Function Of Sweep Rate Research Articles

Magnetic field sweep rate influence on the critical current capabilities of a Fe(Se,Te) crystal

The relaxation phenomena of a FeSe0.5Te0.5 single crystal sample, with twinned morphology, exhibiting a second magnetization peak effect have been analyzed by means of dc magnetization measurements as a function of magnetic field (H). Using different magnetic field sweep rates for performing the superconducting hysteresis loops m(H), a change in the width of these curves has been observed together with a shift of the second peak field position. A consequent and significant variation of critical current density Jc has been extracted from the superconducting m(H) curves within the Bean critical state model. In this framework, the ratio between the critical current densities Jc calculated at 200 Oe/s and 5 Oe/s has been calculated showing interesting results in terms of transport capabilities. From the Jc(H) curves at T = 10 K for different sweep rates, the irreversibility field has been obtained for T = 10 K and fitted with a power law. The increasing trend of the irreversibility field as a function of sweep rate could suggest the use of this material for power applications where overheating due to vortices movement inside the superconductor has to be limited.

Effect of Adscititious Water on the Mechanism of Mg2+ Intercalation in Tungsten Oxides from Non-Aqueous Electrolytes

There is a high demand for low-cost energy storage devices with high energy density and excellent safety. Rechargeable magnesium batteries (RMBs) have the potential to achieve better performance than Li-ion batteries (LIBs) as they allow for the use of a dendrite-free Mg anode, which has about five times the volumetric capacity of the graphite anode in LIBs. One challenge for Mg-ion batteries is the improvement of intercalation kinetics in oxide-based cathode materials. The slow kinetics have been attributed to the higher cation charge/radius ratio of Mg2+­, which results in a high desolvation barrier at the electrode/electrolyte interface and introduces difficult redistribution of charges in the electrode and significant Coulombic interaction between the intercalating species and the host lattice. The addition of water in non-aqueous electrolytes has been shown to improve the kinetics of Mg2+ intercalation, but the mechanism and the effect of water concentration are still under debate. To shed light on these issues, this research focuses on a systematic addition of water into a 0.1 M Mg(ClO4)2 in acetonitrile electrolyte and its effect on Mg2+ intercalation in WO3 and WO3·H2O. Cyclic voltammetry (CV) was used to analyze the electrochemical performance. Solid-state 1H nuclear magnetic resonance spectroscopy (NMR), inductively coupled plasma – optical emission spectrometry (ICP-OES), and X-ray diffraction (XRD) were used to study the intercalation mechanisms in the cathodes. Solution 1H and 25Mg NMR and molecular dynamic (MD) simulation were used to study the electrolytes. An improved rate capability as a function of sweep rate and a decreased peak separation of the redox couples for both materials were found as more water was introduced to the electrolyte until the water concentration reached around 14,000 ppm. Based on these studies, we find that the most likely intercalation mechanism in these electrolytes is the co-intercalation of H+ and Mg2+. The findings elucidate how water improves the kinetic performance of Mg2+ intercalation in WO3 and WO3·H2O in non-aqueous electrolytes and is likely general to other oxides benefitting from the addition of water into non-aqueous multivalent electrolytes.

(Invited) First Principles Studies of Nitrogen Electrochemistry and the Electrocatalytic Properties of Ultrathin (hydroxy)Oxide Films

Advances in the theoretical understanding of interfacial electrochemistry have, over the past decade, permitted the extension of periodic Density Functional Theory studies, which have traditionally been applied to probe chemistry at gas/solid interfaces, to electrochemical systems where potential-dependent structural and chemical phase transformations occur at liquid/solid interfaces. Indeed, such techniques have been employed to study a surprisingly wide class of electrochemical processes, ranging from electrocatalysis to corrosion. In this talk, we will discuss how these strategies can be applied to predict the detailed, atomic-scale properties of monolayer (hydroxy)oxide base metal films on precious metal and precious metal alloy substrates as a function of applied potential. We will describe the analysis of Moire patterns, variable oxidation states, and three-phase boundaries of these films, and we will demonstrate how these results may be used to predict the shape and oxidation states of supported two-dimensional nanoislands as a function of electrochemical conditions. We will next discuss how the three-phase boundaries may promote hydrogen evolution rates in alkaline environments, and we will close with some perspectives on the possibilities for electrocatalyst design offered by these systems. If time permits, we will also discuss a new approach, based on a combination of DFT and kinetic Monte Carlo simulations, that permits direct simulation of polarization curves as a function of sweep rate and that rigorously predicts intrinsic reaction pathways for both electroreduction of nitrates and NO in acidic environments.

Manipulation of the nuclear spin ensemble in a quantum dot with chirped magnetic resonance pulses.

The nuclear spins in nanostructured semiconductors play a central role in quantum applications. The nuclear spins represent a useful resource for generating local magnetic fields but nuclear spin noise represents a major source of dephasing for spin qubits. Controlling the nuclear spins enhances the resource while suppressing the noise. NMR techniques are challenging: the group III and V isotopes have large spins with widely different gyromagnetic ratios; in strained material there are large atom-dependent quadrupole shifts; and nanoscale NMR is hard to detect. We report NMR on 100,000 nuclear spins of a quantum dot using chirped radiofrequency pulses. Following polarization, we demonstrate a reversal of the nuclear spin. We can flip the nuclear spin back and forth a hundred times. We demonstrate that chirped NMR is a powerful way of determining the chemical composition, the initial nuclear spin temperatures and quadrupole frequency distributions for all the main isotopes. The key observation is a plateau in the NMR signal as a function of sweep rate: we achieve inversion at the first quantum transition for all isotopes simultaneously. These experiments represent a generic technique for manipulating nanoscale inhomogeneous nuclear spin ensembles and open the way to probe the coherence of such mesoscopic systems.

Development of Tritium Recovery by Flowing O2+Ar Gases at Steam Generator in Fast Breeder Reactor

The tritium recovery technique at the steam generator in fast breeder reactor under the double pipe concept was studied by both of experiment and simulation. The permeation of tritium was lowered at ∼1000ppm oxygen in Ar as a recovery gas. But tritium is easily converted to water form by adding 10ppm oxygen. To explain these experimental results and expand the tritium behavior at double pipe concept, DFT and Monte Carlo simulations were applied. The surface oxide layer mode was developed and stability of tritium was evaluated. It was found that most stable structure was formed in the oxide layer although tritium is unstable at the surface of oxide layer. Tritium permeation rate was almost the same even if the oxide layer was formed, but the tritium retention is enhanced by adding the oxide layer. To expand these results to tritium permeation and recovery model, numerical analysis was performed as a function of sweep rate, material thickness and thickness of surface oxide layer. It was found that control of sweep rate is one of key factors. But the design restriction, control of oxide layer thickness by flowing O2+Ar gas will be potential option for the recovery of tritium at steam generator.

Enhancement of CMP pad lifetime for shallow trench isolation process using profile simulation

Abstract In the present work, the role of disk sweep condition in a pad profile has been investigated with the help of pad conditioning simulation with parameters proposed on the basis of the Preston polishing model, in order to enhance the lifetime of the polymer pad material for shallow trench isolation (STI)-chemical mechanical polishing (CMP). From the comparison of the degree of mechanical wear experimentally measured with those numerically simulated as a function of sweep rate, the pad profile has been optimized. Furthermore, the application of the results to STI process for 0.18 μm DRAM memory showed a significant extension of pad lifetime.

Field sweep rate dependence of domain-wall speed distributions in a thin Ni80Fe20 film

The magnetization reversal in a thin (100nm) Ni80Fe20∕GaAs(001) film prepared by molecular-beam epitaxy has been investigated using a focused spot Kerr magnetometer. The field was sinusoidal and applied along an in-plane easy axis, with sweep rate at the coercive point in the range ∼1kOe∕s–1MOe∕s. Real time measurements of the Kerr response enabled a study of the probability distributions P(V) of the domain-wall speed as a function of sweep rate. The shape of P(V) changes from being characteristic of stochastic domain-wall motion at low sweep rate to being characteristic of quasicontinuous domain-wall motion at high sweep rate. Increasing the diameter of the focused spot from 2to80μm increases the number of domain walls participating in the reversal within the probed area, which leads to an averaging effect and dulls the transition from stochastic to quasicontinuous wall motion seen in the probability distributions.

An in situ electrochemical quartz crystal microbalance study of polycrystalline gold electrodes in nitric acid solution

The dissolution and redeposition processes of Au in HNO 3 solution at pH 1 and 0 were investigated as a function of sweep rate by in situ EQCM experiments. The results demonstrate that, at pH 1 and ν≤10 mV s −1, Au dissolves through a 3 e − oxidation at E>+1.0 V versus saturated calomel electrode (SCE), a process that, at ν≥10 mV s −1, is kinetically hindered with respect to upd of OH surface sublattices and subsequent 2-D-phase oxide formation. The inhibition arises from the presence of a close packed layer of nitrate oxyanions at the gold surface, although the layer is disrupted and the inhibition removed by the Au dissolution and reprecipitation processes that occur during potential cycling at low ν.

Magnetization dynamics in crossed AC and DC fields

We have measured the DC magnetization of melt textured and single crystal YBCO samples in crossed AC and DC fields, as a function of sweep rate, time and orientation ( h AC‖ c, h AC‖ ab plane). We observe that besides decreasing with h AC amplitude, the DC magnetization in swept fields ( Ḣ>0) also decreases as the log of AC field frequency. The rate of decrease 1/ M 0(Δ M/Δ ln f) is observed to be close to the flux creep rate. Magnetic relaxation both in zero and crossed fields are found to obey logarithmic time variation, with time constants decreasing with increasing f. The short time relaxation clearly shows the effects of frequency and enables an interpretation of the ln f dependence in terms of flux creep effects. AC magnetization measurements confirm both the homogenizing of the DC flux distribution due to the AC fields and the effect of field sweep in competing with the depinning due to the AC field.

Growth of a passive film on iron in a neutral borate solution by three-parameter ellipsometry

Abstract The growth of passive film on iron has been traced during potential sweep at various sweep rates in a neutral borate solution at pH 8.4. The transient thickness increase from a stationary state at 0.0 V (vs. AgAgCl) was measured by automated ellipsometry by which the ellipsometric parameters Ψ and Δ, and the reflectivity change ΔR/R, are simultaneously obtained. The transient thickness change and the complex refractive index, N = n − jk, of the film were calculated by the three parameters. The complex refractive index of the film during the transient growth is estimated to be N = 2.18 – 0.352j for light of 632.8 nm wave length. The linear potential increase initially causes an increase of the potential difference at the film/solution interface, where the film thickness remains constant and the observed current increases gradually. In the latter stage, where the interfacial potential difference reaches a constant value, steady growth of the film thickness takes place and the current reveals an almost constant value. The interfacial potential difference is a function of the potential sweep rate, and accordingly the current at the steady film growth stage is also a function of the sweep rate. From the transient change of the film thickness and current during the potential sweep at various sweep rates, the interfacial ionic transfer reactions and the mechanism of the film growth are discussed.

Thermal relaxation, textural and sweep rate effects on reversible transverse susceptibility of magnetic particles

We investigated the effect of thermal relaxation on reversible transverse susceptibility (RTS), χ, of single domain Stoner–Wohlfarth particles. We studied such an effect as a function of the orientation β of the easy axis with respect to the drive field (the z axis) within a non-interacting bi-state model. At β=00 one prominent cusp occurs for both χt1 and χt2 along the direction perpendicular to the drive field at H≂HC<HN (nucleation field) at high values KV/kBT (the ratio of the anisotropy energy versus thermal energy). The height of the cusp varies with β and reduces with decreasing values of KV/kBT. Correspondingly, the switching field distribution (SFD) becomes broadened with decreasing values of KV/kBT. The RTS may exhibit one, two, or three prominent cusps at high values of KV/kBT depending upon the textural distribution of the easy axes. For cos2 θ distribution of the easy axis about the x axis, y axis, and z axis there exists two, three, and one cusps, respectively. For random distribution of the easy axis in 2-D in the XZ and YZ plane there are one and three cusps, respectively, while there are three for random distribution in 3-D. Finally, we studied coercivity, RTS and SFD as a function of sweep rate. All these quantities are found to increase with sweeping frequency of the drive field. The peak field value of RTS is consistently the smallest of the three, while that of SFD is equal to or a shade larger than HC depending upon whether the hysteresis loop is rectangular or severely sheared.

Theory of Cyclic Voltammetry for Quasi‐Reversible Electrodeposition Reactions with insoluble Products

AbstractThe Matsuda theory of cyclic voltammetry for quasi‐reversible reactions is extended to metal dissolution and electrodeposition. Kinetic data can be conveniently obtained from the measurement of peak potentials and peak currents as a function of sweep rate and switching potentials. As an example, the rate constant for the Zn(s)/Zn++ (aq) couple has been measured to be k0 = 7.5 · 10−7 cm s−1.

Influence of sweep rate on the power spectrum and pulse height distribution of Barkhausen noise in pipeline steel : Nondestructive Testing and Evaluation, Vol. 5, No. 4, pp. 271–275 (1990)

Barkhausen noise (BN) measurements were made on a half section of a pipe as a function of sweep rate. Power spectral analysis and pulse height distribution studies weremade on the BN data. The rms BN voltage was found to increase with increasing sweep rate. The power density of BN spectra was found to increase and BN jumps with large amplitude take place at higher sweep rates. Increasing sweep rate is also found to increase the total number of BN jumps.

INFLUENCE OF SWEEP RATE ON THE POWER SPECTRUM AND PULSE HEIGHT DISTRIBUTION OF BARKHAUSEN NOISE IN PIPELINE STEEL∗

Barkhausen noise (BN) measurements were made on a half section of a pipe as a function of sweep rate. Power spectral analysis and pulse height distribution studies weremade on the BN data. The rms BN voltage was found to increase with increasing sweep rate. The power density of BN spectra was found to increase and BN jumps with large amplitude take place at higher sweep rates. Increasing sweep rate is also found to increase the total number of BN jumps.

Mono- and multilayer formation studies of cobalt on glassy carbon electrode

This paper reports the results of the study of mono- and multilayer formation of cobalt on glassy carbon electrode as a function of sweep rate, cathodic potential limit of the triangular scan and concentration of cobalt. Cyclic and linear potential sweep techniques were employed in carrying out these studies. The multilayer formation of cobalt occurs by 3-D nucleation-growth processes only at concentration ⩾ 10 −3 M of cobalt. On the other hand, the monolayer stripping pattern shows two peaks. The characterization of these peaks by the theoretical models reported in literature revealed that the monolayer formation of cobalt occurs by nucleation-growth and des-ad kinetic processes.

Zinc Oxidation and Redeposition Processes in Aqueous Alkali and Carbonate Solutions: II . Distinction Between Dissolution and Oxide Film Formation Processes

The early stages of the process of anodic zinc oxidation in , , and Cl− solutions around pH 11.5, were studied by cyclic voltammetry, as in part I. Unusual peak current dependence on sweep rate is observed at the first anodic peak. This behavior is explained in terms of a mixed process involving coupled diffusion and film formation. By correlating the shapes of peaks and peak potentials for different Zn surface preparations, and the relation of the peak current to sweep rate and to electrode rotation rate, , the roles of film formation and diffusion of solution species are distinguished. A new method of plotting out cyclic voltammetry peak currents, , as a function of sweep rate, , is proposed that treats the anodic currents in terms of parallel components for dissolution into solution, with diffusion (proportional to ), and for film formation or reduction (proportional to ). This allows a separation of diffusion‐controlled and film formation currents to be made. The RDE experiments yield and sweep rate experiments showed relations apply to the for the peak. Two processes therefore take place: diffusion‐controlled dissolution and direct film formation. The importance of studies at single‐crystal surfaces is stressed where resolution of the various processes involved is much clearer. Thus, it is shown that only the direct oxide film formation process is predominant at the single‐crystal Zn(0001) face. This compact film is responsible for passivation. The results enable a model for dissolution and coupled‐film formation, associated with passivation, at the Zn electrode, to be suggested. The participation of these two types of process depends on pH and the types of ions present.

Experimental response of MOS devices to a fast linear voltage ramp

An experimental investigation is undertaken of the response of an MOS device to a linear voltage ramp of such speed as to take the device into non-equilibrium, but to allow sufficient generation to take place during the voltage sweep to provide structure in the C- V curves which can be analysed quantitatively. The main aim has been to investigate the effect of sweep rate per se, but additional data is presented which considers the voltage dependence of the space-charge width, the maximum sweep rate for quasi-equilibrium, and the effect of temperature. It is demonstrated that the technique provides quantitative information on bulk traps and a qualitative measure of the relative role of interface traps in the generation process. Transitions are observed between quasi-equilibrium and non-equilibrium which are a function of sweep rate. This is in contrast to the pulse technique, where the response is of a purely transient nature.

Theoretical analysis of the influence of the adosorption process on the voltammetric curves in the case of a second order adsorption step followed by a first order charge transfer reaction: Part II. Comparison between linear potential sweep voltammetry and steady state cyclic voltammetry

The voltammetric curves for a 2-step sequential reaction involving a 2nd order adsorption process (such as the catalytic mechanism met in the anodic oxidation of hydrogen) are investigated theoretically by computer calculations. Steady state cyclic voltammetry (s.s.c.v.) is particularly treated by repeating forward and backward sweeps as many times as necessary to reach the steady state. For both l.p.s.v. and s.s.c.v., the usual characteristic features are considered, i.e. E M, θ M, i M as a function of sweep rate υ, especially in the range of υ, where the computed data fit the results derived from analytical solution (quasi-reversible charge transfer, and irreversible charge transfer). In s.s.c.v., indications are given to obtain the kinetic parameters ( k 1, k 2, α) from experimental plots.

Non-equilibrium response of MOS devices to a linear voltage ramp—I. Bulk discrete traps

A study is presented of MOS devices containing discrete bulk traps, subjected to a triangular voltage waveform, such that the rate of change of voltage is sufficiently high to take the device into the non-equilibrium mode of operation. Consequently, the dynamics of the system response are related to the parameters of the traps involved in the generation and recombination processes occurring within the device. The technique is in contrast with Kuhn's method in which the device, and hence the various generation and recombination processes, are always in quasi-equilibrium. Analytical parametric equations relating the current, and hence the small-signal capacitance and the gate voltage to the width of the depletion region, are obtained. From these equations current and small-signal capacitance vs gate voltage plots are obtained as a function of sweep rate and temperature, for both forward and reverse voltage sweeps. These plots are rich in structure, and physical discussion relating to the salient features of these plots is presented. Suggestions are made of how various device parameters such as generation rate and life-time, trap density, and capture cross-section, can be extracted from the theory.

An investigation of anodic film formation on electrodeposited ruthenium by potential sweep techniques

Potential sweep techniques were used to investigate the anodic behaviour of reduced ruthenium surfaces, prepared by electrodeposition on gold-plated substrates, as a function of sweep rate, temperature and pH. The most important factor appeared to be pH as this strongly influenced the oxide layer thickness and both the number and location of the peaks on the voltammogram. The formation of thin oxide films on ruthenium at intermediate pH values (3.5–9.5) is attributed to the growth of a compact amorphous film with significant metal-oxygen-metal bridging in the structure. Heavier oxide growth in strong acid is attributed to protonation of the oxide lattice resulting in the formation of a more porous anodic film. Thicker oxide growth in strong base is attributed to the growth of a higher (+6) oxide under these conditions. The effects of both sweep rate and temperature on anodic behaviour in strong acid are attributed to activation-controlled rearrangement of the oxide film.