Electrode Edge Research Articles

A micropore nanoband electrode array for enhanced electrochemical generation/analysis in flow systems.

Our previous work has established that micron-resolution photolithography can be employed to make microsquare nanoband edge electrode (MNEE) arrays. The MNEE configuration enables systematic control of the parameters (electrode number, cavity array spacing, and nanoelectrode dimensions and placement) that control geometry, conferring a consistent high-fidelity electrode response across the array (e.g., high signal, high signal-to-noise, low limits of detection and fast, steady-state, reproducible and quantitative response) and allowing the tuning of individual and combined electrode interactions. Building on this, in this paper we now produce and characterise a micropore nanoband electrode (MNE) array designed for flow-through detection, where an MNEE edge electrode configuration is used to form a nanotube electrode embedded in the wall of each micropore, formed as an array of pores of controlled size and placement through an insulating membrane of sub-micrometer thickness. The success of this approach is established by the close correspondence between experiment and simulation and the enhanced and quantitative detection of redox species flowing through the micropores over the very wide range of flow rates relevant, e.g., to applications in (bio)sensing and chromatography. Quantitative electrochemical reaction with low conversion, suitable for analysis, is demonstrated at high flow, whilst quantitative electrochemical reaction with high conversion, suitable for electrochemical product generation, is enabled at lower flow. The fundamental array response is analysed in terms of established flow theories, demonstrating the additive contributions of within-pore enhanced diffusional (nanoband edge) and advective (Levich-type) currents, the control of the degree of diffusional overlap between pores through pore spacing and flow rate, the control by design across length scales ranging from nanometer through micrometer to a centimetre array, and the ready determination of physicochemical parameters, enabling discussion of the potential of this breakthrough technology to address unmet needs in generation and analysis.

Ar/CF4 capacitively coupled plasma generated using 40 MHz sinusoidal and 800 kHz rectangular waveform voltages

Abstract This article discusses the characteristics of an Ar/CF4 capacitively coupled plasma (CCP) excited using 40 MHz sinusoidal and 800 kHz rectangular voltage waveforms. The simulations focus on the effect of the low frequency (LF) rectangular wave duty cycle (defined as the period at negative voltage) on the plasma properties and uniformity for constant 100 W power at 40 MHz and 20 mTorr gas pressure. Given the importance of kinetic effects in low pressure CCPs, a hybrid plasma model is used. This model treats electrons as particles using the particle-in-cell formalism while ions and neutral species are represented as fluids. By incorporating electron kinetic effects, this approach allows for the accurate modeling of low-pressure CCPs with complex plasma chemistries. Results show that, at 80% duty cycle, the peak in the density of all species is near the edge of the electrodes. As the LF rectangular wave duty cycle is decreased while keeping the 40 MHz power fixed, the species’ densities increase, the 40 MHz radio-frequency voltage decreases, and the peak in species’ densities shifts towards the chamber center. These trends can be explained based on how the LF voltage modulates the coupling of 40 MHz power to the electrons. Under the conditions considered, the plasma is mostly produced through electron stochastic heating at the sheath edge by the 40 MHz voltage. The 40 MHz couples to the electrons more efficiently when the LF voltage at the powered electrode sheath is small and the sheath is thin. The plasma is produced relatively uniformly in the inter-electrode region during this phase. Therefore, at small duty cycles when the powered electrode sheath is thin for a long time, the plasma is uniform and requires a smaller 40 MHz voltage to deposit 100 W at 40 MHz in the plasma. When the LF voltage in the powered electrode sheath is large and negative, plasma production is weak and occurs at the edge of the powered electrode where the sheath is thinner. At large duty cycles, the plasma is efficiently produced for only a short period, necessitating a larger 40 MHz voltage. The plasma density also peaks near the electrode edge at large duty cycles.

Transparent Zinc Oxide Memristor Structures: Magnetron Sputtering of Thin Films, Resistive Switching Investigation, and Crossbar Array Fabrication.

This paper presents the results of experimental studies of the influence of high-frequency magnetron sputtering power on the structural and electrophysical properties of nanocrystalline ZnO films. It is shown that at a magnetron sputtering power of 75 W in an argon atmosphere at room temperature, ZnO films have a relatively smooth surface and a uniform nanocrystalline structure. Based on the results obtained, the formation and study of resistive switching of transparent ITO/ZnO/ITO memristor structures as well as a crossbar array based on them were performed. It is demonstrated that memristor structures based on ZnO films obtained at a magnetron sputtering power of 75 W exhibit stable resistive switching for 1000 cycles between high resistance states (HRS = 537.4 ± 26.7 Ω) and low resistance states (LRS = 291.4 ± 38.5 Ω), while the resistance ratio in HRS/LRS is ~1.8. On the basis of the experimental findings, we carried out mathematical modeling of the resistive switching of this structure, and it demonstrated that the regions with an increase in the electric field strength along the edge of the upper electrode become the main sources of oxygen vacancy generation in ZnO film. A crossbar array of 16 transparent ITO/ZnO/ITO memristor structures was also fabricated, demonstrating 20,000 resistive switching cycles between LRS = 13.8 ± 1.4 kΩ and HRS = 34.8 ± 2.6 kΩ for all devices, with a resistance ratio of HRS/LRS of ~2.5. The obtained results can be used in the development of technological processes for the manufacturing of transparent memristor crossbars for neuromorphic structures of machine vision, robotics, and artificial intelligence systems.

Development of Zinc Electrodes as Recyclable Fuel for Mechanically Rechargeable Zinc Air Batteries

Zinc air batteries are safe batteries because they are composed of an aqueous electrolyte. In addition, they also have an energy density several times higher than that of lithium-ion batteries. For this reason, the zinc-air battery is being considered for use as a rechargeable battery [1], but due to various issues, it has not been put to practical use. One of them is dendrite growth in the zinc anode during charging, which makes it difficult to create a rechargeable battery in a sealed space and requires a different methodology. In this study, instead of converting a zinc-air battery into a secondary battery, we focused on a mechanical-charge type, in which the active material is mechanically replaced. The fuel produced by this method is expected to be a medium that can efficiently store, and transport energy as shown in Fig.1. The key point of this system is that the zinc oxide is charged, and the zinc is regenerated. It has been reported that the regenerated zinc is not only prone to dendrites, but also takes on various shapes depending on the charging method [2].Therefore, we proposed the compression method as a method that minimizes changes in discharge characteristics due to shape changes, with the aim of establishing a resource recycling system that integrates current collectors and zinc.The positive electrode (Ni plated SUS mesh) was placed along the inner wall of a PP cylindrical container (250 mL volume) as the charging device, and a brass mesh (#200) cut to 2 cm × 2 cm was used as the negative electrode collector. Electrolyte concentration and charging rate were varied as charging conditions for zinc. The electrolyte was 5wt%, 15wt%, 30wt%, and 48wt% KOH solution (250g), and the charging rates were 20 mA/cm2, 50 mA/cm2, 100 mA/cm2, and 200 mA/cm2. 12.5 g of zinc oxide powder was introduced into the electrolyte to generate zinc equivalent to 820 mAh. The generated zinc was taken out together with the current collector, rinsed twice with pure water, and then made into a zinc plate of about 0.5 mm using a flat plate press, and the moisture was dried in air, which was used as the zinc fuel electrode. As in the case of charging, a PP cylindrical container was used as the discharging device for this fuel, with a graphite rod as the reference electrode in the center, and the zinc fuel electrode as the working electrode and the zinc plate as the counter electrode on either side of the graphite rod. The discharge current was set at 100 mA and discharged until the potential of the zinc fuel electrode reached 0.5 V.As is known from previous studies, various forms of zinc could be observed depending on the charging conditions, but by compressing the charged zinc, a discharge efficiency of about 80% of the theoretical capacity could be obtained under all conditions. The remaining 20% is considered to be capacity loss due to oxidation during the post-processes of rinsing, compressing, and drying after charging. Therefore, it is thought that the oxidized area on the zinc surface can be reduced by rinsing after compressing, resulting in a smaller capacity loss. Comparing the energy density calculated from the discharge capacity of the zinc anode fabricated without compression treatment and the zinc fuel electrode with compression treatment, it was confirmed that the zinc charged in the alkaline electrolyte is in a very sparse state and has a low volumetric energy density as it is, and that it can be made dense by compression to achieve a high energy density. The zinc fuel electrode was found to have a high energy density by compressing the zinc. In this zinc fuel electrode, the ratio of current collector to zinc is 25.3% and 74.7%, indicating that the current collector accounts for about a quarter of the total. Therefore, it is considered necessary to increase the charging capacity to obtain a higher energy density. However, it has been confirmed that zinc precipitation is biased toward the electrode edges when the charging capacity is increased, and the zinc spreads when the electrode is compressed, so the energy density cannot be increased even if the charging capacity is increased. Therefore, the lecture will also discuss methods to suppress the edge concentration of zinc that occurs when the charging capacity is increased, as well as a resource recycling system using zinc as fuel.[1] Zequan Zhao, ACS Energy Lett., 4, (9), (2019)[2] R. Y. Wang, Journal of The Electrochemical Society, 153, (5), (2006) Figure 1

Degradation and Safety Analysis of Large Format LiFePO4/Graphite Battery

Large format LiFePO4/Graphite (LFP/Gr) Lithium-ion battery (LIB) have been developed for electric vehicles (EV) and stationary use. In case of large surface electrodes, intrinsic two-phase reaction of LFP has a risk to induce inhomogeneous reaction in planar electrode surface. We applied >200 Ah class LFP/Gr LIBs and cycled them around 80-65 % SOH levels. Among them, we applied non-destructive differential voltage analysis (dV/dQ) to three cells (Cell1:SOH 80.9 %, Cell2:SOH 73.5 %, Cell3:SOH 68.4 %), and determined the degree of inhomogeneity of the electrodes by disassembly of the cell in the Ar-filled glove box.We could obtain dV/dQ peak corresponds to Gr 2nd stage single phase by charge curve analysis between SOC 0 and 100 % at C/20. Based on the assumption that Gr capacity is twice of the Gr 2nd stage peak capacity, Gr capacity was sufficiently larger than cell capacity. Therefore, cell capacity fade was not related to the capacity fade of Gr but caused by the shift of the cathode / anode operation window (SOW) due to loss of lithium inventory (LLI) and/or capacity fade of LFP.After dV/dQ analysis with capacity check, cells were disassembled at 2.5 V, and confirmed LFP and Gr capacity by reassembling coin cells with Li counter electrode. Reassembled LFP/Li cells was discharged to 2 V, and Gr/Li cells were deintercalated to 2.5 V. The subtracted value of these residual capacities, we could estimate SOW capacity. The obtained estimated cell capacity by LFP-SOW showed strong correlation with SOH of cells before disassembly (R=0.98). Therefore, we confirmed that capacity fade of the cell was due to increase in SOW and/or capacity fade of LFP.To determine the degree of inhomogeneity in electrode planar, we applied XRD to LFP. As LFP reaction proceeds typical two-phase reaction, we can indirectly estimate Li content by estimating ratio of LFP and FePO4(FP). The LFP/FP ratio was optimized by Rietveld refinement of the diffraction peaks in various sampling points of the electrode sheet. We confirmed several macroscale inhomogeneous Li distributions in planar LFP electrode. Li poor area was observed at the beginning and the final edge of the roll electrode. The correlation details between cell SOH and degree of inhomogeneity will be discussed in the presentation.In addition, we applied two kinds of abuse test, overcharge and forced internal short circuit test by laser spot heating to three cells with different SOH. In case of overcharge, cell was charged at 0.78 C from SOC 100 %. In case of laser heating, pulse laser with 0.5 sec supply / 0.1 sec rest at 2000 W applied to the cell. The difference of the obtained parameters, and correlation with SOH will be discussed in the presentation.

A Biosensor for miRNA Detection By Electrorotation Rate of Glass Micro-Rods Modified with Peptide Nucleic Acid

[Introduction] MicroRNA (miRNA), which is RNA molecule with approximately 22 nucleotides in length, has attracted attention as novel biomarkers for the diagnosis of cancer, hepatitis, and other conditions. The miRNA has been commonly detected by RT-qPCR, used for synthesizing and quantifying cDNA. We can detect minute quantities of miRNA by this method. However, it requires laborious procedures, complex reagents, and fluorescent probes for labeling DNA. Thus, simple and rapid detection methods of miRNA have been required for point-of-care testing. When microparticles are exposed to a rotating electric field, the electrostatic interaction between the induced polar charges on the particles and the rotating electric field generates the torque on the particles. This phenomenon is called electrorotation (ROT). The rotation rate depends on the electrical properties of the particle surface. We developed the miRNA detection system based on the decrease of ROT rate of rod-shaped glass microparticles (micro-rods) by binding miRNA. The surface of micro-rods was modified by peptide nucleic acid (PNA) with a complementary sequence of target miRNA. The recognition of miRNA charged negatively to the modified PNA gives rise to the increase of surface conductivity of micro-rods and thereby the decrease of the rotation rate. In addition, the surface conductivity of micro-rods was almost constant by introducing PNA without the charge. Thus, the system could provide the simple detection of miRNA required no labeling with fluorescence molecules.[Experimental Methods] ROT measurements of micro-rods were conducted by a three-dimensional interdigitated array electrode device (3D-IDA) (Fig. A). The device consisted of two glass substrates with micropatterns of IDA (35 µm in electrode width and 70 µm in gaps between electrodes) made of indium-tin-oxide (ITO). A substrate was mounted orthogonally to another substrate via double adhesive tape (60 µm in thickness), resulting in the formation of microgrids (70 µm in length) surrounded by four microband electrodes. Applying AC voltages with a phase difference of 90 degrees each to the four microband electrodes generates a rotational electric field in microgrids. Micro-rods were treated with 100 mM 3-aminopropyltriethoxysilane for 1 hour, 10 mM 3-Sulfo-N-succinimidyl 4-(N-Maleimide-methyl) cyclohexane-1-carboxylate sodium salt for 1 hour, and 5 µM thiolated single-stranded PNA for 4 hours to modify the surface by PNA. The PNA-modified micro-rods were then treated with miRNA for 1 hour. The temperature gradually decreased from 45 ºC to 20 ºC at 0.83 ºC min-1 and then kept at room temperature for 30 min. The treated micro-rods were injected into the 3D-IDA and subjected to the ROT measurement.[Results and Discussion] The application of voltage (10 Vpp, 100 kHz) to the 3D-IDA caused the micro-rods to rotate at the center of each grid (Fig. B). The rotation rate decreased with increasing the length of micro-rods. The micro-rods with the length of 40 µm that is the maximum frequency value of the length were selectively observed in this work. The PNA-modified micro-rods introduced in the device adsorbed on the IDA substrate. The adsorption could be due to the electrostatic interaction between the positive charge on micro-rods derived from unreacted amino group introduced for the PNA modification and the negative charge on the IDA substrate. Most of micro-rods treated with miRNA were rotated at the center of grids. For the micro-rods treated with 5 nM miRNA, the rotation rate slightly increased with increasing the applied frequency up to 50 kHz, followed by a decrease of the rate (Fig. C). Rotation rate decreased with increasing the miRNA concentration. Furthermore, the frequency with maximum rate shifted to higher-frequency region with increasing the concentration. These results were attributed to the increase of the surface conductivity by binding miRNA with the negative charge on the micro-rods. However, the micro-rods treated with non-complementary miRNA absorbed on the IDA substrate to observe no electrorotation. In addition, the rotation was inhibited by the shift of the rotation center of microrods to the edge of electrodes by applying AC voltage with over 200 kHz. The shift of the center is due to the force of the negative dielectrophoresis. These results indicate that the rotation rate of micro-rods in lower frequency region allows to the determination of miRNA with target sequence without fluorescence label. Figure 1

Investigating the Impact of Various Binder Contents and Compression on Graphite Electrode Thickness Change Measurements

Volume change of active materials during the insertion of Li+-ions into the electrode’s host structure in lithium-ion batteries (LiBs) has become an increasingly researched topic. Reversible and irreversible thickness changes occur during operation because of active material volume change upon lithiation/delithiation and SEI growth. In LiBs, particularly the volume change of the negative active material can cause mechanical disintegration of the composite coating [1], causing loss of active material. LiBs are usually operated in a compressed state maintained by geometrical boundary conditions to ensure uniform contact between electrode layers. Therefore, the thickness changes can cause increased stack pressure and, subsequently, microstructural changes [2] and thus affect the performance and lifetime of the battery [3]. To better understand the aforementioned phenomena, accurate thickness measurements are required.Measuring the thickness change of a cell stack does not provide accurate information about the individual thickness change of the two electrodes. Therefore, single-electrode electrochemical dilatometry (ECD) can help to better understand the impact of the individual electrodes on cell stack thickness change. Due to the common use of a commercially available setup (EL-Cell, ECD-3-nano, Germany) in literature, most ECD experiments were conducted at a pressure of ~ 16 kPa onto a Ø10 mm working electrode (WE). Only in some publications higher pressures > 0.1 MPa were applied during single electrode measurements [4]. The applied pressure in lab-scale coin cell setups and state-of-the-art LiBs is usually significantly higher (0.1 – 0.5 MPa) than that of single-electrode ECD investigations. Therefore, the question arises whether the pressure has an impact on the measured thickness change.Thus, this work integrates a wave spring washer into a commercially available single-electrode ECD Setup (ECD-3-nano, El-Cell GmbH, Germany) to apply additional pressure onto the WE, without requiring geometrical modifications of the setup. The integration of the wave spring washer increases the applied pressure from 16 kPa to > 100 kPa. Graphite electrodes with different binder types and contents are investigated since distinct measurement artifacts were observed for electrodes with certain binder compositions in preliminary experiments. Electrodes without additional pressure show a first-cycle lithiation thickness increase of up to 30% (see Figure 1), which is much higher than the active material volume change of graphite obtained from XRD data [5] would suggest. For all examined electrodes at lower pressure the first and tenth cycle lithiation thickness change is more than 50 % higher compared to the setup at high pressure. The mechanism causing the discrepancy between measurements at the two pressure levels is identified as the curvature of the electrode edges at low pressures present in commercially available ECDs. Therefore, the setup at increased pressure enables a meaningful investigation of the influence of the binder content on irreversible and reversible thickness change for the electrodes under investigation using more realistic mechanical boundary conditions. Measurements show that irreversible thickness change decreases with increasing binder content. Possibly the higher binder content helps to prevent restructuring of the particles during cycling due to higher mechanical strength of the electrode. Delithiation thickness change is similar among electrodes with normal to high binder contents. Only electrodes with a very low binder content have a significantly lower reversible thickness change.Overall, this study shows that the influence of pressure onto the WE should be considered for future ECD-experiments and setups. This work presents an easy to implement solution to apply additional pressure onto the WE for a common commercially available ECD-setup.

Microfluidic Device for in Situ Observation of Bottom-up Copper Deposition in a TSV-like Structure- Improved Adhesion of Working Electrode Edge

The high performance of modern integrated circuits is now owing to packaging technologies. 3d-packaging using TSVs (Through Silicon Vias) has attracted large attention. Copper electroplating is used for filling conductor into the vias, because extreme bottom-up is available using a combination of additives. Even though extreme bottom-up is available with single addition of leveler without other additives and theoretical model, such as S-NDR model proposed by Moffat and Josell, can predict the filling behavior, still combination of leveler, suppressor and accelerator is generally used in industry and filling mechanism with the combination is not clear yet. To understand the mechanism of copper filling and the function of each additive, we have proposed microfluidic devices. In our previous study, a TSV-like structure was built in a micro channel as shown in figure 1, and real-time observation of copper bottom-up deposition was demonstrated. Though the observation was successful, observation period was limited to short periods of time, because abnormal deposition occurred at mouse of the TSV-like structure. In this study, we assumed that poor adhesion around the edge of the working electrode on a substrate caused the abnormal deposition, because insufficient adsorption of leveler is expected if the working electrode thin film was floating from the substrate. Then, fabrication process of the working electrode was changed from etching to lift-off patterning technique. Several processes were optimized and abnormal deposition along the edge was successfully suppressed as show in figure 2. Using the lift-off technique, a TSV-like structure was built and electrodeposition was examined. Electrodeposition was started at 30 s after feeding a plating solution containing the leveler. Results are shown in figure 3. No abnormal deposition around the opening of TSV-like structure more than 10 min, and we succeeded in the observation of suppression breakdown inside the via. Further study with various combination of additives will be planned. Figure 1

A passive, flexible dual-function sensor for simultaneous pressure and sliding direction detection

Flexible pressure and omnidirectional slide sensors show significant potential in wearable devices and robotics. However, the integration of various sensor types to achieve multi-functionality introduces challenges. Complex structures and processing difficulties limit their miniaturization and flexibility, while dependence on external power sources further constrains their practical use. Here, we report a novel strategy that utilizes a piezoelectric-conductive nanoresistance network with edge electrodes to develop an advanced pressure sensor. This sensor is capable of simultaneously detecting pressure and sliding direction through multiple-channel pulses. We demonstrate its functionality using a polyacrylonitrile/polypyrrole nanofiber membrane (PAN/PPY NFM) configured with either two or three electrodes. By exploiting the signal transmission characteristics of the nanoresistance network, the sensor simultaneously responds to both force and sliding direction through amplitude-frequency analysis of the output signals from multiple channels. Additionally, the sensor operates without an external power supply. This streamlined approach simplifies sensor design and processing, providing a promising solution for advanced touch sensing applications.

Ionic wind produced by volume corona discharges and surface dielectric barrier discharges: What role do streamers play?

The present study compares the ionic wind produced by volume DC and AC corona discharges, and by surface dielectric barrier discharges (DBD). On the one hand, in the case of a volume corona discharge ignited between a high-voltage needle and a grounded plate, our measurements highlight that the ionic wind velocity increases in the presence of positive breakdown streamers. On the other hand, in the case of a surface AC DBD, the ionic wind velocity decreases when streamers occur. Why such a difference? The answer is not easy and the debate remains open. However, one answer would be that the streamers occurring in a volume needle-to-plate discharge leave an abundance of positive ions in the inter-electrode space and that these ions drift because of the electric field, just after the streamer propagation. On the other hand, in the case of a surface DBD, the streamers can leave positive ions in their wake but their heads especially deposit positive ions at the location where they stop propagating, i.e. a few millimetres from the electrode (up to about 10–15 mm). Then this positive space charge deposited at a few millimetres from the active electrode edge on the dielectric surface acts as a screen against the electric field due to the applied high voltage, thus preventing the drift of the ions remaining on the surface of the dielectric, close to the electrode edge. Having said that, the reality is that this explanation is certainly very simplistic compared with the very complex phenomena taking place in these two discharges, particularly at the times when the streamers form and propagate.

A wafer-level characterization method of thin film transverse piezoelectric coefficient evaluation

Accurate measurement of the piezoelectric property of thin films is critical for thin film process development and device design optimization. In this paper, we proposed a wafer-level thin film characterization method that provides a non-destructive, single-side measurement solution for evaluating and in-process monitoring the transverse piezoelectric coefficient (e31,f). The e31,f of piezoelectric films was determined by measuring the deflection of circular electrode induced by the converse piezoelectric effect, with the electrodes fabricated on top of piezoelectric thin film on a silicon substrate. The constitutive equation of the unimorph plate reveals a quadratic dependence of top electrode deflection (δ) on the radius (r), which was subsequently utilized to calculate the e31,f while considering the electrode edge effect. Determined by non-constant variations of |δ/r2| from finite element method (FEM) simulation results, the electrode edge effect leads to the specification of electrode size and substrate thickness for evaluating piezoelectric coefficient. A comprehensive FEM simulation analysis of the influence of wafer size and electrode location on the accuracy of the proposed method demonstrated its reliability for wafer-level characterization. The e31,f measurement results of single-crystal (s-PZT) and polycrystalline PZT (p-PZT) exhibit good agreement between the proposed wafer-level method and the die-level cantilever method. These results demonstrated that the proposed single-side wafer-level method provides a reliable measurement technique for e31,f characterization of piezoelectric thin film.

The time evolution of electrical and thermodynamic characteristics of surface dielectric barrier discharge caused by dielectric degradation

Abstract The degradation of the dielectric layer is a common issue in dielectric barrier discharge (DBD). The performance of DBD devices may suffer from instability due to potential corrosion of the dielectric layer caused by discharge, which could even result in structural failure. To gain a comprehensive understanding of the degradation of DBD devices during discharge, the evolution of the performance of DBD devices with various dielectric materials over time is studied. Periodic patterns are found to form on the dielectric surface along the edge of the high-voltage electrode. The electrical data, emission spectra, and surface morphologies of DBD devices with three different dielectric materials, namely ceramics, glass, and PCB, are obtained during an eight-hour discharge. The electrical and thermodynamic characteristics of DBD devices with the three dielectric materials are found to initially decrease by about 20~40%. Subsequently, they remain stable in devices with ceramics and PCB dielectric layers but increase in devices with glass dielectric layers until the end. Surface morphologies reveal that periodic patterns consisting of metal accumulations, etching pits, and metal depositions form on the surfaces of ceramics, glass, and PCBs, respectively. Some organic compounds vaporize from the surface of PCBs. The deposition, etching, and vaporization could be reasons for changes in the electrical and thermodynamic characteristics. It shows that degradation occurs not only in organic dielectrics like polymers but also in inorganic dielectrics such as ceramics and glass. To enhance stability and prevent potential failures and overestimations, electrical and optical measurements could be utilized as diagnostic methods in applications involving DBD devices.


Highly sensitive Ga2O3 MSM solar-blind UV photodetector with impact ionization gain.

In this study, a (400) crystal-oriented β-Ga2O3 thin film with a thickness of approximately 400 nm was grown on a c-plane sapphire substrate using atomic layer deposition. Schottky contact-type metal-semiconductor-metal solar-blind ultraviolet detectors with an Au/Ni/Ga2O3/Ni/Au structure were fabricated on the epitaxial thin films. The Schottky barrier height is about 1.1 eV. The device exhibited a high responsivity of up to 800 A/W, and a detectivity of 6 × 1014 Jones while maintaining a relatively fast response speed with a rise time of 4 ms and a fall time of 12 ms. The photo-to-dark current ratio was greater than 103, and the external quantum efficiency exceeded 103, indicating a significant gain in the device. Through the analysis of TCAD simulation and experimental results, it is determined that the impact ionization at the edge of the MSM electrode and channel contact is the main source of gain. Barrier tunneling effects and the photoconductive effect due to different carrier mobilities were not the primary reasons for the gain.

(Energy Technology Division Graduate Student Award sponsored by BioLogic) In-Situ, Non-Destructive, 3D Neutron Imaging of Lithium Plating Following Extreme Fast-Charging of Full-Cell Lithium-Ion Batteries

One of the primary challenges impeding extreme fast-charging (XFC) of current lithium-ion batteries (LIBs) for electric vehicles (EVs) within 10–15 minutes is the deposition of Li metal on graphite known as “Li plating”.1-2 After Li plates, it either re-intercalates into the graphite electrode or is stripped off during battery discharging to form “active Li”or becomes electronically disconnected resulting in “dead Li.” Previous studies have indicated that dead Li is the main contributor to the XFC-related capacity loss of LIBs. However, mechanistic understanding of the 3D morphological behavior and spatial heterogeneities of dead Li; and how they differ from those of plated and active Li during the XFC is not well understood.3-4 Here, we present an in-situ, non-destructive 3D characterization of the morphological behavior and spatial heterogeneities of plated, dead, and active Li on graphite electrodes in full-cell LIBs using high-resolution neutron micro-computed tomography. We performed neutron µCT5 (pixel size: ~ 5.74 µm; effective spatial resolution: ~10-15 µm) at the ICON beamline6 at the Swiss Spallation Neutron Source at the Paul Scherrer Institute. We imaged two batteries in the charged and discharged states: (1) after 4 cycles of 1C charging and (2) after 6 cycles of 6C charging.Our results show that Li plates at and around the edges of the graphite electrodes, indicating that graphite edges and the areas around these edges are the most susceptible to Li plating. However, certain edges and areas around these edges formed dead Li whereas others formed active Li, suggesting 3D spatial heterogeneities in the formation of dead and active Li at both 1C and 6C. Mainly, we discuss these heterogeneities at four regions: (1) near the Cu CC, (2) in the middle of the graphite electrode, (3) near the graphite-separator interface, and (4) in the separator. Specifically, we found that Li near the Cu CC remains active whereas most of the plated Li at the graphite-separator interface and in the separator becomes dead at both 1C and 6C.Morphologically, we observed porous nature of plated and dead Li at both 1C and 6C. Our 3D visualizations noticeably show nodules of varying densities of metallic Li. However, we observed different 3D behavior of Li plating at 1C and 6C. For example, tip-like Li deposits were seen laterally closer to the center of the graphite electrode, near the graphite-separator interface, and into the separator at 6C. In contrast, at 1C, no tip-like Li deposits were observed near the graphite-separator interface and into the separator. Based on our findings, we concluded that higher XFC-charging rate and cycling number (6 cycles of 6C charging) cause the formation of tip-like Li deposits as compared to the relatively slower XFC-charging rate and cycling number (4 cycles of 1C charging). We believe that insights derived from this work will guide the design of thick graphite electrodes with minimized-plating for fast-charged EVs.

Automated Scanning Dielectric Microscopy Toolbox for Operando Nanoscale Electrical Characterization of Electrolyte‐Gated Organic Transistors

AbstractElectrolyte‐gated organic transistors (EGOTs) leveraging organic semiconductors' electronic and ionic transport characteristics are the key enablers for many biosensing and bioelectronic applications that can selectively sense, record, and monitor different biological and biochemical processes at the nanoscale and translate them into macroscopic electrical signals. Understanding such transduction mechanisms requires multiscale characterization tools to comprehensively probe local electrical properties and link them with device behavior across various bias points. Here, an automated scanning dielectric microscopy toolbox is demonstrated that performs operando in‐liquid scanning dielectric microscopy measurements on functional EGOTs and carries out extensive data analysis to unravel the evolution of local electrical properties in minute detail. This paper emphasizes critical experimental considerations permitting standardized, accurate, and reproducible data acquisition. The developed approach is validated with EGOTs based on blends of organic small molecule semiconductor and insulating polymer that work as accumulation‐mode field‐effect transistors. Furthermore, the degradation of local electrical characteristics at high gate voltages is probed, which is apparently driven by the destruction of local crystalline order due to undesirable electrochemical swelling of the organic semiconducting material near the source electrode edge. The developed approach paves the way for systematic probing of EGOT‐based technologies for targeted optimization and fundamental understanding.

Discharge characteristics of the planar microscale gap electrodes with various geometry structures in the atmosphere environment

The discharge of microscale gaps for MEMS systems is a serious issue. To reveal the dark discharge characteristics of the microscale gap, electrodes with various gap feature sizes were prepared, and the DC current–voltage characteristics for the electrodes were implemented in atmospheric air. The results showed minor differences in dark discharge current on a nanoampere scale among electrodes with varying gap sizes of micro-protrusions. The current formation mechanism was consistent with the electron avalanche theory. Morphological characterization identified the presence of non-ideal thin-layer trailings at the electrode edges. To evaluate the effect of trailings on the dark discharge characteristics of the microscale gap structures, the electrodes with varying trailing lengths were fabricated. It showed that the current increased exponentially in the presence of long thin-layer trailing. In this case, the breakdown is most pronounced with an effective gap distance of 30 μm and a trailing length of 14.34 μm for the electrodes. For this structure, the dark discharge current was 198 nA at 36 V bias voltage, while the discharge current increased to 50 µA when the bias was increased to 37 V, and stabilized at 100 µA when the bias voltage was higher than 39 V. The rapid increase in current caused by trailing originates from the field emission as judged by the Fowler-Nordheim theory. Simulation results showed that the field strength can reach up to 3.76 × 109 V/m at a thin layer trailing length of 3.5 μm and a bias voltage of 200 V, which matches the conditions for the field emission. By calculating the effective secondary electron emission coefficient, it was found that thin-layer trailing significantly intensifies the ion-enhanced effect, further lowering the threshold for field emission and resulting in a rapid increase in microscale gap current at lower voltages.

In Situ and 2D and 3D in Silico Redox Cycling Studies for Design Optimization of Coplanar Arrays of Microband Electrodes in a 70 μm × 100 μm Electroactive Footprint

Optimization of redox-cycling currents was performed by adjusting the height (sidewalls, h), width (w), and length (l) of band electrodes and their spacing (w gap) in coplanar arrays restricted to a small-electroactive window of 70 × 100 μm. These arrays can function in μL-volumes for chemical analysis (e.g., in-vivo dopamine detection using probes). Experiments were conducted with an array of five electrodes (N E = 5), w = 4.3 μm, w gap = 3.7 μm, h = 0.150 μm, and l = 99.2 μm. Reasons for disparities between currents from experiments and approximate equations were determined by high-density mesh simulations and were found to arise from sluggish heterogeneous electron transfer kinetics and diffusion at electrode ends, edges, and heights. Ferricyanide, with its moderately slow kinetics, exhibits redox-cycling currents that fall below predictions by the equations as w gap decreases and diffusional flux outpaces reaction rates. Simulations aid investigations of various array designs, achievable through conventional photolithography, by decreasing w and w gap and increasing N E to fit within the electroactive window. A coplanar array, N E = 58, w = w gap = 0.6 μm, h = 0.150 μm and l = 100 μm, yielded ferricyanide sensitivities of 0.266, 0.259 nA·μM−1, enhancements of 8 × and 9 × over w = w gap = 4 μm, and projected dopamine lower limits of quantitation of 139 nM, 171 nM at generator and collector electrodes, respectively.

The Child Langmuir Illusion

A Particle in Cell (PIC) model of ion beam extraction from a plasma provides strong evidence that the origin of the observed V(3/2) relationship between the applied extraction voltage and beam current is caused by meniscus shape and collimation on the extraction electrode, not by space charge limited extraction. Excellent correlation between the PIC model, a gun code and experiment is shown for 100 µA Ar+ beams. The s-shape in the emittance phase space is shown to be caused by the radial electric field created by the external edge of the plasma electrode.

Development of High-Voltage Electrodes for Neutron Scattering Sample Environment Devices

The sample environment is essential to neutron scattering experiments as it induces the sample under study into a phase or state of particular interest. Various sample environments have been developed, yet the high-voltage electric field has rarely been documented. In this study, Bruce electrodes with various sectional geometries and chamber sizes were examined by using simulation modeling based on ANSYS Maxwell. A large uniform field region where samples would sit could be achieved in the planar region for all specifications, but the size of the region and the field strength varied with the gap distance between electrodes. The edging effect was inherently observed even for bare electrodes, about 1.7% higher in the sinusoidal region than the planar region, and was significantly deteriorated when a chamber was applied. This effect, however, presented an exponential decrease as the minimum distance between the electrode edge and the chamber shell increased. A compromise between the spatial confinement and the achievable field (strength and uniform region) could be reached according to the unique applicability of neutron instruments. This research provides a theoretical basis for the subsequent design and manufacturing of high-voltage sample environment devices.

Inhomogeneous domain switching near an electrode edge in orthorhombic K0.5Na0.5NbO3 piezoceramic

To characterize the inhomogeneous field distributions and their effect on ferroelectric/ferroelastic domain switching in potassium sodium niobate-based piezoceramics, a partially electroded orthorhombic phase K0.5Na0.5NbO3 ceramic sample containing a distinct edge was investigated using micro-beam, high-energy XRD with applied fields. Under the field application, the partial-electrode sample exhibits orientation-dependent and position-sensitive domain switching. The experimental measurements of micro-scale domain texture correlate reasonably with simulated electric fields calculated from a finite element analysis. Both experimental and simulated results reveal that the domain switching is induced inhomogeneously up to the millimeter-scale across the sample and that the electric field is significantly concentrated near the electrode edge. Integrating the experimental results with the model demonstrates that the local electric field directions and amplitudes drive the local orientation dependence of domain switching and, conversely, the direction of the local electric field can be inferred from the direction in which the maximum domain switching is measured.