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ABSTRACT: Single-walled carbon nanotubes were deposited on one end of the etched carbon fiber electrodes by an electrophoretic method. The carbon nanotube bundles formed a dense network on the carbon fiber surface. The electrochemical properties of the composite carbon electrodes were studied in the buffered neutral solutions. The results in cyclic voltammetry's characteristic indicate that the electrons on the electrodes transfer very fast. Furthermore, the redox reactions of dopamine (DA) on the composite electrodes show good sensitivity. When the DA concentration was 0.02 mM, the peak current in differential pulse technique reached 1.33 microA after performing the background subtraction. In addition, the simultaneous detection of DA and ascorbic acid (AA) showed that the interference effect was not observed. It was suggested that the carbon composite microelectrodes have potential applications as electrochemical sensors inside a single cell.
Journal of Nanoscience and Nanotechnology 03/2012; 12(3):1972-8. · 1.56 Impact Factor
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ABSTRACT: We report measurements of the shear modulus of each shell and the friction between the two shells of double-shell carbon nanotubes in single nanotube-based nanoelectromechanical devices operated in a transmission electron microscope. In situ nanobeam electron diffraction is applied to obtain the chiral indices of each shell of the nanotube and it allows us to establish a quantitative correlation between the atomic structure and properties of the nanotube under investigation.
Physical Review Letters 11/2011; 107(20):206101. · 7.37 Impact Factor
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ABSTRACT: Carbon fiber clothes are a promising material for electrodes of supercapacitors owing to their unique 3-D structure, high surface area, remarkable chemical stability, and electrical conductivity. In this Article, electro-etched carbon fiber cloth is explored as an electrode for supercapacitors by coating polyaniline nanowires. The as-prepared electro-etched carbon fiber cloth and polyaniline nanowires, which were characterized by scanning electron microscopy and transmission electron microscopy, were assembled into supercapacitors. The polyaniline nanowires can reach a mass-normalized specific capacitance of 673 F/g and an area-normalized specific capacitance of 3.5 F/cm2. We also studied the etching and coating of single carbon fibers using the same processing method. The single fiber shows almost the same specific capacitance as the carbon fiber cloth of the same coating density, indicating good accessibility of etched carbon fiber cloth electrode. This work suggests that our polyaniline-based etched carbon fiber cloth electrodes can be a low-cost and scalable solution for the high-performance energy storage devices.
10/2011;
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ABSTRACT: We describe a graphene and single-walled carbon nanotube (SWCNT) composite film prepared by a blending process for use as electrodes in high energy density supercapacitors. Specific capacitances of 290.6 F g(-1) and 201.0 F g(-1) have been obtained for a single electrode in aqueous and organic electrolytes, respectively, using a more practical two-electrode testing system. In the organic electrolyte the energy density reached 62.8 Wh kg(-1) and the power density reached 58.5 kW kg(-1). The addition of single-walled carbon nanotubes raised the energy density by 23% and power density by 31% more than the graphene electrodes. The graphene/CNT electrodes exhibited an ultra-high energy density of 155.6 Wh kg(-1) in ionic liquid at room temperature. In addition, the specific capacitance increased by 29% after 1000 cycles in ionic liquid, indicating their excellent cyclicity. The SWCNTs acted as a conductive additive, spacer, and binder in the graphene/CNT supercapacitors. This work suggests that our graphene/CNT supercapacitors can be comparable to NiMH batteries in performance and are promising for applications in hybrid vehicles and electric vehicles.
Physical Chemistry Chemical Physics 09/2011; 13(39):17615-24. · 3.57 Impact Factor
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ABSTRACT: Graphene, two-dimensional layers of sp2-bonded carbon, has many unique properties. In this paper, graphene is decorated with flower-like MnO2 nanostructures for the application in energy storage devices. The as-prepared graphene and MnO2 nano-flowers, which were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), were assembled into an asymmetric supercapacitor. The specific capacitance of the graphene electrode reached 245 F/g at a charging current of 1 mA. The MnO2 nano-flowers which consisted of tiny rods with a diameter of less than 10 nm were coated onto the graphene electrodes by electrodeposition. The specific capacitance after the MnO2 deposition is 328 F/g at the charging current of 1 mA with an energy density of 11.4Wh/kg and power density of 25.8 kW/kg. This work suggests that our graphene-based electrodes can be a promising candidate for high-performance energy storage devices.
MRS Proceedings. 12/2010; 1303.
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ABSTRACT: Electron diffraction technique has been developed and refined to establish a systematic procedure to determine the chirality (chiral indices) of each and every shell in a carbon nanotube. We have introduced a zoning scheme to sort the reflection layer lines from the multiple shells of a carbon nanotube. An application of the procedure is demonstrated as an example for an eleven-shell carbon nanotube whose chiral indices of each and every shell were determined unambiguously. The revealed structure of the carbon nanotube suggests that there is no strong correlation among the shells as the nanotube was formed. The limitations of the current method are also discussed.
Ultramicroscopy 10/2010; 111(1):66-72. · 2.47 Impact Factor
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ABSTRACT: LaB(6) nanowires are ideal for applications as an electrical field-induced ion and electron point source due to their miniature dimensions, low work function, as well as excellent electrical, thermal, and mechanical properties. We present here a reliable method to fabricate and assemble single LaB(6) nanowire-based field emitters of different crystal orientations. The atomic arrangement, emission brightness from each crystal plane, and field emission stability have been characterized using field ion microscopy (FIM) and field emission microscopy (FEM). It is found that the 001 oriented LaB(6) nanowire emitter has the highest field emission symmetry while the 012 oriented LaB(6) nanowire has the lowest apical work function. The field emission stability from the single LaB(6) nanowire emitter is significantly better than either the LaB(6) needle-type emitter or W cold field emitters.
Nano Letters 09/2010; 10(9):3539-44. · 13.20 Impact Factor
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ABSTRACT: We have assembled single-wall carbon nanotubes into ultrathin long fibrils using a dielectrophoretic technique and studied the mechanical and electrochemical properties of carbon nanotube fibrils. The diameter of the fibrils can be controlled in the range of 200 nm to 2 mum, and the length can reach as long as 1 cm. The obtained fibrils have a tensile strength of about 65 MPa, electrical conductivity ranging from 80 to 200 S cm(-1), and specific capacitance more than 200 F g(-1). The results indicate that these ultrathin long carbon nanotube fibrils are of great potential for applications as conductive wires and probe electrodes.
ACS Nano 10/2009; 3(11):3679-83. · 10.77 Impact Factor
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ABSTRACT: We have employed the atomic force microscopy based (a) three-point bending and (b) nanoindentation methods to obtain the Young’s modulus and hardness of single LaB6 nanowires. The Young’s modulus, E = 467.1±15.8 GPa, is the same as that of the LaB6 single crystals but larger than the sintered polycrystalline LaB6 samples. The nanoindentation hardness of the LaB6 nanowire is H = 70.6±2.1 GPa at an indent depth of 4.6 nm, which is higher than that of the LaB6 single crystals, LaB6 polycrystals, and W metals. A superior resistance against thermal vibration, field modification, and ion bombardment is expected for the LaB6 nanowires as a field-emission point electron source.
Applied Physics Letters 05/2008; 92(17):173121-173121-3. · 3.84 Impact Factor
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Lu-Chang Qin
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ABSTRACT: The atomic structure of a carbon nanotube can be defined by the chiral indices, (n,m), that specify its perimeter vector (chiral vector), with which the diameter and helicity are also determined. The fine electron beam available in a modern Transmission Electron Microscope (TEM) offers a unique and powerful probe to reveal the atomic structure of individual nanotubes. This article covers two aspects related to the use of the electron probe in the TEM for the study of carbon nanotubes: (i) to express the electron diffraction intensity distribution in the electron diffraction patterns of carbon nanotubes and (ii) to obtain the chiral indices (n,m) of carbon nanotubes from their electron diffraction patterns. For a nanotube of given chiral indices (n,m), the electron scattering amplitude from the carbon nanotube can be expressed analytically in closed form using the helical diffraction theory, from which its electron diffraction pattern can be calculated and understood. The reverse problem, i.e., assignment of the chiral indices (n,m) of a carbon nanotube from its electron diffraction pattern, is approached from the relationship between the electron diffraction intensity distribution and the chiral indices (n,m). The first method is to obtain indiscriminately the chiral indices (n,m) by reading directly the intensity distribution on the three principal layer lines, l(1), l(2), and l(3), which have intensities proportional to the square of the Bessel functions of orders m, n, and n + m: I(l1) proportional, variant |J(m) (pidR)|(2), I(l2) proportional, variant |J(n) (pidR)|(2), and I(l3) proportional, variant |J(n+m) (pidR)|(2). The second method is to obtain and use the ratio of the indices n/m = (2D(1)-D(2))/(2D(2)-D(1)) in which D(1) and D(2) are the spacings of principal layer lines l(1) and l(2), respectively. Examples of using these methods are also illustrated in the determination of chiral indices of isolated individual single-walled carbon nanotubes, a bundle of single-walled carbon nanotubes, and multi-walled carbon nanotubes.
Physical Chemistry Chemical Physics 02/2007; 9(1):31-48. · 3.57 Impact Factor
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ABSTRACT: The authors report the effects of Cs doping on the field emission properties of a five-shell single carbon nanotube. The chiral indices of each shell of this carbon nanotube have been determined using nanobeam electron diffraction, which has four semiconducting shells and one metallic shell in the middle. From the Fowler-Nordheim plots, a reduction from 4.8 to 3.8 eV has been observed in the work function of the single carbon nanotube before and after Cs doping.
Applied Physics Letters 12/2006; 89(26):263113-263113-3. · 3.84 Impact Factor
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ABSTRACT: Individual carbon nanotube electron field emitters with good controllability have been fabricated in a two-step process involving (a) producing micron-size carbon fibers which contain single carbon nanotubes at their cores by a chemical vapor deposition method and (b) exposing the nanotubes by fracturing the fiber with mechanical forces and mounting the fiber to a copper wire. These fiber-nanotube electron emitters show low operating voltage, generate high field enhancement, and produce fine electron beams. The field emission characteristics and durability of this structure offer promising applications for analytical instruments where high performance point electron sources are required.
Applied Physics Letters 11/2006; 89(19):193113-193113-3. · 3.84 Impact Factor
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ABSTRACT: A unique type of carbon nanotubes with 2 to 5 layers of sidewalls and diameters less than 10 nm was synthesized by the thermal chemical vapor deposition (CVD) method with MgO supported Fe/Mo catalyst. Unlike the typical CVD grown multi-walled carbon nanotubes, these few-walled carbon nanotubes (FWNTs) have a high degree of structural perfection. They have enhanced electron field emission characteristics compared to the current commercial nanotubes, with a low threshold field for emission and improved emission stability.
Journal of Nanoscience and Nanotechnology 06/2006; 6(5):1346-9. · 1.56 Impact Factor
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ABSTRACT: Having the lowest work function in the rare-earth hexaboride family, GdB6 nanowires of rectangular cross-section with about 50 nm in lateral dimension and several microns in length have been successfully produced using a CVD method. The nanowires are grown in the 001 lattice direction, and both the tip-top and the side surfaces are terminated with the {100} lattice planes. A GdB6 single nanowire field emitter has also been built with an emission current of more than 150 nA at an applied field of less than 3.2 V/mum. The work function of the nanowire emitter was estimated to be about 1.5 eV.
Journal of the American Chemical Society 10/2005; 127(38):13120-1. · 9.91 Impact Factor
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ABSTRACT: The extinction and orientational dependence of electron diffraction from single-walled carbon nanotubes have been observed experimentally and investigated in detail theoretically using both algebraic analysis and numerical simulations. Electron diffraction from only achiral carbon nanotubes of zigzag or armchair structure shows observable orientational dependence and extinction of certain layer lines in experiment due to the interference of two primary Bessel functions of the same order that contribute to the scattering intensities on these layer lines.
09/2005;
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ABSTRACT: A simple, one-step method has been utilized to synthesize functional ternary alkali titanate nanowires of single crystallinity. Nanostructural characterization shows that the nanowires are Na2Ti6O13 with [010] growth direction and KTi8O16.5 with [001] growth direction.
Journal of the American Chemical Society 09/2005; 127(33):11584-5. · 9.91 Impact Factor
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ABSTRACT: Considered to be one of the best electron emission materials, CeB6 nanowires are of great scientific and industrial interest. CeB6 nanowires of square cross section with about 50 nm in lateral dimension and more than several micrometers in length have been successfully produced using a chemical vapor deposition method. The nanowires are grown in the 100 lattice direction, and both the tip top and the side surfaces are terminated with the {100} lattice planes.
Journal of the American Chemical Society 07/2005; 127(22):8002-3. · 9.91 Impact Factor
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ABSTRACT: A direct method is described to determine the chiral indices (u, v) of a carbon nanotube from a nanobeam electron diffraction pattern of the nanotube with high accuracy. This method is a one-step procedure and allows rapid and precise assignment of the chiral indices of carbon nanotubes. Using a contemporary electron microscope, we have been able to achieve an accuracy that enables us to assign the chiral indices unambiguously up to the range of (30, 30), corresponding to a diameter of 4.0 nm. Examples of determination of the chiral indices for two single-walled carbon nanotubes are presented as an illustration of the method.
05/2005;
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ABSTRACT: Considered to be one of the best electron emission materials, CeB6 nanowires are of great scientific and industrial interest. CeB6 nanowires of square cross section with about 50 nm in lateral dimension and more than several micrometers in length have been successfully produced using a chemical vapor deposition method. The nanowires are grown in the 100 lattice direction, and both the tip top and the side surfaces are terminated with the {100} lattice planes.
05/2005;
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ABSTRACT: We report a method that allows direct, systematic, and accurate determination of the atomic structure of multiwalled carbon nanotubes by analyzing the scattering intensities on the nonequatorial layer lines in the electron diffraction pattern. Complete structure determination of a quadruple-walled carbon nanotube is described as an example, and it was found that the intertubular distance varied from 0.36 nm to 0.5 nm with a mean value of 0.42 nm.
Applied Physics Letters 05/2005; 86(19):191903-191903-3. · 3.84 Impact Factor
