Triode Structure Research Articles

Influence of quantum well thickness on the Cathodoluminescent properties of AlGaN-based UVC light source tube with CNT field emitters

Far ultraviolet C (UVC) light sources work well for a variety of applications, such as water purification, bacteria and virus sterilization, and sensing, because of their short wavelength. Herein, the recognized problems with a conventional UVC-LED are solved by creating a triode structure UVC light source tube (UVC-LST) operating at ∼268 nm employing a carbon nanotube (CNT) electron emitter as an excitation source. The UVC light emission of an aluminum reflector-capped AlGaN multiple quantum well (MQW) heterostructures synthesized on a nanopatterned sapphire substrate based on a cathodoluminescence (CL) layer is assessed. For luminescence results comparison, the heterostructure of AlGaN-based MQWs was fabricated with various QW layer thicknesses of 1, 1.5, and 2 nm. The utilization of a thinner QW layer with a thickness of 1 nm significantly improved the UVC light emission efficiency compared to the UVC-LSTs fabricated with thicker QW layers of 1.5 nm and 2 nm. The UVC-LST with the 1 nm QW layer exhibited approximately a 30 % improvement in light output power compared to the UVC-LST with a 1.5 nm QW layer, and closely a 33 % improvement compared to the UVC-LST with a 2 nm QW layer. Moreover, the UVC-LST with the thinner QW layer demonstrated a high power efficiency of 5.24 % when operating on a 2-inch light-emitting area, while consuming a low power of 7 W. This high power efficiency indicates that a significant portion of the input electrical power is effectively converted into UVC light output, highlighting the superior performance of the UVC-LST based on the 1 nm QW layer design.

Field emission in vacuum resonant tunneling heterostructures with high current densities

We analyse the steady-state thermal regime of a one-dimensional triode resonant tunnelling structure. The high currents generated by resonant tunnelling produce a large amount of heat that could damage the structure. Establishing the conditions under which it can operate at optimum efficiency is therefore a problem of great relevance for applications. The tunnel current is found via eigenvalues of the Schrödinger equation in quantum wells. By calculating the current generated in the device and using the energy conservation law in the electrodes, the temperature reached is obtained for different types of electrodes and the importance of heat conduction and thermal radiation is analysed. In the cases discussed, conduction is dominant. When the electrode material is copper, the temperature reached is similar to that of the thermostat for a wide range of electrode lengths, whereas when the cathode material is diamond-graphite and the anode material is copper, the temperature increases significantly as a function of length. The results obtained allow the temperature to be controlled for optimum performance of the field-emitting triode structures.

A Review of Different Types of Solar Cell Materials Employed in Bifacial Solar Photovoltaic Panel

Conventionally accessible silicon solar cells experience two major drawbacks, such as reduced efficiency and increased fabrication costs. The prospects for the reduction in the cost of the photovoltaic form of energy conversion are bifacial solar cells. Bifacial solar cells show potential opportunity in reducing the cost of solar energy conversion when analyzed with respect to monofacial cells. The bifacial solar cells exploit sunlight occurrence on both sides of the cell more efficiently. Bifacial-based solar photovoltaic (PV) is a technology that increases the generation of electrical energy per square meter of PV module through the utilization of light absorption from the albedo. This technology can generally be categorized based on the type of solar cell material and the fabrication technique. PV devices are classified as a silicon-based, thin film, organic, and advanced nano PV. This paper takes a second look at some recent initiatives and significant issues in enhancing the efficiency of bifacial solar cells from material sciences and chemical composition aspects. From this review, it is concluded that screen-printed solar cells have produced a maximum efficiency of 22%. Additionally, triode structure single-crystalline cells produced a maximum front side efficiency of 21.3% and rear side efficiency of 19.8%. Considering the recycling of solar panels, organic solar panels can be developed.

X-ray ultrashort pulse emission characteristic of carbon nanotube cold cathode X-ray source by pulse driving mode

In the present work, we build a triode structure of carbon nanotube (CNT) cold cathode X-ray source driven by pulse voltage in dynamic vacuum system. The results show that the grid voltage and pulse width affect the amplitude, delay time and relative pulse spread of X-ray. The X-ray emission delay time decreases sharply from 102 to 75 ns when the grid voltage increases from 600 to 650 V. The relative pulse spread tends to be saturated with approximately 350 ns (±20 ns) when the voltage increases from 600 to 650 V. The theoretical limit frequency of this X-ray pulsed emission system is approximately 2.86 MHz (1/350 ns). This work reveals the ultrashort pulse emission characteristics and affecting factors of CNT cold cathode X-ray source, promoting the development of CNT cold cathode X-ray source in pulse application.

A robust and scalable electron transparent multi-stacked graphene gate for effective electron-beam convergence in field emission digital X-ray sources

Recently, carbon nanotube (CNT)-based field emission digital X-ray sources have received enormous attention in medical and industrial imaging systems. For high-resolution X-ray images, the field-emitted electron-beam (e-beam) must create a small focal spot size onto an anode by properly converging and focusing of e-beam. Here, multi-stacked graphene by using a layer-by-layer (LBL) stacking method was fabricated as an electron transparent graphene gate (ETGG) for effective e-beam convergence. The ETGG that was completely made on molybdenum (Mo) apertures with scalable diameters of 300 µm extracted and then effectively converged e-beams onto the anode in a triode structure. From the current–voltage measurements, the ETGG reduced turn-on voltage of CNT paste emitters by approximately 24%, as compared with an aperture-gate. The e-beam area originating from the CNT paste emitters with the ETGG was largely converged (almost 77%) compared to the aperture-gate, and scattering of the primary e-beams was eliminated with an optimized collimation module. Long-term durability of the ETGG was confirmed, as the graphene on the apertures robustly remained without any deterioration even upon the 140,000 shots of several-keV-electron bombardment in pulse operation mode. These results demonstrate the potential and suitability of the ETGG for application in field emission digital X-ray sources.

Overall control of field emission from carbon nanotube paste-emitters through macro-geometries for high-performance electron source applications

Field-emitted electron beams from nanometer-scale materials like carbon nanotubes (CNTs) have the potential to regenerate electron source devices based on performance, form factor, and usability. Practically, digital X-ray tubes fabricated with strongly adhesive CNT paste-emitters produce very short and exact X-ray pulses compared with conventional thermionic devices, providing greatly enhanced X-ray images with minimal X-ray dose. Although screen-printed CNT paste-emitters have been studied for a relatively long time, their field electron emissions have not been fully understood or optimally designed for specific electron source applications, because of the complexity arising from the intrinsic printing property, along with process reproducibility and device configurations. Here, we report an approach for the overall control of field electron emissions from multi-dot CNT paste-emitters, including electron-beam trajectories based on emitter dot size, dot array distribution, and triode configurations, using experiments and computational simulations. The crucial factors, such as the unit dot size of the CNT emitters and the aspect ratio of the triode structure, were successfully extracted, and can be used in designing and producing high-performance field-emitted electron source devices.

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).

Research on Local Sound Field Control Technology Based on Acoustic Metamaterial Triode Structure

Cell photoacoustic detection faces the problem where the strength of the sound wave signal is so weak that it easily gets interfered by other acoustic signals. A sonic triode model based on an artificial periodic structure is designed by COMSOL Multiphysics 5.3a software (Stockholm, Sweden), and software simulations are conducted. Experiments show that when a sound wave with a specific frequency is input by the sound wave triode, it can produce an energy amplification effect on the sound wave signals of the same frequency and a blocking effect on the sound wave signals of other frequencies. This contrast effect is more obvious after increasing the sound pressure intensity of the input sound wave signal. It can effectively filter out interference sound signals. The study of the acoustic triode model provides a new approach for the acquisition and identification of acoustic signals in cell photoacoustic detection, which can significantly improve the working efficiency and accuracy of cell photoacoustic detection.

Simple planar field-electron emitter using highly crystalline single-walled carbon nanotubes in a triode structure with in-plane under-gate electrode

The authors investigated the field-electron emission characteristics of a planar field-emission (FE) electron source with a planar conductive layer as a gate electrode embedded under a cathode composed of highly crystalline single-walled carbon nanotubes (hc-SWCNTs) as an emitter. They designed a flat-panel electron emission device that could control electron emission switching arbitrarily, and the device stably emitted electrons on the flat panel. After they assembled the FE electronic device using a wet chemical process, they attained low power consumption and high luminance efficiency. These results show that the application of hc-SWCNTs effectively conserves energy in FE electron sources. The fabrication of FE electron sources and other devices with ultralow power consumption, along with applications that utilize such devices, is expected in the future.

Field-Emission Staggered Structure Based on Diamond–Graphite Clusters

We have proposed and designed a vacuum field-emission triode structure with high-resistivity semiconducting or insulating micrometer-size right parallelepipeds deposited in the staggered order on the conducting substrate (cathode), as well as a structure with a nanofilm on the cathode, which is formed by evaporated diamond–graphite clusters. It has been shown theoretically and experimentally that the emissivity of these structures is much higher than that of an uncoated cathode.

Properties of quarter-wavelength coaxial cavity for triode-type thermionic RF gun

A quarter-wavelength coaxial cavity with a longitudinal radio-frequency power supply was fabricated and tested. The cavity was designed as a pre-buncher for a thermionic triode-type radio-frequency gun of a mid-infrared free electron laser facility. The triode structure was formed to ensure the reduction of the back-bombarding effect, which usually appears in thermionic radio-frequency guns. The coaxial cavity was tested using a tungsten dispenser cathode. From the results of the cold test, a cavity voltage of about 25 kV can be attained, which corresponds to designed characteristics. In contrast, the hot test showed a sudden drop in voltage, resulting in an unstable operation. The small dimensions of the cavity caused some low-field effects, which led to multipactoring. In this paper, we report the tested characteristics of the pre-bunching cavity.

Preparation of a miniature carbon nanotube paste emitter for very high resolution X-ray imaging

A miniature carbon nanotube (CNT) paste emitter dot with a diameter of ∼50 μm was fabricated onto the cross-sectional surface of Kovar (nickel-cobalt ferrous alloy) rod without using a sophisticated photolithography. A highly adhesive CNT paste was prepared with silicon carbide and nickel nanoparticles, and then the small CNT emitter was fabricated by a novel and facile technique, called point contact method. The prepared emitter generates very high current density of ∼11.2 A/cm2 when measured using a diode configuration. We further observed for the first time the brightness of electron beam generated from the CNT paste emitter that is a more practical point electron source than the individual CNT emitter. The triode structure fabricated with a miniature CNT paste emitter and a gate aperture (20 μm in diameter) generated a collimated electron beam by which very high resolution (>16 lp/mm) X-ray imaging was achieved.

Flat-panel light source with lateral-gate triode structure and urchin-like α-Fe2O3 microspheres as field emitters

Urchin-like α-Fe2O3 microspheres (radial α-Fe2O3 nanowires on α-Fe2O3 microspheres) are used as field emitters for a flat-panel lighting device with a lateral-gate-electrode structure. The urchin-like α-Fe2O3 microspheres are in situ grown on the cathode electrode via thermal oxidation at 350 °C for 12 h after the screen-printing of pattern Fe microspheres on the cathode electrode. The lateral-gate triode structure comprises an Ag cathode and a pair of Ag gate electrodes screen-printed laterally on both sides of the cathode. The role of the gate electrodes is to enhance the emission current and increase luminance uniformity and that of the anode electrode is to control the luminance intensity. The radial nanowire emitters on the spheres ensure good field emission performance without any pretreatment and in situ growth of the material enhances the contact between the electrode and the material. The microspheric emitters and the lateral-gate structure, which covers a small part (4.32%) of the printed area over the entire panel (3.5 cm × 5 cm) leads to, high luminance, excellent luminance uniformity and tunable luminance characteristics of the field-emission light source. A maximum luminance of 8330 cd/m2 and a luminance uniformity of 92.4% are achieved with a gate voltage of 500 V, an anode voltage of 4000 V, and the anode current of 1.32 mA.

Flat Panel Light Source with Lateral Gate Structure Based on SiC Nanowire Field Emitters.

A field-emission light source with high luminance, excellent luminance uniformity, and tunable luminance characteristics with a novel lateral-gate structure is demonstrated. The lateral-gate triode structure comprises SiC nanowire emitters on a Ag cathode electrode and a pair of Ag gate electrodes placed laterally on both sides of the cathode. The simple and cost-effective screen printing technique is employed to pattern the lateral-gates and cathode structure on soda lime glass. The area coverage of the screen-printed cathode and gates on the glass substrate (area: 6 × 8 cm2) is in the range of 2.04% – 4.74% depending on the set of cathode-gate electrodes on the substrate. The lateral-gate structure with its small area coverage exhibits a two-dimensional luminance pattern with high brightness and good luminance uniformity. A maximum luminance of 10952 cd/cm2 and a luminance uniformity of >90% can be achieved with a gate voltage of 500 V and an anode voltage of 4000 V, with an anode current of 1.44 mA and current leakage to the gate from the cathode of about 10%.

Submicron source of free electrons

An original way of fabricating multitip microemitters based on the track membrane technology is suggested. Reproducibility of the geometrical parameters of microemitters with a tip diameter of 20–40 nm is achieved. For such tip diameters, the field emission mode sets in at a potential difference of 100–300 V. With these emitters used in diode and triode structures, the speed may be as high as ∼10−12 s. In experimental micro-emitters, a tip density of ∼106 cm−2 is reached. According to calculations, this value may provide technically reasonable field-emission currents. The suggested method of creating multitip microemitters is fairly simple, so that samples several tens of square centimeters in area can be obtained under laboratory conditions. Using special equipment, multitip microemitter arrays several hundred square meters in area can be fabricated.

Tunnel current and I–V characteristics of vacuum extremely-high-frequency microelectronic structures

Tunneling (cold emission) through potential barriers of a complex shape in vacuum microelectronic diode and triode structures, including those with several electrodes, is theoretically investigated and I–V characteristics of these structures are obtained.

Effect of a concave grid mesh in a carbon nanotube-based field emission X-ray source

This study introduces a simple approach to improve the X-ray image quality produced by the carbon nanotube (CNT) field emitter X-ray source by altering the geometrical shape of the grid mesh from the conventional flat shape to a concave one in a typical triode structure. The concave shape of the grid electrode increases the effective number of the grid cells in the mesh, which exerted an electric field in the direction of the emitted electrons, thereby increasing the emission current reaching the anode. Furthermore, the curved mesh (concave grid mesh), which was responsible for the extraction of electrons from the field emitter, exhibited a focusing effect on the electron beam trajectory thereby, reducing the focal spot size impinging on the anode and resulted in a better spatial resolution of the X-ray images produced.

A triode-type carbon nanotube ionizer for micro mass spectrometer

This article presents an ionizer based on a triode structure for a micromachined time-of-flight mass spectrometer (TOFMS). The fabricated device has two components in one chip: a triode-type field emitter for ionization and an ion separator with acceleration electrodes. The electron emitter is an array of carbon-nanotube (CNT) pillars grown by hot-filament chemical vapor deposition (HFCVD). The anode current measured in the field-emission characteristic test of the fabricated device is high, up to 72.1 µA. The gate current is about 5% of the anode current, which implies low electron interception. We confirmed the ionization by electron impact and obtained the mass spectrum of the air from the fabricated device using a microchannel plate (MCP). The results show that the fabricated TOFMS is feasible for cheap miniature mass spectral analyzers.

Fabrication and Characterization of a Planar Triode Structure Based on Honeycomb Carbon Nanotubes

We report a planar triode with metal-gate-free electrode based on carbon nanotubes. Excellent field emission properties with 1.4 mA/cm2 at the gate voltage of 32 V are obtained. A turn-off phenomenon is observed when the gate voltage decreases to 0 V. The field emission at 1.2 mA/cm2 is recorded for 20 h with the fluctuation of the emission current . The results would be of significance to the development of field emission triode structure in the future.

Optimized performances of tetrapod-like ZnO nanostructures for a triode structure field emission planar light source.

Tetrapod-like ZnO (T-ZnO) nanostructures were synthesized by a simple vapor phase oxidation method without any catalysts or additives. We optimized the performances of T-ZnO nanostructures by adjusting the partial pressure of Zn vapour in the total pressure of the quartz chamber and obtained T-ZnO nanostructure materials of high purity, uniform morphology and size and high aspect ratio with a low turn-on electric field of 2.75 V μm(-1), a large field enhancement factor of 3410 and good field emission stability for more than 70 hour continuous emission. Besides, based on the optimized T-ZnO, we developed metal grid mask-assisted water-based electrostatic spraying technology, and fabricated a large-scale, pollution-free, hole-shaped array T-ZnO nanostructure cathode used in a triode structure field emission planar light source. The controllable performances of the triode device were intensively investigated and the results showed that the triode device uniformly illuminated with a luminous intensity as high as 8000 cd m(-2) under the conditions of 200 V grid voltage and 3300 V anode voltage. The research in this paper will benefit the development of a high performance planar light source based on T-ZnO nanostructures.