Showing papers on "Field electron emission published in 2021"

Significantly enhanced NO2 gas-sensing performance of nanojunction-networked SnO2 nanowires by pulsed UV-radiation

Abstract: A unique combination of high response and fast response-recovery is still a challenge in the development of room-temperature gas sensors. Herein, we demonstrated the on-chip growth of nanojunction-networked SnO2 NW sensors to work under UV-radiation at room temperature. The morphological, compositional, and structural properties of synthesized SnO2 nanowires were examined using field emission electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and high-resolution transmission electron microscopy, respectively. The results presented the SnO2 NWs with smooth surfaces were entangled between the Pt electrode. Besides, the internal properties showed the SnO2 NWs were crystallized as the tetragonal rutile structure of SnO2. The use of UV-radiation with the optimum intensity of 50 μW/cm2 increased the gas response to 5 ppm NO2 up to 7-fold, while response and recovery times decreased about 8- and 4-fold, respectively. Moreover, alternative use of pulsed UV-radiation (provided only during the air recovery phase) can enhance significant gas response as compared with continuous UV-radiation. The enhancement of gas response could be attributed to the photo-adsorption and -desorption of NO2 molecule due to the photogeneration of electron-hole pairs. The combination of NW-NW nanojunctions and pulsed UV-radiation is expected to be a novel strategy for high-performance room temperature gas sensors.

Field emission applications of graphene-analogous two-dimensional materials: recent developments and future perspectives

Abstract: 2D layered materials are widely recognized as the revolutionary class of materials, and hold great promise in the modern device technology industries. The 2D materials family covers almost the entire spectrum of condensed mater physics and devices associated with metal, semi-metal, superconductor, Mott insulator, Bose–Einstein condensates properties. Due to their tunable and suitable electronic, thermal and mechanical properties, different inorganic 2D materials have emerged as possible cathode materials for high performance field emission (FE)-based vacuum micro/nanoelectronic devices. The 2D materials possess more active sites, and strident edges in atomic dimension, vacancies, and defects, which are favourable for high current density cathodes associated with reduced turn-on voltages. Hence, expulsion of electrons from the 2D materials are expected to be noticeably higher due to the reductions in the dimensionality, quantum restraint effect of electrons in 2D fissionable layers, and the occurrence of random and sharp protruding active edges. Furthermore, the enhanced FE characteristics of inorganic 2D materials are achieved by several methodologies, such as phase engineering, defect and vacancy engineering, heterostructure/hybrid materials design, gating, alloying, and photoexcitation. Owing to their exotic mechanical properties, high stretching ability and flexibility nature, the 2D materials-based field emitters have emerged as potential candidates for flexible displays and miniaturized X-ray tubes. For this current review, we proffer an exclusive overview of various emerging 2D materials that are being recognized for efficient and high-performance FE-based applications. Furthermore, the fundamentals of the field emission working principles, recent developments, future perspectives and alternative tunable schemes for enrichment of the field emission functions are herein elaborated comprehensively.

Hole-dominated Fowler–Nordheim tunneling in 2D heterojunctions for infrared imaging

Abstract: Heterostructures based on diverse two-dimensional (2D) materials are effective for tailoring and further promoting device performance and exhibit considerable potential in photodetection. However, the problem of high-density thermionic carriers can be hardly overcome in most reported heterostructure devices based on type I and type II band alignment, which leads to an unacceptably small Iphoto/Idark and strong temperature dependence that limit the performance of photodetectors. Here, using the MoTe2/h-BN/MoTe2/h-BN heterostructure, we report the hole-dominated Fowler–Nordheim quantum tunneling transport in both on and off states. The state-of-the-art device operating at room temperature shows high detectivity of >108 Jones at a laser power density of

The Rise of Carbon Materials for Field Emission

Abstract: Carbon-based materials exhibit distinct structures and dimensionality which allow modification of their electrical properties and enable them to be integrated in various commercial systems One of the interesting characteristics of carbon-based materials is efficient electron field emission (FE), which makes them good candidates for displays, in electron microscopy, lithography, sensing, micro- and nanoelectronics, X-ray sources and medical applications While nano carbon materials have been extensively studied for FE applications, their usefulness, electron emission concerns, and fundamental mechanisms for FE technologies are buried in the reported literature, and cross comparison of all nano carbon materials together is rarely explored Here we present a comprehensive overview of fundamental and FE properties of all carbon-based materials including diamond, nanocrystalline diamond, graphite, carbon nanotubes, carbon nanofibers, carbon nanowires, carbon nanorods, graphene, and amorphous and nanostructured carbon Some of these carbon materials, such as amorphous and nanostructured carbon, possess the added benefit of room temperature production over large areas on a variety of substrates We have compiled an up to date summary which critically discusses the material factors, and the factors that control electron emission of these materials We also propose unique ideas to further improve electron emission for the design of energy efficient carbon-based cold cathode materials for next generation large area electronic devices

Cyan Broad-Band Emission Phosphor with Scandium Silicon Multiple-Ring Structure for White Light-Emitting Diodes and Field Emission Displays.

Abstract: Silicate phosphor KBaScSi2O7:Ce3+ (KBSS:Ce3+), as a novel material, has been prepared by the solid-state method in this study. The crystal structure, luminescent properties, thermal stability, and cathodoluminescence (CL) properties of this material were analyzed systematically. It concludes that the phosphor can emit cyan light with emission peak at 509 nm under n-UV light excitation (300-400 nm). By coating KBSS:Ce3+ with a red-emitting CaAlSiN3:Eu2+ on a n-UV (365 nm) light-emitting diode (LED) chip, the intense warm white light with high RA (83.4) and low CCT (3652) can be produced under a 350 mA forward bias current.In addition, the CL performance shows that KBSS:0.10Ce3+ has high saturation current and voltage and good color stability under low voltage conditions. All these results indicate that KBSS:Ce3+ phosphor will be very promising in LED and field emission display applications.

Enhanced field emission performance of MXene–TiO2 composite films

Abstract: A facile method to produce an MXene–TiO2 composite is demonstrated for enhanced field emission display applications. The field emission performance of two-dimensional free-standing and linear-shaped field emitters has been systematically investigated and enhanced electron emission behaviors (e.g. emission current, stability and emission patterns) are achieved by compositing MXene and TiO2 nanowires. The relationship between the emission current density, electric field and anode-cathode gap distance is studied and the emitters, especially the cross-section of the composite film, show good performance. The emission current from the cross-section of the composite film can reach 289 mA cm−2, which is the best result of the state of the art compared to single MXene and TiO2 nanowires. We have also reported a triboelectric nanogenerator powered by free-standing MXene–TiO2 composite emitters, implying the feasibility of the self-powering field emission devices and possibly enlarging the applications of cold emitters in various fields.

Linkage of electron emission and breakdown mechanism theories from quantum scales to Paschen's law

Abstract: Numerous applications such as micro- and nanoelectromechanical systems, microplasmas, and directed energy increasingly drive device miniaturization to nanoscale and from vacuum to atmospheric pressure. This wide range of operating conditions and relevant mechanisms complicates the derivation of a single scaling law for electron emission and gas breakdown; therefore, theoretical studies often unify two or three mechanisms piecemeal. This study defines a common set of scaling parameters across the range of dominant mechanisms to derive a theory that links electron emission and breakdown mechanism theories from quantum scales to Paschen's law and yields asymptotic solutions for quantum space-charge limited emission (QSCL), classical space-charge limited emission (CSCL), space-charge limited emission with collisions (MG), Fowler–Nordheim field emission (FN), field emission driven gas breakdown, and classical gas breakdown defined by Paschen's law (PL). These non-dimensionalized equations are universal (true for any gas) across all regimes except for PL, which contains a single, material-dependent parameter. This approach reproduces various nexuses corresponding to the transitions across multiple mechanisms, such as QSCL to CSCL, CSCL to FN, CSCL to MG to FN, and field emission-driven breakdown as described by FN to PL, using a single non-dimensionalization scheme to facilitate experimental designs concerned with crossing these regimes. Furthermore, we demonstrate the conditions for more complicated nexuses, such as matching QSCL, CSCL, MG, and FN. This provides valuable information to experimentalists concerning regimes where slight perturbations in conditions may alter the electron emission mechanism and to theorists concerning the applicability of the asymptotic solutions or reduced nexus theories.

High Current Field Emission from Large-Area Indium Doped ZnO Nanowire Field Emitter Arrays for Flat-Panel X-ray Source Application

Abstract: Large-area zinc oxide (ZnO) nanowire arrays have important applications in flat-panel X-ray sources and detectors. Doping is an effective way to enhance the emission current by changing the nanowire conductivity and the lattice structure. In this paper, large-area indium-doped ZnO nanowire arrays were prepared on indium-tin-oxide-coated glass substrates by the thermal oxidation method. Doping with indium concentrations up to 1 at% was achieved by directly oxidizing the In-Zn alloy thin film. The growth process was subsequently explained using a self-catalytic vapor-liquid-solid growth mechanism. The field emission measurements show that a high emission current of ~20 mA could be obtained from large-area In-doped sample with a 4.8 × 4.8 cm2 area. This high emission current was attributed to the high crystallinity and conductivity change induced by the indium dopants. Furthermore, the application of these In-doped ZnO nanowire arrays in a flat-panel X-ray source was realized and distinct X-ray imaging was demonstrated.

Generation of runaway electrons in plasma after a breakdown of a gap with a sharply non-uniform electric field strength distribution

Abstract: The paper is devoted to the study of the initiation and formation of a negative streamer in a sharply inhomogeneous electric field and the generation of runaway electrons (REs) in air and helium at atmospheric pressure and below, as well as in sulfur hexafluoride at low pressure. Nanosecond voltage pulses of negative polarity with an amplitude of 18 kV were applied across a point-to-plane gap 8.5 mm long. The studies were carried out using broadband measuring sensors and equipment with picosecond time resolution, as well as using a four-channel ICCD camera. Using a special method for measuring the dynamic displacement current caused by the redistribution of the electric field during streamer formation, the waveforms of voltage, discharge current, RE current, and dynamic displacement current were synchronized to each other, as well as to ICCD images. Data on the generation of REs with respect to the dynamics of streamer formation were obtained. It was found that REs are generated not only during the breakdown of the gap, but also after that. It has been found that the formation time of explosive emission centers affects the generation of REs after breakdown. Based on the measurement data of the voltage, discharge current, and dynamic displacement current, the electron concentration in the plasma channel after breakdown and the electric field strength near the surface of the grounded electrode were calculated.

Thermodynamic parameters, microstructure, and electrochemical properties of equiatomic TiMoVWCr and TiMoVNbZr high-entropy alloys prepared by vacuum arc remelting

Abstract: This study investigated the thermodynamic parameters, microstructures and electrochemical properties of TiMoVWCr and TiMoVNbZr bio-refractory high-entropy alloys (bio-RHEAs) prepared using the vacuum arc remelting process. The alloys were characterized using field emission scanning electron microscopy, field emission electron probe microanalyzer, X-ray diffraction analysis, and potentiodynamic polarization tests. The determined thermodynamic values of Ω-parameter, atomic size difference and valence electron concentration for the TiMoVWCr and TiMoVNbZr bio-RHEAs were within the range of solid solution formation. A high-temperature stable single BCC1 phase was obtained using the thermodynamic equilibrium calculations for the TiMoVWCr and TiMoVNbZr systems. The TiMoVWCr alloy microstructure comprised a dendrite, an inter-dendrite, and a second phase, while TiMoVNbZr alloy comprised a dendrite and an inter-dendrite. The TiMoVWCr alloy forming the stable single body-centered cubic solid solution demonstrated homogeneous microstructure and high phase stability. Moreover, pitting resistances of TiMoVWCr and TiMoVNbZr bio-RHEAs were remarkably superior to that of ASTM F75 alloy.

Field Effect-Controlled Space-Charge Limited Emission Triode With Nanogap Channels

Abstract: Nanoscale vacuum (airgap) channels have garnered attention as conduits for ballistic electron transport even under ambient atmospheric conditions. To date only single nanogap devices that cannot be integrated have been developed. This report presents a nanoscale space charge limited field emission (SCL-FE) triode based on a combination of one lateral and two vertical nanoscale airgaps in a Metal-oxide-semiconductor (MOS). Two identical MOS-shared p-Si substrates are separated by a $\sim 50$ -nm-wide etched trench to create a combined lateral bidirectional SCL-FE metal–air device and dual vertical nanoscale vacuum diodes. The lateral device provides bidirectional SCL-FE electron current, and the vertical devices provide rectifying behavior for carrier transport. The ballistic trajectories of electrons within the nanoscale airgap can be controlled by driving the two MOSs in different operational regimes. The triode operates at a low voltage of $\sim 2$ V and has an emission-capture efficiency of up to $\sim 95$ %, with a total emission current density of $\sim 2\times 10^{3}$ A/cm2.

Field emission from two-dimensional GeAs

Abstract: GeAs is a layered material of the IV-V groups that is attracting growing attention for possible applications in electronic and optoelectronic devices. In this study, exfoliated multilayer GeAs nanoflakes are structurally characterized and used as the channel of back-gate field-effect transistors. It is shown that their gate-modulated p-type conduction is decreased by exposure to light or electron beam. Moreover, the observation of a field emission current demonstrates the suitability of GeAs nanoflakes as cold cathodes for electron emission and opens up new perspective applications of two-dimensional GeAs in vacuum electronics. Field emission occurs with a turn-on field of ~80 V/{\mu}m and attains a current density higher than 10 A/cm^2, following the general Fowler-Nordheim model with high reproducibility.

Enhancement of field emission performance of graphene nanowalls: the role of compound-cathode architecture and anode proximity effect

Abstract: The Schottky Conjecture (SC) suggests the use of a multiscale cathode to increase the local electric field at a field-emitting tip. A similar increase in local field also occurs when the anode is in close proximity to the cathode. The authors take advantage of these twin effects to design a compound cathode consisting of a macroscopic base with a much smaller wire-protrusion having an end-cap. Field emission experiments were performed using two different compound-cathode setups, each consisting of an adjustable-height Kovar wire with graphene nanowalls deposition as the end-cap, and a macroscopic base on which the Kovar wire is mounted. The field emission data was recorded for both compound-cathodes at different anode positions. Experimental results indicate remarkable improvement in field emission current density while adopting an optimized diode architecture. Stable emission was observed and a maximum current density of 46 mA/cm 2 was extracted from the sample. An analysis of the experimental data, aided by additional numerical simulations, clearly shows the combined effect of the recently proposed Corrected Schottky Conjecture and the anode proximity effect. It is thus possible to realize an efficient field emitter device by tweaking the geometry of the diode structure.

The temperature induced current transport characteristics in the orthoferrite YbFeO 3-δ thin film/p-type Si structure

Abstract: The perovskite ytterbium ferrite is a new ferroelectric semiconductor material. We presented the temperature induced current-voltage (I-V) characteristics of the Al/YbFeO3-δ/p-Si/Al hetero-junction. The orthoferrite YbFeO3-δ thin films were deposited on a single crystal p-type Si substrate by a radio frequency magnetron sputtering system. The potential barrier height (BH) [Formula: see text] and ideality factor n of the heterojunction were obtained by thermionic emission current method based on the recommendations in the literature. The fact that the calculated slopes of I-V curves become temperature independent implying that the field emission current mechanism takes place across the device, which has been explained by the presence of the spatial inhomogeneity of BHs or potential fluctuations. Moreover, a tunneling transmission coefficient value of 26.67 was obtained for the ferroelectric YbFeO3-δ layer at the Al/p-Si interface.

Enhancement of Pseudocapacitive Behavior, Cyclic Performance, and Field Emission Characteristics of Reduced Graphene Oxide Reinforced NiGa2O4 Nanostructured Electrode: A First Principles Calculation to Correlate with Experimental Observation

Abstract: The rational construction and design of supercapacitors (SCs) with electrochemically favorable structural configuration and appreciable cyclic performances are highly demanding. Herein, a novel Ga-...

Quantitative Backscattered Electron Imaging of Bone Using a Thermionic or a Field Emission Electron Source

Abstract: Quantitative backscattered electron imaging is an established method to map mineral content distributions in bone and to determine the bone mineralization density distribution (BMDD). The method we applied was initially validated for a scanning electron microscope (SEM) equipped with a tungsten hairpin cathode (thermionic electron emission) under strongly defined settings of SEM parameters. For several reasons, it would be interesting to migrate the technique to a SEM with a field emission electron source (FE-SEM), which, however, would require to work with different SEM parameter settings as have been validated for DSM 962. The FE-SEM has a much better spatial resolution based on an electron source size in the order of several 100 nanometers, corresponding to an about $$10^5$$ to $$10^6$$ times smaller source area compared to thermionic sources. In the present work, we compare BMDD between these two types of instruments in order to further validate the methodology. We show that a transition to higher pixel resolution (1.76, 0.88, and 0.57 μm) results in shifts of the BMDD peak and BMDD width to higher values. Further the inter-device reproducibility of the mean calcium content shows a difference of up to 1 wt% Ca, while the technical variance of each device can be reduced to $$\pm 0.17$$ wt% Ca. Bearing in mind that shifts in calcium levels due to diseases, e.g., high turnover osteoporosis, are often in the range of 1 wt% Ca, both the bone samples of the patients as well as the control samples have to be measured on the same SEM device. Therefore, we also constructed new reference BMDD curves for adults to be used for FE-SEM data comparison.

Field emission mitigation studies in the SLAC Linac Coherent Light Source II superconducting rf cavities via in situ plasma processing

Abstract: Field emission is one of the main factors that can limit the performance of superconducting radio frequency cavities. To reduce possible field emission in the Linac Coherent Light Source II (LCLS-II), we are developing plasma processing for 1.3 GHz nine-cell cavities. The ultimate goal of plasma processing will be to apply the technique in situ in the cryomodules in order to mitigate hydrocarbon-related field emission without disassembling them. Herein is presented the first systematic study of plasma processing applied to LCLS-II superconducting radio frequency cavities. Having developed a new method of plasma ignition for LCLS-II cavities, we applied plasma processing to 1.3 GHz cavities starting with a clean nitrogen doped cavity and proceeding with studying natural field emission and artificially contaminated cavities. All the cavities were cold tested before and after plasma cleaning in order to compare their performances. It was proved that this technique successfully removes carbon-based contamination from the cavity iris and that it is able to eliminate field emission in a naturally field emitting cavity. The effect of plasma processing on cavities exposed to vacuum failures was also investigated, showing positive results in some cases. This work shows how successful plasma processing is in removing hydrocarbon related contamination from the cavity surface without affecting the high Q-factors and quench fields characteristic of nitrogen doped cavities.

Characteristics of Field Emitters on the Basis of Pd-Adsorbed ZnO Nanostructures by Photochemical Method

Abstract: In this investigation, field electron emission (FE) performances of pure zinc oxide (ZnO) nanorod (NR) arrays and ZnO NRs with adsorbed palladium nanoparticles (Pd-ZnO) were explored under high-vac...

A nanoscale vacuum field emission gated diode with an umbrella cathode

Abstract: A nanoscale field emission vacuum channel gated diode structure is proposed and a tungsten cathode with an umbrella-like geometry and sharp vertical edge is fabricated. The edge of the suspended cathode becomes the field emission surface. Unlike in the traditional transistor with the gate typically located between the source and the drain, the bottom silicon plate becomes the gate here and the anode terminal is located between the umbrella cathode and the gate. The fabricated devices show excellent diode characteristics and the gated diode structure is attractive for extremely low gate leakage.

A stable LaB6 nanoneedle field-emission point electron source

Abstract: A material with a low work function exhibiting field-emission of electrons has long been sought as an ideal point electron source to generate a coherent electron beam with high brightness, long service life, low energy spread, and especially stable emission current. The quality and performance of the electron source are now becoming limiting factors for further improving the spatial resolution and analytical capabilities of the electron microscope. While tungsten (W) is still the only material of choice as a practically usable field emission filament since it was identified more than six decades ago, its electron optical performance remains unsatisfactory, especially the poor emission stability (>5% per hour), rapid current decay (20% in 10 hours), and relatively large energy spread (0.4 eV), even in an extremely high vacuum (10−9 Pa). Herein, we report a LaB6 nanoneedle structure having a sharpened tip apex with a radius of curvature of about 10 nm that is fabricated and finished using a focused ion beam (FIB) and show that it can produce a field emission electron beam meeting the application criteria with a high reduced brightness (1010 A m−2 sr−1 V−1), small energy spread (0.2 eV), and especially high emission stability (<1% fluctuation in 16 hours without decay). It can now be used practically as a next-generation field-emission point electron source.