High Electric Field Research Articles

A low-cost and convenient route of fabricating GaN films with P-type mixed microcrystalline and amorphous structure deposited via Ga target of magnetron sputtering

GaN, a third-generation semiconductor, has gained widespread attention owing to its high temperature resistance, wide bandgap, and high critical breakdown electric fields. Magnetron sputtering has a broad potential in the field of low-cost growth of GaN on account of high efficiency, superior quality, and convenient operation. However, challenges caused from the pure Ga targets with a huge refrigeration system need to be resolved for wide practices. Here, a new and cost-effective Ga target for magnetron sputtering was fabricated by utilizing the wetting properties of CuGa2 and Ga. Mixed microcrystalline and amorphous GaN films were obtained via reactive magnetron sputtering employing the Ga target. The average deposition rate is about 1.68 nm/min, and the average roughness is ∼7.45 ± 0.26 nm under 100 W of sputtering power. In addition, the sputtered GaN films were found to be wide-bandgap and p-type semiconductors with high transmittance, as revealed by x-ray photoelectron spectroscopy and absorption spectra. The GaN films display a bandgap of ∼3.60 eV and a transmittance exceeding 88.5% in the visible range. Furthermore, field-effect transistors and metal–semiconductor–metal photodetectors have been fabricated using the obtained GaN films, demonstrating favorable response characteristics. The prospects of microcrystalline/amorphous GaN films in sensing, power devices, and flexible electronics were forecasted. Overall, a low-cost and pervasive route of target fabrication process expands the possibilities of using low melting point metals in magnetron sputtering.

Detachable acoustofluidic droplet-sorter

BackgroundCell sorting is crucial in isolating specific cell populations. It enables detailed analysis of their functions and characteristics and plays a vital role in disease diagnosis, drug discovery, and regenerative medicine. Fluorescence-activated cell sorting (FACS) is considered the gold standard for high-speed single-cell sorting. However, its high cost, complex instrumentation, and lack of portability are significant limitations. Additionally, the high pressure and electric fields used in FACS can harm cell integrity. In this work, an acoustofluidic device was developed in combination with surface acoustic wave (SAW) and droplet microfluidics to isolate single-cell droplets with high purity while maintaining high cell viability. ResultHuman embryonic kidney cells, transfected with fluorescent reporter plasmids, were used to demonstrate the targeted droplet sorting containing single cells. The acoustofluidic sorter achieved a recovery rate of 81 % and an accuracy rate higher than 97 %. The device maintained a cell viability rate of 95 % and demonstrated repeatability over 20 consecutive trials without compromising efficiency, thus underscoring its reliability. Thermal image analysis revealed that the temperature of the interdigital transducer (IDT) during SAW operation remained within the permissible range for maintaining cell viability. SignificanceThe findings highlighted the sensitivity and effectiveness of the developed acoustofluidic device as a tool for single-cell sorting. The detachable microfluidic chip design enables the reusability of the expensive IDT, making it cost-effective and reducing the risk of cross-contamination between different biological samples. The results underscore its capability to accurately isolate individual cells on the basis of specific criteria, showcasing its potential to advance research and clinical applications requiring precise cell sorting methodologies.

Flexible High‐Temperature Polymer Dielectrics Induced by Ultraviolet Radiation for High Efficient Energy Storage

AbstractPolymer‐based dielectrics with fast electrostatic energy storage and release, are crucial for advanced electronics and power systems. However, the deterioration of insulation performance and charge–discharge efficiency of polymer dielectrics at elevated temperatures and high electric fields hinder the applications of capacitors in harsh environments. Herein, a facile and scalable approach is reported to fabricating flexible high‐temperature polymer dielectrics for high‐efficiency energy storage by ultraviolet irradiation. The resultant dielectric films exhibit an augment of 493% in energy density and exceeding 800% in discharge efficiency at 200 °C (3.2 J cm−3 and over 90% discharge efficiency at 480 M V−1m for irradiated polyetherimide (PEI), 0.54 J cm−3, and below 10% discharge efficiency at 400 MV m−1 for pristine PEI) and excellent cycle performance. The injected space charge is found to be the dominant contributor to energy loss during the charge–discharge process. Free radicals introduced by ultraviolet irradiation can act as deep traps to capture injected charge and suppress space charge migration. This work clarifies the contribution of space charge to energy loss and demonstrates the effectiveness of ultraviolet irradiation in improving the capacitive performance of high‐temperature polymer dielectrics. These findings provide a novel paradigm for the rational design of high‐temperature polymer dielectrics for high‐efficiency energy storage.

Design of High‐Entropy Relaxor Ferroelectrics for Comprehensive Energy Storage Enhancement

AbstractFor an ideal electrostatic energy storage dielectric capacitor, the pursuit of simultaneously high energy density and efficiency presents a formidable challenge. Typically, under an applied electric field, an increase in energy density is usually accompanied with a deteriorated energy storage efficiency due to the escalated hysteretic loss, which is harmful to the reliability of the capacitor. Thus, a well‐balanced performance of improved energy density and maintained high efficiency is highly demanded. In this work, a structure with amorphous phases embedded in polycrystalline nanograins using the entropy tactic, leading to a higher transport barrier of carrier is constructed. Hence, the hysteretic loss is largely suppressed at a high electric field and the high polarization is still sustained in the high‐entropy film. Consequently, an ultrahigh energy density of 139.5 J cm−3 with a high efficiency of 87.9%, and a high figure of merit of 1153 are simultaneously achieved in the high‐entropy Ba2Bi4Ti5O18‐based relaxor ferroelectric. This work offers a promising avenue in materials structure design for advanced high‐power energy storage applications.

Collection of serum albumin aggregate nanoparticles from human plasma by dielectrophoresis.

Dielectrophoresis (DEP) is a fast and reliable nanoparticle recovery method that utilizes nonuniform electric fields to manipulate particles based on their material composition and size, enabling recovery of biologically-derived nanoparticles from plasma for diagnostic applications. When applying DEP to undiluted human plasma, collection of endogenous albumin proteins was observed at electric field gradients much lower than predicted by theory to collect molecular proteins. To understand this collection, nanoparticle tracking analysis of bovine serum albumin (BSA) dissolved in 0.5× phosphate-buffered saline was performed and showed that albumin spontaneously formed aggregate nanoparticles with a mean diameter of 237nm. These aggregates experienceda dielectrophoretic force as a function of aggregate radius rather than the diameter of individual protein molecules which contributed to their collection. In high conductance buffer (6.8mS/cm), DEP was able to move these aggregates into regions of high electric field gradient, and in lower conductance buffer (0.68mS/cm), these aggregates could be moved into high or low gradient regions depending on the applied frequency. Disruption of BSA aggregates using a nonionic detergent significantly decreased the particle diameter, resulting in decreased dielectrophoretic collection of albumin which increased the collection consistency of particles of interest. These results provide techniques to manipulate albumin aggregates via DEP, which impacts collection of diagnostic biomarkers.

Au Nanoparticles@Si Nanowire Oligomer Arrays for SERS: Dimers Are Best.

We report the synthesis of vertically aligned silicon nanowire (VA-SiNW) oligomer arrays coated with Au nanoparticle (NP) monolayers via a combination of colloidal lithography, metal-assisted chemical etching, and directed NP assembly. Arrays of SiNW monomers (i.e., isolated NWs), dimers, and tetramers are synthesized, decorated with AuNPs, and tested for their performance in surface-enhanced Raman spectroscopy. The ∼20 nm AuNPs easily enter within the ca. 40 nm gaps of the SiNW oligomers, thus reaching the hot spot region. At 785 nm excitation, the AuNPs@SiNW dimer arrays provide the highest Raman signal, in agreement with electromagnetic simulations showing a high electric field enhancement at the Au/Si interface within the dimer gap region.

Exploring the Charge-Transport and Optical Characteristics of Organic Doublet Radicals: A Theoretical and Experimental Study with Photovoltaic Applications.

Herein, we present a series of stable radicals containing a trityl carbon-centered radical moiety exhibiting interesting properties. The radicals demonstrate the most blue-shifted anti-Kasha doublet emission reported so far with high color purity (full width at half-maximum of 46 nm) and relatively high photoluminescence quantum yields of deoxygenated toluene solutions reaching 31%. The stable radicals demonstrate equilibrated bipolar charge transport with charge mobility values reaching 10-4 cm2/V·s at high electric fields. The experimental results in combination with the results of TD-DFT calculations confirm that the blue emission of radicals violates the Kasha rule and originates from higher excited states, whereas the bipolar charge transport properties are found to stem from the particularity of radicals to involve the same molecular orbital(s) in electron and hole transport. The radicals act as the efficient materials for interlayers, passivating interfacial defects and enhancing charge extraction in PSCs. Consequently, this leads to outstanding performance of PSC, with power conversion efficiency surpassing 21%, accompanied by a remarkable increase in open-circuit voltage and exceptional stability.

Plasmon-Free Surface-Enhanced Raman Spectroscopy Using α-Type MoO3 Semiconductor Nanorods with Strong Light Scattering in the Visible Regime.

Recent developments in semiconductor-based surface-enhanced Raman scattering (SERS) have achieved numerous advancements, primarily centered on the chemical mechanism. However, the role of the electromagnetic (electromagnetic mechanism) contribution in advancing semiconductor SERS substrates is still underexplored. In this study, we developed a SERS substrate based on densely aligned α-type MoO3 (α-MoO3) semiconductor nanorods (NRs) with rectangular parallelepiped ribbon shapes with width measuring several hundred nanometers. These structural attributes strongly affect light transport in the visible range by multiple light scattering generated in narrow gaps between NRs, contributing to the improvement of SERS performance. Engineering the nanostructure and chemical composition of NRs realized high SERS sensitivity with an enhancement factor of 2 × 108 and a low detection limit of 5 × 10-9 M for rhodamine 6G (R6G) molecules, which was achieved by the stoichiometric NR sample with strong light scattering. Furthermore, it was observed that the scattering length becomes significantly shorter compared with the excitation wavelength in the visible regime, which indicates that light transport is strongly modified by mesoscopic interference related to Anderson localization. Additionally, high electric fields were found to be localized on the NR surfaces, depending on the excitation wavelength, similar to the SERS response. These optical phenomena indicate that electromagnetic excitation processes play an important role in plasmon-free SERS platforms based on α-MoO3 NRs. We postulate that our study provides important guidance for designing effective EM-based SERS-active semiconductor substrates.

Design optimization of wide-gate swing E-mode GaN HEMTs with junction barrier Schottky gate

To increase the gate swing, a GaN-based high-electron-mobility transistor with a junction barrier Schottky gate (JBS-HEMT) was proposed. Compared to conventional p-GaN Schottky gate HEMTs (Conv-HEMT), the high electric field at the surface is transferred to the pn junction inside the body, and the extended depletion region of the pn junction shields the surface Schottky contact interface for the JBS-HEMT. After fitting the model to the reported device, the proposed JBS-HEMT was simulated and optimized using the Sentaurus TCAD tool. The simulation results of the optimized JBS-HEMT demonstrate a high gate breakdown voltage (17.6 V), which is 158.5% higher than the gate breakdown voltage of the Conv-HEMT (11.1 V) and a lower gate leakage current of six orders of magnitude than the Conv-HEMT at the gate-to-source voltage of 10 V. The proposed JBS-HEMT exhibits a positive threshold voltage (1.68 V) and excellent threshold voltage stability, and the maximum threshold voltage drift of the JBS-HEMT (+0.237 V) is smaller than that of the Conv-HEMT (−0.714 V) under gate stress conditions. The peak transconductance of the JBS-HEMT (186 mS mm−1) at athe drain-to-source voltage of 10 V showed almost no reduction compared to the Conv-HEMT (189 mS mm−1), which solves the problem of decreased transconductance capability of the reported GaN HEMT with a p-n junction gate (PNJ-HEMT). It was confirmed that the JBS-HEMT has excellent gate stability and potential for power electronics applications.

Improvement of Boron Dopant Quantification Accuracy in Atom Probe Tomography via High Electric Field Analysis

Improvement of Boron Dopant Quantification Accuracy in Atom Probe Tomography via High Electric Field Analysis

Improved Energy Density at High Temperatures of FPE Dielectrics by Extreme Low Loading of CQDs.

Electrostatic capacitors, with the advantages of high-power density, fast charging-discharging, and outstanding cyclic stability, have become important energy storage devices for modern power electronics. However, the insulation performance of the dielectrics in capacitors will significantly deteriorate under the conditions of high temperatures and electric fields, resulting in limited capacitive performance. In this paper, we report a method to improve the high-temperature energy storage performance of a polymer dielectric for capacitors by incorporating an extremely low loading of 0.5 wt% carbon quantum dots (CQDs) into a fluorene polyester (FPE) polymer. CQDs possess a high electron affinity energy, enabling them to capture migrating carriers and exhibit a unique Coulomb-blocking effect to scatter electrons, thereby restricting electron migration. As a result, the breakdown strength and energy storage properties of the CQD/FPE nanocomposites are significantly enhanced. For instance, the energy density of 0.5 wt% CQD/FPE nanocomposites at room temperature, with an efficiency (η) exceeding 90%, reached 9.6 J/cm3. At the discharge energy density of 0.5 wt%, the CQD/FPE nanocomposites remained at 4.53 J/cm3 with an efficiency (η) exceeding 90% at 150 °C, which surpasses lots of reported results.

High-throughput phase field simulation and machine learning for predicting the breakdown performance of all-organic composites

All-organic dielectric polymers are materials of choice for modern power electronics and high-density energy storage, and their performance can be significantly improved by doping trace amounts of organic molecular semiconductors with strong electron-affinity energy to suppress charge conduction losses. Insight into the breakdown mechanism of polymers/organic molecular semiconductor composites is essential for the design of high-performance dielectric polymers. This study investigates the impact of the doping concentration of organic molecular semiconductors, dielectric constants, and trap depths on the breakdown performance of dielectric polymers under high temperature and electric fields. A modified phase-field model, incorporating deep traps and carriers’ coulomb capture radius, has been developed to facilitate high-throughput simulations of electrical breakdown in polymer/organic molecular semiconductor composites. This work accurately predicted the breakdown strength of all-organic composites using high-throughput phase-field simulation data as input for machine learning, which provides crucial theoretical support for designing all-organic composite dielectric polymers for energy storage capacitors under extreme conditions.

Interface engineering of polymer composite films for high-temperature capacitive energy storage

Polymer film capacitors encounter challenges in harsh conditions of high temperatures and electric fields because of large conduction loss and degraded breakdown strength (Eb). Herein, an interface engineering strategy is proposed to fluorinate the interfaces between the polyetherimide (PEI) matrix and wide bandgap boron nitride nanosheets (BNNSs) fillers. The composite films exhibit high-performance capacitive energy storage with a remarkable energy density of 5.73 J/cm3 and an ultrahigh efficiency of 91.22 % in conditions of 575 kV/mm and 150 °C. By adopting interfacial fluorination, the band structure of BNNSs is tailored to achieve a type II band alignment with PEI, promoting the dual trapping for both electrons and holes. It highly suppresses leakage current and reduces conduction loss. Typically, introducing fillers can compromise the properties of interfacial layers, creating weak points that trigger breakdown. Conversely, fluorinated interfaces exhibit an increased Young’s modulus and a reduced dielectric constant. According to the electromechanical breakdown theory, the interfacial Eb is increased. The breakdown phase propagation along the interfaces is thereby impeded, ultimately resulting in a further increase in overall Eb, reaching up to 589 kV/mm at 150 °C. Fluorinated interface engineering addresses interfacial challenges posed by fillers, enabling high-temperature energy storage capability in PEI-based capacitors.

Pilot Study on the Production of Negative Oxygen Ions Based on Lower Voltage Ionization Method and Application in Air Purification

In the current highly industrialized living environment, air quality has become an increasing public health concern. Natural environments like forests have excellent air quality due to high concentrations of negative oxygen ions originating from low-voltage ionization, without harmful ozone. Traditional negative oxygen ion generators require high voltage for corona discharge to produce ions. However, high voltage can increase electron collisions and excitations, leading to more dissociation and recombination of oxygen molecules and consequently higher ozone production. To address the challenge of generating negative oxygen ions without accompanying ozone production, this study designed and constructed a low-voltage negative oxygen ion generator based on nanometer-tip carbon fiber electrodes. The advantage of this device lies in the high curvature radius of carbon fibers, which provides high local electric field strength. This allows for efficient production of negative oxygen ions at low operating voltages without generating ozone. Experiments demonstrated that the device can efficiently generate negative oxygen ions at a working voltage as low as 2.16 kV, 28% lower than the lowest voltage reported in similar studies. The purification device manufactured in this study had a total decay constant for PM2.5 purification of 0.8967 min−1 within five minutes, compared to a natural decay constant of only 0.0438 min−1, resulting in a calculated Clean Air Delivery Rate (CADR) of 0.1535 m3/min. Within half an hour, concentrations of PM2.5, PM1, PM10, formaldehyde, and TVOC were reduced by 99.09%, 99.40%, 99.37%, 94.39%, and 99.35%, respectively, demonstrating good decay constants and CADR. These findings confirm its effectiveness in improving indoor air quality, highlighting its significant application value in air purification.

Excellent low-E energy storage and fluorescence temperature sensing features in Bi0.5Na0.5TiO3-based transparent ceramics

Transparent dielectric ceramics with ultrafast discharge rates and gigantic power densities are ideal candidates for transparent pulse capacitors (TPCs). However, the requirement of a high external electric field and inferior temperature stability hinder practical applications. (Bi0.5Na0.5)TiO3-based ceramics exhibit large polarization and two characteristic dielectric peaks, easy to obtain high energy-storage density under low electric fields (low-E) and maintain stable energy-storage performance (ESP) within a wide temperature range. However, their low optical transmittance (T%) limits their development into TPCs. In this work, to concurrently obtain high T% and excellent ESP and stability under low-E conditions, we propose a collaborative optimization strategy for determining the regulations of grain size, bandgap energy and domain structure. The results show that the pellucidity and energy-storage characteristics improve with decreasing grain and domain sizes. A relatively high T% of 45.6 % (at 710 nm) and recoverable energy-storage density (Wrec ∼ 3.46 J cm−3 at 197 kV cm−1) are obtained for the (1-x)[0.85(Bi0.5-3yNa0.5-yYb3yHoyTiO3)-0.15SrZrO3]-xBaHfO3 ceramics. Additionally, the dielectric temperature stability also results in splendid storage temperature stability (ΔWrec/Wrec < 3.1 % in the range of 0–200 °C). Importantly, codoping Ho/Yb in the ceramics induces excellent fluorescence temperature sensing feature. The multifunctional TPCs have application potential in the field of search and rescue signal transmission, providing ideas for developing novel optoelectronic devices.

High Curvature of Polymer‐Based Miniaturized Flexible Actuator at Very Low Electric Field

AbstractThe use of high electric fields, as well as pre‐stressing, are the two main obstacles to the widespread use of poly(vinylidene fluoride (PVDF)‐based actuators. In response, a new double‐sided multilayer device has been developed which, coupled with a polarization procedure, enables high bending performance at low voltages. The actuator's symmetry allows zero bending at rest, while the high number of layers enables a strong field to be maintained while reducing the applied voltage. X‐ray and permittivity studies reveal the ultimate links between the microscopic material displacement and the actuator deflection. These results, coupled with the analytical model developed in this work, demonstrate that the optimization of complex multilayer systems requires a detailed understanding of mechanics, design, and microstructure. Experimental, analytical and finite element results confirm that such a double‐sided multilayer actuator is of 50% more efficient than a conventional single‐sided actuator, up to 40 V µm−1. These achievements open up new prospects for PVDF‐based actuators in application of healthcare, such as arterial navigation.

Effects of quenching on domain switching and electric field-induced phase transformations in Na0.5Bi0.5TiO3-NaNbO3 ceramics

Quenching from high temperatures has been identified as a useful means to enhance the piezoelectric properties and thermal stability of bismuth-based perovskite ferroelectrics. In the present work, it is demonstrated that quenching leads to improvement of depolarization temperature, ferroelectric and piezoelectric properties in Na0.5Bi0.5TiO3-NaNbO3 (NBT-0.1NN) ceramics. In-situ synchrotron x-ray diffraction measurements indicated an irreversible transformation from cubic to coexisting cubic and rhombohedral phases during the application of a high electric field, for both as-sintered and quenched ceramics. These results confirm the non-ergodic relaxor ferroelectric nature of the materials. DC poling induced a transformation to single-phase rhombohedral structure in both cases, with highly textured domain configurations. These well-oriented ferroelectric domain states were relatively stable under subsequent bipolar electric field cycling. For the pre-poled NBT-0.1NN ceramics, the quenched samples were found to exhibit the highest intrinsic (lattice strain) and extrinsic (domain switching) contributions to electrostrain, due to the increased rhombohedral distortion.

Ligand‐Pinning Induced Size Modulation of CsPbI3 Perovskite Quantum Dots for Red Light‐Emitting Diodes

AbstractPerovskite quantum dots (PQDs) show high potential for new‐generation light‐emitting diodes (LEDs) due to their outstanding optoelectronic properties. Even though the red PQD‐LEDs can be realized through mixing halide in the PQDs to tune their spectroscopies, the PQDs may suffer from phase separation under a high electric field, predominantly affecting LED applications. Herein, a ligand‐pinning‐assisted approach is reported to tune the spectroscopies of CsPbI3 PQDs, in which vinyl phosphonic acid (VPA) is applied as function ligands to regulate the nucleation and growth of PQDs during the synthesis. Systematically experimental studies and theoretical calculations are conducted to comprehensively understand the functions of the VPA ligands during the PQD synthesis, which reveals that the VPA ligands with high binding energy with Pb2+ cations could firmly anchor on the surface matrix of PQDs without desorption, regulating the growth of PQDs and thus resulting in tunable spectroscopies being realized. Meanwhile, VPA could also renovate the defective surface matrix of PQDs, substantially diminishing trap‐induced nonradiative recombination. Consequently, red PQD‐LEDs deliver a high external quantum efficiency of 22.83%, which is significantly improved compared with the control devices. This work provides a new avenue to tune the spectroscopies of PQDs toward high‐performing LEDs.

LiF-Rich Alloy-Doped SEI Enabling Ultra-Stable and High-Rate Li Metal Anode.

Li metal is regarded as the "Holy Grail" in the next generation of anode materials due to its high theoretical capacity and low redox potential. However, sluggish Li ions interfacial transport kinetics and uncontrollable Li dendrites growth limit practical application of the energy storage system in high-power device. Herein, separators are modified by the addition of a coating, which spontaneously grafts onto the Li anode interface for in situ lithiation. The resultant alloy possessing of strong electron-donating property promotes the decomposition of lithium bistrifluoromethane sulfonimide in the electrolyte to form a LiF-rich alloy-doped solid electrolyte interface (SEI) layer. High ionic alloy solid solution diffusivity and electric field dispersion modulation accelerate Li ions transport and uniform stripping/plating, resulting in a high-power dendrite-free Li metal anode interface. Surprisingly, the formulated SEI layer achieves an ultra-long cycle life of over 8000 h (20,000 cycles) for symmetric cells at a current density of 10 mA cm-2. It also ensures that the NCM(811)//PP@Au//Li full cell at ultra-high currents (40 C) completes the charging/discharging process in only 68 s to provide high capacity of 151 mAh g-1. The results confirm that this scalable strategy has great development potential in realizing high power dendrite-free Li metal anode.

LiF‐Rich Alloy‐Doped SEI Enabling Ultra‐Stable and High‐Rate Li Metal Anode

AbstractLi metal is regarded as the “Holy Grail” in the next generation of anode materials due to its high theoretical capacity and low redox potential. However, sluggish Li ions interfacial transport kinetics and uncontrollable Li dendrites growth limit practical application of the energy storage system in high‐power device. Herein, separators are modified by the addition of a coating, which spontaneously grafts onto the Li anode interface for in situ lithiation. The resultant alloy possessing of strong electron‐donating property promotes the decomposition of lithium bistrifluoromethane sulfonimide in the electrolyte to form a LiF‐rich alloy‐doped solid electrolyte interface (SEI) layer. High ionic alloy solid solution diffusivity and electric field dispersion modulation accelerate Li ions transport and uniform stripping/plating, resulting in a high‐power dendrite‐free Li metal anode interface. Surprisingly, the formulated SEI layer achieves an ultra‐long cycle life of over 8000 h (20,000 cycles) for symmetric cells at a current density of 10 mA cm−2. It also ensures that the NCM(811)//PP@Au//Li full cell at ultra‐high currents (40 C) completes the charging/discharging process in only 68 s to provide high capacity of 151 mAh g−1. The results confirm that this scalable strategy has great development potential in realizing high power dendrite‐free Li metal anode.