Showing papers on "Electric field published in 2021"

Interfacial chemical bond and internal electric field modulated Z-scheme Sv-ZnIn2S4/MoSe2 photocatalyst for efficient hydrogen evolution

Abstract: Construction of Z-scheme heterostructure is of great significance for realizing efficient photocatalytic water splitting. However, the conscious modulation of Z-scheme charge transfer is still a great challenge. Herein, interfacial Mo-S bond and internal electric field modulated Z-scheme heterostructure composed by sulfur vacancies-rich ZnIn2S4 and MoSe2 was rationally fabricated for efficient photocatalytic hydrogen evolution. Systematic investigations reveal that Mo-S bond and internal electric field induce the Z-scheme charge transfer mechanism as confirmed by the surface photovoltage spectra, DMPO spin-trapping electron paramagnetic resonance spectra and density functional theory calculations. Under the intense synergy among the Mo-S bond, internal electric field and S-vacancies, the optimized photocatalyst exhibits high hydrogen evolution rate of 63.21 mmol∙g−1·h−1 with an apparent quantum yield of 76.48% at 420 nm monochromatic light, which is about 18.8-fold of the pristine ZIS. This work affords a useful inspiration on consciously modulating Z-scheme charge transfer by atomic-level interface control and internal electric field to signally promote the photocatalytic performance. The construction of Z-scheme heterostructures is of great significance for realizing efficient photocatalytic water splitting. Here, the authors report an interfacial chemical bond and internal electric field modulated Z-Scheme Sv-ZnIn2S4/MoSe2 photocatalyst for efficient hydrogen evolution.

Electric field–tunable superconductivity in alternating-twist magic-angle trilayer graphene

Abstract: Engineering moire superlattices by twisting layers in van der Waals (vdW) heterostructures has uncovered a wide array of quantum phenomena We constructed a vdW heterostructure that consists of three graphene layers stacked with alternating twist angles ±θ At the average twist angle θ ~ 156°, a theoretically predicted “magic angle” for the formation of flat electron bands, we observed displacement field–tunable superconductivity with a maximum critical temperature of 21 kelvin By tuning the doping level and displacement field, we found that superconducting regimes occur in conjunction with flavor polarization of moire bands and are bounded by a van Hove singularity (vHS) at high displacement fields Our findings display inconsistencies with a weak coupling description, suggesting that the observed moire superconductivity has an unconventional nature

Chiral-induced spin selectivity enables a room-temperature spin light-emitting diode

Abstract: In traditional optoelectronic approaches, control over spin, charge, and light requires the use of both electrical and magnetic fields. In a spin-polarized light-emitting diode (spin-LED), charges are injected, and circularly polarized light is emitted from spin-polarized carrier pairs. Typically, the injection of carriers occurs with the application of an electric field, whereas spin polarization can be achieved using an applied magnetic field or polarized ferromagnetic contacts. We used chiral-induced spin selectivity (CISS) to produce spin-polarized carriers and demonstrate a spin-LED that operates at room temperature without magnetic fields or ferromagnetic contacts. The CISS layer consists of oriented, self-assembled small chiral molecules within a layered organic-inorganic metal-halide hybrid semiconductor framework. The spin-LED achieves ±2.6% circularly polarized electroluminescence at room temperature.

Local negative permittivity and topological phase transition in polar skyrmions

Abstract: Topological solitons such as magnetic skyrmions have drawn attention as stable quasi-particle-like objects. The recent discovery of polar vortices and skyrmions in ferroelectric oxide superlattices has opened up new vistas to explore topology, emergent phenomena and approaches for manipulating such features with electric fields. Using macroscopic dielectric measurements, coupled with direct scanning convergent beam electron diffraction imaging on the atomic scale, theoretical phase-field simulations and second-principles calculations, we demonstrate that polar skyrmions in (PbTiO3)n/(SrTiO3)n superlattices are distinguished by a sheath of negative permittivity at the periphery of each skyrmion. This enhances the effective dielectric permittivity compared with the individual SrTiO3 and PbTiO3 layers. Moreover, the response of these topologically protected structures to electric field and temperature shows a reversible phase transition from the skyrmion state to a trivial uniform ferroelectric state, accompanied by large tunability of the dielectric permittivity. Pulsed switching measurements show a time-dependent evolution and recovery of the skyrmion state (and macroscopic dielectric response). The interrelationship between topological and dielectric properties presents an opportunity to simultaneously manipulate both by a single, and easily controlled, stimulus, the applied electric field.

Built-in Electric Field Triggered Interfacial Accumulation Effect for Efficient Nitrate Removal at Ultra-Low Concentration and Electroreduction to Ammonia.

Abstract: A built-in electric field in electrocatalyst can significantly accumulate higher concentration of NO3 - ions near electrocatalyst surface region, thus facilitating mass transfer for efficient nitrate removal at ultra-low concentration and electroreduction reaction (NO3 RR). A model electrocatalyst is created by stacking CuCl (111) and rutile TiO2 (110) layers together, in which a built-in electric field induced from the electron transfer from TiO2 to CuCl (CuCl_BEF) is successfully formed . This built-in electric field effectively triggers interfacial accumulation of NO3 - ions around the electrocatalyst. The electric field also raises the energy of key reaction intermediate *NO to lower the energy barrier of the rate determining step. A NH3 product selectivity of 98.6 %, a low NO2 - production of <0.6 %, and mass-specific ammonia production rate of 64.4 h-1 is achieved, which are all the best among studies reported at 100 mg L-1 of nitrate concentration to date.

B-Doped 2D-InSe as a bifunctional catalyst for CO2/CH4 separation under the regulation of an external electric field.

Abstract: The separation of CO2 or CH4 from a CO2/CH4 mixture has drawn great attention in relation to solving air pollution and energy shortage issues. However, research into using bifunctional catalysts to separate CO2 and CH4 under different conditions is absent. We have herein designed a novel B-doped two-dimensional InSe (B@2DInSe) catalyst, which can chemically adsorb CO2 with covalent bonds. B@2DInSe can separate CO2 and CH4 in different electric fields, which originates from different regulation mechanisms by an electric field (EF) on the electric properties. The hybridization states between CO2 and B@2DInSe near the Fermi level have experienced gradual localization and eventually merged into a single narrow peak under an increased EF. As the EF further increased, the merged peak shifted towards higher energy states around the Fermi level. In contrast, the EF mainly alters the degree of hybridization between CH4 and B@2DInSe at states far below the Fermi level, which is different from the CO2 situation. These characteristics can also lead to perfect linear relationships between the adsorption energies of CO2/CH4 and the electric field, which may be beneficial for the prediction of the required EF without large volumes of calculations. Our results have not only provided novel clues for catalyst design, but they have also provided deep understanding into the mechanisms of bifunctional catalysts.

High-k Oxide Field-Plated Vertical (001) β-Ga 2 O 3 Schottky Barrier Diode With Baliga’s Figure of Merit Over 1 GW/cm 2

Abstract: We report a vertical (001) $\beta $ -Ga2O3 field-plated (FP) Schottky barrier diode (SBD) with a novel extreme permittivity dielectric field oxide. A thin drift layer of $1.7~\mu {m}$ was used to enable a punch-through (PT) field profile and very low differential specific on-resistance ( $\text{R}_{\text {on-sp}}$ ) of 0.32 $\text{m}\Omega $ -cm2. The extreme permittivity field plate oxide facilitated the lateral spread of the electric field profile beyond the field plate edge and enabled a breakdown voltage ( ${V}_{\textit {br}}$ ) of 687 V. The edge termination efficiency increases from 13.2% for non-field plated structure to 61% for high permittivity field plate structure. The surface breakdown electric field was extracted to be 5.45 MV/cm at the center of the anode region using TCAD simulations. The high permittivity field plated SBD demonstrated a record high Baliga’s figure of merit (BFOM) of 1.47 GW/cm2 showing the potential of Ga2O3 power devices for multi-kilovolt class applications.

Electric field control of superconductivity at the LaAlO 3 /KTaO 3 (111) interface.

Abstract: The oxide interface between LaAlO3 and KTaO3(111) can harbor a superconducting state. We report that by applying a gate voltage (VG) across KTaO3, the interface can be continuously tuned from superconducting into insulating states, yielding a dome-shaped Tc-VG dependence, where Tc is the transition temperature. The electric gating has only a minor effect on carrier density but a strong one on mobility. We interpret the tuning of mobility in terms of change in the spatial profile of the carriers in the interface and hence, effective disorder. As the temperature is decreased, the resistance saturates at the lowest temperature on both superconducting and insulating sides, suggesting the emergence of a quantum metallic state associated with a failed superconductor and/or fragile insulator.

Semiconductor-to-metal transition in bilayer MoSi2N4 and WSi2N4 with strain and electric field

Abstract: With exceptional electrical and mechanical properties and at the same time air-stability, layered MoSi2N4 has recently drawn great attention. However, band structure engineering via strain and electric field, which is vital for practical applications, has not yet been explored. In this work, we show that the biaxial strain and external electric field are effective ways for the bandgap engineering of bilayer MoSi2N4 and WSi2N4. It is found that strain can lead to indirect bandgap to direct bandgap transition. On the other hand, electric field can result in semiconductor to metal transition. Our study provides insights into the band structure engineering of bilayer MoSi2N4 and WSi2N4 and would pave the way for its future nanoelectronics and optoelectronics applications.

Photocatalytic H2O Overall Splitting into H2 Bubbles by Single Atomic Sulfur Vacancy CdS with Spin Polarization Electric Field.

Abstract: Low efficient transfer of photogenerated charge carriers to redox sites along with high surface reaction barrier is a bottleneck problem of photocatalytic H2O overall splitting. Here, in the absence of cocatalysts, H2O overall splitting has been achieved by single-atomic S vacancy hexagonal CdS with a spin polarization electric field (PEF). Theoretical and experimental results confirm that single-atomic S vacancy-induced spin PEF with opposite direction to the Coulomb field accelerates charge carrier transport dynamics from the bulk phase to surface-redox sites. By systematically tuning the spin PEF intensity with single-atomic S vacancy content, common pristine CdS is converted to a photocatalyst that can efficiently complete H2O overall splitting by releasing a great number of H2 bubbles under natural solar light. This work solves the bottleneck of solar energy conversion in essence by single atom vacancy engineering, which will promote significant photocatalytic performance enhancement for commercialization.

In situ construction of Sn-doped structurally compatible heterojunction with enhanced interfacial electric field for photocatalytic pollutants removal and CO2 reduction

Abstract: Fabrication of heterojunction photocatalysts is a promising strategy for achieving spatial charge separation, for which the interfacial electric field is the linchpin. However, the current density of interfacial electric field still have room for enhancement. In this study, we first demonstrated the regulation of interfacial electric field between bismuth semiconductors assisted by stannum (Sn) doping, raising the surface charge transfer efficiency from 27.25 % of BiOBr/BiOIO3 to 38.08 % of Sn-BiOBr/BiOIO3 composite. Correspondingly, the visible-light induced degradation rates towards tetracycline, 2, 4-chlorophenol and Rhodamine B exhibited 4.2-, 4.7- and 31.5-fold increase, respectively. Meanwhile, the CO2 photoreduction activity was also improved. The density functional theory calculation results unveiled that the Sn2+/Sn4+ redox couple could cause charge redistribution at interface and a distinctly unidirectional interfacial electric field with the direction from BiOIO3 to Sn-BiOBr was formed. This study provides a universal strategy for the design of bismuth-containing heterojunction with tunable interfacial electric field.

Asymmetric response of interfacial water to applied electric fields

Abstract: Our understanding of the dielectric response of interfacial water, which underlies the solvation properties and reaction rates at aqueous interfaces, relies on the linear response approximation: an external electric field induces a linearly proportional polarization. This implies antisymmetry with respect to the sign of the field. Atomistic simulations have suggested, however, that the polarization of interfacial water may deviate considerably from the linear response. Here we present an experimental study addressing this issue. We measured vibrational sum-frequency generation spectra of heavy water (D2O) near a monolayer graphene electrode, to study its response to an external electric field under controlled electrochemical conditions. The spectra of the OD stretch show a pronounced asymmetry for positive versus negative electrode charge. At negative charge below 5 × 1012 electrons per square centimetre, a peak of the non-hydrogen-bonded OD groups pointing towards the graphene surface is observed at a frequency of 2,700 per centimetre. At neutral or positive electrode potentials, this ‘free-OD’ peak disappears abruptly, and the spectra display broad peaks of hydrogen-bonded OD species (at 2,300–2,650 per centimetre). Miller’s rule1 connects the vibrational sum-frequency generation response to the dielectric constant. The observed deviation from the linear response for electric fields of about ±3 × 108 volts per metre calls into question the validity of treating interfacial water as a simple dielectric medium. Experimental measurements of vibrational sum-frequency generation spectra indicate that the dielectric response of water near an electrode may be strongly asymmetric, with different responses to positive and negative electrode charge.

β-Ga2O3 vertical heterojunction barrier Schottky diodes terminated with p-NiO field limiting rings

Abstract: In this Letter, high-performance β-Ga2O3 vertical heterojunction barrier Schottky (HJBS) diodes have been demonstrated together with the investigation of reverse leakage mechanisms. In HJBS configurations, NiO/β-Ga2O3 p-n heterojunctions and p-NiO field limiting rings (FLRs) are implemented by using a reactive sputtering technique at room temperature without intentional etching damages. Determined from the temperature-dependent current-voltage characteristics, the reverse leakage mechanism of the HJBS diode is identified to be Poole-Frenkel emission through localized trap sates with an energy level of EC-0.72 eV. With an uniform FLR width/spacing of 2 μm in HJBS, a maximum breakdown voltage (BV) of 1.89 kV and a specific on-resistance (Ron,sp) of 7.7 mΩ·cm2 are achieved, yielding a high Baliga's figure-of-merit (FOM, BV2/Ron,sp) of 0.46 GW/cm2. The electric field simulation and statistical experimental facts indicate that the electric field crowding effect at device edges is greatly suppressed by the shrinkage of p-NiO FLR spacing, and the capability of sustaining high BV is enhanced by the NiO/β-Ga2O3 bipolar structure, both of which contribute to the improved device performance. This work makes a significant step to achieve high performance β-Ga2O3 power devices by implementing alternative bipolar structures to overcome the difficulty in p-type β-Ga2O3.

Impact ionization coefficients and critical electric field in GaN

Abstract: Avalanche multiplication characteristics in a reverse-biased homoepitaxial GaN p–n junction diode are experimentally investigated at 223–373 K by novel photomultiplication measurements utilizing above- and below-bandgap illumination. The device has a non-punch-through one-side abrupt p–-n+ junction structure, in which the depletion layer mainly extends to the p-type region. For above-bandgap illumination, the light is absorbed at the surface p+-layer, and the generated electrons diffuse and reach the depletion layer, resulting in an electron-injected photocurrent. On the other hand, for below-bandgap illumination, the light penetrates a GaN layer and is absorbed owing to the Franz–Keldysh effect in the high electric field region (near the p–n junction interface), resulting in a hole-induced photocurrent. The theoretical (non-multiplicated) photocurrents are calculated elaborately, and the electron- and hole-initiated multiplication factors are extracted as ratios of the experimental data to the calculated values. Through the mathematical analyses of the multiplication factors, the temperature dependences of the impact ionization coefficients of electrons and holes in GaN are extracted and formulated by the Okuto–Crowell model. The ideal breakdown voltage and the critical electric field for GaN p–n junctions of varying doping concentration are simulated using the obtained impact ionization coefficients, and their temperature dependence and conduction-type dependence were discussed. The simulated breakdown characteristics show good agreement with data reported previously, suggesting the high accuracy of the impact ionization coefficients obtained in this study.

On-chip sampling of optical fields with attosecond resolution

Abstract: We demonstrate an on-chip, optoelectronic device capable of sampling arbitrary, low-energy, near-infrared waveforms under ambient conditions with sub-optical-cycle resolution. Our detector uses field-driven photoemission from resonant nanoantennas to create attosecond electron bursts that probe the electric field of weak optical waveforms. Using these devices, we sampled the electric fields of ~5 fJ (6.4 MV m−1), few-cycle, near-infrared waveforms using ~50 pJ (0.64 GV m−1) near-infrared driving pulses. Beyond sampling these weak optical waveforms, our measurements directly reveal the localized plasmonic dynamics of the emitting nanoantennas in situ. Applications include broadband time-domain spectroscopy of molecular fingerprints from the visible region through the infrared, time-domain analysis of nonlinear phenomena and detailed investigations of strong-field light–matter interactions. An on-chip, sub-optical-cycle sampling technique for measuring arbitrary electric fields of few-femtojoule near-infrared optical pulses in ambient conditions is demonstrated, offering an improvement of roughly six orders of magnitude in energy sensitivity compared with those previous works in the near-infrared.

Remarkably enhanced energy-storage density and excellent thermal stability under low electric fields of (Na0.5Bi0.5)TiO3-based ceramics via composition optimization strategy

Abstract: High energy density and high thermal stability of energy-storage properties (ESP) under low electric fields are extremely crucial for the application of dielectric ceramics in miniaturized equipment. In present work, we use a composition-optimization approach to break the long-range ferroelectric order and modulate polar nanoregions (PNRs) in the local structure of (1-x)[0.7(Na0.5Bi0.5)TiO3-0.3(Sr0.7Bi0.2)TiO3]-xBi(Mg0.5Ti0.5)O3 system. The large Pmax value is maintained due to the existence of Bi ions in both the matrix and dopants. As a result, a high Wrec of 3.03 J/cm3 together with a moderate η of 79.5 % was obtained in x = 0.05 sample at a low electric field of 200 kV/cm. Meanwhile, the high Wrec (2.41–2.52 J/cm3) and excellent thermal stability of ESP (Wrec varying less than 4.3 % and η > 90 %) from 50 °C to 200 °C at 150 kV/cm were also observed. The current system will be a promising candidate in energy-storage capacitor applications under low-fields and high-temperature.

Few-Mode Field Quantization of Arbitrary Electromagnetic Spectral Densities

Abstract: We develop a framework that provides a few-mode master equation description of the interaction between a single quantum emitter and an arbitrary electromagnetic environment. The field quantization requires only the fitting of the spectral density, obtained through classical electromagnetic simulations, to a model system involving a small number of lossy and interacting modes. We illustrate the power and validity of our approach by describing the population and electric field spatial dynamics in the spontaneous decay of an emitter placed in a complex hybrid plasmonic-photonic structure.

High-temperature all-organic energy storage dielectric with the performance of self-adjusting electric field distribution

Abstract: As a key component of the dielectric capacitor, the dielectric material directly determines the performance of the capacitor. Poly(vinylidene fluoride) (PVDF) has received extensive attention for its large dielectric constant. However, PVDF has poor temperature resistance and cannot be used in high-temperature areas. In this work, a symmetrical sandwich structure was prepared by compounding polycarbonate (PC) and PVDF, in which PC has higher insulation and heat resistance than PVDF. It was found that as the temperature increases, the applied electric field would gradually concentrate on the PC layer, while the electric field borne by the PVDF layer gets much lower. In this way, a similarity-intelligent dielectric with the performance of self-adjusting electric field distribution was obtained, which can effectively avoid premature breakdown of PVDF under high-temperature conditions. Besides, when the PC is on the outside (CFC), it can not only increase the difficulty of carrier injection at the electrode, but also improve the heat resistance of the composite dielectric, and interface charge generated by this structure can effectively trap the carriers injected at the electrode. Finally, CFC-2 has excellent temperature stability and energy storage performance; it can withstand a breakdown strength of 500 MV m−1 even at 100 °C, and its energy storage density (6.35 J cm−3) and charge–discharge efficiency (77.21%) are 93.52% and 91.31% of room temperature, respectively. This work effectively improves the high-temperature energy storage characteristics of PVDF and broadens its application fields. Thus, improving the high-temperature energy storage characteristics of polymer dielectrics is of great significance.

High-Accuracy Complex Permittivity Characterization of Solid Materials Using Parallel Interdigital Capacitor- Based Planar Microwave Sensor

Abstract: This paper presents a planar microwave sensor for the sensitive and accurate characterization of complex permittivity of solid materials. To realize the proposed sensor, the combination of a parallel interdigital capacitor and a dual wide gap resonator was etched on the ground plane and coupled with a transmission line in the top plane of a printed circuit board. The main advantage of the proposed sensor configuration lies in the generation of a high-intensity coupled resonating electric field suitable for the sensitive measurement of complex permittivity of solid materials. The high-intensity electric field enhances the coupling and field interaction, and thereby produces a high-accuracy permittivity characterization of a solid material exposed to the maximum field of the proposed sensor. Our developed microwave permittivity sensor, which characterized the complex permittivity of several materials by exploiting the measured shifts in resonance frequencies, exhibited a high sensitivity (up to 37% shift in resonance frequency for 20% change in permittivity) at least 1.5 times higher than previously reported microwave permittivity sensors. In addition, the proposed sensor exhibited 99.9% and 99.7% sensing accuracies for real and imaginary parts of permittivity, respectively, and the measurement results revealed an excellent (0.06758) and high sensitivity (67.58 MHz per unit change in real permittivity).

Effects of electric field on multiple vibrational resonances in Hindmarsh-Rose neuronal systems

Abstract: The effects of electric field on vibrational resonance in single Hindmarsh-Rose (HR) neuron and coupled HR neurons system are investigated by using Fourier coefficient, respectively. It is found that the multiple vibrational resonances (MVR) can be observed in a single HR neuron model no matter the electric field is considered or not, and the electric field weakens the MVR. When bidirectional coupling between two HR neurons is considered, the occurrence of MVR can also be detected, it is very interesting to observe that the electric field can enhance the MVR. The higher the frequency of the low-frequency signal is, the less the number of resonance peaks of the system response to the low-frequency signal will be. Moreover, the local anti-resonance is also observed when appropriate parameters are selected. The effects of coupling strength and other system parameters on Fourier coefficient are also illustrated here. The systems manifesting MVR have better capacity for detecting and propagating signals.