Efficient Field Emission Research Articles

Enhanced field emission from large scale uniform monolayer graphene supported by well-aligned ZnO nanowire arrays

Large scale, uniform single-layer graphene was transferred onto well-aligned ZnO nanowire arrays to produce high density nanoscale protrusions within graphene for efficient field emission. Polymethyl methacrylate (PMMA) was used as a supporting layer to provide a quasi-flat surface for graphene transfer. Highly efficient (maximum current density of ∼500 μA/cm2) and stable field emission with low turn-on fields (5.4 V/μm) was observed due to highly localized electric field, which is much better than those without using PMMA. F-N plot showed an unique up-bending feature of single-layer graphene. Our approach provides an efficient way to produce high quality single-layer graphene field emitters.

Vertically aligned nanorods of lanthanum hexaboride with efficient field emission properties

The present study describes a borothermal reduction process to obtain nanostructured lanthanum hexaboride (LaB6) particles and their films. The morphology (nanorods and nanoparticles) of the boride nanostructures could be controlled by using a lanthanum hydroxide precursor (with controlled shape and size) obtained by a microemulsion mediated process. The LaB6 films fabricated by spin coating of nanorods of LaB6 led to an assembly of vertically oriented nanorods with excellent field emission properties (field enhancement factor of 4522). This methodology does not require any template for obtaining these vertically aligned nanorods. The field emission properties can be tuned by controlling the shape and size of the lanthanum hexaboride nanostructures.

Synthesis of crystalline carbon nanofern-like structure by dc-PECVD and study of its electrical and field emission properties

Carbon nanofern-like structure was synthesized by direct current plasma enhanced chemical vapor deposition at 400°C using acetylene as carbon precursor and nickel particle as seed. High resolution transmission electron microscopy (HRTEM) study confirmed the fern-like structure of the as-synthesized sample. It was seen that when nickel was not used a cluster deposition took place without forming any structure. Atomic force microscopy study showed the surface topology of the as-prepared samples. X-ray photoelectron spectroscopy as well as HRTEM studies confirmed the presence of nickel in the carbon matrix. Current (I)–voltage (V) characteristics have been taken for three different temperatures. A non-linear I–V characteristic was obtained for the fern like sample. Field emission study showed that carbon nanofern showed efficient field emission with a turn-on field as low as 4.8V/μm. Also, the field emission has been studied for different inter-electrode distances.

Electro-optical analysis in determining the field emission characteristics of carbon nanofibers on an acute tip substrate

The shape of an acute tungsten (W) tip substrate coated with palladium (Pd) and carbon nanofibers (CNFs) was optimized in order to generate efficient field emission (FE) currents. By adjusting the apex angle of the tip, we succeeded in controlling the FE properties and electron beam convergence. When the apex angle was close to 50º, a narrow convergence of electron beams was observed. By employing an original computation tool based on the surface charge method, we conducted a numerical analysis of the convergence mechanism of the FE device; this was dependent on FE properties, and displayed its maximum around the same apex angle. By simulating the electrical field distribution above the CNF, we concluded that the optimum values of the electro-optical properties of CNFs on the tip substrate were found at an angle of approximately 50º with a narrow divergence angle. After determining the relationship between the divergence angle and the tip apex angle, the electron emission property was optimized. Analysis of the characteristics of the maximum electron emission state using our computation method indicated that an acute tip covered with CNFs has potential for use as a cathode in electrical devices which require a large FE current with low power consumption.

Efficient field emission properties of ZnO (core)/graphite (shell) nanowires

In this work the field emission studies of a new type of field emitter, zinc oxide (ZnO) core/graphitic (g-C) shell nanowires are presented. The nanowires are synthesized by chemical vapor deposition of zinc acetate at 1300 degrees C Scanning and transmission electron microscopy characterization confirm high aspect ratio and novel core-shell morphology of the nanowires. Raman spectrum of the nanowires mat represents the characteristic Raman modes from g-C shell as well as from the ZnO core. A low turn on field of 2.75 V/mu m and a high current density of 1.0 mA/cm(2) at 4.5 V/mu m for ZnO/g-C nanowires ensure the superior field emission behavior compared to the bare ZnO nanowires. (C) 2012 Elsevier B.V. All rights reserved.

Enhancement in field emission characteristics of multifunctional ZnO/C hybrid nanostructures

Multifunctional hybrid nanostructures have recently drawn immense attention due to their interesting physical and chemical properties and also due to their potential for applications in novel electronic devices. Herein, we report the luminescence and enhancement of field emission (FE) properties of multifunctional ZnO/C hybrid nanostructures prepared by the decomposition of zinc acetate and dextrose inside the nanopores of anodic aluminium oxide templates, which are fabricated by controlled electrochemical anodization of pure aluminium. Microscopic investigations show that the average pore diameter of the as prepared templates is ∼50 nm and ZnO/C hybrid nanostructures are formed around the inner pore walls. The template, containing the ZnO/C hybrids, exhibits visible light emission in blue wavelength region along with luminescence in the ultra-violet region. Investigations on the field emission property of the hybrid ZnO/C nanostructures reveals, that they are better and more efficient field emission material compared to one dimensional ZnO nanostructures.

Improving the field emission of graphene by depositing zinc oxide nanorods on its surface

Zinc oxide (ZnO) nanorods were vertically grown on the surface of graphene sheets by chemical vapor deposition, and their use in a field emission device was demonstrated. In comparison with pristine graphene, the graphene/ZnO nanorod hybrid structure exhibited efficient field emission with low turn-on field, low threshold field, high emission spot density, high field enhancement factor and excellent emitting stability. It is proposed that the introduction of mid-density ZnO nanorods on the surface of graphene sheets can increase the number of emitters, enhance tunneling probability, and lead to optimized field emission for the hybrid emitters. The results showed that the field emission properties of graphene can be tailored by growing various ZnO nanostructures on its surface.

Field Emission in Vertically Aligned ZnO/Si-Nanopillars with Ultra Low Turn-On Field

An effective method of fabricating vertically aligned silicon nanopillars (Si-NPs) was realized by using the self-assembled silver (Ag) nanodots as natural metal-nanomask during dry etching process. The obtained Si-NPs were preferentially aligned along the c-axis direction. Ultrathin ZnO films (~9 nm) were subsequently deposited on the Si-NPs by atomic layer deposition (ALD) to enhance the field emission property. The average diameter of the ZnO/Si-NPs is in the order of tens of nanometers, which enables efficient field emission and gives rise to marked improvement in the field enhancement factor, β. The turn-on field defined by the 10 μA/cm(2) current density criterion is ~0.74 V/μm with an estimated β ≈ 1.33×10(4). The low turn-on field and marked enhancement in β were attributed to the small radius of curvature, high aspect ratio, and perhaps more importantly, proper density distribution of the ZnO/Si-NPs.

Highly Efficient Electron Field Emission from Graphene Oxide Sheets Supported by Nickel Nanotip Arrays

Electron field emission is a quantum tunneling phenomenon whereby electrons are emitted from a solid surface due to a strong electric field. Graphene and its derivatives are expected to be efficient field emitters due to their unique geometry and electrical properties. So far, electron field emission has only been achieved from the edges of graphene and graphene oxide sheets. We have supported graphene oxide sheets on nickel nanotip arrays to produce a high density of sharp protrusions within the sheets and then applied electric fields perpendicular to the sheets. Highly efficient and stable field emission with low turn-on fields was observed for these graphene oxide sheets, because the protrusions appear to locally enhance the electric field and dramatically increase field emission. Our simple and robust approach provides prospects for the development of practical electron sources and advanced devices based on graphene and graphene oxide field emitters.

Synthesis and efficient field emission characteristics of patterned ZnO nanowires

Patterned ZnO nanowires were successfully synthesized on ITO electrodes deposited on the glass substrate by using a simple thermal evaporation approach. The morphology, crystallinity and optical properties of ZnO nanowires were characterized by scanning electron microscopy, X-ray diffraction, energy dispersive X-ray and photoluminescence spectroscopy. Their field emission characteristics were also investigated. SEM images showed that the ZnO nanowires, with a diameter of 100–200 nm and length up to 5 μm, were highly uniform and well distributed on the linear ITO electrodes. The field emission measurement indicated that patterned ZnO nanowire arrays have a turn-on field of 1.6 V/μm at current density of 1 μA/cm2 and a threshold field of 4.92 V/μm at current density of 1 mA/cm2 at an emitter-anode gap of 700 μm. The current density rapidly reached 2.26 mA/cm2 at an applied field of 5.38 V/μm. The fluctuation of emission current was lower than 5% for 4.5 h. The low turn-on field, high current density and good stability of patterned ZnO nanowire arrays indicate that it is a promising candidate for field emission application.

Promising electron field emitters composed of conducting perovskite LaNiO3 shells on ZnO nanorod arrays

We report a semiconductor–perovskite composite system with promising field emission properties. The composite system was fabricated by sputtering perovskite LaNiO3 (LNO) shells on one dimensional (1D) well-aligned hydrothermally produced ZnO nanorod arrays (ZNAs). The ZNA–LNO core–shell hetero-structures were demonstrated to be much more efficient field emitters than ZNAs. Since the work function of LNO (4.5 eV) is lower than that of ZnO (5.3 eV), a shallow well is formed in thermal equilibrium in the ZNA–LNO heterojunction. When an electric field is applied, the produced well is of much benefit for the flow of electrons from the GZO seed layers through the ZNA to the LNO shells. Consequently, the emission of electrons into vacuum by tunneling is easily realized due to the low work function of the LNO coatings. Our 1D semiconductor–perovskite composite system provides a prospect for the development of practical field emission electron sources.

Growing uniform copolymer nanowire arrays for high stability and efficient field emission

In this report, we present a novel platform to study the formation of two π-conjugated conducting copolymer nanowire arrays based on 3,4-ethylenedioxythiophene (EDOT) and thieno[3,4-b]thiophene (T34bT). The resulting nanostructures have a highly uniform wire array architecture with tunable diameters. This combination of nanoporous templates and in situ electropolymerization strategy offers a versatile route to prepare copolymers, forming uniform one-dimensional nanomaterials potentially useful in electronic conductor and field emission applications.

Vertical arrays of SiNWs–ZnO nanostructures as high performance electron field emitters

Multicomponent hybrid materials of nanostructured building blocks are essential for the development of complex devices and advanced applications due to their role as either functional or interconnecting elements. This study introduces a simple and cost effective strategy for the synthesis of vertical arrays of silicon nanowires and ZnO nanostructures (nanorod and multipod structures). Formation of vertical nanostructured arrays is confirmed by SEM and HRTEM imaging as well as XRD and Raman measurements. We have investigated field emission properties of the as-synthesized vertical nanostructured arrays. Our results show that these SiNWs–ZnO nanostructures are highly efficient and stable field emitters.

Manipulating the anisotropy and field emission of lanthanum hexaboride nanorods

The present study describes the controlled synthesis of lanthanum hexaboride nanostructures with efficient field emission properties. The synthesis is mediated by a nanostructured lanthanum hydroxide precursor, which is controlled by varying the capping agent and pH using a hydrothermal route. The effect of charge on the capping agent (surfactant) strongly affects the shape and size of the precursor (neutral surfactants lead to the formation of nanorods while a cationic surfactant results in the formation of particles). This precursor mediated route leads to lanthanum hexaboride nanostructures at much lower temperatures (∼500 °C lower than the conventional solid state route) and allows for variation of morphology of nanostructured films. Vertically aligned nanorods (30 nm × 200–400 nm), nanoparticles (25 nm) and sub-micron particles (0.2–0.25 microns) could be precisely obtained. Field emission studies of these vertically aligned nanorods show a very high field enhancement factor (4191), which is required for an efficient field emitter.

Floral-clustered few-layer graphene nanosheet array as high performance field emitter

Graphene sheet is expected to be a highly efficient field emitter due to its unique electrical properties and open surface with sharp edges. However, it is still a tremendous technical challenge to grow and align a graphene sheet in one particular direction to protrude its sharp edges for good field emission. Here, we report an ideal graphene field emitter of flower-like graphene nanosheets grown on a silicon nanocone array, wherein nanocone array guides the alignment of vertical nanosheets and produces high-density sharp edge protrusions on the conical tip. We observe high performance and stable field emission with low turn-on fields from floral-clustered graphene nanosheets. Protrusive sharp edges on the nanocone tip and optimized spacing between clusters both appear to locally enhance the electric field and dramatically increase field emission. Our new graphene emitter design provides a robust approach to the prospect for development of practical electron sources and advanced devices based on graphene field emitters.

Field emission from hydrogen titanate nanotubes

Hydrothermally synthesized hydrogen titanate (H2Ti3O7) nanotube meshes and arrays exhibit excellent field emission characteristics. The turn-on field is as low as 1.4 V μm−1 for the mesh and 2.6 V μm−1 for the array, while the electric field corresponding to an emission current density of 10 μA cm−2 is 2 V μm−1 (mesh) and 3.8 V μm−1 (array). The H2Ti3O7 nanotube mesh has one of the lowest reported turn-on voltages and highest enhancement factors. The emission current also shows good long term stability. We attribute the efficient field emission to the presence of mid-gap states arising from the negative surface charge on the H2Ti3O7 nanotubes.

Highly efficient field emission from nanodiamond films treated by fast reactive ion etching process

A fast reactive ion etching (RIE) treatment method is presented for dramatic enhancement of the field emission performances of nanocrystalline diamond (NCD) films. In this method a moment RIE treatment is able to modify the surface morphologies of NCD films and form a large area of nanoneedle-like arrays on the NCD films, in which the diamond nanoparticles were seeded on the film to serve as an etching mask. These elaborated diamond nanoneedle-like structures showed good uniformity and dense morphology with a controllable aspect ratio and distribution density and thereby significantly increased the electron field emission properties of the NCD films due to the formation of more emitting tips and enhanced field enhancement factor.

Experimental study on electron field emission, Raman scattering, and low temperature electrical properties of nanocrystalline lead selenide thin films

We report the electron field emission properties, Raman scattering, and low (77 K) and room temperature electrical properties of nanocrystalline PbSe thin films. Structural characterizations (high resolution x-ray diffraction, atomic force microscopy, and high resolution transmission electron microscopy) revealed the formation of cubic PbSe with an average crystallite diameter of ca. 8 nm. Raman analysis showed a strong peak at 136 cm−1. Due to the nanocrystalline nature, the threshold field (5.5 V/μm) and approximate work function values were high, making the films a very efficient field emitter.

Enhanced Field Emission Properties of α-Fe2O3 Nanostructures with the Removal of Adsorbed Gas Molecules

Quasi-1D α-Fe2O3 nanostructure arrays of four different morphologies (random nanoflakes, random nanobelts, quasi-aligned nanostrips and quasi-aligned nanoneedles) were successfully synthesized via a simple heating process. Field emission measurements indicate that the α-Fe2O3 nanoneedle arrays are superior field emitter exhibiting low turn-on voltage, high current density, and large field-enhancement factor due to better vertical alignment and higher aspect ratio. In addition, we found that adsorbed oxygen molecules greatly hindered the field emission performance of the nanostructures. Prolonged field emission process could drive the oxygen molecules away and give rise to markedly improved and efficient α-Fe2O3 nanostructures field emitter. The improved field emission is attributed to desorption of the oxygen molecules during the field emission process.

Epitaxially Integrating Ferromagnetic Fe1.3Ge Nanowire Arrays on Few-Layer Graphene

We report vertical growth of ferromagnetic and metallic Fe1.3Ge nanowire (NW) arrays on few-layer graphene in a large area, induced by a relatively good epitaxial lattice match. Integrating well-aligned NW arrays onto graphene would offer a good opportunity to combine superb material properties of graphene with versatile properties of NWs into novel applications. Fe1.3Ge NWs are also synthesized on highly ordered pyrolytic graphite (HOPG). Fe1.3Ge NWs on graphene and HOPG show quite efficient field emission, which are ascribed to the well-interfaced vertical growth, a pointed tip, and high field-enhancement factor (β) of the NWs. The development of ferromagnetic metal NW−graphene hybrid structures would provide an important possibility to develop graphene-based spintronic, electronic, and optoelectronic devices.