Showing papers on "Field electron emission published in 2008"
TL;DR: In this article, a simple and general solution based method for the deposition of field emitting graphene/polymer composite thin films is described, where the graphene sheets are oriented at some angles with respect to the substrate surface leading to field emission at low threshold fields (∼4Vμm−1).
Abstract: Field emission from graphene is challenging because the existing deposition methods lead to sheets that lay flat on the substrate surface, which limits the field enhancement. Here we describe a simple and general solution based method for the deposition of field emitting graphene/polymer composite thin films. The graphene sheets are oriented at some angles with respect to the substrate surface leading to field emission at low threshold fields (∼4Vμm−1). Our method provides a route for the deposition of graphene based thin film field emitter on different substrates, opening up avenues for a variety of applications.
278 citations
TL;DR: In this article, the electric field emission behavior of vertically aligned few-layer graphene was studied in a parallel plate-type setup, and it was found to be a good field emitter, characterized by turn-on fields as low as 1V/μm and field amplification factors up to several thousands.
Abstract: The electric field emission behavior of vertically aligned few-layer graphene was studied in a parallel plate–type setup. Few-layer graphene was synthesized in the absence of any metallic catalyst by microwave plasma enhanced chemical vapor deposition with gas mixtures of methane and hydrogen. The deposit consists of nanostructures that are several micrometers wide, highly crystalline stacks of four to six atomic layers of graphene, aligned vertically to the substrate surface in a high density network. The few-layer graphene is found to be a good field emitter, characterized by turn-on fields as low as 1 V/μm and field amplification factors up to several thousands. We observe a clear dependence of the few-layer graphene field emission behavior on the synthesis parameters: Hydrogen is identified as an efficient etchant to improve field emission, and samples grown on titanium show lower turn-on field values and higher amplification factors when compared to samples grown on silicon.
264 citations
TL;DR: The field emission performance of the ZnO emitters was found to be strongly correlated with the resistance of each individual ZnNO nanostructure, indicating that the uniformity in conductivity of the emitters in an array should be ensured, in order to meet the requirement of device application.
Abstract: Both electrical and field emission measurements were carried out to study the correlation between resistance and field emission performance of individual one-dimensional (1D) ZnO nanostructures. Three types of 1D ZnO nanostructures were investigated (i.e., agave-like shape, pencil-like shape, and hierarchical structure) and were prepared by thermal chemical vapor transport and condensation without using any catalyst. The 1D ZnO nanostructures have obvious differences in resistance and thus conductivity from type to type. In addition, in the same type of 1D ZnO nanostructure, each individual emitter may also have variation in resistance and thus in conductivity. The field emission performance of the ZnO emitters was found to be strongly correlated with the resistance of each individual ZnO nanostructure: (i) a ZnO emitter with low resistance will have better emission; (ii) a high resistance region in a ZnO nanostructure is liable to the initiation of a vacuum breakdown event. The results indicate that, bes...
137 citations
TL;DR: In this paper, the particle size, lattice parameters and crystal structure of ZnO nanopowder are characterized by in situ high temperature X-ray diffraction (XRD) using transmission electron microscopy (TEM) and field emission electron microscope (FESEM).
Abstract: Ultrasonic mist chemical vapour deposition (UM-CVD) system has been developed to prepare ZnO nanopowder. This is a promising method for large area deposition at low temperature inspite of being simple, inexpensive and safe. The particle size, lattice parameters and crystal structure of ZnO nanopowder are characterized by in situ high temperature X-ray diffraction (XRD). Surface morphology of powder was studied using transmission electron microscopy (TEM) and field emission electron microscope (FESEM). The optical properties are observed using UV-visible spectrophotometer. The influence of high temperature vacuum annealing on XRD pattern is systematically studied. Results of high temperature XRD showed prominent 100, 002 and 101 reflections among which 101 is of highest intensity. With increase in temperature, a systematic shift in peak positions towards lower 2θ values has been observed, which may be due to change in lattice parameters. Temperature dependence of lattice constants under vacuum shows linear increase in their values. Diffraction patterns obtained from TEM are also in agreement with the XRD data. The synthesized powder exhibited the estimated direct bandgap (E
g) of 3.43 eV. The optical bandgap calculated from Tauc’s relation and the bandgap calculated from the particle size inferred from XRD were in agreement with each other.
120 citations
TL;DR: In this paper, a metal-insulator heterostructure made of twinned Ga2O3 nanowires embedding discrete gold particles along the twin boundary was formed through a reaction between gold, gallium, and silica at 800 degrees C during simple thermal annealing.
Abstract: A novel metal-insulator heterostructure made of twinned Ga2O3 nanowires embedding discrete gold particles along the twin boundary was formed through a reaction between gold, gallium, and silica at 800 degrees C during simple thermal annealing. The Au-in-Ga2O3 peapods spontaneously crystallized under phase separation induced by the formation of twin boundaries. The nanostructures were analyzed by field emission scanning (FESEM) and transmission electron microscopes (FETEM), and their photoresponse was investigated using a double-frequency Nd:YAG laser with a wavelength of 532 nm on a designed single-nanowire device. The surface plasmon resonance (SPR) effects of embedded Au nanoparticles are proposed to be responsible for the remarkable photoresponse of these novel structures.
108 citations
TL;DR: In this paper, an oblique angle deposition (OAD) method was proposed to directly synthesize aligned Ge nanowire arrays on a Si substrate, by tilting the Si substrate and adjusting the incident angle of the evaporated Ge vapor flux with respect to the substrate normal to 87°.
Abstract: We report a simple method, oblique angle deposition, to directly synthesize aligned Ge nanowire arrays on a Si substrate. This process is accomplished by tilting the Si substrate and adjusting the incident angle of the evaporated Ge vapor flux with respect to the substrate normal to 87°. The resultant crystallinity of the Ge nanostructures can be tuned to either amorphous or poly- and single-crystalline, depending on the substrate temperature and evaporation rate. The effects of thermal treatment on the morphology and structure of the Ge nanowires are discussed in detail. The field-emission measurements show that increasing the annealing temperatures to about 550 °C results in a gradual increase in the maximum current density and a decrease in the turn-on voltage, because of the decreased wire density originating from melting of the Ge nanowires. The field-enhancement factor analysis shows there is an optimum range for Ge wire density and aspect ratio to obtain good emission performance. Ge nanowire arrays might find potential application in the field emitters of the future.
103 citations
TL;DR: In this paper, the density variation was accompanied by the change of both diameter and height of the nanowires, which leads to a change in aspect ratio, and both changes in density and aspect ratio were found to affect the field emission characteristics.
Abstract: We report on how to tune the density of zinc oxide (ZnO) nanowire arrays in a wide range (more than 5 orders of magnitude) in a low temperature (80 °C) solution-phase growth process. A model based on the coexistence of nanowire growth and etching of the ultrathin ( 3.5 nm), the variation is very narrow, and if it is too thin (<1.5 nm), no nanowires can grow. In addition, the density variation was accompanied by the change of both diameter and height of the nanowires, which leads to a change in aspect ratio. Both changes in density and aspect ratio were found to obviously affect the field emission characteristics. It was demonstrated that optimal conditions can be found to grow ZnO nanowire films with better field emission characteristics.
101 citations
Journal Article•
TL;DR: The surface plasmon resonance (SPR) effects of embedded Au nanoparticles are proposed to be responsible for the remarkable photoresponse of these novel structures made of twinned Ga2O3 nanowires embedding discrete gold particles along the twin boundary.
Abstract: A novel metal-insulator heterostructure made of twinned Ga2O3 nanowires embedding discrete gold particles along the twin boundary was formed through a reaction between gold, gallium, and silica at 800 degrees C during simple thermal annealing. The Au-in-Ga2O3 peapods spontaneously crystallized under phase separation induced by the formation of twin boundaries. The nanostructures were analyzed by field emission scanning (FESEM) and transmission electron microscopes (FETEM), and their photoresponse was investigated using a double-frequency Nd:YAG laser with a wavelength of 532 nm on a designed single-nanowire device. The surface plasmon resonance (SPR) effects of embedded Au nanoparticles are proposed to be responsible for the remarkable photoresponse of these novel structures.
101 citations
TL;DR: In this article, a pyramid-like micropatterns were firstly prepared via capillarity-driven self-assembly from aligned CNT arrays, and then grown via vapor-phase transport (VPT) method.
100 citations
TL;DR: This study provides a simple but rapid approach that is compatible with microtechnology and is capable of fabricating metal oxide nanorods at low substrate temperatures, on a large scale.
Abstract: When heated in a rapid thermal processor at 350 °C in air, cobalt thin (50 nm thick) films were transformed into Co3O4 nanorods in minutes. The nanorods are single-crystalline and are typically several hundred nanometers long and several tens of nanometers in diameter. They exhibited room-temperature photoluminescence in the visible range and good field emission properties, i.e. a low turn-on field of ~2.8 V µm−1 and good stability at high emission currents. This study provides a simple but rapid approach that is compatible with microtechnology and is capable of fabricating metal oxide nanorods at low substrate temperatures, on a large scale.
98 citations
TL;DR: In this article, a novel method, electrospinning, was explored to prepare europium-doped YBO3 nanocrystalline phosphors, which were obtained, varying from 40 to 500 nm.
Abstract: A novel method, electrospinning, was explored to prepare europium-doped YBO3 nanocrystalline phosphors. Narrow and size-controllable YBO3 nanotubes and nanowires were obtained, varying from 40 to 500 nm. The average wall thickness of the nanotubes was only 5−10 nm. The structural properties were characterized by X-ray diffraction (XRD), Fourier-transform infrared absorption (FTIR), electron spin resonance (ESR), field emission scanning electron micrographs (FE-SEM), and high-resolution transmission electron micrographs (HR-TEM). The results indicate that theYBO3 nanotubes and nanowires were hexangular in phase and single crystals or polycrystalline in structure. Some surface dangling bonds caused by transition metal ions lead to a change of the coordination number of boron from +3 to +4. The photoluminescent properties of the YBO3: Eu3+ nanowires and nanotubes were also characterized. It was observed that the charge-transfer excitation bands of Eu3+ in the nanowires and nanotubes blue-shifted in contrast ...
TL;DR: In this article, an array of boron nanowires (ca. 5 mu m long) vertically aligned in high density on a Si substrate is shown. But they are not shown in this paper.
Abstract: Aligned single crystalline boron nanowire arrays are formed by thermal carbon reduction. The SEM image shows an array of boron nanowires (ca. 5 mu m long) vertically aligned in high density on a Si substrate. These nanowires have a high enhancement factor, good emission stability, and can endure high current, which suggest they are an excellent candidate for field-emission applications.
TL;DR: In this article, a technique to achieve contrast between Ni and yttria stabilized zirconia (YSZ) in scanning electron microscopy (SEM) is described.
TL;DR: In this article, the authors describe the synthesis of novel and highly porous boron nitride (BN) nanospheres (100-400 nm o.d.) that exhibit a rough surface consisting of open BN nanocones and corrugated BN ribbons.
Abstract: We first describe the synthesis of novel and highly porous boron nitride (BN) nanospheres (100-400 nm o.d.) that exhibit a rough surface consisting of open BN nanocones and corrugated BN ribbons. The material was produced by reacting B2O3 with nanoporous carbon spheres under nitrogen at ca. 1750 degrees C. The BN nanospheres were characterized using scanning electron microscopy, high-resolution electron microscopy, and electron energy loss spectroscopy. The porous BN spheres show relatively large surface areas of ca. 290 m2/g and exhibit surprisingly stable field emission properties at low turn-on voltages (e.g., 1-1.3 V/microm). We attribute these outstanding electron emission properties to the presence of finite BN ribbons located at the surface of the nanospheres (exhibiting zigzag edges), which behave like metals as confirmed by first-principles calculations. In addition, our ab initio theoretical results indicate that the work function associated to these zigzag BN ribbons is 1.3 eV lower when compared with BN-bulk material.
TL;DR: In this paper, a catalyst free method to synthesize single crystal quality Nb2O5 nanowire arrays was reported, which achieved a remarkably high current density of ∼4 mA/cm2 at an applied field of 11 V/μm.
Abstract: We report a catalyst free method to synthesize single crystal quality Nb2O5 nanowire arrays. Vertically oriented Nb2O5 nanowires directly on Nb foils were synthesized by a thermal oxidation method. The electron field emission (FE) properties of the as-synthesized Nb2O5 nanowires were investigated in detail. Our results showed that the Nb2O5 nanowires are excellent FE emitters with fairly low turn on and threshold field. A remarkably high current density of ∼4 mA/cm2 was achieved at an applied field of 11 V/μm. At moderate applied fields, a continuous and uniform electron emission can be acquired from the Nb2O5 nanowire emitters for a total testing time of 10 h without any noticeable diminution.
TL;DR: In this article, an elegant Bi 2 S 3 nanoflowers were prepared via a simple vapor deposition process, and the conductivity of the nanorods was shown to be much more sensitive to simulated sunlight exposure.
Abstract: Elegant Bi 2 S 3 nanoflowers were prepared via a simple vapor deposition process. Compared to the Bi 2 S 3 nanorods bundles, the conductivity of the nanoflowers is much more sensitive to simulated sunlight exposure. The light-induced conductivity increase allows us to reversibly switch the nanoflowers between "OFF' and "ON" states, an optical gating phenomenon analogous to the commonly used electrical gating, which show the possibility of creating highly sensitive photodetectors and optical switches using these Bi 2 S 3 nanoflowers. Moreover, the field emission measurements confirm that the present nanoflowers are excellent field emitters with the turn-on field of 7.45 eV. Therefore, these Bi 2 S 3 nanoflowers with large proportion of free open edges may be attractive in novel nanoscale electric and optoelectronic devices.
Journal Article•
TL;DR: Novel and highly porous boron nitride (BN) nanospheres that exhibit a rough surface consisting of open BN nanocones and corrugated BN ribbons are synthesised that behave like metals as confirmed by first-principles calculations.
Abstract: We first describe the synthesis of novel and highly porous boron nitride (BN) nanospheres (100-400 nm o.d.) that exhibit a rough surface consisting of open BN nanocones and corrugated BN ribbons. The material was produced by reacting B2O3 with nanoporous carbon spheres under nitrogen at ca. 1750 degrees C. The BN nanospheres were characterized using scanning electron microscopy, high-resolution electron microscopy, and electron energy loss spectroscopy. The porous BN spheres show relatively large surface areas of ca. 290 m2/g and exhibit surprisingly stable field emission properties at low turn-on voltages (e.g., 1-1.3 V/microm). We attribute these outstanding electron emission properties to the presence of finite BN ribbons located at the surface of the nanospheres (exhibiting zigzag edges), which behave like metals as confirmed by first-principles calculations. In addition, our ab initio theoretical results indicate that the work function associated to these zigzag BN ribbons is 1.3 eV lower when compared with BN-bulk material.
TL;DR: High-resolution transmission electron microscopy (HRTEM) showed that the as-grown nanowires were of single crystal hexagonal wurtzite structure, growing along the [101] direction.
Abstract: ZnO nanowire arrays were synthesized on zinc foil by a simple thermal evaporation process at relatively low temperature. Morphology and size controlled synthesis of the ZnO nanostructures was achieved by variation of the synthesis temperature, reaction time and the surface roughness of the substrate. A gas–solid and self-catalytic liquid–solid mechanism is proposed for the growth of nanowires at different temperatures. High-resolution transmission electron microscopy (HRTEM) showed that the as-grown nanowires were of single crystal hexagonal wurtzite structure, growing along the [101] direction. Photoluminescence exhibited strong UV emission at ~382 nm and a broad green emission at ~513 nm with 325 nm excitation. Raman spectroscopy revealed a phonon confinement effect when compared with results from bulk ZnO. The nanowire arrays also exhibited a field emission property.
TL;DR: In this article, the mechanical resonances of six nanowires, which were glued to the ends of tungsten support tips, were electrostatically excited and detected visually in the scanning electron microscopy (SEM) configuration and then by FE microscopy image processing.
Abstract: We present here comparative measurements by scanning electron microscopy (SEM) and field emission (FE) of the mechanical resonances of singly clamped, batch-fabricated SiC nanowires as well as an extensive theoretical description. The mechanical resonances of six nanowires, which were glued to the ends of tungsten support tips, were electrostatically excited and detected visually in the SEM configuration and then by FE microscopy image processing. The large tensions generated by electric field pulling in FE that tune the resonance frequencies and the complex boundary conditions at both the free and clamped nanowire ends complicate the interpretation of the resonance frequencies necessary for extracting intrinsic mechanical parameters. Our model fully takes into account these effects and results in an excellent agreement with the measured resonance modes in both configurations. Analytical solutions with their validity conditions are given for the low and high tension ranges and semianalytical solutions for the intermediary range. Viable estimates of Young's modulus are thus achieved for the ultra high vacuum (UHV) environment of FE. Progressive in situ cleaning was performed in the FE-UHV configuration in the range of $600--1350\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, which increased the $Q$ factor of the first mechanical resonance by up to $\ifmmode\times\else\texttimes\fi{}100$ and did not alter the value of the Young's modulus measured previously in the SEM configuration. The agreement between the SEM and FE techniques means that we can now profit from their different strengths for better understanding the mechanics of nanowires and nanotubes.
TL;DR: In this paper, a SiC porous nanowire (NW) array on Si substrate has been shown to be an excellent field emitter with large field emission current denstity at very low electric field.
Abstract: Highly oriented SiC porous nanowire (NW) arrays on Si substrate have been achieved via in situ carbonizing aligned Si NW arrays standing on Si substrate. The resultant SiC NW arrays inherit the diameter and length of the mother Si NW arrays. Field emission measurements show that these oriented SiC porous NW arrays are excellent field emitter with large field emission current denstity at very low electric field. The in situ conversion method reported here might be exploited to fabricate NW arrays of other materials containing silicon.
TL;DR: The investigation of field emission properties of ZnO nanorod arrays revealed a strong dependency on the aspect ratio and their density, which shows that an optimum density and aspect ratio of ZNO nan orod arrays have high efficiency of field emissions.
Abstract: ZnO nanorod arrays are prepared on a silicon wafer through a multi-step hydrothermal process. The aspect ratios and densities of the ZnO nanorod arrays are controlled by adjusting the reaction times and concentrations of solution. The investigation of field emission properties of ZnO nanorod arrays revealed a strong dependency on the aspect ratio and their density. The aspect ratio and spacing of ZnO nanorod arrays are 39 and 167 nm (sample C), respectively, to exhibit the best field emission properties. The turn-on field and threshold field of the nanorod arrays are 3.83 V/μm and 5.65 V/μm, respectively. Importantly, the sample C shows a highest enhancement of factorβ, which is 2612. The result shows that an optimum density and aspect ratio of ZnO nanorod arrays have high efficiency of field emission.
TL;DR: For several multiwalled carbon nanotubes, reproducible and quite stable emission current behaviour was obtained, with a dependence on the applied voltage well described by a series resistance modified Fowler-Nordheim model.
Abstract: Electron field emission characteristics of individual multiwalled carbon nanotubes have been investigated by a piezoelectric nanomanipulation system operating inside a scanning electron microscopy chamber. The experimental setup ensures a high control capability on the geometric parameters of the field emission system (CNT length, diameter and anode-cathode distance). For several multiwalled carbon nanotubes, reproducible and quite stable emission current behaviour has been obtained with a dependence on the applied voltage well described by a series resistance modified Fowler-Nordheim model. A turn-on field of about 30 V/um and a field enhancement factor of around 100 at a cathode-anode distance of the order of 1 um have been evaluated. Finally, the effect of selective electron beam irradiation on the nanotube field emission capabilities has been extensively investigated.
TL;DR: In this article, the electron field emission characteristics of individual multi-walled carbon nanotubes were investigated by a piezoelectric nanomanipulation system operating inside a scanning electron microscopy chamber.
Abstract: The electron field emission characteristics of individual multiwalled carbon nanotubes were investigated by a piezoelectric nanomanipulation system operating inside a scanning electron microscopy chamber. The experimental set-up ensures a precise evaluation of the geometric parameters (multiwalled carbon nanotube length and diameter and anode–cathode separation) of the field emission system. For several multiwalled carbon nanotubes, reproducible and quite stable emission current behaviour was obtained, with a dependence on the applied voltage well described by a series resistance modified Fowler–Nordheim model. A turn-on field of ∼30 V μm −1 and a field enhancement factor of around 100 at a cathode–anode distance of the order of 1 μm were evaluated. Finally, the effect of selective electron beam irradiation on the nanotube field emission capabilities was extensively investigated.
TL;DR: In this paper, the surface morphology, microstructure, and composition of 11 sample groups have been carefully characterized and the consequence of the material property and the plasma gas chemistry on the electrode performance in plasma treatments of screen-printed carbon nanotube (CNT) films was investigated.
TL;DR: In this article, SiC nanowires were grown directly on Si substrates by thermal evaporation of WO3 and graphite powders at high temperature using NiO catalyst.
TL;DR: Comparison of the field emission characteristics of the ZnO nanoflower arrays and ZnNO nanoneedles showed that the arrays had excellent electron emission characteristics, with a low turn-on electric field and high emission current density.
Abstract: The electron emission of position-controlled grown ZnO nanoflowers was investigated for application in cold cathode electron emission devices. ZnO nanoflower arrays, composed of several nanoneedles with sharp tips, were grown selectively on a conducting glass substrate using a chemical solution deposition method. The morphology and position of the ZnO nanoflowers were controlled by preparing polymethylmethacrylate submicron patterns using electron-beam lithography. Without the patterns, in contrast, vertical ZnO nanoneedles were randomly grown on the substrates with high density. Several samples prepared at the same conditions exhibited almost the same nanoflower morphology and field emission characteristics. Comparison of the field emission characteristics of the ZnO nanoflower arrays and ZnO nanoneedles showed that the arrays had excellent electron emission characteristics, with a low turn-on electric field of 0.13 V µm−1 at 0.1 µA cm−2 and a high emission current density of 0.8 mA cm−2 in an applied electric field of 9.0 V µm−1. Furthermore, light-emitting devices made using ZnO nanoflower arrays demonstrated strong light emission, and micropixels for display application were clearly displayed.
TL;DR: The fabrication of a carbon nanotube field emission backlight unit (CNT-BLU) and its application for liquid crystal displays (LCD) showed long-term emission stability and high luminance uniformity.
Abstract: We report on the fabrication of a carbon nanotube field emission backlight unit (CNT-BLU) and its application for liquid crystal displays (LCD). The CNT-BLU was operated with locally controllable luminance and impulse-type scanning. The local luminance control, which is based on a very small block size of 1 cm 2 , consisted of local dimming and local brightening. This resulted in the contrast ratio of the LCD-TV to be as high as 300 000:1. A fast response time of ∼5.7 ms was also achieved from the LCD-TV lit by CNT-BLU, originating from the impulse-type scanning. In addition, the CNT-BLU showed long-term emission stability and high luminance uniformity.
TL;DR: In this article, a conical nanostructures and promising field electron emitters have been produced using a simple one-step thermal reaction under acetone vapor at 850°C.
Abstract: Quasialigned nanoarrays consisting of TiO2 nanowire cores and carbon nanocone shells have been produced directly on titanium foils via a simple one-step thermal reaction under acetone vapor at 850°C. The nanowire cores are single-crystalline rutile TiO2 with diameters of 15–20nm and the conical carbon shells are amorphous with gradually decreasing thicknesses from 200–300nm at the bases to 5–10nm at the tips. Disparity of precipitation and etching of carbon shell give rise to the conical shape. Such TiO2∕C nanocone arrays on a conducting substrate are a new member of the conical nanostructures and promising field electron emitters.
TL;DR: The enhanced field emission results for these multistage emitters are a consequence of higher field concentration, which is ∼3 times more than MWNTs.
Abstract: In this work we report on the synthesis and field emission properties of carbon nanotube multistage emitter arrays grown on porous silicon by catalytic thermal chemical vapor deposition. The vertically oriented multistage array structures consisted of SWNTs and thin MWNTs grown on MWNTs, confirmed by TEM and Raman analysis. Higher field emission current ∼32 times and low threshold field ∼1.5 times were obtained for these structures in comparison to only MWNT arrays. The enhanced field emission results for these multistage emitters are a consequence of higher field concentration, which is ∼3 times more than MWNTs.