Surface Voltage Research Articles

Study on imprinting and replica molding of quasi-grey scale soft mold curved surface microstructure mold

The aim of this paper is to fabrication of quasi-greyscale microstructures by curved surface soft magnetic mold. In this paper, a photocuring system is first developed and built independently, then created the magnetic curved surface microstructure soft mold, the magnetic force of the magnetic curved surface via to different heights was obtained after tested and recorded. The experimental results show that, under different surface curvatures and voltage control conditions, will have different quasi-grey scale array microstructures. In addition, this paper conducts research on the imprinting and replica molding of photoresist composite magnetic powder in order to discuss the formability of magnetic photoresist, and finally, the experimental result is combined with the simulation to obtain more accurate prediction and results.

Experimental Investigation of the Filtration Characteristics of Charged Porous Fibers

Nanofibers fabricated through electrospinning technology have been successfully applied in various industries. The filtration advantages of nanosized electrospun fibers, particularly their high filtration efficiency and low pressure drop, make them highly suitable for addressing the problems of particulate pollution. Previous research has shown that the higher surface-to-volume ratios of nanoscale porous fibers contribute to their physical properties. However, little research on the filtration characteristics of charged porous fibers has been reported. Accordingly, this study used electrospinning to fabricate micro- and nanoscale PMMA fibers in order to investigate the surface voltage, pressure drop, and filtration efficiency of charged porous fiber filters. The outcomes showed that porous PMMA fibers were successfully fabricated as the mass ratios of DMF:CHCl3 gradually reached 1:15. After corona discharge, the surface voltage of the fine porous fiber (~500 nm) was –0.650 kV higher than the –0.562 kV voltage of fine smooth fiber. Filtration efficiency was evaluated using particles with an average concentration of 1.16 × 106 and with sizes ranging from 21.58–660.62 nm. After negative corona discharge, the most penetrating particulate size of filters made from fine porous fiber decreased from 168.5 to 121.9 nm, and the penetration rate dropped from 34.09% to 5.84%. For smooth fiber, the most penetrating particulate size remained unchanged at 135.8 nm, but the penetration rate dropped from 32.64% to 18.19%. This study also showed that porous fiber performed better than smooth fiber in terms of surface voltage decay and single fiber efficiency.

Discharge Characteristics of Short Air Gap and Insulation Surface Under Flame Conditions

An experimental study was conducted to investigate the discharge characteristics of short air gap and insulation surface under flame conditions. The influence of ac electric field on flame and the mechanism leading to the reduction of breakdown voltage under flame conditions are analyzed. Results show that under the ac electric field, the flame is deflected to the high voltage electrode, and compared with normal conditions (without flame), the breakdown voltage of the short air gap and the insulation surface is decreased by 74.4% and 70%, respectively. Besides, arc levitation appears at high probability under the flame conditions. Furthermore, the decrease of the breakdown voltage of short air gap and the flashover voltage of insulation surface under the flame conditions are mainly due to the increase of the air conductivity and the decrease of the air density. For the insulating dielectric, the change of the flashover path is also one of the main reasons for the decrease of the flashover voltage.

Model for screened, charge-regulated electrostatics of an eye lens protein: Bovine gammaB-crystallin.

We model screened, site-specific charge regulation of the eye lens protein bovine gammaB-crystallin (γB) and study the probability distributions of its proton occupancy patterns. Using a simplified dielectric model, we solve the linearized Poisson-Boltzmann equation to calculate a 54×54 work-of-charging matrix, each entry being the modeled voltage at a given titratable site, due to an elementary charge at another site. The matrix quantifies interactions within patches of sites, including γB charge pairs. We model intrinsic pK values that would occur hypothetically in the absence of other charges, with use of experimental data on the dependence of pK values on aqueous solution conditions, the dielectric model, and literature values. We use Monte Carlo simulations to calculate a model grand-canonical partition function that incorporates both the work-of-charging and the intrinsic pK values for isolated γB molecules and we calculate the probabilities of leading proton occupancy configurations, for 4<pH<8 and Debye screening lengths from 6 to 20 Å. We select the interior dielectric value to model γB titration data. At pH 7.1 and Debye length 6.0 Å, on a given γB molecule the predicted top occupancy pattern is present nearly 20% of the time, and 90% of the time one or another of the first 100 patterns will be present. Many of these occupancy patterns differ in net charge sign as well as in surface voltage profile. We illustrate how charge pattern probabilities deviate from the multinomial distribution that would result from use of effective pK values alone and estimate the extents to which γB charge pattern distributions broaden at lower pH and narrow as ionic strength is lowered. These results suggest that for accurate modeling of orientation-dependent γB-γB interactions, consideration of numerous pairs of proton occupancy patterns will be needed.

Recent Advancement in Charge and Photo-Assisted Non-Contact Electrical Characterization of SiC, GaN, and AlGaN/GaN HEMT

Development of semiconductor devices and control of the manufacturing process require cost effective metrology with rapid feedback to pilot or manufacturing lines. In this respect, silicon IC’s have been benefiting from inventions (by IBM, Fishkill, NY and by SDI, Tampa, FL) that created unique corona-Kelvin non-contact electrical metrology [1]. Corresponding commercial tools designed for Si wafers [2] reduced the need for fabrication of electrical test devices and electric contacts, reducing the manufacturing cost and shortening the data feedback time from weeks to less than one hour. Developments, reported in this work are directed toward new possibilities for corona-Kelvin application for wide-bandgap semiconductors, including SiC, GaN, and GaN/AlGaN heterostructures. In charge-assisted corona-Kelvin metrology the low kinetic energy (thermalized) corona ions are placed on the surface. They produce an electrical field in dielectric and/or in semiconductor surface space charge region. The change of the surface voltage, DV, induced by charge dose DQ, is measured in a non-contact manner with a vibrating Kelvin probe. Non-contact differential capacitance is obtained as C=DQ/DV. Knowing the net surface voltage, V and the net charge density Q = SDQ the set of (C,V,Q) characteristics is determined. This unique corona-Kelvin data set enables determination of dielectric, interface, and semiconductor parameters [3]. Applications in silicon IC concentrated on characterization of wafers with dielectrics. Extension of the metrology to wide-bandgap semiconductors includes very important measurement of wafers with bare surfaces. Critical is charge-assisted profiling of dopant concentration and use of corona-kelvin CV as a non-contact alternative to mercury probe CV, MCV [4]. Large charging range and superior precision of corona charging for such measurement achieved only recently with the constant surface potential method [4]. In wide-bandgap semiconductors, the bare epi-surfaces in depletion were found to have excellent corona charge retention. In addition, the long- time constant of deep bulk traps and interface traps practically eliminates trap contribution to deep depletion capacitance. This increases the precision of dopant measurement and dopant-depth profiling. Repeatability of measurements is very important for metrology acceptance in semiconductor manufacturing. In the charge-assisted measurement repeatability requires neutralization of the deposited charge. According to recent developments complete removal of corona deposited charge can be achieved using a photo-assisted process, namely, illumination with UV light with photon energy larger than the semiconductor energy gap. Photogenerated excess carriers neutralize corona ions and neutralized ions detach from the surface. This process enables to return to initial pre-charging condition as verified by the value of surface voltage. The results of repeated dopant density measurement on epitaxial SiC and GaN demonstrated 1s in 10 repeats of 0.06% for doping in 1014 cm-3 range and about 0.1% for dopant from 1018cm-3 to 1019cm-3. In the range from 1014cm-3 to 2 x 1019cm-3 very good correlation was obtained for SiC and GaN between corona-Kelvin noncontact CV and standard mercury probe MCV results. These results demonstrate present performance levels and confirms that corona-Kelvin represents an industry ready alternative to Hg-CV [5]. Recent results obtained on heteroepitaxial GaN/AlGaN/GaN with two dimensional electron gas, 2DEG, demonstrate the unique advantage of capacitance-charge characteristic C-Q available in corona-Kelvin method. This characteristic enables direct determination of the fully depleted 2DEG condition, and corresponding value of “charge to deplete” the 2DEG, and the pinch-off voltage value based on Q-V data. For GaN/AlGaN/GaN heterostructures these measurements confirmed the 2DEG location at the bottom AlGaN/GaN interface. The electron density depth profile of 2DEG determined from noncontact CV agreed very well with MCV results. The techniques gave the same pinch-off voltage values and the same total capacitance corresponding to AlGaN and GaN layers above the 2DEG. Wafer level interfacial instability testing is the newest corona-Kelvin application for oxidized SiC and for GaN/AlGaN HEMT with dielectric capping. The fundamental advantage of charge-assisted technique is twofold: 1. larger dose corona charging provides a bias-stress inducing instability and 2. low dose corona charge-Kelvin measurement gives (C,V,Q) characteristics used for evaluation of instability magnitude. In HEMT heterostructures the instability is manifested by the shift in pinch-off point, that in accelerated photo-assisted testing is enhanced using illumination. In oxidized SiC the instability is manifested by CV shift corresponding to threshold voltage shift caused by charging of near-interfacial oxide traps. The practical advantage of wafer level instability testing is rapid data feedback and elimination of test device fabrication cost, similar to corona-Kelvin advantages established in silicon IC development and manufacturing. An additional well proven advantage of the corona-Kelvin technique is whole wafer mapping capability for all measured parameters. Figure 1

Kelvin Force Probe Microscopy of Ferroelectric Si:HfO2

Since the demonstration of the ferroelectric properties in hafnium based oxides in 2011 there is large interest to such films for ferroelectric FET, memory, and other applications. Engineering of ferroelectricity in HfO2 relies on doping and annealing. For Si-doped HfO2films, a top metal electrode capping layer is deposited prior to annealing which is shown to cause ferroelectric behavior. In this paper we present results of non-contact corona-Kelvin characterization of poling phenomena for ferroelectric Si:HfO2 thin films. Measurements were performed on free dielectric surfaces. The method uses corona charging and Kelvin force probe measurements. Corona charging pulses are analogous to voltage biasing, except that no top electrode is needed. Corona charging enables biasing the Si:HfO2to a near coercive field where onset of poling occurs. Mapping of the surface voltage with a small diameter Kelvin force probe allows to quantify poling phenomena, its uniformity and degradation during repetitive switching (Fig. 1). These results are of importance for fundamental understanding of switching mechanisms of ferroelectric Si:HfO2 films. Figure 1

Recent Advancement in Charge and Photo-Assisted Non-Contact Electrical Characterization of SiC, GaN, and AlGaN/GaN HEMT

The charge-based corona-Kelvin noncontact metrology, originally developed for Si IC fabrication, has recently been extended to wide energy gap semiconductors. We discuss principles of this extension and key applications, namely: high precision dopant measurement on SiC and GaN; two-dimensional electron gas characterization in AlGaN/GaN HEMT structures; interface and dielectric characterization on epi-layers with SiO2, SiN and Al2O3; comprehensive interfacial instability characterization of oxidized SiC; and whole wafer mapping of defects with a charge-assisted surface voltage technique. This powerful set of measurements is performed without fabrication of any test structures or electrical contact. Corresponding commercial tools are currently being introduced. Based on the historical example of silicon IC, we believe that this approach shall offer enhanced testing for research and for manufacturing process control with reduced cost and fast data feedback benefiting the wide-bandgap device technology.

A Potential-Based Inverse Spectral Method to Noninvasively Localize Discordant Distributions of Alternans on the Heart From the ECG.

Image the spatial distribution of TWA on the heart surface from ECG measurements. We introduced the inverse spectral method (ISM), a tailored inverse (or ElectroCardioGraphic Imaging) solution designed specifically to noninvasively image cases of TWA on the heart. We evaluate the ISM on its capacity to reliably detect the spatial distributions of TWA compared against a standard TWA detection method applied directly to the electrograms on the heart surface. We report on results from both a series of synthetic simulations of TWA generated using the ECGSIM software and a set of continuous epicardial surface voltage recordings from a canine experiment. ISM detected TWA distributions that matched the phase of the true underlying out-of-phase regions over and of the heart surface, respectively. Our results suggest that ISM is capable of reliably detecting the different regions present in a TWA distribution across a wide variety of TWA locations on the heart in simulation and in the face of transients and nonidealities in the canine recordings.

Low-Temperature Fusible Silver Micro/Nanodendrites-Based Electrically Conductive Composites for Next-Generation Printed Fuse-Links.

We systematically investigate the long-neglected low-temperature fusing behavior of silver micro/nanodendrites and demonstrate the feasibility of employing this intriguing property for the printed electronics application, i.e., printed fuse-links. Fuse-links have experienced insignificant changes since they were invented in the 1890s. By introducing silver micro/nanodendrites-based electrically conductive composites (ECCs) as a printed fusible element, coupled with the state-of-the-art printed electronics technology, key performance characteristics of a fuse-link are dramatically improved as compared with the commercially available counterparts, including an expedient fabrication process, lower available rated current (40% of the minimum value of Littelfuse 467 series fuses), shorter response time (only 3.35% of the Littelfuse 2920L030 at 1.5 times of the rated current), milder surface temperature rise (16.89 °C lower than FGMB) and voltage drop (only 24.26% of FGMB) in normal operations, easier to mass produce, and more flexible in product design. This technology may inspire the development of future printed electronic components.

A pseudo 3D electrochemical-thermal modeling and analysis of a lithium-ion battery for electric vehicle thermal management applications

This paper presents an improved pseudo 3D coupled electrochemical-thermal model that can be implemented into active or passive battery thermal management systems (BTMS). The model features more accurate estimate of battery temperature distribution under various discharge rates compared with lumped or empirical models. In this work, a simplified electrochemical model is solved in 1D to make the coupled model streamlined enough to be embedded into BTMS. The Ohmic heat generation and heat conduction in the cells are evaluated in 3D to investigate the non-uniform temperature distribution during the battery operation. The validity of electrical and thermal aspects of the modeling procedure is demonstrated experimentally for a 4Ah NCA prismatic cell. The predicted battery surface temperature distribution and voltage profile are in agreement with infrared imaging and the measured voltage variation. The proposed model reduces the required time for battery modeling which enables the designers to simultaneously simulate the active or passive BTMS in an affordable computational time. The effects of design parameters such as electrode format, active material thickness and tab location on the battery thermal behavior can be evaluated under various cooling scenarios.

Physics-based parametrization of the surface impedance for radio frequency sheaths

The properties of sheaths near conducting surfaces are studied for the case where both magnetized plasma and intense radio frequency (rf) waves coexist. The work is motivated primarily by the need to understand, predict, and control ion cyclotron range of frequency (ICRF) interactions with tokamak scrape-off layer plasmas and is expected to be useful in modeling rf sheath interactions in global ICRF codes. Employing a previously developed model for oblique angle magnetized rf sheaths [J. R. Myra and D. A. D'Ippolito, Phys. Plasmas 22, 062507 (2015)], an investigation of the four-dimensional parameter space governing these sheath is carried out. By combining numerical and analytical results, a parametrization of the surface impedance and voltage rectification for rf sheaths in the entire four-dimensional space is obtained.

Calculation of Grounding Grids Parameter at Arbitrary Geometry

This paper deals with the computation of ground resistance, surface voltage, touch voltage and step voltage, to mesh with horizontal wires arranged in different angles. The computer program implemented used in the mathematical modeling is based on the method proposed by Heppe, which allows obtaining the grounding parameters for homogeneous soil and soil stratified in two layers. The results obtained with the proposed method will be compared with other methods in literature. Also will be presented the results of a grounding grid using wires at various angles.

Preparation of thermally and chemically robust superhydrophobic coating from liquid phase deposition and low voltage reversible electrowetting

Superhydrophobic surfaces and electrowetting have found applications in many fields. Two of the most desired features in these applications are a robust surface and low voltage actuation electrowetting. A thermally and chemically robust nano-scale superhydrophobic surface was prepared using facile techniques of sol-gel and hot water treatment to obtain rough pseudoboehmite alumina structures; and layer-by-layer coating, using Nafion®, to achieve the hydrophobization. It exhibited a contact angle of 167.2±0.8°; thermal stability of up to 300°C; stability to acid, base, organic solvents and UV irradiation. Subsequently replacing Nafion® with 1H, 1H, 2H, 2H-perfluorodecyltrimethoxysilane and a conductive Au under layer coating, an extremely low voltage, 3V, electrowetting and reversible electrowetting were achieved in air and dodecane media, respectively.

Ferroelectric HfO2 thin film testing and whole wafer mapping with non‐contact corona‐Kelvin metrology

We present results of a non‐contact, real‐time feedback corona‐Kelvin characterization of the ferroelectric properties of Si:HfO2 thin films. Measurements were performed on free dielectric surfaces. The method uses corona charging pulses coupled with Kelvin probe‐measured surface voltage and gives non‐contact QV and CV characteristics. Analogous to voltage biasing of metal‐insulator‐metal (MIM) capacitors, large corona charge biasing is found to provide an effective means for poling of the ferroelectric films. Subsequent small increment corona charging is used to acquire hysteresis loops and determine the coercive field and permittivity characteristics. Negative and positive coercive fields of about ±1.2 MV/cm for the 3.5 mol% Si film and ±1.0 MV/cm for the 4.6 mol% Si film were determined from the hysteresis loops. These findings were in agreement with MIM capacitor measurements on sister wafers. Non‐ferroelectric behavior was also confirmed for the 11.3 mol% Si film. Another strength of the corona‐Kelvin method is the ability to perform full wafer mapping to assess spatial non‐uniformities of important dielectric properties. Results of this work indicate a radial symmetry of ferroelectric film properties, such as the permittivity at the coercive field, that are consistent with processing conditions during the crystallization anneal.

Mitigating the Surface Degradation and Voltage Decay of Li1.2Ni0.13Mn0.54Co0.13O2 Cathode Material through Surface Modification Using Li2ZrO3.

In the quest to tackle the issue of surface degradation and voltage decay associated with Li-rich phases, Li-ion conductive Li2ZrO3 (LZO) is coated on Li1.2Ni0.13Mn0.54Co0.13O2 (LNMC) by a simple wet chemical process. The LZO phase coated on LNMC, with a thickness of about 10 nm, provides a structural integrity and facilitates the ion pathways throughout the charge–discharge process, which results in significant improvement of the electrochemical performances. The surface-modified cathode material exhibits a reversible capacity of 225 mA h g–1 (at C/5 rate) and retains 85% of the initial capacity after 100 cycles. Whereas, the uncoated pristine sample shows a capacity of 234 mA h g–1 and retains only 57% of the initial capacity under identical conditions. Electrochemical impedance spectroscopy reveals that the LZO coating plays a vital role in stabilizing the interface between the electrode and electrolyte during cycling; thus, it alleviates material degradation and voltage fading and ameliorates the electrochemical performance.

Micro-structures and growth mechanisms of plasma electrolytic oxidation coatings on aluminium at different current densities

In this study, plasma electrolytic oxidation (PEO) coatings were produced on pure aluminum in an in-house developed composite electrolyte at three current densities of 2.2A/dm2, 4.4A/dm2 and 8.8A/dm2, respectively. The coatings were investigated based on the observation and measurement of the working voltage, surface microdischarges and morphologies of surface, polished cross-section, fracture cross-section and inner surface of the coatings, by using scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS), data acquisition module, single-lens reflex camera. Especially, an in-house developed electrochemical detachment technique of the coatings was employed to observe some details of the internal micro-structure and coating/substrate interface morphology of the coatings. It was noted that the results from the above investigations are much related to the current densities going through the PEO coatings and the different growth mechanisms of coatings at low and high current densities were proposed and discussed.

Laser-induced persistent photovoltage on the surface of a ternary topological insulator at room temperature

Using time- and angle-resolved photoemission, we investigate the ultrafast response of excited electrons in the ternary topological insulator (Bi1-xSbx)2Te3 to fs-infrared pulses. We demonstrate that at the critical concentration x = 0.55, where the system becomes bulk insulating, a surface voltage can be driven at room temperature through the topological surface state solely by optical means. We further show that such a photovoltage persists over a time scale that exceeds ∼6 μs, i.e, much longer than the characteristic relaxation times of bulk states. We attribute the origin of the photovoltage to a laser-induced band-bending effect which emerges near the surface region on ultrafast time scales. The photovoltage is also accompanied by a remarkable increase in the relaxation times of excited states as compared to undoped topological insulators. Our findings are relevant in the context of applications of topological surface states in future optical devices.

Excitation of surface plasmon polaritons by electron beam with graphene ribbon arrays

Graphene has emerged as an alternative material to support surface plasmon polaritons (SPPs) with its excellent properties such as the tight electromagnetic field localization, low dissipative loss, and versatile tunability. Thus, graphene surface plasmon polaritons (GSPs) provide an exciting platform to develop a series of novel devices and systems from the optical band to the terahertz (THz) band. In this paper, theoretical and simulated studies about the excitation of SPPs by an injected electron beam with periodic graphene ribbon arrays deposited on a dielectric medium are presented. The analytical dispersion expression of the GSP mode on the graphene ribbon arrays is obtained by using a modal expansion method along with periodic boundary conditions in the structure. With this result, the dispersion relation, propagation loss, and field pattern of the propagating GSPs for both periodic graphene microribbon arrays and the complete graphene sheet are investigated and analyzed in the THz band. It is shown that the electromagnetic field with a better concentration on the interface can be realized with graphene ribbon arrays compared with the graphene sheet for a given frequency. Besides, the excitation of GSPs by an injected electron beam with graphene ribbon arrays is modeled and implemented by the particle-in-cell simulation based on the finite difference time domain algorithm. GSPs can be excited effectively when the dispersion line of the electron beam and SPPs on the graphene ribbon arrays is matched with each other well. Besides, the dependences of output power on electron beam parameters such as the distance of the electron beam above the graphene ribbon surface and beam voltage are studied and analyzed. Finally, the tunability of graphene conductivity via biased voltage with a ground metal is considered and the tunable excitation of GSPs on the structure with biased drive voltage by the injected electron beam is also realized. The present work can find a lot of potential applications such as low loss plasmonic waveguides, graphene metamaterials, and tunable THz electronic sources.

Inductive Loop in the Impedance Response of Perovskite Solar Cells Explained by Surface Polarization Model.

The analysis of perovskite solar cells by impedance spectroscopy has provided a rich variety of behaviors that demand adequate interpretation. Two main features have been reported: First, different impedance spectral arcs vary in combination; second, inductive loops and negative capacitance characteristics appear as an intrinsic property of the current configuration of perovskite solar cells. Here we adopt a previously developed surface polarization model based on the assumption of large electric and ionic charge accumulation at the external contact interface. Just from the equations of the model, the impedance spectroscopy response is calculated and explains the mentioned general features. The inductance element in the equivalent circuit is the result of the delay of the surface voltage and depends on the kinetic relaxation time. The model is therefore able to quantitatively describe exotic features of the perovskite solar cell and provides insight into the operation mechanisms of the device.

Uneven temperature and voltage distributions due to rapid discharge rates and different boundary conditions for series-connected LiFePO4 batteries

This paper presents the surface temperature and voltage distributions on a prismatic lithium-ion battery pack at 1C, 2C, 3C, and 4C discharge rates and 5°C, 15°C, 25°C, and 35°C boundary conditions (BCs) for water cooling and ~22°C for air cooling methods. It provides quantitative data regarding thermal behaviour of lithium-ion batteries for designing thermal management systems and developing reliable thermal models. In this regard, three large LiFePO4 20Ah capacity, prismatic batteries are connected in series with four cold plates used between cells and eighteen thermocouples are placed at distributed locations on the principle surface of all three cells: the first six for the first cell, the second six for the second cell, and the third six for the third cell, and the average and peak surface temperatures as well as voltage distributions are measured and presented in this study. In addition, the simulated heat generation rate, temperature and voltage distributions are validated with an experimental data for the above mentioned C-rates and BCs. The present study shows that increasing discharge rates and BCs results in increase in the maximum and average surface temperatures at the three locations (near the anode, cathode, and mid surface of the body). The highest value of the average surface temperature is obtained for 4C and 35°C BC (36.36°C) and the lowest value is obtained for 1C and 5°C BC (7.22°C) for water cooling method.