Weaker Electric Field Research Articles

Quadrupolar and dipolar excitons in symmetric trilayer heterostructures: insights from first principles theory

Excitons in van der Waals heterostructures come in many different forms. In bilayer structures, the electron and hole may be localized on the same layer or they may be separated forming an interlayer (IL) exciton with a finite out-of-plane dipole moment. Using first principles calculations, we investigate the excitons in a symmetric WS2/MoS2/WS2 heterostructure in the presence of a vertical electric field. The excitons exhibit a quadratic Stark shift for low field strengths and a linear Stark shift for stronger fields. This behavior is traced to the coupling of IL excitons with opposite dipole moments, which lead to the formation of quadrupolar excitons at small fields. The formation of quadrupolar excitons is determined by the relative size of the electric field-induced splitting of the dipolar excitons and the coupling between them given by the hole tunneling across the MoS2 layer. For the inverted structure, MoS2/WS2/MoS2, the dipolar excitons are coupled by electron tunneling across the WS2 layer. Because this effect is much weaker, the resulting quadrupolar excitons are more fragile and break at a weaker electric field.

Mechanisms of Mg2+/Li+ separation regulated by ion dynamics near the entrance of 2D nanochannels under applied electric fields

Molecular dynamics simulations were employed to investigate the separation mechanism of Mg2+/Li+ by 2D nanochannels under applied electric fields. The results show that the differences between the Mg2+-Cl− and Li+-Cl− association characteristics both inside nanochannels and near the entrance of nanochannels under an electric field are decisive factors for the selective transport of ions by the 2D nanochannel with a large interlayer spacing, especially near the entrance of the nanochannel. At the entrance, Li+ ions are more susceptible to interaction with Cl− and are relatively slowed under weak electric fields while Mg2+ ions are less affected. The Li+-Cl− association near the entrance of the nanochannel is enhanced by the synergistic effect of the ion migration dynamics inside the nanochannel and in the bulk phase. Due to the ion association characteristics, excellent separation efficiency of Mg2+/Li+ can be obtained under a weaker electric field by the nanochannel with a large spacing.

Turbulence-induced electrical discharges in charged particle-laden Martian boundary layers

Martian dust storms in the planetary boundary layer share many qualitative similarities to terrestrial sandstorms. Both of these turbulence-driven, particle-laden boundary layer flows are known to generate electric fields due to the transport of differentially charged particles; this charge separation can be strong enough to lead to dielectric breakdown in the form of sparks or lightning. Using wall-modelled large-eddy simulations supplemented with conservation of equations for the charged particle transport, representative simulations of neutrally stable Martian and terrestrial particle-laden boundary layer flows are compared. The simulations, albeit canonical in nature, provide evidence to support previous observations of the less frequent occurrence of lightning on Mars but a higher occurrence of localised electric discharge events due to the much lower breakdown potential. The rarefied Martian atmosphere impedes charged particle transport, resulting in a weaker electric field than the equivalent terrestrial sandstorm. The lower drag force in the rarefied Martian atmosphere means that the electrostatic force plays a more significant role in the particle transport, which results in a self-regulation of the electric field. The strongest Martian dust storms show evidence of significant breakdown events and these discharge events only occur very close to the ground despite the very large boundary layer on Mars.

Effects of Thermal and Electric Field Distribution on Tree Growth in EPDM for HVDC Cable Accessories

In this article, electrical tree growth characteristics of ethylene propylene diene monomer (EPDM) are studied under combined dc and ac voltages with different temperature gradients (Ts). The temperature difference between needle tip and ground electrodes varies from −90 °C to 90 °C, forming a ΔT within EPDM insulation. Variance is used as a new method to indicate the overall length of the electrical tree. Experimental results show that ΔT can accelerate the growth of electrical tree. Electrical tree tends to grow toward the ground electrode under negative ΔT, while it distributes around needle electrode under positive ΔT. Specific electric field distribution, determined by dc conductivity, is employed to explain the treeing process under different ΔTs. It is concluded that temperature-dependent conductivity results in weaker electric field near needle electrode and a quicker decreasing speed of electric field as it goes ahead to ground electrode under positive ΔT, thus leading to the electrical trees being more concentrated to the needle tip.

Multiple Li+ extraction mechanisms of sulfate saline by graphene nanopores: Effects of ion association under electric fields

In this work, the extraction of Li+ from sulfate solution by functionalized nanopores under various electric fields was investigated by molecular dynamics simulation. It was found that the dynamics of ion association and dissociation near nanopores play an important role in regulating the ion selectivity mechanism. When a strong electric field is applied (1.4 V nm−1), the ion transport can be affected by ion association enhanced near nanopore and the following dissociation near nanopore. Mg2+ is affected more apparently by ion association characteristics near nanopores than Li+, and thus rendering Li+ selectivity. Good separation of Mg2+ and Li+ can also be achieved by large nanopores of 3.5 nm, which is beneficial for the reverse migration of Mg2+ included in negatively charged structures. Alternatively, the strong association of Mg2+ with the COO− groups of nanopores may also be an important factor of Li+ selectivity under a relatively weaker electric field (0.6 V nm−1) for smaller nanopores (∼1.2 nm) and a dilute solution. Our results provide inspiration for the practical separation and purification of Li+ from sulfate-type saline.

Insights into CrS2 monolayer and [formula omitted]-CrS2/[formula omitted]-HfN2 interface for low-power digital and analog nanoelectronics

CrS2 monolayers exhibit excellent mechanical, electronic, piezoelectric and thermal properties as compared to other well-known transition metal dichalcogenides. CrS2/HfN2 van der Waals heterobilayer (vdWH) forms a pn-heterojunction where CrS2 and HfN2 act as an n-type and p-type semiconductor respectively, thereby suggesting its utility in nano-electronics and photodetectors. The perpendicular electric field is effective in manipulating band alignments and band gap in CrS2/HfN2 vdWH. Weaker electric field is able to close the band gap in the vdWH relative to CrS2 ML. Therefore, the vdWH may be a promising candidate in low-power analog and digital nano-electronics. Vertical electric field is found to drive the nearly free electron gas (NFEG) states to near the Fermi level in CrS2 ML. These surface states, reported in a few low-dimensional materials, will enhance charge transport and conductivity in electronics. Furthermore, the combined effect of spin–orbit coupling and a small magnitude of vertical electric field helps to reach a type-II band alignment in the CrS2/HfN2 vdWH. It unusually shows a large spin splitting at both conduction and valence band edges, which is very crucial for ambipolar spin transport. This work demonstrates possibilities for futuristic nano-electronic devices based on CrS2 ML & CrS2 based vdWH.

Preferential acceleration of positrons by a filamentation instability between an electron–proton beam and a pair plasma beam

Particle-in-cell simulations of jets of electrons and positrons in an ambient electron–proton plasma have revealed an acceleration of positrons at the expense of electron kinetic energy. We show that a filamentation instability, between an unmagnetized ambient electron–proton plasma at rest and a beam of pair plasma that moves through it at a non-relativistic speed, indeed results in preferential positron acceleration. Filaments form that are filled predominantly with particles with the same direction of their electric current vector. Positron filaments are separated by electromagnetic fields from beam electron filaments. Some particles can cross the field boundary and enter the filament of the other species. Positron filaments can neutralize their net charge by collecting the electrons of the ambient plasma, while protons cannot easily follow the beam electron filaments. Positron filaments can thus be compressed to a higher density and temperature than the beam electron filaments. Filament mergers, which take place after the exponential growth phase of the instability has ended, lead to an expansion of the beam electron filaments, which amplifies the magnetic field they generate and induces an electric field in this filament. Beam electrons lose a substantial fraction of their kinetic energy to the electric field. Some positrons in the beam electron filament are accelerated by the induced electric field to almost twice their initial speed. The simulations show that a weaker electric field is induced in the positron filament and particles in this filament hardly change their speed.

Effects of Thinner Compliant Electrodes on Self-Clearability of Dielectric Elastomer Actuators

A metalized plastic capacitor stands a higher chance to clear faults when embodied with thinner electrodes. However, it is not clear whether the same thickness effect applies to carbon-based compliant electrodes in clearing the defects in dielectric elastomer actuators (DEA). This experimental study showed that charcoal-powder compliant electrodes act like fuses and current limiters to successfully clear the defects of an acrylic dielectric elastomer actuator, provided a very thin electrode coating. For example, DEAs with 3 μm thick (average) charcoal-powder electrodes fast cleared faults and sustained high breakdown strength (300 to 400 MV/m), but the ones with thicker charcoal-powder electrodes (30 μm thick on average) succumbed to persisting breakdowns in a weaker electric field (200 to 300 MV/m). Thermo-gravitational analysis and differential scanning calorimetry showed that dielectric elastomer (3M VHB F9473PC) started to ignite at 350 ∘C, and charcoal powders (Mungyo charcoal pastel MP-12CP) started burning above 450 ∘C. This confirmed that flash ignition and its damping of charcoal powder is possible only with a very thin electrode coating relative to acrylic elastomer substrate thickness. Too thick of a charcoal-powder coating could lead to the spread of burning beyond the initial flash point, and incomplete burning that punctures the dielectric layer but shorts across opposite electrodes. With this insight, one can design self-clearable electrodes to improve the dielectric strength of dielectric elastomer actuators.

Evolution of PERC from Al-BSF: optimization based on root cause analysis

Passivated emitter rear contact (PERC) solar cell involves upgraded adaptation of technology over the existing silicon wafer-based aluminium back surface field (Al-BSF) solar cell. The lower efficiency of Al-BSF is caused by a few drawbacks e.g. higher rear surface recombination and weaker electric field at the rear surface. These technical shortcomings can be mitigated by incorporating field-effect passivation (FEP) layer viz. aluminium oxide (Al2O3) at the rear surface with a capping layer of SiNX on it. Conventionally two new processing steps utilizing two expensive equipments, green laser (532 nm) for laser ablation of the FEP and SiNX capping layer stack at the rear surface and single side etcher for rear side polishing of wafer are used for manufacturing of PERC cells. In this paper, we have shown that instead of these two new expensive processing equipments we can use the IR laser (1024 nm) and RIE etcher, which are commonly available for Al-BSF manufacturing line, for the fabrication of PERC solar cells. Using p-type wafers of rather modest quality (minority carrier lifetime of ≥10 µs) we have demonstrated improvement of the efficiency from 18.71 to 19.62% and enhancements in VOC and JSC from 628 to 646 mV and 38.59 mA/cm2 to 39.82 mA/cm2, respectively. A thorough root-cause analysis has been carried out to optimize the two new approaches within the existing Al-BSF line for the fabrication of PERC solar cell.

Influence of Hot Carriers and Illumination Stress on a-InGaZnO TFTs With Asymmetrical Geometry

In this study, the influence of hot carriers and illumination stress on InGaZnO thin-film-transistors (TFTs) with asymmetrical geometry was investigated by measuring the drain current-gate voltage ( $\text{I}_{\text {D}}$ - $\text{V}_{\text {G}}$ ) and capacitance-voltage (C-V) characteristics. Reversed $\text{I}_{\text {D}}$ - $\text{V}_{\text {G}}$ in saturated operation shows that the sub-channel effect was caused by the electric field distribution. Furthermore, COMSOL simulation of the device under stress was performed to demonstrate the abnormal degradation behavior. Upon illumination, electron–hole pairs are generated. This causes carrier trapping in the gate insulator (GI) and etch-stop-layer (ESL). Based on the weaker electric field around the U-electrode observed in the COMSOL simulation, it was concluded that uniform hole-trapping was more dominant than electron-trapping, which lowers the barrier, as can be inferred from the measured gate-to-drain ( $\text{C}_{\text {GD}}$ ) and gate-to-source capacitances ( $\text{C}_{\text {GS}}$ ).

Migration behaviors of leaky dielectric droplets with electric and hydrodynamic forces.

The external electric field enables separation and transport of droplets effectively in microfluidic devices. Herein, a volume-of-fluid (VOF) + level-set (LS) + smoothed physical parameters (SPP) method associated with the dynamically adaptive grid technique is extended to simulate three-dimensional leaky dielectric droplets in the electric field. The effects of electric and hydrodynamic forces on droplet behaviors are investigated. It is demonstrated that the electric force could act toward the outside or inside of a droplet and produce different droplet deformations. For the dielectrophoretic migration of droplets in the nonuniform electric field, the electric force has a dominant effect. It is found that when the electric conductivity ratio is greater than 1, an unbalanced electric force toward a stronger electric field is generated, bringing about the migration toward a stronger electric field. In contrast, when the electric conductivity ratio is smaller than 1, the unbalanced electric force direction is reversed and the droplet migrates toward a weaker electric field. The hydrodynamic force produces little promotion or hindrance to droplet migration. A greater permittivity ratio usually produces greater electric force and migration velocity. The droplet migrates along one direction in a symmetric nonuniform electric field but tends to migrate along the normal direction of electric potential profiles in an asymmetric nonuniform electric field.

Uniform field electrospinning for 3D printing of fibrous configurations as strain sensors

Electrospinning is becoming an efficient method to produce fibers in the submicron range, but the bending instability of conventional electrospinning system (CES) brings limitations in the distinctive deposition of electrospun fibers. Herein, we proposed a strategy to update the electrospinning system through establishment of a uniform electric field, realizing 3D printing of electrospun fibers with well-controlled, low-cost, and template-free manners. The uniform field electrospinning (UFES) apparatus is configured by inserting the electrospinning nozzle into the center of an aided metal plate. The electric field simulation of UFES indicates a uniform distribution between the aided metal plate and the collector, while a diverging and weaker electric field is produced by CES. The collector of UFES is mounted on a translation stage, which moves along x and y axes under computer control. The distinctive deposition of electrospun fibers produces fibrous mats with rectangular patterns of different grid sizes, and butterfly and TaiJi figures with high resolutions are directly written by UFES. The layer-by-layer deposition of electrospun fibers under UFES produces microscale Mongolian yurts with distinct hollow structure. Fibrous blocks with an average width of 120 μm and height of 630 μm were printed by UFES from conductive polymer composites and constructed into strain sensors. The electric current strength of fibrous microblocks changes sharply in response to the finger bending and release, indicating the capability to monitor human motions. Thus, this study demonstrates that the UFES becomes an easy-handling strategy for 3D printing of electrospun fibers to create complex geometries.

Optimizing the thickness of sputtering-Zn(O, S) buffer layer for all-dry Cd-free CIGS solar cells

Recently, research on the Zn(O, S) thin films as an alternative buffer layer for CIGS thin film solar cells has gained increasing popularity. The replacement of CdS and i-ZnO films by the sputtered Zn(O, S) films not only overcomes the shortcomings of using the heavy metal (Cd) and a non-vacuum production process, but also simplifies the in-line process in the industrial level. In this paper, the effects of varying the Zn(O, S) films thickness on its material properties and the corresponding device performance are investigated. At the same time, the wxAMPS simulation software is applied to studying the impact of thickness of Zn(O, S) films on the energy band structure, the built-in electric field distribution, and the generation/recombination rate of carriers. It’s found that defect density in the bulk of Zn(O, S) and at the interface of CIGS/Zn(O, S) will increase with a thinner film, which further enhances interface recombination. Moreover, a deteriorated device performance is observed as a result of a very thick film, which is likely caused by the light-loss and a weaker electric field. The optimum thickness is determined based on the results of the experiment and simulation. Finally, insights are provided on reducing the defect density at the heterojunction interface in order to improve the performance of Cd-free device prepared by all-dry processes.

Response of aquatic protists to electric field exposure

Purpose: To test the effects of short-term exposure of aquatic organisms to electric field (EF) with negligible magnetic component.Materials and methods: We built a plate capacitor that served as a source of EF of strengths that can be found in nature near transmission lines. We exposed two cultured protist species Euglena viridis and Paramecium caudatum to EFs for 24 hours and monitored their abundance, morphology, intracellular superoxide anion (by dihydroethidium [DHE]), hydrogen peroxide by (H2DCF) and lipid peroxidation (MDA) contents, catalase (CAT) and superoxide dismutase (SOD) activity.Results: We found that even short-term exposure to low strength EF causes changes in population abundance, morphology and oxidative stress response in both species. As the EF strength increased, abundance of both species decreased. However, at weaker EFs, fission rates were seemingly promoted. We noted a decrease in size in both organisms in directions perpendicular to their fission planes correlated with EF strength. DHE and H2DCF fluorescence intensity and SOD activity were higher in organisms exposed to the stronger EFs.Conclusions: We suggest that the electric component of the field, rather than the magnetic, is the main cause of all the noted effects. As a result, aquatic organisms should be given greater importance in studies assessing the effects of EMFs in spite of the attenuating effects of water to EF strengths.

Revisiting benzene cluster cations for the chemical ionization of dimethyl sulfide and select volatile organic compounds

Abstract. Benzene cluster cations were revisited as a sensitive and selective reagent ion for the chemical ionization of dimethyl sulfide (DMS) and a select group of volatile organic compounds (VOCs). Laboratory characterization was performed using both a new set of compounds (i.e., DMS, β-caryophyllene) as well as previously studied VOCs (i.e., isoprene, α-pinene). Using a field deployable chemical-ionization time-of-flight mass spectrometer (CI-ToFMS), benzene cluster cations demonstrated high sensitivity (> 1 ncps ppt−1) to DMS, isoprene, and α-pinene standards. Parallel measurements conducted using a chemical-ionization quadrupole mass spectrometer, with a much weaker electric field, demonstrated that ion–molecule reactions likely proceed through a combination of ligand-switching and direct charge transfer mechanisms. Laboratory tests suggest that benzene cluster cations may be suitable for the selective ionization of sesquiterpenes, where minimal fragmentation (< 25 %) was observed for the detection of β-caryophyllene, a bicyclic sesquiterpene. The in-field stability of benzene cluster cations using CI-ToFMS was examined in the marine boundary layer during the High Wind Gas Exchange Study (HiWinGS). The use of benzene cluster cation chemistry for the selective detection of DMS was validated against an atmospheric pressure ionization mass spectrometer, where measurements from the two instruments were highly correlated (R2 > 0.95, 10 s averages) over a wide range of sampling conditions.

On the Debye–Hückel effect of electric screening

The paper considers non-linear self-consistent electric potential equation (Sec. I), due to a cloud made of a single species of electric charges, satisfying a Boltzmann distribution law (Sec. II). Exact solutions are obtained in a simple logarithmic form, in three cases: (Sec. III) spherical radial symmetry; (Sec. IV) plane parallel symmetry; (Sec. V) a special case of azimuthal-cylindrical symmetry. All these solutions, and their transformations (Sec. VI), involve the Debye-Hückel radius; the latter was originally defined from a solution of the linearized self-consistent potential equation. Using an exact solution of the self-consistent potential equation, the distance at which the potential vanishes differs from the Debye-Hückel radius by a factor of 2. The preceding (Secs. II–VI) simple logarithmic exact solutions of the self-consistent potential equations involve no arbitrary constants, and thus are special or singular integrals not the general integral. The general solution of the self-consistent potential equation is obtained in the plane parallel case (Sec. VII), and it involves two arbitrary constants that can be reduced to one via a translation (Sec. VIII). The plots of dimensionless potential (Figure 1), electric field (Figure 2), charge density (Figure 3), and total charge between ζ and infinity (Figure 4), versus distance normalized to Debye-Hückel radius ζ ≡ z/a, show that (Sec. IX) there is a continuum of solutions, ranging from a charge distribution concentrated inside the Debye-Hückel radius to one spread-out beyond it. The latter case leads to the limiting case of logarithmic potential, and stronger electric field; the former case, of very concentrated charge distribution, leads to a fratricide effect and weaker electric field.

New Insight Into PBTI Evaluation Method for nMOSFETs With Stacked High- $k$/IL Gate Dielectric

In this letter, a strategy to minimize the error in lifetime projections using a positive bias temperature instability (PBTI) test has been proposed. Two distinctly different projection slopes were observed in a plot of time to failure versus oxide electric field. A small slope in the high-field region, which means weaker electric field dependence, led to an underestimation of lifetime. This result was attributed to a filled trap cluster at a specific trap energy level, locally reducing the oxide electric field. Thus, different lifetimes can be projected depending on stress bias. Maintaining a PBTI stress bias range below this trap energy level is recommended for accurate projections.

The direct measurement of the signal charge behavior in pnCCDs with subpixel resolution

In the MPI-Halbleiterlabor (MPI-HLL) we are developing fully depleted pn-type Charge Coupled Devices (pnCCD) with a thick radiation-sensitive region. Since 1997, the mesh experiment has been established as an unique technique to determine an X-ray interaction position with subpixel resolution. In order to investigate the signal charge behavior in pnCCDs, we performed the mesh experiment using various characteristic X-ray lines. Cu-L (0.9 keV), Al-K (1.5 keV) and Ti-K (4.5 keV) were used and the device operated under various conditions, e.g. register voltages. We obtained the restored pixel images for various X-ray event patterns. The photon entrance window of the back illuminated pnCCD shows highly uniform detection efficiency within a pixel. We measured the charge cloud size generated by an X-ray photon inside the CCD. The measured charge cloud sizes are around 6 μ m (rms) depending on the X-ray energy. The operation with different register conditions revealed asymmetries and regions with a weaker electric field around pixel boundaries.

Peculiar CIP transport in CoFe/Al 2O 3 granular layered films across a micro-gap

Current-in-plane (CIP) transport properties are reported in discontinuous granular layers of CoFe/Al 2O 3 across a 10 μm gap between lithographed Al contacts. CIP magnetoresistance is found to degrade sensibly with bias voltage V, e.g., from 7% to 3.5% (at room temperature) with V growing from 100 mV to 14 V. The I– V characteristics display a strong non-linear dependence, similar to the high-field tunneling regime known for current-perpendicular-to-plane (CPP) transport, but here it occurs under much weaker electric field and even at room temperature when Coulomb blockade is ruled out. We explain these anomalies by the processes of dynamic charge accumulation under the macroscopic contacts.

The propagation of positive streamers in a weak and uniformbackground electric field

Theresults of numerical simulations of a positive streamer development in airin a weak and uniform electric field are presented. Streamer dynamics isconsidered in an electrode gap of 33 mm in length and the configurationwas `protrusion on a plate-plate'. This particular configuration waschosen in order to perform direct comparison between simulated results andexperimental data. The electrostatic field in such a system decreasesrapidly with increase of the distance from the protrusion (anode) and theregion with a weak and uniform background field covers ~30 mm of thegap. The parameters of the propagating streamer are studied at sixdifferent values of the background field strength: 0.24; 0.30; 0.345;0.37; 0.43 and 0.50 MV m-1. Stable streamer development (withconstant velocity) takes place in a field of 0.5 MV m-1 (thestability field) but the streamer is able to cross the gap in a backgroundfield of 0.3 MV m-1. These values are in excellent agreement withexperimental data. During the stable streamer propagation, the electrondensity and plasma conductivity in the discharge channel and the electricfield at its front remain constant. In a background field lower than0.5 MV m-1, the discharge front velocity and the electric field atthe front decrease linearly with an increase of streamer length. Thedischarge propagation in the stability field is associated with anincrease of electrostatic energy at the streamer front but it decreases ifthe streamer develops in a weaker electric field. This behaviour isaccompanied by a constant Joule dissipation at 0.5 MV m-1 anddecreasing energy losses at the streamer front in a weaker backgroundelectric field.