Bias Electric Field Research Articles

Resonant tunneling properties of laser dressed hyperbolic Pöschl-Teller double barrier potential

We examine the resonant tunneling properties of the laser-dressed hyperbolic Pöschl-Teller double quantum barrier structure. We use the non-equilibrium Green's function method to investigate structure parameters and electric field bias on the transmission properties of the system. The transmission probabilities and resonance energy levels are significantly influenced by the well widths and barrier heights. The barrier height increases, resonance energy levels shift toward higher values, and the resonance peak width narrows, leading to sharper and more selective tunneling behavior. Our results show that increasing the electric field bias leads to a decrease in the transmission probability at the first resonance peak, but this effect is not as strong for the subsequent peaks. Moreover, we find that changes in the laser field's parameter and structure parameters allow for fine control over the electronic spectra, allowing for modifications like red or blue shifts based on particular needs. The significance of comprehending the interaction among structural factors, external fields, and transmission qualities in quantum barrier structures is highlighted by our research, providing valuable information for the development and enhancement of electronic and optoelectronic systems with customized functionality. Our findings show the laser field has a considerable impact on resonant tunneling properties, opening the door to new device applications.

Simulation of Dendrite Growth with a Diffusion-Limited Aggregation Model Validated by MRI of a Lithium Symmetric Cell during Charging

Lithium metal batteries offer high energy density but are challenged by dendrite growth, which can lead to short circuits and battery failure. Multiple models with varying degrees of accuracy and computational cost have been developed to understand and predict dendrite growth. This study presents a simple model to simulate macroscale dendrite growth on lithium metal electrodes. The model uses a 3D single-particle Diffusion-Limited Aggregation (DLA) algorithm with an electric field bias to simulate dendrite growth. The electric field bias was introduced into the model with an important parameter, namely the biasing factor c, which determines the balance between diffusion and electric field effects. Before performing the simulation with the proposed model, the dendrite growth in a lithium symmetric cell during charging was measured by sequential 3D magnetic resonance imaging (MRI). These data were then used to validate the simulation, as the dendrite structure in each measured MRI time frame was used a starting point for a new simulation, the results of which were then validated with the measured dendrite structure of the next time frame. The best agreement between the simulated and measured dendrite structures using the overlap and displacement of deposition sites metrics was obtained at the biasing factor c = 0.7. This agreement was also good in terms with the fractal dimension of the dendrite structures. The proposed method offers a simple, accurate, and scalable framework for predicting dendrite growth over long deposition periods, making it a valuable tool for studying dendrite suppression under real-world battery charging conditions.

Analysis of carrier dynamics and thermal effect of the GaAs photoconductive semiconductor switch in lock-on mode

Abstract The lock-on effect of the gallium arsenide photoconductive semiconductor switch (GaAs PCSS) at repetition rate aggravates the current crowding and electric field distortion, which significantly increases the risk of switch damage or even failure. Therefore, it is of great significance to investigate the carrier transport and the heat generation mechanism for improving the performance and longevity of GaAs PCSS in lock-on mode. The internal physical process of an opposed-electrode GaAs PCSS at low optical energy and strong electric field is analysed and discussed by experiment and simulation. A device-circuit hybrid simulation is employed to investigate the transient electric field, carrier concentration, and lattice temperature distribution within the GaAs PCSS in lock-on mode. The device temperature exhibits a positive correlation with the applied bias electric field, resulting in a peak temperature of 1037.25 K at an electric field of 38 kV/cm. The temperature distribution within the GaAs PCSS indicates a greater possibility for thermal breakdown and damage near the electrodes.

Development of Reconfigurable High-Frequency Devices Using Liquid Crystal in Substrate-Integrated Gap Waveguide Technology

This article presents the theoretical study, numerical simulation and fabrication of a phase shifter and a stub resonator for use in microstrip ridge gap waveguide (MRGW) technology, using a liquid crystal (LC) in the substrate as a reconfigurable material. The phase shifter and the stub resonator are filled with LC, and thanks to the LC’s dielectric anisotropy properties, the phase shift and the resonance response can be easily controlled using an external electric or magnetic bias field. The phase shifter was designed to operate in the range of 10 to 20 GHz, and the resonator was designed to operate in the range of 7.8 to 8.8 GHz. The phase shifter’s responses (including both phase shift and insertion losses), associated with both the parallel and perpendicular permittivity values of the LC, were computed and measured, and then the corresponding figure of merit (FoM) was extracted. The resonator’s frequency responses, associated with both the LC’s parallel and perpendicular permittivity, were computed. The resonator’s frequency responses, which provided different polarization voltages, were measured and compared to the simulation results. All technological issues related to both prototypes are also discussed here. The good agreement between the simulation and measurement results confirm this technology as a viable approach to the practical implementation of these microwave reconfigurable devices.

Enhancing the dielectric and piezoelectric properties of Pb0.99Gd0.01Zr0.53Ti0.47O3 ferroelectric ceramics by Sr-doping

Recently, high-performance lead zirconate titanate (Pb([Formula: see text]Tix)O3, PZT) ferroelectric ceramics have attracted intensive attention due to their wider operating temperature range, better temperature stability, as well as larger piezoelectric properties and higher energy conversion efficiency. In this study, the perovskite-type ferroelectric ceramics with a chemical formula of [Formula: see text][Formula: see text]Srx[Formula: see text][Formula: see text]O3 ([Formula: see text] and 0.02, abbr. PGZT and PGSZT, respectively) were prepared by the traditional solid-state reaction route. The influences of Sr-doping on the phase structure, dielectric properties, ferroelectric properties and piezoelectric properties of the PGZT ceramics were comprehensively investigated. The field-dependent P–E hysteresis loops of PGSZT were measured in the frequency range of 0.05–10[Formula: see text]Hz and temperature range of 20–100∘C. The results show that Sr-doping not only enhances the dielectric permittivity and piezoelectric coefficient of PGZT, but also decreases its dielectric loss tangent, with the [Formula: see text] value of 473[Formula: see text]pC/N, [Formula: see text] value of 1586 and [Formula: see text] value of 0.016 found in PGSZT. Also, PGSZT shows a high Curie temperature ([Formula: see text]) of [Formula: see text]C. The underlying mechanisms of the property enhancement were identified as that the introduced [Formula: see text] replaces the volatile [Formula: see text] located at the A-site of the perovskite structure, thereby reducing the concentration of lead vacancies and promoting the grain growth of the ceramics, consequently enhancing the dielectric and piezoelectric properties of PGZT. On the other hand, the frequency change in the low-frequency range ([Formula: see text][Formula: see text]Hz) played a significant impact on the remanent polarization ([Formula: see text]) and internal biased electric field ([Formula: see text]) of PGSZT, but the frequency dependence of coercive field ([Formula: see text]) tends to diminish in the high-frequency range ([Formula: see text][Formula: see text]Hz).

Large piezoelectric property of Bi(Fe0.93Mn0.05Ti0.02)O3 film by constructing internal bias electric field

BiFeO3 (BFO), Mn-doped-BFO (BFMO), Ti-doped-BFO (BFTO), and (Mn,Ti)-codoped-BFO (BFMTO) thin films are fabricated on the Pt/TiO2/SiO2/Si substrates via a sol–gel method combined with spin-coating and the subsequent layer-by-layer annealing technique. Compared with BFO film, the BFMTO film exhibits the lowest leakage current density ([Formula: see text][Formula: see text]A/cm2@290[Formula: see text]kV/cm). Notably, the polarization–electric field (P–E) loop of BFMTO film exhibits a positive displacement along the x-axis due to the existence of internal bias electric field, which is in agreement with the results of the PFM phase and amplitude curves. Especially, a very prominent inverse piezoelectric constant of [Formula: see text][Formula: see text]pm/V was obtained, which overcomes other related thin films. The internal bias electric field of BFMTO film can be caused by the different work functions of the thin film and the bottom electrode, accumulation of oxygen vacancies and the formation of defect dipoles. Besides, the internal bias electric field of BFMTO film has a good stability at the same electric field after experiencing the test cycle from low electric field to high electric field (400–1900[Formula: see text]kV/cm). These results indicate that self-polarized BFMTO film can be integrated to devices without additional polarization process, and have a wide range of application in microelectromechanical systems.

High-voltage AlGaN/GaN heterojunction lateral photoconductive semiconductor switch based on semi-insulating 4H-SiC substrate

A novel high-power AlGaN/GaN heterojunction lateral photoconductive semiconductor switch (PCSS) based on the SiC substrate is proposed, which achieves high dark-state resistance characteristics by groove etching. Under the action of biased electric field and incident laser, a high concentration of two-dimensional electron gas is formed at the heterojunction interface. The photo-generated free carriers transport along the heterojunction interface, which improves the utilization efficiency of photo-generated carriers. Moreover, the simulation of the current density distribution of the PCSS provides theoretical support for this phenomenon. Compared with the conventional GaN PCSS, the power capacity and conduction characteristics are further improved. The test results show that the output current of the device increases significantly after the introduction of the AlGaN/GaN heterojunction. At the biased voltage of ∼34 kV, the maximum output current of the AlGaN/GaN PCSS reaches 205 A.

Terahertz photon to dc current conversion via magnetic excitations of multiferroics

Direct conversion from terahertz photon to charge current is a key phenomenon for terahertz photonics. Quantum geometrical description of optical processes in crystalline solids predicts existence of field-unbiased dc photocurrent arising from terahertz-light generation of magnetic excitations in multiferroics, potentially leading to fast and energy-efficient terahertz devices. Here, we demonstrate the dc charge current generation from terahertz magnetic excitations in multiferroic perovskite manganites with spin-driven ferroelectricity, while keeping an insulating state with no free carrier. It is also revealed that electromagnon, which ranges sub-terahertz to 2 THz, as well as antiferromagnetic resonance shows the giant conversion efficiency. Polar asymmetry induced by the cycloidal spin order gives rise to this terahertz-photon-induced dc photocurrent, and no external magnetic and electric bias field are required for this conversion process. The observed phenomena are beyond the conventional photovoltaics in semi-classical regime and demonstrate the essential role of quantum geometrical aspect in low-energy optical processes. Our finding establishes a paradigm of terahertz photovoltaic phenomena, paving a way for terahertz photonic devices and energy harvesting.

Influence of electric field, liquid film thickness, and sodium chloride deposition on atmospheric corrosion of Cu

Printed circuit boards (PCBs) are prone to failure due to the influence of environmental factors such as humidity, salt spray, and electric fields during usage. As the lead pitch of PCBs decreases and these environmental factors become challenging to control, corrosion becomes unavoidable. This study used a self-built thin liquid film–electric field coupling environment in an in situ electrochemical testing apparatus. PCB-Cu electrodes were evaluated using open-circuit potential and polarization curve tests on the thin liquid film. This study systematically investigated the effects of external electric field bias, sodium chloride deposition, and liquid film thickness on PCB-Cu corrosion. The results showed that increased bias promoted Cu corrosion in the coupled environment and altered electrode reactions. The cathodic process transitioned from activation control at 0–1 V to hydrogen evolution electrochemical control at 3 V for electrode reactions. Increased sodium chloride deposition enhanced the Cu corrosion rate in the coupled environment primarily due to Cl− damaging the corrosion product film. Under different liquid film thickness conditions, the corrosion rates can be ranked as 200 μm > 300 μm > 100 μm, with 200 μm exhibiting the highest corrosion rate and marking the transition point from the cathodic to anodic control of the corrosion reactions. Orthogonal analysis results indicated that bias was the most influential factor affecting Cu corrosion, followed by liquid film thickness and sodium chloride deposition.

Enhanced electromagnetic tunability of barium strontium titanate films via coating Pr modified yttrium iron garnet layer

It is hard to simultaneously realize the high dielectric tunability and low loss for the single Ba0.6Sr0.4TiO3 (BST) dielectric film made through chemical method. Garnet structured Y2.80Pr0.20Fe5O12 (YPrIG) exhibits the merits of high saturation magnetization and a much high resistivity, which are helpful for realizing magnetoelectric double tuning and suppressing the dielectric loss of BST film. In this work, Y2.80Pr0.20Fe5O12/Ba0.6Sr0.4TiO3 (YPrIG/BST) composite films were fabricated by sol-gel method. The composite films exhibited a low dielectric loss (0.0087), and got a magnetic tunability of 11.73% at 10 kOe and 1.44 MHz. Compared with BST film, the tunability of YPrIG/BST film was enhanced from 56.25% to 73.24% under the bias electric field of 800 kV/cm. Additionally, YPrIG/BST films exhibited an electromagnetic double adjustability. The electromagnetic tunability of YPrIG/BST composite films was as high as 80.40% at 1.44 MHz, under the DC bias electric field of 800 kV/cm and magnetic field of 10 kOe. This phenomenon can be explained in terms of the superposition effect of electric field and magnetic field.

Rf chopper for prebunched radioactive ion beams

An rf chopper system is being designed for the ReAccelerator (ReA) linac at the Facility for Rare Isotope Beams at Michigan State University. The 80.5 MHz ReA radio-frequency quadrupole accelerates prebunched 16.1 MHz beams, producing four satellite bunches for every main bunch. The chopper system includes an rf deflector that kicks every bunch vertically to spatially separate main and satellite bunches. A constant magnetic field superimposed with the chopper electric field biases the beam trajectory to ensure the high-intensity bunches do not experience a net deflection and are injected straight to the ReA6 cryomodule or sent for experiments. The kicked bunches are low in intensity and will be sent to a beam dump, resulting in a clean 16.1 MHz beam structure, which allows for a reliable time-of-flight separation of the isotopes. Published by the American Physical Society 2024

Influence of the Schottky Junction on the Propagation Characteristics of Shear Horizontal Waves in a Piezoelectric Semiconductor Semi-Infinite Medium

In this paper, a theoretical model of the propagation of a shear horizontal wave in a piezoelectric semiconductor semi-infinite medium is established using the optimized spectral method. First, the basic equations of the piezoelectric semiconductor semi-infinite medium are derived with the consideration of biased electric fields. Then, considering the propagation of a shear horizontal wave in the piezoelectric semiconductor semi-infinite medium, two equivalent mathematical models are established. In the first mathematical model, the Schottky junction is theoretically treated as an electrically imperfect interface, and an interface characteristic length is utilized to describe the interface effect of the Schottky junction. To legitimately confirm the interface characteristic length, a second mathematical model is established, in which the Schottky junction is theoretically treated as an electrical gradient layer. Finally, the dispersion and attenuation curves of shear horizontal waves are numerically calculated using these two mathematical models to discuss the influence of the Schottky junction on the dispersion and attenuation characteristics of shear horizontal waves. Utilizing the equivalence of these two mathematical models and the above numerical results, the numerical value of the interface characteristic length is reliably legitimately confirmed; this value is independent of the thickness of the upper metal layer, the doping concentration of the lower n-type piezoelectric semiconductor substrate, and biasing electric fields. Only the biasing electric field parallel to the Schottky junction can provide an evident influence on the attenuation characteristics of shear horizontal waves and enhance the interface effect of the Schottky junction. Since the second mathematical model is also a validation of our previous mathematical model established through the state transfer equation method, some numerical results calculated using these two mathematical models are compared with those obtained using the previous method to verify the correctness and superiority of the research work presented in this paper. Since these two mathematical models can better calculate the dispersion and attenuation curves of high-frequency waves in micro- and nano-scale piezoelectric semiconductor materials, the establishment of mathematical models and the revelation of physical mechanisms are fundamental to the analysis and optimization of micro-scale resonators, energy harvesters, and amplifications.

High hysteresis-free dielectric tunability in silver niobate-based ceramics

Moderate dielectric constant, low dielectric loss, and high dielectric tunability around or above Curie temperature are essential characteristics of dielectric tunable devices. Silver niobate (AgNbO3), known for its antiferroelectric (AFE) and weak ferroelectric (FE) nature, offers a natural “composite” system combining AFE and FE attributes, making it an attractive candidate for tunable device materials. Microstructural modification through chemical methods can enhance its dielectric tunability. To this end, we propose and prepare a doped AgNbO3 ceramic system, denoted as (1-x) AgNbO3-xLiTaO3 (ANLT100x, x ≤ 3.8 mol%). Structural analysis reveals that all samples maintain an average AFE-like polar structure. The introduction of dopants disrupts the ordered AFE-like structure, altering the proportion of AFE and FE states. This disruption leads to a notably improved relaxor dielectric response and an FE transition around room temperature. Consequently, we achieve a ceramic material (x = 3.8 %) with a moderate dielectric constant (εr = 520) and low dielectric loss (tanδ = 0.008), accompanied by a hysteresis-free dielectric tunability (nr = 37.2 %) under an applied bias electric field of 40 kV cm−1, which is four times larger than that in AgNbO3 (nr = 8 %) ceramic. These findings open new possibilities for developing dielectric tunable materials in device design.

Switching jitter of avalanche gallium arsenide photoconductive semiconductor switch influenced by multiple avalanche domains.

The stability of synchronous operation is directly related to the time jitter of the gallium arsenide photoconductive semiconductor switch (GaAs PCSS). In this work, a numerical model for the switching jitter of avalanche GaAs PCSS is established, and the impacts of triggering optical energy and bias electric field on the switching jitter are investigated numerically based on an equivalent bulk current channel. The proposed numerical model predicts well the changing characteristics of switching time as well as switching jitter, which has been demonstrated by the experimental results. On this basis, the theory of multiple avalanche domains is introduced to compare the domain evolutions influenced by the bias electric field and triggering optical energy. The results indicate that the reduction of switching jitter is significantly determined by the accelerated formation and evolution of avalanche domains, which provides a good explanation of the jitter mechanism of switching time.

The Origin of Collective Dielectric Relaxation Process in Ferroelectric and Antiferroelectric Phases of Liquid Crystals

Dielectric spectroscopy has proven as an important tool for the characterization of ferroelectric and antiferroelectric phases observed in the thermotropic chiral liquid crystals compounds. These compounds generally have paraelectric smectic A (SmA*) phase, ferroelectric smectic C (SmC*) phase and antiferroelectric smectic C (SmCA*) phase. In some compounds, ferroelectric (SmCg*) phase is also found. Dielectric spectra of these phases under planar alignment of the molecules are sometimes complex but rich in information and are very helpful in the determination of the structure of these phases. In the SmA* phase, a mode in high kHz region is observed. In the SmC* phase, a relaxation mode observed in low kHz region having high dielectric strength. However, in the SmCg* phase observed mode relaxation frequencies lies in same frequency window as SmC* phase but their dielectric strength was less than at least one order magnitude in comparison to observed mode of SmC* phase. In the SmCA* phase, dielectric spectrum contains two relaxation modes observed in kHz and MHz regions respectively. The dielectric strengths of these two modes are very small and less than at least one/two order magnitude in comparison to observed mode of SmA*/ SmC* phases. These observed relaxation processes are discussed as a function of temperature and bias electric field and their origin is also examined in the light of the experimental work. Dielectric parameters of the above phases observed in such material are discussed with regards to their structure property relationship.

Kinetics of the Domain Structure in Uniform Electric Field in LiNbO3 with Surface Layer Modified by Soft Proton Exchange

The creation of periodic domain structures in lithium niobate crystals makes it possible to realize highly efficient nonlinear optical interactions in optical waveguides. The influence of near‐surface H+ ion concentration gradient on the domain kinetics in uniform electric field in lithium niobate crystals modified by soft proton exchange is studied. The spatial distribution of the H+ ions concentration in the surface layer is obtained by confocal Raman microscopy. The observed anomalous evolution of the domain structure at the surface represents the formation of stripe domains and their anisotropic growth along three directions. The domain imaging in the bulk allows revealing a comb‐like domain shape. The obtained strong influence of the proton exchange duration on the threshold field is attributed to the action of the concentration gradient in the near‐surface layer, which is considered as an analog of the internal bias electric field. It is shown that the internal bias field is proportional to the increase in the concentration gradient in the surface layer. The mechanism of the comb‐like domain formation is proposed. The obtained results can be used for development of domain engineering methods in optical waveguides.

Immobilization of photorefractive solitons by charge anchoring on conductive walls

Spatial solitons have shown great promise for various applications, but their limited stability in terms of beam movement has been a significant hindrance. This limitation is especially prominent in the conventional configuration where the bias electric field is oriented perpendicular to the soliton propagation direction, leading to instability caused by the drift–diffusion processes. To address this issue, we explore a novel, to the best of our knowledge, approach where solitons are propagated from one bias plate to the other, with a tilted angle with respect to the field and to the optical axis of the photorefractive crystal. By directing the solitons toward the bias electrodes, we observe an intriguing anchoring effect that immobilizes the soliton beam, resulting in reduced self-bending. The charge distribution on the conductive walls is numerically investigated as a function of the crystallographic orientation of the c-axis. The immobilization of the soliton beams is a fundamental issue for their technological applications as waveguides in integrated photonic circuits, which would result in an addressable but perfectly stable waveguide over time.

Ultrahigh strain in PZ-PT-BNT piezoelectric ceramic

Low strain limits the further application of Pb(Zr,Ti)O3 (PZT) piezoelectric ceramics in actuators. Herein, a ternary piezoelectric ceramic xPbTiO3-(0.95-x)PbZrO3-0.05(Bi0.5Na0.5)TiO3 (xPT-PZ-BNT) is proposed and prepared by solid-state method to improve the strain characteristics. Results indicate that a biased electric field is intentionally constructed by defects arising from the incorporation of BNT into PZ-PT ceramic, which promotes non-180° domains to restore to initial states, thereby contributing to the increase in strain. Moreover, the electric domain configuration is efficiently modified by adjusting the component proportion in xPT-PZ-BNT ceramics, in which the 0.42 PT-PZ-BNT presents short and broad domains with fast response to external electric field. Rayleigh analysis indicates that the strain contributed by domain switching is dominant in PT-PZ-BNT ceramics under a high electric field. Consequently, a large strain of 0.4% is achieved in 0.42 PT-PZ-BNT ceramic with the variation less than 10% in the temperature range of 25∼175 °C. This study not only deeply analyzes the effect of domain configuration on the strain for PZT piezoelectric ceramics, but also demonstrates an effective approach to increase the strain through constructing internal biased electric field and regulating domain configuration.

A Diamond Terahertz Large Aperture Photoconductive Antenna Biased by a Longitudinal Field

The novel design of a terahertz large aperture photoconductive antenna (LAPCA) is reported. It features a longitudinal orientation of the bias electric field within the photoconductive substrate, and has the advantage of a small interelectrode gap, resulting in a higher field for the same applied voltage. The proposed LAPCA configuration has been tested with a nitrogen-doped (∼10 ppm) synthetic monocrystalline diamond, which is a promising material for high-intensity and high-power terahertz sources. Two antennas with different high-voltage electrode realizations were assembled, pumped by a 400 nm femtosecond laser, and tested for THz emitter function. The experimental data are found to be in good correlation with the numerical simulation results. The performance of antennas with the conventional transverse E-field configuration and the novel longitudinal configuration is compared and discussed.

Synergy Effect of the Enhanced Local Electric Field and Built-In Electric Field of CoS/Mo-Doped BiVO4 for Photoelectrochemical Water Oxidation.

Bismuth vanadate is a promising material for photoelectrochemical water oxidation. However, it suffers from a low quantum efficiency, poor stability, and slow water oxidation kinetics. Here, we developed a novel photoanode of CoS/Mo-BiVO4 with excellent photoelectrochemical water oxidation performance. It achieved a photocurrent density of 4.5 mA cm-2 at 1.23 V versus the reversible hydrogen electrode, ∼4 times that of BiVO4. The CoS/Mo-BiVO4 photoanode also exhibited good stability, and the photocurrent density generated by the CoS/Mo-BiVO4 photoanode did not significantly decrease after light irradiation for 2 h. Upon replacement of part of the V with Mo doping in BiVO4, the local electric field around the Mo-O bond was enhanced, thus promoting carrier separation in BiVO4. The CoS was deposited on the surface of Mo-BiVO4, forming a built-in electric field at the interface. Under the action of the bias electric field and the built-in electric field, the carriers of CoS/Mo-BiVO4 were efficiently separated in the direction of the inverse type II heterojunction. In addition, CoS improved the light absorption and charge injection efficiency of the CoS/Mo-BiVO4 photoanode.