate times and correlated them with the time needed for penetrant water molecules to explore the available large, fast-diffusing CNT pores before Fickian diffusion is reached.

Incorporation of Fe3O4/CNTs nanocomposite in an epoxy coating for corrosion protection of carbon steel

NASA Astrophysics Data System (ADS)

Pham, Gia Vu; Truc Trinh, Anh; To, Thi Xuan Hang; Duong Nguyen, Thuy; Trang Nguyen, Thu; Hoan Nguyen, Xuan

2014-09-01

In this study Fe3O4/CNTs composite with magnetic property was prepared by attaching magnetic nanoparticles (Fe3O4) to carbon nanotubes (CNTs) by hydrothermal method. The obtained Fe3O4/CNTs composite was characterized by Fourier transform infrared (FTIR) spectroscopy, powder x-ray diffraction and transmission electron microscopy. The Fe3O4/CNTs composite was then incorporated into an epoxy coating at concentration of 3 wt%. Corrosion protection of epoxy coating containing Fe3O4/CNTs composite was evaluated by electrochemical impedance spectroscopy and adhesion measurement. The impedance measurements show that Fe3O4/CNTs composite enhanced the corrosion protection of epoxy coating. The corrosion resistance of the carbon steel coated by epoxy coating containing Fe3O4/CNTs composite was significantly higher than that of carbon steel coated by clear epoxy coating and epoxy coating containing CNTs. FE-SEM photographs of fracture surface of coatings showed good dispersion of Fe3O4/CNTs composite in the epoxy matrix.

Carbon nanotubes: potential medical applications and safety concerns.

PubMed

Amenta, Valeria; Aschberger, Karin

2015-01-01

Carbon nanotubes (CNTs) have unique atomic structure, as well as outstanding thermal, mechanical, and electronic properties, making them extremely attractive materials for several different applications. Many research groups are focusing on biomedical applications of carbon-based nanomaterials, however the application of CNTs to the biomedical field is not developing as fast as in other areas. While CNTs-based products are already being used in textiles, polymer matrices to strengthen materials, sports articles, microelectronics, energy storage, etc., medicinal products and medical devices for in vivo application based on CNTs have not been commercialized yet. However, CNTs for biomedical application, i.e., CNTs conjugated to siRNA for cancer therapy, or CNTs for imaging of colorectal cancer and many other products may enter clinical trials in the next years. Concerns related to the toxicity of CNTs must be overcome in order to have these products commercialized in a near future. This article reviews emerging biomedical applications of CNTs, specifically for therapy. It also deals with challenges associated with possible medical applications of CNTs, such as their not fully understood toxicological profile in the human body. © 2014 Wiley Periodicals, Inc.

A new approach to design safe CNTs with an understanding of redox potential.

PubMed

Tsuruoka, Shuji; Cassee, Flemming R; Castranova, Vincent

2013-09-02

Carbon nanotubes (CNTs) are being increasingly industrialized and applied for various products. As of today, although several toxicological evaluations of CNTs have been conducted, designing safer CNTs is not practiced because reaction kinetics of CNTs with bioactive species is not fully understood. The authors propose a kinetic mechanism to establish designing safe CNTs as a new goal. According to a literature search on the behavior of CNTs and the effects of impurities, it is found that chemical reactions on CNT surface are attributed to redox reactions involving metal impurities and carbon structures at the CNT surface. A new goal is proposed to design safer CNTs using the redox potential hypothesis. The value of this hypothesis must be practically investigated and proven through the further experiments.

Catalytic decomposition of toxic chemicals over metal-promoted carbon nanotubes.

PubMed

Li, Lili; Han, Changxiu; Han, Xinyu; Zhou, Yixiao; Yang, Li; Zhang, Baogui; Hu, Jianli

2011-01-15

Effective decomposition of toxic gaseous compounds is important for pollution control at many chemical manufacturing plants. This study explores catalytic decomposition of phosphine (PH(3)) using novel metal-promoted carbon nanotubes (CNTs). The cerium-promoted Co/CNTs catalysts (CoCe/CNTs) are synthesized by means of coimpregnation method and reduced by three different methods (H(2), KBH(4), NaH(2)PO(2)·H(2)O/KBH(4)). The morphology, structure, and composition of the catalysts are characterized using a number of analytical instrumentations including high-resolution transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, BET surface area measurement, and inductively coupled plasma. The activity of the catalysts in PH(3) decomposition reaction is measured and correlated with their surface and structural properties. The characterization results show that the CoCe/CNTs catalyst reduced by H(2) possesses small particles and is shown thermally stable in PH(3) decomposition reaction. The activities of these catalysts are compared and are shown in the following sequence: CoCe/CNTs > Co/CNTs > CoCeBP/CNTs> CoCeB/CNTs. The difference in reduction method results in the formation of different active phases during the PH(3) decomposition reaction. After a catalytic activity test, only the CoP phase is formed on CoCe/CNTs and Co/CNTs catalysts, whereas multiphases CoP, Co(2)P, and Co phases are formed on CoCeBP/CNTs and CoCeB/CNTs. Results show that the CoP phase is formed predominantly on the CoCe/CNTs and Co/CNTs catalysts and is found to likely be the most active phase for this reaction. Furthermore, the CoCe/CNTs catalyst exhibits not only highest activity but also long-term stability in PH(3) decomposition reaction. When operated in a fixed-bed reactor at 360 °C, single-pass PH(3) conversion of about 99.8% can be achieved.

Catalytic decomposition of toxic chemicals over iron group metals supported on carbon nanotubes.

PubMed

Li, Lili; Chen, Can; Chen, Long; Zhu, Zixue; Hu, Jianli

2014-03-18

This study explores catalytic decomposition of phosphine (PH3) using iron group metals (Co, Ni) and metal oxides (Fe2O3, Co(3)O4, NiO) supported on carbon nanotubes (CNTs). The catalysts are synthesized by means of a deposition-precipitation method. The morphology, structure, and composition of the catalysts are characterized using a number of analytical instrumentations, including high-resolution transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, BET surface area measurement, and inductively coupled plasma. The activity of the catalysts in the PH3 decomposition reaction is measured and correlated with their surface and structural properties. The characterization results show that phosphidation occurs on the catalyst surface, and the resulting metal phosphides act as an active phase in the PH3 decomposition reaction. Cobalt phosphide, CoP, is formed on Co/CNTs and Co(3)O4/CNTs, whereas iron phosphide, FeP, is formed on Fe2O3/CNTs. In contrast, phosphorus-rich phosphide NiP2 is formed on Ni/CNTs and NiO/CNTs. The initial activities of the catalysts are shown in the following sequence: Ni/CNTs > Co/CNTs > Co(3)O4/CNTs >NiO/CNTs > Fe2O3/CNTs, whereas activities of metal phosphides are shown in the following order: CoP > NiP2 > FeP. The catalytic activity of metal phosphides is attributed to their electronic properties. Cobalt phosphide formed on Co/CNTs and Co(3)O4/CNTs exhibits not only the highest activity, but also long-term stability in the PH3 decomposition reaction.

Mathematical modelling of anisotropy of illite-rich shale

USGS Publications Warehouse

Chesnokov, E.M.; Tiwary, D.K.; Bayuk, I.O.; Sparkman, M.A.; Brown, R.L.

2009-01-01

The estimation of illite-rich shale anisotropy to account for the alignment of clays and gas- or brine-filled cracks is presented via mathematical modelling. Such estimation requires analysis to interpret the dominance of one effect over another. This knowledge can help to evaluate the permeability in the unconventional reservoir, stress orientation, and the seal capacity for the conventional reservoir. Effective media modelling is used to predict the elastic properties of the illite-rich shale and to identify the dominant contributions to the shale anisotropy. We consider two principal reasons of the shale anisotropy: orientation of clay platelets and orientation of fluid-filled cracks. In reality, both of these two factors affect the shale anisotropy. The goal of this study is, first, to separately analyse the effect of these two factors to reveal the specific features in P- and S-wave velocity behaviour typical of each of the factors, and, then, consider a combined effect of the factors when the cracks are horizontally or vertically aligned. To do this, we construct four models of shale. The behaviour of P- and S-wave velocities is analysed when gas- and water-filled cracks embedded in a host matrix are randomly oriented, or horizontally or vertically aligned. The host matrix can be either isotropic or anisotropic (of VTI symmetry). In such a modelling, we use published data on mineralogy and clay platelet alignment along with other micromechanical measurements. In the model, where the host matrix is isotropic, the presence of a singularity point (when the difference VS1 - VS2 changes its sign) in shear wave velocities is an indicator of brine-filled aligned cracks. In the model with the VTI host matrix and horizontally aligned cracks filled with gas, an increase in their volume concentration leads to that the azimuth at which the singularity is observed moves toward the symmetry axis. In this case, if the clay content is small (around 20 per cent), the singularity point may even vanish. The Thomsen parameters are helpful in fluid type indication in shale. An indicator of gas-filled aligned cracks is ?? > ??. If aligned cracks in illite-rich shale are brine-filled, ?? < ??. Negative value of ?? indicates brine-filled cracks in illite-rich shale. A shale with brine-filled cracks exhibits higher Vp/Vs ratio in the vertical direction as compared to the gas-filled shale. A disorientation of clay platelets and brine-filled cracks may lead to that the singularity point is absent for brine-saturated shale as well. In this case one can also observe ?? > ?? and decreased values of Vp/Vs in the vertical direction as in the case of gas-filled cracks. In the presence of vertically aligned cracks, shales exhibit distinctly revealed features of orthorhombic symmetry. The results have important applications where seismic measurements are applied to predict the maturity state of the shale. ?? 2009 The Authors Journal compilation ?? 2009 RAS.

Ultralight anisotropic foams from layered aligned carbon nanotube sheets.

PubMed

Faraji, Shaghayegh; Stano, Kelly L; Yildiz, Ozkan; Li, Ang; Zhu, Yuntian; Bradford, Philip D

2015-10-28

In this work, we present large scale, ultralight aligned carbon nanotube (CNT) structures which have densities an order of magnitude lower than CNT arrays, have tunable properties and exhibit resiliency after compression. By stacking aligned sheets of carbon nanotubes and then infiltrating with a pyrolytic carbon (PyC), resilient foam-like materials were produced that exhibited complete recovery from 90% compressive strain. With density as low as 3.8 mg cm(-3), the foam structure is over 500 times less dense than bulk graphite. Microscopy revealed that PyC coated the junctions among CNTs, and also increased CNT surface roughness. These changes in the morphology explain the transition from inelastic behavior to foam-like recovery of the layered CNT sheet structure. Mechanical and thermal properties of the foams were tuned for different applications through variation of PyC deposition duration while dynamic mechanical analysis showed no change in mechanical properties over a large temperature range. Observation of a large and linear electrical resistance change during compression of the aligned CNT/carbon (ACNT/C) foams makes strain/pressure sensors a relevant application. The foams have high oil absorption capacities, up to 275 times their own weight, which suggests they may be useful in water treatment and oil spill cleanup. Finally, the ACNT/C foam's high porosity, surface area and stability allow for demonstration of the foams as catalyst support structures.

Benchmark study of ionization potentials and electron affinities of armchair single-walled carbon nanotubes using density functional theory

NASA Astrophysics Data System (ADS)

Zhou, Bin; Hu, Zhubin; Jiang, Yanrong; He, Xiao; Sun, Zhenrong; Sun, Haitao

2018-05-01

The intrinsic parameters of carbon nanotubes (CNTs) such as ionization potential (IP) and electron affinity (EA) are closely related to their unique properties and associated applications. In this work, we demonstrated the success of optimal tuning method based on range-separated (RS) density functionals for both accurate and efficient prediction of vertical IPs and electron affinities (EAs) of a series of armchair single-walled carbon nanotubes C20n H20 (n  =  2–6) compared to the high-level IP/EA equation-of-motion coupled-cluster method with single and double substitutions (IP/EA-EOM-CCSD). Notably, the resulting frontier orbital energies (–ε HOMO and –ε LUMO) from the tuning method exhibit an excellent approximation to the corresponding IPs and EAs, that significantly outperform other conventional density functionals. In addition, it is suggested that the RS density functionals that possess both a fixed amount of exact exchange in the short-range and a correct long-range asymptotic behavior are suitable for calculating electronic structures of finite-sized CNTs. Next the performance of density functionals for description of various molecular properties such as chemical potential, hardness and electrophilicity are assessed as a function of tube length. Thanks to the efficiency and accuracy of this tuning method, the related behaviors of much longer armchair single-walled CNTs until C200H20 were studied. Lastly, the present work is proved to provide an efficient theoretical tool for future materials design and reliable characterization of other interesting properties of CNT-based systems.

Time-Dependent Subcellular Distribution and Effects of Carbon Nanotubes in Lungs of Mice

PubMed Central

Købler, Carsten; Poulsen, Sarah S.; Saber, Anne T.; Jacobsen, Nicklas R.; Wallin, Håkan; Yauk, Carole L.; Halappanavar, Sabina; Vogel, Ulla; Qvortrup, Klaus; Mølhave, Kristian

2015-01-01

Background and Methods Pulmonary deposited carbon nanotubes (CNTs) are cleared very slowly from the lung, but there is limited information on how CNTs interact with the lung tissue over time. To address this, three different multiwalled CNTs were intratracheally instilled into female C57BL/6 mice: one short (850 nm) and tangled, and two longer (4 μm and 5.7 μm) and thicker. We assessed the cellular interaction with these CNTs using transmission electron microscopy (TEM) 1, 3 and 28 days after instillation. Results TEM analysis revealed that the three CNTs followed the same overall progression pattern over time. Initially, CNTs were taken up either by a diffusion mechanism or via endocytosis. Then CNTs were agglomerated in vesicles in macrophages. Lastly, at 28 days post-exposure, evidence suggesting CNT escape from vesicle enclosures were found. The longer and thicker CNTs more often perturbed and escaped vesicular enclosures in macrophages compared to the smaller CNTs. Bronchoalveolar lavage (BAL) showed that the CNT exposure induced both an eosinophil influx and also eosinophilic crystalline pneumonia. Conclusion Two very different types of multiwalled CNTs had very similar pattern of cellular interactions in lung tissue, with the longer and thicker CNTs resulting in more severe effects in terms of eosinophil influx and incidence of eosinophilic crystalline pneumonia (ECP). PMID:25615613

49 CFR 581.7 - Test procedures.

Code of Federal Regulations, 2014 CFR

2014-10-01

... is vertical and the impact line is horizontal at the specified height. (3) For impacts at a height... Figure 1 so that Plane A is vertical and the impact line is horizontal at the specified height. (3) For... that Plane A is vertical and the impact line is horizontal at a height within the range. (4) Align the...

Improved carbon nanotube growth inside an anodic aluminum oxide template using microwave radiation

NASA Astrophysics Data System (ADS)

Dadras, Sedigheh; Faraji, Maryam

2018-05-01

In this study, we achieved superfast growth of carbon nanotubes (CNTs) in an anodic aluminum oxide (AAO) template by applying microwave (MW) radiation. This is a simple and direct approach for growing CNTs using a MW oven. The CNTs were synthesized using MW radiation at a frequency of 2.45 GHz and power was applied at various levels of 900, 600, and 450 W. We used graphite and ferrocene in equal portions as precursors. The optimum conditions for the growth of CNTs inside a MW oven were a time period of 5 s and power of 450 W. In order to grow uniform CNTs, an AAO template was applied with the CNTs synthesized under optimum conditions. The morphology of the synthesized CNTs was investigated by scanning electron microscopy analysis. The average diameters of the CNTs obtained without the template were 22-27 nm, whereas the diameters of the CNTs prepared inside the AAO template were about 4-6 nm.

Direct Assembly of Modified Proteins on Carbon Nanotubes in an Aqueous Solution

NASA Technical Reports Server (NTRS)

Kim, Jae-Woo; Lillehei, Peter T.; Park, Cheol; Harrison, Joycelyn S.

2007-01-01

Carbon nanotubes (CNTs) have superior mechanical and electrical properties that have opened up many potential applications. However, poor dispersibility and solubility, due to the substantial van der Waals attraction between tubes, have prevented the use of CNTs in practical applications, especially biotechnology applications. Effective dispersion of CNTs into small bundles or individual tubes in solvents is crucial to ensure homogeneous properties and enable practical applications. In addition to dispersion of CNTs into a solvent, the selection of appropriate solvent, which is compatible with a desired matrix, is an important factor to improve the mechanical, thermal, optical, and electrical properties of CNT-based fibers and composites. In particular, dispersion of CNTs into an aqueous system has been a challenge due to the hydrophobic nature of CNTs. Here we show an effective method for dispersion of both single wall CNTs (SWCNTs) and few wall CNTs (FWCNTs) in an aqueous buffer solution. We also show an assembly of cationized Pt-cored ferritins on the well dispersed CNTs in an aqueous buffer solution.

Thermal buckling behavior of defective CNTs under pre-load: A molecular dynamics study.

PubMed

Mehralian, Fahimeh; Tadi Beni, Yaghoub; Kiani, Yaser

2017-05-01

Current study is concentrated on the extraordinary properties of defective carbon nanotubes (CNTs). The role of vacancy defects in thermal buckling response of precompressed CNTs is explored via molecular dynamics (MD) simulations. Defective CNTs are initially compressed at a certain ratio of their critical buckling strain and then undergo a uniform temperature rise. Comprehensive study is implemented on both armchair and zigzag CNTs with different vacancy defects including monovacancy, symmetric bivacancy and asymmetric bivacancy. The results reveal that defects have a pronounced impact on the buckling behavior of CNTs; interestingly, defective CNTs under compressive pre-load show higher resistance to thermal buckling than pristine ones. In the following, the buckling response of defective CNTs is shown to be dependent on the vacancy defects, location of defects and chirality. Copyright © 2017 Elsevier Inc. All rights reserved.

Directed aggregation of carbon nanotube on curved surfaces by polymer induced depletion attraction

NASA Astrophysics Data System (ADS)

Lee, Hsin-Chieh; Jiang, Hong-Ren

2017-12-01

In this study, we show that by chemically grafting macromolecule, polyethylene glycol (PEG), onto CNTs, PEG-CNTs become dispersible in an aqueous solution with tunable depletion interactions with each other. The aggregation of the PEG-CNTs can be controlled by adding PEG polymers into the solution. PEG-CNTs not only aggregate with each other but also tend to aggregate on curved surfaces. Due to this property, we show that PEG-CNTs can be directed to aggregate on particles and patterned surfaces. Depletion interaction induced aggregation of PEG-CNTs may provide a method to place PEG-CNTs on a specific position for different applications ranging from biomedical to industrial usages.

Stacked multilayers of alternating reduced graphene oxide and carbon nanotubes for planar supercapacitors.

PubMed

Moon, Geon Dae; Joo, Ji Bong; Yin, Yadong

2013-12-07

A simple layer-by-layer approach has been developed for constructing 2D planar supercapacitors of multi-stacked reduced graphene oxide and carbon nanotubes. This sandwiched 2D architecture enables the full utilization of the maximum active surface area of rGO nanosheets by using a CNT layer as a porous physical spacer to enhance the permeation of a gel electrolyte inside the structure and reduce the agglomeration of rGO nanosheets along the vertical direction. As a result, the stacked multilayers of rGO and CNTs are capable of offering higher output voltage and current production.

Preparation and properties of in-situ growth of carbon nanotubes reinforced hydroxyapatite coating for carbon/carbon composites.

PubMed

Liu, Shoujie; Li, Hejun; Su, Yangyang; Guo, Qian; Zhang, Leilei

2017-01-01

Carbon nanotubes (CNTs) possess excellent mechanical properties for their role playing in reinforcement as imparting strength to brittle hydroxyapatite (HA) bioceramic coating. However, there are few reports relating to the in-situ grown carbon nanotubes reinforced hydroxyapatite (CNTs-HA) coating. Here we demonstrate the potential application in reinforcing biomaterials by an attempt to use in-situ grown of CNTs strengthen HA coating, using a combined method composited of injection chemical vapor deposition (ICVD) and pulsed electrodeposition. The microstructure, phases and chemical compositions of CNTs-HA coatings were characterized by various advanced methods. The scanning electron microscopy (SEM) images indicated that CNTs-HA coatings avoided the inhomogeneous dispersion of CNTs inside HA coating. The result show that the interfacial shear strength between CNTs-HA coating and the C/C composite matrix reaches to 12.86±1.43MPa. Potenitodynamic polarization and electrochemical impedance spectroscopy (EIS) studies show that the content of CNTs affects the corrosion resistance of CNTs-HA coating. Cell culturing and simulated body fluid test elicit the biocompatibility with living cells and bioactivity of CNTs-HA coatings, respectively. Copyright © 2016 Elsevier B.V. All rights reserved.

[Preparation and catalytic activity of surface-modification CNTs/TiO2 composite photocatalysts].

PubMed

Wang, Huan-Ying; Li, Wen-Jun; Chang, Zhi-Dong; Zhou, Hua-Lei; Guo, Hui-Chao

2011-09-01

A novel kind of carbon nanotubes/titanium dioxide (CNTs/TiO2) composite photocatalyst was prepared by a modified sol-gel method in which the nanoscaled TiO2 particles were uniformly deposited on the CNTs modified with poly(vinyl pyrrolidone) (PVP). The composites were characterized by a range of analytical techniques including high resolution transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The results show the successful covering of the CNTs with PVP, forming core-shell structure. The nanoscaled TiO2 particles were uniformly deposited on the surface of CNTs reducing the bare CNTs which avoid losing the absorption and scattering of photons. The combination of CNTs and TiO2 particles imply the enhanced interactions between the CNTs and TiO2 interface which possibly becomes heterojunction. The composites become mesoporous crystalline TiO2 (anatase) clusters after annealing at 500 degrees C, and the surface area increases obviously. The photocatalytic activities of surface modification CNTs/TiO2 (smCNTs/TiO2) composites are extremely enhanced from the results of the photodegradation of methylene blue (MB).

Refractive index sensing characteristics of carbon nanotube-deposited photonic crystal fiber SPR sensor

NASA Astrophysics Data System (ADS)

Jing, Jian-Ying; Wang, Qi; Wang, Bo-Tao

2018-07-01

In this paper, the carbon nanotubes (CNTs)-deposited Au film photonic crystal fiber (PCF) surface plasmon resonance (SPR) sensor (CNTs/Au-PCF sensor) and CNTs-deposited Ag film PCF SPR sensor (CNTs/Ag-PCF sensor) were developed and utilized to conduct a series of experiments for the refractive index sensing characteristics study of the CNTs-deposited SPR sensors. The PCF, spliced between two sections of multimode fibers (MMFs), was coated with a metal (Au or Ag) film and then deposited with CNTs for further sensing. CNTs coating can enhance the confined electric field intensity surrounding the sensing layer, making the SPR sensor more sensitive to the changes in the ambient medium. Compared with conventional Au film PCF SPR sensor (Au-PCF sensor), the sensitivity of CNTs/Au-PCF sensor increases by 1016.09 nm/RIU. Compared with conventional Ag film PCF SPR sensor (Ag-PCF sensor), the sensitivity of CNTs/Ag-PCF sensor increases by 709.22 nm/RIU. Therefore, we find that CNTs have a more significant effect on the Au-PCF sensor than the Ag-PCF sensor. The experimental measurements results agreed well with the simulation results. Furthermore, CNTs have high surface-to-volume ratio and extremely excellent biocompatibility. Bovine serum albumin (BSA) was employed as the target analyte to evaluate the feasibility of the CNTs/Au-PCF sensor for the detection of biomolecules, and the sensor exhibits higher sensitivity (8.18 nm/(mg/mL)), lower limit of detection (LOD) (2.5 μg/mL), and faster response time (8 s) than the Au-PCF sensor. Such CNTs-deposited SPR sensors with high sensitivities and fast response present highly promising potential for application in the field of biochemistry.

Facile preparation of carbon nanotubes-graphene hybrids and the effect of aspect ratio of carbon nanotubes on electrical and thermal properties of silicone rubber based composites

NASA Astrophysics Data System (ADS)

Zhao, Shizhen; Bai, Lu; Zheng, Junping

2018-01-01

Thermal exfoliation, as an effective and easily scalable method, was widely used to produce graphene (GE). In order to prevent the severe stacking of GE sheets after thermal exfoliation process, a facile technique was used to solve this problem through the barrier effect of carbon nanotubes (CNTs). Two kinds of CNTs with different aspect ratios (AR) were taken to prepare CNTs-GE hybrids using this technique, and then the effect of AR of CNTs (namely CNTs-L for low AR and CNTs-H for high AR) in the hybrids on the performance of silicone rubber (SR) composites was investigated. The results indicate that the presence of CNTs can effectively impede the stacking of GE sheets and the hybrids are dispersed uniformly in the SR matrix. With the addition of CNTs-GE hybrids, the resulted SR composites exhibit greatly improved electrical and thermal properties, especially for the composites filled with CNTs-H-GE hybrid. At the hybrids content of 3.0 wt%, the volume resistivity of CNTs-H-GE/SR composite is 5 × 104 Ω cm (about 10 orders of magnitude decrease compared with pure SR). And the thermal conductivity increases by 78% compared to the pure SR. But as for the CNTs-L-GE/SR composite, the corresponding values are 3 × 106 Ω cm and 59%, respectively. In terms of thermal stability, the CNTs-H-GE/SR composite containing 1.0 wt% hybrid exhibits the maximum improvement of initial degradation temperature (419 °C) compared with the CNTs-L-GE/SR composite (393 °C) and pure SR (365 °C).

Antimicrobial Properties of 2D MnO2 and MoS2 Nanomaterials Vertically Aligned on Graphene Materials and Ti3C2 MXene.

PubMed

Alimohammadi, Farbod; Sharifian Gh, Mohammad; Attanayake, Nuwan H; Thenuwara, Akila C; Gogotsi, Yury; Anasori, Babak; Strongin, Daniel R

2018-06-07

Two-dimensional (2D) nanomaterials have attracted considerable attention in biomedical and environmental applications due to their antimicrobial activity. In the interest of investigating the primary antimicrobial mode-of-action of 2D nanomaterials, we studied the antimicrobial properties of MnO 2 and MoS 2 , toward Gram-positive and Gram-negative bacteria. Bacillus subtilis and Escherichia coli bacteria were treated individually with 100 μg/mL of randomly oriented and vertically aligned nanomaterials for ∼3 h in the dark. The vertically aligned 2D MnO 2 and MoS 2 were grown on 2D sheets of graphene oxide, reduced graphene oxide, and Ti 3 C 2 MXene. Measurements to determine the viability of bacteria in the presence of the 2D nanomaterials performed by using two complementary techniques, flow cytometry, and fluorescence imaging showed that, while MnO 2 and MoS 2 nanosheets show different antibacterial activities, in both cases, Gram-positive bacteria show a higher loss in membrane integrity. Scanning electron microscopy images suggest that the 2D nanomaterials, which have a detrimental effect on bacteria viability, compromise the cell wall, leading to significant morphological changes. We propose that the peptidoglycan mesh (PM) in the bacterial wall is likely the primary target of the 2D nanomaterials. Vertically aligned 2D MnO 2 nanosheets showed the highest antimicrobial activity, suggesting that the edges of the nanosheets were likely compromising the cell walls upon contact.

Alignment of nematic liquid crystals by inhomogeneous surfaces

NASA Astrophysics Data System (ADS)

Ong, Hiap Liew; Hurd, Alan J.; Meyer, Robert B.

1985-01-01

Variable oblique alignment of nematic liquid crystals has been achieved on microscopically inhomogeneous surfaces. The surfaces consist of small patches favoring vertical (homeotropic) alignment surrounded by a matrix favoring a planar alignment. The construction of these surfaces employs randomly distributed microscopic metal islands formed by certain metals as vapor-deposited films. Larger scale periodic patterns were made as well to verify the techniques. The results are interpreted in terms of a continuum elasticity theory and azimuthal degeneracy is also discussed.

FRICTION-FREE BALANCE

DOEpatents

Carson, N.J. Jr.; Ostrander, H.W.; Munter, C.N.

1964-03-01

A weighing device having a load-supporting vertical shaft buoyed up by mutually repellant magnets is described. The shaft is aligned by an air bearing and has an air gage to sense vertical displacement caused by weights placed on the top end of the shaft. (AEC)

Synergistic effects between TiO2 and carbon nanotubes (CNTs) in a TiO2/CNTs system under visible light irradiation.

PubMed

Wu, Chung-Hsin; Kuo, Chao-Yin; Chen, Shih-Ting

2013-01-01

This study synthesized a TiO2/carbon nanotubes (CNTs) composite via the sol-gel method. The surface characteristics of the TiO2/CNTs composite were determined by X-ray diffraction, transmission electron microscopy, specific surface area analyser, ultraviolent (UV)-vis spectroscopy, X-ray photoelectron spectroscopy and Raman spectrometer. The photocatalytic activity ofthe TiO2/CNTs composite was evaluated by decolourizing C.I. Reactive Red 2 (RR2) under visible light irradiation. Furthermore, the effects of calcination temperature, pH, RR2 concentration, and the TiO2/CNTs composite dosage on RR2 decolourization were determined simultaneously. The optimal calcination temperature to generate TiO2 and the TiO2/CNTs composite was 673 K, as the percentage of anatase crystallization at this temperature was highest. The specific surface area of the TiO2/CNTs composite and TiO2 were 45 and 42 m2/g, respectively. The band gap of TiO2 and the TiO2/CNTs composite was 2.97 and 2.71 eV by UV-vis measurements, respectively. Experimental data indicate that the Ti-O-C bond formed in the TiO2/CNTs composite. The RR2 decolourization rates can be approximated by pseudo-first-order kinetics; moreover, only the TiO2/CNTs composite had photocatalytic activity under visible light irradiation. At pH 7, the RR2 decolourization rate constant of 0.5, 1 and 2 g/L TiO2/CNTs addition was 0.005, 0.0015, and 0.0047 min(-1), respectively. Decolourization rate increased as pH and the RR2 concentration decreased. The CNTs functioned as electron acceptors, promoting separation of photoinduced electron-hole pairs to retard their recombination; thus, photocatalytic activity of the TiO2/CNTs composite exceeded that of TiO2.

Carbon nanotubes for stabilization of nanostructured lipid particles

NASA Astrophysics Data System (ADS)

Gaunt, Nicholas P.; Patil-Sen, Yogita; Baker, Matthew J.; Kulkarni, Chandrashekhar V.

2014-12-01

Carbon nanotubes (CNTs) are increasingly studied for innovative biotechnological applications particularly where they are combined with essential biological materials like lipids. Lipids have been used earlier for enhancing the dispersibility of CNTs in aqueous solutions. Here we report a novel application of CNTs for stabilization of internally self-assembled nanostructured lipid particles of 2-5 μm size. Single-walled (pristine) as well as -OH and -COOH functionalized multi-walled CNTs were employed to produce nanostructured emulsions which stayed stable for months and could be re-dispersed after complete dehydration. Concentrations of CNTs employed for stabilization were very low; moreover CNTs were well-decorated with lipid molecules. These features contribute towards reducing their toxicity and improving biocompatibility for biomedical and pharmaceutical applications. Our approach paves the way for future development of combination therapies employing both CNTs and nanostructured lipid self-assembly together as carriers of different drugs.Carbon nanotubes (CNTs) are increasingly studied for innovative biotechnological applications particularly where they are combined with essential biological materials like lipids. Lipids have been used earlier for enhancing the dispersibility of CNTs in aqueous solutions. Here we report a novel application of CNTs for stabilization of internally self-assembled nanostructured lipid particles of 2-5 μm size. Single-walled (pristine) as well as -OH and -COOH functionalized multi-walled CNTs were employed to produce nanostructured emulsions which stayed stable for months and could be re-dispersed after complete dehydration. Concentrations of CNTs employed for stabilization were very low; moreover CNTs were well-decorated with lipid molecules. These features contribute towards reducing their toxicity and improving biocompatibility for biomedical and pharmaceutical applications. Our approach paves the way for future development of combination therapies employing both CNTs and nanostructured lipid self-assembly together as carriers of different drugs. Electronic supplementary information (ESI) available: Concentration series studies with Raman spectroscopy and small angle X-ray diffraction pattern for dry lipid and dehydrated CNT-lipid particles support the article. See DOI: 10.1039/c4nr05593d

The Electrochemical Behavior of Carbon Fiber Microelectrodes Modified with Carbon Nanotubes Using a Two-Step Electroless Plating/Chemical Vapor Deposition Process

PubMed Central

Lu, Longsheng; Liang, Linsheng; Teh, Kwok Siong; Xie, Yingxi; Wan, Zhenping; Tang, Yong

2017-01-01

Carbon fiber microelectrode (CFME) has been extensively applied in the biosensor and chemical sensor domains. In order to improve the electrochemical activity and sensitivity of the CFME, a new CFME modified with carbon nanotubes (CNTs), denoted as CNTs/CFME, was fabricated and investigated. First, carbon fiber (CF) monofilaments grafted with CNTs (simplified as CNTs/CFs) were fabricated in two key steps: (i) nickel electroless plating, followed by (ii) chemical vapor deposition (CVD). Second, a single CNTs/CF monofilament was selected and encapsulated into a CNTs/CFME with a simple packaging method. The morphologies of as-prepared CNTs/CFs were characterized by scanning electron microscopy. The electrochemical properties of CNTs/CFMEs were measured in potassium ferrocyanide solution (K4Fe(CN)6), by using a cyclic voltammetry (CV) and a chronoamperometry method. Compared with a bare CFME, a CNTs/CFME showed better CV curves with a higher distinguishable redox peak and response current; the higher the CNT content was, the better the CV curves were. Because the as-grown CNTs significantly enhanced the effective electrode area of CNTs/CFME, the contact area between the electrode and reactant was enlarged, further increasing the electrocatalytic active site density. Furthermore, the modified microelectrode displayed almost the same electrochemical behavior after 104 days, exhibiting remarkable stability and outstanding reproducibility. PMID:28358344

Controlled manipulation of flexible carbon nanotubes through shape-dependent pushing by atomic force microscopy.

PubMed

Yang, Seung-Cheol; Qian, Xiaoping

2013-09-17

A systematic approach to manipulating flexible carbon nanotubes (CNTs) has been developed on the basis of atomic force microscope (AFM) based pushing. Pushing CNTs enables efficient transport and precise location of individual CNTs. A key issue for pushing CNTs is preventing defective distortion in repetitive bending and unbending deformation. The approach presented here controls lateral movement of an AFM tip to bend CNTs without permanent distortion. The approach investigates possible defects caused by tensile strain of the outer tube under uniform bending and radial distortion by kinking. Using the continuum beam model and experimental bending tests, dependency of maximum bending strain on the length of bent CNTs and radial distortion on bending angles at a bent point have been demonstrated. Individual CNTs are manipulated by limiting the length of bent CNTs and the bending angle. In our approach, multiwalled CNTs with 5-15 nm diameter subjected to bending deformation produce no outer tube breakage under uniform bending and reversible radial deformation with bending angles less than 110°. The lateral tip movement is determined by a simple geometric model that relies on the shape of multiwalled CNTs. The model effectively controls deforming CNT length and bending angle for given CNT shape. Experimental results demonstrate successful manipulation of randomly dispersed CNTs without visual defects. This approach to pushing can be extended to develop a wide range of CNT based nanodevice applications.

ZrB2-CNTs Nanocomposites Fabricated by Spark Plasma Sintering

PubMed Central

Jin, Hua; Meng, Songhe; Xie, Weihua; Xu, Chenghai; Niu, Jiahong

2016-01-01

ZrB2-based nanocomposites with and without carbon nanotubes (CNTs) as reinforcement were prepared at 1600 °C by spark plasma sintering. The effects of CNTs on the microstructure and mechanical properties of nano-ZrB2 matrix composites were studied. The results indicated that adding CNTs can inhibit the abnormal grain growth of ZrB2 grains and improve the fracture toughness of the composites. The toughness mechanisms were crack deflection, crack bridging, debonding, and pull-out of CNTs. The experimental results of the nanograined ZrB2-CNTs composites were compared with those of the micro-grained ZrB2-CNTs composites. Due to the small size and surface effects, the nanograined ZrB2-CNTs composites exhibited stronger mechanical properties: the hardness, flexural strength and fracture toughness were 18.7 ± 0.2 GPa, 1016 ± 75 MPa, and 8.5 ± 0.4 MPa·m1/2, respectively. PMID:28774087

ZrB₂-CNTs Nanocomposites Fabricated by Spark Plasma Sintering.

PubMed

Jin, Hua; Meng, Songhe; Xie, Weihua; Xu, Chenghai; Niu, Jiahong

2016-11-29

ZrB₂-based nanocomposites with and without carbon nanotubes (CNTs) as reinforcement were prepared at 1600 °C by spark plasma sintering. The effects of CNTs on the microstructure and mechanical properties of nano-ZrB₂ matrix composites were studied. The results indicated that adding CNTs can inhibit the abnormal grain growth of ZrB₂ grains and improve the fracture toughness of the composites. The toughness mechanisms were crack deflection, crack bridging, debonding, and pull-out of CNTs. The experimental results of the nanograined ZrB₂-CNTs composites were compared with those of the micro-grained ZrB₂-CNTs composites. Due to the small size and surface effects, the nanograined ZrB₂-CNTs composites exhibited stronger mechanical properties: the hardness, flexural strength and fracture toughness were 18.7 ± 0.2 GPa, 1016 ± 75 MPa, and 8.5 ± 0.4 MPa·m 1/2 , respectively.

A review on protein functionalized carbon nanotubes.

PubMed

Nagaraju, Kathyayini; Reddy, Roopa; Reddy, Narendra

2015-12-18

Carbon nanotubes (CNTs) have been widely recognized and used for controlled drug delivery and in various other fields due to their unique properties and distinct advantages. Both single-walled carbon nanotubes (SWCNTs) and multiwalled (MWCNTs) carbon nanotubes are used and/or studied for potential applications in medical, energy, textile, composite, and other areas. Since CNTs are chemically inert and are insoluble in water or other organic solvents, they are functionalized or modified to carry payloads or interact with biological molecules. CNTs have been preferably functionalized with proteins because CNTs are predominantly used for medical applications such as delivery of drugs, DNA and genes, and also for biosensing. Extensive studies have been conducted to understand the interactions, cytotoxicity, and potential applications of protein functionalized CNTs but contradicting results have been published on the cytotoxicity of the functionalized CNTs. This paper provides a brief review of CNTs functionalized with proteins, methods used to functionalize the CNTs, and their potential applications.

New concept for in-line OLED manufacturing

NASA Astrophysics Data System (ADS)

Hoffmann, U.; Landgraf, H.; Campo, M.; Keller, S.; Koening, M.

2011-03-01

A new concept of a vertical In-Line deposition machine for large area white OLED production has been developed. The concept targets manufacturing on large substrates (>= Gen 4, 750 x 920 mm2) using linear deposition source achieving a total material utilization of >= 50 % and tact time down to 80 seconds. The continuously improved linear evaporation sources for the organic material achieve thickness uniformity on Gen 4 substrate of better than +/- 3 % and stable deposition rates down to less than 0.1 nm m/min and up to more than 100 nm m/min. For Lithium-Fluoride but also for other high evaporation temperature materials like Magnesium or Silver a linear source with uniformity better than +/- 3 % has been developed. For Aluminum we integrated a vertical oriented point source using wire feed to achieve high (> 150 nm m/min) and stable deposition rates. The machine concept includes a new vertical vacuum handling and alignment system for Gen 4 shadow masks. A complete alignment cycle for the mask can be done in less than one minute achieving alignment accuracy in the range of several 10 μm.

Influence of packing density and surface roughness of vertically-aligned carbon nanotubes on adhesive properties of gecko-inspired mimetics.

PubMed

Chen, Bingan; Zhong, Guofang; Oppenheimer, Pola Goldberg; Zhang, Can; Tornatzky, Hans; Esconjauregui, Santiago; Hofmann, Stephan; Robertson, John

2015-02-18

We have systematically studied the macroscopic adhesive properties of vertically aligned nanotube arrays with various packing density and roughness. Using a tensile setup in shear and normal adhesion, we find that there exists a maximum packing density for nanotube arrays to have adhesive properties. Too highly packed tubes do not offer intertube space for tube bending and side-wall contact to surfaces, thus exhibiting no adhesive properties. Likewise, we also show that the surface roughness of the arrays strongly influences the adhesion properties and the reusability of the tubes. Increasing the surface roughness of the array strengthens the adhesion in the normal direction, but weakens it in the shear direction. Altogether, these results allow progress toward mimicking the gecko's vertical mobility.

Adsorption of methyl green dye onto multi-walled carbon nanotubes decorated with Ni nanoferrite

NASA Astrophysics Data System (ADS)

Bahgat, Mohamed; Farghali, Ahmed Ali; El Rouby, Waleed; Khedr, Mohamed; Mohassab-Ahmed, Mohassab Y.

2013-06-01

This research was carried out to evaluate the capability of multi-walled carbon nanotubes (CNTs) and NiFe2O4-decorated multi-walled carbon nanotubes (NiFe2O4-CNTs) toward waste water treatment relevant to organic dyes. CNTs were prepared via chemical vapor deposition method. NiFe2O4-CNTs were prepared by in-situ chemical precipitation of metal hydroxides followed by hydrothermal processing. The samples were characterized using XRD and TEM. The adsorption efficiency of CNTs and NiFe2O4-CNTs of methyl green dye at various temperatures was examined. The adsorbed amount increased with the CNTs and NiFe2O4-CNTs dosage. The linear correlation coefficients and standard deviations of Langmuir and Freundlich isotherms were determined. It was found that Langmuir isotherm fitted the experimental results well in both adsorption cases n of methyl green onto CNTs and NiFe2O4-CNTs. Kinetics analyses were conducted using pseudo first-order, second-order and the intraparticle diffusion models. The results showed that the adsorption kinetics was controlled by a pseudo second-order model for adsorption of methyl green onto CNTs and best controlled by pseudo first-order in case of NiFe2O4-CNTs. Changes in the free energy of adsorption (Δ G°), enthalpy (Δ H°), entropy (Δ S°), and the activation energy ( E a) were determined. The Δ H°, Δ G° and E a values indicated that the adsorption of methyl green onto MWCNTs and NiFe2O4-MWCNTs was physisorption.

Preparation of Magnetic Carbon Nanotubes (Mag-CNTs) for Biomedical and Biotechnological Applications

PubMed Central

Masotti, Andrea; Caporali, Andrea

2013-01-01

Carbon nanotubes (CNTs) have been widely studied for their potential applications in many fields from nanotechnology to biomedicine. The preparation of magnetic CNTs (Mag-CNTs) opens new avenues in nanobiotechnology and biomedical applications as a consequence of their multiple properties embedded within the same moiety. Several preparation techniques have been developed during the last few years to obtain magnetic CNTs: grafting or filling nanotubes with magnetic ferrofluids or attachment of magnetic nanoparticles to CNTs or their polymeric coating. These strategies allow the generation of novel versatile systems that can be employed in many biotechnological or biomedical fields. Here, we review and discuss the most recent papers dealing with the preparation of magnetic CNTs and their application in biomedical and biotechnological fields. PMID:24351838

Preparation of magnetic carbon nanotubes (Mag-CNTs) for biomedical and biotechnological applications.

PubMed

Masotti, Andrea; Caporali, Andrea

2013-12-18

Carbon nanotubes (CNTs) have been widely studied for their potential applications in many fields from nanotechnology to biomedicine. The preparation of magnetic CNTs (Mag-CNTs) opens new avenues in nanobiotechnology and biomedical applications as a consequence of their multiple properties embedded within the same moiety. Several preparation techniques have been developed during the last few years to obtain magnetic CNTs: grafting or filling nanotubes with magnetic ferrofluids or attachment of magnetic nanoparticles to CNTs or their polymeric coating. These strategies allow the generation of novel versatile systems that can be employed in many biotechnological or biomedical fields. Here, we review and discuss the most recent papers dealing with the preparation of magnetic CNTs and their application in biomedical and biotechnological fields.

Substitutional doping of carbon nanotubes with heteroatoms and their chemical applications.

PubMed

Zhang, Yexin; Zhang, Jian; Su, Dang Sheng

2014-05-01

The electronic properties of carbon nanotubes (CNTs) can be tuned by substitutional doping with heteroatoms (mainly B and N) to expand the applications of CNTs. Based on the comprehensive understanding of the substitutional doping of CNTs, it should be possible to deliberately design doped CNTs for specific purposes. Thus, relevant experimental and theoretical works are reviewed herein in an attempt to correlate the synthetic methods, electronic properties, and applications of heteroatom-doped CNTs. The distribution and arrangement of heteroatoms in the graphitic lattice of CNTs can be modulated through the choice of synthetic conditions, which would further lead to different electronic properties of CNTs for their chemical applications. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Synthesis of Pt@TiO2@CNTs Hierarchical Structure Catalyst by Atomic Layer Deposition and Their Photocatalytic and Photoelectrochemical Activity.

PubMed

Liao, Shih-Yun; Yang, Ya-Chu; Huang, Sheng-Hsin; Gan, Jon-Yiew

2017-04-29

Pt@TiO2@CNTs hierarchical structures were prepared by first functionalizing carbon nanotubes (CNTs) with nitric acid at 140 °C. Coating of TiO2 particles on the CNTs at 300 °C was then conducted by atomic layer deposition (ALD). After the TiO2@CNTs structure was fabricated, Pt particles were deposited on the TiO2 surface as co-catalyst by plasma-enhanced ALD. The saturated deposition rates of TiO2 on a-CNTs were 1.5 Å/cycle and 0.4 Å/cycle for substrate-enhanced process and linear process, respectively. The saturated deposition rate of Pt on TiO2 was 0.39 Å/cycle. The photocatalytic activities of Pt@TiO2@CNTs hierarchical structures were higher than those without Pt co-catalyst. The particle size of Pt on TiO2@CNTs was a key factor to determine the efficiency of methylene blue (MB) degradation. The Pt@TiO2@CNTs of 2.41 ± 0.27 nm exhibited the best efficiency of MB degradation.

ROS evaluation for a series of CNTs and their derivatives using an ESR method with DMPO.

PubMed

Tsuruoka, S; Takeuchi, K; Koyama, K; Noguchi, T; Endo, M; Tristan, F; Terrones, M; Matsumoto, H; Saito, N; Usui, Y; Porter, D W; Castranova, V

Carbon nanotubes (CNTs) are important materials in advanced industries. It is a concern that pulmonary exposure to CNTs may induce carcinogenic responses. It has been recently reported that CNTs scavenge ROS though non-carbon fibers generate ROS. A comprehensive evaluation of ROS scavenging using various kinds of CNTs has not been demonstrated well. The present work specifically investigates ROS scavenging capabilities with a series of CNTs and their derivatives that were physically treated, and with the number of commercially available CNTs. CNT concentrations were controlled at 0.2 through 0.6 wt%. The ROS scavenging rate was measured by ESR with DMPO. Interestingly, the ROS scavenging rate was not only influenced by physical treatments, but was also dependent on individual manufacturing methods. Ratio of CNTs to DMPO/ hydrogen peroxide is a key parameter to obtain appropriate ROS quenching results for comparison of CNTs. The present results suggest that dangling bonds are not a sole factor for scavenging, and electron transfer on the CNT surface is not clearly determined to be the sole mechanism to explain ROS scavenging.

Synthesis of Pt@TiO2@CNTs Hierarchical Structure Catalyst by Atomic Layer Deposition and Their Photocatalytic and Photoelectrochemical Activity

PubMed Central

Liao, Shih-Yun; Yang, Ya-Chu; Huang, Sheng-Hsin; Gan, Jon-Yiew

2017-01-01

Pt@TiO2@CNTs hierarchical structures were prepared by first functionalizing carbon nanotubes (CNTs) with nitric acid at 140 °C. Coating of TiO2 particles on the CNTs at 300 °C was then conducted by atomic layer deposition (ALD). After the TiO2@CNTs structure was fabricated, Pt particles were deposited on the TiO2 surface as co-catalyst by plasma-enhanced ALD. The saturated deposition rates of TiO2 on a-CNTs were 1.5 Å/cycle and 0.4 Å/cycle for substrate-enhanced process and linear process, respectively. The saturated deposition rate of Pt on TiO2 was 0.39 Å/cycle. The photocatalytic activities of Pt@TiO2@CNTs hierarchical structures were higher than those without Pt co-catalyst. The particle size of Pt on TiO2@CNTs was a key factor to determine the efficiency of methylene blue (MB) degradation. The Pt@TiO2@CNTs of 2.41 ± 0.27 nm exhibited the best efficiency of MB degradation. PMID:28468248

Fabrication of Low Temperature Carbon Nanotube Vertical Interconnects Compatible with Semiconductor Technology

PubMed Central

Vollebregt, Sten; Ishihara, Ryoichi

2015-01-01

We demonstrate a method for the low temperature growth (350 °C) of vertically-aligned carbon nanotubes (CNT) bundles on electrically conductive thin-films. Due to the low growth temperature, the process allows integration with modern low-κ dielectrics and some flexible substrates. The process is compatible with standard semiconductor fabrication, and a method for the fabrication of electrical 4-point probe test structures for vertical interconnect test structures is presented. Using scanning electron microscopy the morphology of the CNT bundles is investigated, which demonstrates vertical alignment of the CNT and can be used to tune the CNT growth time. With Raman spectroscopy the crystallinity of the CNT is investigated. It was found that the CNT have many defects, due to the low growth temperature. The electrical current-voltage measurements of the test vertical interconnects displays a linear response, indicating good ohmic contact was achieved between the CNT bundle and the top and bottom metal electrodes. The obtained resistivities of the CNT bundle are among the average values in the literature, while a record-low CNT growth temperature was used. PMID:26709530

Toxicity of carbon nanotubes to freshwater aquatic invertebrates

USGS Publications Warehouse

Mwangi, Joseph N.; Wang, Ning; Ingersoll, Christopher G.; Hardesty, Doug K.; Brunson, Eric L.; Li, Hao; Deng, Baolin

2012-01-01

Carbon nanotubes (CNTs) are hydrophobic in nature and thus tend to accumulate in sediments if released into aquatic environments. As part of our overall effort to examine the toxicity of carbon-based nanomaterials to sediment-dwelling invertebrates, we have evaluated the toxicity of different types of CNTs in 14-d water-only exposures to an amphipod (Hyalella azteca), a midge (Chironomus dilutus), an oligochaete (Lumbriculus variegatus), and a mussel (Villosa iris) in advance of conducting whole-sediment toxicity tests with CNTs. The results of these toxicity tests conducted with CNTs added to water showed that 1.00g/L (dry wt) of commercial sources of CNTs significantly reduced the survival or growth of the invertebrates. Toxicity was influenced by the type and source of the CNTs, by whether the materials were precleaned by acid, by whether sonication was used to disperse the materials, and by species of the test organisms. Light and electron microscope imaging of the surviving test organisms showed the presence of CNTs in the gut as well as on the outer surface of the test organisms, although no evidence was observed to show penetration of CNTs through cell membranes. The present study demonstrated that both the metals solubilized from CNTs such as nickel and the "metal-free" CNTs contributed to the toxicity.

High dispersity of carbon nanotubes diminishes immunotoxicity in spleen.

PubMed

Lee, Soyoung; Khang, Dongwoo; Kim, Sang-Hyun

2015-01-01

From the various physiochemical material properties, the chemical functionalization order of single-walled carbon nanotubes (swCNTs) has not been considered as a critical factor for modulating immunological responses and toxicological aspects in drug delivery applications. Although most nanomaterials, including carbon nanotubes, are specifically accumulated in spleen, few studies have focused on spleen immunotoxicity. For this reason, this study demonstrated that the dispersity of swCNTs significantly influenced immunotoxicity in vitro and in vivo. For cytotoxicity of swCNTs, MTT assay, reactive oxygen species production, superoxide dismutase activity, cellular uptake, and confocal microscopy were used in macrophages. In the in vivo study, female BALB/c mice were intravenously administered with 1 mg/kg/day of swCNTs for 2 weeks. The body weight, organ weight, hematological change, reverse-transcription polymerase chain reaction, and lymphocyte population were evaluated. Different orders of chemical functionalization of swCNTs controlled immunotoxicity. In short, less-dispersed swCNTs caused cytotoxicity in macrophages and abnormalities in immune organs such as spleen, whereas highly dispersed swCNTs did not result in immunotoxicity. This study clarified that increasing carboxyl groups on swCNTs significantly mitigated immunotoxicity in vitro and in vivo. Our findings clarified the effective immunotoxicological factors of swCNTs by increasing dispersity of swCNTs and provided useful guidelines for the effective use of nanomaterials.

Multiwalled carbon nanotubes in alfalfa and wheat: toxicology and uptake.

PubMed

Miralles, Pola; Johnson, Errin; Church, Tamara L; Harris, Andrew T

2012-12-07

Data on the bioavailability and toxicity of carbon nanotubes (CNTs) in the environment, and, in particular, on their interactions with vascular plants, are limited. We investigated the effects of industrial-grade multiwalled CNTs (75 wt% CNTs) and their impurities on alfalfa and wheat. Phytotoxicity assays were performed during both seed germination and seedling growth. The germinations of both species were tolerant of up to 2560 mg l(-1) CNTs, and root elongation was enhanced in alfalfa and wheat seedlings exposed to CNTs. Remarkably, catalyst impurities also enhanced root elongation in alfalfa seedlings as well as wheat germination. Thus the impurities, not solely the CNTs, impacted the plants. CNT internalization by plants was investigated using electron microscopy and two-dimensional Raman mapping. The latter showed that CNTs were adsorbed onto the root surfaces of alfalfa and wheat without significant uptake or translocation. Electron microscopy investigations of internalization were inconclusive owing to poor contrast, so Fe(3)O(4)-functionalized CNTs were prepared and studied using energy-filter mapping of Fe(3)O(4). CNTs bearing Fe(3)O(4) nanoparticles were detected in the epidermis of one wheat root tip only, suggesting that internalization was possible but unusual. Thus, alfalfa and wheat tolerated high concentrations of industrial-grade multiwalled CNTs, which adsorbed onto their roots but were rarely taken up.

Multiwalled carbon nanotubes in alfalfa and wheat: toxicology and uptake

PubMed Central

Miralles, Pola; Johnson, Errin; Church, Tamara L.; Harris, Andrew T.

2012-01-01

Data on the bioavailability and toxicity of carbon nanotubes (CNTs) in the environment, and, in particular, on their interactions with vascular plants, are limited. We investigated the effects of industrial-grade multiwalled CNTs (75 wt% CNTs) and their impurities on alfalfa and wheat. Phytotoxicity assays were performed during both seed germination and seedling growth. The germinations of both species were tolerant of up to 2560 mg l−1 CNTs, and root elongation was enhanced in alfalfa and wheat seedlings exposed to CNTs. Remarkably, catalyst impurities also enhanced root elongation in alfalfa seedlings as well as wheat germination. Thus the impurities, not solely the CNTs, impacted the plants. CNT internalization by plants was investigated using electron microscopy and two-dimensional Raman mapping. The latter showed that CNTs were adsorbed onto the root surfaces of alfalfa and wheat without significant uptake or translocation. Electron microscopy investigations of internalization were inconclusive owing to poor contrast, so Fe3O4-functionalized CNTs were prepared and studied using energy-filter mapping of Fe3O4. CNTs bearing Fe3O4 nanoparticles were detected in the epidermis of one wheat root tip only, suggesting that internalization was possible but unusual. Thus, alfalfa and wheat tolerated high concentrations of industrial-grade multiwalled CNTs, which adsorbed onto their roots but were rarely taken up. PMID:22977097

The geometry and volume of melt beneath Ethiopia

NASA Astrophysics Data System (ADS)

Kendall, J. M.; Hammond, J. O. S.

2016-12-01

A range of seismic measurements can be used to map melt distribution in the crust and uppermost mantle. These include seismic P- and S-wave velocities derived from surface- and body-wave tomography, Vp/Vs ratios obtained from receiver functions, and estimates of seismic anisotropy and attenuation. The most obvious melt parameter that seismic data might be sensitive to is volume fraction. However, such data are more sensitive to the aspect ratio of melt inclusions, which is controlled by the melt wetting angle or in other words the shape of the melt inclusion. To better understand this we perform numerical modelling, varying the shape and amount of melt, to show how various seismic phases are effected by melt. To consider the effects on seismic anisotropy we assume that the melt can be stored in pockets of melt that are either horizontally or vertically aligned (e.g., sills versus dykes). We then consider a range of seismic observations from the rifting environment of Ethiopia. Recent studies of P- and S-wave tomography, Rayleigh and Love waves, and Pn or wide angle P-wave refractions provide provide complimentary constraints on melt volume, orientation and inclusion aspect ratio. Furthermore, receiver functions and shear-wave splitting in body waves show strong anisotropy in this region and can be used to constrain the strike of vertically-aligned partial melt. We show that melt in the mantle beneath Ethiopia is likely stored in low aspect ratio disk-like inclusions, suggesting melt is not in textural equilibrium. We estimate that 2-7% vertically aligned melt is stored beneath the Main Ethiopian Rift, >6% horizontally and vertically aligned melt is stored beneath the Afar-region of the Red Sea Rift and 1-6% horizontally aligned melt is stored beneath the Danakil microplate. This supports ideas of strong shear-derived segregation of melt in narrow parts of the rift and large volumes of melt beneath Afar.

Monolayer formation of human osteoblastic cells on vertically aligned multiwalled carbon nanotube scaffolds.

PubMed

Lobo, Anderson O; Antunes, Erica F; Palma, Mariana Bs; Pacheco-Soares, Cristina; Trava-Airoldi, Vladimir J; Corat, Evaldo J

2010-03-12

Monolayer formation of SaOS-2 (human osteoblast-like cells) was observed on VACNT (vertically aligned multiwalled carbon nanotubes) scaffolds without purification or functionalization. The VACNT were produced by a microwave plasma chemical vapour deposition on titanium surfaces with nickel or iron as catalyst. Cell viability and morphology studies were evaluated by LDH (lactate dehydrogenase) release assay and SEM (scanning electron microscopy), respectively. The non-toxicity and the flat spreading with monolayer formation of the SaOs-2 on VACNT scaffolds surface indicate that they can be used for biomedical applications.

Dielectric properties of vertically aligned multi-walled carbon nanotubes in the terahertz and mid-infrared range

NASA Astrophysics Data System (ADS)

Thomson, Mark D.; Zouaghi, Wissem; Meng, Fanqi; Wiecha, Matthias M.; Rabia, Kaneez; Heinlein, Thorsten; Hussein, Laith; Babu, Deepu; Yadav, Sandeep; Engstler, Jörg; Schneider, Jörg J.; Nicoloso, Norbert; Rychetský, Ivan; Kužel, Petr; Roskos, Hartmut G.

2018-01-01

We investigate the broadband dielectric properties of vertically aligned, multi-wall carbon nanotubes (VACNT), over both the terahertz (THz) and mid-infrared spectral ranges. The nominally undoped, metallic VACNT samples are probed at normal incidence, i.e. the response is predominantly due to polarisation perpendicular to the CNT axis. A detailed comparison of various conductivity models and previously reported results is presented for the non-Drude behaviour we observe in the conventional THz range (up to 2.5 THz). Extension to the mid-infrared range reveals an absorption peak at \

Growth rate of plasma-synthesized vertically aligned carbon nanofibers

NASA Astrophysics Data System (ADS)

Merkulov, Vladimir I.; Melechko, A. V.; Guillorn, M. A.; Lowndes, D. H.; Simpson, M. L.

2002-08-01

Vertically aligned carbon nanofibers (VACNFs) were synthesized by direct-current plasma enhanced chemical vapor deposition using acetylene and ammonia as the gas source. The mechanisms responsible for changing the nanofiber growth rate were studied and phenomenological models are proposed. The feedstock for VACNF growth is suggested to consist mainly of radicals formed in the plasma and not the unexcited acetylene gas molecules. The growth rate is shown to increase dramatically by changing the radical transport mechanism from diffusive to forced flow, which was accomplished by increasing the gas flow in the direction perpendicular to the substrate.

[Correction of refractive errors in patients with strabismus. Part I. Clinical problems associated with refraction, accommodation and convergence].

PubMed

Tokarz-Sawińska, Ewa

2012-01-01

In Part I the problems associated with refraction, accommodation and convergence and their role in proper eye position/visual alignment of the eyes as well as convergent, divergent and vertical alignment of the eyes have been described.

Discrimination of Mirror-Image shapes by Young Children

ERIC Educational Resources Information Center

Thompson, G. Brian

1975-01-01

Conducted two experiments which employed discrimination learning methods to test predictions related to the difficulty of discrimination of lateral reversals and of inversions when shapes are presented: (1) successively, (2) simultaneously in lateral alignment, and (3) simultaneously in vertical alignment. Subjects were 6-year-old children. (SDH)

Degradation of nitrobenzene-containing wastewater by carbon nanotubes immobilized nanoscale zerovalent iron

NASA Astrophysics Data System (ADS)

Jiao, Weizhou; Feng, Zhirong; Liu, Youzhi; Jiang, Huihui

2016-07-01

Nanoscaled zerovalent iron (NZVI)-multiwalled carbon nanotubes (CNTs) composite materials were prepared by in situ reduction of Fe2+ onto CNTs for nitrobenzene (NB) degradation. The morphologies and the composites of the prepared materials were characterized by SEM, TEM, and XRD. The results showed that the agglomeration of NZVI decreased with NZVI dispersed well onto the surfaces of CNTs, the particle size of NZVI on CNTs was about 20-50 nm. The BET surface areas of NZVI-CNTs was about 95.8 m2/g, which was 39 % higher than that of bare NZVI. For storage, the prepared NZVI-CNTs were concentrated into slurry and stored in situ as fresh slurry without drying. Contrast experiment results showed that the removal efficiency of NB by NZVI-CNTs fresh slurry was 30 % higher than that of vacuum-dried NZVI-CNTs, which indicates that storing in situ as fresh slurry can be an alternative strategy for nanoparticle storage. Batch experiment results showed that NB could be degraded to aniline by NZVI-CNTs rapidly, and the appropriate pH can be conducted at a relatively wide range from 2.0 to 9.0. The optimum mass ratio of iron-carbon was 1:1, and removal efficiency of NB by NZVI-CNTs with this mass ratio can achieve 100 % within 1 min. The degradation process of NB to intermediates was accelerated significantly by NZVI-CNTs, however, there was still a long term for the intermediates to transfer completely into the final product of aniline. The existence of CNTs can improve the formation of aniline through accelerating the electron transfer by forming microscopic galvanic cells with NZVI.

Molecular dynamics simulations of the effect of waviness and agglomeration of CNTs on interface strength of thermoset nanocomposites.

PubMed

Alian, A R; Meguid, S A

2017-02-08

Most existing molecular dynamics simulations in nanoreinforced composites assume carbon nanotubes (CNTs) to be straight and uniformly dispersed within thermoplastics. In reality, however, CNTs are typically curved, agglomerated and aggregated as a result of van der Waal interactions and electrostatic forces. In this paper, we account for both curvature and agglomeration of CNTs in extensive molecular dynamic (MD) simulations. The purpose of these simulations is to evaluate the influence of waviness and agglomeration of these curved and agglomerated CNTs on the interfacial strength of thermoset nanocomposite and upon their load transfer capability. Two aspects of the work were accordingly examined. In the first, realistic carbon nanotubes (CNTs) of the same length but varied curvatures were embedded in thermoset polymer composites and simulations of pull-out tests were conducted to evaluate the corresponding interfacial shear strength (ISS). In the second, the effect of the agglomerate size upon the ISS was determined using bundles of CNTs of different diameters. The results of our MD simulations revealed the following. The pull-out force of the curved CNTs is significantly higher than its straight counterpart and increases further with the increase in the waviness of the CNTs. This is attributed to the added pull-out energy dissipated in straightening the CNTs during the pull-out process. It also reveals that agglomeration of CNTs leads to a reduction in the ISS and poor load transferability, and that this reduction is governed by the size of the agglomerate. The simulation results were also used to develop a generalized relation for the ISS that takes into consideration the effect of waviness and agglomeration of CNTs of CNT-polymer composites.

Vertically aligned single-walled carbon nanotubes by chemical assembly--methodology, properties, and applications.

PubMed

Diao, Peng; Liu, Zhongfan

2010-04-06

Single-walled carbon nanotubes (SWNTs), as one of the most promising one-dimension nanomaterials due to its unique structure, peculiar chemical, mechanical, thermal, and electronic properties, have long been considered as an important building block to construct ordered alignments. Vertically aligned SWNTs (v-SWNTs) have been successfully prepared by using direct growth and chemical assembly strategies. In this review, we focus explicitly on the v-SWNTs fabricated via chemical assembly strategy. We provide the readers with a full and systematic summary covering the advances in all aspects of this area, including various approaches for the preparation of v-SWNTs using chemical assembly techniques, characterization, assembly kinetics, and electrochemical properties of v-SWNTs. We also review the applications of v-SWNTs in electrochemical and bioelectrochemical sensors, photoelectric conversion, and scanning probe microscopy.

Long Range In-Plane Order of Oriented Diblock Copolymer Thin Films by Graphoepitaxy

NASA Astrophysics Data System (ADS)

Fontana, Scott; Dadmun, Mark; Lowndes, Douglas

2003-03-01

Previous work by Russell and coworkers has demonstrated that controlling the interfacial energies and wetting behavior of an asymmetric diblock copolymer enables the control of the orientation of its microphases. In particular the cylindrical phase can be readily aligned perpendicular to a substrate when it is placed on a surface that is neutral to both components of the copolymer. The minor phase, PMMA may then be removed using UV radiation leaving a nanoporous template. In this work, we will report long range, in-plane ordering of the hexagonally packed nanopores that is achieved using graphoepitaxy. The long range ordered and vertically aligned diblock copolymer film can be used to produce arrays of catalytic nickel dots, which grow vertically aligned carbon nano-fibers (VACNF), resulting in a well ordered array of VACNFs.

A facile approach towards increasing the nitrogen-content in nitrogen-doped carbon nanotubes via halogenated catalysts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ombaka, L.M.; Ndungu, P.G.; Department of Applied Chemistry, Doornfontein Campus, University of Johannesburg, P.O. Box 17011, Johannesburg 2028

Nitrogen-doped carbon nanotubes (N-CNTs) have been synthesized at 850 °C via a CVD deposition technique by use of three ferrocenyl derivative catalysts, i.e. para-CN, -CF{sub 3} and -Cl substituted-phenyl rings. The synthesized catalysts have been characterized by NMR, IR, HR-MS and XRD. The XRD analysis of the para-CF{sub 3} catalyst indicates that steric factors influence the X-ray structure of 1,1′-ferrocenylphenyldiacrylonitriles. Acetonitrile or pyridine was used as carbon and nitrogen sources to yield mixtures of N-CNTs and carbon spheres (CS). The N-CNTs obtained from the para-CF{sub 3} catalysts, in pyridine, have the highest nitrogen-doping level, show a helical morphology and aremore » less thermally stable compared with those synthesized by use of the para-CN and -Cl as catalyst. This suggests that fluorine heteroatoms enhance nitrogen-doping in N-CNTs and formation of helical-N-CNTs (H-N-CNTs). The para-CF{sub 3} and para-Cl catalysts in acetonitrile yielded iron-filled N-CNTs, indicating that halogens promote encapsulation of iron into the cavity of N-CNT. The use of acetonitrile, as carbon and nitrogen source, with the para-CN and -Cl as catalysts also yielded a mixture of N-CNTs and carbon nanofibres (CNFs), with less abundance of CNFs in the products obtained using para-Cl catalysts. However, para-CF{sub 3} catalyst in acetonitrile gave N-CNTs as the only shaped carbon nanomaterials. - Graphical abstract: Graphical abstract showing the synthesis of N-CNTs using halogenated-ferrocenyl derivatives as catalyst with pyridine or acetonitrile as nitrogen and carbon sources via the chemical vapour deposition technique. - Highlights: • N-CNTs were synthesized from halogenated ferrocenyl catalysts. • Halogenated catalysts promote nitrogen-doping and pyridinic nitrogen in N-CNTs. • Halogenated catalysts facilitate iron filling of N-CNTs.« less

In vitro bacterial cytotoxicity of CNTs: reactive oxygen species mediate cell damage edges over direct physical puncturing.

PubMed

Rajavel, Krishnamoorthy; Gomathi, Rajkumar; Manian, Sellamuthu; Rajendra Kumar, Ramasamy Thangavelu

2014-01-21

Understanding the bacterial cytotoxicity of CNTs is important for a wide variety of applications in the biomedical, environmental, and health sectors. A majority of the earlier reports attributed the bactericidal cytotoxicity of CNTs to bacterial cell membrane damage by direct physical puncturing. Our results reveal that bacterial cell death via bacterial cell membrane damage is induced by reactive oxygen species (ROS) produced from CNTs and is not due to direct physical puncturing by CNTs. To understand the actual mechanism of bacterial killing, we elucidated the bacterial cytotoxicity of SWCNTs and MWCNTs against Gram-negative human pathogenic bacterial species Escherichia coli, Shigella sonnei, Klebsiella pneumoniae, and Pseudomonas aeruginosa and its amelioration upon functionalizing the CNTs with antioxidant tannic acid (TA). Interestingly, the bacterial cells treated with CNTs exhibited severe cell damage under laboratory (ambient) and sunlight irradiation conditions. However, CNTs showed no cytotoxicity to the bacterial cells when incubated in the dark. The quantitative assessments carried out by us made it explicit that CNTs are effective generators of ROS such as (1)O2, O2(•-), and (•)OH in an aqueous medium under both ambient and sunlight-irradiated conditions. Both naked and TA-functionalized CNTs showed negligible ROS production in the dark. Furthermore, strong correlations were obtained between ROS produced by CNTs and the bacterial cell mortality (with the correlation coefficient varying between 0.7618 and 0.9891) for all four tested pathogens. The absence of bactericidal cytotoxicity in both naked and functionalized CNTs in the dark reveals that the presence of ROS is the major factor responsible for the bactericidal action compared to direct physical puncturing. This understanding of the bactericidal activity of the irradiated CNTs, mediated through the generation of ROS, could be interesting for novel applications such as regulated ROS delivery in cancer therapy and the sanitation of potable water supplies.

[Anti-tumor effect of 5-FU-PLLA-CNTs on human gastric carcinoma cell lines in vitro].

PubMed

Gu, Jun; Li, Maolan; Wu, Xiangsong; Wu, Wenguang; Zhang, Lin; Ding, Qichen; Yang, Jiahua; Weng, Hao; Ding, Qian; Bao, Runfa; Shu, Yijun; Liu, Yingbin

2014-04-01

To prepare cisPLLAtin-loaded polylactic acid/cnts, and to study the anti-tumor effect of 5-FU-PLLA-CNTs on human gastric carcinoma cell lines(MGC803 and MNK45). 5-FU-PLLA-CNTs were prepared with ultrasound emulsification. The morphology of 5-FU-PLLA-CNTs was determined by scanning electron microscope(SEM), and its drug loading and drug release curve in vitro were detected by UV-Vis-NIR spectrophotometer. Cells were divided into experiment, positive control and negative control groups. CCK8 method was used to test the cytotoxic effect of 5-FU-PLLA-CNTs in different concentrations on MGC803 and MNK45 cell proliferation. Flow cytometry was employed to measure the apoptotic rate of MGC803 and MNK45 cells before and after the intervention of 5-FU-PLLA-CNTs. Deep layer film of 5-FU-PLLA-CNTs was successfully established, whose drug-load rate was(4.54±0.43)%, entrapment rate was(21.56±2.36)%. In vitro release test showed release rate within 24 h of 5-FU-PLLA-CNTs was 23.9% in a as lowly increasing manner, and accumulating release rate was 85.3% at day 31. CCk8 experiment revealed, as compared to control group, 5-FU-PLLA-CNTs significantly inhibited the proliferation of two cell lines in dose-dependent and time-dependent manner. The best 5-FU-PLLA-CNTs concentration of inhibition for human gastric cancer cell lines was 1 mg/well. Flow cytometry indicated the apoptotic rate of MGC803 and MNK45 cells in experiment group treated by 1 mg/well 5-FU-PLLA-CNTs significantly increased as compared to negative control group (P<0.05), while the difference was not significant as compared to positive control group (P>0.05). The 5-FU-PLLA-CNTs has good drug sustained-release capacity, and can significantly kill and inhibit the proliferation of MGC803 and MNK45 cell lines.

[Influence of CNTs on Photodegradation of Salbutamol in Water Environment].

PubMed

Wang, Qi; Han, Jia-rui; Wei, Bo-fan; Zhou, Lei; Zhang, Ya; Yang, Xi

2015-08-01

The influence of CNTs on the photolysis of organic pollutant was investigated by studying the photodegradation kinetics of SAL under 1000 W Xenon lamp, in the presence of three kinds of CNTs (SCNT, MWNT-COOH, MWNT-OH). In addition, the interaction between CNTs and Fe3" was also investigated. The results showed that the photodegradation of salbutamol followed pseudo-first-order kinetics, which could be inhibited by all three kinds of CNTs through light screening effect. Formation of singlet oxygen was detected during the photolysis, using the molecular probe furfuryl alcohol. All three kinds of CNTs could absorb electrons through competition, i.e., inhibit SAL photodegradation by light screening effect; meanwhile, the CNTs could generate singlet oxygen through photoexcitation to promote the photodegradation reaction. Both mechanisms coexisted, and in most cases, the inhibition effect was dominant. In addition, CNTs could inactivate the photoactive substance Fe3 in the water body by electrostatic adsorption, and affect the photochemical behavior of organic pollutants in natural water body.

Carbon nanotubes (CNTs) based strain sensors for a wearable monitoring and biofeedback system for pressure ulcer prevention and rehabilitation.

PubMed

Boissy, Patrick; Genest, Jonathan; Patenaude, Johanne; Poirier, Marie-Sol; Chenel, Vanessa; Béland, Jean-Pierre; Legault, Georges-Auguste; Bernier, Louise; Tapin, Danielle; Beauvais, Jacques

2011-01-01

This paper presents an overview of the functioning principles of CNTs and their electrical and mechanical properties when used as strain sensors and describes a system embodiment for a wearable monitoring and biofeedback platform for use in pressure ulcer prevention and rehabilitation. Two type of CNTs films (multi-layered CNTs film vs purified film) were characterized electrically and mechanically for potential use as source material. The loosely woven CNTs film (multi-layered) showed substantial less sensitivity than the purified CNTs film but had an almost linear response to stress and better mechanical properties. CNTs have the potential to achieve a much higher sensitivity to strain than other piezoresistors based on regular of conductive particles such as commercially available resistive inks and could become an innovative source material for wearable strain sensors. We are currently continuing the characterization of CNTs based strain sensors and exploring their use in a design for 3-axis strain sensors.

Functionalizing CNTs for Making Epoxy/CNT Composites

NASA Technical Reports Server (NTRS)

Chen, Jian; Rajagopal, Ramasubramaniam

2009-01-01

Functionalization of carbon nanotubes (CNTs) with linear molecular side chains of polyphenylene ether (PPE) has been shown to be effective in solubilizing the CNTs in the solvent components of solutions that are cast to make epoxy/CNT composite films. (In the absence of solubilization, the CNTs tend to clump together instead of becoming dispersed in solution as needed to impart, to the films, the desired CNT properties of electrical conductivity and mechanical strength.) Because the PPE functionalizes the CNTs in a noncovalent manner, the functionalization does not damage the CNTs. The functionalization can also be exploited to improve the interactions between CNTs and epoxy matrices to enhance the properties of the resulting composite films. In addition to the CNTs, solvent, epoxy resin, epoxy hardener, and PPE, a properly formulated solution also includes a small amount of polycarbonate, which serves to fill voids that, if allowed to remain, would degrade the performance of the film. To form the film, the solution is drop-cast or spin-cast, then the solvent is allowed to evaporate.

Quantitative measurement of carbon nanotubes released from their composites by thermal carbon analysis

NASA Astrophysics Data System (ADS)

Ogura, I.; Kotake, M.; Ata, S.; Honda, K.

2017-06-01

The release of free carbon nanotubes (CNTs) and CNTs partly embedded in matrix debris into the air may occur during mechanical and abrasion processes involving CNT composites. Since the harmful effects of CNT-matrix mixtures have not yet been fully evaluated, it is considered that any exposure to CNTs, including CNT-matrix mixtures, should be measured and controlled. Thermal carbon analysis, such as Method 5040 of the National Institute for Occupational Safety and Health, is one of the most reliable quantitative methods for measuring CNTs in the air. However, when CNTs are released together with polymer matrices, this technique may be inapplicable. In this study, we evaluated the potential for using thermal carbon analysis to determine CNTs in the presence of polymer matrices. Our results showed that thermal carbon analysis was potentially capable of determining CNTs in distinction from polyamide 12, polybutylene terephthalate, polypropylene, and polyoxymethylene. However, it was difficult to determine CNTs in the presence of polyethylene terephthalate, polycarbonate, polyetheretherketone, or polyamide 6.

Carbon nanotube fiber terahertz polarizer

NASA Astrophysics Data System (ADS)

Zubair, Ahmed; Tsentalovich, Dmitri E.; Young, Colin C.; Heimbeck, Martin S.; Everitt, Henry O.; Pasquali, Matteo; Kono, Junichiro

2016-04-01

Conventional, commercially available terahertz (THz) polarizers are made of uniformly and precisely spaced metallic wires. They are fragile and expensive, with performance characteristics highly reliant on wire diameters and spacings. Here, we report a simple and highly error-tolerant method for fabricating a freestanding THz polarizer with nearly ideal performance, reliant on the intrinsically one-dimensional character of conduction electrons in well-aligned carbon nanotubes (CNTs). The polarizer was constructed on a mechanical frame over which we manually wound acid-doped CNT fibers with ultrahigh electrical conductivity. We demonstrated that the polarizer has an extinction ratio of ˜-30 dB with a low insertion loss (<0.5 dB) throughout a frequency range of 0.2-1.1 THz. In addition, we used a THz ellipsometer to measure the Müller matrix of the CNT-fiber polarizer and found comparable attenuation to a commercial metallic wire-grid polarizer. Furthermore, based on the classical theory of light transmission through an array of metallic wires, we demonstrated the most striking difference between the CNT-fiber and metallic wire-grid polarizers: the latter fails to work in the zero-spacing limit, where it acts as a simple mirror, while the former continues to work as an excellent polarizer even in that limit due to the one-dimensional conductivity of individual CNTs.

Carbon Nanotubes in Water: MD Simulations of Internal and External Flow, Self Organization

NASA Technical Reports Server (NTRS)

Jaffe, Richard L.; Halicioglu, Timur; Werder, Thomas; Walther, Jens; Koumoutsakos, Petros; Arnold, James (Technical Monitor)

2001-01-01

We have developed computational tools, based on particle codes, for molecular dynamics (MD) simulation of carbon nanotubes (CNT) in aqueous environments. The interaction of CNTs with water is envisioned as a prototype for the design of engineering nano-devices, such as artificial sterocillia and molecular biosensors. Large scale simulations involving thousands of water molecules are possible due to our efficient parallel MD code that takes long range electrostatic interactions into account. Since CNTs can be considered as rolled up sheets of graphite, we expect the CNT-water interaction to be similar to the interaction of graphite with water. However, there are fundamental differences between considering graphite and CNTs, since the curvature of CNTs affects their chemical activity and also since capillary effects play an important role for both dynamic and static behaviour of materials inside CNTs. In recent studies Gordillo and Marti described the hydrogen bond structure as well as time dependent properties of water confined in CNTs. We are presenting results from the development of force fields describing the interaction of CNTs and water based on ab-initio quantum mechanical calculations. Furthermore, our results include both water flows external to CNTs and the behaviour of water nanodroplets inside heated CNTs. In the first case (external flows) the hydrophobic behaviour of CNTs is quantified and we analyze structural properties of water in the vicinity of CNTs with diagnostics such as hydrogen bond distribution, water dipole orientation and radial distribution functions. The presence of water leads to attractive forces between CNTs as a result of their hydrophobicity. Through extensive simulations we quantify these attractive forces in terms of the number and separation of the CNT. Results of our simulations involving arrays of CNTs indicate that these exhibit a hydrophobic behaviour that leads to self-organising structures capable of trapping water clusters. In the second case (internal flows) we study the behaviour of water droplets confined inside CNTs. Constant temperature simulations allow us to capture structural properties such as the contact angles and density profiles of the equilibrated drops. By heating and subsequently cooling of the CNT, we are able to measure the evaporation and the condensation rate of the entrapped water.

Vertical Si nanowire arrays fabricated by magnetically guided metal-assisted chemical etching

NASA Astrophysics Data System (ADS)

Chun, Dong Won; Kim, Tae Kyoung; Choi, Duyoung; Caldwell, Elizabeth; Kim, Young Jin; Paik, Jae Cheol; Jin, Sungho; Chen, Renkun

2016-11-01

In this work, vertically aligned Si nanowire arrays were fabricated by magnetically guided metal-assisted directional chemical etching. Using an anodized aluminum oxide template as a shadow mask, nanoscale Ni dot arrays were fabricated on an Si wafer to serve as a mask to protect the Si during the etching. For the magnetically guided chemical etching, we deposited a tri-layer metal catalyst (Au/Fe/Au) in a Swiss-cheese configuration and etched the sample under the magnetic field to improve the directionality of the Si nanowire etching and increase the etching rate along the vertical direction. After the etching, the nanowires were dried with minimal surface-tension-induced aggregation by utilizing a supercritical CO2 drying procedure. High-resolution transmission electron microscopy (HR-TEM) analysis confirmed the formation of single-crystal Si nanowires. The method developed here for producing vertically aligned Si nanowire arrays could find a wide range of applications in electrochemical and electronic devices.

Enhanced solar photoelectrochemical conversion efficiency of the hydrothermally-deposited TiO2 nanorod arrays: Effects of the light trapping and optimum charge transfer

NASA Astrophysics Data System (ADS)

An, Gil Woo; Mahadik, Mahadeo A.; Chae, Weon-Sik; Kim, Hyun Gyu; Cho, Min; Jang, Jum Suk

2018-05-01

The vertically aligned TiO2 nanorod arrays (NRA) with manipulated aspect ratio were hydrothermally synthesized by changing the amount of the titanium (Ti) precursor in the initial growth solution. FE-SEM images show the optimum morphology, density and aspect ratio of the well-aligned TB-1.2 NRs on the surface of the FTO substrate. The UV-vis-absorption measurements revealed that a sample prepared at TB-1.2 can provide an increased light trapping effect. PEC analyses demonstrated that the TiO2 nanorods deposited at TB-1.2 of Titanium butoxide show a relatively high PEC conversion efficiency (3.5 times) compared with the TB-0.8 prepared TiO2 at a 1.0 V versus RHE. The higher PEC performance is believed to be the result of an enhancement of the optimum aspect ratio, light trapping, an efficient charge separation, and the high carrier transport in the vertically aligned TiO2 NRs. Further, the PEC based organic dye degradation experiments showed 77% and 94% removal of Orange II and methylene blue respectively. Additionally, 109 μmol h-1 cm-2 hydrogen generations were attributed using optimized vertically aligned TiO2 NRA's. Thus, the appropriate morphology manipulated the TiO2 NRAs are useful for solar conversion applications.

Microwave-Hydrothermal Synthesis of SnO2-CNTs Hybrid Nanocomposites with Visible Light Photocatalytic Activity.

PubMed

Wu, Shuisheng; Dai, Weili

2017-03-03

SnO2 nanoparticles coated on carbon nanotubes (CNTs) were prepared via a simple microwave-hydrothermal route. The as-obtained SnO2-CNTs composites were characterized using X-ray powder diffraction, Raman spectroscopy, and transmission electron microscopy. The photocatalytic activity of as-prepared SnO2-CNTs for degradation of Rhodamine B under visible light irradiation was investigated. The results show that SnO2-CNTs nanocomposites have a higher photocatalytic activity than pure SnO2 due to the rapid transferring of electrons and the effective separation of holes and electrons on SnO2-CNTs.

Microwave-Hydrothermal Synthesis of SnO2-CNTs Hybrid Nanocomposites with Visible Light Photocatalytic Activity

PubMed Central

Wu, Shuisheng; Dai, Weili

2017-01-01

SnO2 nanoparticles coated on carbon nanotubes (CNTs) were prepared via a simple microwave-hydrothermal route. The as-obtained SnO2-CNTs composites were characterized using X-ray powder diffraction, Raman spectroscopy, and transmission electron microscopy. The photocatalytic activity of as-prepared SnO2-CNTs for degradation of Rhodamine B under visible light irradiation was investigated. The results show that SnO2-CNTs nanocomposites have a higher photocatalytic activity than pure SnO2 due to the rapid transferring of electrons and the effective separation of holes and electrons on SnO2-CNTs. PMID:28336888

Carbon Nanotubes Filled with Different Ferromagnetic Alloys Affect the Growth and Development of Rice Seedlings by Changing the C:N Ratio and Plant Hormones Concentrations.

PubMed

Hao, Yi; Yu, Feifan; Lv, Ruitao; Ma, Chuanxin; Zhang, Zetian; Rui, Yukui; Liu, Liming; Cao, Weidong; Xing, Baoshan

2016-01-01

The aim of this study was to investigate the phytotoxicity of thin-walled carbon nanotubes (CNTs) to rice (Oryza sativa L.) seedlings. Three different CNTs, including hollow multi-walled carbon nanotubes (MWCNTs), Fe-filled carbon nanotubes (Fe-CNTs), and Fe-Co-filled carbon nanotubes (FeCo-CNTs), were evaluated. The CNTs significantly inhibited rice growth by decreasing the concentrations of endogenous plant hormones. The carbon to nitrogen ratio (C:N ratio) significantly increased in rice roots after treatments with CNTs, and all three types of CNTs had the same effects on the C:N ratio. Interestingly, the increase in the C:N ratio in roots was largely because of decreased N content, indicating that the CNTs significantly decreased N assimilation. Analyses of the Fe and Co contents in plant tissues, transmission electron microscope (TEM) observations and energy dispersive X-ray spectroscopy (EDS) analysis proved that the CNTs could penetrate the cell wall and the cell membrane, and then enter the root cells. According to the author's knowledge, this is the first time to study the relationship between carbon nanotubes and carbon nitrogen ratio and plant hormones.

Carbon Nanotubes Filled with Different Ferromagnetic Alloys Affect the Growth and Development of Rice Seedlings by Changing the C:N Ratio and Plant Hormones Concentrations

PubMed Central

Lv, Ruitao; Ma, Chuanxin; Zhang, Zetian; Rui, Yukui; Liu, Liming; Cao, Weidong; Xing, Baoshan

2016-01-01

The aim of this study was to investigate the phytotoxicity of thin-walled carbon nanotubes (CNTs) to rice (Oryza sativa L.) seedlings. Three different CNTs, including hollow multi-walled carbon nanotubes (MWCNTs), Fe-filled carbon nanotubes (Fe-CNTs), and Fe-Co-filled carbon nanotubes (FeCo-CNTs), were evaluated. The CNTs significantly inhibited rice growth by decreasing the concentrations of endogenous plant hormones. The carbon to nitrogen ratio (C:N ratio) significantly increased in rice roots after treatments with CNTs, and all three types of CNTs had the same effects on the C:N ratio. Interestingly, the increase in the C:N ratio in roots was largely because of decreased N content, indicating that the CNTs significantly decreased N assimilation. Analyses of the Fe and Co contents in plant tissues, transmission electron microscope (TEM) observations and energy dispersive X-ray spectroscopy (EDS) analysis proved that the CNTs could penetrate the cell wall and the cell membrane, and then enter the root cells. According to the author's knowledge, this is the first time to study the relationship between carbon nanotubes and carbon nitrogen ratio and plant hormones. PMID:27284692

Laser-fiber coupling by means of a silicon micro-optical bench and a self-aligned soldering process

NASA Astrophysics Data System (ADS)

Schmidt, Jan P.; Cordes, A.; Mueller, Joerg; Burkhardt, Hans

1995-02-01

The alignment of laser diodes to monomode fibers has to meet extremely close tolerances for a low coupling loss. Typically < 0.5 micrometers in lateral and vertical direction and less than two degrees in angle deviation are allowed for a coupling loss below 2 dB. Presently such close tolerances can only be met by gluing or soldering both components on separate base plates and combining them via piezoactivated alignment monitoring the output of the circuit and then gluing them using UV-hardening epoxies. Such a procedure is not very economical and not useful for mass applications. This paper presents the principle and realization of a silicon micro-optical bench for laser-fiber-coupling, which avoids the above mentioned disadvantages. The micro-optical bench is realized using well controlled plasma etching processes to transfer the guiding patterns for the laser and the fiber into the silicon substrate, keeping geometry tolerances below +/- 0.5 micrometers in lateral and vertical direction. Mounting the laser diode by means of a self-aligned soldering process, an additional contribution to the precise alignment of the laser is further improved.

Wear of carbon nanotubes grafted on carbon fibers and this influence on the properties of composites materials

NASA Astrophysics Data System (ADS)

Guignier, Claire; Bueno, Marie-Ange; Camillieri, Brigitte; Durand, Bernard

2017-10-01

Carbon nanotubes (CNTs) grafted on carbon surfaces can be used to reinforce composite materials. During an industrial process of CNTs production and composite processing, friction stresses will be applied on CNTs. This study showed that CNTs formed a transfer film under friction stresses and that the wear of the CNTs has no influence on the wettability of the surface, so we can predict no decrease in the properties of composites.

Cytotoxicity of Protein-Carbon Nanotubes on J774 Macrophages Is a Functionalization Grade-Dependent Effect

PubMed Central

Montes-Fonseca, Silvia Lorena; Sánchez-Ramírez, Blanca; Luna-Velasco, Antonia; Arzate-Quintana, Carlos; Silva-Cazares, Macrina Beatriz; González Horta, Carmen

2015-01-01

Carbon nanotubes (CNTs) are used as carriers in medicine due to their ability to be functionalized with chemical substances. However, cytotoxicity analysis is required prior to use for in vivo models. The aim of this study was to evaluate the cytotoxic effect of CNTs functionalized with a 46 kDa surface protein from Entamoeba histolytica (P46-CNTs) on J774A macrophages. With this purpose, CNTs were synthesized by spray pyrolysis and purified (P-CNTs) using sonication for 48 h. A 46 kDa protein, with a 4.6–5.4 pI range, was isolated from E. histolytica HM1:IMSS strain trophozoites using an OFFGEL system. The P-CNTs were functionalized with the purified 46 kDa protein, classified according to their degree of functionalization, and characterized by Raman and Infrared spectroscopy. In vitro cytotoxicity was evaluated by MTT, apoptosis, and morphological assays. The results demonstrated that P46-CNTs exhibited cytotoxicity dependent upon the functionalized grade. Contrary to what was expected, P46-CNTs with a high grade of functionalization were more toxic to J774 macrophages than P46-CNTs with a low grade of functionalization, than P-CNTs, and had a similar level of toxicity as UP-CNT. This suggests that the nature of the functionalized protein plays a key role in the cytotoxicity of these nanoparticles. PMID:26075262

Fabrication and Water Treatment Application of Carbon Nanotubes (CNTs)-Based Composite Membranes: A Review

PubMed Central

Ma, Lining; Dong, Xinfa; Chen, Mingliang; Zhu, Li; Wang, Chaoxian; Yang, Fenglin; Dong, Yingchao

2017-01-01

Membrane separation technology is widely explored for various applications, such as water desalination and wastewater treatment, which can alleviate the global issue of fresh water scarcity. Specifically, carbon nanotubes (CNTs)-based composite membranes are increasingly of interest due to the combined merits of CNTs and membrane separation, offering enhanced membrane properties. This article first briefly discusses fabrication and growth mechanisms, characterization and functionalization techniques of CNTs, and then reviews the fabrication methods for CNTs-based composite membranes in detail. The applications of CNTs-based composite membranes in water treatment are comprehensively reviewed, including seawater or brine desalination, oil-water separation, removal of heavy metal ions and emerging pollutants as well as membrane separation coupled with assistant techniques. Furthermore, the future direction and perspective for CNTs-based composite membranes are also briefly outlined. PMID:28335452

Augmenting static and dynamic mechanical strength of carbon nanotube/epoxy soft nanocomposites via modulation of purification and functionalization routes.

PubMed

Billing, Beant Kaur; Dhar, Purbarun; Singh, Narinder; Agnihotri, Prabhat K

2018-01-03

A detailed experimental investigation was carried out to establish the relationship between CNT purification and functionalization routes and the average response of CNT/epoxy nanocomposites under static and dynamic loading. It was shown that the relative improvement in the mechanical properties of the epoxy matrix due to the addition of CNTs depends on the choice of purification and functionalization steps. A better dispersion of CNTs was recorded for the functionalized CNTs as compared to the oxidized and CVD grown CNTs. Moreover, tensile, 3-point bending and nanoDMA testing performed on nanocomposites processed with CVD-grown, oxidized and functionalized CNTs revealed that COOH functionalization after the oxidation of CNTs at 350 °C is the optimized processing route to harness the excellent properties of CNTs in CNT/epoxy nanocomposites.

[Anti-tumor effects of DDP-PLLA-CNTs on human cholangiocarcinoma cell line in vitro].

PubMed

Li, Maolan; Lu, Wei; Zhang, Fei; Ding, Qichen; Wu, Xiangsong; Tan, Zhujun; Wu, Wenguang; Weng, Hao; Wang, Xuefeng; Shi, Weibin; Dong, Ping; Gu, Jun; Liu, Yingbin

2014-11-04

To explore the antitumor effects of DDP-PLLA-CNTs on human cholangiocarcinoma cell line. DDP-PLLA-CNTs were prepared with the method of ultrasound emulsification. The morphology of DDP-PLLA-CNTs was determined by scanning electron microscope (SEM). And its drug loading and drug release curve in vitro was detected by UV-Vis-NIR spectrophotometer. CCK8 was used to test the cytotoxic effects of DDP-PLLA-CNTs at different concentrations on QBC939 cell proliferation.Flow cytometry was employed to measure the changes of apoptotic rate. With excellent controlled-release characteristic of in vitro drug release, DDP-PLLA-CNTs inhibited the proliferation and significantly increased the apoptotic rate of QBC939 cell line. DDP-PLLA-CNTs have drug sustained-release characteristics and can significantly inhibit the proliferation of QBC939 cell line.

Fabrication and Water Treatment Application of Carbon Nanotubes (CNTs)-Based Composite Membranes: A Review.

PubMed

Ma, Lining; Dong, Xinfa; Chen, Mingliang; Zhu, Li; Wang, Chaoxian; Yang, Fenglin; Dong, Yingchao

2017-03-18

Membrane separation technology is widely explored for various applications, such as water desalination and wastewater treatment, which can alleviate the global issue of fresh water scarcity. Specifically, carbon nanotubes (CNTs)-based composite membranes are increasingly of interest due to the combined merits of CNTs and membrane separation, offering enhanced membrane properties. This article first briefly discusses fabrication and growth mechanisms, characterization and functionalization techniques of CNTs, and then reviews the fabrication methods for CNTs-based composite membranes in detail. The applications of CNTs-based composite membranes in water treatment are comprehensively reviewed, including seawater or brine desalination, oil-water separation, removal of heavy metal ions and emerging pollutants as well as membrane separation coupled with assistant techniques. Furthermore, the future direction and perspective for CNTs-based composite membranes are also briefly outlined.

Application of Carbon Nanotubes for Plant Genetic Transformation

NASA Astrophysics Data System (ADS)

Burlaka, Olga M.; Pirko, Yaroslav V.; Yemets, Alla I.; Blume, Yaroslav B.

In this chapter, the current state of using carbon nanotubes (CNTs; single- and multi-walled) that have attracted great interdisciplinary interest in recent decades due to their peculiar properties for genetic transformation of prokaryotic and eukaryotic cells will be enlightened. The covalent and non-covalent surface chemistry for the CNT functionalization with focus on the potential applications of surface modifications in design of biocompatible CNTs will be discussed. The properties of CNTs that are favorable for biotechnological use and current status of technical approaches that allow the increase in biocompatibility and lower nanotoxicity of engineered CNTs will be described. Decisions proposed by non-covalent surface modification of CNTs will be discussed. Existing data concerning mechanisms of CNT cell entry and factors governing toxicity, cellular uptake, intracellular traffic, and biodegradation of CNTs along with bioavailability of molecular cargoes of loaded CNTs will be discussed. Eco-friendly production of water dispersions of biologically functionalized multi-walled and single-walled CNTs for use as nano-vehicles for the DNA delivery in plant genetic transformation of plants will be described. The background, advantages, and problems of using CNTs in developing of novel methods of genetic transformation, including plant genetic transformation, will be highlighted. Special attention will be paid to the limitations of conventional gene transfer techniques and promising features of CNT-based strategies having improved efficacy, reproducibility, and accuracy along with less time consumption. Issues impeding manipulation of CNTs such as entangled bundle formation, low water solubility, inert properties of pristine CNTs, etc., and ways to solve arising tasks will be overviewed.

A facile method to align carbon nanotubes on polymeric membrane substrate

PubMed Central

Zhao, Haiyang; Zhou, Zhijun; Dong, Hang; Zhang, Lin; Chen, Huanlin; Hou, Lian

2013-01-01

The alignment of carbon nanotubes (CNT) is the fundamental requirement to ensure their excellent functions but seems to be desolated in recent years. A facile method, hot-press combined with peel-off (HPPO), is introduced here, through which CNT can be successfully vertically aligned on the polymeric membrane substrate. Shear force and mechanical stretch are proposed to be the main forces to align the tubes perpendicular to the substrate surface during the peel-off process. The alignment of CNT keeps its orientation in a thin hybrid membrane by dip-coating cellulose acetate dope solution. It is expected that the stable alignment of CNT by HPPO would contribute to the realization of its potential applications. PMID:24326297

Self-aligned gated field emission devices using single carbon nanofiber cathodes

NASA Astrophysics Data System (ADS)

Guillorn, M. A.; Melechko, A. V.; Merkulov, V. I.; Hensley, D. K.; Simpson, M. L.; Lowndes, D. H.

2002-11-01

We report on the fabrication and operation of integrated gated field emission devices using single vertically aligned carbon nanofiber (VACNF) cathodes where the gate aperture has been formed using a self-aligned technique based on chemical mechanical polishing. We find that this method for producing gated cathode devices easily achieves structures with gate apertures on the order of 2 mum that show good concentric alignment to the VACNF emitter. The operation of these devices was explored and field emission characteristics that fit well to the Fowler-Nordheim model of emission was demonstrated.

A reliable method to grow vertically-aligned silicon nanowires by a novel ramp-cooling process

NASA Astrophysics Data System (ADS)

Ho, Tzuen-Wei; Hong, Franklin Chau-Nan

2012-08-01

We have grown silicon nanowires (SiNWs) on Si (1 1 1) substrates by gold-catalyzed vapor-liquid-solid (VLS) process using tetrachlorosilane (SiCl4) in a hot-wall chemical vapor deposition reactor. Even under the optimized conditions including H2 annealing to reduce the surface native oxide, epitaxial SiNWs of 150-200 nm in diameter often grew along all four <1 1 1> family directions with one direction vertical and three others inclined to the surface. Therefore, the growth of high degree ordered SiNW arrays along [1 1 1] only was attempted on Au-coated Si (1 1 1) by a ramp-cooling process utilizing the liquid phase epitaxy (LPE) mechanism. The Au-coated Si substrate was first annealed in H2 at 650 °C to form Au-Si alloy nanoparticles, and then ramp-cooled at a controlled rate to precipitate epitaxial Si seeds on the substrate based on LPE mechanism. The substrate was further heated in SiCl4/H2 to 850 °C for the VLS growths of SiNWs on the Si seeds. Thus, almost 100% vertically-aligned SiNWs along [1 1 1] only could be reproducibly grown on Si (1 1 1), without using a template or patterning the metal catalyst. The high-density vertically-aligned SiNWs have good potentials for solar cells and nano-devices.

Taxel-addressable matrix of vertical nanowire piezotronic transistors

DOEpatents

Wang, Zhong Lin; Wu, Wenzhuo; Wen, Xiaonan

2015-05-05

A tactile sensing matrix includes a substrate, a first plurality of elongated electrode structures, a plurality of vertically aligned piezoelectric members, an insulating layer infused into the piezoelectric members and a second plurality of elongated electrode structures. The first plurality of elongated electrode structures is disposed on the substrate along a first orientation. The vertically aligned piezoelectric members is disposed on the first plurality of elongated electrode structures and form a matrix having columns of piezoelectric members disposed along the first orientation and rows of piezoelectric members disposed along a second orientation that is transverse to the first orientation. The second plurality of elongated electrode structures is disposed on the insulating layer along the second orientation. The elongated electrode structures form a Schottky contact with the piezoelectric members. When pressure is applied to the piezoelectric members, current flow therethrough is modulated.

The Development of High-Density Vertical Silicon Nanowires and Their Application in a Heterojunction Diode.

PubMed

Chang, Wen-Chung; Su, Sheng-Chien; Wu, Chia-Ching

2016-06-30

Vertically aligned p-type silicon nanowire (SiNW) arrays were fabricated through metal-assisted chemical etching (MACE) of Si wafers. An indium tin oxide/indium zinc oxide/silicon nanowire (ITO/IZO/SiNW) heterojunction diode was formed by depositing ITO and IZO thin films on the vertically aligned SiNW arrays. The structural and electrical properties of the resulting ITO/IZO/SiNW heterojunction diode were characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and current-voltage (I-V) measurements. Nonlinear and rectifying I-V properties confirmed that a heterojunction diode was successfully formed in the ITO/IZO/SiNW structure. The diode had a well-defined rectifying behavior, with a rectification ratio of 550.7 at 3 V and a turn-on voltage of 2.53 V under dark conditions.

Fiber optics welder having movable aligning mirror

DOEpatents

Higgins, Robert W.; Robichaud, Roger E.

1981-01-01

A system for welding fiber optic waveguides together. The ends of the two fibers to be joined together are accurately, collinearly aligned in a vertical orientation and subjected to a controlled, diffuse arc to effect welding and thermal conditioning. A front-surfaced mirror mounted at a 45.degree. angle to the optical axis of a stereomicroscope mounted for viewing the junction of the ends provides two orthogonal views of the interface during the alignment operation.

Tunable carbon nanotube-tungsten carbide nanoparticles heterostructures by vapor deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xia, Min; Guo, Hongyan; Ge, Changchun

2014-05-14

A simple, versatile route for the synthesis of carbon nanotube (CNT)-tungsten carbide nanoparticles heterostructures was set up via vapor deposition process. For the first time, amorphous CNTs (α-CNTs) were used to immobilized tungsten carbide nanoparticles. By adjusting the synthesis and annealing temperature, α-CNTs/amorphous tungsten carbide, α-CNTs/W{sub 2}C, and CNTs/W{sub 2}C/WC heterostructures were prepared. This approach provides an efficient method to attach other metal carbides and other nanoparticles to carbon nanotubes with tunable properties.

Toxicity of Carbon Nanotubes and its Implications for Occupational and Environmental Health

NASA Technical Reports Server (NTRS)

Lam, Chiu-wing; James, John T.

2007-01-01

This viewgraph document reviews the sources of Nano particles in the environment, the structure and properties of Carbon Nanotubes (CNTs), the physical characteristics of CNT materials, pulmonary and other health concerns of exposure to CNTs. The toxicity of CNT in rodents is summarized and some natural, and man-made sources of CNTs are shown. CNTs are electrically and thermally conductive, fibrous, biopersistent and very complicated in structures. The factors affecting toxicity of CNTs are more than size and surface area.

Hydrothermal conversion of graphite to carbon nanotubes (CNTs) induced by bubble collapse

NASA Astrophysics Data System (ADS)

Zhang, Yong; Liu, Fang

2016-11-01

Cu-Fe-CNTs and Ni-Fe-CNTs coatings were deposited on gray cast iron by a hydrothermal approach. It was demonstrated that, the flaky graphite of gray cast iron was exfoliated to graphene nanosheets under hydrothermal reactions, and graphene nanosheets were scrolled to CNTs. After high temperature treatments, the volume losses of Cu-Fe-CNTs and Ni-Fe-CNTs coatings were 52.6 % and 40.0 % of gray cast iron substrate at 60 min wear tests, respectively, obviously increasing the wear properties of gray cast iron. During hydrothermal reactions, water jets and shock waves were produced by bubble collapse. Induced by the water jets and shock waves, exfoliation of flaky graphite was performed, producing exfoliated graphene nanosheets. Attacked by the radially distributed water jets and shock waves, graphene nanosheets were curved, shaped to semicircle morphology and eventually scrolled to tubular CNTs.

Aqueous suspensions of carbon nanotubes: surface oxidation, colloidal stability and uranium sorption.

PubMed

Schierz, A; Zänker, H

2009-04-01

The objective of this study is to obtain information on the behaviour of carbon nanotubes (CNTs) as potential carriers of pollutants in the case of accidental CNT release to the environment and on the properties of CNTs as a potential adsorbent material in water purification. The effects of acid treatment of CNTs on (i) the surface properties, (ii) the colloidal stability and (iii) heavy metal sorption are investigated, the latter being exemplified by uranium(VI) sorption. There is a pronounced influence of surface treatment on the behaviour of the CNTs in aqueous suspension. Results showed that acid treatment increases the amount of acidic surface groups on the CNTs. Therefore, acid treatment has an increasing effect on the colloidal stability of the CNTs and on their adsorption capacity for U(VI). Another way to stabilise colloids of pristine CNTs in aqueous suspension is the addition of humic acid.