Charge Electric Field Research Articles

Tracking electronic band alignment across 2D bridge-channel MoS2 during charge transport

Commanding charge carrier diffusion in semiconducting channels requires the precise and realistic experimental realization of electronic energy band alignments at the interfaces and within the channels. We have demonstrated a non-contact and direct way to accurately probe the energy band bending at nanoscale spatial precision on MoS2 flakes laid on gold electrodes by mapping the surface potential landscape at non-equilibrium conditions during carrier injection. By systematically varying the charge carrier injection, the contrast gradient in surface potential profiles is studied along the MoS2 channel. Corresponding interfacial parameters, such as surface electric field (ξ), built-in potential (Ψbi), and space charge density (σ), are experimentally determined.

Chiral nanohelmet array films with Three-Dimensional (3D) resonance cavities

Chiral nanohelmet array (NHA) films are prepared via an efficient and low-cost colloidal lithography and exhibit strong chiroptical properties. The chirality can be tailored by the opening-angle of the nanounits in the ultraviolet–visible light range, and optical g-factor reaches about 0.26. Such properties can be attributed to the dissymmetric charge oscillations and electric field distributions. Continuous chiral films can be facilely transferred onto other functional substrates and even, inverted in the transferring process, indicating more flexible application scenarios. Especially, benefiting from the three-dimensional (3D) resonance cavities, change of surrounding environment could further result in distinct surface plasmon (SP) modes, thus diverse chiroptical activities. Label-free enantiodiscrimination of biomolecules was demonstrated based on the chiral resonator with pronounced local superchiral fields. Overall, with strong chirality, excellent tunability, transferability and scalable fabrication, the chiral plasmonic NHA will benefit the study of chiral metamaterials and provide a reliable platform for various photonic applications and label-free chiral sensors.

Lattice Boltzmann modeling of two-phase electrohydrodynamic flows under unipolar charge injection.

In this work, a two-dimensional droplet confined between two parallel electrodes under the combined effects of a nonuniform electric field and unipolar charge injection is numerically investigated using the lattice Boltzmann method (LBM). Under the non-Ohmic regime, the interfacial tension and electric forces at the droplet surface cooperate with the volumetric Coulomb force, leading to complex deformation and motion of the droplet while at the same time inducing a bulk electroconvective flow. After we validate the model by comparing with analytical solutions at the hydrostatic state, we perform a quantitative analysis on the droplet deformation factor D and bulk flow stability criteria T_{c} under different parameters, including the electric capillary number Ca, the electric Rayleigh number T, the permittivity ratio ɛ_{r}, and the mobility ratio K_{r}. It is found that the bulk flow significantly modifies the magnitude of D, which in turn decreases T_{c} of the electroconvective flow. For a droplet repelled by the anode, ɛ_{r}>1, an interesting linear relationship can be observed in the D-Ca curves. However, for a droplet attracted to the anode, ɛ_{r}<1, the system is potentially unstable. After first evolving into a quasisteady state, the droplet successively experiences steady flow, periodic flow, second steady flow, and oscillatory flow with increasing T. Moreover, discontinuities can be observed in the D-T curves due to the transitions of bulk flow.

Experiment and numerical simulation on the fine particle migration behaviors for the collection efficiency enhancement of a wire-plate electrostatic precipitator in pig house

In this paper, an integrated numerical model is presented and validated to investigate the particle charging and migration behaviors in a wire-plate electrostatic precipitator (ESP) for the collection efficiency (η) enhancement of the ESP in the piggery. Calculations of the RNG k-ε model, corona model, and particle tracking model are coupled in our model by utilizing MATLAB and COMSOL Multiphysics. This model is used to investigate the influence of various factors, such as the particle diameter (dp), flow velocity (u), and applied voltage (V), on the performance of ESP. Simultaneously, a visual experimental platform for PM2.5 migration is established for verification. The calculated results show that the predicted values of potential distribution, u distribution, and η are in good agreement with the previously reported experimental data. Moreover, the calculated results indicate that two elliptical shapes are produced by a relatively high electric potential and space charge density in the surrounding of the discharge corona wires. Furthermore, η first decreases with the increase of dp, remains unchanged in the range of 0.1–1.0 μm, and then increases until became constant in the range of 1.0–10 μm, revealing the interaction between diffusion charging, electric field charge, and fluid drag. In addition, the experimental and calculation results indicate that the η of PM2.5 increases with the decrease of u and increase of V. Notably, η of 2.0 μm is 100% at u = 1 m/s, V = 50 kV. Therefore, both the migration behavior solution method and the rules of η dependence on PM2.5 provide a scientific parameter control method for improving the air quality in pig house.

Designing HVDC GIS/GIL spacer to suppress charge accumulation

To suppress the charge accumulation on the spacer surface in direct current (DC) gas insulated transmission line (GIL) is an important and emergent issue for the development of a clean, safe and economic smart grid. A design method of the DC spacer is proposed, and a spacer prototype is prepared and evaluated both by simulation and type test. The DC withstand voltage test and polarity reversal test are performed using the new DC spacer compared with a commercialised 220 kV AC spacer. The simulation results indicate that the surface electric field and surface charge of the DC spacer are lower than those of the alternating current (AC) spacer under DC voltage. The test results verify that the surface flashover voltage of this DC spacer is higher than that of the AC spacer. The potential feasibility of the spacer design for HVDC is discussed. It is hoped that the content of this paper can bring new ideas in the development of HVDC gas insulated equipment.

Encoding Manipulation of DNA-Nanoparticle Assembled Nanorobot Using Independently Charged Array Nanopores.

During the past decades, scientists have developed different kinds of nanorobots based on various driving principles to realize controlled manipulation of them for potential applications like medical diagnosis and directed cargo delivery. In order to design a nanorobot with advantages of simple operation and precise control that can enrich the familyof intelligent nanorobots, an encoding manipulation method is proposed to control the movement of a DNA-nanoparticle assembled nanorobot by combing electrophoresis and electroosmosis effect in independently charged array nanopores. The nanorobot is composed of one nanoparticle and one or two ssDNAs. ssDNAs act as the legs of the nanorobot. The selective ion transport through charged nanopores can induce cooperation and competition between the electroosmosis and electrophoresis, which is the main power to activate the nanorobot. Thus by simply switching the applied electric field and surface charge density of each nanopore which is defined as the encoded nanopore according to a predetermined strategy, the well-controlled encoding manipulation including capturing, releasing, jumping, and crawling of the nanorobot is realized in this work. The study is expected to realize its value in many interesting applications like drug delivery, nanosurgery, and so on in the near future.

The interaction between silica flat substrate and functional group-modified nanoparticles.

Inspired by nature, the research of functionalized nanoparticles and nanodevices has been in-depth developed in recent years. In this paper, we theoretically studied the interaction between functional polyelectrolyte brush layer-modified nanoparticles and a silica flat substrate. Based on the Poisson-Nernst-Planck equations, the mathematical model is established. The changes of the volume charge density and electric field energy density when the nanoparticle interacts with the silica flat substrate under multi-ions regulation were investigated. The results show that when there is a strong interaction between the silica flat substrate and nanoparticles, such as the distances between the nanoparticle and silica flat substrate, which are 2 or 5nm, the isoelectric point shift under the influence of silica flat substrate and the total charge density in the brush layer is jointly controlled by the cations in the solution and the volume charge density of the brush layer. With the increase of the distances between the nanoparticle and silica flat substrate, the regulation of the volume charge density of the brush layer dominates. These results will provide guidance for the movement mechanism of functionalized nanoparticles in silica nanochannels.

How do external forces related to mass and charge affect the structures and dynamics of an ionic liquid?

Ionic liquids (ILs) are novel promising materials widely used in various fields. Their structures and properties can be tuned by means of external perturbations, thus further broadening their applications. Herein, forces proportional to atomic mass (mass-related field) and atomic charge (electric field) are applied in molecular dynamics simulations to the IL 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide to investigate the origin of the resulting changes in structures and dynamics. The results show that both electric and mass-related fields cause the ion cages to expand and deform, eventually leading to their breakdown to produce a transformation of ILs from the cage structure to a channel-like structure, which results in faster self-diffusion of ions in the directions of the applied force and to a lesser extent other directions. Further comparison of electric and mass-related fields demonstrates that only the electric fields reorientate cations to produce a hydrodynamically favored conformation in the force direction, which shows faster diffusion. The cis isomer of the anion is preferred in the presence of the electric fields, whereas applying the forces proportional to mass does not change the anion conformer equilibrium significantly. The results presented in this work aid in the understanding of how ions adjust their structures to adapt to external perturbations and facilitate the application of ILs as electrolytes.

Scrutinizing thermally stimulated current transients originating from trapped charges in organic semiconductors: A drift-diffusion study

Thermally stimulated current (TSC) is a widely used technique to assess trap states and extract their density, energy, and capture rate using analytical expressions. In many cases, the latter are derived from physical models pertaining to inorganic semiconductors stipulating the absence of space charge or constant lifetime of free charge carriers. Especially for organic semiconductors, the validity of these equations can, therefore, be argued. Here, we investigate the validity range of this approach by fitting the classical equations to synthetic TSC data obtained from drift-diffusion simulation using representative input parameters for organic semiconductors. We find that the equation derived for slow recapture rate as well as the initial rise method provide excellent trap parameter predictions. On the other hand, the equation using the temperature of the peak current as well as the one derived for fast retrapping have a limited range of validity. An important merit of drift-diffusion modeling is the possibility to access local variables such as charge carrier density, electric field, and recombinaton. We unravel that a small fraction of traps nearby the electrode cannot be emptied even at high temperature due to the diffusion of charge carriers from the electrode into the semiconductor. Additionally, we find that an important electrostatic factor relates the extracted charge carriers measured by the external circuit and the input trap density. For the homogeneously distributed trap states used here, this factor is precisely two. Finally, extensions of the model are analyzed by implementing temperature and field dependent mobility into the drift-diffusion model.

Charged strange stars with dust and phantom regimes in Rastall gravity

In this paper, we are focused on studying the possibility of providing a new well-behaved class of exact solutions for viable anisotropic stellar systems with dust and phantom regimes in the framework of Rastall gravity theory. This gravity theory modifies the matter sector only, incorporating new ingredients to the physical parameters that describe the model like charge density, electric field, density, and pressure components. Furthermore, other significant amounts are influenced, such as subliminal speeds of the pressure waves in radial and transversal directions, observational parameters such as the surface redshift associated with the total mass M and the radius R of the compact stellar configurations. Likewise, a transcendent mechanism such as equilibrium via generalized Tolman–Oppenheimer–Volkoff equation and stability of the stellar system is upset. The unidentified constraints are evaluated via the boundary conditions along with the dust and phantom models to describe as exterior space–times considering experimental statistics of five different stars i.e., EXO 1785 - 248, SMC X - 1, SAX J 1808.4 - 3658, 4U 1538 - 52, and HER X - 1. Various physical aspects have been analyzed with the help of modified dynamical equations. Exclusively, all the stellar configurations under observations are realistic, stable, and are free from all singularities. After witnessing the minor differences between our proposed models in both cases, Andréasson’s limit M≤R/3+R/9+Q2/3R has been fulfilled as required by the charged stellar structures. In such an astrophysical scenario, our new results provide circumstantial evidence in favor of super-massive pulsars.

Achieving high insulating strength and energy storage properties of all-organic dielectric composites by surface morphology modification

Dielectric polymers with high energy density have received widespread attention in the fields of modern electronics and power systems. Thus far, it is urgent to increase stored energy density of dielectric materials owing to the unappeasable energy density of the current commercial dielectric film caused by the inherent low dielectric constant. Herein, all-organic blended dielectric films consisting of acrylonitrile butadiene rubber (NBR) as organic fillers and poly (vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) as matrix were fabricated. Moreover, thermal treatment including hot press and quenching process was utilized to modify the surface roughness of films. It is demonstrated that flattened surfaces of prepared films with thermal treatment can result in reduction of local electric field distortion and charge injection. An elevated breakdown strength of 510 MV/m, which is 113.8% of P(VDF-HFP) films, and a raised dielectric permittivity of 10.08, which is 116.5% of P(VDF-HFP) films, have been achieved in the thermal treated NBR/P(VDF-HFP) films with 2 wt % loading under room temperature conditions. The enhanced insulating strength could be resulted from the smooth surface morphology by thermal treatment and mitigatory electric field distortion. Consequently, a high energy density of 11.3 J/cm3 is obtained concurrently. In addition, numerical simulations including finite element methods and phase field calculations are calculated to explain the facilitation of insulating properties. The all-organic dielectric polymer with thermal treatment provides a feasible example for fabricating energy storage dielectrics with high breakdown strength.

Control of The Distribution of The Internal Characteristics of The Discharge Using Supersonic Gas Pumping

Theoretical studies of the distribution of glow discharge parameters in a supersonic nitrogen gas flow between the central body of the nozzle and an annular electrode around the central body are carried out. Distributions of charged particle concentrations, potential, and electric field strength are obtained. The possibility of compaction or stretching of the cathode zones has been demonstrated. In the case of the organization of a supersonic gas flow near the central body-the anode, all the near-electrode zones are pressed against the anode. In this case, the cathode is located in the area of reduced pressures. Such a way of organizing the discharge can find application in the processes of applying functional coatings.

Foundations of plasmas for medical applications

Plasma medicine refers to the application of nonequilibrium plasmas at approximately body temperature, for therapeutic purposes. Nonequilibrium plasmas are weakly ionized gases which contain charged and neutral species and electric fields, and emit radiation, particularly in the visible and ultraviolet range. Medically-relevant cold atmospheric pressure plasma (CAP) sources and devices are usually dielectric barrier discharges and nonequilibrium atmospheric pressure plasma jets. Plasma diagnostic methods and modelling approaches are used to characterize the densities and fluxes of active plasma species and their interaction with surrounding matter. In addition to the direct application of plasma onto living tissue, the treatment of liquids like water or physiological saline by a CAP source is performed in order to study specific biological activities. A basic understanding of the interaction between plasma and liquids and bio-interfaces is essential to follow biological plasma effects. Charged species, metastable species, and other atomic and molecular reactive species first produced in the main plasma ignition are transported to the discharge afterglow to finally be exposed to the biological targets. Contact with these liquid-dominated bio-interfaces generates other secondary reactive oxygen and nitrogen species (ROS, RNS). Both ROS and RNS possess strong oxidative properties and can trigger redox-related signalling pathways in cells and tissue, leading to various impacts of therapeutic relevance. Dependent on the intensity of plasma exposure, redox balance in cells can be influenced in a way that oxidative eustress leads to stimulation of cellular processes or oxidative distress leads to cell death. Currently, clinical CAP application is realized mainly in wound healing. The use of plasma in cancer treatment (i.e. plasma oncology) is a currently emerging field of research. Future perspectives and challenges in plasma medicine are mainly directed towards the control and optimization of CAP devices, to broaden and establish its medical applications, and to open up new plasma-based therapies in medicine.

Optical and electrical analysis in various organic-inorganic stacked structures

Understanding heterojunctions in layered organic semiconductor devices is crucial in achieving efficient optoelectronic and advanced organic electronic devices. In this paper, we investigated the formation of charge transfer complex (CTC) and the generation of free carriers at the interface of the transition metal oxide (TMO)/organic semiconductor (OS) bi-layer structures. First, the relationship between the CTC and conductivity is analyzed for bi-layers composed of molybdenum oxide (MoO 3 ) and OSs with different highest occupied molecular orbital (HOMO) levels, respectively. Same analysis is done for bi-layers involving N,N′-Bis(naphthalen-1-yl)-N,N′-bis(phenyl)benzidine (NPB) and various TMOs with different work-functions, respectively. It is investigated that CTC is formed at the interface of the TMO/organic bi-layer structure and the conductivity in the TMO is increased. The absorbance intensities of the CTCs at the heterojunctions are proposed to depend on the density of the OS radicals formed from the charge transfer process. It is demonstrated that conductivity is low at bi-layer interfaces with high density of CTC. This is because the CTC aligned at the interface acts as a hindrance to electron mobility. Consequently, it is demonstrated that MoO 3 /2TNATA and MoO 3 /NPB exhibited low conductivity despite the formation of more CTCs than MoO 3 /CBP. We propose that the CTCs at the OS/TMO heterojunction with low charge separation efficiency, causes negative charges to align at the interface. This negatively charged electric field at interface act as resistance to the mobility of electrons inside the TMO layer. The investigation is key in achieving efficient organic electronic devices and stacked organic semiconductor functional structures. • Heterojunctions with organic hosts and transition metal oxides are investigated. • The formation of CTC and free carriers at the heterojunctions are analyzed. • Conductivity is low at the heterojunctions with high CTCs. • CTCs with low charge separation efficiency cause resistance to electron flow.

Investigation on effect of semiconducting screen on space charge behaviour of polypropylene‐based polymers for HVDC cables

High voltage direct current (HVDC) power transmission cable is critical for realising sustainability through renewable energy revolution. Eco-friendly thermoplastic polypropylene (PP)-based polymers/nanocomposites are regarded as promising candidates for replacing current thermoset crosslinked polyethylene (XLPE) cables. As an essential component of the extruded HVDC cable for improving conductor/insulation interface and suppressing charge injection to insulation at high DC electrical stresses, developing semiconducting (SC) screens that are compatible with PP-based insulation is of similar importance but has not been well studied yet. This work aims at designing PP-based semiconducting screens and investigating space charge behaviours of SC/PP/SC sandwich specimen to unfold the effect of semiconducting materials, bonding methods, applied DC electric field, and temperature on charge injection, accumulation, transportation, and dissipation in PP-based insulation. Although conventional thermal, mechanical, and low field electrical characterisations demonstrated that all of the developed semiconducting materials meet the performance criteria of commercial semiconducting materials, their space charge and local electric field distribution varied significantly at high DC fields. Compared with the traditional non-bonded configuration used at lab-scale, charge injection was enhanced in hot-pressed SC/PP/SC samples with tightly bonded interfaces, which better reflects the real situation in extruded cables. High temperature further intensified charge injections. Besides, our results also revealed that high temperature and electric field strongly influence charge mobilities and consequently their distribution and local electric field in PP-based insulations.

Impact of azimuthal forcing on the Brillouin limit in a collisional two-species Ohkawa filter

This paper investigates the physics of plasma separation in a two species rotating collisional Ohkawa filter, when the source of rotation is an orbital angular momentum carrying wave. The electric field is treated self-consistently with ion and electron radial motion. The injection of angular momentum causes radial currents leading to charge penetration and electric field build up. The electric field varies until an equilibrium with the friction forces is reached. Both collisions with neutrals and Coulomb collisions are considered. In the case where the electric field is driven by the resonant wave, there is no collisional breakdown of the Brillouin limit [Rax et al., Phys. Plasmas 22, 092101 (2015)]; on the contrary, the maximum achievable electric field decreases when the collision frequency is increased. When two species are present, one that undergoes the wave forcing while the second does not interact with the wave, we find the following: the first species is confined, while the second species can be expelled or confined depending on the charge to mass ratio and the collisionalities. Assuming equal charge numbers, if the second species is the heavy one, it is always expelled, which is a standard result. When the second species is the light one, it can also be expelled in the common case where neutral collisions dominate over Coulomb collisions, which constitutes a new result.

Research on electromagnetic environment of HVDC transmission line under sand and dust conditions

To study the impact of dust weather on the electromagnetic environment of the HVDC transmission line, this paper first analyzes the changes of transmission line corona field intensity under different dust conditions, and puts forward the prediction formula of transmission line corona field intensity under dust conditions. According to the Deutsch hypothesis and Kaptzov hypothesis, the calculation formula of ground synthetic electric field under sand and dust conditions is deduced, and the ±500 kV HVDC transmission line is analyzed and calculated. The results show that with the increase of dust particle size and dust concentration, the ground synthetic electric field shows a similar attenuation trend to the Halo electric field, which shows that the dust conditions mainly affect the ground synthetic electric field by affecting the space charge electric field. In the study of dust conditions on the line electromagnetic environment, coarse sand shows a greater impact, and the worse the dust weather intensity, the more obvious the decline of the ground synthetic electric field intensity.

High frequency doubling efficiency THz GaAs Schottky barrier diode based on inverted trapezoidal epitaxial cross-section structure

A high-performance terahertz Schottky barrier diode (SBD) with an inverted trapezoidal epitaxial cross-sectional structure featuring high varactor characteristics and reverse breakdown characteristics is reported in this paper. Inductively coupled plasma dry etching and dissolution wet etching are used to define the profile of the epitaxial layer, by which the voltage-dependent variation trend of the thickness of the metal-semiconductor contact depletion layer is modified. The simulation of the inverted trapezoidal epitaxial cross-section SBD is also conducted to explain the physical mechanism of the electric field and space charge region area. Compared with the normal structure, the grading coefficient M increases from 0.47 to 0.52, and the capacitance modulation ratio (C max/C min) increases from 6.70 to 7.61. The inverted trapezoidal epitaxial cross-section structure is a promising approach to improve the variable-capacity ratio by eliminating the accumulation of charge at the Schottky electrode edge. A 190 GHz frequency doubler based on the inverted trapezoidal epitaxial cross-section SBD also shows a doubling efficiency of 35% compared to that 30% of a normal SBD.

An inventive multi-scale, multiphysics modelling approach and comparative analysis of distinctive features of planar ionization waves in air: II. Positive streamers

A robust numerical framework for positive streamer modelling based on electro-hydrodynamic equations coupled with Poisson and Helmholtz differential equations for the photoionization process is presented. The proposed multi-layer meshing scheme in a 2D non-axisymmetric finite-element model along with a hybrid meshing technique presented in part I of this series paper for negative streamers provide high accuracy, spatial resolution, and capability to present the major features of both positive and negative streamers. In addition, the presented model is utilized to simulate multi positive and negative streamers propagation in a non-uniform electric field in the air. The main characteristics of the positive and negative streamers including the morphology, distribution pattern of space charges, local electric field, diameter, length, and velocity are presented, discussed, and compared with the experiment. Moreover, the impacts of initial seed density and voltage on the propagation of streamers are presented and explained. The branching mechanism arising from Laplacian instability and its impact on the streamer parameters such as tip electric field and dominant charge density is explained.

Resolving Multi-Path Interference in Compressive Time-of-Flight Depth Imaging with a Multi-Tap Macro-Pixel Computational CMOS Image Sensor.

Multi-path interference causes depth errors in indirect time-of-flight (ToF) cameras. In this paper, resolving multi-path interference caused by surface reflections using a multi-tap macro-pixel computational CMOS image sensor is demonstrated. The imaging area is implemented by an array of macro-pixels composed of four subpixels embodied by a four-tap lateral electric field charge modulator (LEFM). This sensor can simultaneously acquire 16 images for different temporal shutters. This method can reproduce more than 16 images based on compressive sensing with multi-frequency shutters and sub-clock shifting. In simulations, an object was placed 16 m away from the sensor, and the depth of an interference object was varied from 1 to 32 m in 1 m steps. The two reflections were separated in two stages: coarse estimation based on a compressive sensing solver and refinement by a nonlinear search to investigate the potential of our sensor. Relative standard deviation (precision) and relative mean error (accuracy) were evaluated under the influence of photon shot noise. The proposed method was verified using a prototype multi-tap macro-pixel computational CMOS image sensor in single-path and dual-path situations. In the experiment, an acrylic plate was placed 1 m or 2 m and a mirror 9.3 m from the sensor.