High Electric Field Research Articles

Revealing Surface/Interface Chemistry of the Ordered Aramid Nanofiber/MXene Structure for Infrared Thermal Camouflage and Electromagnetic Interference Shielding.

The past decade has witnessed the advances of infrared (IR) thermal camouflage materials, but challenges remain in breaking the trade-off nature between emissivity and mechanical properties. In response, we identify the key role of a moderate reprotonation rate in the aramid nanofiber (ANF)/MXene film toward a surface-to-bulk alignment. Theoretical simulation demonstrates that the ordered ANF/MXene surface eliminates the local high electric field by field confinement and localization, responsible for the low IR emissivity. By scrutinizing the surface/interface chemistry, the processing optimization is achieved to develop an ordered and densely stacked ANF/MXene film, which features a low emissivity of 16%, accounting for sound IR thermal camouflage performances including a wide camouflage temperature range of 50-200 °C, a large reduction in radiation temperature from 200.5 to 63.6 °C, and long-term stability. This design also enables good mechanical performance such as a tensile strength of 190.8 MPa, a toughness of 12.1 MJ m-3, and a modulus of 7.9 GPa, responsible for better thermal camouflage applications. The tailor-made ANF/MXene film further attains an electromagnetic interference (EMI) shielding effectiveness (40.4 dB) in the X-band, manifesting its promise for IR stealth compatible EMI shielding applications. This work will shed light on the dynamic topology reconstruction of camouflage materials for boosting thermal management technology.

Deep ultraviolet AlGaN-multiple quantum wells with photoluminescence enhanced by topological corner state

The AlGaN-based deep ultraviolet light-emitting diode (DUV LED) has advantages of environmentally friendly materials, tunable emission wavelength, and easy miniaturization. However, an increase in Al composition leads to a decline in the lattice quality, thereby reducing the internal quantum efficiency (IQE). In addition, the light extraction efficiency (LEE) is limited due to the strong transverse magnetization polarization emission from the multiple quantum wells. Here, we designed the topological corner structure in AlGaN-MQWs, and the high electric field intensity in a tiny space at the corner results in an extremely high local density of optical states (LDOS), which could shorten the luminescence decay time of the emitter and increase the radiative rate by 26 times. Meanwhile, because the excited topological corner state resonance mode is a transverse-electric mode, enhancing only the transverse-electric luminescence without any gain for transverse-magnetic luminescence, thereby significantly improving the light extraction efficiency. Finally, according to theoretical calculations, the IQE could reach 68.75% at room temperature.

Single-event burnout resilient design of 4H-SiC MOSFETs through staircase-like buffer layer

With the rapid development of SiC materials, high-power devices such as SiC MOSFETs have been widely used in aerospace, new energy, nuclear applications, and other fields. This places higher demands on their reliability, especially about radiation effects. This paper proposes a 4H-SiC staircase-like buffer layer MOSFET (SBL-MOSFET) with a hardened structure against single-event burnout (SEB). A comparison is made with conventional VD-MOSFET, gauss buffer layer MOSFET (GBL-MOSFET), and double buffer layer MOSFET (DBL-MOSFET) through TCAD simulations. The performance of the SBL-MOSFET against single-event burnout is studied by investigating the electric field distribution, impact ionization rate, hole concentration, and lattice temperature. The simulation results demonstrate that the staircase-like buffer layer structure effectively improves the distribution of high electric field, reduces the impact ionization rate, and thus increases the SEB threshold voltage compared to other structures. The proposed SBL-MOSFET exhibits a 67.5 % improvement in single-event burnout threshold voltage compared to the conventional VD-MOSFET, with slight degradation of breakdown voltage and leakage current. Meanwhile, there is no significant change in other electrical parameters.

Study on the single-event burnout mechanism of GaN MMIC power amplifiers

In this Letter, a single-event burnout (SEB) mechanism in gallium nitride (GaN) microwave monolithic integrated circuit power amplifiers with a high linear energy transfer of 78.1 MeV·cm2/mg has been investigated in detail. A typical SEB phenomenon was observed. With the aid of photon emission measurements and scanning electron microscopy, it is found that catastrophic burnout occurs in the power-stage GaN high electron mobility transistors (HEMTs) and the metal–insulator–metal (MIM) capacitors, respectively. For the GaN HEMT, the incident heavy ions will generate electron–hole pairs within it, which can gain enough energy with the transverse high electric field. The high-energy electrons will collide with the lattice near the drain electrode and induce significant electron trapping, which will result in a significant longitudinal local electric field. When a critical electric field is achieved, catastrophic burnout occurs. For the MIM capacitor, the burnout is attributed to the single-event dielectric rupture via severe impact ionization or latent tracks when heavy ions strike it.

High Electric Field Enhancement Induced by Modal Coupling for a Plasmonic Dimer Array on a Metallic Film

A giant electric field on a subwavelength scale is highly beneficial for boosting the light–matter interaction. In this paper, we investigated a hybrid structure consisting of a hemispheric dimer array and a gold film and realized resonant mode coupling of the surface lattice resonance (SLR) and surface plasmon polariton (SPP). Mode coupling is demonstrated by observing anti-crossing in reflection spectra, which corresponds to Rabi splitting. Although the resonance coupling does not enter the strong coupling regime, an improved quality factor (Q~350) and stronger electric field enhancement in the gap region of the dimer (i.e., hot spot) in our hybrid structure are obtained compared to those of the single dimer or dimer array only. Remarkably, the magnitude of electric field enhancement over 500 can be accessible. Such high field enhancement makes our hybridized structure a versatile platform for the realization of ultra-sensitive biosensing, low-threshold nanolasing, low-power nonlinear optical devices, etc.

One Stone, Two Birds: Using High Electric Fields to Enhance the Mobility and the Concentration of Point Defects in Ion-Conducting Solids.

Improving the ionic conductivity of outstanding, composition-optimized crystalline electrolytes is a major challenge. Achieving increases of orders of magnitude requires, conceivably, highly nonlinear effects. One known possibility is the use of high electric fields to increase point-defect mobility. In this study, we investigate quantitatively a second possibility that high electric fields can increase substantially point-defect concentrations. As a model system, we take a pyrochlore oxide (La2Zr2O7) for its combination of structural vacancies and dominant anti-Frenkel disorder; we perform molecular-dynamics simulations with many-body potentials as a function of temperature and applied electric field. Results within the linear regime yield the activation enthalpies and entropies of oxygen-vacancy and oxygen-interstitial migration, and from three independent methods, the enthalpy and entropy of anti-Frenkel disorder. Transport data for the nonlinear regime are consistent with field-enhanced defect concentrations and defect mobilities. A route for separating the two effects is shown, and an analytical expression for the quantitative prediction of the field-dependent anti-Frenkel equilibrium constant is derived. In summary, we demonstrate that the one stone of a nonlinear driving force can be used to hit two birds of defect behavior.

Knitting Interconnected Perovskite Grains with A Π‐Conjugated Passivator for Blue Light‐Emitting Diodes

AbstractMetal halide perovskite light‐emitting diode (PeLED) is the most promising candidate for next‐generation display technology. However, the development of the blue PeLEDs is far behind the expectations. Mixed‐halide perovskites demonstrate to be the most facile method to realize blue emission, which confronts serious spectra stability problem arising from the halide segregation. Here, a polymerizable passivator is introduced into the Cl/Br‐mixed perovskites, which can simultaneously cross‐link perovskite grains by interconnecting halides through hydrogen bonding, and transport the carriers through its π‐conjugated backbone. Consequently, this cross‐linked blue perovskite film demonstrates a significantly improved spectra stability under various external stimuli of high humidity, UV radiation, and electrical field, and the corresponding PeLED yields a decent external quantum efficiency of 12.0% at high brightness of 3390 cd m−2 with the emission at 478 nm. Notably, this work provides a unique cross‐link agent with in situ polymerizability to address the ion migration and phase segregation issues without sacrificing the conducting capacity in mixed‐halide perovskites.

Particle removal performance of a novel ESP type air cleaning system for indoor air quality in a subway station

A novel electrostatic precipitation type air cleaning technology with near zero ozone emission for indoor air quality of a subway station was developed. To minimize ozone emission and achieve high particle removal performance against ultrafine particulate matters (PMs), a multi-channel charging method using soft ionization by micrometre carbon fibers and a narrow gap collection method using high electric field by thin conductive plastic sheets as a high voltage electrode were used. In this study, the novel electrostatic charging and collection technologies were applied to a real scale air cleaning system in an Air Handling Unit (AHU) with air flow rate of 950 m3/min in Yuseong Oncheon subway station with an area of 3000 m2 in Daejeon, South Korea. The particle removal performance of the demonstration system was evaluated with real suspended particles in the subway station during test period with high PM concentrations in Korea over 40 μg/m3. Particle collection efficiency, pressure drop and ozone emission were evaluated, and compared to those of the a minimum efficiency reporting value (MERV) 10 and 14 filters used in the typical subway stations in Korea. In the field researches, the developed ESP achieved over 80% of the PM collection efficiency higher than those of the filters with MERV-10 and -14, and even 10% higher efficiency against PM1.0, while generating only 10% of pressure drop and also emitting nearly zero ozone. It is concluded that a novel ESP type air cleaning system with near zero ozone emission could be a promising air cleaning method for a large indoor environment such as a subway station where polluted air with ultrafine particles flowed in with a very high flow rate.

Effect of proton radiation on gallium nitride light emitting diodes

The compound semiconductor gallium nitride offers enormous potential for facilitating economic expansion in the silicon-based semiconductor industry, which is currently seeing decreasing performance returns compared to investment costs. Its high electron mobility and electric field strength at the material level have already demonstrated enormous potential for photonics and high-frequency communications applications. However, its application in devices used in the radiation-prone environment is hindered by degradation and failure caused by the radiation. In this paper, the effect of proton radiation on the electrical properties of InGaN light emitting diodes (LEDs) for the fluence range of 1×1014 cm-2 to 3×1014 cm-2 is performed. On comparing the results before and after radiation, it is found that radiation mainly affected the reverse IV characteristics of the device with little or no effect on forward IV or CV characteristics. Apart from the electric properties, the optical properties of the LEDs show improvement after radiation as the light intensity increases post-irradiation.

Design, characterization and installation of the NEXT-100 cathode and electroluminescence regions

NEXT-100 is currently being constructed at the Laboratorio Subterráneo de Canfranc in the Spanish Pyrenees and will search for neutrinoless double beta decay using a high-pressure gaseous time projection chamber (TPC) with 100 kg of xenon. Charge amplification is carried out via electroluminescence (EL) which is the process of accelerating electrons in a high electric field region causing secondary scintillation of the medium proportional to the initial charge. The NEXT-100 EL and cathode regions are made from tensioned hexagonal meshes of 1 m diameter. This paper describes the design, characterization, and installation of these parts for NEXT-100. Simulations of the electric field are performed to model the drift and amplification of ionization electrons produced in the detector under various EL region alignments and rotations. Measurements of the electrostatic breakdown voltage in air characterize performance under high voltage conditions and identify breakdown points. The electrostatic deflection of the mesh is quantified and fit to a first-principles mechanical model. Measurements were performed with both a standalone test EL region and with the NEXT-100 EL region before its installation in the detector. Finally, we describe the parts as installed in NEXT-100, following their deployment in Summer 2023.

β-Barrel channel’s response to high electric fields: Functional gating or reversible denaturation?

β-Barrel channel’s response to high electric fields: Functional gating or reversible denaturation?

High-performance solar-blind photodetector based on amorphous BN in harsh environment operations

High-performance solar-blind photodetectors capable of operating in extreme environments are desirable for a wide range of applications, such as engine control, down hole drilling, space exploration, and environmental monitoring. Boron nitride (BN), with an ultrawide bandgap and high band edge absorption coefficient, is especially suitable for such application scenarios owing to its chemical and structural stability at high temperatures and radiative conditions, which, however, in turn, brings difficulties in synthesis of large-area continuous single crystalline BN. Here, we report highly robust solar-blind photodetectors based on amorphous BN (a-BN) films that can operate at high temperatures and high electric fields. The a-BN films are dense and uniform, grown at 500 °C using dual beam-assisted deposition method. The a-BN-based photodetectors exhibit high performance with a responsivity of 0.56 mA/W at 20 V under UV illumination of 222 nm and a high rejection ratio (R222 nm/R295 nm > 200 and R222 nm/R315 nm > 500). More importantly, these photodetectors demonstrate excellent responsivity and stability at high temperatures up to 500 K and high bias of 200 V without breakdown. The photocurrent mechanism at elevated temperatures is analyzed by temperature-dependent decay time of the temporal response, showing the electron–phonon interaction and self-trapped holes are dominant. Our work suggests that the deposition of such a-BN films offers a promising strategy toward highly environment-resistant solar-blind photodetectors.

Probing Electronic Band Structures of Dielectric Polymers via Pre-Breakdown Conduction.

The electronic band structure, especially the defect states at the conduction band tail, dominates electron transport and electrical degradation of a dielectric material under an extremely high electric field. However, the electronic band structure in a dielectric is barely well studied due to experimental challenges in detecting the electrical conduction to an extremely high electric field, i.e., prebreakdown. In this work, the electronic band structure of polymer dielectric films is probed through an in situ prebreakdown conduction measurement method in conjunction with a space-charge-limited-current spectroscopic analysis. An exponential distribution of defect states at the conduction band tail with varying trap levels is observed in accordance with the specific morphological disorder in the polymer dielectric, and the experimental defect states show also a favorable agreement with the calculated density of states from the density functional theory. The methodology demonstrated in this work bridges the molecule-structure-determined electronic band structure and the macro electrical conduction behavior with a highly improved understanding of material properties that control the electrical breakdown, and paves a way for guiding the modification of existing material and the exploration of novel materials for high electric field applications.

DC surface flashover characteristics of Al2O3/epoxy composites at cryogenic temperature

Epoxy resin is essential in the superconducting system as an insulating and supporting material. Extreme conditions such as cryogenic temperature, high vacuum, and high electric field could result in insulation failure for Epoxy resin. Surface flashover voltage is usually lower than breakdown voltage for solid materials. In this paper, the DC surface flashover characteristics of nano-Al2O3/epoxy composites (0, 1, 2, 3, 4, and 5%) have been investigated at cryogenic and room temperature. The nano-Al2O3 particles were modified by silane coupling agent (KH560). Epoxy doped with nano-Al2O3 was poured into a self-made mold and experienced a thermosetting process for 14 h. DC flashover tests were performed according to the IEC 60243–1:2013 international standard. The results were evaluated by the Weibull distribution method. The result shows that the DC surface flashover voltage of nano-Al2O3/epoxy composite is strongly related to the addition of nanoparticles and different temperatures. It can be explained by secondary electron emission avalanche (SEEA) and Li’s model.

Dielectric permittivity of PZT 95/5 ferroelectric ceramics and 0.27PIN-PMN-0.26PT single crystals under pulsed high electric fields

The dependence of the dielectric permittivity of ferroelectric materials on electric field magnitude impacts the performance of ferroelectric devices. In a ferroelectric generator, a shock wave travels through the ferroelectric element and depolarizes it, and surface charges are released from the element electrodes, resulting in the generation of a megawatt power level for several microseconds. The dielectric properties of the compressed and uncompressed zones of the ferroelectric element affect the generated voltage and energy. The results of previous studies indicate that the low-field dielectric permittivity of poled Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3 (PZT 95/5) ferroelectrics in the uncompressed zone differs significantly from the high-field permittivity. Herein, the results are presented from the experimental investigation of the high-field permittivity of poled uncompressed PZT 95/5 ferroelectric ceramics and films, PZT 52/48 ferroelectric ceramics, and rhombohedral 0.27Pb(In1/2Nb1/2)O3–0.47Pb(Mg1/3Nb2/3)O3–0.26PbTiO3 (0.27PIN-PMN-0.26PT) and 0.68Pb(Mg1/3Nb2/3)O3–0.32PbTiO3 (0.68PMN-0.32PT) ferroelectric single crystals. The dependences of the permittivity on the electric field were determined using a pulsed electric field ranging from 0.1 to 10 kV/mm. The data indicate that the application of a pulsed high electric field results in a fourfold increase in the relative permittivity of PZT 95/5 ceramics and films over the small signal value (from 300 to 1200), and a threefold increase in the permittivity of single-domain [111]c cut and poled 0.27PIN-PMN-0.26PT crystals (from 700 to 2100), while a high electric field does not have a significant impact on the permittivity of PZT 52/48 ceramics or 0.27PIN-PMN-0.26PT and 0.68PMN-0.32PT crystals cut and poled in the domain engineered [001]c or [011]c direction.

Enhancing energy storage efficiency in lead-free dielectric ceramics through relaxor and lattice strain engineering

Dielectric capacitors with high power density and fast charge-discharge speed play an essential role in the development of pulsed power systems. The increased demands for miniaturization and practicality of pulsed power equipment also necessitate the development of dielectric materials that possess high energy density while maintaining ultrahigh efficiency (η). In particular, ultrahigh efficiency signifies minimal energy loss, which is essential for practical applications but challenging to effectively mitigate. Here, we demonstrate a strategy of incorporating heterovalent elements into Ba(Zr0·1Ti0.9)O3, which contributes to achieving relaxor ferroelectric ceramics and reducing lattice strain, thereby improving the comprehensive energy storage performance. Finally, optimal energy storage performance is attained in 0.85Ba(Zr0·1Ti0.9)O3-0.15Bi(Zn2/3Ta1/3)O3 (BZT-0.15BiZnTa), with an ultrahigh η of 97.37% at 440 kV/cm (an advanced level in the lead-free ceramics) and an excellent recoverable energy storage density (Wrec) of 3.74 J/cm3. Notably, the BZT-0.15BiZnTa ceramics also exhibit exceptional temperature stability, maintaining fluctuations in Wrec within ∼10% and η consistently exceeding 90% across the wide temperature range of −55 °C to160 °C, and under a high electric field of 250 kV/cm. All these features demonstrate that the relaxor and lattice strain engineering strategies have been successful in achieving high-performance lead-free ceramics, paving the way for designing high-efficiency dielectric capacitors with a wide temperature range.

Electron and ion emission characteristics of metal irradiated by nanosecond laser

Clarifying the electron and ion emission characteristics of metals irradiated by nanosecond focused laser in low pressure environment is crucial for improving applications based on laser-produced plasmas. This paper investigates the emission characteristics through electrical and optical diagnosis. The emission process is investigated through joint analysis of electrons and ions behavior, and relevant influencing factors are studied. The emission process of electrons and ions is divided into four stages, characterized by the arrival of prompt electrons e1, ultrafast electrons e2/ions i1, fast ions i2 and thermal electrons e3/ions i3, respectively. e1 is mainly related to thermal emission and photoemission, which can be improved by high electric field, gas pressure (within a certain range), laser energy and melting boiling points of target. e2/e3 and i1/i2/i3 mainly originate from laser ablation, and their expansion process follows obvious bipolar diffusion characteristics, while the latter is related to the different mass and charge states of the ions. The amplitude of i2 and e3 can be improved by using low density and melting point metals, and they are easily blocked by background gas, almost independent of the weak electric field.

Physics-based modeling of surface potential and leakage current for vertical Ga2O3 FinFET

Gallium oxide (Ga2O3) is a promising ultra-wide bandgap material offering a large bandgap (>4.7 eV) and high critical electric fields. The increasing demand for electronic devices for high-power applications in electric automobiles, high-performance computing, green energy technologies, etc., requires higher voltages and currents with enhanced efficiency. Vertical transistors, such as fin-shaped field-effect transistors (FinFETs) have emerged to meet the growing need with improved current handling capabilities, reduced resistance, and enhanced thermal performance. However, to fully exploit the Ga2O3 power transistors, precise and reliable physics-driven models are crucial. Therefore, a comprehensive surface potential model has been developed in this work for a vertical Ga2O3 FinFET. The electric potential across the channel is explained by analyzing the two-dimensional (2D) Poisson equation employing parabolic approximation. Such a surface potential model is instrumental in determining the performance of the Ga2O3 FinFET as it affects the threshold voltage, the drain current, and fringing capacitance. Exploiting the surface potentials, a fringing capacitance model is derived which is crucial in analyzing the speed of the device in compact integrated circuits. In addition, statistical analysis of the Ga2O3 FinFET using the Monte Carlo simulation technique is performed to determine the leakage current fluctuation due to doping variations. The validation of the analytical model with experimental results confirms the effectiveness and prospects of the developed models in the rapid development and characterization of next-generation high-performance vertical Ga2O3 power transistors.

Characterization of migration behavior of organic electric-field regulator in polyethylene composite based on the synchronous spectra of space charge and polarization current

Organic electric-field regulator has the ability to suppress the space charge accumulation in the composite due to its electric-field and filler-content enhanced conductivity. Moreover, it can also migrate towards the high electric field region under the electric field gradient force, which further homogenizes the non-uniform electric field distribution. To characterize the migration behavior of the organic electric-field regulator in the composite under electric field, a distributed equivalent circuit model is firstly introduced, and it is solved to obtain the space-time distribution of conductivity in composite based on the synchronous spectra of space charge and polarization current. Combining the mathematical relationship between the direct current (DC) conductivity and electric field as well as regulator content, the space-time distribution of organic electric-field regulator in the composite is then settled. The allyloxy polyethylene glycol (APEG) is used as an example organic electric-field regulator and is filled into low-density polyethylene (LDPE) matrix to prepare composites. The DC conductivity and the synchronous spectra of space charge and polarization current are measured, respectively. The composites show noticeable electric-field and regulator-content enhanced conductivities. The space charge distribution shows that the APEG is capable of suppressing the space charge and homogenizing the electric field distribution compared with pure LDPE. The space-time distribution of regulator content in the 0.5 wt% composite is determined by the proposed method, and the regulator content near the electrodes is much higher than in the bulk, which is consistent with the infrared microscope images. The higher filler content means a higher DC conductivity, which lowers the high electric field near the electrodes and contributes to more uniform electric field distribution in the composite. The proposed method experimentally characterizes the migration behavior of the organic electric-field regulator in the polymer composite for the first time, and provides an effective way to study the migration mechanism of organic molecules (e.g. organic electric-field regulator) in the polymer composite.

XLPE high voltage insulation; A link between DC conductivity and microstructure

Crosslinked low-density polyethylene (XLPE) with its simple chemical composition is currently used as the most promising material for the insulation layer in extruded power cables. The processability of low-density polyethylene during extrusion followed by its crosslinking results in an infusible network that withstands high operating temperatures. One of the most important electrical properties that determine the insulation performance is the high voltage DC conductivity (direct-current conductivity under a high electric field). A lower DC conductivity at elevated temperatures decreases the losses in the insulation and hence lowers the risk of thermal runaway. The DC conductivity in pure polyethylene (PE) is predominantly due to electronic transport, and in the case of XLPE the DC conductivity is also affected by the combined effects of the concentration of crosslinking byproducts and the semicrystalline microstructure. The semicrystalline microstructure is complex, and it includes the lamellar morphology, the micrometer-sized superstructure, and the degree of crystallinity. These parameters inter-play to affect the final DC conductivity. This article first describes an overview of XLPE insulation of extruded HVDC cable and then addresses the less-known link among polymer processing, microstructure, and macroscale property (DC conductivity) of XLPE. The revealing of this link leads to a deep understanding of XLPE microstructure and possible ways to improve XLPE insulating properties during polymer processing.