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ABSTRACT: Carbon nanotube (CNT) ferroelectric field-effect transistors (FeFETs) with well-defined memory switch behaviors are promising for nonvolatile, nondestructive read-out (NDRO) memory operation and ultralow power consumption. Here, we report two-bit CNT-FeFET memories by assembling two top gates on individual nanotubes coated with ferroelectric thin films. Each bit of the nanotube transistor memory exhibits a controllable memory switching behavior induced by the reversible remnant polarization of the ferroelectric films, and its NDRO operation is demonstrated. The low driving voltage of 2 V, high carrier mobility over 1000 cm2 V(-1) s(-1), and potential ultrahigh integration density over 200 Gbit inch(-2) of the two-bit FeFET memory are highlighted in this paper.
Nanotechnology 11/2009; 20(47):475305. · 3.98 Impact Factor
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ABSTRACT: In situ electrical transport measurements on individual bent ZnO nanowires have been performed inside a high-resolution transmission electron microscope, where the crystal structures of ZnO nanowires were simultaneously imaged. A series of consecutively recorded current-voltage (I-V) curves along with an increase in nanowire bending show the striking effect of bending on their electrical behavior. The bending-induced changes of resistivity, electron concentration, and carrier mobility of ZnO nanowires have been retrieved based on the experimental I-V data, which suggests the applications of ZnO nanowires as nanoelectromechanical sensors.
Applied Physics Letters 05/2008; 92(21):213105-213105-3. · 3.84 Impact Factor
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ABSTRACT: Field electron emission of GaN-filled carbon nanotubes, grown by microwave plasma enhanced chemical vapor deposition, was investigated. The detailed structural characterization shows that the filled nanotube has a GaN-core/C-shell structure, in which the GaN wire corresponds to a wurtzite structure. The field emission properties of the GaN-filled carbon nanotubes have been achieved with high and stable emission current. It is attributed to the unique cable-like structure, which makes the GaN-core/C-shell composite mechanically solid and chemically stable. This study suggests the GaN-filled carbon nanotube as an ideal candidate for future high-current and high-power field emitter applications.
Journal of Nanoscience and Nanotechnology 04/2007; 7(3):1080-3. · 1.56 Impact Factor
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ABSTRACT: The mechanical properties of individual tungsten oxide (WO3) nanowires, directly grown onto tungsten scanning tunneling microscopy tips, have been investigated by a custom-built in situ transmission electron microscopy (TEM) measurement system. Young’s modulii (E) of the individual WO3 nanowires were measured with the assistance of electric-induced mechanical resonance. The results indicate that E basically keeps constant at diameter larger than 30 nm, while it largely increases with decreasing diameter when diameter becomes smaller than 30 nm. This diameter dependence is attributed to the lower defect density in nanowires with smaller diameter, as imaged by in situ TEM.
Applied Physics Letters 11/2006; 89(22):221908-221908-3. · 3.84 Impact Factor
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ABSTRACT: Controlled preparation of nanoscale materials and the underlying mechanisms are essential issues nowadays. Here, we report a significant subtractive formation process of large-area diamond conical nanostructure arrays using a hot filament chemical vapor deposition (HFCVD) system with negative biasing of the substrates, and the etching effect of energetic ions on the formation of diamond cone arrays with controlled morphology has been studied in detail. It shows that methylic ions dominantly contribute to diamond cone formation based on a neutral-ion charge exchange collision model. The self-organized selective sputtering process of as-formed hillock bottoms on a roughened surface by low energetic ions plays a key role for the formation and development of diamond cones. The cone morphologies under various experimental parameters are systematically studied, and they nicely confirm and supplement the as-established cone formation mechanism.
Journal of Applied Physics. 08/2006; 100(3):034312-034312-5.
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ABSTRACT: Direct synthesis of large-scale ternary boron carbonitride single-walled nanotubes (BCN-SWNTs) via a bias-assisted HFCVD process was presented. The BCN-SWNTs were grown over the powdery Fe-Mo/MgO catalyst by using CH4, B2H6, and ethylenediamine vapor as the reactant gases. As high as 16 atom % nitrogen can be incorporated within the nanotube shells, with the boron content in the range of 2-4 atom %. The ternary covalent bonding nature of the BCN-SWNTs was well characterized, and the B, C, and N elemental maps were clearly imaged by energy-filtered transmission electron microscopy.
Journal of the American Chemical Society 06/2006; 128(20):6530-1. · 9.91 Impact Factor
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ABSTRACT: Field emission of an individual multiwalled carbon nanotube, driven by a customer-built piezomanipulator, was measured in a transmission electron microscope. The measurement geometry and the nanotube structure were imaged in situ. A linear dependence of field enhancement factor β on the distance d between the nanotube tip and its counteranode is found. The enhanced field emission mechanism is studied by a tip-flat emission model. The results indicate that the radius of emission apex r is an important factor in field emission with a relationship of β∝r<sup>-1/2</sup> , while the tube length has little influence on β .
Applied Physics Letters 04/2006; · 3.84 Impact Factor
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ABSTRACT: Uniform and well-crystallized beta-Ga2O3 nanowires are prepared by reacting metal Ga with water vapor based on the vapor-liquid-solid (VLS) mechanism. Electron microscopy studies show that the nanowires have diameters ranging from 10 to 40 nm and lengths up to tens of micrometers. The contact properties of individual Ga2O3 nanowires with Pt or Au/Ti electrodes are studied, respectively, finding that Pt can form Schottky-barrier junctions and Au/Ti is advantageous to fabricate ohmic contacts with individual Ga2O3 nanowires. In ambient air, the conductivity of the Ga2O3 nanowires is about 1 (Omega.m)-1, while with adsorption of NH3 (or NO2) molecules, the conductivity can increase (or decrease) dramatically at room temperature. The as-grown Ga2O3 nanowires have the properties of an n-type semiconductor.
The Journal of Physical Chemistry B 02/2006; 110(2):796-800. · 3.70 Impact Factor
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ABSTRACT: Low temperature (500–700 °C) synthesis of high-quality single-walled carbon nanotubes (SWNTs) via microwave plasma assisted chemical vapor deposition (MPCVD) was demonstrated by pyrolysis of methane over the Fe–Mo bimetallic catalyst nanoparticles sup-ported on porous MgO powders. In comparison with higher temperature (800 °C) growth by the conventional thermal CVD using the same batch of catalyst, the SWNTs grown by the low temperature MPCVD show small diameters with narrow distribution. Moreover, it was found that the lower the growth temperature, the smaller and more homogenous the tube diameter, showing the feasibility of con-trolling the SWNTs diameters by tuning the growth temperature.
01/2006;
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ABSTRACT: The dynamic field emission of a carbon nanotube at mechanical resonance has been studied by in situ transmission electron microscopy. The coupling between the field emission (FE) of a nanotube under a dc voltage applied longitudinally and its mechanical resonance stimulated transversely by an ac field shows that the frequency of the FE oscillating current is twice that of the mechanical resonance. This result has been modelled using the Fowler–Nordheim equation. The nanoscale configuration of the nanoelectromechanical system makes it possible to create novel devices that could correlate the mechanical behaviour with their sensitive FE, and the FE current could provide feedback signals for controlling the devices.
Journal of Physics Condensed Matter 11/2005; 17(46):L507. · 2.55 Impact Factor
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ABSTRACT: Silicon nanocone arrays are formed on porous silicon substrates by plasma etching in a hot filament chemical vapour deposition system. The as-formed Si nanocones were characterized by means of scanning electron microscopy, high resolution transmission electron microscopy, energy dispersive x-ray analysis, and Raman spectroscopy. The results indicate that the nanocone is composed of a silicon core coated with a thin amorphous carbon (a-C) layer produced by carbon-bearing plasma etching. Plasma etching is a key factor in the formation of the nanocone arrays, while re-condensation of evaporated silicon atoms on the tip of the as-etched cone also occurs. Field emission measurements show that the a-C coating can effectively enhance the field emission ability of the nanocone arrays due to the decrease of the surface work function from 4.15 to 2.37 eV.
Nanotechnology 10/2005; 16(12):2919. · 3.98 Impact Factor
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ABSTRACT: Tubular carbon cones (TCCs) with nanometer-sized tips and micrometer-sized roots, having a herringbone hollow interior surrounded by helical sheets of graphite coiling around, were grown on Au wires by hot filament chemical vapor deposition (HFCVD). These TCCs exhibit excellent field emission properties with a very low threshold field of 0.27 V/μm and a corresponding current density of about 1 μA/cm2; and a stable emitting current density of 1.9 mA/cm2 can be obtained at only 0.6 V/μm. Their low effective work function of ∼ 0.0056 eV and their conical bases—which effectively reduce the screening effect due to sufficient distance between adjacent tubular cones—are both favorable to field emission enhancement.
Applied Physics Letters 09/2005; 87(14):143107-143107-3. · 3.84 Impact Factor
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ABSTRACT: The electric transport properties of an individual vertical multiwall carbon nanotube (MWCNT) were studied in situ at room temperature in a scanning electron microscope chamber. It was found that the single MWCNT has a large current-carrying capacity, and the maximum current can reach 7.27 mA. At the same time, a very low resistance of about 34.4 ohms and a high conductance of about (460-490)G0 were obtained. The experimental observations imply a multichannel quasiballistic conducting behavior occurring in the MWCNTs with large diameter, which can be attributed to the participation of multiple walls in electrical transport and the large diameter of the MWCNTs.
Physical Review Letters 09/2005; 95(8):086601. · 7.37 Impact Factor
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ABSTRACT: Large-area highly aligned GaAs nanowires were synthesized directly by etching GaAs wafer covered with Au film using H plasma. The characterizations by scanning electron microscopy and transmission electron microscopy reveal that the as-grown nanowires are uniform in distribution and the individual nanowires are well crystallized. The field-electron-emission behavior of the GaAs nanowire was studied and a low turn-on field of 2.0 V/μm was achieved, which suggests its potential application as cold electron sources. The mechanism for field-emission enhancement is also discussed.
Applied Physics Letters 05/2005; 86(21):213108-213108-3. · 3.84 Impact Factor
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ABSTRACT: Semiconductor nanowires, such as InAs, InP, β-Ga2O3, and GaP are synthesized by annealing semiconductor wafers covered with Au film at an appropriate temperature in the region of 550°–650°C in a N2 atmosphere. The composition of the resulting semiconductor nanowires is determined by both the substrate and the chemical conditions of growth. High-resolution transmission electron microscopy and selected area electron diffraction reveal high degrees of crystallization of the as-grown nanowires. The characteristics of the annealing method for synthesis of semiconductor nanowires are discussed.
Applied Physics Letters 09/2004; 85(10):1802-1804. · 3.84 Impact Factor
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ABSTRACT: Resonance Raman spectra of boron carbonitride (BCN) nanotubes synthesized by hot-filament chemical vapor deposition were investigated. The intensity of the D band is insensitive to laser excitation energy (Elaser), while the intensity of the G and G′ bands increases as Elaser increases, and saturates at Elaser = 2.67 eV. This particular resonance behavior is ascribed to an electronic transition process different from the π–π∗ transition that occurs in carbon materials. The dispersive behavior of the D-related bands also shows an inflection at Elaser = 2.67 eV and different ∂ω/∂Elaser compared to carbon materials. These results indicate there are special electronic and phonon structures in BCN nanotubes. © 2004 American Institute of Physics.
Applied Physics Letters 02/2004; 84(9):1549-1551. · 3.84 Impact Factor
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ABSTRACT: The field emission capability of the carbon nanotubes (CNTs) has been improved by hydrogen plasma treatment, and the enhanced emission mechanism has been studied systematically using Fourier-transform infrared spectroscopy, Raman, and transmission electron microscopy. The hydrogen concentration in the samples increases with increasing plasma treatment duration. A Cδ−–Hδ+ dipole layer may form on CNTs’ surface and a high density of defects results from the plasma treatment, which is likely to make the external surface of CNTs more active to emit electrons after treatment. In addition, the sharp edge of CNTs’ top, after removal of the catalyst particles, may increase the local electronic field more effectively. The present study suggests that hydrogen plasma treatment is a useful method for improving the field electron emission property of CNTs. © 2002 American Institute of Physics.
Applied Physics Letters 08/2002; 81(9):1690-1692. · 3.84 Impact Factor
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ABSTRACT: A systematic Raman study of boron carbonitride (BCN) nanotubes, synthesized by bias-assisted hot filament chemical vapor deposition, is reported. Raman spectra up to the fourth order are observed from the BCN nanotubes. Comparing with pure carbon nanotubes, the Raman bands in BCN nanotubes are broadened and the relative intensity of the D mode with respect to the G mode varies with increasing B and N atomic concentrations. The underlying mechanism has been studied on the basis of the microstructures obtained by high-resolution transmission electron microscopy. © 2002 American Institute of Physics.
Applied Physics Letters 05/2002; 80(19):3590-3592. · 3.84 Impact Factor
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ABSTRACT: The adjustable photoluminescence (PL) and field electron emission (FEE) properties of boron carbonitride (B–C–N) nanotubes grown under well-controlled conditions are studied systematically. Large-scale highly aligned B–C–N nanotubes are synthesized directly on Ni substrates by the bias-assisted hot filament chemical vapor deposition method. Single-walled B–C–N nanotubes and nanometric B–C–N heterojunctions are obtained by the pulsed-arc-discharge technique and pause-reactivation two-stage process, respectively. It is found that the microstructures, orientations, and chemical compositions of the nanotubes can be controlled by varying growth parameters. The mechanism of the controllable growth is also investigated. Intense and stable PL from the nanotubes is observed in both blue-violet (photon energies 3.14–2.55 eV) and yellow-green bands (photon energies 2.13–2.34 eV) and the emission bands are adjusted by varying the compositions of the nanotubes. FEE properties are also studied and optimized by varying the B or N atomic concentrations in the nanotubes. All these results verify the controllability of the electronic band structure of the B–C–N nanotubes. © 2002 American Institute of Physics.
Journal of Applied Physics 04/2002; 91(8):5325-5333. · 2.17 Impact Factor
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ABSTRACT: Carbon nanoparticles were prepared from H2 and CH4 at various temperatures. The carbon nanoparticles were well graphitized, and the degree of graphitization increased with increasing growth temperature. Field-emission measurements showed that the carbon nanoparticles were excellent electron field emitters, comparable to carbon nanotubes. The field-emission properties became better with increasing growth temperature, and the threshold fields of the carbon nanoparticles deposited at 400, 500, 670 °C were 3.2, 3, and 1 V/μm, respectively. The low-threshold field of the carbon nanoparticles is attributed to the field-enhancement effect and the higher degree of graphitization. © 2001 American Institute of Physics.
Applied Physics Letters 04/2001; 78(15):2226-2228. · 3.84 Impact Factor
