Showing papers on "Field electron emission published in 2005"
TL;DR: In this article, a review of field emission cold cathode materials has been presented, focusing on several kinds of novel cold cathodes that have been developed in the past decade, including materials for microfabricated field-emitter arrays, diamond and related films, carbon nanotubes, other quasi one-dimensional nanomaterials and printable composite materials.
Abstract: Field emission (FE) is based on the physical phenomenon of quantum tunneling, in which electrons are injected from the surface of materials into vacuum under the influence of an applied electric field. A variety of field emission cold cathode materials have been developed to date. In this review, we shall focus on several kinds of novel cold cathode materials that have been developed in the past decade. These include materials for microfabricated field-emitter arrays, diamond and related films, carbon nanotubes, other quasi one-dimensional nanomaterials and printable composite materials. In addition, cold cathode materials have a wide range of applications such as in flat panel displays, high-power vacuum electronic devices, microwave-generation devices, vacuum microelectronic devices and vacuum nanoelectronic devices. Applications are in consumer goods, military industries and also space technology. A comprehensive overview of the various applications is presented. Recently, recognizing the strong possibility that vacuum nanoelectronic devices using quasi one-dimensional nanomaterials, such as carbon nanotubes may emit electrons with driving voltages comparable to that of a solid-state device, there is a growing interest in novel applications of such devices. With such exciting opportunities, there is now a flurry of activities to explore applications far beyond those considered for the conventional hot cathodes that operate on thermionic emission. We shall discuss the details of a number of fascinating potential applications.
539 citations
TL;DR: An extensive review of the current state of the art in nitrogen doping of carbon nanotubes, including synthesis techniques, and comparison with nitrogen doped carbon thin films and azofullerenes is presented.
Abstract: Nitrogen doping of single and multi-walled carbon nanotubes is of great interest both fundamentally, to explore the effect of dopants on quasi-1D electrical conductors, and for applications such as field emission tips, lithium storage, composites and nanoelectronic devices. We present an extensive review of the current state of the art in nitrogen doping of carbon nanotubes, including synthesis techniques, and comparison with nitrogen doped carbon thin films and azofullerenes. Nitrogen doping significantly alters nanotube morphology, leading to compartmentalised 'bamboo' nanotube structures. We review spectroscopic studies of nitrogen dopants using techniques such as X-ray photoemission spectroscopy, electron energy loss spectroscopy and Raman studies, and associated theoretical models. We discuss the role of nanotube curvature and chirality (notably whether the nanotubes are metallic or semiconducting), and the effect of doping on nanotube surface chemistry. Finally we review the effect of nitrogen on the transport properties of carbon nanotubes, notably its ability to induce negative differential resistance in semiconducting tubes.
441 citations
TL;DR: In this article, a simple method of direct heating of bulk copper plates in air, oriented CuO nanowire films were synthesized on a large scale, and the length and density of nanowires could be controlled by growth temperature and growth time.
Abstract: Using a simple method of direct heating of bulk copper plates in air, oriented CuO nanowire films were synthesized on a large scale. The length and density of nanowires could be controlled by growth temperature and growth time. Field emission (FE) measurements of CuO nanowire films show that they have a low turn-on field of 3.5–4.5 V µm−1 and a large current density of 0.45 mA cm−2 under an applied field of about 7 V µm−1. By comparing the FE properties of two types of samples with different average lengths and densities (30 µm, 108 cm−2 and 4 µm, 4 × 107 cm−2, respectively), we found that the large length–radius ratio of CuO nanowires effectively improved the local field, which was beneficial to field emission. Verified with finite element calculation, the work function of oriented CuO nanowire films was estimated to be 2.5–2.8 eV.
347 citations
323 citations
258 citations
TL;DR: The photoluminescence spectrum reveals a broad blue emission band with a fine photon structure while the field emission study shows a notable emission current with a moderate turn-on field as expected, suggesting their potential applications in light and electron emission nanodevices.
Abstract: Aluminum nitride nanostructures are attractive for many promising applications in semiconductor nanotechnology. Herein we report on vapor−solid growth of quasi-aligned aluminum nitride nanocones on catalyst-coated wafers via the reactions between AlCl3 vapor and NH3 gas under moderate temperatures around 700 °C, and the growth mechanism is briefly discussed. The as-prepared wurtzite aluminum nitride nanocones grow preferentially along the c-axis with adjustable dimensions of the sharp tips in the range of 20−60 nm. The photoluminescence spectrum reveals a broad blue emission band with a fine photon structure while the field emission study shows a notable emission current with a moderate turn-on field as expected, suggesting their potential applications in light and electron emission nanodevices.
250 citations
TL;DR: In this paper, the field-emission properties of ordered ZnO nanorod arrays with different morphologies were investigated in detail, and it was found that the morphology of the nanorods has considerable effect on their field emission properties, especially the turn-on field and the emission current density.
Abstract: The field-emission properties of ordered ZnO nanorod arrays with different morphologies were investigated in detail. After comparison of three different morphologies, it was found that the morphology of the ZnO nanorods has considerable effect on their field emission properties, especially the turn-on field and the emission current density. Among them, the ZnO nanoneedle arrays have the lowest turn-on field, highest current density, and the largest emission efficiency, which is ascribed to the small emitter radius on the nanoscale. On the other hand, high nanorod density remarkably reduces the local field at the emitters owing to the screening effect, which is related to the density of the emitters. The analysis results could be valuable for the application of field-emission-based devices using ZnO nanorod arrays as cathode materials.
241 citations
TL;DR: A detailed analysis of the luminescence data indicated a local-field-enhanced quantum efficiency of 58% for the Si nanocrystals coupled to the nanoporous gold layer.
Abstract: We report local-field-enhanced light emission from silicon nanocrystals close to a film of nanoporous gold. We resolve photoluminescence as the gold-Si nanocrystal separation distance is varied between 0 and 20 nm and observe a fourfold luminescence intensity enhancement concomitant with increases in the coupled silicon nanocrystal/nanoporous gold absorbance cross section and radiative decay rate. A detailed analysis of the luminescence data indicated a local-field-enhanced quantum efficiency of 58% for the Si nanocrystals coupled to the nanoporous gold layer.
225 citations
TL;DR: In this article, large-area quasialigned nanotips of tungsten oxide have been grown by a two-step high-temperature, catalyst-free, physical evaporation deposition process.
Abstract: Large-area, quasialigned nanotips of tungsten oxide have been grown by a two-step high-temperature, catalyst-free, physical evaporation deposition process. The tungsten oxide nanotips are single crystalline with growth direction of [010]. The tungsten oxide nanotips exhibit excellent field-emission properties with a low threshold field (for an emission current density of 10mA∕cm2) ∼4.37MV∕m and uniform emission from the entire arrays, as well as high time stability. These results make tungsten oxide nanotip arrays a competitive candidate for field-emission displays.
221 citations
TL;DR: In this article, a gated carbon nanotube field emission cathode with an array of electron emitting pixels are individually addressable via a metaloxide-semiconductor field effect transistor-based electronic circuit.
Abstract: We report a field emission x-ray source that can generate a scanning x-ray beam to image an object from multiple projection angles without mechanical motion. The key component of the device is a gated carbon nanotube field emission cathode with an array of electron emitting pixels that are individually addressable via a metal–oxide–semiconductor field effect transistor-based electronic circuit. The characteristics of this x-ray source are measured and its imaging capability is demonstrated. The device can potentially lead to a fast data acquisition rate for laminography and tomosynthesis with a simplified experimental setup.
TL;DR: In this article, the electrical and optical properties of de-doped nanotubes and nanowires were controlled through various synthetic conditions, such as doping level, dopant, and template-dissolving solvents.
TL;DR: The excellent field emission properties were observed in the as-grown Ag TCNQ and CuTCNQ nanowires, which should have great potential in vacuum device applications.
Abstract: In this contribution, large-area organic charge-transfer complex (AgTCNQ and CuTCNQ) nanowires were synthesized by organic vapor−solid-phase reaction at mild experimental conditions. These nanowires were facilitated on the surface of Cu and Ag foils or different kinds of substrates coated with a layer of silver and copper on a large scale. The excellent field emission properties were observed in the as-grown AgTCNQ and CuTCNQ nanowires. They should have great potential in vacuum device applications.
TL;DR: Using rapid thermal annealing to improve both the crystallinity of the carbon nanotubes and their electrical contact to the substrate, it is possible to reduce this voltage drop, allowing very high currents of up to 100 microA to be achieved per emitter with no significant deviation from the classical Fowler-Nordheim behavior.
Abstract: When a carbon nanotube emitter is operated at high currents (typically above 1 μA per emitter), a small voltage drop (∼few volts) along its length or at its contact generates a reverse/canceling electric field that causes a saturation-like deviation from the classical Fowler−Nordheim behavior with respect to the applied electric field. We present a correction to the Fowler−Nordheim equation to account for this effect, which is experimentally verified using field emission and contact electrical measurements on individual carbon nanotube emitters. By using rapid thermal annealing to improve both the crystallinity of the carbon nanotubes and their electrical contact to the substrate, it is possible to reduce this voltage drop, allowing very high currents of up to 100 μA to be achieved per emitter with no significant deviation from the classical Fowler−Nordheim behavior.
TL;DR: In this paper, the authors synthesize ZnO nanopencils on a silicon wafer without catalysts at a low temperature of 550°C through a simple two-step pressure controlled thermal evaporation.
Abstract: ZnO nanopencils were synthesized on a silicon wafer without catalysts at a low temperature of 550 ° C through a simple two-step pressure controlled thermal evaporation. Penholders were well-hexagonal faceted and the diameter of pen tips on the nanopencils was in the range of 20–30 nm. High-resolution transmission electron microscopy shows that the nanopencils were single crystals growing along the [0001] direction and the pen tips subtend a small angle with multiple surface perturbations. Field-emission measurements on the nanopencils show a low turn-on field of 3.7V∕μm at a current density of 10μA∕cm2. The emission current density reached 1.3mA∕cm2 at an applied field of 4.6V∕μm. The emission at the low field is attributed to the sharp tip and surface perturbations on the nanopencils.
TL;DR: In this paper, single crystalline TiO 2 nanowires have been successfully grown on alumina substrates using a high-frequency (350-KHz) dielectric heater at 1050-°C by a two-step of thermal evaporation method without using any catalyst.
TL;DR: In this paper, a direct linking of field emission with the in situ emitter structure and the real work function at the emitter tip was proposed, which showed that the field enhancement factor at the nanotube tip depends strongly on its structure and surface condition.
Abstract: The field emission properties of individual multiwalled carbon nanotubes have been measured simultaneously in correlation to the emitter images and their real work functions at tips by the in situ transmission electron microscopy method. The field emission of a single nanotube still follows the Fowler-Nordheim law. The field enhancement factor has been determined by the real work function rather than a given constant. In situ imaging and measurement show that the work function at the nanotube tip depends strongly on its structure and surface condition. This study provides an approach of direct linking field emission with the in situ emitter structure and the real work function at the emitter tip.
TL;DR: In this paper, spherical SiO2 particles have been coated with Y2O3:Eu3+ phosphor layers by a Pechini sol-gel process, and the obtained core-shell phosphors consist of well dispersed submicron spherical particles with narrow size distribution.
Abstract: Spherical SiO2 particles have been coated with Y2O3:Eu3+ phosphor layers (SiO2@Y2O3:Eu3+) by a Pechini sol-gel process. X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, photoluminescence, and cathodoluminescence spectra were utilized to characterize the SiO2@Y2O3:Eu3+ core-shell-structured phosphor particles. The obtained core-shell phosphors consist of well dispersed submicron spherical particles with narrow size distribution. The thickness of Y2O3:Eu3+ shell could be easily controlled by changing the number of deposition cycles (60nm for three deposition cycles). The SiO2@Y2O3:Eu3+ core-shell particles show a strong red emission corresponding to D05-F27 (611nm) of Eu3+ under the excitation of ultraviolet (250nm) and low-voltage electron beams (2–6kV), which have potential application for field emission displays.
TL;DR: These phenomena point to the use of single QRs as spectrally tunable charge sensitive fluorophores with polarized emission in fluorescence tagging and optical switching applications.
Abstract: The exceptional fluorescence properties of single CdSe quantum rods (QRs) arising from internal and external electric fields are studied. Reversible external field induced switching of the emission in single QRs is reported for the first time. This effect was correlated with local field induced emission intensity reduction and newly observed darkening mechanism. Bimodal spectral jumps under a zero field were also observed and assigned to charged exciton emission, a phenomenon that was likewise directly controlled through an external field. These phenomena point to the use of single QRs as spectrally tunable charge sensitive fluorophores with polarized emission in fluorescence tagging and optical switching applications.
TL;DR: Field emission results of core-shell SiC-SiO(2) and bare SiC nanowires showed that the SiC Nanowires coated with an optimum SiO( 2) thickness have a higher field emission current than the bare Si cnanowires.
Abstract: A simple, direct synthesis method was used to grow core–shell SiC–SiO2 nanowires by heating NiO-catalysed silicon substrates. A carbothermal reduction of WO3 provided a reductive environment and carbon source to synthesize crystalline SiC nanowires covered with SiO2 sheaths at the growth temperature of 1000–1100 °C. Transmission electron microscopy showed that the SiC core was 15–25 nm in diameter and the SiO2 shell layer was an average of 20 nm in thickness. The thickness of the SiO2 shell layer could be controlled using hydrofluoric acid (HF) etching. Field emission results of core–shell SiC–SiO2 and bare SiC nanowires showed that the SiC nanowires coated with an optimum SiO2 thickness (10 nm) have a higher field emission current than the bare SiC nanowires.
TL;DR: The structure of the nanowires was determined to be of the orthorhombic phase, the growth direction was along [001], and the growth mechanism was investigated based on extensive high-resolution transmission electron microscopy observations.
Abstract: A simple one-step hydrothermal method for large-scale synthesis of ultralong single-crystalline Bi2S3 nanowires was reported, and the nanowires were comprehensively characterized. The diameters of the nanowires are about 60 nm, and their lengths range from tens of microns to several millimeters. The structure of the nanowires was determined to be of the orthorhombic phase, the growth direction was along [001], and the growth mechanism was investigated based on extensive high-resolution transmission electron microscopy observations. Optical absorption experiments revealed that the Bi2S3 nanowires are narrow-band semiconductors with a band gap E(g) approximately 1.33 eV. Electrical transport measurements on individual nanowires gave a resistivity of about 1.2 ohms cm and an emission current of 3.5 microA at a bias field of 35 V/microm. This current corresponds to a current density of about 10(5) A/cm2, which makes the Bi2S3 nanowire a potential candidate for applications in field-emission electronic devices.
TL;DR: In this paper, single crystalline TiO2 nanowires were grown over an Au-doped Si substrate at 850°C by thermal evaporation using a radio frequency (RF) heater.
TL;DR: In this article, the hierarchical AlN comb-like nanostructures self-assemble through a chemical-vapor transport and condensation (CVTC) process were investigated.
Abstract: The hierarchical AlN comb-like nanostructures self-assembled through a chemical-vapor transport and condensation (CVTC) process were investigated. Field emission (FE) measurements showed that low-threshold FE can be obtained from the synthesized AlN hierarchical nanostructures. Energy dispersive x-ray (EDX) spectroscopy analysis indicated that the synthesized nanostructures were composed of pure Al and N in a molar ratio of 1:0.99. The results show that the intrinsically small value of electron affinity of AlN and the emission from the sharp nanotips and thin edges of the AlN nanoarchitectures contribute to the high emission current.
TL;DR: In this paper, structural, optical, and field-emission properties of ZnO nanowire arrays grown at 90°C were investigated, and stable electron emission at low field strengths for nanowires grown on polystyrene and polyethylene foils, making them promising candidates for fabrication of flexible cold cathodes.
Abstract: Structural, optical, and field-emission properties of ZnO nanowire arrays grown at 90°C are investigated. Single-crystalline ZnO nanowires with low level of oxygen vacancies are obtained at low temperatures. The nanowire growth is strongly dependent on the seeding method used but independent of the substrate materials, which enable large scale growth of ZnO arrays on all kinds of substrates including polymers. We have demonstrated stable electron emission at low-field strengths for nanowires grown on polystyrene and polyethylene foils, making them promising candidates for fabrication of flexible cold cathodes. Deposition of a few nanometers of gold on ZnO nanowires significantly lowers the field required for electron emission, which is explained in terms of additional field enhancement from Au islands on top of the ZnO nanowires.
TL;DR: In this paper, three different methods to prepare nanostructured materials using highly ordered porous alumina membranes as templates were reported. And the structure and composition of these nanowires were determined by field emission scanning electron microscopy (FEM) and energy dispersive X-ray spectroscopy.
TL;DR: In this paper, a soft and template-free electrochemical deposition method was proposed for preparing wafer-scale ZnO nanoneedle arrays on an oriented gold film coated silicon substrate.
Abstract: We report a soft and template-free electrochemical deposition method for preparing wafer-scale ZnO nanoneedle arrays on an oriented gold film coated silicon substrate. It has been shown that the ZnO nanoneedles possess single-crystal wurtzite structure and grow along the c-axis perpendicularly on the substrate. Raman and resonant Raman scattering studies have confirmed that the ZnO nanoneedles are of good crystal quality. The room temperature photoluminescence spectrum of such ZnO nanoneedle arrays exhibits a strong ultraviolet emission but negligible visible emission. The time-resolved photoluminescence spectral analysis discloses the excitonic origin of the ultraviolet emission. The field electron emission study, showing notable emission current in a moderate turn-on field, demonstrates potential applications of such ZnO nanoneedle arrays in field emission display devices. The formation of such a ZnO nanoneedle array is attributed to the formation of {0001}-oriented ZnO nuclei on the oriented gold coated silicon substrate and preferential growth along .
TL;DR: In this article, an ion-enhanced field emission mechanism was proposed to explain deviations from the Paschen curve in gaps smaller than 5 µm in large-scale systems.
Abstract: Gas breakdown in large scale systems has been widely studied and is reasonably well understood. Deviations from the well-known Paschen law, however, have been reported in microgaps. One possible mechanism responsible for these deviations is the increase of the secondary electron emission yield due to the quantum tunnelling of electrons from the metal electrodes to the gas phase. The high electric fields obtained in small gaps combined with the lowering of the potential barrier seen by the electrons in the cathode as an ion approaches lead to the onset of ion-enhanced field emissions. Particle-in-cell/Monte Carlo simulations including ion-enhanced field emission have been performed to evaluate the importance of these mechanisms in the discharge breakdown. Deviations from the Paschen curve in gaps smaller than 5 µm can be explained based on this mechanism.
TL;DR: This work provides a strategy for fabricating a supramolecular polymer, in which ordered polydiacetylene nanowires can be obtained by associated self-polymerization and self-assembly processes, and shows excellent field emission properties.
Abstract: The paper described here concerns a challenge of general interest for producing a novel structure of a polymer aggregate, the achievement of nanowires with controlled diameters. We provide a strategy for fabricating a supramolecular polymer, in which ordered polydiacetylene nanowires can be obtained by associated self-polymerization and self-assembly processes. The polymer nanowire film shows excellent field emission properties with the turn-on field of 8.2 V/mum at 10 muA/cm2 and the maximum current density of 5 mA/cm2 at an applied field of 15 V/mum.
TL;DR: In this article, the effect of microwave power on surface morphology of carbon petals has been investigated by scanning electron microscopy, which revealed characteristics of disordered microcrystalline graphite, which became more disordered with an increase in microwave power.