Field Emission Devices Research Articles

Suspended Nanoscale Field Emitter Devices for High-Temperature Operation

In this work, we demonstrate suspended two- and four-terminal field emission devices for high-temperature operation. The planar structures were fabricated with tungsten on a 200-nm silicon nitride membrane. The insulator in the vicinity of the terminals was removed to minimize undesirable Frenkel–Poole emission and increase the resistance of leakage current pathways. The effects of temperatures up to 450 °C on Fowler–Nordheim emission characteristics and parasitic leakage resistance were studied. Turn-on voltages with magnitudes under 15 V that further decreased as a function of increasing temperature for the two-terminal device were reported. Gating at temperatures of 150 °C and 300 °C was shown for the four-terminal device, and corresponding transconductance and cutoff frequency values were computed.

Fabrication of Field Emission Device With Lateral-Cathode Triode for Lighting Applications

Field emission (FE) devices are advanced lighting devices that have a 2-D planar configuration, different from the 0-D (dot) and 1-D (line) configurations of light-emitting diode (LED) and fluorescent lighting, respectively. The purpose of this study is to develop a FE lighting device with a lateral-cathode triode. Carbon nanotubes (CNTs) are used as emitters and ZnS particles are used as a green phosphor. The materials were screen-printed onto two soda lime glass substrates. To increase the device lifetime and performance, we applied pulsewidth modulation (PWM) to the gate electrode. A high luminance of 12 690 cd/m2 and a good luminance uniformity of 84% were achieved for a lighting device with a lateral-cathode structure.

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

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/cm2 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.

Facile Fabrication and High Field Emission Performance of 2-D Ti₃C₂Tₓ MXene Nanosheets for Vacuum Electronic Devices

Although Ti3C2T x has been widely studied in applications such as electrical storage devices, there are very few reports about the field emission properties of Ti3C2T x . In this work, 2-D Ti3C2T x MXene was fabricated by simple etching Al layer from Ti3AlC2 in hydrofluoric acid (HF) at room temperature and employed as a cold cathode for field emission devices. The device presents a high field emission performance with a low turn-on field of 2.7 V/ $\mu \text{m}$ and excellent stability, much lower than the reported value of the former work (around 5 V/ $\mu \text{m}$ ), its relative 1-D TiC nanowires (7.1 V/ $\mu \text{m}$ ), and most of other 2-D cathode materials, such as MoS2 and graphene, which is found due to its unique accordion structure with evenly distributed sharp edges and enlarged layer spacing reducing the field screening effect. The results confirmed by numerical simulation demonstrate that the local electric intensity at sharp edges indeed significantly higher than that of elsewhere. In other words, more sharp edges owning to the increased interlayer spacing exposed, which can considerably boost field emission performance. Based on experimental data and simulation analysis, the edge effect was found to correspond well with other former reports. Hence, 2-D MXene can be a promising candidate for vacuum electronic applications other than energy storage and conversion devices.

Enhancement of Electron Emission Properties of Carbon Nanotubes by the Decoration with Low Work Function Metal Oxide Nanoparticles.

In the present report, the properties of the field emission devices of carbon nanotubes (CNTs) were remarkably improved by decorating their surface with magnesium oxide nanoparticles (MgO NPs). The MgO NPs were attached effectively on the surface of CNTs via thermal evaporation. The Raman spectra confirm the graphitic order of as-grown pristine CNTs with RBM (radial breathing mode), D band and G band peaks at the 282 cm-1, 1347 cm-1 and 1594 cm-1 respectively. The peak at 471 cm-1 indicates successful attachment of MgO NPs to the CNTs. The enhanced field emission properties of CNTs were mainly attributed to the MgO NPs which increased the field enhancement factor and the density of emission sites. The decreased work function and increased field enhancement factor were responsible for the improved FE properties of the CNTs. Our results indicate that the MgO decorated CNTs can be used as an effective field emitter for various electron emission devices. The turn-on field decrease from 1.6 V/μm to 1.3 V/μm and the maximum current density increases from 1.581 to 3.678 mA/cm2 after the decoration of CNTs with MgO NPs. The value of field enhancement factor (β) also increases from 2.814×10³ to 9.823×10³.

Iron oxide-coated MWCNTs nanohybrid field emitters: a potential cold cathode for next-generation electron sources

In this paper, we have reported that the field emission properties of multiwall carbon nanotubes (MWCNTs) were significantly increased by decorating their surface by iron oxide nanoparticles. MWCNTs were prepared on silicon substrate through low-pressure chemical vapour deposition using acetylene as source gas. The iron oxide nanoparticles were grown on the surface of MWCNTs by thermal evaporation technique. Modified surface morphologies of the prepared films were characterized through field emission scanning electron microscope (FESEM), Raman spectroscopy and X-ray diffraction. A significant change in current density, stability and turn-on voltage has been observed in iron oxide-coated MWCNT films. Decoration of iron oxide nanoparticles reduces turn-on voltage from 4 to 3.4 V/μm, while current density increases from 10.15 to 33.26 mA/cm2. For practical MWCNT-based field emission devices, it is necessary to improve the emission current density and stability. The excellent field emission parameters are obtained and calculated which make them useful for high-performance field emission-based devices. The mechanism of emission of electrons is well described by the Fowler Nordheim theory.

Molybdenum rods assembled with nanosheets: a high catalytic material for phenol sensing

The phenol (PhOH) is a toxic chemical and can affect to the environment and human directly and indirectly. Due to their toxic nature it is listed as a carcinogenic compound for human health. The sensitivity of the PhOH in liquid medium can be detemine through various techniques in liquid medium was detected through various techniques for instance HPLC, mass, fluorescence and spectrophotometry etc but all of these techniques are expensive and not easily available to detect the longer range of samples in a very less time. To keep this view the present manuscript was designed to shows the utilization of metal oxide nano and microstructures as sensor material, therefore, initially highly crystalline molybdenum oxide rods assembled with nanosheets (referred to as α-MoO3 RANs) was synthesized via solution process and utilized for sensing against PhOH. The α-MoO3RANs exhibit numerous applications in various directions such as catalyst, LEDs, Field emission devices, batteries etc. The α-MoO3RANs were formed from the solution processes in a short time span. The formed powder was well characterized through the techniques such as XRD, SEM, TEM and FTIR. From the analysis, it reveals that the size of each NS is ∼200 nm in diameter whereas rods shaped structures length goes to 2–6 μm with good structural and chemical characteristics. The crystalline α-MoO3RANs were applied for the electro chemical studies as three electrode system (GCE as working electrode, Ag/AgCl as reference and pt wire as counter electrode) with PhOH as an analyte in PBS. The electrochemical studies were conducted through cyclic voltammetry (CV) in terms of their low to high conc-entration ranges from 7.8 to 1000 μM in PBS, scan rate at different potential from 5 to 100 mV with the α-MoO3RANs based working electrode (α-MoO3RANs/GCE). The designed working electrode sensor having excellent reproducibility, sustained in presence of 62.25 μM (PhOH) for seven consecutive cycles. Including this, the chronoamperometry (0–1500s) and electrochemical impedance spectra (EIS) were also analyzed. A probable mechanism was also discussed based on the analysis and their observations.

Si Nanowire With Integrated Space-Charge- Limited Conducted Schottky Junction for Enhancing Field Electron Emission and Its Gated Devices

Integrated field emission electron sources with low driving voltage are desired for micro/nano vacuum electronics. Herein, we demonstrate the enhanced and stable electron emission from crystalline gold-silver (Au-Ag) alloy nanoparticle capped Si nanowires (SiNWs) and the achieved gated electron sources with low driving voltage (<; 50 V). Thermally induced self-assembly hemispherical (50-80 nm) crystalline Au-Ag nanoparticles were prepared and used as masks in plasma etching to form vertically aligned high aspect ratio (~14) SiNWs. The nanoparticles were preserved after the etching, forming in situ integrated Au-Ag/Si junctions with each individual SiNWs. The SiNWs with capped nanoparticles possess superior field emission current density (45.80 mA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) and current stability (fluctuation ~6%). A self-aligned process was developed to fabricate gated field emission devices, using the Au-Ag nanoparticle capped SiNWs as cathode. The gated devices showed field emission at low gate voltage (69.52-μA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 42.1 V). Experimental and numerical simulation studies demonstrated the Au-Ag/Si contact behaved as space-charge-limited (SCL) Schottky conduction. The idea behind the enhancing and stable emission is that the SCL-Schottky junction undergoes a process of negative feedback and thus suppressed the current and shot-noise from the outstanding SiNWs. Accordingly, more SiNWs were activated and contributed stable and higher field emission current.

Development of a high-brightness field-emission lighting device with ITO electrode

Field-emission (FE) devices have two-dimensional luminescence characteristics, unlike the zero- and one-dimensional characteristics of light-emitting diodes and fluorescent tubes, respectively, and thus have potential for lighting applications. However, there are currently no FE lighting devices with high luminance, long lifetime, and high efficiency. In this study, a triode structure that consists of gate and lateral cathode electrodes is fabricated using transparent indium tin oxide glass. Carbon nanotubes are patterned using screen printing onto the cathode as field emitters. FE studies show that the proposed device, with pulse width modulation used to adjust the on/off ratio of the voltage, can achieve high brightness (19,451 cd/m2), high uniformity (82%), and high luminance stability (luminance drop of 9% after 120 min).

Preparation and Field Emission Performance of Metal-Doped ZnO NRAs/Graphene Composite Material

Al doped and Cu doped ZnO NRAs/Graphene composite material are synthesized by introducing the concentrations of 0%, 2%, 4%, 6%, 8% using hydrothermal method, and their structure and morphology are characterized by XRD, EDS and SEM, XPS. The results show that Al:6% doped and Cu:4% doped ZnO/Graphene nanorod array have the best crystal quality and morphology compared to other concentrations of doped samples. Other than that, the field emission performances of Al:6% doped and Cu:4% doped ZnO NRAs/Graphene are measured. The turn-on field and field enhancement factor of Al:6% doped ZnO NRAs/Graphene are 1.51 V/mm and 11264. The turn-on field and field enhancement factor of Cu:4% doped ZnO NRAs/Graphene are 1.80 V/mm and 10076. It is found that the field emission performance of Al: 6% doped ZnO NRAs/Graphene is higher than the sample with doped Cu, which indicating that Al-doped ZnO NRAs/Graphene might have promising applications for various field emission devices.

Morphology role in 3D flower like GaN nanostructures as excellent field emitters

Flower-like (waterlily) GaN nanostructures comprising sharp tip petals as building blocks have been synthesized on Si (100) substrate by chemical vapor deposition (CVD) technique without using any catalyst. The obtained nano-structures have been characterized by FESEM, XRD, EDS, TEM and HRTEM. The measured sharp tip angle of the petals of the nanostructures is almost 50° which has key role in admirable field emission properties. The flower-like GaN nanostructures have exhibited amazing lower turn-on field value of 3.25 Vμm−1 (10 μAcm−2) at room temperature with insignificant field emission current fluctuation portraying its high stability. Importantly, this turn-on field value is low enough for utilization in field emission devices.

ZnO Nanowire-Based Field Emission Devices Through a Microelectronic Compatible Route

Nanostructured zinc oxide (ZnO) has attracted considerable interest for a wide range of applications, including its use as an active layer in gas sensor devices and as promising emitters for field emission devices. Although it is interesting for FE purposes, the synthesis of this material can be complex and non-compatible with microelectronic processes. To overcome this issue, this paper explores ZnO nanowires growth through thermal oxidation of zinc thin films. We applied this IC-compatible procedure to fabricate field emission cathodes. Analyses of Raman spectroscopy, X‑ray photoelectron spectrometry, X‑ray diffractometry and scanning electron microscopy confirmed that the processes applied were well succeeded in obtaining nanoscale structures of ZnO with dimensions up to 4 micrometers in length and 30‑100 nanometers in diameter. Electrical characterization showed an intense electron field emission on the active area of the device, with a low turn-on electric field (2.4 volts/micrometer). An innovative system based on image processing allowed electrical current mapping throughout the active area of the devices, providing information about the uniformity of the emitted current. These results demonstrate that the low-complex fabrication procedures adopted as well as the ZnO nanomaterial itself are suitable for FE devices development.

First-principles study of the electronic properties of graphene nanostructures for high current density cathodes

Graphene is a crystalline allotrope of carbon with 2D properties. Its carbon atoms are densely packed in a nanoscale hexagonal pattern. Graphene has many unusual properties. In this study, the authors study the electronic properties of graphene nanostructures using first-principles or ab initio calculations based on density functional theory as implemented in the Vienna ab initio simulation package in order to explore its applications in field-emission devices. The density of states and work function of graphene nanoribbons are calculated. The work function value is a key parameter in determining the field emission from a cathode surface according to the Fowler–Nordheim theory. For practical applications, the work functions of graphene nanoribbons with different widths and terminating edges, with and without passivation, have been investigated. Specifically, with the decoration of different alkali and alkaline earth metal species, the reduction of the work function has been systematically studied and determined for achieving higher current density emission.

Fabrication and properties of non-balance electric bridge gas sensor based on a single Sb doped ZnO microwire

Zinc oxide (ZnO) is a wide direct band gap (3.37 eV) II-VI semiconductor material with a wide range of applications in light emitting devices, solar cells, field emission devices, gas sensors, etc. Over the past decades, metal oxide semiconductors have been investigated extensively for sensing various types of vapors and toxic gases. Among the various metal oxides for gas sensing applications, ZnO is one of the potential materials for high response, stability and sensitivity to volatile organic gases. At present, the ZnO-based gas sensor has a relatively high operating temperature. However, the stability and lifetime of gas sensors operating under high temperature conditions with a long term will be greatly reduced. In addition, the power consumption of gas sensors is also significantly increased. Furthermore, there can exist the potential of explosion when gas sensors are used to detect the flammable gases at high temperature. Therefore, it is necessary to improve the sensing properties and reduce the operating temperature of gas sensors. In this paper, ultra-long, large-sized Sb doped ZnO microwires are successfully prepared by using chemical vapor deposition. The gas sensor is based on the principle of non-balance electric bridge, and a single Sb doped ZnO microwire is used as a bridge arm &lt;i&gt;R&lt;/i&gt;&lt;sub&gt;4&lt;/sub&gt; of non-balance electric bridge to produce a gas sensor that can work at room temperature. The results show that the response-recovery curves of sensors at the acetone and ethanol concentrations of 20 ppm, 50 ppm, 100 ppm and 200 ppm (1 ppm = 10&lt;sup&gt;–6&lt;/sup&gt;) are rectangular at room temperature, and have stable current values in air and measured gas, and the response value of the device gradually increases with gas concentration increasing. Furthermore, the detection of acetone and ethanol gas reveal that the device has better selectivity for acetone gas. The response of the gas sensor to 200 ppm acetone is about 243%, with response and recovery time of 0.2 s and 0.3 s, respectively. Compared with the traditional resistive gas sensor, this non-balanced electric bridge sensor has high response, fast response and recovery time. In addition, the sensing mechanism of the device is also studied.

Study of film thickness effect on carbon nanotube based field emission devices

Carbon nanotube (CNT) has been considered as an ideal cathode material for field emission application for a long time. To improve field emission properties, coating CNT films to form a composite cathode is an effective approach. However, few reports have studied and revealed the effect of coated layer thickness. Hence, in this study, we employed an Au layer to coat CNT cathodes with capability to precisely control the coated film thickness and systematically investigated the film thickness effect on field emission properties of the CNT composite field-emission devices. A nonmonotonic relationship between field emission performances and cathode film thickness was observed, and a high performance with a rather low turn-on field of 0.60 V/μm and an ultrahigh field enhancement factor near to 20000 was optimally demonstrated for the CNT composite cathode with an Au layer thickness of 3 nm. Based on experimental data and analysis, the nonmonotonic tendency was found mainly due to effective field emitter density, and the cathode conductivity works only for ultrathin films. Besides, the CNT composite cathode had good stability and uniformity for low heat contact resistant. The superior performance of the CNT cathode composited with a proper Au layer demonstrated potential applications in vacuum electronic devices and an optimized thickness of the coated layer was important for field emission enhancement of composite cathodes.

Fabrication and field emission characteristics of surface-conduction electron-emission with ZnO nanorods based on planar-gate

In this paper, surface-conduction field emission (SCFE) device based on planar-gate triode with in-situ grown ZnO nanorods as the emitter has been fabricated. The ZnO nanorods are controlled to orientable grow by thermal evaporation on a substrate, and their microstructures are analyzed through XRD and SEM. The results show that the one-dimensional ZnO nanorods were rod-shaped, up to 200 nm in diameter and approximately 15 μm in length. They are of oriental growth, uniform in size and perpendicular to the substrate. With the screen-printing, a planar-gate surface conduction device is fabricated, and its field emission characteristics are tested. The test results indicate that the threshold voltage of the planar-gate ZnO-SCFE device decreases with the increase of the anode voltage. When the gate voltage is 62 V, the electron emission efficiency of the device is 36.1%, higher than the reported surface emission display (SED) emission efficiency. Besides, the proposed device has good modulated effect and stability, indicating that it is of good field emission characteristics.

Darcy–Forchheimer Radiative Flow of Micropoler CNT Nanofluid in Rotating Frame with Convective Heat Generation/Consumption

Since 1991, from the beginning of the carbon nanotube era, this has been a focus point for investigation due to its synthetic and simple nature. Unique properties like good stiffness, high surface area, and resilience of carbon nanotubes (CNTs) have been investigated in many engineering applications such as hydrogen storage, composite material, energy storage, electrochemical super-capacitors, transistors, sensors, and field-emitting devices. Keeping in view these applications, we investigate single and multi-walled CNTs nanofluid flow having water as the base fluid between parallel and horizontal rotating plates with microstructure and inertial properties. The thermal radiation effect is considered for variable phenomenon of heat generation/consumption. The principal equations are first symmetrically transformed to a system of nonlinear coupled ordinary differential equations (ODEs), and then, Homotopy Analysis Technique (HAM) and numerical method are employed for solving these coupled equations. The obtained analytical and numerical results are explained graphically and through different tables. The HAM and numerical results show an excellent agreement. The Skin friction and the Nusselt number are numerically calculated and then analyzed with the already published results, and these results are found to be in agreement with one another. The impact of important parameters are shown graphically.

Field emission from mono and two-dimensional nanostructures

Abstract In recent years, nanostructured materials have been deeply investigated for field emission applications. The exploitation of different geometries and morphologies is a key ingredient for the realization of proficient field emitter devices. In this work, we highlight the features of two differently shaped nanostructured materials such as molybdenum disulphide and gallium oxide. We show that Mo S 2 nanoflowers and β-Ga2O3 nanopillars can achieve different field emission performance in terms of maximum current density, turn-on field and field enhancement factor.

Work Function Lowering of Graphite by Sequential Surface Modifications: Nitrogen and Hydrogen Plasma Treatment.

Graphite-related materials play an important role in various kinds of devices and catalysts. Controlling the properties of such materials is of great significance to widen the potential applications and improve the performance of such applications as field emission devices and catalyst for fuel cells. In particular, the work function strongly affects the performance, and thus development of methods to tune the work function widely is urgently required. Here, we achieved wide-range control of the work function of graphite by nitrogen and hydrogen plasma treatments. The time of hydrogen plasma treatment and the amount of nitrogen atoms doped beforehand could control the work function of graphite from 2.9 to 5.0 eV. The formation of a surface dipole layer and the nitrogen-derived electron donation contributed to such lowering of the work function, which is advantageous for applications in various fields.

Study of self-masking nanostructuring of boron doped diamond films by RF plasma etching

The surface nanostructuring of boron doped diamond (BDD) can further enhance its unique properties e.g. in electrochemical sensing, photoelectrochemical cells, field emission devices and various kinds of sensors. Here we present an investigation of plasmatic nanostructuring of BDD films without use of a time-consuming masking process. RF plasma technique was used to etch surface nanostructures with dimensions ranging from tenths to hundreds of nm in width and height. The size and shape of achieved diamond nanostructures were influenced only by applied etching parameters. We have found that the etched carbon is re-deposited in an amorphous form creating a mask and this self-masking process is responsible for the final shape of obtained structures.Therefore, this technique is effectively controllable by changing plasma power, gas type and pressure which influence the energy of incident ions and thus the sputtering yield and re-deposition of masking material. Utilization of various gas types, pressures and RF powers revealed the physical type of etching to be dominant over the chemical at both high and low energy ions. The nanostructured surfaces were then observed and characterized by SEM and Raman spectroscopy to investigate the nanostructures dimensions and to confirm the remaining diamond quality.