Internal Electric Field Strength Research Articles

Unveiling the formic acid dehydrogenation dynamics steered by Strength-Controllable internal electric field from barium titanate

Formic acid is a desirable liquid hydrogen storage compound for solving transport and storage problems of hydrogen for onboard fuel cells. Optimizing adsorption/desorption energy of intermediates can directly modulate the performance of Pd catalysts in formic acid dehydrogenation (FAD). Herein, we introduce internal electric field with controllable strength to regulate the adsorption/desorption of intermediates on Pd. Non-ferroelectric cubic-phase barium titanate (CBT) is heat-treated at high temperature to obtain ferroelectric tetragonal-phase barium titanate (TBT(C)), which exhibits internal electric field. The strength of the internal electric field is successfully adjusted by heat treatment at different temperatures. The size of Pd nanoparticles is restricted between 2.2 and 2.7 nm, and the electronic effect of Pd is effectively eliminated by coating TBT(C) with mesoporous carbon shell (TBT(C)@SC). Experimental results prove that the internal electric field promotes the desorption of hydrogen on Pd. Pd/TBT(C)@SC-800 obtained by heat treatment at 800 °C, with the optimal internal electric field strength, exhibits high activity and hydrogen selectivity for FAD. This work provides a new strategy for designing FAD catalysts.

Precise surface machining of fused silica using high stability atmospheric pressure microwave plasma jet with a new internal electrode

Plasma is a promising approach for machining of fused glass substrates. Developing high-performance microwave torch is the core element to ensure the processing accuracy of this technology. In this study, a spline curve-based microwave torch internal electrode structure was proposed, which increased the internal electric field strength by 54 %. The discharge dynamics simulation based on this electrode shows that the plasma is excited at the inner electrode tip and the bottom of the resonant cavity, then it expands to form a linear discharge region and eventually fill the discharge tube. It was revealed by CCD images that with the increase of carrier gas flow rate, turbulent flow state appears in the tail of the jet. OES data shows that microwave Ar plasma can effectively dissociate CF4, and due to the oxidation effect of oxygen, CFx and C2 content decrease significantly with the addition of oxygen. The machining experiment on fused silica shows that the material removal stability of this torch reaches 3.69 %, and the removal rate increases nYarly with dwell time due to thermal effect. Finally, the machining performance of the atmospheric pressure microwave plasma jet was verified by figuring of a planar fused silica surface reducing the form error from 108.1 nm RMS to 16.5 nm RMS.

Enhancing power capacity and performance of wide-drift-channel transit-time oscillators for long-pulse high-power microwave generation

This paper addresses the challenge of extending the pulse duration of high-power microwave (HPM) sources, a critical focus in HPM technology. Transit-time oscillators (TTOs) typically modulate electron beams by forming standing waves through the cutoff of the TM01 mode in the modulation cavity. This study proposes enhancing the power capacity of TTOs by widening the drift channel. To enhance modulation capability without compromising power capacity, front and rear reflectors are strategically introduced. In particle-in-cell simulations, the device exhibits an output power of 1.65 GW at a frequency of 12.6 GHz, with an efficiency of 33.6%. The saturation time for the output microwave is 30 ns, and the maximum internal electric field strength is 860 kV/cm. The presented TTO, with design improvements, offers a promising solution for applications requiring prolonged pulse durations in high-power microwave sources.

Boosting Photovoltaic Output by Dual External Manipulations on 1D Ferroelectric Nanorods Solar Cell: Electric Field and Giant Dielectric Constant Variation

Unlike common photovoltaic (PV) cells whose performance has been anchored, the merits for the cells made of ferroelectric crystals, due to the non‐centrosymmetric structure, provide possibility to further enhance the efficiency by dual external manipulations through increasing the internal electric field strength and the dielectric screening effect, based on anomalous photovoltaic (APV) arisen by the external poling and giant dielectric constant variation through temperature‐controlled ferro‐paraelectric phase transition. In this study, a synergistic effect achieving a 67% improvement in power conversion efficiency (PCE) of the n‐i‐p configuration solar cell by ferroelectric polarization and high dielectricity is observed, taking c‐axis‐aligned single‐crystalline ferroelectric SbSI nanorods as the active layer. The opposite poling effects are revealed leading to asymmetric characteristics in the n‐i‐p configuration. The enhancements of Jsc induced by inherent giant variation imply strong dielectric screening facilities to lower carrier cross section captured by charged defects, uniformly suppressing various recombination mechanisms, understood by the Langevin model. Therefore, solar cells employing n‐i‐p structured ferroelectric thin films as absorbing layers hold promising potential for achieving defect‐tolerance high performance through rational design, external polarization, and dielectric property control.

Evaluation of dynamics of charge accumulation and dissipation processes in Ge15Se85 thin film under electron beam irradiation by mapping surface potential distribution

The interaction of Ge15Se85 amorphous chalcogenide films with an electron beam has been studied. Three ranges of electron irradiation doses, in which a surface relief of various shapes is formed, are found. The presence and persistence of the surface potential for a long time after film irradiation have been established using the Kelvin probe force microscopy (KPFM). It is shown that the formation of surface relief is result of the charge accumulation in the interaction region. Based on the mapping of surface potential distribution in irradiated regions using KPFM we propose models of electric field distribution in the irradiated spots and suggest mechanism of electron-induced mass transfer. It has been suggested that the formation of a high surface relief structures is due to the electron-induced plastic effect. It is shown that the appearance of asymptotically sharp Taylor cones in chalcogenide films is due to charge collapse in the interaction region when the volume charge density and internal electric field strength exceed their critical values.

Fabrication of Ultrafine Cu2 O Nanoparticles on W18 O49 Ultra-Thin Nanowires by In-Situ Reduction for Highly Efficient Photocatalytic Nitrogen Fixation.

Photocatalytic ammonia synthesis technology is one of the important methods to achieve green ammonia synthesis. Herein, two samples of Cu ion-doped W18 O49 with different morphologies, ultra-thin nanowires (Cu-W18 O49 -x UTNW) and sea urchin-like microspheres (Cu-W18 O49 -x SUMS), are synthesized by a simple solvothermal method. Subsequently, Cu2 O-W18 O49 -x UTNW/SUMS is synthesized by in situ reduction, where the NH3 production rate of Cu2 O-W18 O49 -30 UTNW is 252.4µmolg-1 h-1 without sacrificial reagents, which is 11.8 times higher than that of the pristine W18 O49 UTNW. The Cu2 O-W18 O49 -30 UTNW sample is rich in oxygen vacancies, which promotes the chemisorption and activation of N2 molecules and makes the N≡N bond easier to dissociate by proton coupling. In addition, the in situ reduction-generated Cu2 O nanoparticles exhibit ideal S-scheme heterojunctions with W18 O49 UTNW, which enhances the internal electric field strength and improves the separation and transfer efficiency of the photogenerated carriers. Therefore, this study provides a new idea for the design of efficient nitrogen fixation photocatalysis.

Quality attributes of pork tenderloin frozen under different high voltage electric fields with ultrahigh permittivity ceramic-enhanced electrodes

A novel high voltage electric field assisted freezing (HVEFF) system improved by ultrahigh permittivity ceramic electrodes was developed, and its effects on the quality attributes of frozen pork tenderloin were investigated. The relationship between the initial internal electric field strength of pork and the quality of frozen pork was studied. Results showed that the frozen samples obtained under the internal electric field strength of 6.25 × 104 V/m (corresponding to 6 kV) had less drip loss, less total colour change value, and better texture, other than the frozen samples under 12 kV and 18 kV. These results were confirmed by a further investigation into water distribution, protein thermal stability, and ice crystal size. Thereby, this study showed a great potential of ultrahigh permittivity material in improving the small sample-treating capacity of HVEFF.

Effects of GaN cap layer thickness on photoexcited carrier density in green luminescent InGaN multiple quantum wells

The effects of GaN cap layers on the optical properties of green luminescent InGaN-based multiple quantum wells were studied by photoluminescence (PL) spectroscopy. The PL peak energy under the selective excitation of the InGaN well layers was lower than that under the band-to-band excitation of the GaN barrier layers. The difference in the PL peak energies between the selective and band-to-band excitations decreased as the cap layer thickness increased, indicating an increase in the nonradiative recombination of photogenerated carriers in the barrier layers. Moreover, the internal quantum efficiency under selective excitation decreased as the cap layer thickness increased because of the increase in the internal electric field strength.

The Precision Defect Engineering with Nonmetallic Element Refilling Strategy in g-C3 N4 for Enhanced Photocatalytic Hydrogen Production.

Traditional defect engineering and doping strategies are considered effective means for improving H2 evolution, but the uncontrollability of the modification process does not always lead to efficient activity. A defect-induced heteroatom refilling strategy is used here to synthesize heteroatoms introduced carbon nitride by precisely controlling the "introduction" sites on efficient N1 sites. Density functional theory calculations show that the refilling of B, P, and S sites have stronger H2 O adsorption and dissociation capacity than traditional doping, which makes it an optimal H2 production path. The large internal electric field strength of heteroatom-refilled catalysts leads to fast electron transfer and the hydrogen production of the best sample is up to 20.9mmolg-1 h-1 . This work provides a reliable and clear insight into controlled defect engineering of photocatalysts and a universal modification strategy for typical heteroatom and co-catalyst systems for H2 production.

Numerical simulation of intracerebral hemorrhage detection using magnetic induction spectroscopy

Magnetic Induction Spectroscopy (MIS) is an emerging technique for contactless measurement of bioimpedance with promising application in intracerebral hemorrhage (ICH) detection. Here, we report numerical simulations of ICH detection based on the MIS. A novel MIS sensor using two planar rectangular spiral coils (TPRSC) as the exciter with frequency range 120 kHz-9 MHz is proposed for the first time. The exciter can generate an antisymmetric normal magnetic field at the detection sensor, and hence the primary voltage can be canceled theoretically. We construct symmetry-based and asymmetry-based ICH models with realistic anatomic structure and hexahedral discretization feature for numerical simulations. The numerical simulations based on the finite integration technique are conducted in the three-dimensional electromagnetic analysis software CST. The voltage phase spectrum, the phase change spectrum and the relative conductivity change spectrum at different hemorrhage volumes are calculated. We compare sensitivities between the TPRSC-based MIS sensor and the conventional type (CC MIS sensor) which uses the single planar rectangular spiral coil as the exciter. Using the constructed ICH models, the specific absorption rate (SAR) and the internal electric field strength are computed to evaluate the electromagnetic safety of the TPRSC-based MIS sensor. Results show that compared with the CC MIS sensor, the sensitivity of the TPRSC-based MIS sensor for measuring the voltage phase is improved by two orders of magnitude, and for measuring the phase change is improved by more than ten times. The phase change and relative conductivity change spectra for the TPRSC-based MIS sensor demonstrate good separability between different small-volume hemorrhages. In addition, the electromagnetic safety of the TPRSC-based MIS is also superior to that of the CC MIS sensor, which conforms to the IEEE standard and the ICNRP guidelines over a wide range of the amplitude of the excitation current.

Regulating crystallinity in linear conjugated polymer to boost the internal electric field for remarkable visible-light-driven disinfection

• A new poly-imines, ODA-BPAH was used for photocatalysis disinfection • The high crystallinity greatly enhanced Internal electric field (IEF) • Giant IEF boosting photogenerated charge separation and transport • The ODA-BAPH exhibited excellent broad-spectrum water disinfection performance • This sterilization ability is higher than reported noble metal-free photocatalysts Conjugated linear polymers are promising metal-free photocatalysts for visible-light-driven photocatalytic water disinfection, but it was still bottlenecked by the insufficient photogenerated charge separation and transport (CST) process. Herein, we obtained the highly crystalline imine-linked conjugated linear polymer (ODA-BPAH) with a greatly enhanced CST process. The highly crystalline ODA-BPAH exhibited excellent broad-spectrum water disinfection efficiency up to 99.99999% in 1 h, which is among the reported highest of state-of-the-art photocatalysts. The crystallinity of ODA-BPAH was regulated by simply turning the solvent and the experiment results revealed that the ODA-BPAH with high crystallinity exhibited higher internal electric field strength and photocatalytic performance than that with low crystallinity, which indicates that higher crystallinity in linear conjugated polymers contributes to superior CST efficiency as well as the generation of reactive oxygen species. This work highlights the impact of polymer crystallinity on the internal electric field and proves that linear poly-imine could be a new type of promising metal-free photocatalyst for water treatment.

The effect of the sodium content on the structure and the optical properties of thermally poled sodium and niobium borophosphate glasses

Six niobium rich glasses presenting different sodium contents were synthetized. On the basis of complementary infrared and Raman analysis, the influence of the sodium content and its role on the structure of the glasses prior to and following poling was examined. Correlative second harmonic generation (SHG)/Raman microscopy on the poled glasses cross section has shown a co-localization of the SHG signal and the structural variations. It also evidenced similar structural rearrangements whether sodium is removed through poling (230–300 °C) or through the alkali content defined by the starting glass compositions (melted at 1300–1500 °C). The effect of the sodium content on the optical properties, prior to and after thermal poling, is also discussed. It was found that refractive index variations induced by poling (ranging between 10−3 and 3 × 10−2) are mainly the result of a density decrease in the poled region rather than compositional and structural changes. The electro-optic origin of the poling-induced second order nonlinear response is confirmed by the Maker Fringe SHG analysis, and the evolution of χ(2) (2–2.5 pm/V) with the sodium content is discussed based on a selection of parameters influencing either the third order susceptibility [χ(3)] or the internal electric field strength of the poled layer.

Reciprocal Relation Between Intraband Carrier Generation and Interband Recombination at the Heterointerface of Two-Step Photon Up-Conversion Solar Cells

Photon up-conversion processes are considered beneficial for energy-conversion devices. The recently proposed two-step photon up-conversion (TPU) solar-cell design employs an intermediate level with a high electron occupation probability. To understand the device physics, a quantitative evaluation of the different current-generation and loss mechanisms is required. In the present work, we use a TPU solar cell containing an $\mathrm{In}\mathrm{As}$/$\mathrm{Ga}\mathrm{As}$ quantum-dot layer located 10 nm in front of an ${\mathrm{Al}}_{0.3}{\mathrm{Ga}}_{0.7}\mathrm{As}$/$\mathrm{Ga}\mathrm{As}$ heterointerface. We study the relation between the photocurrent (PC), radiative recombination, and nonradiative recombination as a function of the bias voltage. The radiative interband recombination is evaluated by integrating the photoluminescence (PL) over the range from 1000 to 1300 nm. The magnitudes of the PC and PL signals generated via interband excitation of the $\mathrm{Ga}\mathrm{As}$ layer depend on the bias voltage; a higher forward bias reduces the PC and increases the PL intensity. We verify that, under additional infrared light illumination at 1319 nm, which induces intraband transitions, the PC density increases while the PL intensity significantly decreases. This PC enhancement exhibits a maximum at \ensuremath{-}0.6 V, which reflects the optimum internal electric field strength for maximizing the TPU efficiency.

Interface property and band offset investigation of GaN based MOS heterostructures with diffusion-controlled interface oxidation technique

This paper presents the interface analysis and band offset of Al2O3/AlGaN/GaN metal-oxide-semiconductor (MOS) heterostructures with diffusion-controlled interface oxidation (DCIO) treatment. After conventional surface pre-treatment with wet cleaning and nitridation plasma, 1 nm Al2O3 was prepared with atomic layer deposition, followed by in situ plasma-assisted interface oxidation for 30 minutes. The interface oxidation process is limited by oxidant diffusion through the pre-deposited Al2O3 layer, contributing to the formation of a high quality crystalline interfacial oxide layer. For MOS heterostructures with 24.1 nm Al2O3, a positive threshold voltage shift by 1.8 V was obtained by using the DCIO technique. The energy band structures and band offset at the Al2O3/AlGaN interface was investigated with x-ray photoelectron spectroscopy (XPS). XPS results show that DCIO treatment causes an increase in conduction band offset from 2.29 ± 0.37 eV to 2.92 ± 0.36 eV. There is also a decrease in Al2O3 band slope, indicating a decrease in internal electrical field strength and interface charges. The Al2O3 energy band for these two cases may also cross with each other at a certain point, defining the critical thickness of gate oxide. Generally, the decrease in interface charges by DCIO causes a positive voltage shift, while the voltage shift will change sign with Al2O3 thickness smaller than the critical value. The MOS heterostructures with and without DCIO exhibit very nice relations between threshold voltage and Al2O3 thickness, giving a critical oxide thickness of about 1 nm. DCIO results in a decrease in the slope of linear function by about 0.08 V nm−1, indicating the reduced interface charges by 3.96 × 1012 cm−2.

Investigation into the Internal Electric-Field Strength in the Active Region of InGaN/GaN-Based LED Structures with Various Numbers of Quantum Wells by Electrotransmission Spectroscopy

The internal electric fields of InGaN/GaN-based green-emission LED heterostructures with various numbers of quantum wells in the active region are investigated by electrotransmission spectroscopy. The frequencies of the observed spectral lines are attributed to possible types of interband transitions. An increase in the number of interband transitions of the “quantum well—quantum barrier” type with an increase in the number of quantum wells is found. This is explained by the nonidentical degree of segregation of In atoms in different GaN barriers layers. The strength of internal electric fields in quantum wells is calculated for various values of the bias of the p–n junction using a series of electrotransmission spectra. It is found that the strength of the internal piezoelectric field decreases from 3.20 to 2.82 MV/cm with an increase in the number of quantum wells.

Experimental and numerical analyses of electro-pulse rock-breaking drilling

The electro-pulse boring (EPB) of deep and ultra-deep wells has great market prospects. It uses controllable energy and is pollution-free. In this paper, research into high-voltage short-pulse power supplies and EPB electrode bits is reviewed. The simulation model was established according to the common coaxial cylindrical structure of the electric pulse rock breaking bit. The effects of the electrode spacing and the shape of the high-voltage electrode on the electric pulse rock breaking were then studied. According to the simulation results, the maximum electrode spacing was determined and the shape of the high-voltage electrode was optimized. The electrode bits with 45- mm spacing and 25-mm spacing were designed. Numerical simulations of EPB using these two bit sizes were conducted in which the actual structure size of the electrode bits and rock physical parameters were used. Simulation revealed an electric field distortion in the rock due to naturally-occurring air gaps, which can enhance the internal electric field strength. An experimental EPB system based on a transformer-type pulse generator was then developed. Transformer oil was used as a drilling fluid and red sandstone was drilled. Electric breakdown of sandstone by 25-mm and 45-mm electrode bits was conducted at a voltage of 80 kV, which produced drilling diameters of 60 mm and 100 mm, respectively. According to the simulation analysis and experimental research of EPB, the effective technological parameters and the law of EPB were obtained, which provided theoretical and practical guidance for electrode bit design and the selection of drilling parameters in practical applications.

Исследование напряжeнности внутренних электрических полей в активной области светодиодных структур на основе InGaN/GaN с разным числом квантовых ям методом спектроскопии электропропускания

Abstract The internal electric fields of InGaN/GaN-based green-emission LED heterostructures with various numbers of quantum wells in the active region are investigated by electrotransmission spectroscopy. The frequencies of the observed spectral lines are attributed to possible types of interband transitions. An increase in the number of interband transitions of the “quantum well—quantum barrier” type with an increase in the number of quantum wells is found. This is explained by the nonidentical degree of segregation of In atoms in different GaN barriers layers. The strength of internal electric fields in quantum wells is calculated for various values of the bias of the p – n junction using a series of electrotransmission spectra. It is found that the strength of the internal piezoelectric field decreases from 3.20 to 2.82 MV/cm with an increase in the number of quantum wells.

A new extrapolation expression for exposure evaluation inside a human-equivalent liquid phantom in the vicinity of wireless power transfer systems

To ensure human safety against electromagnetic exposures from wireless power transfer (WPT) systems operating at MHz-band frequencies, a compliance test must be conducted using either numerical simulations or measurements. In practice, measurements of the specific absorption rate (SAR) inside a human-equivalent liquid phantom are required for exposure evaluation. However, accurate measurements of SAR are difficult, especially at a location close to the phantom boundary, owing to the boundary effect, caused by the field disturbance due to the SAR probe itself. Hence, it is necessary to use an extrapolation method to determine the internal electric field or SAR. In this study, we propose a new extrapolation expression based on the characteristic of electromagnetic fields inside the phantom in order to estimate internal electric field strength or SAR. The validity of the proposed expression was demonstrated both numerically and experimentally. From the results, we confirmed that the difference in the internal electric field strength inside a liquid phantom was less than 3% between our proposed extrapolation expression and the method of moments (MoM). For SAR measurements using two types of actual WPT systems, i.e., solenoid and flat-spiral types, we found that the proposed expression can be used to evaluate the spatial peak 10-g average SAR with a difference of less than 30% compared with those numerically obtained by MoM.

Effect of turbulent flow on an atmospheric-pressure AC powered gliding arc discharge

A high-power gliding arc (GA) discharge was generated in a turbulent air flow driven by a 35 kHz alternating current electric power supply. The effects of the flow rate on the characteristics of the GA discharge were investigated using combined optical and electrical diagnostics. Phenomenologically, the GA discharge exhibits two types of discharge, i.e., glow type and spark type, depending on the flow rates and input powers. The glow-type discharge, which has peak currents of hundreds of milliamperes, is sustained at low flow rates. The spark-type discharge, which is characterized by a sharp current spike of several amperes with duration of less than 1 μs, occurs more frequently as the flow rate increases. Higher input power can suppress spark-type discharges in moderate turbulence, but this effect becomes weak under high turbulent conditions. Physically, the transition between glow- and spark-type is initiated by the short cutting events and the local re-ignition events. Short cutting events occur owing to the twisting, wrinkling, and stretching of the plasma columns that are governed by the relatively large vortexes in the flow. Local re-ignition events, which are defined as re-ignition along plasma columns, are detected in strong turbulence due to increment of the impedance of the plasma column and consequently the internal electric field strength. It is suggested that the vortexes with length scales smaller than the size of the plasma can penetrate into the plasma column and promote mixing with surroundings to accelerate the energy dissipation. Therefore, the turbulent flow influences the GA discharges by ruling the short cutting events with relatively large vortexes and the local re-ignition events with small vortexes.

Investigation of Photoluminescence, Stimulated Emission, Photoreflectance, and 2DEG Properties of Double Heterojunction AlGaN/GaN/AlGaN HEMT Heterostructures Grown by Ammonia MBE

A series of double heterojunction AlGaN/GaN/AlGaN high electron mobility transistor (HEMT) heterostructures are grown by ammonia MBE on sapphire substrates using AlN buffer layers with varying thicknesses and growth conditions. The grown heterostructures are investigated by atomic force microscopy as well as photoluminescence (PL), stimulated emission (SE), and photoreflectance (PR) measurements. It is shown that PL intensity cannot be used as a reliable criterion for quality control of HEMT heterostructures because of an influence of surface roughness. A new method of quality control of the active GaN layer in HEMTs is proposed based on determination of the SE threshold excitation level. An advantage of the method is that no reference sample is needed for comparison of different HEMT structures. Internal electric field strength values are determined from PR spectra and their correlation with 2DEG density is demonstrated.