Showing papers on "Field electron emission published in 2009"
TL;DR: Graphene nanosheets were synthesized in large quantities using a chemical approach as mentioned in this paper, and field emission electron microscopy observation revealed that loose graphene nanoparticles agglomerated and crumpled naturally into shapes resembling flower-petals.
1,295 citations
TL;DR: In this paper, a homogeneous single-layer graphene films are fabricated using an electrophoretic deposition technique, and their field-emission properties are investigated. The graphene films show high density, uniform thickness, numerous edges normal to the film surface, and good interface contact and adhesion with the substrate.
Abstract: Homogeneous single-layer graphene films are fabricated using an electrophoretic deposition technique, and their field-emission properties are investigated. The graphene films show high density, uniform thickness, numerous edges normal to the film surface, and good interface contact and adhesion with the substrate, and consequently show excellent field-emission properties.
650 citations
TL;DR: It is shown that the tip of an atomic force microscope can be used to pattern polarization domains in a thin film of lead zirconate titanate in high electric fields similar to those for field emission tips.
Abstract: We demonstrate a highly reproducible control of local electron transport through a ferroelectric oxide via its spontaneous polarization. Electrons are injected from the tip of an atomic force microscope into a thin film of lead-zirconate titanate, Pb(Zr0.2Ti0.8)O3, in the regime of electron tunneling assisted by a high electric field (Fowler-Nordheim tunneling). The tunneling current exhibits a pronounced hysteresis with abrupt switching events that coincide, within experimental resolution, with the local switching of ferroelectric polarization. The large spontaneous polarization of the PZT film results in up to 500-fold amplification of the tunneling current upon ferroelectric switching. The magnitude of the effect is subject to electrostatic control via ferroelectric switching, suggesting possible applications in ultrahigh-density data storage and spintronics.
451 citations
TL;DR: In this article, X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, field emission scanning electron microscopy (FESEM), TEM, HRTEM, photoluminescence (PL) spectra, kinetic decay, and electron paramagnetic resonance (EPR) were used to characterize the obtained Ca5(PO4)3OH samples.
Abstract: Hydroxyapatite (Ca5(PO4)3OH) nano- and microcrystals with multiform morphologies (separated nanowires, nanorods, microspheres, microflowers, and microsheets) have been successfully synthesized by a facile hydrothermal process. X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL) spectra, kinetic decay, and electron paramagnetic resonance (EPR) were used to characterize the samples. The experimental results indicate that the obtained Ca5(PO4)3OH samples show an intense and bright blue emission under long-wavelength UV light excitation. This blue emission might result from the CO2•− radical impurities in the crystal lattice. Furthermore, the organic additive (trisodium citrate) and pH values have an obvious impact on the morphologies and luminescence properties of the products to some degree. The possible formation ...
271 citations
TL;DR: The charge transport mechanism of oligo(p-phenylene ethynylene)s with lengths ranging from 0.98 to 5.11 nm was investigated using modified scanning tunneling microscopy break junction and conducting probe atomic force microscopy methods, and an intrinsic transition from tunneling to hopping charge transport mechanisms was observed.
Abstract: The charge transport mechanism of oligo(p-phenylene ethynylene)s with lengths ranging from 0.98 to 5.11 nm was investigated using modified scanning tunneling microscopy break junction and conducting probe atomic force microscopy methods. The methods were based on observing the length dependence of molecular resistance at single molecule level and the current-voltage characteristics in a wide length distribution. An intrinsic transition from tunneling to hopping charge transport mechanism was observed near 2.75 nm. A new transitional zone was observed in the long length molecular wires compared to short ones. This was not a simple transition between direct tunneling and field emission, which may provide new insights into transport mechanism investigations. Theoretical calculations provided an essential explanation for these phenomena in terms of molecular electronic structures.
217 citations
TL;DR: The well-aligned CdS nanorod arrays had the lower threshold for stimulated emission, and quasi-aligned nanowire arrays produced the higher field-emission current and possessed the lower turn-on fields.
Abstract: Highly ordered CdS nanostructure arrays were successfully fabricated via a simple two-step metal-organic chemical vapor deposition process. Both stimulated emission and field-emission measurements were carried out in an attempt to understand the correlation between the morphologies, alignments, and emission performances of five ordered CdS nanostructure array types (well-aligned truncated nanocones, nanorods, cleft nanorods, quasi-aligned nanowires, and nanowires). The 1D CdS nanostructures of various types displayed notable differences in stimulated and field-emission performances. The stimulated emission strongly correlated with the structure alignment: the better the alignment, the lower the threshold. Both of the alignments and aspect ratios greatly affected the field-emission properties; the CdS emitters of higher aspect ratio and better alignment exhibited better field-emission performance. Thus the well-aligned CdS nanorod arrays had the lower threshold for stimulated emission, and quasi-aligned nanowire arrays produced the higher field-emission current and possessed the lower turn-on fields.
181 citations
TL;DR: An electrophoretic process to fabricate composite CNT films with controlled nanotube orientation and surface density, and enhanced adhesion is developed and the cathodes have significantly enhanced macroscopic field emission current density and long-term stability under high operating voltages.
Abstract: Carbon nanotube (CNT) field emitters are now being evaluated for a wide range of vacuum electronic applications. However, problems including short lifetime at high current density, instability under high voltage, poor emission uniformity, and pixel-to-pixel inconsistency are still major obstacles for device applications. We developed an electrophoretic process to fabricate composite CNT films with controlled nanotube orientation and surface density, and enhanced adhesion. The cathodes have significantly enhanced macroscopic field emission current density and long-term stability under high operating voltages. The application of this CNT electron source for high-resolution x-ray imaging is demonstrated.
176 citations
Journal Article•
TL;DR: In this paper, the correlation between the morphologies, alignments, and emission performances of five ordered CdS nanostructure array types (well-aligned truncated nanocones, nanorods, cleft nanorod, quasi-aligned nanowires, and nanowire) was investigated.
Abstract: Highly ordered CdS nanostructure arrays were successfully fabricated via a simple two-step metal-organic chemical vapor deposition process. Both stimulated emission and field-emission measurements were carried out in an attempt to understand the correlation between the morphologies, alignments, and emission performances of five ordered CdS nanostructure array types (well-aligned truncated nanocones, nanorods, cleft nanorods, quasi-aligned nanowires, and nanowires). The 1D CdS nanostructures of various types displayed notable differences in stimulated and field-emission performances. The stimulated emission strongly correlated with the structure alignment: the better the alignment, the lower the threshold. Both of the alignments and aspect ratios greatly affected the field-emission properties; the CdS emitters of higher aspect ratio and better alignment exhibited better field-emission performance. Thus the well-aligned CdS nanorod arrays had the lower threshold for stimulated emission, and quasi-aligned nanowire arrays produced the higher field-emission current and possessed the lower turn-on fields.
175 citations
TL;DR: This work introduced a simple and convenient method suitable for large scale on different substrates, paving the way for more applications of graphene films.
Abstract: The electron field emission performance of screen-printed graphene cathode was studied. High-yield graphene was prepared by a modified Hummers method and hydrazine hydrate reduction process, and screen printing technology was used to prepare the graphene field emission cathode. This cathode structure satisfies the requirements of both good electrical conductivity and a high surface field enhancement factor, leading to excellent and stable field emission properties with a low threshold field (~1.5 V µm−1). Our work introduced a simple and convenient method suitable for large scale on different substrates, paving the way for more applications of graphene films.
164 citations
TL;DR: In this article, a single-step melt-quench technique involving selective thermochemical reduction was used to synthesize Ag-antimony glass nanocomposites in a dielectric matrix K2O-B2O3-Sb2O 3 by a single step melt-QUench technique.
Abstract: Er3+:Ag-antimony glass nanocomposites are synthesized in a new reducing glass (dielectric) matrix K2O–B2O3–Sb2O3 by a single-step melt-quench technique involving selective thermochemical reduction. The UV-vis-near-infrared absorption spectra show typical surface plasmon resonance (SPR) band of Ag0 nanoparticles (NPs) in addition to the distinctive absorption peaks of Er3+ ion. X-ray diffraction and selected area electron diffraction results indicate formation of Ag0 NPs along the (200) plane direction. The transmission electron microscopic image reveals the formation of spherical, fractal, and rod-shaped Ag0 NPs having maximum size ∼31 nm. The rod-shaped Ag0 NPs have aspect ratio ∼2.4. The field emission scanning electron microscopic image shows development of three dimensional cornlike microstructures. Photoluminescent upconversion under excitation at 798 nm exhibit two prominent emission bands of Er3+ ions centered at 536 (green) and 645 (red) nm due to S43/2→I415/2 and F49/2→I415/2 transitions, respect...
154 citations
TL;DR: In this article, a base growth mechanism using plasma-enhanced chemical vapor deposition was used to grow pyramid-like graphene sheets on Ni-coated ZnO nanowires via a "base growth" mechanism.
Abstract: There is a problem with field emission from graphene sheets (GSs) because existing deposition methods lead to sheets that have planar morphological features along entire substrates, which limits field enhancement. To overcome this problem, here we grow pyramid-like GSs on Ni-coated ZnO nanowires via a “base growth” mechanism using plasma-enhanced chemical vapor deposition. The surface morphologies of ZnO−GSs can be controlled by the density of the Ni nanoparticles and deposition time. The ZnO−GSs has a lower turn-on field, 1.3 V/μm, compared to that, 2.5 V/μm, of pure ZnO at a current density of 1 μA/cm2, implying avenues for potential applications of graphene and ZnO.
TL;DR: In this paper, a combination method of sol-gel process and electrospinning was used to combine one-dimensional CaWO4 and CaWOWO4:Tb3+ nanowires and nanotubes, and the results of X-ray diffraction, scanning electron microscopy (SEM), TEM, high-resolution transmission electron microscope (HRTEM), photoluminescence, and time-resolved emission spectra, as well as kinetic decays were used to characterize the resulting samples.
Abstract: One-dimensional CaWO4 and CaWO4:Tb3+ nanowires and nanotubes have been prepared by a combination method of sol-gel process and electrospinning. X-Ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL), low voltage cathodoluminescence (CL) and time-resolved emission spectra, as well as kinetic decays were used to characterize the resulting samples. The results of XRD, FT-IR, TG-DTA indicate that the CaWO4 and CaWO4:Tb3+ samples begin to crystallize at 500 °C with the scheelite structure. Under ultraviolet excitation and low-voltage electron beams excitation, the CaWO4 samples exhibit a blue emission band with a maximum at 416 nm originating from the WO42−groups, while the CaWO4:Tb3+ samples show the characteristic emission of Tb3+ corresponding to 5D4–7F6,5,4,3 transitions due to an efficient energy transfer from WO42− to Tb3+. The energy transfer process was further studied by the time-resolved emission spectra as well as kinetic decay curves of Tb3+ upon excitation into the WO42−groups. Furthermore, the PL emission colour of CaWO4: x mol %Tb3+ can be tuned from blue to green by changing the concentrations (x) of the Tb3+ ion, making the materials have potential applications as fluorescent lamps and field emission displays (FEDs).
TL;DR: In this paper, the structural, cathodoluminescence and field-emission properties of one-dimensional Cds micro/nanostructures with different morphologies are systematically investigated.
Abstract: High-quality, uniform one-dimensional Cds micro/nanostructures with different morphologies-microrods, sub-microwires and nanotips-are fabricated through an easy and effective thermal evaporation process. Their structural, cathodoluminescence and field-emission properties are systematically investigated. Microrods and nanotips exhibit sharp near-band-edge emission and broad deep-level emission, whereas sub-microwires show only the deep-level emission. A significant decrease in a deep-level/near-band-edge intensity ratio is observed along a tapered nanotip towards a smaller diameter part. This behaviour is understood by consideration of defect concentrations in the nanotips, as analyzed with high-resolution transmission electron microscopy. Field-emission measurements show that the nanotips possess the best field-emission characteristics among all 1D Cds nanostructures reported to date, with a relatively low turn-on field of 5.28 V mu m(-1) and the highest field-enhancement factor of 48.19. The field-enhancement factor, turn-on and threshold fields are discussed related to structure morphology and vacuum gap variations under emission.
TL;DR: The emission colors of CaMoO(4):Ln( 3+) nanofibers can be tuned from blue-green to green, yellow, and orange-red easily by changing the doping concentrations of Ln(3+) ions, making the materials have potential applications in fluorescent lamps and field emission displays (FEDs).
Abstract: One-dimensional CaMoO(4):Ln(3+) (Ln = Eu, Tb, Dy) nanofibers have been prepared by a combination method of sol-gel and electrospinning process. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL), and low voltage cathodoluminescence (CL) as well as kinetic decays were used to characterize the resulting samples. SEM and TEM analyses indicate that the obtained precursor fibers have a uniform size, and the as-formed CaMoO(4):Ln(3+) nanofibers consist of nanoparticles. Under ultraviolet excitation, the CaMoO(4) samples exhibit a blue-green emission band with a maximum at 500 nm originating from the MoO(4)(2-) groups. Due to an efficient energy transfer from molybdate groups to dopants, CaMoO(4):Ln(3+) phosphors show their strong characteristic emission under ultraviolet excitation and low-voltage electron beam excitation. The energy transfer process was further studied by the emission spectra and the kinetic decay curves of Ln(3+) upon excitation into the MoO(4)(2-) groups in the CaMoO(4):x mol % Ln(3+) samples (x = 0-5). Furthermore, the emission colors of CaMoO(4):Ln(3+) nanofibers can be tuned from blue-green to green, yellow, and orange-red easily by changing the doping concentrations (x) of Ln(3+) ions, making the materials have potential applications in fluorescent lamps and field emission displays (FEDs).
TL;DR: In this paper, Ru-decorated double-walled carbon nanotubes (DWCNTs) were remarkably improved by decorating their surface with ruthenium (Ru) metal nanoparticles.
TL;DR: In this paper, a direct transfer method for fabricating flexible electronics without the assistance of an adhesive layer and stamp is reported, which provides an approach for the application of vertically aligned carbon nanotubes (VA-CNTs) on plastic substrates.
Abstract: A direct transfer method for fabricating flexible electronics without the assistance of an adhesive layer and stamp is reported in this paper. This rapid and simple method provides an approach for the application of vertically aligned carbon nanotubes (VA-CNTs) on plastic substrates. After transfer, the VA-CNTs maintained their initial orientation in the designed pattern and showed sufficient adhesion to the substrate under extreme bending conditions. The flexible device performed an emission on the transparent substrate and showed a low turn-on of 1.13 V/μm. This VA-CNT-based flexible device, which exhibits electrical resistance sensitive to bending, is also described herein.
TL;DR: In this paper, N-doped carbon nanotubes (CNTs) were grown from two precursors: (i) from a cage-like carbon source: camphor, using dimethylformamide (DMF) as a nitrogen source; and (ii) from linear-chain aminohydrocarbon: octadecylamine, as a dual source of carbon and nitrogen.
TL;DR: In this paper, a new structure of molybdenum oxides, named a nanostar, is grown by thermal vapor deposition with a length of ∼ 1 μm, a thickness of ∼ 50 nm, and its width in the range of 500−700 nm.
Abstract: The field emission properties of MoO2 nanostars grown on a silicon substrate and their emission performance in various vacuum gaps are reported in this article. A new structure of molybdenum oxides, named a nanostar, is grown by thermal vapor deposition with a length of ∼1 μm, a thickness of ∼50 nm, and its width in the range of 500−700 nm. The morphology, structure, composition, and chemical states of the prepared nanostars were characterized by scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). According to XRD analysis, the grown nanostructures are composed of both crystalline Mo4O11 and crystalline MoO2 structures. XPS analysis showed that the synthesized nanostructures contained ∼21.2% Mo6+, ∼16.2% Mo5+, ∼39.8% Mo4+, and ∼22.8% Moδ+ (where 0 < δ < 4). TEM observations indicate that the synthesized sample consists of MoO2 nanostars over a crystalline thin film containing Mo4O11 nanoparticles. The turn-on ...
TL;DR: In this article, a simple but effective way to control the orientational arrangement of MoO3 nanoflakes is presented, which offers an opportunity to investigate the anisotropic properties of different crystallographic faces.
Abstract: A simple but effective way to control the orientational arrangement of MoO3 nanoflakes is presented, which offers an opportunity to investigate the anisotropic properties of different crystallographic faces. Their electrical and optical properties are investigated. According to the polarized micro-Raman spectra, oxygen vacancies preferred to be located at the sharp side edges of the lamella, which might play an important role in the catalytic properties of samples. Ascribing to the unique structural geometry and the oxygen-defects-induced reduction of the work function, the electron field emission properties of the samples show that the erect MoO3 nanoflakes are potential candidates for the cold-cathode-based electronics. Furthermore, strong optical birefringence properties of samples are also first observed.
TL;DR: In this article, the first experimental data for the work function shift of Ag(001) induced by 1, 3, and 8 monolayers of MgO is measured in situ by three independent scanning probe techniques on the same surface area, making the different approaches comparable.
Abstract: The metal work function is a suggested key parameter for charging adsorbates with high electron affinity on thin oxide films grown on metal single crystal surfaces. Here, the first experimental data for the work function shift of Ag(001) induced by 1, 3, and 8 monolayers of MgO is measured in situ by three independent scanning probe techniques on the same surface area, making the different approaches comparable. Furthermore, the results are compared to density functional theory calculations. The measurements are performed using a dual-mode dynamic force microscope and scanning tunneling microscope working in ultrahigh vacuum at low temperature (5 K). The methods to detect the work function shift are based on Kelvin probe force microscopy measuring the contact potential difference, I(z) curves and field emission resonances.
TL;DR: In this paper, the interlocked cubes of hausmannite Mn3O4 thin films were synthesized by simple, inexpensive, and low temperature chemical route from urea containing bath These films were characterized by using X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), Fourier transform infrared spectra (FT-IR), optical absorption and wettability test.
TL;DR: In this article, the nitrogen doping effect and field emission properties of double-walled carbon nanotubes (DWCNTs) were investigated and it was found that the field emission was controlled by pyridine-like N in the graphite due to N doping.
TL;DR: In effect, this work has realized an ultrafast pulsed field-emission source with site selectivity induced by femtosecond laser pulses, and simulations of local fields on the tip apex and of electron emission patterns based on photoexcited nonequilibrium electron distributions explain the observations quantitatively.
Abstract: We have investigated field-emission patterns from a clean tungsten tip apex induced by femtosecond laser pulses. Strongly asymmetric modulations of the field-emission intensity distributions are observed depending on the polarization of the light and the laser incidence direction relative to the azimuthal orientation of tip apex. In effect, we have realized an ultrafast pulsed field-emission source with site selectivity. Simulations of local fields on the tip apex and of electron emission patterns based on photoexcited nonequilibrium electron distributions explain our observations quantitatively.
TL;DR: A model of polycrystalline C60 field-effect transistors (FETs) that incorporates the microscopic structural and electronic details of the C60 films is presented, suggesting that even relatively disordered films have charge mobilities that are only a factor of 2 smaller than mobilities in single crystals.
Abstract: We present a model of polycrystalline C60 field-effect transistors (FETs) that incorporates the microscopic structural and electronic details of the C60 films. We generate disordered polycrystalline thin films by simulating the physical-vapor deposition process. We simulate electron hopping transport using a Monte Carlo method and electronic structure calculations. Our model reproduces experimentally observed FET characteristics, including electrical characteristics, electrochemical potentials, and charge mobilities. Our results suggest that even relatively disordered films have charge mobilities that are only a factor of 2 smaller than mobilities in single crystals.
TL;DR: The results indicate that the reduction of gap distance by molecular tilt configuration enhances the transition of the electronic transport mechanism from direct tunneling to field emission transport through molecules.
Abstract: We studied the molecular configuration-dependent charge transport of alkyl metal−molecule−metal junctions using conducting atomic force microscopy (CAFM). The inflection point (or transition voltage VT) on the plot of ln(I/V2) versus 1/V shifted to a lower voltage with increasing CAFM tip-loading force and decreasing molecular length. Our results indicate that the reduction of gap distance by molecular tilt configuration enhances the transition of the electronic transport mechanism from direct tunneling to field emission transport through molecules. The obtained results are consistent with a barrier height decrease, as affected by the enhancement of the intermolecular chain-to-chain tunneling as molecular tilt, predicted by a multibarrier tunneling model.
TL;DR: In this article, BZT thin films were analyzed by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, field emission gun-scanning electron microscopy (FEG-SEM) and atomic force microscopy.
Abstract: Ba[Zr0.25Ti0.75]O3 (BZT) thin films were synthesized by the complex polymerization method and heat treated at 400 °C for different times and at 700 °C for 2 h. These thin films were analyzed by X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectroscopy, field emission gun-scanning electron microscopy (FEG-SEM) and atomic force microscopy (AFM), Ultraviolet–visible (UV–vis) absorption spectroscopy, electrical and photoluminescence (PL) measurements. FEG-SEM and AFM micrographs showed that the microstructure and thickness of BZT thin films can be influenced by the processing times. Dielectric constant and dielectric loss of BZT thin films heat treated at 700 °C were approximately 148 and 0.08 at 1 MHz, respectively. UV–vis absorption spectra suggested the presence of intermediary energy levels (shallow and deep holes) within the band gap of BZT thin films. PL behavior was explained through the optical band gap values associated to the visible light emission components.
TL;DR: In this article, MoO3 nanoflowers were successfully synthesized on a Si substrate by a facility microwave hydrothermal method and the nanobelts had a relatively low turn-on field of ∼4.3 V/μm and their emission was a barrier tunneling quantum-mechanical process.
TL;DR: SiC nanowires have been fabricated by a simple catalyst-free method using detonation soot powders and silicon wafers as mentioned in this paper, and their microstructures by X-ray diffraction, scanning electron m...
Abstract: SiC nanowires have been fabricated by a simple catalyst-free method using detonation soot powders and silicon wafers. We characterize their microstructures by X-ray diffraction, scanning electron m...
TL;DR: Using tunneling spectroscopy via a superconducting probe, the shape of the local electron distribution functions, and hence energy relaxation rates, in carbon nanotubes that have bias voltages applied between their ends was studied in this paper.
Abstract: We report measurements of the nonequilibrium electron energy distribution in carbon nanotubes. Using tunneling spectroscopy via a superconducting probe, we study the shape of the local electron distribution functions, and hence energy relaxation rates, in nanotubes that have bias voltages applied between their ends. At low temperatures, electrons interact weakly in nanotubes of a few microns channel length, independent of end-to-end-conductance values. Surprisingly, the energy relaxation rate can increase substantially when the temperature is raised to only 1.5 K.
TL;DR: In this article, the authors show that the field emission screening effect is underestimated and diminishes at far greater separations of five times the height of the emitter, and they further observe that to achieve maximum emission efficiency in an array, one requires a trade off between screening and emitter number, resulting in a separation of three times their height.
Abstract: The field emission screening effect is one of great importance when aiming to design efficient and powerful cathodes. It has long been assumed that the degrading effect is at a minimum when neighboring emitters are at least twice their height from each other. In this work, we show that the screening effect is underestimated and diminishes at far greater separations of five times the height of the emitter. We further observe that to achieve maximum emission efficiency in an array, one requires a trade off between screening and emitter number, resulting in a separation of three times their height.