Direction Of Electric Field Research Articles

Electric field induced bandgap enlargement of S- and N-hyperdoped silicon

In this paper, the effect of the electric field on the electronic structure of S-hyperdoped silicon and N-hyperdoped silicon is studied in detail by theory. The results show that the total bandgap initially increases and subsequently decreases with the increase of the electric field. Specifically, at an electric field of 0.1 V, the total bandgap reaches the maximum. With further increasing the electric field, the total bandgap decreases, but it is still larger than that in the absence of any electric field. The bandgap difference of the configuration in 2 × 2 × 2 supercell with and without electric field is approximately 0.2 eV. When 0.1 V of the electric field in the x and y directions is applied to the 2 × 2 × 3 supercell of the S- and N-hyperdoped silicon, the changes of the electronic structure are consistent. However, the band gap expansion is more obvious than that in the z direction electric field. While for 3 × 3 × 2 supercells of the S- and N-hyperdoped silicon, the band gap expansion is more significant under the z direction electric field than that under electric fields in the x and y directions. The difference in the bandgap variation under different directions of the electric field should be due to the direction-dependence of the impurity density in the 2 × 2 × 3 and 3 × 3 × 2 supercells. The results indicate that applying an electric field can further enlarge the bandgap of the S- and N-hyperdoped silicon and bring it closer to the optimal bandgap of an intermediate-band photovoltaic material.

Toward the Electrostatic Catalysis of Nucleophilic Substitutions: A Surface Chemistry Study of the Menshutkin Reaction.

The catalysis of nonredox reactions by external electric fields is one of the most rapidly expanding areas of chemistry. The Menshutkin reaction, a classic example of bimolecular nucleophilic substitution (SN2), involves the conversion of a tertiary amine to a quaternary ammonium salt by coupling it with an alkyl halide. The reaction barrier of the Menshutkin reaction is theoretically predicted to be highly sensitive to the magnitude and direction of an external electric field experienced by the transition state. In this study, we investigate how near-surface electric fields can drive this prototypical nucleophilic substitution by examining the coupling of a diffusive redox-tagged tertiary amine with an electrode-tethered alkyl bromide under a variable external bias. Our findings reveal a competition between electrostatically assisted reactions, solvent effects, and electrochemically triggered side reactions involving radical intermediates. We estimate that only about 5% of the coupling events are attributable to the external field, while the majority of the reaction products originate from electrochemically generated radical intermediates.

Enhancing optical absorbance and accelerating rotational speed in molecular motors through oriented external electric fields

Accelerating the rotational speed of light-driven molecular motors is among the foremost concerns in molecular machine research, as this speed directly influences the performance of a motor. Controlling the motor’s rotation is crucial for practical applications, and using an oriented external electric field (OEEF) represents a feasible method to achieve this objective. We have investigated the impact of an OEEF on the optical and kinetic properties of a novel π-donor/acceptor di-substituted molecular motor, R2,3-(NH2, CHO). We employed density functional theory (DFT) and time-dependent DFT methods to analyze the electronic excitation and thermal isomerization behavior. Our results demonstrate that the absorption wavelength, absorption efficiency of the motor, and rate constant of the thermal isomerization reaction can be adjusted by applying OEEFs, which are predictable based on the dipole moment and polarizability of the molecules under consideration. In particular, we observed a shift in the absorption wavelength toward longer ranges, an enhancement in light absorption intensity, and an acceleration in the rotation rate when applying a weak positive directional external electric field to the R2,3-(NH2, CHO) motor. In summary, this theoretical study highlights the potential of OEEFs for improving the performance of molecular motors.

Electromechanical properties of different phases in ferroelectric crystals regulated by variously oriented electric fields

Electric fields offer a convenient and tunable way to induce phase transitions for regulating the electromechanical properties of ferroelectrics. However, regulating the electromechanical properties by using electric fields in various directions for different ferroelectric phases has yet to be systematically investigated, especially for lead-free material KNbO3. Based on the nonlinear thermodynamics analysis, the electric field-temperature phase diagrams of KNbO3 single crystals under different electric field directions (E[001], E[011], E[111]) have been constructed, along with the electric-field-induced electromechanical responses. The results show that the phase diagrams are markedly different under different electric field directions. Specifically, the electric field-temperature phase diagram appears as a "line"-shaped phase boundary under E[001], while it appears as a "U"-shaped phase boundary under E[011], and an arrowhead-shaped phase boundary under E[111]. It is also found that there are excellent electromechanical responses near both "U"-shaped and arrowhead-shaped phase boundaries due to the significant alterations in polarization slopes near the phase boundaries, offering an alternative pathway to regulate and enhance the electromechanical properties in ferroelectrics.

Co/Co3O4@NC-CNTs modified separator of Li-S battery achieving the synergistic effect of adsorption-directional migration-catalysis via built-in electric field

The shuttle effect of lithium polysulfides (LiPSs) and sluggish sulfur conversion kinetics have seriously hindered the commercial application of lithium-sulfur (Li-S) batteries. Currently, the adsorption and catalysis processes are emphasized; however, the diffusion process is often neglected. The delayed diffusion of the adsorbed LiPSs significantly reduce battery performance. Herein, the directional migration of Sn2- was realized by adjusting the characteristics of heterostructure materials. The heterostructure consists of Co with a high Fermi level and excellent catalytic activity and Co3O4 with a low Fermi level and strong adsorption ability. This configuration regulated the direction of the built-in electric field (BIEF) at the heterogeneous interface, which promoted the migration of Sn2− from Co3O4 to Co side and realised a continuous “adsorption-directional migration-catalysis” mechanism. Experimental and theoretical results indicated that the Co/Co3O4 heterostructure modified by nitrogen-doped carbon nanotubes (Co/Co3O4@NC-CNTs), as the separator of Li-S batteries, not only enhanced the adsorption of LiPSs but also accelerated the kinetic conversion process. Consequently, the battery modified by the Co/Co3O4@NC-CNTs separator exhibited a high initial specific capacity of 1423 mAh g−1 at 0.2C, and maintained 735.5 mAh g−1 at a current density of 1C after 400 cycles.

Binding Energy of Cylindrical Quantum Dots: Effects of External Electric Field and Impurity Position

We have investigated the binding energy properties of a cylindrical quantum dot (CQD) system layered as GaAs/AlGaAs under external electric fields. In our numerical calculations, we considered both on- and off-center impurity cases using the effective mass approximation. The eigenvalues and corresponding eigenfunctions of the system are obtained using a three-dimensional finite difference approach. It is found that the ground-state binding energy is significantly affected by the CQD dimensions (radius and height), impurity position, and the strength and direction of the external electric field. Additionally, the electron probability distributions are examined to provide deeper insight into the physical reasons underlying the behavior of the binding energy. These findings enhance our understanding of the tunable properties of CQDs, which may be useful in the design of optoelectronic and quantum devices.

Fabricated S-scheme CoS/CeO2 heterojunction photocatalyst efficiently activates peroxymonosulfate for polyethylene terephthalate plastic degradation: Insight into radicals and electron transfer

Polyethylene terephthalate (PET) plastics are widely utilized, yet they also give rise to significant environmental contamination. In this study, a CoS/CeO2 material with an S-scheme heterojunction was constructed using CoS with CeO2 derived from MOFs and employed for the photocatalytic activation of peroxomonosulfate (PMS) for the degradation of PET. The CoS/CeO2/vis/PMS system demonstrated a degradation rate of up to 95.75 % (weight loss rate) for PET plastic. The performance of this system is much better than that of simple photocatalytic or PMS systems. Photogenerated carriers generated by heterojunctions upon illumination accelerate the fast electron cycling of Co2+/Co3+ through the S-scheme transfer pathway driven by a directional interfacial electric field. This promoted efficient mass transfer in the inhomogeneous phase system (such as SO4•−, e−) and acted as an adsorption activation site for PMS. In-situ X-ray photoelectron spectroscopy (In-situ XPS) and ESR test proved that the electron flow in the heterojunction conforms to the S-scheme mechanism. Density functional theory (DFT) calculations revealed the material of the CoS/CeO2 interface and the successful construction of the modulated electronic structure led to the accumulation of holes on CeO2 and electrons on CoS. Bader analysis on charge density distribution further demonstrated that the formation of the heterojunction decreased the adsorption energy of the PMS on the Co sites, which in turn lowered the energy barrier for the generation of SO4•−. This work would provide a novel solution to the problem of removing plastic pollutants from water, as well as new insight into the construction of S-scheme heterojunctions and the mechanism of photocatalytic PMS activation.

Synthesis of Porous Metal Oxides Utilizing Nanosheet Colloid with Liquid Crystallinity

Activated carbon, a high specific surface area microporous carbon(>2000 m2 g–1), has been used as the electrode material for electrochemical double layer capacitors.1 The structure of activated carbon is characterized by a three-dimensional network consisting of graphene-like layers. Preparation of metal oxides with a similar porous structure is anticipated to behave as pseudocapacitive electrode materials with high energy density. However, the hierarchical porous structure of activated carbon is obtained by gas-phase or chemical activation treatment and is applicable only to carbonaceous materials. Thus, an alternative strategy is necessary to prepare metal oxides with porous architectures similar to activated carbon.Assembly of inorganic oxide nanosheets is one of the promising methods to prepare hierarchical porous metal oxides. Here, we focus on the phenomenon where inorganic oxide nanosheets form liquid crystal structures in colloids and align macroscopically under an electric field. A highly concentrated hexaniobate nanosheet ([Nb6O17]4 –(ns)) colloid is known to exhibit liquid crystalline behavior.2 Additionally, the orientation of nanosheet with micro-mesoscale sheet spacing (< tens of nm) forms a hierarchical macroscopic structure (< several hundred µm) under an electric field.3 Therefore, the liquid crystalline structure and its responsiveness to electric fields in nanosheet colloids are effective for controlling the hierarchically nanosheet-assembled structure. In this study, we applied the freeze-drying method of nanosheet liquid crystals (NLC) to transfer the structure within the fluid nanosheet colloid to the dried aggregates (Figure 1).[Nb6O17]4 –(ns) colloids with developed liquid crystal domains form stripe-shaped macrostructures by applying an alternating current (AC) electric field (10 Vp–p, 50 kHz) perpendicular to the direction of gravity.3 Figure 1(a) shows the polarized optical microscopy (POM) image of the stripe-shaped macrostructures with a width of 100 µm and intervals of 200 µm composed of [Nb6O17]4 –(ns). In the birefringent regions, NLC oriented perpendicular to the direction of the AC electric field and parallel to the direction of the gravity. After applying an electric field to the cell, the cell was immersed in liquid nitrogen with applying the electric field and then dried in vacuum, resulting in the formation of a sponge-like nanosheet aggregate between the electrodes. The bright-field optical microscope image of the freeze-dried aggregates shows the similar stripe-shaped macrostructures to that of NLC under the electric field (Figure 1(b)). Therefore, the macrostructure of NLC oriented in an electric field can be transferred into the porous nanosheet aggregates by freeze-drying method. These results indicate that the liquid crystalline and electric field responsive properties of nanosheet colloids are useful for structural design of nanosheet-assembled materials. References P. Simon and Y. Gogotsi, Nat. Mater., 7, 845 (2008).N. Miyamoto and T. Nakato, Adv. Mater., 14, 1267 (2002).T. Nakato, Y. Nono, E. Mouri and M. Nakata, Phys. Chem. Chem. Phys., 16, 955 (2014). Figure 1

Domain switching and shear-mode piezoelectric response induced by cross-poling in polycrystalline ferroelectrics

The mechanisms contributing to the electromechanical response of piezoelectric ceramics in the shear mode have been investigated using high-energy synchrotron x-ray diffraction. Soft lead zirconate titanate ceramic specimens were subjected to an electric field in the range 0.2–3.0 MV m−1, perpendicular to that of the initial poling direction, while XRD patterns were recorded in transmission. At low electric field levels, the axial strains remained close to zero, but a significant shear strain occurred due to the reversible shear-mode piezoelectric coefficient. Both the axial and shear strains increased substantially at higher field levels due to irreversible ferroelectric domain switching. Eventually, the shear strain decreased again as the average remanent polarization became oriented toward the electric field direction. The lattice strain and domain orientation distributions follow the form of the total strain tensor, enabling the domain switching processes to be monitored by the rotation of the principal strain axis. Reorientation of this axis toward the electric field direction occurred progressively above 0.6 MV m−1, while the angle of rotation increased from 0° to approximately 80° at the maximum field of 3.0 MV m−1. A strong correlation was established between the effective strains associated with different crystallographic directions, which was attributed to the effects of elastic coupling between grains in the polycrystal.

Two distinct current systems in the ionosphere of Mars

When the solar wind interacts with the ionosphere of an unmagnetized planet, it induces currents that form an induced magnetosphere. These currents and their associated magnetic fields play a pivotal role in controlling the movement of charged particles, which is essential for understanding the escape of planetary ions. Unlike the well-documented magnetospheric current systems, the ionospheric current systems driven by solar wind and atmospheric neutral winds have not been quantitatively observed, which constrains the quantification of energy transfer from stars to these planets. Here, utilizing eight years of data from the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission, we investigate the global distribution of ionospheric currents on Mars. We identify two distinct current systems in the ionosphere: one aligns with the solar wind electric field but exhibits hemispheric asymmetry perpendicular to the solar wind electric field direction; the other corresponds to the flow pattern of annually averaged neutral winds. We propose that these two current systems are driven by the solar wind and atmospheric neutral winds, respectively. Our findings reveal that Martian ionospheric dynamics are influenced by the neutral winds from below and the solar wind from above, highlighting the complex and intriguing nature of current systems on unmagnetized planets.

Electrically enhanced adsorption and photocatalytic properties of g-C3N4/TiO2 heterostructure for removal of tetracycline in water: A study by molecular dynamics simulation and experiment

Here, molecular dynamics (MD) simulations and experimental studies were carried out to investigate the effect and mechanism of external applied electric fields on the adsorption efficiency of g-C3N4/TiO2 heterostructure for removing tetracycline (TC) from water. The MD simulation results indicate that the electric fields in the X and Y directions have little effect, while the electric field in the Z direction has a significant impact on the adsorption system. The Z direction electric field significantly reduces the number of water molecules near the surface of the heterostructure, improves the adsorption energy between the heterostructure and TC molecules, and thereby enhances the adsorption effect. The experimental research results show that the removal rate of tetracycline increases from 26 % to 33 % in 90 min when an electric field of 3000 V/m is applied, which indicates that the presence of an external electric field can improve the adsorption and removal performance of g-C3N4/TiO2 heterostructure for TC in water, and verifies the research conclusion of MD simulations. Alkaline conditions are more conducive to the removal of TC. In addition, applying an external electric field can effectively improve the light absorption performance of heterostructures, thereby enhancing the photocatalytic degradation efficiency of TC.

Electroosmotic Flow-Driven DNA-CNT Nanomotor via Tunable Surface-Charged Nanopore Array.

Nanomotors are usually designed to work in liquid media and carry cargo; they exhibit excellent potential for biosensing and disease treatment applications due to their small size. Graphene and carbon nanotubes (CNTs) are crucial components of rotary nanomotors because of excellent mechanical properties and adaptability to the human body. Herein, we introduce a DNA-CNT-based nanomotor that achieves its rotational control through an array of nanopores with tunable surface charges. The findings demonstrate that by adjusting the surface charge density of the nanopores and the direction of electric field, a DNA strand can be sequentially captured by the nanopores, thereby rotating the connected CNT. The transition from a four-nanopore array to a six-nanopore array reveals that reducing the step angle to 60° significantly enhances the rotational stability of the nanomotor and reduces random fluctuations caused by Brownian motion. This method improves the control stability of the nanomotor, providing robust support for future applications in nanoscale manipulation.

Radial electric field driven by vertical neutral beamlet injection under future fusion reactor conditions

Abstract The fast ions and electrons generated by neutral beam injection (NBI) can induce charge separation, resulting in radial electric fields. Employing beamlet injection of small cross-section may effectively generate radial electric field, and adjusting beamlet parameters allows active control over their distribution. A new NBI injection geometry system has been developed in the NEOE code to explore the potential for vertical beamlets injection in future fusion reactor scenarios. Both high-field side and low-field side beamlet vertical injections can establish radial electric fields. In scenarios dominated by collision effects, the direction of the radial electric field is influenced by the toroidal angle of the beamlet. Adjusting the poloidal angle can alter the location of the electric field shear. Injecting particles into the trapped region using broader banana orbits can establish electric fields within the plasma core. Alternatively, injecting particles into the passing region can yield higher electric fields. Under future reactor conditions, conservative estimates of the electric field shear may even surpass critical velocities, potentially contributing to instability suppression.

An electro-thermo-mechanical coupling phase-field model of defect evolution induced by electromigration in interconnects

In this paper, the defect evolution caused by electromigration induced surface diffusion in interconnects is investigated using a newly-developed electro-thermo-mechanical coupling phase-field model. The Joule heat and its resulting thermomigration are included into the phase-field model. The governing equation of the phase-field is solved by semi-implicit spectral methods and the accompanied governing equations of applied physics fields are solved by finite volume methods. Comparative investigation into defect evolution with and without the influence of Joule heating is conducted. It is deduced that thermomigration facilitates local elongation of the defect in the “current crowding” region and exerts a substantial influence on the defect morphological evolution. Subsequently, the effect of the inclination angle of the electric field on the void morphology evolution and crack propagation is discussed. We find that the defect achieves the largest characteristic length when the electric field direction is perpendicular to the uniaxial tension direction, implying a higher threat to the circuit safety. This study may help to deepen people's understanding of how the thermal effect functions in electromigration process and sheds light on different modes of defect evolution in interconnects.

Surface acoustic wave amplification by drifting electrons in semiconducting epitaxial graphene on silicon carbide

Abstract A theory is presented for the amplification of a surface acoustic wave (SAW) due to its interaction with conduction electrons in gate-controlled epitaxial graphene (epigraphene) on a SiC substrate. It is assumed that the SAW is launched onto the substrate in the direction of an external dc electric field applied to the graphene sample and causing the conduction electrons to drift at a speed greater than the speed of the SAW. The wavelength of the SAW is assumed to be shorter than the mean free path of the electrons, so that the quantum regime of interaction of those electrons with the SAW is realized. The Green’s function method is used to calculate the SAW gain as a function of the electron concentration in epigraphene and the external dc electric field strength. It is shown that the substrate-induced band gap in the electronic spectrum of epigraphene leads to a significant (at least an order of magnitude) increase in the SAW gain as compared to the case of gapless graphene. In addition, the opening of the band gap results in a non-monotonic dependence of the SAW gain on the electron concentration, controlled by the gate voltage applied to the graphene sample. This dependence is characterized by the presence of a distinct maximum at a certain value of electron concentration (of about 2 × 10 12 cm−2 for typical values of the other parameters involved), which distinguishes it from the monotonic concentration dependence of the SAW gain in gapless graphene.

Multi-physical quantities sensing based on the nematic liquid crystal Janus metastructure in theory

Breaking through the idea limitation of traditional single-scale and single-function sensors, a multi-scale and multi-function Janus metastructure (JMS) is proposed in this article, which is constructed by the specific methods to break its parity. Using the change of transmission spectrum, JMS can realize multi-physical quantities detection with different sensing performances, when electromagnetic waves propagate on positive and negative scales respectively. For selective gas detection, JMS can conveniently detect 0–3.5 % methane concentrations with sensitivity (S) of 22.932 THz/RIU and 0–3 % hydrogen concentrations with S of 43.494 THz/RIU, avoiding the problem of complex and dangerous external operation conditions required for previous gas sensors. Based on the electro-optical effect of nematic liquid crystal, JMS can realize wide-range electric field direction (EFD) sensing of 10°–80° and 100°–170° by taking the advantages of multi-scale detection, which is wider than existing 0°–90° EFD sensors. Because nematic liquid crystal is thermotropic, JMS can also achieve accurate temperature detection of 283.15–318.15 K. Finally, through comparison, it is proved that JMS proposed has the potential of multi-scenario applications, and meets the urgent demand for excellent performance sensors in the fields of dangerous gas transportation, atmospheric EFD detection and industrial manufacturing temperature control.

Measurement of microwave polarization using two polarization orthogonal local microwave electric fields in a Rydberg atom-based mixer.

We propose and demonstrate what we believe to be a novel method for measuring the polarization direction of a microwave electric field in a single measurement using a Rydberg atom-based mixer with two orthogonally polarized local microwave electric fields. This approach eliminates the need for physical rotation of the local field, allowing the polarization angle of the signal field to be determined directly by measuring the ratio of the two beat signals. Furthermore, introducing a weak static magnetic field enables the utilization of the Zeeman effect and exploitation of polarization asymmetry. This distinction allows for determining the polarization direction of the microwave field is θ or 180° - θ within the 0 to 180-degree range. The capability to measure microwave polarization in real-time across this range is very valuable for applications in microwave sensing and information transmission.

Picometer-Level In Situ Manipulation of Ferroelectric Polarization in Van der Waals layered InSe.

Ferroelectric 2D van der Waals (vdW) layered materials are attracting increasing attention due to their potential applications in next-generation nanoelectronics and in-memory computing with polarization-dependent functionalities. Despite the critical role of polarization in governing ferroelectricity behaviors, its origin and relation with local structures in 2D vdW layered materials have not been fully elucidated so far. Here, intralayer sliding of approximately six degrees within each quadruple-layer of the prototype 2D vdW ferroelectrics InSe is directly observed and manipulated using sub-angstrom resolution imaging and in situ biasing in an aberration-corrected scanning transmission electron microscope. The in situ electric manipulation further indicates that the reversal of intralayer sliding can be achieved by altering the electric field direction. Density functional theory calculations reveal that the reversible picometer-level intralayer sliding is responsible for switchable out-of-plane polarization. The observation and manipulation of intralayer sliding demonstrate the structural origin of ferroelectricity in InSe and establish a dynamic structural variation model for future investigations on more 2D ferroelectric materials.

Spontaneous built-in electric field in W-W2C@C heterostructure: Accelerating Sn2- directed migration in Li-S batteries

The commercialization of Li-S batteries is severely hindered by shuttle effect and sluggish redox reaction kinetics of LiPSs. Heterostructure can resolve the above shortcomings through the synergistic effect of adsorption and catalysis. However, long-chain LiPSs dissolving in electrolyte tend to cluster, resulting in low sulfur utilization and preventing kinetic conversion Thus, it is necessary to regulate the diffusion of Sn2− to achieve the directional diffusion from adsorbent to catalyst. Nevertheless, the design principle has not yet been clarified. W-W2C@C heterostructure with W of strong adsorption ability and high work function and W2C of excellent catalytic activity and low work function is designed by theoretical screening. Due to work function difference, this heterostructure controls the direction of the interface built-in electric field (BIEF), realizing the directional migration process of Sn2− from adsorptive W to catalytic W2C, thereby achieving a continuous “trapping-directional migration-conversion” reaction mechanism. The batteries have an excellent Li+ diffusion rate, high initial discharge specific capacity (1400.6 mAh/g at 0.2C), excellent rate capability (853.2 mAh/g at 2C), high reversible capacity (977.9 mAh/g after 150 cycles at 0.2C) and an extremely low capacity decay rate of 0.09 % per cycle after 300 cycles at 1C.

Structural design of hierarchical porous biomass carbon with a built-in electric field for efficient peroxymonosulfate activation

Biomass-derived carbon materials have excellent adsorption capacity and cost-effectiveness, and the electron interactions between multiphase composite materials improve the efficiency of water pollutant removal by advanced oxidation processes (AOPs). Herein, a multistage biochar catalyst in which metallic cobalt-embedded carbon tubes are prepared uniformly on the surface of kapok tubes is designed and fabricated. The closely connected structure grown in situ accelerates electron migration and forms a directional transfer electric field. The N-doped carbon nanotube encapsulated Co nanoparticles growth on the kapok biochar/PMS (Co-N-KBC/PMS) system removes tetracycline hydrochloride (TCH) at a rate 11.8 times higher than that of KBC/PMS. Free radicals (SO4•−, •OH, and •O2–) and non-free radicals (1O2) are generated in conjunction with electron transfer during PMS activation. The cobalt sites and C=O groups are possible active sites. Density-functional theory (DFT) calculations verify the built-in electric field from N-KBC to the Co surface, which accelerates electron transfer and improves TCH removal. The results reveal an effective strategy to activate PMS and address environmental remediation by utilizing carbon materials derived from biomass.