Large Electric Field Research Articles

ICRF resonance cones in the low-density scrape-off-layer of ASDEX Upgrade

Abstract The ICRF slow wave is a potential carrier for parallel RF electric fields known to cause unwanted plasma-wall interactions in magnetic confinement fusion experiments.
In nowadays machines the slow wave is usually confined to the far scrape-off layer or the limiter shadow, but conditions in future experiments and reactors may allow the slow wave to be propagative in a larger region.

Simulations with RAPLICASOL for various geometries show that the ICRF slow waves appear as the so-called resonance cones characterized by large localized electric fields.
The resonance cones emerge from the points along the plasma-antenna interface where (in the cold plasma approximation) the radio frequency electric field diverges.
We demonstrate that in the parameter range of interest, the propagation of the resonance cones in a plasma with a density gradient is defined by a simple geometric model, using the local plasma density and the frequency as input parameters.
In the context of experiments at ASDEX Upgrade, simulations illustrate that the resonance cones can emerge from a single tile of the ICRF antenna limiter.
Experiments at the Ion-cyclotron System Hardware Test ARrangement (ISHTAR) were conducted to test the detection principle in a simple environment.
In agreement with simulations and with predicted characteristics which depend on operation parameters, the resonance cones are excited by an RF antenna and propagate through the relatively homogeneous plasma in ISHTAR. 
The cones are detected at a distance from the antenna using two probes scanning through the plasma.
In ASDEX Upgrade, a single tile of an antenna limiter was modified to launch RF power into a specially tailored low-density scrape-off layer.
Probes at the midplane manipulator were then used to detect the wave electric fields at a distance from the RF source.
The detected RF signals show that the signal maxima are located close to the lower hybrid resonance density and are highest when the source and the probes are connected along magnetic field lines.
These observations agrees with the model for resonance cones from the simulations.

Improving the polarization switching properties of wurtzite AlN by introducing IV–IV/AlN superlattice and P-doping

The large coercive electric field is the main obstacle for the application of wurtzite ferroelectrics in the memory devices. To explore the effective methods to reduce the coercive electric field of wurtzite ferroelectrics, in this work, after screening a series of possible candidates, (MC)1/(AlN)n (M = Ti, Zr) superlattices and anion P-doping are both chosen to regulate the switching energy barrier of wurtzite AlN based on the density functional theory calculations. It is found that the polarization switching energy barriers of wurtzite AlN gradually decrease by increasing the ratio of the MC (M = Ti, Zr) layer. When the ratio of the MC layer is up to 33%, the polarization switching energy barriers of (TiC)1/(AlN)n and (ZrC)1/(AlN)n are decreased by 68% and 55%, respectively, compared with that of pure wurtzite AlN. The anionic P-doping in AlN results in a 48% lower energy barrier. Also, the ferroelectric polarization in the designed superlattices and P-doped AlN is well maintained compared to pure AlN. Thus, the results show that the (MC)1/(AlN)n (M = Ti, Zr) superlattices and anion P-doping approaches are effective in improving the polarization switching properties of wurtzite AlN.

Manipulating microfluidic freezing phenomena of electrolytes using electromagnetic stimuli

We investigate the transients of freezing of a flowing electrolyte between cold microfluidic domain walls. We explore the novel effect of morphing the solidification characteristics of the flow system using externally applied electric and magnetic fields. The spatiotemporal evolution of solid–liquid (S–L) interface is simulated using arbitrary Lagrangian–Eulerian approach. We show that the solidification rate is highly influenced by advection effects, and for increasingly high liquid flow rates, solidification stops way before the event of channel closure. Due to electro-magneto-hydrodynamic interactions, a substantial decrease in channel closing time is observed with imposed fields. However, a considerably large electric field may lead to a significant increase in Joule heating, which marginally increases the channel closing time. The magnetic field is observed to produce smoother, curved frozen layers. The electric field tends to enhance the solidification rates more uniformly along the channel length, resulting in much flatter S–L front, hence trapping lesser liquid at channel closure. The results reveal that freezing kinetics in microfluidic devices can be morphed by using electric and magnetic fields, governed by the electric field number (En) and Hartmann number (Ha). The findings may be crucial for phase-change based microfluidic-systems, micro-castings, flow freezing valves, and diodes.

Why Doesn't the Observed Field‐Aligned Current Saturate With Increasing Interplanetary Electric Field?

AbstractTheoretical studies indicate that electric potential saturation in a polar cap ionosphere is regulated by the limited reconnection rate at the magnetopause associated with field‐aligned currents (FACs), predicting the possible saturation of FACs under large interplanetary electric field (IEF). However, recent statistical studies have shown that observed FACs increase linearly with IEF. To reconcile this disparity, numerical experiments are conducted to explore the response of FACs under large IEF. Results show that FACs may exhibit either linear or saturated responses, depending on the Alfvén Mach number. The magnetospheric closure paths of region 1 currents differ significantly between the linear and saturated conditions. In the linear case, essential parts of the region 1 current extend toward dayside and connect to the magnetopause currents, whereas these parts of currents almost disappear in the saturation state. Saturation usually occurs under sub‐Alfvénic solar wind conditions, so the observed FACs generally grow linearly with IEF.

Improving the Nonvolatile Memory Characteristics of Sol-Gel-Processed Y2O3 RRAM Devices Using Mono-Ethanolamine Additives.

In this study, Y2O3-based resistive random-access memory (RRAM) devices with a mono-ethanolamine (MEA) stabilizer fabricated using the sol-gel process on indium tin oxide/glass substrates were investigated. The effects of MEA content on the structural, optical, chemical, and electrical characteristics were determined. As the MEA content increased, film thickness and crystallite size decreased. In particular, the increase in MEA content slightly decreased the oxygen vacancy concentration. The decreased film thickness decreased the physical distance for conductive filament formation, generating a strong electric field. However, owing to the lowest oxygen vacancy concentration, a large electrical field is required. To ensure data reliability, the endurance cycles across several devices were measured and presented statistically. Additionally, endurance performance improved with the increase in MEA content. Reduced oxygen vacancy concentration can successfully suppress the excess formation of the Ag conductive filament. This simplifies the transition from the high- to the low-resistance state and vice versa, thereby improving the endurance cycles of the RRAM devices.

Hydrogen- assisted synthesis of defective triazine/heptazine homostructured nanosheets for efficient CO2photoreduction.

Homostructure construction has been demonstrated to be an effective way for boosting the photocatalytic activity of polymeric carbon nitride. However, the contribution of the intrinsic activity of molecular fragments in the catalytic performance of homostructured carbon nitride is yet to be explored. In this paper, a facile hydrogen-assisted strategy was used to synthesize triazine/heptazine intermolecular homojunctions (g-C3N4(MU-H)) with an ultrathin and defective structure, via the co-pyrolysis of melamine and urea precursors. Experimental characterizations and theoretical calculations revealed the copolymerization of triazine- and heptazine-based carbon nitride generated a homostructured interface with a large build-in electric field for efficient separation of photogenerated carriers. Due to the synergestic effect between the homostructured interface and nitrogen vacancies, as-synethesized g-C3N4(MU-H) exhibited an outstanding activity for photocatalytic CO2 reduction, with a CO yield rate of 14.45 μmol h-1, which was 23.5 and 3.64 times higher than those of bulk g-C3N4 and g-C3N4(M-H) synthesized from a single precursor, respectively. This study provides a new avenue for optimizing the charge separation efficiency of CO2 photoreduction catalysts by constructing intramolecular homojunction.

Modeling of planar germanium hole qubits in electric and magnetic fields

Hole-based spin qubits in strained planar germanium quantum wells have received considerable attention due to their favorable properties and remarkable experimental progress. The sizeable spin-orbit interaction in this structure allows for efficient qubit operations with electric fields. However, it also couples the qubit to electrical noise. In this work, we perform simulations of a heterostructure hosting these hole spin qubits. We solve the effective mass equations for a realistic heterostructure, provide a set of analytical basis wavefunctions, and compute the effective g-factor of the heavy-hole ground state. Our investigations reveal a strong impact of highly excited light-hole states located outside the quantum well on the g-factor. We find that sweet spots, points of operations that are least susceptible to charge noise, for out-of-plane magnetic fields are shifted to impractically large electric fields. However, for magnetic fields close to in-plane alignment, partial sweet spots at low electric fields are recovered. Furthermore, sweet spots with respect to multiple fluctuating charge traps can be found under certain circumstances for different magnetic field alignments. This work will be helpful in understanding and improving the coherence of germanium hole spin qubits.

Strong Energy Conversion by a Ribbon‐Like Magnetic Structure in Tailward High‐Speed Flow

AbstractThe tailward high‐speed flows, in which various kinetic processes and magnetic structures can be embedded, are usually produced by the magnetic reconnection in the Earth's magnetotail. Here, using high‐resolution measurements from the Magnetospheric Multiscale (MMS) mission, we report an intense current in the tailward high‐speed flow. The current density can reach ∼180 nA/m2 and is primarily carried by electrons. Taking advantage of the First‐Order Taylor Expansion (FOTE) method, we reveal that such an intense current is associated with a ribbon‐like magnetic structure. A large electric field, reaching ∼90 mV/m, is also observed at the magnetic structure. The Hall term dominates the electric field, however, the contribution from the pressure gradient term and the electron inertial term is nonnegligible and can lead to strong energy conversion (E ⋅ J > 2 nW/m3) through the synergistic action with the intense current. This study improves the understanding of the current behaviors and energy conversion associated with magnetic structures in the Earth's magnetotail.

Universal droplet propulsion by dynamic surface-charge wetting

Controllable droplet propulsion on solid surfaces plays a crucial role in various technologies. Many actuating methods have been developed; however, there are still some limitations in terms of the introduction of additives, the versatilities of solid surfaces, and the speed of transportation. Herein, we have demonstrated a universal droplet propulsion method based on dynamic surface-charge wetting by depositing oscillating and opposite surface charges on dielectric films with unmodified surfaces. Dynamic surface-charge wetting propels droplets by continuously inducing smaller front contact angles than rear contact angles. This innovative imbalance is built by alternately storing and spreading opposite charges on dielectric films, which results in remarkable electrostatic forces under large gradients and electric fields. The method exhibits excellent droplet manipulation performance characteristics, including high speed (~130 mm/s), high adaptability of droplet volume (1 μL–1 mL), strong handling ability on non-slippery surfaces with large contact angle hysteresis (CAH) (maximum angle of 35°), significant programmability and reconfigurability, and low mass loss. The great application potential of this method has been effectively demonstrated in programmable microreactions, defogging without gravity assistance, and surface cleaning of photovoltaic panels using condensed droplets.

Ultrafast Switching of Sliding Polarization and Dynamical Magnetic Field in van der Waals Bilayers Induced by Light.

Sliding ferroelectricity is a unique type of polarity recently observed in van der Waals bilayers with a suitable stacking. However, electric-field control of sliding ferroelectricity is hard and could induce large coercive electric fields and serious leakage currents that corrode the ferroelectricity and electronic properties, which are essential for modern two-dimensional electronics and optoelectronics. Here, we proposed laser-pulse deterministic control of sliding polarization in bilayer hexagonal boron nitride by first principles and molecular dynamics simulation with machine-learned force fields. The laser pulses excite shear modes that exhibit certain directional movements of lateral sliding between bilayers. The vibration of excited modes under laser pulses is predicted to overcome the energy barrier and achieve the switching of sliding polarization. Furthermore, it is found that three possible sliding transitions-between AB (BA) and BA (AB) stacking-can lead to the occurrence of dynamical magnetic fields along three different directions. Remarkably, the magnetic fields are generated by the simple linear motion of nonmagnetic species, without any need for more exotic (circular, spiral) pathways. Such predictions of deterministic control of sliding polarization and multistates of dynamical magnetic field thus expand the potential applications of sliding ferroelectricity in memory and electronic devices.

Modulating the fracture behavior of interface cracks via electric field gradient in flexoelectric solids

Interface cracks seriously affect the performance and service life of layered electronic devices. At nanoscale, the electric field concentration can be generated at the tip of insulating cracks by solely applying a uniform electric field loading, resulting in a large electric field gradient and thus inducing a significant converse flexoelectric effect. The deformation generated by the converse flexoelectric effect is expected to achieve crack shielding, however, its mechanism is still not clear. In this paper, the role of electric field gradients on interface crack behavior is studied by the collocation mixed finite element method (MFEM) and the J-integral. The result shows that the electric field gradient generated by a uniform electric displacement loading can reduce the J-integral of crack tips, achieving crack shielding. The result provides new ideas for the study of failure assessment, nanoscale fracture experiment and others.

Nonlinear Electrophoresis of Microparticles in Shear Thinning Fluids.

The nonlinear electric field dependence of particle electrophoresis has been demonstrated to occur in Newtonian fluids for highly charged particles under large electric fields. It has also been predicted to arise from the rheological effects of non-Newtonian fluids even at small electric fields. We present in this work an experimental verification of nonlinear electrophoresis in shear thinning xanthan gum solutions through a straight rectangular microchannel. The addition of polymer into a Newtonian buffer solution is found to change the electric field dependence from linear to superlinear for electroosmotic, electrokinetic, and electrophoretic velocities. The nonlinear index of each of these electrokinetic phenomena increases with the increasing polymer or buffer concentration, among which electrophoresis exhibits the strongest nonlinearity. Both these observed trends are captured by a dimensionless electrokinetic shear thinning number that depends on the power-law index of fluid viscosity and the Debye length.

Large power dynamic range microwave electric field sensing in a vapor cell

Large power dynamic range microwave electric field sensing in a vapor cell

Tunable electronic and optical properties of a Type-ⅡViolet Phosphorus/MoS2 heterojunction: First-principles calculation

Photodetectors based on heterostructures have garnered significant research interest due to their superior self-powering and responsiveness capabilities. In this work, the optoelectronic properties of a violet phosphorus (VP/MoS2)/MoS2 heterojunction are investigated through first-principles calculations. The results reveal that the VP/MoS2 heterojunction possesses an indirect bandgap and a type-II band alignment. The interface potential drop (Ep) of the VP/MoS2 heterojunction is 5.45 eV by studying the interfacial interaction, suggesting the formation of a large in-built electric field and an excellent self-powering capability. The absorption coefficient of VP/MoS2 heterojunction are significantly higher in the UV and visible regions. Under biaxial strain, the VP/MoS2 heterostructure can undergo transformations from a semiconductor to a metal, from an indirect to a direct bandgap, and from a type-II to a type-I energy band structure. Moreover, the light trapping ability in the near-infrared region is significantly enhanced. These findings underscore the broader potential application of VP/MoS2 heterostructures in high-performance optoelectronic devices.

High-frequency irreversible electroporation ablation for the prostate in Beagle dogs.

Ablation procedures have garnered significant attention as a minimally invasive treatment of prostate diseases. However, the feasibility and safety of applying high-frequency irreversible electroporation (H-FIRE) to ablate the Beagle prostate for benign prostatic hyperplasia (BPH) treatment have not been thoroughly explored, the appropriate range of parameters has not been determined. In order to ensure the feasibility and safety of prostate ablation surgery, we conducted a study using Beagle dogs as subjects to investigate prostate tissue. We utilized a composite steep pulse therapy device to perform ablations on 26 lateral lobes of the prostate in 13 Beagles, employing various parameters for different needle distances. The effectiveness of this device was assessed through the observation of the ablation area, intraoperative muscle tremors, postoperative hematological examination, and gross inspection. The findings of our study revealed that 1,000 to 2,000 v/cm in electric field strength, combined with 5 µs pulse width and pulse number 100, is a safe parameter range for ablation of prostate tissue. At the same time, the large electric field strength (2,000 v/cm) has the best ablation effect with the biggest continuous and thorough ablation area. All parameters of H-FIRE were safe for Beagles. H-FIRE ablation for prostate is safe and effective in dogs, which has the potential to be a useful addition to the range of minimally invasive treatments available for the treatment of BPH against this backdrop of increasing surgical practice.

Electrochemical migration and dendrite growth between two electrodes: Experiments and Brownian dynamics simulations

Electrochemical migration (ECM) is a common cause of failure in printed circuit boards (PCB) due to dendrite growth between exposed metallic conductors under moisture especially in the presence of flux residues. Understanding this phenomenon, therefore, is of interest from technological and economical points of view. Here, we report experimental results of water drop tests on surfaces contaminated by various amount of flux residues, which are supplemented with Brownian dynamics (BD) results to gain molecular insight into ECM and dendrite growth. BD is a particle simulation method where the ions are modeled explicitly. We show dendrite growth curves (the length of the longest dendrite as a function of time) obtained from visual examination with digital video microscope and from BD simulations. Results for the time to failure are also shown for various values of the electric field strength and cation (Sn2+) concentration (dilution of contamination). We report a mapping of experimental and simulation results that is necessary due to the large concentrations and electric field strengths used in the BD simulations.

Remarkable Plasmonic Enhanced Luminescence of Ce3+doped Lanthanide Downconversion Nanoparticles in NIR‐II Window by Silver Hole‐Cap Nanoarrays

AbstractLanthanide downconversion nanoparticles (DCNPs) have huge potential in biosensing and imaging applications in the NIR‐II window. However, DCNPs inherently suffer from low quantum efficiency, due to low absorption cross‐section and the restricted doping concentration of lanthanide ions. In this work, a combined strategy for downconversion luminescence in the NIR‐II window is investigated by the integration of Ce3+ ions into the conventional NaYF4: Yb3+, Er3+ DCNPs and incorporation of periodic silver hole‐cap coupled Nanoarrays (Ag‐HCNAs) simultaneously. Over two orders of magnitude, luminescence enhancement is achieved by the combination of optimized Ce3+ doping and plasmonic effects, compared to NaYF4: Yb3+, Er3+ DCNPs immobilized on the glass substrate. Moreover, 3D Finite‐Difference Time‐Domain (FDTD) simulations and time‐resolved luminescence measurements are combined to gain important insights into the mechanism of downconversion luminescence enhancement. The results show that there is a large electric field enhancement between the Ag nanoholes and the Ag hemisphere cap at 980 nm (excitation enhancement), while the lifetime shortening at 1525 nm revealed an increased radiative decay rate and enhanced quantum yield (emission rate enhancement). The strategy for downconversion luminescence enhancement demonstrated in this work holds a significant potential for advancing the next generation biosensing and bioimaging based on DCNPs in the NIR‐II window.

Significantly enhanced high-temperature energy storage performance for polymer composite films with gradient distribution of organic fillers

Film capacitors as one of the most important electronic devices are heading in large capacity, heightened integration and excellent extreme-condition tolerance, which faces the challenges in maintaining outstanding performance under harsh conditions of high temperature and large electric field. Nonetheless, polymer capacitive films, which are renowned for their exceptional thermal stability, experience an escalation in conduction losses at elevated temperatures, resulting in degradation of energy storage performance. This study presents the gradient distribution of organic fillers content in all-organic polymer capacitive films utilizing electrospinning technique, the significantly improved high-temperature energy storage performance has been achieved. Glucose (GLC), a weak polar molecule rich in hydroxyl groups, is blended with the most promising polyetherimide (PEI). Experimental and theoretical calculations confirm that the formed hydrogen bond between GLC and PEI acts as a trapping site for capturing carriers and suppressing conduction losses. Furthermore, the spatial distribution of organic fillers was designed on the basis of direct mixing. The results demonstrate that the gradient composite film introduces interlayer interfacial polarization, while the dielectric mismatch between adjacent layers increases the height of potential barriers for the charge carriers across the interfaces, thereby achieving a synergistic enhancement of dielectric response and insulation strength. The maximum discharge energy density of 6.52 J/cm3 with an efficiency of 85.6 % has been achieved at 150℃ for the modified capacitive films. This work establishes a decoupling relationship between permittivity and electric breakdown strength, offering insights for the advancement of polymer films with outstanding energy storage capabilities in extreme environments.

Spin-filtering properties of topological structures based on stanene and bismuthene nanoribbons with one edge magnetism

The transport properties of spin filters based on two-dimensional magnetic topological insulators (TI) with magnetism at one edge are theoretically studied. The non-equilibrium-Green’s-function (NEGF) formalism based on density functional theory (DFT) derived Hamiltonian is used to study the one-way helical edge states in these structures. We investigated the electronic and magnetic properties of stanene and bismuthene nanoribbons with various metal edge modifications. Our DFT simulations predict the formation of one-way helical edge states in stanene nanoribbons with asymmetric edge passivation. Our results suggest that the spin filtering properties of such structures outperform a comparable spin filter based on spin-polarized quantum-anomalous-Hall effect, as it bypasses a need for a strict interplay of magnetism, topology, and a large electric field (around 2 V gate voltage difference).

THz generation by AlGaAs/GaAs heterostructured p-i-n diode

The generation of terahertz radiation by heterostructure p-i-n AlxGa1−xAs/GaAs diodes excited by femtosecond optical pulses was studied experimentally and using the Monte Carlo method. It is shown that when the reverse bias varies, the terahertz generation mechanism changes. With a positive bias on the p-i-n diode, the THz generation mechanism is due to the reflection of the photoexcited electrons from the interface. With a large internal electric field, THz generation in the p-i-n diode occurs due to the acceleration of electrons at the ballistic stage of their movement in the electric field to velocities significantly exceeding the steady state velocity (“velocity overshoot”). The subsequent sharp decrease in velocity of electrons is associated with their inter-valley transitions from the Γ-valley to the L-valley of the conduction band. At electric fields less than 22 kV/cm, the effect of electric field screening by photoexcited carriers has a significant impact on the formation of photocurrent and, accordingly, on the THz generation mechanism. As the reverse bias decreases, this effect leads to a shift in the maximum of the THz pulse toward shorter times and it begins to dominate at electric fields less than 10 kV/cm.