Emission Cathode Research Articles

Experimental investigation of thermionic cathode properties of ultrafine tungsten filament

The thermionic cathode emission properties of an ultrafine tungsten filament are investigated with the accurate filament temperature (T) measured by an infrared pyrometer. The results show that the tungsten filament begins to emit electrons at T of about 1800 K, and the maximum electron emission efficiency (∼20 mA/W) occurs at T of about 2900 K. Moreover, the effective filament area for electron emission reaches saturation after T exceeds 2700 K. For a tungsten hot-cathode, a using standard is recommended that its operating temperature should not exceed 2600 K, the electron emission current density should not exceed 0.5 A/cm2, and the electron emission efficiency should be less than 5 mA/W. Additionally, the relation between the thermal emissivity of tungsten filament and T is also studied, showing a nearly linear increase of the thermal emissivity from 0.23 to 0.31 with T increasing from 1700 K to 2500 K and a saturated thermal emissivity of 0.48 at T of about 2900 K.

Cu2O@PdAg-quenched CdS@CeO2 heterostructure electrochemiluminescence immunosensor for determination of prostate-specific antigen

Based on the resonance energy transfer between CdS@CeO2 and Cu2O@PdAg, a quenching immunosensor for sensitive detection of prostate specific antigen (PSA) was constructed. The CdS@CeO2 heterostructure was obtained by in situ growth of CeO2 particles on the surface of CdS nanorods, and stable cathodic ECL emission was achieved usingK2S2O8 as coreactant. Cu2O@PdAg was composed of Cu2O with tetradecahedral structure and bimetallic PdAg nanospheres and has a UV-V is absorption range between 600 and 800nm. It overlaps with the ECL emission spectrum of CdS@CeO2, realizing the effective quenching of the ECL signal, which provides feasibility for subsequent practical application. The immunosensor exhibited good linearity in the concentration range 10fg·mL-1 ~ 100ng·mL-1, with a detection limit of5.6fg·mL-1. In sample analysis, the recoveries were 99.8-101%, and the relative standard deviation (RSD) was 0.85-1.6% showing great potential and development value for the sensitive detection of prostate cancer.

Thermal Assessment of Dielectric Microspacer Technology Using an Advanced Three-Dimensional Simulation Model

Dielectric microspacers (DMS) are a novel micro-technology that can be used to achieve a fixed micron/sub-micron gap distance between two separated surfaces, such as the emitter (cathode) and the PV cell (anode) of a near-field thermophotovoltaic converter (TPV). One of the system’s challenges is the flow of undesirable excess thermal energy from the cathode to the anode that might cause the PV cell to overheat. This work investigates the possibility of integrating this technology into a hybrid thermionic-photovoltaic (TIPV) converter operating at ultra-high temperatures (>1000 °C) without any risk of collector’s overheating, which might lead to its mechanical failure. A steady-state 3-D CFD model was developed in Fluent v17.1 solver to assess the system’s thermal behavior when the two electrodes were separated by a distance of 8–10 μm. The heat transfer through conduction across the system components and the net photon/electron flux between the two electrodes were simulated. Different cathode temperatures within the range of 1500–2500 K and various DMS shapes (capillary, cylindrical), patterns (e.g., ring-shaped) and sizes were studied. Results show that thermal performance is not affected by the DMS pattern, even for thermal conductivities of 80 W/(m·K), whereas the possibility of mechanical failure is considerable for Tcathode > 2000 K.

Simulation and Optimization of CNTs Cold Cathode Emission Grid Structure

Carbon nanotubes (CNTs) show significant advantages in the development of cold cathode X-ray tubes due to their excellent field emission performance; however, there are still some problems, such as short lifetime and the low emission current of large-area CNTs. In this paper, a front-grid carbon nanotube array model was established, and the electric field intensity near the tip of the CNTs' electric field enhancement factor was analytically calculated. A simulation model of a CNT three-dimensional field emission electron gun was established by using computer simulation technology (CST). The effects of grid wire diameter, grid aperture shape, and the distribution of grid projection on the cathode surface on the cathode current, anode current, and electron transmission efficiency were analyzed. The aperture ratio was used to evaluate the grid performance, and the simulation results show that the ideal aperture ratio should be between 65% and 85%. A grid structure combining a coarse grid and a fine grid was designed, which can make the electric field intensity around the grid evenly distributed, and effectively increased the cathode emission current by 24.2% compared with the structure without the fine grid. The effect of grid aperture ratio on the electron transmission efficiency was tested. The simulation results and optimized structure can provide a reference for the grid design of cold cathode emission X-ray tubes.

Two-Dimensional Half-Metallic and Semiconducting Lanthanide-Based MXenes.

As a large family of two-dimensional materials, MXenes have attracted intensive attention in recent years. For more functional applications, it is of great significance to determine new MXene members. Here, we theoretically expand the M elements of MXenes to the lanthanide series. Based on density functional theory calculations, the bare lanthanide-based carbides M2C (M = Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb) and the corresponding fluorine- and hydroxyl-terminated configurations are investigated. Most of the fluorine- and hydroxyl-terminated MXenes investigated are half-metals. Specifically, in the half-metallic Eu2CF2, the spin-down states show a band gap larger than 2 eV, implying this configuration's potential applications in spin generation and injection. Both Gd2CT2 (T = F and OH) are magnetic semiconductors. The former shows an indirect band gap of 1.38 eV, while the latter presents a direct one of 0.882 eV. These two configurations also show large magnetic moments higher than 13.7 μB per unit cell. All the hydroxyl-terminated MXene members show relatively low work functions, with the lowest value of 1.46 eV determined in Tm2C(OH)2. These predicted electronic properties imply that the lanthanide-based MXenes could have potential applications in spintronics, information storage, near-infrared detectors, field effect transistors, and field emitter cathodes.

Quantitative evaluation of emission uniformity of the annular explosive emission cathode

Explosive emission cathodes (EECs) are widely used in the field requiring intense electron beams. The uniform emission of EECs is vital for applications. To effectively evaluate the emission uniformity of annular EECs, this paper proposes a quantitative evaluation model based on the analysis of cathode plasma images and constructs a parameter which is named as the non-uniformity value to describe the extent of emission uniformity. The experiment designed to investigate the cathode emission uniformity under different circumstances demonstrates that the model is valid. The experimental results give quantitative information of uniformity change in explosive emission and show that the non-uniformity values of graphite and aluminum cathodes can be significantly decreased by increasing the guiding magnetic field and the diode voltage.

Electrochemistry and electrochemiluminescence of resorufin dye: Synergetic reductive-oxidation boosted by hydrogen peroxide

To develop robust field diagnostic systems capable of responding to medical needs, miniaturization of devices and high target sensitivity remain significant challenges. Electrochemiluminescence (ECL) is an ideal analysis tool to meet these challenges, and developing novel ECL materials is essential. Here we report the reversible electrochemical properties of resorufin, a commercial fluorescent dye, and its highly stable cathodic ECL. We find the cathodic ECL emission from the resorufin quantitatively changes upon the H2O2 content and propose the selective ECL molecular sensor against it. Resorufin undergoes reversible two-electron-transfer electrochemical reduction, and it generates cathodic ECL via a reductive-oxidation pathway with the S2O82− co-reactant. Interestingly, highly enhanced, synergetic ECL is produced in the dual K2S2O8–H2O2 co-reactant system, and especially, it can be used for selective molecular recognition of H2O2. Via the chronoamperometric application, the resorufin ECL signal reveals the linear correlation with the H2O2 concentration range of 0–150 µM with a detection limit of 6.8 µM. Resorufin exhibits strong potential as a new ECL luminophore. Also, selective enhancement of ECL suggests potential applicability to various immunoassays using H2O2.

Fabrication of a ratiometric electrochemiluminescence biosensor using single self-enhanced nanoluminophores for the detection of spermine

A ratiometric electrochemiluminescence strategy using a single luminophore for accurate and sensitive biomolecule detection could be immensely valuable in bioanalysis. Herein, an ultrasensitive ratiometric electrochemiluminescence sensing system was fabricated using a self-enhanced luminophore with dual-signal emission for the detection of spermine. A nanocomposite was synthesized by the covalent attachment of N, N-diisopropylethylenediamine onto glutathione-protected Au–Ag bimetallic nanoclusters (DPEA-GSH@Au/Ag BNCs). The nanocomposite exhibited efficient intra-cluster charge transfer to produce strong anodic self-enhanced electrochemiluminescence emission at 0.8 V without external co-reactants. Interestingly, the DPEA@GSH@Au–Ag BNCs exhibited cathodic electrochemiluminescence emission upon the addition of the co-reactant potassium persulfate at −1.6 V, exhibiting stable and efficient dual-signal electrochemiluminescence emission features at a continuous potential window of −1.75 to 1.2 V. Thus, they were used to fabricate a single-luminophore electrochemiluminescence sensor with dual emission. The cathodic emission of the biosensor gradually increased with increasing concentrations of spermine, whereas the anodic electrochemiluminescence intensity remained almost constant, enabling the ratiometric detection of spermine. The fabricated biosensor, with an internal standard, significantly improved the accuracy and reliability of spermine detection in a wide concentration range of 0.85 pM–100 μM, with a low limit of detection of 0.12 pM (S/N = 3) under optimum conditions. This single-luminophore electrochemiluminescence sensing system could be used for the detection of spermine and could guide the construction of ratiometric electrochemiluminescence sensors in the future.

Ratiometric electrochemiluminescence biosensor for hepatitis C virus E2 protein based on block copolymers-solubilized Ir(ppy)3 with high electrochemiluminescence efficiency

Iridium (Ir) complexes have gained remarkable development momentum as candidates for electrochemiluminescence, but their poor solubility in water media greatly limited their application in ECL area. Herein, a facile nanoprecipitation method by encapsulating tris(2-phenylpyridinato)iridium (Ir(ppy)3) into pluronic block copolymers for preparing water-soluble Ir(III) complexes with high ECL emission efficiency was developed. Then, with F-127@Ir(ppy)3 as the anode emitter and g-C3N4 as the cathode emitter, a new ratiometric biosensor based on transition metal complexes was developed for the first time, which was used for ultra-sensitive detection of hepatitis C virus E2 protein. Notably, the ratiometric ECL signal could be mediated by using multifunctional Nb2C nanosheets (Nb2C NSs) with excellent electrocatalytic activity and superoxide dismutase activity, so as to enhance the ECL intensity of anode and quench the response of cathode ECL. Combining Nb2C NSs with the antibody and the specific recognition process, the proposed ECL ratio biosensor showed good performance for E2 with a linear range from 1 × 10−3 ng/mL to 1 × 102 ng/mL and a detection limit of 8.39 × 10−4 ng/mL. The work on designing water-soluble Ir (III) complexes with pluronic block copolymer provides an ingenious approach to broaden the application of poorly soluble complexes in bioassays.

Dual-emitting Iridium nanorods combining dual-regulating coreaction accelerator Ag nanoparticles for electrochemiluminescence ratio determination of amyloid-β oligomers

Iridium(III) complexes have been developed as eminent electrochemiluminescence (ECL) luminophores, but their current applications are only limited to anodic ECL emission because of weak cathodic ECL emission. This work explored poly(styrene-co-maleicanhydride) (PSMA) as functional reagent to modulate iridium(III) complexes to simultaneously emit bipolar ECL signals. The prepared iridium(III) nanorods (Ir NRs) were detected strong bipolar ECL emissions at +0.9 V and −2.0 V with N,N-diisopropylethylenediamine (DPEA) and persulfate (S2O82−) as coreactant, respectively. Meanwhile, Ag nanoparticles (Ag NPs) were developed as dual-regulating coreaction accelerator to boost the bipolar emissions of Ir NRs simultaneously. The dual-emitting Ir NRs coupled with dual-regulating coreaction accelerator Ag NPs facilitated the construction of mono-luminophore-based ECL ratio strategy for detecting amyloid-β oligomers (AβO). When the target AβO appeared, the Mg2+-dependent DNAzyme-powered biped walkers were unlocked to cleave single-stranded S1 immobilized on the surface of magnetic beads (MBs), resulting in the production of massive single-stranded ST. Then, the output ST cleaved hairpin H1 captured by Ir NRs modified electrode to produce numerous single strands, which could initiate the hybridization chain reaction (HCR) between Ag NPs-labeled H2 and Ag NPs-labeled H3 to introduce abundant Ag NPs onto the electrode surface. Due to the enhancement effect of Ag NPs on the bipolar ECL emissions from Ir NRs, the ECL ratio detection of AβO was achieved with the detection limit of 0.62 pM. The unique dual-emitting properties of Ir NRs coupled with dual-regulating effect of Ag NPs provided an interesting mono-luminophore-based ECL ratio sensing platform for biological analysis.

Enhancing the thermionic electron emission performance of hafnium with nanocluster doping

Scandate cathode as a thermionic electron emission material has attracted broad interest owing to its high electron emission capability. Despite the large number of studies on the electron emission of the scandate tungsten cathode, there is a lack of understanding of the performance of scandium oxide incorporated in other refractory metal matrix. In this work, by applying first-principles calculations, we study the role that Sc2O3 nanocluster plays in enhancing the electron emission of the Hf cathode (labeled as Sc2O3@Hf). We find that Sc2O3@Hf is both thermally and mechanically stable, exhibits complex surface structures, and possesses inverse relationship between surface energy and work function. Moreover, the work function of the Hf (0001) surface can be reduced to 3.50 eV due to the change in the vacuum level when Sc2O3 nanocluster is doped, while the work function of the Hf (101¯2) surface can be reduced to 3.39, 3.39, and 3.03 eV when doped with Sc2O3, Y2O3, and CeO2 clusters, respectively.

Molecular engineered graphitic carbon nitride with strong and stable electrochemiluminescence for immunosensing

Graphitic carbon nitride (g-CN) is a semiconductor polymer with strong electrochemiluminescence (ECL) emission. However, the sensing application of g-CN ECL suffers from poor ECL stability due to its low electrical conductivity. In this work, g-CN is molecularly engineered with phenyl groups to improve its electrical conductivity. The prepared Ph-CN nanosheets (Ph-CNNS) show stable and strong cathodic ECL emission benefiting from the synergetic effect of improved conductivity preventing electron over-injection and higher luminescent efficiency of Ph-CNNS as compared to CNNS. Based on the strong and stable ECL emission of Ph-CNNS, a ECL immunosensor with biocatalytic precipitation reaction-mediated signal amplification is developed for the detection of cardiac Troponin I (cTnI), a biomarker of acute myocardium infarction. The ECL immunosensor shows a linear response to cTnI in the concentration range of 1 pg mL−1 ∼ 10 ng mL−1 with a detection limit of 0.5 pg mL−1, and exhibits good specificity, reproducibility and long-term stability. The ECL immunosensor is further used for the detection of cTnI in human serum sample. The good recovery suggests its feasibility in clinical application. This work provides a facile molecular engineering strategy to modulate g-CN ECL property, and would promote g-CN ECL in sensing application.

Experimental Verification of Anode-Induced Phenomena During Prebreakdown Conduction in Vacuum Gaps Under Alternating Voltages With Special Electrode System

The results presented in this article relate to the work conducted to verify the existence of anode-induced phenomena, predominantly anode vaporization and consequent prebreakdown (PBD) current enhancement due to the impact of positive ions and microparticles over a relatively larger area at the cathode (presumably ion-assisted field (I-F) emission like). The verification of this hypothesis is attempted using a three-electrode arrangement. One electrode is comprised of a needle insulated from and projecting through a plane electrode (collector) of 40-mm diameter. It was surmised that if the positive ion beam from the anode spot (due to electron beam impact) were to be macroscopically diffuse, at least the collector would gather a part of it. However, no currents could be detected in the collector circuit even at voltages close to breakdown. The needle currents continued to display the typical characteristics of PBD currents under alternating voltages. The needle currents depended on the spacing between the needle tip and the plane of the collector and the polytetrafluoroethylene (PTFE) insulation used to prevent emission from the immediate vicinity of the needle evaporated significantly. Typical broad-area electrode behavior displayed by needle currents indicated that I-F emission, if any, is limited to the needle itself, which is certainly broad compared to the positive ion beam. Dependence of the PBD currents and breakdown voltages on the melting point of the anode material lend support to such anode-triggered electrode phenomena.

Synthesis and Characterization of MWCNTs/ZnO Nanocomposites for Device Applications

The nanocomposite was created in order to investigate field emission (FE) applications. A MWCNTs/ZnO nanocomposite, by combining ZnO thin films with multi-wall carbon nanotubes (MWCNTs), was synthesized by the use of chemical vapor deposition (CVD) techniques for FE applications. The thin films were then prepared by dip-coating and drop-casting onto a silicon substrate. The field emission scanning electron microscopy (FESEM), Raman spectroscopy and the X-ray diffraction (XRD) techniques were used to characterize the MWCNTs and MWCNTs/ZnO nanocomposite separately and compare the results. From Raman spectra, the calculated values of ID/IG are, respectively, 0.521 and 0.950, which confirm the certain defects and disorders produced after coating of ZnO nanoparticles on the MWCNTs’ surface. From the current density–electric field plot, it is found that the FE properties increased by three times which indicates that MWCNTs/ZnO nanocomposite can be useful for ideal cathode emitters.

Sc-Containing (Scandate) Thermionic Cathodes: Mechanisms for Sc Enhancement of Emission

Although thermionic emission has been studied for more than 100 years, recent interest in novel electron devices for military and civilian use has led to a surge in demand for cathodes with enhanced emission properties (e.g., higher current density, more uniform emission, lower operating temperatures, or extended in-service longevity). Sc-containing “scandate” cathodes have been widely reported to exhibit superior emission properties compared to previous-generation thermionic cathodes, including oxide, B-, and M-type cathodes. Despite extensive study spanning several decades, the mechanism by which the addition of Sc enhances cathode emission remains ambiguous, and nonuniform emission, low reproducibility, and inconsistent longevity continue to prevent widespread commercial integration of scandate cathodes into electron devices. This second part of a two-part review explores the various mechanisms proposed for how Sc enhances electron emission and summarizes ongoing scientific challenges relating to the development and deployment of scandate cathodes.

Sc-Containing (Scandate) Thermionic Cathodes: Fabrication, Microstructure, and Emission Performance

Although thermionic emission has been studied for more than 100 years, recent interest in novel electron devices for military and civilian use has led to a surge in demand for cathodes with enhanced emission properties (e.g., higher current density, more uniform emission, lower operating temperatures, or extended in-service longevity). Sc-containing “scandate” cathodes have been widely reported to exhibit superior emission properties compared to previous-generation thermionic cathodes, including oxide, B-, and M-type cathodes. Despite extensive study spanning several decades, the mechanism by which the addition of Sc enhances cathode emission remains ambiguous, and nonuniform emission, low reproducibility, and inconsistent longevity continue to prevent widespread commercial integration of scandate cathodes into electron devices. This first part of a two-part review explores approaches that have been used for fabricating Sc-containing thermionic cathodes and the microstructures and emitting properties that result.

Single-Atom Iron Enables Strong Low-Triggering-Potential Luminol Cathodic Electrochemiluminescence.

The conventional cathodic electrochemiluminescence (ECL) always requires a more negative potential to trigger strong emission, which inevitably damages the bioactivity of targets and decreases the sensitivity and specificity. In this work, iron single-atom catalysts (Fe-N-C SACs) were employed as an efficient co-reaction accelerator for the first time to achieve the impressively cathodic emission of a luminol-H2O2 ECL system at an ultralow potential. Benefiting from the distinct electronic structure, Fe-N-C SACs exhibit remarkable properties for the activation of H2O2 to produce massive reactive oxygen species (ROS) under a negative scanning potential from 0 to -0.2 V. The ROS can oxidize the luminol anions into luminol anion radicals, avoiding the tedious electrochemical oxidation process of luminol. Then, the in situ-formed luminol anion radicals will directly react with ROS for the strong ECL emission. As a proof of concept, sensitive detection of the carcinoembryonic antigen was realized by glucose oxidase-mediated ECL immunoassay, shedding light on the superiority of SACs to construct efficient cathodic ECL systems with low triggering potential.

Acidic pH and thiol-driven homogeneous cathodic electrochemiluminescence strategy for determining the residue of organophosphorus pesticide in Chinese cabbage

Electrochemiluminescent (ECL) sensors for organophosphorus pesticides (OPs) have received considerable attention, whereas complicated electrode’s immobilization, response to single hydrolysate and anodic emission correlated with ECL assays restrict their potential utilization. Herein, we developed a homogeneous dual-response cathodic ECL system for highly sensitive and reliable analysis of OP using CdTe QDs as emitters. CdTe QDs, emitting red light, were fabricated through a hydrothermal reaction and generated anodic and cathodic ECL emission upon stimulation of tripropyl amine and K2S2O8, respectively. Notably, CdTe QDs-K2S2O8 showed a simultaneous response to thiol and acidic pH, and were regarded as a ECL sensor for methidathion with limit of detection of 0.016 ng/mL based on hydrolysis of acetylthiocholine into thiocholine and CH3COOH by acetylcholinesterase (AChE) and OPs’ inhibition on AChE activity. This sensor also exhibited good practicability to detect methidathion in Chinese cabbage. Overall, the sensor will supply more useful information for ensuring OPs-related food safety.

A Microelectronic Terahertz Source Using Multiple Field Emitter Cathodes With an Array of Coupled Cavities

Compact, high-power, and broad-spectral coverage terahertz sources have application prospects in diverse scientific and technological fields, which attract great interest from researchers. The recently developed microelectronic device, a so- called terahertz laser diode (TLD), affords a promising candidate to develop desirable terahertz sources. However, the performances and the accessibility of TLD have unavoidable restrictions in the practices. In this article, we propose an enhanced TLD, which uses multiple field-emitter cathodes with an array of coupled cavities. The power and efficiency can be several times higher than that in previous TLDs. The required electric field intensity and the emission current density from the field-emitter cathode can be significantly reduced, which enables established field-emitting materials to be applicable and decreases the manufacturing difficulty as well. In addition, the fields in different cavities can be coupled, forming a series of unified oscillation modes, which can work as operation modes with various output frequencies. This improved TLD is attractive for developing compact, high-power, and broad-spectrum coverage terahertz sources for practices.

Improving field emission performance of patterned ZnO electron emission source by optimizing array spacing

The field emission (FE) electron source has a wide range of application in the field of vacuum electronics, and the patterning of cathode emitters is one of the key technology. In this paper, a new idea of cathode structure to achieve good luminescence uniformity with the smallest emitter areas is proposed. First, the inkjet printing is applied to precisely position the patterned layer, and the branched ZnO arrays are grown by electrochemical deposition. Then the effect of array spacings on field emission performance is studied. The results show that with the increase of the array spacing, the FE performance first increases and then decreases, among which the arrays with the moderate spacing have the best FE properties, including the lowest turn-on field (Eon) of ∼0.46 V μm−1 and the most uniform luminescence. Finite element calculations using the ANSYS software were performed. Simulations are carried out to analyze the surface electric field distribution and electron movement trajectory, indicating the moderate array spacing is beneficial for FE due to the balance of the field superposition effect and shielding effect. The efficiency of pattern design helps to realize the high-performance field emission electron source, which is of great significance for flexible manufacturing and large-scale integration.