Electrode Edge Research Articles

Numerical simulation of coaxial–coplanar dielectric-barrier discharge in atmospheric helium

A self-consistent two-dimensional fluid model is employed to investigate the coaxial–coplanar dielectric-barrier discharge (DBD) excited by the sinusoidal voltage in atmospheric helium. Simulation results show that there are two current pulses in the positive half cycle, but only one in the negative half cycle. The discharge is transformed from the Townsend-like mode, through the glow-like mode, and back to the Townsend-like mode in both the positive and negative half cycles, during which the electric field line exhibits an arc-shape profile due to the configuration of coaxial–coplanar electrodes. In the glow-like mode, the cathode fall is located near the inner edge of the ground electrode at the first positive current peak, but close to the outer edge of the ground electrode at the second positive current peak. At the negative current peak, the cathode fall is distributed near the outer edge of the high voltage electrode. Since the instantaneous anode and the instantaneous cathode are on the same side of the discharge space, the dielectric layer is simultaneously covered by positive and negative surface charges due to the movement of charged particles. It is also found that the surface charge density changes significantly on the dielectric layer facing the electrodes. A further study reveals that a stronger discharge always occurs in the central circular area and an alternately complementary discharge takes place in the periphery ring area in the positive half cycle due to the activator–inhibitor effect. This feature is helpful for producing uniform plasma in a whole cycle of DBD.

AC electrokinetic immobilization of influenza virus.

The use of alternating current (AC) electrokinetic forces, like dielectrophoresis and AC electroosmosis, as a simple and fast method to immobilize sub-micrometer objects onto nanoelectrode arrays is presented. Due to its medical relevance, the influenza virus is chosen as a model organism. One of the outstanding features is that the immobilization of viral material to the electrodes can be achieved permanently, allowing subsequent handling independently from the electrical setup. Thus, by using merely electric fields, we demonstrate that the need of prior chemical surface modification could become obsolete. The accumulation of viral material over time is observed by fluorescence microscopy. The influences of side effects like electrothermal fluid flow, causing a fluid motion above the electrodes and causing an intensity gradient within the electrode array, are discussed. Due to the improved resolution by combining fluorescence microscopy with deconvolution, it is shown that the viral material is mainly drawn to the electrode edge and to a lesser extent to the electrode surface. Finally, areas of application for this functionalization technique are presented.

Effect of low frequency voltage waveform on plasma uniformity in a dual-frequency capacitively coupled plasma

In a dual-frequency capacitively coupled plasma (CCP) with disparate frequencies, the low frequency (LF) voltage usually has a strong influence on the ion energy distribution function (IEDF) but contributes less to plasma generation. It is well-known that rectangular LF voltage waveform with a small positive period yields a narrow, nearly monoenergetic IEDF. This paper focuses on the effect of the LF voltage waveform on plasma uniformity in a low-pressure dual-frequency (40 + 0.8 MHz) CCP. A two-dimensional particle-in-cell model is used for this investigation, and the effect of LF voltage amplitude on plasma uniformity is investigated for sinusoidal and rectangular voltage waveforms. When the LF voltage is low, the peak in plasma density is at the chamber center due to ample diffusion at the low pressure considered (20 mTorr) and higher losses to the chamber walls. As the LF voltage is increased, the sheath gets thicker at the powered electrode and charged species densities decrease for a constant 40 MHz voltage. The plasma profile, however, evolves differently for the two LF voltage waveforms. With sinusoidal LF voltage, the plasma spreads out between the electrodes. On the other hand, with rectangular LF voltage waveform, the plasma splits into two regions: a density peak at the chamber center and another peak near the electrode edge. This double-peaked density profile with a rectangular wave can be attributed to the location and timing of plasma generation. 40 MHz produces plasma most efficiently when the LF rectangular wave is positive and the sheath at the powered electrode is thin (frequency coupling). This plasma is produced uniformly between the electrodes, but only for a short period. When the LF voltage becomes negative, the sheath expands at the powered electrode and the plasma is produced near the electrode edge where the sheath is thinner and the electric field is stronger.

Fine structure of streamer-to-filament transition in high-pressure nanosecond surface dielectric barrier discharge

Abstract The fine structure of a streamer-to-filament transition in a single-shot high-voltage nanosecond surface dielectric barrier discharge in molecular nitrogen at pressure P = 6 bar was studied with the help of ICCD microimaging. An intermediate discharge structure, existing for only a few nanoseconds, was observed in the time interval between two discharge modes: streamer discharge, with a typical electron density of n e ∼ 1015 cm−3, and filamentary discharge, with n e ∼ 1019 cm−3. The structure was observed for both polarities of the high-voltage electrode. The structure can be briefly described as a stochastic appearance of thin channels propagating a bit faster than the main ionization front of merged surface streamers, transforming in a few nanoseconds in a bi-directional ionization wave. One wave, which we associate with a feather-like structure in optical emission, propagates further away from the high-voltage electrode, and another, a backward wave of emission, propagates back towards the edge of the high-voltage electrode. When the backward wave of emission almost reaches the high-voltage electrode, the filament appears. Plasma properties of the observed structure were studied to better understand the nature of a streamer-to-filament transition. Theoretical analysis suggests that the instability of a flat front of ionization wave (Laplacian instability) triggers the streamer-to-filament transition, and that a surface stem (a tiny region with enhanced electron density) should be in the origin of the bi-directional ionization wave.

CFD simulation and experimental comparison of bubble-induced convection during electrochemical water splitting

The behavior of gas bubbles produced during electrochemical processes is of large interest because of the increase in cell overpotential induced by their production, the electrode surface covering by them and, finally, the detachment of these bubbles and their direct impact on the energy consumption during the reaction. In this work, we used coupled experimental and computational approaches to investigate bubble formation under those conditions where there are important convective effects. We have measured both normal and parallel velocity of the solution and built up a computational fluid dynamics (CFD) model. The results were compared to experimental data. Then, having the computational model validated by experimental data, we have simulated different conditions following bubble displacement. An important change of the surface covering is observed during the electrochemical reaction. Considering just the covering change, for example, there is up to 23 % increase comparing to the electrode edge and center. • Finite element method is suitable to evaluate the bubble-induced convection. • The bubbles create a vortex in the electrolyte. • The induced convection create a non-homogeneous gas covering over electrode surface. • The bubble size has an important effect in the covering variance.

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.

Toward a Practical Impedimetric Biosensor: A Micro-Gap Parallel Plate Electrode Structure That Suppresses Unexpected Device-to-Device Variations.

We propose a rational electrode design concept for affinity biosensors based on electrochemical impedance spectroscopy to substantially suppress unexpected device-to-device variations. On the basis that the uniformity of the current distribution affects the variation, a novel micro-gap parallel plate electrode (PPE) was developed, where two planar electrodes with edges covered with a SiO2 layer were placed face to face. The structure provides a uniform current distribution over the planar electrode surface and maximizes the contribution of the planar electrode surface to sensing. For a comparative study, we also fabricated a micro-structured interdigitated electrode (IDE) that has been widely adopted for high-sensitivity measurement, although its current is highly concentrated on the electrode edge corner. Protein G (PrG) molecules were immobilized on both electrodes to prepare an immunoglobulin G (IgG) biosensor on which the specific binding of PrG–IgG can occur. We demonstrated that the IgG sensor with the PPE has small device-to-device variations, in strong contrast to the sensor with the IDE having large device-to-device variations. The results indicate that the current distribution on the electrode surface is important to fabricating electrochemical impedance spectroscopy biosensors with small device-to-device variations. Furthermore, it was found that the PPE allows ultrasensitive detection, that is, the sensor exhibited a linear range from 1 × 10–13 to 1 × 10–7 mol/L with a detection limit of 1 × 10–14 mol/L, which is a record sensitivity at low concentrations for EIS-based IgG sensors.

Research on the Induced Electrostatic Discharge of Spacecraft Typical Dielectric Materials under the ESD Pulse Irradiation.

Based on polyimide (PI), epoxy resin (EP), polytetrafluoroethylene (PTFE) typical dielectric materials used in spacecraft, a research platform for charge-discharge experiment under strong field was established. The influence of irradiation field strength, beam energy, dielectric thickness, etc., on electrostatic discharge characters of dielectric materials were studied and summarized. The results show that with the increase of field strength, the frequency of induced electrostatic discharge increases, the accumulated charge on the dielectric surface decreases, and the dielectric surface potential decreases; Under the same conditions, PI has the lowest discharge frequency and the highest surface dynamic balance potential. The thicker the dielectric material, the lower the discharge frequency, the higher the surface dynamic equilibrium potential; The shape and size of the background electrodes also affect the discharge frequency. When the area is the same, the sharper the electrode edge, the higher the discharge frequency. When the shape is the same, the larger the grounding area, the higher the discharge frequency. By proposing the induced discharge test method, the function mechanism of spatial environmental factors on the electrostatic discharge of typical dielectric materials are obtained. Comparative analysis on electrostatic properties of different dielectric materials can provide data reference and technical support for spacecraft electrostatic safety and protection.

Local manipulation and topological phase transitions of polar skyrmions

<h2>Summary</h2> Topological phases such as polar skyrmions have been a fertile playground for ferroelectric oxide superlattices, which demonstrate exotic physical phenomena such as negative capacitance. Herein, using phase-field simulations, we demonstrate the local control of the skyrmion phase with electric potential applied through a top electrode. Under a small bias, the skyrmions underneath the electrode can be erased and recovered reversibly. A topologically protected transition from the symmetric to asymmetric skyrmion bubble is observed near the electrode edge. While a transition to the vortex state requires a large bias, it can switch back to the skyrmion state with a relatively small opposite bias. The topological transition from +1 to 0 occurs before the destruction of the bubble structure. The shrinking and bursting of the skyrmions leads to a large reduction in the dielectric permittivity, the magnitude of which depends on the electrode size and the magnitude of the applied bias.

Reliability improvement of gas discharge tube by suppressing the formation of short-circuit pathways

After cumulative discharge of gas discharge tube (GDT), it is easy to form a short circuit pathway between the two electrodes, which increases the failure risk and causes severe influences on the protected object. To reduce the failure risk of GDT and improve cumulative discharge times before failure, this work aims to suppress the formation of two short-circuit pathways by optimizing the tube wall structure, the electrode materials and the electrode structure. A total of five improved GDT samples are designed by focusing on the insulation resistance change that occurs after the improvement; then, by combining these designs with the microscopic morphology changes inside the cavity and the differences in deposition composition, the reasons for the differences in the GDT failure risk are also analyzed. The experimental results show that compared with GDT of traditional structure and material, the method of adding grooves at both ends of the tube wall can effectively block the deposition pathway of the tube wall, and the cumulative discharge time before device failure is increased by 149%. On this basis, when the iron-nickel electrode is replaced with a tungsten-copper electrode, the difference in the electrode’s surface splash characteristics further extends the discharge time before failure by 183%. In addition, when compared with the traditional electrode structure, the method of adding an annular structure at the electrode edge to block the splashing pathway for the particles on the electrode surface shows no positive effect, and the cumulative discharge time before the failure of the two structures is reduced by 22.8% and 49.7%, respectively. Among these improved structures, the samples with grooves at both ends of the tube wall and tungsten-copper as their electrode material have the lowest failure risk.

Inhomogeneous electric field-induced structural changes in soft lead zirconate titanate ferroelectric ceramics

Under the application of an external voltage, high electric field concentrations can develop around the interdigitated electrode edges inside multilayer ceramic actuators (MLCAs). The spatial distribution of the local electrical field can create local inhomogeneity in the electromechanical response. To investigate the complex field inhomogeneity in MLCAs, partially electroded Nb-doped PbZrxTi1-xO3 samples were investigated via synchrotron-based high-energy X-ray diffraction (XRD) as a function of applied electric field. These in situ experiments allowed us to probe the structural changes as a function of position relative to the electrode edge and calculate the local degree of domain alignment, from which the local electric field directions were inferred. The domain switching behavior, both in amplitude and orientation, was found to be spatially dependent across the inactive regions in partially electroded samples. Specifically, the degree of domain alignment and field-induced phase transitions are amplified near the electrode edge. The orientation-dependent phase transitions are also amplified for the tetragonal composition near the morphotropic phase boundary (MPB), i.e., the Nb-doped PbZr0.53Ti0.47O3 composition. Finite element analysis (FEA) shows spatially-dependent, inhomogeneous electric field distributions in the partial-electrode samples, which closely match the experimentally inferred local electric field directions from XRD. The correlation of FEA and experimental data from XRD corroborates that the ferroelectric domain orientation distributions are being directed, primarily, in the direction of the electric field.

Predicting Voltammetry Using Physics-Informed Neural Networks.

We propose a discretization-free approach to simulation of cyclic voltammetry using Physics-Informed Neural Networks (PINNs) by constraining a feed-forward neutral network with the diffusion equation and electrochemically consistent boundary conditions. Using PINNs, we first predict one-dimensional voltammetry at a disc electrode with semi-infinite or thin layer boundary conditions. The voltammograms agree quantitatively with those obtained independently using the finite difference method and/or previously reported analytical expressions. Further, we predict the voltammetry at a microband electrode, solving the two-dimensional diffusion equation, obtaining results in close agreement with the literature. Last, we apply a PINN to voltammetry at the edges of a square electrode, quantifying the nonuniform current distribution near the corner of electrode. In general, we noticed the relative ease of developing PINNs for the solution of, in particular, the higher dimensional problem, and recommend PINNs as a potentially faster and easier alternative to existing approaches for voltammetric problems.

Influence of Etching Trench on Keff2&nbsp;of Film Bulk Acoustic Resonator.

As radio-frequency (RF) communication becomes more ubiquitous globally, film bulk acoustic resonators (FBAR) have attracted great attention for their superior performance. One of the key parameters of an FBAR, the effective electromechanical coupling coefficient (), has a great influence on the bandwidth of RF filters. In this work, we propose a feasible method to tune the of the FBAR by etching the piezoelectric material to form a trench around the active area of the FBAR. The influence of the position of the etching trench on the of the FBAR was investigated by 3D finite element modeling and experimental fabricating. Meanwhile, a theoretical electrical model was presented to test and verify the simulated and measured results. The of the FBAR tended to be reduced when the distance between the edge of the top electrode and the edge of the trench was increased, but the Q value of the FBAR was not degraded. This work provides a new possibility for tuning the of resonators to meet the requirements of different filter bandwidths.

Numerical investigation of SiO&lt;sub&gt;2&lt;/sub&gt; film deposition enhanced by capacitively coupled discharge plasma

Higher requirements for the performances of thin films need to be fulfilled in the rapid development of integrated circuit technology, due to the more complicate structure and smaller size of chips. In plasma-enhanced chemical vapor deposition , high-density and high-performance thin films can be deposited at low temperature, compared with traditional chemical vapor deposition. In this work, a two-dimensional fluid/MC model coupled with the deposition module is used to describe the capacitively coupled SiH&lt;sub&gt;4&lt;/sub&gt;/N&lt;sub&gt;2&lt;/sub&gt;O/Ar discharges as well as the deposition processes, focusing on the influences of the radial position, gas ratio and gas pressure on the deposition of silicon oxide films. The results show that the edge effect which leads the plasma density to rise near the electrode edges gives rise to the non-uniform deposition rate along the radial direction. It is also found that the more N&lt;sub&gt;2&lt;/sub&gt;O and less Ar content in the gas mixture, as well as an increased gas pressure will improve this uniformity. However, an excessive deposition rate will lead to a series of undesirable phenomena, such as “key hole structure”, vacancies and excessive impurities in films. These problems are also troublesome in the microelectronics manufacture processes. More detailed investigation into the deposition mechanism can be expected in the future .

Identification of DNA nucleotides by conductance and tunnelling current variation through borophene nanogaps.

Rapid and inexpensive DNA sequencing is critical to biomedical research and healthcare for the accomplishment of personalized medicine. Solid-state nanopores and nanogaps have marshalled themselves in the fascinating paradigm of nano-research since the advent of its application in DNA sequencing by analyzing the quantum conductance and electric current signals. In this study, the feasibility of the considered borophene nanogaps for DNA sequencing purposes via the electronic tunnelling current approach was investigated by utilizing combined density functional theory with non-equilibrium Green's function (DFT-NEGF) techniques. The interaction energy (Ei) and the charge density difference (CDD) plots exploit the charge modulation around the nanogap edges due to the presence of each nucleotide. Our results revealed a distinct variation in the tunnelling conductance, as a characteristic fingerprint of each nucleotide at the Fermi level. The calculated tunnelling current variation across the nanogap under an applied bias voltage was also significant due to the effective coupling of nucleotides with the electrode edges. The current was in the picoampere (pA) range, which was fairly higher than the electrical background noise and also experimentally detectable by the canning tunnelling microscopy (STM) technique. Our findings demonstrated that in the borophene nanopore vs. nanogap scenario, the nanogap has several advantages and is a more promising nanobiosensor. Moreover, we also compared our results with various previous experimental and theoretical reports on nanogaps as well as nanopores for gaining better insights.

Локализация энергии лазерного излучения в оптико-терагерцевом преобразователе ультракоротких ИК-импульсов при помощи профилированных сапфировых волокон

We report the seminal approach for localization of photocarriers in a photoconductive antenna (PCA)-emitter via the focusing element comprising the sapphire fiber. Using numerical simulation, we showed that at the certain ratio between the fiber diameter and the gap size, i.e. d/g = 22.5, one can attain a 35-fold enhancement of the laser irradiation in vicinity of the PCA electrodes. This provides the formation of subwavelength EM wave caustics located at the edges of the PCA electrodes which potentially gives rise to an increase of optical-to-terahertz conversion efficiency.

Laser pulse energy localization in a photoconductive THz emitter via sapphire fibers

We report a seminal approach for localization of photocarriers in a photoconductive antenna (PCA)-emitter via a focusing element comprising the sapphire fiber. Using numerical simulation, we showed that at a certain ratio between the fiber diameter and antenna gap size (d/g~ 22.5), one can attain a ~ 35-fold enhancement of laser irradiation in the vicinity of the PCA electrodes. This provides the formation of subwavelength electromagnetic wave caustics located at the edges of the PCA electrodes, which potentially promotes an increase in the optical-to-terahertz conversion efficiency. Keywords: terahertz frequency, terahertz emitters, semiconductors, photoconductive antenna, IR radiation.

Design of multifunctional spin logic gates based on manganese porphyrin molecules connected to graphene electrodes.

The spin-resolved transport properties of molecular logic devices composed of two Mn porphyrin molecules connected to each other via a six-carbon atomic chain were studied using the non-equilibrium Green's function combined with density functional theory. The molecules were symmetrically connected to armchair graphene nanoribbon electrodes through four-carbon atomic chains on the left- and right-hand sides. Our calculations revealed that the spin-resolved current-voltage curves depend on the initial spin setting of the transition metal Mn atoms and carbon atoms on the zigzag edges where the electrodes come in contact with the molecule. By simultaneously regulating the spin orientations of the intermediate functional molecules and the zigzag edges of the armchair graphene nanoribbon electrodes, seven spin polarization configurations were obtained. These configurations were examined in this study considering the spin-related symmetry of molecular junctions. By meticulously selecting different combinations according to the specific input and output signals, YES, NOT, OR, NOR, and XOR multifarious spin logic devices were created. The findings of this study are expected to contribute toward the extension of molecular junction functions in future spintronic integrated circuit design and further miniaturization.

Dynamic response and roughening of ferroelectric domain walls driven at planar electrode edges

Understanding and controlling the motion, stability, and equilibrium configuration of ferroelectric domain walls is key for their integration into potential nanoelectronic applications, such as ferroelectric racetrack memories. Using piezoresponse force microscopy, we analyze the growth and roughness of ferroelectric domains in epitaxial thin film Pb(Zr0.2Ti0.8)O3, driven by the electric fields at straight edges of planar electrodes at two different temperatures. This device relevant geometry allows us to confirm that the domain walls are well described as one-dimensional monoaffine elastic interfaces driven in random-bond disorder. However, we observe a progressive increase in roughness as initially flat domain walls move through the disorder landscape, which could prove a significant limiting factor for racetrack-type memories using ferroelectrics.

Impacts of electrode shape on lithiation performance: the edge effect on lithium intercalation

With respect to the increasing applications of irregular shape electrodes in stretchable and flexible batteries, the impacts of electrode shape on lithiation performance are investigated in this manuscript. Firstly, square and circular side-to-side electrodes are prepared and employed for charge and discharge cycles. The lithiation profiles of the graphite electrode are in-situ observed and the electrochemical cyclic performances are recorded. It is found uneven lithiation is more significant in the square electrode than the circular electrode, leading to more side reaction products and poorer cyclic performance. Numerical simulations are conducted to investigate the intrinsic mechanism of the uneven lithiation. It is found the electric field is extraordinarily strong near the electrode edges, resulting in highly inhomogeneous lithium flux in electrolyte. The electrode edges are exposed to excessive lithium supply in electrolyte, leading to fast lithiation saturation and even lithium dendrite growth. Meanwhile, the core area of the electrode cannot obtain sufficient lithium from electrolyte and, therefore, remain in low lithiation level even after charge operation. The sharper the electrode tip is, the stronger the edge effect is. Finally, different irregular shape face-to-face electrodes are prepared and examined. The edge effects are also found in the face-to-face electrodes and lead to a fake lithiation saturation phenomenon. Therefore, strategies to minimize the edge effects, such as decreasing the curvatures of the electrode sharp tips, are suggested to promote the electrochemical performance.