Decrease In Capacitance Research Articles

Improvement of sintering, nonlinear electrical, and dielectric properties of ZnO-based varistors doped with TiO2

The effects of TiO2 on sintering and nonlinear electrical properties of (98.5 − x)ZnO–0.5MnO2–0.5Co,2O3−0.5Bi2O3–xTiO2 (x = 0.3, 0.5, 0.7, 0.9 mol%) ceramic varistors prepared by the ceramic technique are investigated in this work. The optimum sintering temperature of the prepared samples is deduced by determining the firing shrinkage and water absorption percentages. The optimum sintering temperature is found to be 1200 °C, at which each of the samples shows a maximum firing shrinkage and minimum water absorption. Also minimum water absorption appears in a sample of x = 0.9 mol%. Higher sintering temperature and longer sintering time give rise to a reduction in bulk density due to the increased amount of porosity between the large grains of ZnO resulting from the rapid grain growth induced by the liquid phase sintering. The crystal size of ZnO decreases with increasing TiO2 doping. The addition of TiO2 improves the nonlinear coefficient and attains its maximum value at x = 0.7 mol% of TiO2, further addition negatively affects it. A decrease in capacitance consequently in the dielectric constant is recorded with increasing the frequency in a range of 30 kHz–200 kHz. The temperature and composition dependences of the dielectric constant and AC conductivity are also studied. The increase of temperature raises the dielectric constant because it increases ionic response to the field at any particular frequency.

Measuring depletion-layer capacitance to analyze a decrease in breakdown voltage of 4H-SiC diodes

A decrease in breakdown voltage (VBD) in the termination area of 4H-SiC PN diodes after 64 h reverse-bias stressing was analyzed. To analyze the VBD decrease, a novel analysis method based on the results of measuring depletion-layer capacitance of the PN diodes was proposed. The measurement results indicate that the positive-charge density (QTM) at the SiO2/SiC interface of the termination area increased after the reverse-bias stressing. Besides, in the case of QTM of 1012 cm−2 at the SiO2/SiC interface, the decrease in the measured capacitance showed the same tendency as the decrease in the simulated capacitance. By comparing the measured full depletion voltage and simulated full depletion voltage, the amount of QTM was estimated. It is thus concluded that the proposed method for measuring the depletion-layer capacitance is effective for analyzing the QTM change in the termination area.

Manufacturing of Electric Double‐Layer Capacitors Using Carbon Nanocoils and Evaluation of their Specific Capacitances at a High Scan Rate

SUMMARYElectric double‐layer capacitors (EDLCs) have problems that the specific capacitance decreases by increasing the scan rate. In this study, activated carbon (AC) and various carbon nanomaterials are compared by their specific capacitances. Carbon nanomaterials used in this study were arc‐black (AcB) which was prepared by an arc discharge and carbon nanocoil (CNC) which was prepared by a chemical vapor deposition. CNC and AcB showed the lower charge transfer resistance than AC in the measurement of electrochemical impedance spectroscopy (EIS). This is a reason that the EDLCs using CNC and AcB kept their specific capacitance almost the same even at a high scan rate.

Transparent and Flexible Energy Storage Using Pseudocapacitive Ni(OH)2 coated Cu Nanowires By Solution-Processes

Realization of cost-effective energy storage that is both safe and scalable relies on the ease with which it can be integrated into existing manufacturing technology. Roll-to-roll and solution-based processes are two such technologies that offer the ability to deposit flexible films of controlled thickness for a low cost device. Our work uses one such approach to build a transparent and flexible pseudocapacitive electrode using earth-abundant and low cost materials. The electrode is comprised of a core/shell Cu/Ni(OH)2 structure of nanowires (NWs) on a glass slide. In order to understand the effects of both NW network density and the thickness of the Ni(OH)2 shell, we utilize Meyer rod and electroless plating techniques to control the network density and shell thickness, respectively. Our study uses NW networks with resistance of <50 Ω/sq. and >60% transmittance to investigate the performance of Ni(OH)2shells with 20, 30, and 40 mol% Ni, with respect to the conductive Cu core. Controlling the Cu NW density and Ni(OH)2 shell thickness yields capacitances of 800 F/g and 2550 μF/cm2 at 0.02 mA/cm2 charge-discharge current density with >70% transmittance. The 30 mol% Ni on Cu NW structure exhibits higher gravimetric capacitances than the 20 and 40 mol% Ni structures. We propose that these differences are due to diffusion limitations limiting the amount of electrochemically active material and to the density of active NWs, which impacts the sheet resistance of the underlying conductive NW network. In addition, the quasi-1D Ni(OH)2 structure of our NW devices enabled highly reversible pseudocapacitive intercalation and remarkably stable performance under fast charge-discharge rates, exhibiting coulombic efficiencies of >90% with only a 13% decrease in capacitance after 10,000 cycles for the thicker 40 mol% Ni(OH)2 shell. Our continuing and future work in exploring the Cu/Ni(OH)2 NW material is to further stabilize and improve both areal and gravimetric capacitance while we investigate the use of a flexible polypropylene (PPE) substrate. Preliminary results show that the electrode can be bent at a 90° angle and retain capacitive behavior beyond 12 hrs in solution. Additionally, we seek to match our electrode’s characteristics with a suitable counter electrode and solid-state electrolyte to construct a fully flexible, hybrid supercapacitor device. Figure 1

Effect of Al2O3 Addition in Partially-Stabilized Zirconia Based NOx Sensors

Porous yttria-stabilized zirconia (YSZ) electrolyte based NOx sensors are capable of providing improved sensing capabilities for NO and NO2 gases at concentrations as low as 5 ppm. However, the brittle, porous structure of the electrolyte significantly limits sensor durability. Adding alumina (Al2O3) to YSZ can enhance the mechanical strength and thermal shock resistance of the NOx sensor electrolyte. It is also anticipated that Al2O3 addition to YSZ will improve sensor adhesion to conventional Al2O3-based substrates used for commercial NOx sensors. Although partially-stabilized zirconia (PSZ) has lower ionic conductivity, in comparison to fully-stabilized zirconia, it can provide greater mechanical strength to the NOx sensor. A decrease in ionic conductivity was a common finding in studies where 20 – 30 wt% Al2O3 was added to fully-stabilized zirconia; whereas, the ionic conducting properties were not observed to change for Al2O3 additions below 10 wt%. Keeping these considerations in view, PSZ porous electrolyte based NOx sensors were fabricated with and without the addition of Al2O3 and operated using the impedancemetric method. The aim of this study was to gain understanding of the impact of Al2O3 and the role of ionic transport on NOx sensing behaviour. Standard ceramic processing methods were used to fabricate porous electrolyte based NOx sensors. Partially-stabilized zirconia powder composed of 8 wt% Y2O3-ZrO2 (Advanced Ceramics) was combined with B-76 binder and ball milled in ethanol to form a slurry. A portion of the slurry was dried and the resulting powder was uniaxially pressed at 200 MPa into pellets. Two Au wire electrodes were affixed to the pellets using the remaining PSZ slurry. The Au electrodes were approximately 3 mm apart and were completely covered by the PSZ slurry coating. The entire assembly was co-fired at 1050 for 1 hr. This procedure was repeated with 3.8 wt% Al2O3 (Sigma Aldrich) added to the slurry to form PSZ-Al2O3 electrolyte based sensors. The structure, morphology, and composition of the fabricated sensors were characterized using x-ray diffraction (XRD), and scanning electron microscopy (SEM) coupled with energy dispersive x-ray (EDX). Electrical properties of the sensors were studied using a Gamry Reference 600 to perform impedance spectroscopy for operating temperatures ranging from 550 – 700 °C where the gas concentrations were 0 - 100 ppm for NO and NO2 with 10.5% O2 and N2 as the balance for dry and humidified (3% H2O) conditions. SEM images showed a porous network of particles within the PSZ electrolytes and well dispersed Al2O3 particles throughout the PSZ-Al2O3 material. Using Archimedes method, the porosity for the PSZ and PSZ-Al2O3 electrolytes were determined to be approximately 44% and 42%, respectively. Analysis of the chemical compositions of both sensor electrolytes through EDX and XRD revealed no impurities and presence of α alumina was confirmed. The impedance data for the PSZ and PSZ-Al2O3 sensors contained two distinct arcs describing electrolyte and interfacial reactions. The high and low frequency arcs for the PSZ-Al2O3 sensors were generally about 50% and 25% larger, respectively, than the arcs for the PSZ sensors. This suggested that the alumina addition interfered with ionic transport within the electrolyte, and also limited reaction sites at the electrode/electrolyte interface. Analysis of the capacitance behaviour of the PSZ and PSZ-Al2O3 sensors based on equivalent circuit modelling of the impedance spectra indicated a decrease in capacitance with increasing NOx concentration and operating temperature for both dry and humidified gas conditions. The data also indicated a more substantial capacitance decrease for PSZ-Al2O3 sensors. The capacitance described the oxygen coverage at the electrolyte/electrode interface; and, the data suggests that the addition of Al2O3 further limited oxygen coverage possibly due to Al2O3 occupying O2 sites at the interface. Other key results were determined from the change in capacitance, ΔC = CO2 – CNOx, which is beneficial for interpreting NOx sensitivity as it is independent of frequency, thereby providing a broader interpretation of the NOx response. The terms, CO2 correspond to the capacitance with only 10.5% O2 and N2 present; and, CNOx describe the capacitance with the addition of NO or NO2 in the gas stream. In general, NOx sensitivity based on ΔC for the PSZ-Al2O3 sensors was over 50% higher than sensitivity values determined for PSZ sensors. In addition, it was found that the presence of H2O caused an increase in NOx sensitivity of about 30% for both the PSZ and PSZ-Al2O3 sensors. Overall, based on the operating conditions studied, the addition of 3.8 wt% Al2O3 seemed to limit oxygen at the electrolyte/electrode interface, such that NOx reactions could proceed more readily leading to greater NOx sensitivity.

Enhancement of the Poly(o-methoxyaniline)-Poly(3-thiophene acetic acid) Self-Assembled Electrochemical Capacitor Stability

In recent years, capacitors and rechargeable batteries have attracted attention mainly due to the urgent need for efficient and low emission energy storage devices. Supercapacitors have been investigated due to their pulse power capability, long life cycle, and high kinetic of charge/discharge making them an alternative in the development of friendly energy storage devices. Among the materials which can be using in these devices, conducting polymer has been proposed as active material. In these materials, two different coupled charge transport occur: electron transport inside the polymer chain and an injection and ejection of counter ions to compensate the generated electronic charges. This last one is generally accepted as the slow step of the process. Besides, the same process could lead to the electrochemical degradation of the films. Considering the exposed above, this work aims at the investigation of the ageing process of electrochemical capacitors using LBL POMA/PTAA films and its effect on the electrochemical stability and compare them with poly(o-methoxyaniline) casting film. The films were preparation by both methods, LBL and casting, were followed by UV-VIS spectroscopy and by mass measurements. Their morphologies was measured by Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (FEG-SEM). The electrochemical performance was measured using galvanostatic, cyclic voltammetry and electrochemical impedance spectroscopy techniques. The results show that POMA/PTAA LBL films have a higher electrochemical stability than POMA casting films which is an important property to build electrochemical devices. POMA casting material has a specific capacitance of 98 F g-1 at the beginning of charge/discharge measurement, and, after 3000 cycles, this value falls down to 22 F g-1. On the other hand, LBL POMA/PTAA film presents an initial specific capacitance of 99 F g-1, and, after 3000 cycles of charge/discharge, this value is 98 F g-1. Which is about For LBL film, the initial capacitance value is close to the cast film, on the other hand, a value less than 1% degradation after 3000 cycles. Moreover, the cyclic voltammograms obtained for both films after 3000 cycles reveals that POMA casting film presents no more redox process while POMA/PTAA LBL film shows a small change in its VC fingerprint. Impedance data shows important changes upon electrochemical ageing. Among them, the most important variation occurs in the interface pore/polymer chains. Besides, it was not observed any significant change in the capacitance of the electrical double layer, meaning that the electroactive area of polymers is constant after the ageing which is in agreement with the morphological data. For LBL films, the charge transfer resistance and the charge transfer capacitance, which are related to charge compensation during the electrochemical process, do not change which corroborate the stability of the material. For casting POMA sample, otherwise, there are important increase in the charge transfer resistance and a decrease in the charge transfer capacitance which indicate severe degradation due to the ionic transport from the pores to the polymer chains. In this case, the decrease of charge transfer capacitance values could be related to a decrease in the amount of the ions to compensate the positive charges generated in the polymer chains. In the same direction, the increase of 1000 times in the charge transfer resistance for the casting film indicates also an important decrease in its electrochemical activity. Finally, casting POMA samples presents also a 10 times increase in the polymer resistance, indicating also a polymer chain degradation besides the pore/polymer chain interface. Then, to explain the results described in the previous Figures, we consider the fact that generally, in conducting polymers, the oxidation (reduction) processes leads to the intercalation (deintercalation) of counter ions to compensate the generated charge in the material. This explanation describes the typical behavior observed for POMA casting film. From a different point of view, in POMA/PTAA LBL films, the PTAA layer provides, at least partially, the counter ion balance to the positive charge generated in the POMA chains. As consequence, there is an important decrease in the ion transport from the solution to compensate the positive generated charges leading to an increase of the LBL material electrochemical stability.

Anomalous capacitance characteristics of TFTs with LDD structures in the saturation region

The effect of lightly doped drain (LDD) doping concentration on the capacitance of a low-temperature polycrystalline silicon (LTPS) thin-film transistor (TFT) is investigated. An anomalous gate-to-source capacitance phenomenon is observed: first, the capacitance decreases, and then it increases according to the gate voltage in the saturation region. This phenomenon is not affected by the subgap density-of-states and arises as the doping concentration of the LDD region is reduced. To investigate the effects of each source and the drain LDD dose on the gate-to-source capacitance, two-dimensional device simulations were conducted in which each dose of the source and drain LDD was changed individually. The reduced controllability of the source voltage to the gate charge in the saturation region due to the increased resistance of the source LDD region with low LDD dose is identified as the reason for this anomalous capacitance phenomenon.

Graphene controlled organic photodetectors

Drop casting deposition technique was used to fabricate graphene oxide doped methylene blue (GO doped MB) photodiode, Al/p-Si/GO doped MB/Au. The effects of illumination on the current–voltage (I–V) characteristics of the Al/p-Si/GO doped MB/Au Schottky diode for optical sensing applications were explored. The reverse current of the diode in the reverse bias increases with the increasing illumination intensities. The obtained trends for both ideality factor and barrier height are in agreement, suggesting that they are both affected by GO doping. The photosensitivity of the photodiodes was investigated. The highest photosensitivity was observed for the diode having 0.03 GO:MB ratio with Iphoto/Idark ratio of 8.67×103 at 100mW/cm2 under 10V. The rectification ratio was of the order of 104. In addition, the capacitance–voltage (C–V) and conductance–voltage (G–V) measurements of the diode were studied in the frequency range of 10kHz–1MHz. The measured values of the capacitance decrease with the increasing frequency. The decrease in capacitance was explained on the basis of interface states. The photoelectrical properties of Al/p-Si/GO doped MB/Au devices indicate that the prepared diodes can be used both as a photodiode and a photocapacitor in optoelectronic device applications.

Plasma-induced, nitrogen-doped graphene-based aerogels for high-performance supercapacitors.

Commonly used energy storage devices include stacked layers of active materials on two-dimensional sheets, and the limited specific surface area restricts the further development of energy storage. Three-dimensional (3D) structures with high specific surface areas would improve device performance. Herein, we present a novel procedure to fabricate macroscopic, high-quality, nitrogen-doped, 3D graphene/nanoparticle aerogels. The procedure includes vacuum filtration, freeze-drying, and plasma treatment, which can be further expanded for large-scale production of nitrogen-doped, graphene-based aerogels. The behavior of the supercapacitor is investigated using a typical nitrogen-doped graphene/Fe3O4 nanoparticle 3D structure (NG/Fe3O4). Compared with 3D graphene/Fe3O4 structures prepared by the traditional hydrothermal method, the NG/Fe3O4 supercapacitor prepared by the present method has a 153% improvement in specific capacitance, and there is no obvious decrease in specific capacitance after 1000 cycles. The present work provides a new and facile method to produce large-scale, 3D, graphene-based materials with high specific capacitance for energy storage.

Optimization of electrochemical capacitor stability of poly(o-methoxyaniline)-poly(3-thiophene acetic acid) self-assembled films

In the development of supercapacitors and rechargeable batteries based on conducting polymers, the stability of the material is an important concern. The objective of this work is to investigate the electrochemical aging of layer-by-layer (LBL) films of two polymers, namely poly(o-methoxyaniline) and poly(3-thiophene acetic acid), which present a self-doping effect, and compare them with poly(o-methoxyaniline) casting film electrochemical properties. Cyclic voltammetry and impedance spectroscopy are used to analyze the behavior of the films. The results show that POMA/PTAA LBL films have a higher electrochemical stability than POMA casting films. This last one presents a continuous degradation as the number of ageing cycles are increased resulting in an 80% decrease from the initial specific capacitance value after 3000 cycles. For LBL films, on the other hand, film stability has a different behavior, and after 3000 cycles, only 1% of decrease in the specific capacitance is observed. Impedance data shows a continuous increase in both polymer resistance and ionic charge transfer resistance in the case of the POMA casting film whereas no changes is observed for the LBL one indicating the film degradation is possible related to the counter ion intercalation/deintercalation which occurs mainly in POMA samples.

An impedance biosensor for monitoring cancer cell attachment, spreading and drug-induced apoptosis

In the last three decades, Electrical Cell-substrate Impedance Sensing (ECIS) has emerged as a powerful technique for in vitro cellular research and preclinical testing. In this study, a cell-based impedance biosensor based on ECIS technique, which integrates microelectrode arrays with a small culture chamber has been developed for monitoring the attachment, spreading and drug-induced apoptosis of very few MCF-7 breast cancer cells. It was found out that cell spreading caused a significant increase of impedance magnitude in the frequency range between 10kHz and 100kHz and also pronounced phase shift. Using an electrical equivalent circuit to model the measured spectra, the morphological change of cells was analyzed. Cell spreading induced a slight decrease of membrane capacitance of 2% and a prominent increase of membrane resistance of 57% within incubating for nearly one day. For pharmaceutical assessment, the cells were treated with different concentrations of an anti-cancer drug (Cisplatin) in the range from 10μM to 50μM. We observed a fast decrease of impedance magnitude within the initial 4h of treatment with concentrations of 25μM and 50μM. The results derived from this study demonstrated the usability of cell-based impedance microbiosensors in cell biology and cancer research.

Effect of Novel Nanocomposite Materials for Enhancing Performance of Thin Film Transistor TFT Model

&lt;span&gt;The potential impact of high permittivity gate dielectrics on thin film transistors short channel and circuit performance has been studied using &lt;a name="OLE_LINK110"&gt;&lt;/a&gt;&lt;a name="OLE_LINK118"&gt;&lt;/a&gt;highly accurate analytical models. In addition, the gate-to-channel capacitance and parasitic fringe capacitances have been extracted. The suggested model in this paper has been &lt;a name="OLE_LINK37"&gt;&lt;/a&gt;&lt;a name="OLE_LINK36"&gt;&lt;/a&gt;increased the surface potential and decreased the &lt;a name="OLE_LINK93"&gt;&lt;/a&gt;&lt;a name="OLE_LINK92"&gt;&lt;/a&gt;threshold voltage, whenever the conventional silicon dioxide gate dielectric&lt;a name="OLE_LINK290"&gt;&lt;/a&gt;&lt;a name="OLE_LINK280"&gt;&lt;/a&gt; is replaced by high-K gate dielectric novel nanocomposite PVP/La&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;K&lt;sub&gt;ox&lt;/sub&gt;=25. Also, it has been investigated that a decrease in parasitic outer fringe capacitance and gate-to-channel capacitance, whenever the conventional silicon nitride is replaced by low-K gate sidewall spacer dielectric novel nanocomposite PTFE/SiO&lt;sub&gt;2&lt;/sub&gt;K&lt;sub&gt;sp&lt;/sub&gt;=2.9. Finally, it has been demonstrated that using low-K gate sidewalls with high-K gate insulators can be decreased the gate fringing field and threshold voltage. In addition, fabrication of nanocomposites from polymers and nano-oxide particles found to have potential candidates for using it in a wide range of applications in low cost due to low process temperature of these nanocomposites materials.&lt;/span&gt;

Transparent metal oxide films based sensors for solar tracking applications

Abstract Titanium dioxide:zinc oxide (TiO2:ZnO) composite thin films were prepared onto glass and p-type silicon substrates by the sol–gel spin coating technique. The composite metal oxide films indicate a high transmittance more than 90% in visible region. Optical constants such as optical band gap and refractive index of the films were determined using transmittance and reflectance spectra. TiO2:ZnO/p-Si diodes exhibited a high photocurrent responsivity under various solar illuminations. Electronic parameters like ideality factor, series resistance and barrier height were determined from I–V characteristic curves, Cheung model and Norde equations. The capacitance–voltage and conductance–voltage of the diodes were measured in the range from 10 kHz to 1 MHz. The capacitance of the diodes exhibited a decrease in capacitance and increase in conductance with increasing frequency. The obtained results suggest that TiO2:ZnO/p-Si diodes can be used as a sensor in optic communications and optoelectronic applications.

Frequency dependent negative capacitance effect and dielectric properties of swift heavy ion irradiated Ni/oxide/n-GaAs Schottky diode

The Ni/n-GaAs Schottky barrier diode having thin interfacial oxide layer was subjected to 25MeV C4+ ion irradiation at selected fluences. The in-situ capacitance and dielectric properties were investigated in the 1KHz to 5MHz frequency range. The results show a decrease in capacitance with increase in ion fluence at low frequencies. Interestingly, a negative capacitance effect was also observed in this frequency range in all the samples. As a consequence, changes were observed in parameters like series resistance, conductance, dielectric loss, dielectric constant, loss tangent and ac electrical conductivity. At high frequencies, the capacitance reaches the geometric value ‘C0’. The results were interpreted in terms of the generation of irradiation induced traps, carrier capture and emission from deep and shallow states and its frequency dependent saturation effects.

Chemical deposition of MnO2 nanosheets on graphene-carbon nanofiber paper as free-standing and flexible electrode for supercapacitors

Graphene-carbon nanofiber/MnO2 nanocomposite paper (GMP) is prepared via a simple chemical reaction between KMnO4 and carbon materials in acidic solution, in which MnO2 nanosheets are uniformly deposited on the graphene-carbon nanofiber paper. Owing to its freestanding structure, GMP is directly used as an electrode in the electrochemical tests without addition of any binders or conductive additives. Encouragingly, GMP exhibits an excellent capacitive performance with a high specific capacitance of 298.2 F g−1 at 1 A g−1 in 1 M Na2SO4 electrolyte. Meanwhile, this composite paper can withstand high scan rate loads without a large decrease of capacitance, the specific capacitance can be remaining at 370.4 F g−1 even at 300 mV s−1. In the cycling test, the composite paper presents an outstanding stability with 95.7 % capacitance retention after 3000 cycles. Additionally, the asymmetric supercapacitor is fabricated based on GMP electrode, it not only shows a high operating voltage of 2.0 V but also exhibits a high energy density of 23.0 Wh kg−1 at 450.8 W kg−1. Therefore, this kind of composite paper would be promising as electrode materials for flexible and high performance supercapacitors.

Organic photodetector with coumarin-adjustable photocurrent

Drop casting technique was used to fabricate Al/p-Si/coumarin doped fullerite/Al diodes. The effects of coumarin doping on the photoresponse properties of the diodes were investigated. The forward bias current of the diodes increases exponentially with voltage confirming rectification behavior. The reverse current of the diodes increases with increasing illumination intensities. The photocurrent of the diodes is higher than the dark current. The obtained m value indicates that the photocurrent exhibited a linear photoconducting behavior. The coumarin doped fullerite diodes indicate a non-ideal behavior with obtained ideality factors. The obtained barrier height value of the Al/p-Si/coumarin doped fullerite/Al diode is comparable to that of the conventional Al/p-Si (ϕb=0.58eV) Schottky diode. The measured values of the capacitance decrease with the increasing frequency. The decrease in capacitance was explained on the basis of interface states. It was concluded that the obtained barrier height and interface state density values of the diode are modified doping fullerite with coumarin. The obtained results suggest that the fabricated diodes could be used as an optical sensor in various optoelectronic applications.

Accelerated temperature and voltage life tests on aluminium electrolytic capacitors

Purpose – The purpose of this paper is to focus on conducting accelerated life tests on aluminium electrolytic capacitors under accelerated temperature and voltage stress to study the effect of applied voltage and ambient temperature on the capacitor, its degradation over time, failure data collection, analysis and then modelling the failure times. Principles of DOE are used for studying the effect of temperature and voltage. Design/methodology/approach – Life tests are conducted at three levels of temperature and applied voltage and the life of capacitor is ascertained at each treatment level. Life variation with voltage and temperature is studied to gain an insight as to how these factors affect the lifetime of the capacitor. The interaction effect of temperature and voltage on capacitor life is also established. Findings – The life of the capacitor decreases exponentially with temperature and voltage at all the three factor levels. Ambient temperature, applied voltage and their interaction effect significantly affects the life of the capacitor. Applied voltage has the greatest effect followed by ambient temperature and then their interaction effect. Life of the capacitor has been estimated as 4,206 hrs when only voltage is taken as the accelerated stress using Inverse Power Law and as 4,003 hrs when both temperature and voltage are taken as accelerating stress using combination model. Research limitations/implications – This work consider only decrease in capacitance as the failure criterion. However, as a future scope, it is proposed that test may be conducted by taking into consideration not only the decrease in capacitance as the failure criteria but by monitoring all the performance parameters of the capacitor. This would give a more realistic assessment of life as it is possible that capacitor may have failed much before it reached the lower threshold capacitance value. Practical implications – This work has lots of practical implications. It shows how DOE approach can be used for ALT data analysis and identification and effect of critical stresses acting on capacitors in real practice. Most critical types of stresses affecting the reliability can thus be controlled to ensure better performance. Product manufactures as well as users will be benefited by such findings. The paper has also illustrated how failure data can generated by degradation analysis using life test data collection at discrete intervals. Originality/value – The methodology presents an alternative non traditional approach of accelerated life testing, which does not require continuous monitoring of test items. This only requires intermittent monitoring which reduces the need of test resources. Though the degradation study itself is not new but using degradation study for ALT data generation is new. This approach may considerably reduce the test duration and resources used for ALT. DOE approach gives more tangible result to study the effect of various variables on the dependent variable. As DOE approach uses a fractional factorial design, it can be very helpful to conduct life tests with minimum number of test units (only a fraction of full factorial test units). This will considerably reduce the test duration, resources requirement for testing, easier but accurate data analysis, and faster product development, especially when ALT is to be conducted at several stresses simultaneously.

601 放電加工による石英ガラスの微細穴加工(OS3-1 機械加工の高速・高精度化-切削・研削・特殊加工及び周辺技術-)

Quartz glass high aspect ratio hole by drilling. In the case of the machining of quartz glass, a chipping is occurred caused by the machining stress due to its high hardness and brittleness. On the other hand, electrical discharge machining has a small machining stress. Therefore, in this study, a micro hole machining of the quartz glass was carried. The effect of capacitance of RC discharge circuit was investigated and a high aspect ratio micro hole machining was tried. In this study, an RC discharge circuit was used for machining. The quartz glass was machined using an assisting electrode method, because of its high insulating properties. An Assisting electrode was adhered on the workpiece surface, and the discharge was occurred to the surface. An electrical conductive layer was formed by the thermal decomposition carbon derived from the work oil. A power supply path was formed on the electrical discharge machined surface, and the machining was continued. The removal rate was increased with a decrease in capacitance. And the electrode wear ratio was indicated low in each capacitance. The micro hole drilling of high aspect ratio was carried out by capacitance of 1.1 nF. In this machining, removal rate was decreased as the high machined hole depth.

Hierarchical ternary Ni-Co-Se nanowires for high-performance supercapacitor device design.

Large-scale uniform Ni-Co-Se bimetallic ternary nanowires have been successfully synthesized through a successive cation exchange. First, NiSe nanowires in situ grown on nickel foam (NF) were prepared by a facile solvothermal route. Next, a series of ternary materials possessing different proportions of Ni and Co were fabricated by a Co-exchange method using the Ni@NiSe material as a template, which effectively achieved morphological inheritance from the parent material. To explore the electrochemical performance, all synthetic materials were assembled into asymmetric supercapacitor devices. Among asymmetric supercapacitor devices, the Ni@Ni0.8Co0.2Se//active carbon (AC) device exhibited a high specific capacitance of 86 F g-1 at a current density of 1 A g-1 and excellent cycling stability with virtually no decrease in capacitance after 2000 continuous charge-discharge cycles. This device still delivered an energy density of 17 Wh kg-1 even at a high power density of 1526.8 W kg-1. These superior electrochemical properties of Ni@Ni0.8Co0.2Se as an electrode material for supercapacitor devices confirmed the synergistic effect between Co and Ni ions, suggesting their potential application in the field of energy storage.

Covalent Immobilization of Urease on Poly(Pyrrole-3-carboxylic Acid): Electrochemical Impedance and Mott Schottky Study

Pyrrole-3-carboxylic acid was electropolymerized on a glassy carbon electrode in 0.1 M NaClO4/ACN, Et4NBF4/ACN using cyclic voltammetry. Urease (Urs) was immobilized onto PPCA modified GCE via covalent binding, exploiting EDC/NHS chemistry. Electrochemical impedance spectroscopy was used to investigate the interfacial behavior of Urs immobilized PPCA surfaces at open circuit potential. The impedance spectra were fitted before and after immobilization of Urs using equivalent circuits of R(C(R(Q(RW)))). After immobilization of Urs onto the PPCA matrix, the charge transfer resistance (RCT) increased for electrodes, which RCT of urease immobilized PPCA-NaClO4 matrixes were lower than that of the Urs immobilized PPCA-Et4NBF4 matrixes indicating higher charge transfer ability. A decrease in double layer capacitance (Cdl) values when Urs was immobilized at the PPCA-NaClO4 electrode surface was observed, whereas an increase at the PPCA-Et4NBF4 electrode surface was observed. Urs immobilized electrodes resulted in a n-type semiconducting behavior revealing a positive slope. An increase in acceptor concentration of the electrodes, and a shift of the EFB to more positive values with increasing amount of urease was observed. The Urs based electrode (PPCA-NaClO4-Urs) was used for detection of urea, which was detected in range of 0.9 to 14 mM with a detection limit (LOD) of 8.28 μM.