Reciprocal Capacitance Research Articles

ВЛИЯНИЕ ЭЛЕКТРОХИМИЧЕСКОЙ ПОЛИРОВКИ ТАНТАЛА НА ДИЭЛЕКТРИЧЕСКИЕ ПАРАМЕТРЫ АНОДНОГО ОКСИДА

Изучено анодное поведение Та-электрода в 0.1 M водном растворе H3PO4 после стадии электрохимической полировки поверхности металла. Установлены оптимальные условия проведения процесса электрохимической полировки в электролите HF:C3H7OH:H2SO4. На основе анализа циклических вольтамперных кривых сделано заключение, что эффективность процесса формирования анодного оксида тантала близка к 100 %. Данные импедансной спектроскопии подтверждают образование оксидной пленки с высокими диэлектрическими характеристиками. Проведен расчет диэлектрической проницаемости сформированного оксида, дана оценка фактора шероховатости поверхности тантала после ее электрохимической полировки.

Effect of solution pH on the electrochemical behaviour of AISI 304 austenitic and AISI 430 ferritic stainless steels in concentrated acidic media

In this study, the effect of solution pH on the electrochemical behaviour of AISI 304 austenitic and AISI 430 ferritic stainless steels at open circuit potential (OCP) in concentrated acidic solutions was studied. Polarization curves showed that the corrosion current density of both stainless steels increased with decreasing pH. Mott–Schottky analysis revealed that passive films formed on AISI 304 and AISI 430 stainless steels behave as n-type and p-type semiconductors and the donor and acceptor densities increased with decreasing pH. Electrochemical impedance spectroscopy (EIS) results showed that the reciprocal capacitance of the passive film is directly proportional to its thickness which decreases with decreasing pH. Thus for both austenitic and ferritic stainless steels in acidic solutions, increasing the solution pH offers better conditions for forming passive films with higher protection behaviour, due to the growth of much thicker and less defective films.

Effect of immersion time on the electrochemical behaviour of AZ31B alloy

Effect of immersion time on the electrochemical behaviour of AZ31B alloy in 0.01 M KOH solution under open circuit potential (OCP) conditions was studied by various electrochemical methods. Polarization results revealed that increasing immersion time leads to decrease the corrosion rate of this alloy. Also, electrochemical impedance spectroscopy (EIS) results showed that the reciprocal capacitance of the passive film is proportional to its thickness which increases with increasing immersion time. In Mott–Schottky analysis, no evidence of p-type semiconducting behaviour was found, indicating that the oxygen vacancies preponderated over the cation vacancies. Moreover, the Mott–Schottky results showed that the donor density increases by increasing the immersion time from 1 to 6 h, while it decreases when the immersion time reaches 9 and 24 h. Therefore, it is clear that higher immersion time offers better conditions for forming the passive films with higher protection behaviour, due to the growth of a much thicker and less defective films.

Passivation behavior of a ferritic stainless steel in concentrated alkaline solutions

The passivation behavior of AISI 430 ferritic stainless steel was investigated in concentrated alkaline solutions in relation to several test parameters, using electrochemical techniques. Increasing solution pH (varying from 11.5 to 14.0) leads to an increase in the corrosion rate of the alloy. Mott–Schottky analysis revealed that passive films formed on AISI 430 ferritic stainless steel behave as n-type semiconductor and the donor densities increased with pH. Electrochemical impedance spectroscopy (EIS) results showed that the reciprocal capacitance of the passive film is directly proportional to its thickness, which decreases with pH increase. The results revealed that for this ferritic stainless steel in concentrated alkaline solutions, decreasing the solution pH offers better conditions for forming passive films with higher protection behavior, due to the growth of a much thicker and less defective film.

Investigation of the passive behaviour of AZ31B alloy in alkaline solutions

Abstract In this work, the passivity of AZ31B alloy in NaOH solutions was studied by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and Mott–Schottky analysis. Potentiodynamic polarization results indicated that decreasing NaOH concentration leads to decrease the corrosion rate of this alloy. EIS results showed that the reciprocal capacitance (1/C) of the passive film is directly proportional to its thickness which increases with decreasing NaOH concentration. Therefore, it is clear that dilute NaOH solutions offer better conditions for forming the passive films with higher protection behaviour, due to the growth of a much thicker and less defective films. The Mott–Schottky analysis revealed that the passive films displayed n-type semiconductive characteristics, where the oxygen vacancies and interstitials (over the cation vacancies) preponderated. Also, Mott–Schottky results showed that the donor densities evaluated from Mott–Schottky plots are in the range of 1020 cm−3 and decreased with decreasing NaOH concentration.

Growth Kinetics of Zr-4 in Sodium Bisulphite: Solvent Studies

Anodization of zircaloy-4 in 0.1 M sodium bisulphite has been carried out. Kinetics of anodic oxidation of zircaloy-4 has been studied at a constant current density of 8 mA.cm -2 and at room temperature. The plots of formation voltage vs. time, reciprocal capacitance vs . time and reciprocal capacitance vs . formation voltage were drawn. From these plots, formation rate, current efficiency and differential field were calculated. The addition of solvent (Ethylene glycol) showed better kinetic results. For 20, 40, 60 and 80% aquo-glycolic media, the dielectric constant values are low leading to the marked improvement in the kinetics.

Analysis of Change in Motional Capacitance of the Electrical Equivalent Circuit of Quartz-Crystal Tuning-Fork Tactile Sensor at Resonance by Combining Analytical Models for Elastic Foundation and L-Shaped Bar with Torsion Spring

We derived the analytical formula of the motional capacitance Ca of a quartz-crystal tuning-fork tactile sensor by use of the conservation law of energy that the electrostatic energy in Ca is equal to the sum of the strain energy of its arm and the elastic energy of the material in contact with its base. In this analysis, the strain energy of the arm and the elastic energy of the material in contact with its base were obtained by applying the torsion spring model to the joint of the arm and the base, which were depicted as an L-shaped bar, and the elastic foundation to the materials in contact with its base, and the electrostatic energy of the arm was derived by applying the bimorph flexural model to the arm treated as a piezoelectric material. As a result of calculation, we found that the calculated value of the change in reciprocal motional capacitance Δ(1/Ca) of the quartz-crystal tuning-fork tactile sensor by our model is closer to the measured one for plastics than that given by the theoretical formula of motional capacitance of only one arm and Δ(1/Ca) is affected by the Young's moduli of materials in contact with the sensor's base.

Ferroelectric properties of Ge2Sb2Te5 phase-change films

The aim of this work is to investigate the NaCl-type to a hexagonal phase transition in Ge2Sb2Te5 films using impedance and piezoresponse force microscopy (PFM) measurements. The temperature dependence of the capacitance shows an abrupt change with a maximum at the temperature of 259 °C, which corresponds to the end from a NaCl-type to a hexagonal transition. In addition, the reciprocal capacitance for temperatures above 259 °C shows the Curie–Weiss dependence, which is typical for ferroelectric materials. Application of the external electrical field increases the degree of polarization in the NaCl-type Ge2Sb2Te5 films which allowed observing the ferroelectric domains in PFM measurements.

Effect of Aquo‐glycolic Media and Added Anions on the Anodization of Zircaloy‐4 in Sulphamic Acid

Anodization of zircaloy‐4 in 0.1 M sulphamic acid has been carried out. Kinetics of anodic oxidation of zircaloy‐4 has been studied at a constant current density of 8 mA/cm2 and at room temperature. Thickness estimates were made from capacitance data. The plots of formation voltage vs. time, reciprocal capacitance vs. time, reciprocal capacitance vs. formation voltage and thickness vs. formation voltage were drawn and rate of formation, current efficiency and differential field were calculated. The addition of solvent (ethylene glycol) showed better kinetic results. For 25%, 50% and 75% aquo‐glycolic media, the dielectric constant values are low leading to a marked improvement in the kinetics. In 80% ethylene glycol, though the dielectric constant value of solution is less, the kinetics was slow which may be attributed to the fact that the electrolyte becomes highly non‐polar. Improvement in the kinetics of oxide film formation was observed by the addition of millimolar concentration of anions (CO32-, SO42-, PO43-). The presence of phosphate ions improved the kinetics of anodization to better extent.

Electrochemical Behavior of Sn-Ag Alloys in Alkaline Solutions

Abstract The behavior of four Sn-Ag alloys and their individual metal components in sodium hydroxide (NaOH) solutions was studied using open-circuit potential, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS). The results reveal that each of the initial open-circuit potential at zero time, Ei, and final open-circuit potential after 60 min, Ef, (at concentrations <0.30 M) shifts toward more negative values, indicating a relatively higher rate of dissolution during the spontaneous oxide growth/oxide dissolution process under the currentless conditions. While at concentrations <0.30 M, there is no significant change in potential. The two corrosion parameters (corrosion potential [Ecorr] and corrosion current density [icorr]) show a linear relation with both the solution concentration and alloy composition. EIS results show that each of the total resistance (RT) and reciprocal capacitance (C−1) values decreases with an increase in the tin content up to 50%. After that, there is l...

ELECTROCHEMICAL BEHAVIOR OF MOLYBDENUM ELECTRODE IN ACETIC, FORMIC AND OXALIC ACID SOLUTIONS.

The electrochemical behavior of molybdenum electrode in acetic, formic and oxalic acid solutions is studied. The effect of immersion time, composition medium, applied voltage, applied current density and scanning rate is investigated using potentiodynamic, potentiostatic and galvanostatic polarization measurements. The stability of the oxide film formed on Mo electrode is affected by both the formation medium and the applied potential. In 0.5N oxalic acid, the critical applied voltage below which the current start to oscillate is equal to -80 mV. The rate of dissolution of anodic oxide film formed on Mo in oxalic acid is very rapid compared with that formed in acetic and formic acids. Also in oxalic acid solutions Mo is notably affected by applied current density in which reciprocal capacitance, Cs-1, decrease with increasing applied current density. On the contrary in acetic and formic acids Mo did not affect. In acetic acid solution, the time of anodization has little or no effect on the dissolution process.

Charge collection and capacitance–voltage analysis in irradiated n-type magnetic Czochralski silicon detectors

The depletion depth of irradiated n-type silicon microstrip detectors can be inferred from both the reciprocal capacitance and from the amount of collected charge. Capacitance voltage ( C– V) measurements at different frequencies and temperatures are being compared with the bias voltage dependence of the charge collection on an irradiated n-type magnetic Czochralski silicon detector. Good agreement between the reciprocal capacitance and the median collected charge is found when the frequency of the C– V measurement is selected such that it scales with the temperature dependence of the leakage current. Measuring C– V characteristics at prescribed combinations of temperature and frequency allows then a realistic estimate of the depletion characteristics of irradiated silicon strip detectors based on C– V data alone.

Thickness dependence of intrinsic dielectric response and apparent interfacial capacitance in ferroelectric thin films

We studied theoretically the influence of the progressive strain relaxation and the depolarizing-field effect on the thickness dependence of the out-of-plane dielectric response of epitaxial ferroelectric thin films sandwiched between extended metal electrodes. The calculations show that the inverse of the measured capacitance varies with the film thickness almost linearly in the most part of the thickness range at the majority of temperatures. Extrapolation of this linear dependence to zero thickness usually gives considerable nonzero intercept even in the absence of nonferroelectric interfacial layers. Remarkably, such apparent “interfacial capacitance” in a certain temperature range becomes negative. The physical meaning of the effective dielectric constant, which can be extracted from the slope of the reciprocal capacitance thickness dependence, is also analyzed. The theoretical predictions are compared with the experimental data obtained for single-crystalline SrRuO3∕Ba0.7Sr0.3TiO3∕SrRuO3 and Pt∕Ba0.7Sr0.3TiO3∕SrRuO3 thin-film capacitors.

Formation and Dissolution Behavior of Anodic Oxide Films on Titanium in Oxalic Acid Solutions

Abstract The effect of temperature, oxalic acid concentration, and pH of solution on the growth and dissolution of anodic oxide films on titanium has been investigated using electrochemical impedance spectroscopy (EIS), galvanostatic measurements, and open-circuit potential measurements. An increase in temperature and electrolyte concentration leads to a decrease in the oxide film growth and an increase in the dissolution process of the oxide films. The rate of oxide film formation decreases with lowering the pH of solution from pH = 7 to pH = 2 while the rate of film dissolution increases. The activation energies for the oxide film growth and dissolution processes were calculated and found to be 19.59 kJ/mol and 34.29 kJ/mol, respectively. An equivalent circuit describing the oxide film/electrolyte interface is suggested. The effect of current density on the formation rate of the oxide film was measured. The reciprocal capacitance data was reported as a function of polarizing current density.

The effect of anodizing voltage on the electrical properties of Al–Ti composite oxide film on aluminum

Abstract The Al–Ti composite oxide film with high dielectric constant was prepared by hydrolysis precipitation and anodizing. The depth profiles of the Al–Ti composite oxide films formed at 50 V and 80 V have been detected by glow discharge optical emission spectrometry (GDOES). The electrical properties of the Al–Ti composite oxide film formed at different anodizing voltages have been studied by electrical measurements. The local electric breakdown occurs in the Al–Ti composite oxide films about the anodizing voltage of 70 V. The Al–Ti composite oxide film formed at 80 V presents a thicker outer layer containing titanium than that of the film formed at 50 V. It was established that the dependence of the retention voltage and reciprocal capacitance on the anodizing voltage consisted of two linear regions. It was found that more than one conduction mechanism was involved in the range of electric field used in the experiment. The current conduction is ohmic at low electric field and Schottky emission at high electric field. The film formed at 80 V reveals an additional electric field region when compared with the film formed at 50 V, and its conduction mechanism is space charge limited current. According to our results, the film formed above the anodizing voltage of 70 V exhibits inferior electrical properties than that of the film formed below 70 V.

A new rule for MESFET gate charge division based on the energy conservation principle

AbstractThe energy conservation problem in the MESFET gate charge model is presented. The energy conservation requirement leads to symmetrical transcapacitances in contradiction to the commonly accepted approaches. The transcapacitance symmetry is completely independent of device symmetry. The resulting small‐signal capacitances are reciprocal. Reciprocal capacitances are often considered charge non‐conservative because they do not contain transcapacitances, but in this approach reciprocity is the result of transcapacitance symmetry and the charge conservation problem is avoided since the charge‐based model includes the transcapacitances. A method for dividing the MESFET gate charge into gate‐drain and gate‐source portions based on the energy conservation rule is developed, and the method is applied to the well‐known Statz gate charge as an example. Copyright © 2004 John Wiley &amp; Sons, Ltd.

Chronopotentiometric Responses and Capacitance Behaviors of Passive Film Formed on Iron in Borate Buffer Solution

The passivation process of iron in borate buffer solution (pH 8.4) was investigated by using linear potential sweep voltammetry, current step chronopotentiometry, open circuit chronopotentiometry, and alternative current (ac) impedance spectroscopy. Iron is passivated when the potential is in between −0.45 and 0.9 V (vs. saturated calomel electrode). The capacitance of the passive film on iron in its passive region was obtained by fitting experimental ac impedance spectra with a Randles equivalent circuit. At the potential higher than 0 V in the passive region, the reciprocal capacitance of the passive film was proportional to the potential, which is ascribed to the thickening of the passive film. At the potential lower than 0 V in the passive region, there was a proximately linear relationship between the reciprocal square capacitance and the potential as well as between the reciprocal capacitance and the potential. This is because the capacitance value at this potential region equals almost unity in Only at a narrow potential region (−0.3-0 V) can the linear relationship of reciprocal square capacitance with potential be ascribed to the Mott-Schottky behavior, because there is no change in the thickness of the passive film at this potential region. The donor concentration of the passive film determined by the Mott-Schottky relationship was at −0.3 V. The dielectric constants of the passive film varied from the potential, and were in between the dielectric constants of (250) and © 2004 The Electrochemical Society. All rights reserved.

Structural and electrical properties of Zr oxide film for high-k gate dielectrics by using electron cyclotron resonance plasma sputtering

Zirconium (Zr) oxide films were directly deposited on Si substrate by using Ar and O2 mixed electron cyclotron resonance plasma sputtering. The structural and electrical properties of the deposited ZrO2 film were investigated in detail. According to the X-ray diffraction and Fourier transform infrared spectrometer measurements, polycrystalline films consisting of a monoclinic state were formed at substrate temperatures between 130 and 400 °C. An interfacial Si oxide layer was found and the thickness increased as the substrate temperature increased. It was found from the I–V measurement that the electrical properties of the deposited ZrO2 films were very sensitive to the O2 flow rate, and the dielectric breakdown field of 3∼5 MV/cm was achieved under the optimum condition. Permittivity of the ZrO2 film was extracted by linear fitting of the reciprocal accumulation capacitance versus oxide thickness. The permittivity was 20.5 and an interfacial Si oxide layer was 2.3 nm. Both were very consistent with the result obtained from spectroscopic ellipsometer.

Diffusion length estimation in CuInSe 2-based cells by the photocurrent–capacitance method

Using the photocurrent–capacitance method, measurements have been made on Cu(InGa)Se 2 (CIGS) cells from ZSW, Germany to estimate minority diffusion lengths ( L n). To minimize drift effects, an X– Y recorder was employed in the place of an earlier point-by-point method to measure dark and illuminated current with variation of reverse voltage. However, the obtained L n-values on the same cell had a wider spread of values than usual, with magnitudes too large to be acceptable. Nevertheless, it was found that pre-exposure of the cell to the light used during the measurements had a stabilizing effect on the variation of dark current with reverse bias. As a result, the middle range of the variation of the illuminated-to-dark current change with reciprocal capacitance was made more reproducible. Using different optical filters on light pre-soaked CIGS cells, L n was estimated to be approximately 2.5 μm ±40%.

Dielectric properties of anodic films formed on sputtering-deposited tantalum in phosphoric acid solution

The dielectric properties of anodic films formed on tantalum in dilute phosphoric acid solution, at 20 and 85 °C, have been investigated by electrochemical impedance spectroscopy. Dielectric constants of 28.2±0.9 (20 °C) and 30.2±2.1 (85 °C) were determined from the slopes of the variations of reciprocal capacitance of the anodic film and of film thickness, from transmission electron microscopy, with formation voltage. The slightly higher dielectric constant obtained at 85 °C is due to a reduced amount of incorporated phosphorus species in the outer layer of anodic films formed at this temperature, together with a reduced thickness of the outer layer, compared with those of anodic films formed at 20 °C.