Emission Current Stability Research Articles

Electric field emission in GdNiO3 microflower

GdNiO3 microflowers were synthesized by hydrothermal method with unit sizes of about 2.2–3.5 μm and petal sizes of ∼75–100 nm. The X-ray diffraction pattern (XRD) and Raman spectra reveal an orthorhombic crystal structure with the space group Pbnm and various Raman active vibrational modes i.e., Ag, B1 g, B2 g associated with rare earth nickelates. The total density of states (TDOS) was calculated by density functional theory (DFT) study using a hybrid functional (HSE06) and the volume of TDOS near the Fermi level confirms the semiconducting nature of GdNiO3 with band gap ∼0.688 eV. The local bulk work function (φ) was estimated theoretically at ∼5.35 eV from DFT calculations which is one of the essential parameters for the field enhancement factor (β). Field emission current density (J) vs. applied electric field (E) divulges a low turn-on field (Eto)∼4.6 V/μm@1 μA/cm2 and a threshold field (Eth)∼5.2 V/μm@10 μA/cm2 respectively. The Fowler-Nordheim (F-N) model was introduced to calculate β ∼1637 and long-term field emission current stability was observed experimentally > 4 h at the preset values of current 2 μA and 10 μA, respectively. The easy preparedness, low turn-on field, and long-term current stability without significant decay suggest this material to be an efficient electron field emitting material in the rare-earth nickelates series.

Field emission from two-dimensional (2D) CdSSe flake flowers structure grown on gold coated silicon substrate: An efficient cold cathode.

Field emission finds a vital space in numerous scientific and technological applications, including high-resolution imaging at micro- and nano-scales, conducting high-energy physics experiments, molecule ionization in spectroscopy, and electronic uses. A continuous effort exists to develop new materials for enhanced field emission applications. In the present work, two-dimensional (2D) well-aligned CdSSe flake flowers (CdSSe-FFs) were successfully grown on gold-coated silicon substrate utilizing a simple and affordable chemical bath deposition approach at ambient temperature. The time-dependent growth mechanism from nanoparticles to FFs was observed at optimized parameters such as concentration of precursors, pH (~11), deposition time, and solution temperature. The crystalline nature of CdSSe-FFs is confirmed by high-resolution transmission electron microscopy (HRTEM) results, and selected area electron diffraction (SAED) observations reveal a hexagonal crystal structure. Additionally, the CdSSe-FFs thickness was confirmed by TEM analysis and found to be ~20-30 nm. The optical, photoelectric, and field emission (FE) characteristics are thoroughly explored which shows significant enhancement due to the formation of heterojunction between the gold-coated silicon substrate and CdSSe-FFs. The UV-visible absorption spectra of CdSSe-FFs show enhanced absorption at 700 nm, corresponding to the energy band gap (Eg) of 1.77 eV. The CdSSe-FFs exhibited field emission and photosensitive field emission (PSFE) characteristics. In FE study CdSSe-FFs shows an increase in current density of 387.2 μ A cm-2 in an applied field of 4.1 V m-1 which is 4.08 fold as compared to without light illumination (95.1 μ A cm-2). Furthermore, it shows excellent emission current stability at the preset value of 1.5 μA over 3 h with a deviation of the current density of less than 5% respectively. RESEARCH HIGHLIGHTS: Novel CdSSe flake flowers were grown on Au-coated Si substrate by a cost-effective chemical bath deposition route. The growth mechanism of CdSSe flake flowers is studied in detail. Field emission and Photoluminescence study of CdSSe flake flowers is characterized. CdSSe flake flowers with nanoflakes sharp edges exhibited enhanced field emission properties.

63‐3: An Enhanced Micro‐LED Pixel Circuit: Achieving Low Error Rates through Stable Current Generation with LTPO Technology

This paper proposed a micro‐LED pixel circuit utilizing low‐temperature polycrystalline oxide (LTPO) technology. Unlike conventional designs, our approach leverages coupling effects to nullify threshold voltages in both segments without signal line augmentation. A more stable emission current is achieved through altered emission methods, yielding an error rate below 4%.

Effect of Crystallinity on the Field Emission Characteristics of Carbon Nanotube Grown on W-Co Bimetallic Catalyst.

Carbon nanotube (CNT) is an excellent field emission material. However, uniformity and stability are the key issues hampering its device application. In this work, a bimetallic W-Co alloy was adopted as the catalyst of CNT in chemical vapor deposition process. The high melting point and stable crystal structure of W-Co helps to increase the grown CNT diameter uniformity and homogeneous crystal structure. High-crystallinity CNTs were grown on the W-Co bimetallic catalyst. Its field emission characteristics demonstrated a low turn-on field, high current density, stable current stability, and uniform emission distribution. The Fowler-Nordheim (FN) and Seppen-Katamuki (SK) analyses revealed that the CNT grown on the W-Co catalyst has a relatively low work function and high field enhancement factor. The high crystallinity and homogeneous crystal structure of CNT also reduce the body resistance and increase the emission current stability and maximum current. The result provides a way to synthesis a high-quality CNT field emitter, which will accelerate the development of cold cathode vacuum electronic device application.

Systematic synthesis of Bi2S3 nanoplates by template free solid-state approach and its field emission behaviour

We have demonstrated herewith controlled synthesis of Bi2S3 nanoplates by simple, template free, one step solid-state reaction at moderate temperature. The process parameters viz. precursor ratio, reaction temperature and duration were optimized. Nanostructured Bi2S3 synthesized at optimum conditions was further characterized by XRD, FESEM and FETEM, to study their phase, morphology and structure. The microscopic and XRD study reveals the formation of nanoplates like structures of orthorhombic Bi2S3. An attempt has been made to provide with a plausible growth mechanism as a function of reaction temperature and duration. In order to exploit the high 'aspect ratio' of the Bi2S3 nanoplates and explore its feasibility as potential electron source, field emission (FE) study has been performed at base pressure of ∼1 × 10−8 mbar. The results obtained herein reveal the morphology dependent FE behaviour of Bi2S3 nanoplates. The emitter comprised of Bi2S3 nanoplates synthesized at 180 °C showed better FE properties, lower turn-on field value, delivery of large emission current density (∼1670 µA/cm2 at 6.9 V/µm) and excellent emission current stability which are comparable to alike emitters due to semiconducting nanostructures. Highly crystalline nature and high aspect ratio of Bi2S3 nanoplates might be responsible for their good FE performance. These Bi2S3 nanostructures may have potential for applications in other optoelectronics devices.

Tubular Diamond as an Efficient Electron Field Emitter

Herein, we present a straightforward and cost-effective procedure for producing conductive diamond tubes on the surface of porous carbon nanotube hollow fibers using successive 10-pulsed laser annealing shots and 6 h of hot filament chemical vapor deposition techniques. Room-temperature Raman and X-ray diffraction spectra reveal the signature T2g peaks near 1332.4 cm–1 and 111 planes of diamonds near 43.9°, respectively. A low turn-on field (ETO) ∼1.85 V/μm@1 μA/cm2 and a threshold field (ETH) ∼2.54 V/μm@10 μA/cm2 were observed for the tubular diamond structures. The field enhancement factor (β) was calculated at 3594 and highly stable field emission current stability was observed over a long period of 4 h. For the first time, a good insight into the field emission results of the diamond is established with the structural, electronic properties, and the work function (φ) ∼4.84 eV analysis conducted by the density functional theory simulation. Finite electronic states at the Fermi level are observed beyond a band gap, and it demonstrates the wide-band gap (4.4 eV) semiconducting nature of the diamond. The Bader charge analysis and maximum entropy method pattern revealed the negative electron affinity of the diamond, and it is responsible for the emission of electrons from the conduction band of the diamond. Besides, the accumulation of charge carriers, which contributes to the electric field emission, takes place due to the weak π bonds of carbon atoms. The low turn-on field, the high field enhancement factor, and the good field emission current stability of tubular diamond offer great prospects for future efficient and low-cost field emission devices.

Improvement of the field emission lifetime of freestanding vertically aligned carbon nanotubes by coating with a metallic protective layer

In this article, we present a method to improve the field emission (FE) lifetime of freestanding vertically aligned carbon nanotubes (VACNTs) by uniformly coating the surface of VACNTs with a thin metallic layer that has low work function, high melting point and high electrical conductivity. The effects of three different metal shells on the FE performance are investigated. The FE performances of these VACNTs are evaluated by testing the turn-on electric field and long-term FE performance. The metal coatings do not have pronounced effects on turn-on electric field of VACNTs, but their FE lifetimes were improved to varying degrees. A 5 nm tungsten and gold coatings have the most significant improvement on the FE lifetime and current density stability. They have shown negligible degradation during continuous 48-h FE testing at a current density over 7 mSSA·cm −2. In addition, a 10 nm titanium, gold, and tungsten coatings also provide significant improvements in lifetime and emission current stability. Furthermore, it was observed that the metal shells are uniformly distributed on the surface of VACNTs, and they can effectively protect the VACNT from being melted by the Joule heat generated during FE. Therefore, metal-coated VACNTs have the potential to increase the lifetime of VACNT emitters during high current FE applications.

Vacuum discharge analysis of CNT field cathode using a computerized field projector

The mechanism of vacuum discharge of a multitip field cathode based on carbon nanotubes has been studied. The analysis was carried out using a multichannel field emission information collection system, a computerized field projector, and a program for recording and cyclic playback of the experimental results. The discharge under study occurred in the regime of a relatively stable emission current without an increase in the external voltage level. The time dependences of the local currents of all individual emission sites registered on the cathode surface were obtained. It is shown that the discharge consists of several successive phases, the key of which are an explosion in the region of one of the most active carbon nanotubes and a plasma torch above it. The effect of the discharge on neighboring nanotubes, which is associated with both the destruction of emission sites and their appearance, is also described.

Thickness dependent field emission study of LaB6 coated Si nanowire arrays

A simple physical metal mask is efficiently employed to obtain an array of silicon (Si) nanowires (Si-NWs) on a Si substrate grown using the hot filament chemical vapor deposition route. Well adhered and uniform coating of different thicknesses (20 and 50 nm) of lanthanum hexaboride (LaB6) on Si-NWs was obtained using electron beam evaporation technique. The thickness of LaB6 coating was estimated from ellipsometry measurement. Structural, morphological, and chemical properties of the LaB6 coated Si-NWs (LaB6@Si-NWs) arrays were revealed using x-ray diffraction, field emission scanning electron microscope, transmission electron microscope, Raman spectroscopy, and x-ray photoelectron spectroscopy. Field electron emission characteristics of pristine Si-NW array and LaB6 coated Si-NWs array emitters were studied in planar diode configuration at a base pressure of 1 × 10−8 mbar. The values of turn-on field (current density ∼1 μA/cm2) were observed as ∼2.2, 1.2, and 1.6 V/μm for pristine Si-NWs, LaB6@Si-NWs_20, and LaB6@Si-NWs_50 array emitters, respectively. Furthermore, maximum emission current densities of ∼1276.81, 2763.64, and 2231.81 μA/cm2 have been extracted from the pristine Si-NWs, LaB6@Si-NWS_20, and LaB6@Si-NWS_50 array emitters at an applied field of 3.1, 2.7, and 2.7 V/μm, respectively. The LaB6@Si-NWS_20 array emitter demonstrated superior FEE properties as compared to the pristine Si-NWs and LaB6@Si-NWS_50 emitters. Furthermore, LaB6@Si-NWS_20 emitter depicted very good emission current stability tested at a preset value of 1 μA over a duration of 3 h. The enhanced FEE performance exhibited by the LaB6@Si-NWs_20 array emitter is attributed to reduction in effective work function and enhanced electron tunneling probability across the LaB6–Si interface.

Field emission characterization of nanoFEAs on single crystal CeB6 surface fabricated by focused ion beam milling

The field emission tip arrays with sub-100 nm apices (nanoFEAs) on single crystal cerium hexaboride (CeB6) surface were fabricated by the focused ion beam (FIB) milling microtechnology. The surface morphologies and field emissions of the nanoFEAs are systematically characterized. FIB milling, similar to the physical stripping process, can fabricate the nanoFEAs single crystal CeB6 with uniform morphologies. The nanoFEAs with sharp tips of size about 50 nm demonstrate the lowest turn-on electric fields (2.0 V/[Formula: see text]m), as well as a high current ([Formula: see text]1 mA) at the field of 6.7 V/[Formula: see text]m and a high stable emission current. Such excellent performances make CeB6 nanoFEAs promising candidates for application in field emission electronics.

Field Electron Emission Characteristics of Tungsten–Polyethylene Composite Material As a Source of Electron Emission

Abstract: This work provides an experimental study on the effects of polyethylene coating on the field electron emission characteristics of clean (uncoated) tungsten tips. Several tungsten tips, with different apex radii, have been prepared, coated with different thicknesses of polyethylene layers and then examined using a standard field electron emission microscope. Various field electron emission characteristics have been measured under high-vacuum conditions. These include current-voltage characteristics, Fowler-Nordheim plots, scanning electron micrographs and spatial current distributions (electron-emission images). Based on this work, it is proved that coating tungsten tips with polyethylene layers has caused dramatic improvements on the tip emission properties. In particular, coating the tips improves the current-voltage characteristics, which is reflected in lowering the extraction voltage, getting more stable emission currents, expressing the current-voltage characteristics using Fowler-Nordheim plots and finally, the spatial distributions of the emitted electrons for the coated tips are more stable and uniform. Keywords: Field electron emitter, Polyethylene dielectric layer, Composite emitter, Field electron microscope, Scanning electron microscope.

DIGITAL APPROACH TO THERMIONIC EMISSION CURRENT TO VOLTAGE CONVERSION FOR HIGH-VOLTAGE SOURCES OF ELECTRONS

The thermionic emission current is used in many vacuum devices such as evaporators, rare gas excimers, or electron beam objects for high-energy physics. The stability of the thermionic emission current is a very important requirement for the accuracy of those devices. Hence, there is a number of control systems that use a feedback signal directly proportional to the emission current in order to stabilize the thermionic emission current. Most of them use feedback from a high-voltage anode circuit to a low-voltage cathode circuit. However, there is a novel solution that uses linear cathode current distribution and processing of two cathode circuit voltage signals for converting the emission current to voltage. However, it is based on old-fashioned analog technology. This paper shows the thermionic emission current to voltage conversion method with the use of a digital control system. A digital realization of a multiplicative-additive algorithm is presented and proper work in closed-loop mode is confirmed.

Research and implementation of the adaptive control method for emission current of electron ionization ion source

The electron ionization (EI) ion source has been widely used in the development of the mass spectrometer, and the stability of emission current of EI ion source directly affects important performance such as the sensitivity of the mass spectrometer. Realizing the stable control of emission current is the key to ensuring the accurate measurement of the mass spectrometer. However, the stability of the emission current is easily affected by factors such as filament resistance and pressure of the mass spectrometer chamber. For adaptive control of emission current, two adaptive control methods based on negative feedback operational amplifier and fuzzy logic system (FLS) are proposed and applied to the self-developed quadrupole mass spectrometer (QMS). Further, three emission current control experiments when the QMS is powered on, works stably, and the pressure changes are designed to verify the effectiveness of the adaptive control method proposed. Experimental results show that the two adaptive control methods in this paper are compared to the open-loop control method of stabilizing the output of the heating power supply have faster control response rate, longer stable control time, and better adaptive control ability.

Local Characterization of Field Emission Properties of Graphene Flowers

AbstractAn experimental study about field emission properties of commercially available graphene flowers cloth is reported. Material characterization by means of X‐ray diffraction, Raman spectroscopy, and X‐ray photoemission spectroscopy confirms the formation of high quality vertical few‐layers graphene nanosheets. A tip‐anode setup is exploited in which nanomanipulated tungsten tip is used as the anode at controlled distance from the emitter in order to reduce the effective emitting area below 1 µm2, giving access to local characterization. A turn‐on field as low as 0.07 V nm−1 and field enhancement factor up to 32 for very small cathode–anode separation distances is demonstrated, in the range 400–700 nm. It is also shown that the turn‐on field increases for increasing distances, while the field enhancement factor decreases. Finally, time stability of the field emission current is reported, evidencing a reduction of the fluctuations for lower current levels.

Development of CoFe2O4 scaffolded reduced graphene oxide/carbon nanotube emitter for field emission application

The field emission (FE) characteristics of CoFe2O4/rGO/CNT (CGC) emitter is reported by comparing it with that of CoFe2O4/rGO (CG), CoFe2O4/CNT (CC), rGO/CNT (GC) and individual emitter. Among them, current density was high for CGC emitter i.e. 3.329 mA cm−2 for applied field of 5.4 V μm−1 as well as a good emission current stability. These superior FE characteristics of CGC emitter is due to the decreased bandgap as well as work function and, due to the sharp edges provided by CNTs and CoFe2O4 nanoparticles which results in easy electron liberation. A detailed mechanism for enhanced FE performance has been proposed based on obtained results.

Improving the Response Speed of an Active-Current Controlled Field Emitter Arrays by Modifying the Controlled Current

Using an active-current control (ACC) component such as MOSFET in field emitter arrays (FEAs) is an important way to achieve stable emission current. However, the controlled current of ACC may reduce the response speed of FEAs due to the longer charging process, which limits its application. In this work, a general model for the field emission of MOSFET-controlled FEAs has been established to study the influence of controlled saturation current on its response speed. It is found that the response speed which decreases nearly linearly as the saturation current decreases can be reduced down by above 1 order of magnitude comparing to the intrinsic value. The field emission characteristics of a MOSFET-controlled ZnO nanowire FEAs under different saturation current and duty ratio have been investigated, in which the result is in consistency with the model. A solution using a controlled current which is larger than the induced current during the charging process and can rapidly reduce down to the field emission current has been proposed for balancing the stability and response speed in MOSFET-controlled FEAs. All the results provide a method for obtaining fast response ACC-FEAs, which should be useful in the application that requires pulsed driving FEAs.

Emission Properties and Dielectric Strength of a Nanostructured Tungsten Field-Emissive Cathode

Research of the tungsten “fuzz” emission properties and dielectric strength was carried out. A “fuzzy” sample was made through He+ ion exposure of an initially polished tungsten surface using an inductively coupled plasma (ICP) facility. The eventual He+ ion fluence was <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 1.7\times 10^{25}\,\,\text{m}^{-2}$ </tex-math></inline-formula> . The induced nanostructured layer thickness was estimated to be <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 1~\mu \text{m}$ </tex-math></inline-formula> . The measurements were performed with an automated experimental setup developed. The setup was operated under the control of the programmable DAC/ADC module “LCard E20-10.” As a result, the untypical behavior of a nanostructured cathode in comparison with an ordinary field emissive cathode was registered. Instability of the W “fuzz” emission properties was demonstrated. Typical values of the electric field enhancement factor were found to be in the range of ~120–200 both before a single breakdown and after it. These values are in agreement with the estimations of the enhancement factor performed with taking into account the geometry of protrude cathode structures. Stabilization of the emission properties after the breakdown was observed. The conditioning effect of the nanostructured cathode was found to take place after approximately five breakdowns. After conditioning, an asymptotic value of a breakdown electric field strength was <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 8.5\times 10^{7}$ </tex-math></inline-formula> V/m, which is in agreement with the one for an ordinary tungsten cathode. The conditioning effect and the emission current stabilization are believed to be due to the destruction of the nanostructure under the impact of the breakdowns.

Enhanced field emission behaviour from ethylene glycol mediated synthesis of 2D hexagonal SnS2 disc with nanoparticle decoration

Herein, octahedron and stacked 2D hexagonal disc - like nanostructures of SnS2 were obtained by hydrothermal and ethylene glycol mediated hydrothermal methods, respectively. Attempt has been made to shade light on the plausible growth mechanism. Liquid phase exfoliation followed by centrifugation process leads to presence of tiny single crystalline SnS2 nanoparticles (∼5 nm) on the hexagonal discs over C substrate, characterized by preferred growth along {001} direction. The observed Raman shift and enhanced intensities of A1g and Eg modes infer charge interactions between the SnS2 disc and C substrate. Interestingly, the SnS2-C emitter exhibited superior field emission (FE) behaviour due to the unique morphology, excellent charge transfer, and reduced work function (∼4.1 eV). Here the extraction of large current density of ∼1137 μA/cm2 at an applied field of 3.72 V/μm, with good emission current stability. The present strategy is beneficial to design architectured morphology for multi-functionality.

Registration of the time dependence of the number of emission sites as a tool for analyzing field cathodes current fluctuations

A new tool for obtaining the frequency characteristics of the interaction of emission sites with adsorbates was developed. The technique is based on the use of a computerized field projector with online processing of patterns of the distribution of emission sites over the cathode surface. The resulting dependences reflect the frequency of fluctuations in the activity of individual sites. The influence of the choice of the threshold brightness parameter, the proximity of the sites to each other and the stability of the total emission current on the shape of these curves is considered. The coincidence of the shapes of curves constructed by various methods (in online mode, in post-processing mode and in the mode of random processes modeling) is analyzed. Keywords: field emission, emission current fluctuations, carbon nanotubes, registration of emission sites, adsorption processes on the surface.

CsPbBr3 microarrays with tunable periodicity, optoelectronic and field emission properties using self-assembled polystyrene template and co-evaporation method.

The booming growth of all inorganic cesium lead halide perovskites in optoelectronic applications has prompted extensive research interest in the fabrication of ordered nanostructures or microarrays for enhanced device performances. However, the high cost and complexity of commercial lithographic approaches impede the facile fabrication of perovskite microarrays. Herein, CsPbBr3 microarrays with tunable periodicities have been fabricated using a self-assembled polystyrene nanosphere template and a co-evaporation method. The periodicity of CsPbBr3 microarrays is precisely manipulated by simply modifying the size of polystyrene nanospheres. These microarrays are beneficial for light harvesting, leading to better light absorption ability and prolonged photoinduced carrier lifetime. The longest average carrier lifetime of 58.3 ns is obtained for CsPbBr3 microarrays with a periodicity of 1.0 μm. More importantly, the periodic structures of CsPbBr3 microarrays result in a tunable density of emitter tips in field emission devices. Compared to compact CsPbBr3 films, a 68.2% decrease of the turn-on field is observed for CsPbBr3 microarrays when the periodicity is 150 nm. The higher density of emitter tips leads to larger local field enhancement, and hence the largest field enhancement factor of 3346.6. Finally, a good emission current stability for CsPbBr3 microarray-based field emission devices has been demonstrated.