Surface Voltage Research Articles

Asymmetric electrostatic properties of an electric double layer: a generalized Poisson-Boltzmann approach taking into account non-uniform size effects and water polarization

We theoretically study electrostatic properties of electric double layer using a generalized Poisson-Boltzmann approach taking into account the orientational ordering of water dipoles and the excluded volume effect of water molecules as well as those of positive and negative ions with different sizes in electrolyte solution.Our approach enables one to predict that the number densities of water molecules, counterions and coions and the permittivity of electrolyte solution close to a charged surface, asymmetrically vary depending on both of sign and magnitude of the surface charge density and the volume of counterion. We treat several phenomena in more detail. Firstly, an increase in the volume of counterions and an increase in the surface charge density can cause the position of the minimum number density of water molecules to be farther from the charged surface. Secondly, width of the range of voltage in which the properties at the charged surface symmetrically vary decreases with increasing bulk salt concentration. In addition, we show that the excluded volume effect of water molecules and the orientational ordering of water dipoles can lead to early onset and lowering of the maximum of electric capacitance according to surface voltage. Our approach and results can be applied to describing electrostatic properties of biological membranes and electric double layer capacitor for which excluded volume effects of water molecules and ions with different sizes may be important.

Charge contribution to patch-charged microparticle adhesion

Microparticle adhesion influenced by electrostatic charge has been a significant research interest for over past three decades or so in a wide spectrum of areas of interest from manufacturing (electrophotography, powder technology, metallurgy, and semi-conductor manufacturing) to natural phenomena (desert sandstorms and northern lights (auroras)). However, over the years, as a result of the strong discrepancies between the experimental adhesion measurements data and theoretical predictions, some key issues regarding the contributors of adhesion forces in charged microparticles and the nature of surface charge distribution still remain unresolved. In the current work, a non-contact ultrasonic approach is presented and employed for understanding the nature of charge distribution on a single microparticle and determining the effect of electrostatic charge on its adhesion in a non-invasive manner. From the vibrational spectra of the charged particle response to the ultrasonic substrate oscillations under various electrostatic loading conditions, three distinct shifting patterns of vibrational (rocking) resonance frequencies are observed for each level of applied substrate surface voltage, implying an un-symmetric force field on the particle, thus depicting non-uniform non-symmetric surface charge distribution on its surface. Also, a simple mathematical model was presented and employed for predicting the equivalent bulk charge on a single microparticle (toner) from resonance frequency shifts. In summary, it is found that the charge levels reported here are consistent with the previously published data, and it is demonstrated that, in a non-invasive manner, non-uniform charge distribution on a single microparticle can be observed and its total charge can be predicted.

The use of current source density as electrophysiological correlates in neuropsychiatric disorders: A review of human studies

The use of current source density (CSD), the Laplacian of the scalp surface voltage, to map the electrical activity of the brain is a powerful method in studies of cognitive and affective phenomena. During the last few decades, mapping of CSD has been successfully applied to characterize several neuropsychiatric conditions such as alcoholism, schizophrenia, depression, anxiety disorders, childhood/developmental disorders, and neurological conditions (i.e., epilepsy and brain lesions) using electrophysiological data from resting state and during cognitive performance. The use of CSD and Laplacian measures has proven effective in elucidating topographic and activation differences between groups: i) patients with a specific diagnosis vs. healthy controls, ii) subjects at high risk for a specific diagnosis vs. low risk or normal controls, and iii) patients with specific symptom(s) vs. patients without these symptom(s). The present review outlines and summarizes the studies that have employed CSD measures in investigating several neuropsychiatric conditions. The advantages and potential of CSD-based methods in clinical and research applications along with some of the limitations inherent in the CSD-based methods are discussed in the review, as well as future directions to expand the implementation of CSD to other potential clinical applications. As CSD methods have proved to be more advantageous than using scalp potential data to understand topographic and source activations, its clinical applications offer promising potential, not only for a better understanding of a range of psychiatric conditions, but also for a variety of focal neurological disorders, including epilepsy and other conditions involving brain lesions and surgical interventions.

Fault Diagnosis of Tuning Area Based on Wavelet Neural Network

With the rapid development of china railway, ZPW-2000A track circuit has been widely used. Tuning area, which is an important part of the ZPW-2000A track circuit, is not only the relationship between the signal transmission quality, and determine the effect of electrical insulation between adjacent sections. Therefore, the study of fault diagnosis aspects for tuning area is urgent and significant. In this paper, using the theory of transmission line a model of track circuit is built, the comparison of the actual data and experimental data of the track surface voltage envelope curve shows the correctness of this model. Owning to the good time-frequency characteristics of wavelet and the nonlinear mapping features of neural network, a fault diagnosis of ZPW-2000A tuning area based on the wavelet neural network(WNN) is proposed. Combined with the practical failure situation of railway site, the fault diagnosis method in this paper can accurately identify failure modes of tuning area.

3Development of a novel mapping system to visualise activation in ventricular scar

Introduction: Ventricular scar is characterised by fractionated electrograms (egm) and not well displayed by current 3D mapping systems. We hypothesised that displaying intracardiac egms on 3D geometry as dynamic bars changing height according to the voltage-time relationship relative to a fiduciary egm, would enable visualisation slow conduction channels (SCC) in the infarct scar. Methods: The Ripple Mapping(RM) program was developed using CartoXP(CXP) data on Matlab & validated in atrial tachycardias(AT). Maps were exported and selected egms assessed for ripple bar(RB) height concordance with varying egm voltage & activation sequence. RM guided diagnosis of AT mechanism was compared with entrainment manoeuvres and annotated CXP maps. RM and CXP maps were presented in random order to experienced CARTO users to compare the techniques. Analysis of ischaemic left ventricular(LV) scar was performed on CARTO3 datasets. Sinus rhythm LV maps created during VT ablation were analysed for evidence of RM conduction channels(RMCC) with sequential RB movement whilst concurrently adjusting surface voltage to delineate the border of the channels. Conduction velocity(CV) within RMCCs was compared with healthy myocardium. Co-localisation of RMCC with entrainment sites and ablation lesions was used to assess functional relevance. Results: 10 CXP AT maps were examined and RM activation sequences concurred with entrainment based diagnosis and LAT maps in all cases with confirmation by successful ablation in 9. Blinded assessors (n=11) made the correct diagnosis in 35/44 (80%) using RM vs 22/44 (50%) using CXP (p=0.029). RM was improved to display RBs on a surface bipolar voltage map. 16 AT studies were reviewed (7Carto3; 9MEM). Map density varied (MEM=1136±783 vs Carto3=318±74pts, p<0.02) with MEM maps created more rapidly (3vs17min/100pts(p<0.01)). Considerable annotation was required for a diagnosis (total mapping to ablation MEM=49±32 vs Carto3=64±33min, p=0.4). Analysis of the unannotated maps on RM yielded the correct diagnosis confirmed by entrainment and termination by ablation. Having proved that RM was an accurate mapping system, we were able to assess LV scar during sinus rhythm for evidence of activation channels. In 21 LV maps, 77 RMCCs were seen; 33=0.5–1.5mV, 15=0.30–0.5mV & 29 ≤0.3mV. Mean RMCC CV was 64±31 vs 260±230cm/s in healthy myocardium(p<0.001). 7 sites met conventional criteria for diastolic pathways. All coincided with a RMCC. All 7 patients with ablation lesions co-locating to all RMCCs remained free of VT (F/U=662±317d). 5/14 patients who had at least 1 RMCC with no ablation had recurrence (F/U=479±315d). RMCCs were sensitive(100%) for VT recurrence with specificity(43%) limited by likely ‘blind alley' channels. Conclusion: RM identifies SCCs within LV scar. The main limitation has been the off-line system. RM can now be used in live cases on CARTO3v4 enabling prospective randomised validation of RMCCs to guide substrate based VT ablation. ![Graphic][1] [1]: /embed/inline-graphic-1.gif

Room-Temperature Luminescence from Ion Beam or Atmospheric Pressure Plasma-Treated SrTiO3

<TEX>$SrTiO_3$</TEX> (STO) single crystal irradiated with a 3-MeV proton beam exhibits blue and green mixed luminescence. However, the same proton beam when used to irradiate STO with a very thin layer of deposited Pt does not show any luminescence. This Pt layer prevents any damage which may otherwise be caused by arcing, which stems from the accumulated surface voltage of tens of kV due to the charge induced by secondary electrons on the surface of the insulator during the ion beam irradiation process. Hence, the luminescence of ion-irradiated STO originates from the modification of the STO surface layer caused by arcing rather than from any direct ion beam irradiation effect. STO treated with atmospheric-pressure plasma, a simple and cost-effective method, also exhibits the same type of blue and green mixed luminescence as STO treated with an ion beam, as the plasma also creates a layer of surface damage due to arcing.

XPS for probing the dynamics of surface voltage and photovoltage in GaN

We describe application of two different data gathering techniques of XPS for probing the dynamics of surface voltage and surface photovoltage (SPV) developed in microseconds to seconds time-domain, in addition to the conventional steady-state measurements. For the longer (seconds to milliseconds) regime, capturing the data in the snapshot fashion is used, but for the faster one (down to microseconds), square wave (SQW) electrical pulses at different frequencies are utilized to induce and probe the dynamics of various processes causing the surface voltage, including the SPV, via the changes in the peak positions. The frequency range covers anywhere from 10−3 to 105Hz for probing changes due to charging (slow), dipolar (intermediate), and electronic (fast) processes associated with the external stresses imposed. We demonstrate its power by application to n- and p-GaN, and discuss the chemical/physical information derived thereof. In addition, the method allows us to decompose and identify the peaks with respect to their charging nature for a composite sample containing both n- and p-GaN moieties.

A high accuracy broadband measurement system for time resolved complex bioimpedance measurements

Bioimpedance measurements are useful tools in biomedical engineering and life science. Bioimpedance is the electrical impedance of living tissue and can be used in the analysis of various physiological parameters. Bioimpedance is commonly measured by injecting a small well known alternating current via surface electrodes into an object under test and measuring the resultant surface voltages. It is non-invasive, painless and has no known hazards. This work presents a field programmable gate array based high accuracy broadband bioimpedance measurement system for time resolved bioimpedance measurements. The system is able to measure magnitude and phase of complex impedances under test in a frequency range of about 10–500 kHz with excitation currents from 10 µA to 5 mA. The overall measurement uncertainties stay below 1% for the impedance magnitude and below 0.5° for the phase in most measurement ranges. Furthermore, the described system has a sample rate of up to 3840 impedance spectra per second. The performance of the bioimpedance measurement system is demonstrated with a resistor based system calibration and with measurements on biological samples.

Noninvasive transmural electrophysiological imaging based on minimization of total-variation functional.

While tomographic imaging of cardiac structure and kinetics has improved substantially, electrophysiological mapping of the heart is still restricted to the surface with little or no depth information beneath. The progress in reconstructing 3-D action potential from surface voltage data has been hindered by the intrinsic ill-posedness of the problem and the lack of a unique solution in the absence of prior assumptions. In this work, we propose a novel adaption of the total-variation (TV) prior to exploit the unique spatial property of transmural action potential of being piecewise smooth with a steep boundary (gradient) separating depolarized and repolarized regions. We present a variational TV-prior instead of a common discrete TV-prior for improved robustness to mesh resolution, and solve the TV-minimization by a sequence of weighted, first-order L2-norm minimization. In a large set of phantom experiments, the proposed method is shown to outperform existing quadratic methods in preserving the steep gradient of action potential along the border of infarcts, as well as in capturing the disruption to the normal path of electrical wavefronts. Real-data experiments also further demonstrate the potential of the proposed method in revealing the location and shape of infarcts when quadratic methods fail to do so.

Measuring CET of High-k Dielectrics with Novel Kinetic Approach Using Micro-Site Corona – Kelvin Method

Freshly deposited surfaces of high-k dielectrics revealed a new set of challenges for monitoring capacitance equivalent thickness, CET, using micro-site corona – Kelvin metrology. Specifically, ions deposited by corona discharge may have a queue-time dependent high surface diffusivity, which causes charge spreading away from charging spot under the Kelvin voltage probe. This could result in underestimation of dielectric thickness and unrepeatable results. To overcome this problem, we have developed a kinetic approach based on the analysis of the surface voltage transient after point source corona charging. The mathematical solution of the two-dimensional diffusion equation enables fitting of the voltage transient and reliable determination of two parameters: the surface diffusion coefficient and the dielectric capacitance. The latter one gives CET. The kinetic approach was applied to HfO2 layers deposited by atomic layer deposition. Repeatable CET measurements for a range of high-k surface conditions and thicknesses are presented. Elimination of queue-time dependence achieved with the novel kinetic approach is a significant advantage for fab-line monitoring.

Through Thick and Thin: Tuning the Threshold Voltage in Organic Field-Effect Transistors

Organic semiconductors (OSCs) constitute a class of organic materials containing densely packed, overlapping conjugated molecular moieties that enable charge carrier transport. Their unique optical, electrical, and magnetic properties have been investigated for use in next-generation electronic devices, from roll-up displays and radiofrequency identification (RFID) to biological sensors. The organic field-effect transistor (OFET) is the key active element for many of these applications, but the high values, poor definition, and long-term instability of the threshold voltage (V(T)) in OFETs remain barriers to realization of their full potential because the power and control circuitry necessary to compensate for overvoltages and drifting set points decrease OFET practicality. The drifting phenomenon has been widely observed and generally termed "bias stress." Research on the mechanisms responsible for this poor V(T) control has revealed a strong dependence on the physical order and chemical makeup of the interfaces between OSCs and adjacent materials in the OFET architecture. In this Account, we review the state of the art for tuning OFET performance via chemical designs and physical processes that manipulate V(T). This parameter gets to the heart of OFET operation, as it determines the voltage regimes where OFETs are either ON or OFF, the basis for the logical function of the devices. One obvious way to decrease the magnitude and variability of V(T) is to work with thinner and higher permittivity gate dielectrics. From the perspective of interfacial engineering, we evaluate various methods that we and others have developed, from electrostatic poling of gate dielectrics to molecular design of substituted alkyl chains. Corona charging of dielectric surfaces, a method for charging the surface of an insulating material using a constant high-voltage field, is a brute force means of shifting the effective gate voltage applied to a gate dielectric. A gentler and more direct method is to apply surface voltage to dielectric interfaces by direct contact or postprocess biasing; these methods could also be adapted for high throughput printing sequences. Dielectric hydrophobicity is an important chemical property determining the stability of the surface charges. Functional organic monolayers applied to dielectrics, using the surface attachment chemistry made available from "self-assembled" monolayer chemistry, provide local electric fields without any biasing process at all. To the extent that the monolayer molecules can be printed, these are also suitable for high throughput processes. Finally, we briefly consider V(T) control in the context of device integration and reliability, such as the role of contact resistance in affecting this parameter.

Measuring CET of High-k Dielectrics with Novel Kinetic Approach Using Micro-Site Corona – Kelvin Method

Freshly deposited surfaces of high-k dielectrics revealed a new set of challenges for monitoring capacitance equivalent thickness, CET, using micro-site corona – Kelvin metrology. Specifically, ions deposited by corona discharge may have a queue-time dependent high surface diffusivity, which causes charge spreading away from charging spot under the Kelvin voltage probe. This could result in underestimation of dielectric thickness and unrepeatable results. To overcome this problem, we have developed a kinetic approach based on the analysis of the surface voltage transient after point source corona charging. The mathematical solution of the two-dimensional diffusion equation enables fitting of the voltage transient and reliable determination of two parameters: the surface diffusion coefficient and the dielectric capacitance. The latter one gives CET. The kinetic approach was applied to HfO2 layers deposited by atomic layer deposition. Repeatable CET measurements for a range of high-k surface conditions and thicknesses are presented. Elimination of queue-time dependence achieved with the novel kinetic approach is a significant advantage for fab-line monitoring.

Plasma Damage Improvement during Cu Capping Layer Deposition for Advanced Nodes

Cu capping layer deposition plays an important role in BEOL plasma induced damage. In this paper, PID issue by Cu capping layer deposition process studied. The PID performance was studied with Cu capping layer deposition recipe optimization. And, the impact on PID performance of different Cu capping layer equipment was also compared. The PID performance is different with antenna ratio increase, both NMOS and PMOS PID performance with different antenna ratio have been investigated. In order to get clear supporting evidence for plasma damage, plasma charged voltage of wafer surface is also studied by Quantax in this paper. Finally we developed an optimized Cu capping layer deposition process with acceptable PID performance and without any reliability degradation.

New Approach to Surface Voltage Based Non-Visual Defect Inspection

Measurement speed and resolution of surface voltage based non-visual defect inspection are examined. There is a tradeoff between high measurement speed in whole wafer inspection which requires a larger measurement probe and resolution of the method which requires a smaller measurement probe. In this paper we overcome this tradeoff by using different diameter Kelvin probes. Full wafer inspection is performed using a 2mm diameter Kelvin probe enabling high throughput. Only when a suspected failure is detected, an inspection of a localized smaller area is performed with a 10 μm diameter Kelvin probe.

Visualizing and Quantifying Charge Distributions Correlated to Threshold Voltage Shifts in Lateral Organic Transistors

Lateral organic field-effect transistors (OFETs), consisting of a polystyrene (PS) polymer gate material and a pentacene organic semiconductor (OSC), were electrically polarized from bias stress during operation or in a separate charging step, and investigated with scanning Kelvin probe microscopy (SKPM) and current-voltage determinations. The charge storage inside the polymer was indicated, without any alteration of the OFET, as a surface voltage with SKPM, and correlated to a threshold voltage (VT) shift in the transistor operation. The SKPM method allows the gate material/OSC interface of the OFET to be visualized and the surface voltage variation between the two gate material interfaces to be mapped. The charge distribution for three samples was derived from the surface voltage maps using Poisson's equation. Charge densities calculated this way agreed with those derived from the VT shifts and the lateral gate-OSC capacitance. We also compared the behavior of two other polymers with PS: PS accepted the most static charge in its entire volume, poly(2-trifluoromethylstyrene) (F-PS) had the most stability to bias stress, and poly(methyl methacrylate) (PMMA) showed the most leakage current and least consistent response to static charging of the three polymers. This work provides a clear demonstration that surface voltage on a working OFET gate material can be related to the quantity of static charge responsible for bias stress and nonvolatility in OFETs.

Generation and detection of electromagnetic field with charged material oscillation

Abstract We generated an electromagnetic field using the spatial oscillation of a charged material such as a polyimide film. The film was vibrated with acoustic waves at 1 Hz–1 kHz. For charged films, changes in electric field intensity with acoustic wave irradiation were detected using an antenna. The electric field intensity and phase were found to be related to the surface voltage and electrical polarity. The surface potential distribution matches the electric field distribution that was measured by scanning the local excitation. These results indicate that this phenomenon can be used to measure the electrical properties of charged materials.

Pioneering Application of Corona Charge-Kelvin Probe Metrology to Noncontact Characterization of In0.53 Ga0.47 As/Al2O3/HfO2 Stack

ABSTRACTWe report the first successful application of corona charging noncontact C-V and I-V metrology to interface and dielectric characterization of high-k/III-V structures. The metrology, which has been commonly used in Si IC manufacturing, uses incremental corona charge dosing, ΔQC, on the dielectric surface, and the measurement of surface voltage response, ΔVS, using a Kelvin-probe. Its application to In0.53Ga0.47As with a high-k stack required modifications related to the effects of dielectric trap induced voltage transients. The developed Corona Charge-Kelvin Probe Metrology adopted strictly differential measurements using ΔQC and ΔV, and corresponding differential capacitance rather than measurements based on total global charge, Q, and voltage, V, values.Electrical characterization data including interface trap density, electrical oxide thickness, and dielectric leakage are presented for a sample containing an In0.53 Ga0.47 As channel overlaid with a bilayer (2nm Al2O3/5nm HfO2) dielectric stack that is considered to be very promising for application in performance NFETs with high-mobility channels.

Ultrahigh Vacuum Cryostat System for Extended Low-Temperature Space Environment Testing

The range of temperature measurements have been significantly extended for an existing space environment simulation test chamber used in the study of electron emission, sample charging and discharge, electrostatic discharge and arcing, electron transport, and luminescence of spacecraft materials. This was accomplished by incorporating a new two-stage, closed-cycle helium cryostat which has an extended sample temperature range from to , with long-term controlled stability of . The system was designed to maintain compatibility with an existing ultrahigh vacuum chamber (base pressure ) that can simulate diverse space environments. These existing capabilities include controllable vacuum and ambient neutral gases conditions , electron fluxes (5-30-keV monoenergetic, focused, and pulsed sources over 10-4-1010 nA-cm-2), ion fluxes ( monoenergetic sources for inert and reactive gases with pulsing capabilities), and photon irradiation (numerous continuous and pulsed monochromated and broad band IR/VIS/UV [0.5-7 eV] sources). The new sample mount accommodates one to four samples of 1-2.5-cm diameter in a low-temperature carousel, which allows rapid sample exchange and controlled exposure of the individual samples. Custom hemispherical grid retarding field analyzer and Faraday cup detectors, custom high speed, high-sensitivity electronics, and charge neutralization capabilities used with , , and electrons/pulse pulsed-beam sources permit high-accuracy electron emission measurements of extreme insulators with minimal charging effects. In situ monitoring of surface voltage, arcing, and luminescence (250-5000 nm) have recently been added.

Effect of Surface Discontinuities and Electrical Network Architecture on the Flashover

Flashover corresponds to the differential charging neutralization of dielectric parts on satellite surfaces when an electrostatic discharge (ESD) is triggered. In solar panels, it is supposed to have effects on solar cells aging and secondary arc occurrence. Laboratory experiments show that flashover propagation sometimes involves the whole charged surface, but is generally partial in terms of charge amount and covered surface. An assumption is made that these charged dielectric surfaces are never plain due to many discontinuities as for solar panels, intercell gaps, inserts, and so on. To establish which parameters monitor or stop flashover propagation, we study neutralization ratio of the flashover on 1- m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> charged surfaces. We test and modified Kapton surfaces with different types of discontinuities added on the surface as dielectric sheathed and unsheathed wires. We also test a 1- m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> solar panel coupon and compare results with Kapton surface. Based on this coupon, different electrical network architectures for solar cell strings are tested (parallel, series, and interlaced circuit) to verify if they have an effect on flashover characteristics and to determine the way the replacement current circulates in the solar cell strings. These tests are performed in the JONAS facility, which is a 9- m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> vacuum chamber equipped with two electron guns and several measurement devices as surface potential probe and transient current probes. The sample under test is biased at a negative high voltage and charged with electrons to be in an inverted potential gradient situation to trigger ESDs. In Kapton film tests, ESDs are triggered on a six solar cells coupon set in the center of the Kapton surface. Results show 2-D surface voltage before and after flashover correlated to neutralized charges and solar cell strings replacement current. Effect or noneffect of surface topology on neutralization ratio and flashover propagation is shown for the Kapton film and the solar panel coupon.

Voltage calculations for annular tanks partly-filled with charged liquid

A Bessel function expression is developed for the voltages produced when annular tanks (vertical axis cylindrical tanks with central conductors) are filled with liquids of uniform charge density. The expression is used to calculate the maximum surface voltage and this is compared with the maximum voltage predicted for tanks without a central conductor. Previous estimates of the percentage voltage reduction produced by a central conductor during tank filling have indicated a reduction of about 42% for practical tank dimensions. The new results, which are obtained with a more realistic model geometry, suggest a reduction of only about 29%.