Absolute Current Density Research Articles

Practical Magnetic Pinning in YBCO

Iron-containing oxide inclusions have been incorporated as nanoscale ferromagnetic precipitate flux pinning centers within pulsed laser deposited YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-delta</sub> (YBCO) thin films via a simple process utilizing a composite deposition target. The resultant films exhibit a coexistence of superconductivity and ferromagnetism at 77 K, and a consequent significant enhancement in their absolute critical current density, J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> , compared to pure YBCO films prepared under the same conditions. dasiaPoisoningpsila effects due to the incorporation of Fe into the YBCO matrix are avoided at sufficiently low concentrations of inclusions, where the greatest self-field J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> enhancement is seen, but do become increasingly evident as the concentration is increased. The process outlined has practical application in the synthesis of high-J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> YBCO films, with the absolute J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> values obtained in initial samples lying at the upper bound of reported values for samples produced worldwide to date.

Growth of Nitrogen-Doped MgxZn1-xO for Use in Visible Rejection Photodetectors

Improvement in the Schottky behavior of metal (Au) contacts with Mg0.01Zn0.99O and Mg0.01Zn0.99O:N thin films were observed by treating the films with hydrogen peroxide (H2O2) (dipping of samples in H2O2 at 100 _C for 3 min). Contacts formed on untreated film showed Ohmic behavior in the current-voltage (I-V ) measurements. The H2O2 treatment led to a smooth surface morphology for the films and resulted in Schottky contact of Au fabricated on the treated films with barrier heights of 0.82≈0.85 eV. The absolute current density at a reverse bias of 3 V was 1≈6 × 10−6 A/cm2 for Au contacts on H2O2-treated films. The treated films showed lower electron concentration than the untreated films due to removal of the relatively high conducting top layers of the thin films. A metal-semiconductor-metal (MSM) detector was fabricated using a Mg0.05Zn0.95O:N film and was characterized for its spectral response.

Atomic Fluorine Anion Storage Emission Material C12A7-F−and Etching of Si and SiO2 by Atomic Fluorine Anions

The present study provides a novel approach to produce pure and stable atomic fluorine anions (F−) in the gas phase by using the F− storage emission material of [Ca24Al28O64]4+·(O2−)0.35(F−)3.30 (abbreviated as C12A7-F−), synthesized by the solid-state reaction of CaF2, CaCO3, and γ-Al2O3. The anionic species stored in the C12A7-F− material were dominated by the F− anions, about (1.9 ± 0.3) × 1021 cm−3, accompanied by a small amount of O2−, O−, and O2−, via ion chromatography and electron paramagnetic resonance measurements, which corroborates that the anionic species emitted from the C12A7-F− surface were dominated by the F− anions (about 90%) together with a small amount of the O− anions and electrons, identified by a time-of-flight mass spectroscopy. The absolute emission current density of F− was sensitive to the surface temperature and extraction field, reaching about 16.7 ± 0.8 µA/cm2 at 800 °C and 1200 V/cm. A pure and stable atomic fluorine anion beam was developed by using an electrochemistry imp...

A high-throughput study of PtNiZr catalysts for application in PEM fuel cells

The effects of adding Zr to PtNi oxygen reduction reaction (ORR) electrocatalyst alloys were examined in a study aimed at probing the possibility of creating catalysts with enhanced resistance to corrosion in a PEM fuel cell environment. Samples consisting of pure Pt or PtNiZr alloys with a range of compositions (not exceeding 11 at.% Zr) were fabricated using co-sputter deposition. A high-throughput fabrication approach was used wherein 18 distinct thin film catalyst alloy samples with varying compositions were deposited onto a large-area substrate with individual Au current collector structures. A multi-channel pseudo-potentiostat allowed for the simultaneous quantitative study of catalytic activity for all 18 electrodes in a single test bath, a first for the study of ORR electrocatalysts. A properly stirred oxygenated 1 M H 2SO 4 electrolyte solution was used to provide each electrode with a steady-state flow of reactants during electrochemical evaluation. The onset potentials, absolute current density values, and Tafel analysis data obtained using this technique were compared with literature reports. The analyses showed that most PtNiZr alloys tested offered improvements over pure Pt, however those surfaces with a high mole fraction (>4 at.%) of Zr exhibited reduced activity that was roughly inversely correlated to the amount of Zr present. Film composition, morphology, and crystallographic properties were examined using X-ray energy dispersive spectroscopy (XEDS), X-ray photoelectron spectroscopy (XPS), SEM, and synchrotron X-ray diffraction. These data were then correlated with electrochemical data to elucidate the relationships between composition, structure, and relative performance for this ternary system.

Electromagnetic modelling of current flow in the heart from TASER devices and the risk of cardiac dysrhythmias

Increasing use by law enforcement agencies of the M26 and X26 TASERTASER is an acronym for Thomas A. Swift's Electric Rifle from the book Tom Swift and His Electric Rifle (1911) by Victor Appleton, ISBN-10: 1594561257. electrical incapacitation devices has raised concerns about the arrhythmogenic potential of these weapons. Using a numerical phantom constructed from medical images of the human body in which the material properties of the tissues are represented, computational electromagnetic modelling has been used to predict the currents arising at the heart following injection of M26 and X26 waveforms at the anterior surface of the chest (with one TASER ‘barb’ directly overlying the ventricles). The modelling indicated that the peak absolute current densities at the ventricles were 0.66 and 0.11 mA mm−2 for the M26 and X26 waveforms, respectively. When applied during the vulnerable period to the ventricular epicardial surface of guinea-pig isolated hearts, the M26 and X26 waveforms induced ectopic beats, but only at current densities greater than 60-fold those predicted by the modelling. When applied to the ventricles in trains designed to mimic the discharge patterns of the TASER devices, neither waveform induced ventricular fibrillation at peak currents >70-fold (for the M26 waveform) and >240-fold (for the X26) higher than the modelled current densities. This study provides evidence for a lack of arrhythmogenic action of the M26 and X26 TASER devices.For more information on this article, see medicalphysicsweb.org

Ferromagnetic 0–π Josephson junctions

We present a study on low-Tc superconductor-insulator-ferromagnet-superconductor (SIFS) Josephson junctions. SIFS junctions have gained considerable interest in recent years because they show a number of interesting properties for future classical and quantum computing devices. We optimized the fabrication process of these junctions to achieve a homogeneous current transport, ending up with high-quality samples. Depending on the thickness of the ferromagnetic layer and on temperature, the SIFS junctions are in the ground state with a phase drop of either 0 or π. By using a ferromagnetic layer with variable step-like thickness along the junction, we obtained a so-called 0–π Josephson junction, in which 0 and π ground states compete with each other. At a certain temperature the 0 and π parts of the junction are perfectly symmetric, i.e. the absolute critical current densities are equal. In this case the degenerate ground state corresponds to a vortex of supercurrent circulating clock- or counterclockwise and creating a magnetic flux which carries a fraction of the magnetic flux quantum Φ0.

Hydrogen-evolution and -oxidation on Ag(1 1 1) covered by Pt

Physical vapour deposited Pt on Ag(1 1 1) forms inhomogeneous films, leaving access to the Ag(1 1 1) surface, as proven by electroreflectance. The overpotential of the hydrogen evolution reaction at Ag(1 1 1) by water splitting in neutral perchlorate and sulphate electrolytes and by H 3O + discharge in acidic perchlorate and sulphate electrolytes is considerably reduced by the Pt coverage, but does not vanish. The transfer coefficient for water splitting is more than 50% lower than for H 3O + discharge. In H 2-saturated neutral electrolytes, the potential gap between hydrogen evolution by water splitting and H 2-oxidation decreases with the increasing number of Pt monolayers. In acidic electrolytes, this gap does not exist. Here, the absolute current densities of H +-reduction and H 2-oxidation grow with the number of Pt monolayers. In the neutral electrolytes, sulphate strongly inhibits the H 2-oxidation (by a factor of about 25 with respect to perchlorate).

Desorption of the C2- Anion from the Au−C-Deposited Y2O3-Stabilized ZrO2 Surface

Carbon dimer anions (C2-) and atomic oxygen radical anions (O-) desorbed from an Au−C-deposited Y2O3-stabilized ZrO2 (YSZ) surface have been observed. Both the emitted anions and electrons were found to be strongly dependent on the surface temperature and applied extraction field. The Arrhenius plots for the anions and electrons exhibit double-linear behavior, resulting in lower apparent activation energies in the high-temperature region (>913 K). It was found that the apparent activation energies can be reduced by the extraction field. Measurements of the absolute emission current density show similar temperature and field features as derived by TOF (time-of-flight) spectroscopic investigations. The observed anions of O- are attributed to the detachment of the transient anions of O2-(s) (i.e., O2-(s) → O-(s) + e-(s)), which migrate from the YSZ bulk onto the emission surface. The C2-(s) anions are attributed to the surface anion-exchange reactions between O-(s) and surface carbon atoms. An emission mecha...

A novel procedure for measuring the absolute current density profile of a focused gallium-ion beam

A simple and sensitive method has been developed for measuring the absolute current density profile of a focused gallium-ion beam down to six orders of magnitude below its peak intensity. This method exploits both physical sputtering and a chemical etch-stop mechanism that occurs on Si(100) substrates after Ga-ion implantation. Sputtering creates craters on the substrate while the ion implanted area becomes insoluble in aqueous NaOH. This etch-stop layer can be used as negative resistance for creating hillocks on the substrate. By measuring the topographs of sputtered craters and etched hillocks using atomic force microscopy, the absolute current density profile of the focused ion beam is deduced.

Nonlinear electrical properties of lead-lanthanum-titanate thin films deposited by multi-ion-beam reactive sputtering

The high-field electrical properties of ferroelectric lead-lanthanum-titanate (PLT) thin films deposited by multi-ion-beam reactive sputtering are presented. Space-charge-limited (SCL) conduction theory incorporating the effects of electron traps is used to explain the current-density dependence on applied voltage. Three conduction mechanisms, ohmic, SCL, and trap-filled limited (TFL), were observed with increasing applied potential. Increasing excess PbO content in PLT films increases the absolute current density measured in all three conduction regions and decreases the potential required for the transition between ohmic conduction and SCL conduction. Electron trap density is increased with the addition of La, resulting in increased voltages for the transition between SCL and TFL conduction. Permittivity and polarization hysteresis behavior is interpreted by considering the conduction contributions under linear low-field conditions and nonlinear high-field conditions. Hysteresis loop frequency dependence, asymmetry, and off-center shift from the zero-field and zero-polarization origin arise from conduction contributions and nonlinear internal fields, which are explained by applying SCL theory. Pulse switching results, which eliminate conduction contributions, are compared with normal Sawyer–Tower hysteresis loop measurements of the remanent polarization.

39] Scanning electrode localization of transport pathways in epithelial tissues

Publisher Summary This chapter describes the scanning electrode localization of transport pathways in epithelial tissues. Scanning micropipet methods measure voltage gradients in the medium above the epithelial surface. The voltage gradients are interpreted either implicitly or explicitly as current densities. The conversion factor from voltage gradient to current density is the conductivity of the medium, so that interpretation of the measurement as absolute current density is always subject to an assumption about the local conductivity of the medium. The rationale of the technique is that by measuring a voltage gradient over a short enough distance, close enough and perpendicular to the tissue surface, a good representation of the current density through the epithelial surface is obtained. The physics of electric fields implies that the representation becomes perfect as the distance approaches zero. Unfortunately, the signal-to-noise ratio concomitantly goes to zero. Thus, finite distances must be used, which places a limitation on the spatial resolution—that is, transepithelial current away from the point of recording contributes to the measurements. The extracellular recording approach has been taken using essentially two different methodologies in which either electrolytefilled glass microelectrodes or metal-filled electrodes have been employed.

Fertilization alters the spatial distribution and the density of voltage-dependent sodium current in the egg of the ascidian Boltenia villosa

The spatial distribution of voltage-dependent ionic currents was characterized in Boltenia villosa eggs before and after fertilization using two-microelectrode voltage clamp of paired animal-vegetal halves of eggs (merogones) made surgically. Major voltage-dependent conductances in the Boltenia egg are a transient inward Na current, a transient inward Ca current, and an inwardly rectifying K current. These currents were randomly distributed along the animal-vegetal axis in the unfertilized egg. When paired merogones (surgically prepared egg fragments) were made at the vegetal cap stage, 15–30 min after fertilization, Ca and K currents remained randomly distributed along the animal-vegetal axis. In contrast, the relative Na current density was found to be twofold lower in the vegetal vs the animal merogones made at the vegetal cap stage. By making pairs of merogones from unfertilized eggs and subsequently fertilizing one merogone of a pair, we showed that this change in current density ratio was due to a loss of absolute Na current density in the vegetal hemisphere shortly after fertilization. These results also show that this loss was intrinsic to the vegetal hemisphere, rather than being determined solely by the point of sperm entry. A second decrease in Na current was observed during the hour before first cleavage, 60–120 min after fertilization ( M. L. Block and W. J. Moody, 1987, J. Physiol. 393, 619–634), both in fertilized eggs and in animal merogones fertilized after isolation. This second loss of Na current was not observed in vegetal merogones fertilized after isolation or in either animal or vegetal merogones made from fertilized eggs at the vegetal cap stage. Possible mechanisms for the rapid (complete by 40 min after fertilization) and the late (occurring from ca. 60 to 120 minutes after fertilization) Na current losses are discussed.

Electromigration and low-frequency resistance fluctuations in aluminum thin-film interconnections

Low-frequency noise spectra originating from resistance fluctuations in Al films during electromigration were measured in the absolute temperature and current density intervals 327 \leq T \leq 396 K and 1.34 \times 10^{6} \leq j \leq 2.22 \times 10^{6} A/cm2. The values of S R , the resistance power spectral density, at 20 × 10-3Hz allowed the construction of an Arrhenius plot from which a grain-boundary activation energy value of about 0.6 eV was deduced. This value lies in the range of values found by other authors using different techniques. A first attempt to model the observed dependence of S R on j and T is also described.

Charge Carrier Transport in Oxidized Polyethylene

AbstractThe conduction currents of low‐density polyethylene containing additionally introduced C = O‐groups pass through maxima when stressed by a constant de‐voltage. This maximum is shifted to shorter times after application of the electric field with increasing temperature and field strength. The normalized current/time relationships are identical and they may be described in terms of a hopping process with a distribution of event times according to Scher/ Montroll. The shift of the maximum with temperature and independently the absolute current density both yield a thermal activation energy of 1.1 eV. This value is not to be understood as a mean activation energy characterizing the relaxation or event time spectrum, but represents essentially the depth of the dipolar traps (C = O‐groups) out of which the charge carriers have to be activated prior to their motion in the electric field.

Measurement of the absolute tunneling current density in field emission from tungsten(110)

The phenomenon of quantum-mechanical tunneling of an electron through a barrier in the potential energy has been well established in a variety of experiments. The quantity which is usually measured in these experiments is the rate of change of tunneling current and not the absolute current density. This paper reports on a direct measurement of the tunneling current density, which is found to be in good agreement with free-electron theory for W(110).

Simultaneous determination of atomic and molecular ion and metastable densities in a helium afterglow between 1 and 100 Torr

The experimental apparatus described allows simultaneous measurements of helium ion (He +, He 2 +) and metastable (He (2 3S), He 2 (2s 3Σu +)) densities in a He afterglow at room temperature. By properly considering both problems connected with sample extraction and calibration of the mass spectrometer itself, a method for measuring absolute ionic current densities at the wall is discussed. These measurements have been performed in a wider pressure range (1–100 Torr) than in previous studies. Experimental data are analised, not only in the purely exponential decay region (late afterglow), but also in the early afterglow period, enabling rate coefficients to be deduced for the various collision processes governing the relaxation of the plasma.

Nonlinear electromagnetic phenomena in a liquid with nonequilibrium electrical conductivity in an alternating magnetic field

On the basis of [1] this note examines nonlinear electromagnetic phenomena in a dense plasma brought about by the variation in its electrical conductivity as the electrical field changes. It is well known that the electrical conductivity depends on the electric field strength due to the following causes. The electrons in moving in the electric field receive energy from the field which may be considerable over the free path length. However it is difficult for this energy to be transferred to the heavy particles. In monatomic gases the energy exchange between electrons and heavy particles comes about basically as a result of elastic collisions. Thus a noticeable difference in electron and ion temperature, determined by the electron energy balance taking radiation losses into account, turns out to be possible even for relatively weak electric fields. In molecular gases, on the other hand, the fundamental energy exchange mechanism is the excitation of the rotational and oscillatory degrees of freedom of the molecules. Thus the electron energy in these gases is dissipated relatively easily, and the electron temperature is not observed to be noticeably higher than the atomic temperature. The concept of the characteristic “plasma field” Ep is introduced in [2], which is determined for an Isotropic plasma by the relation $$E_R = \sqrt {3kTme^{ - 2\delta } (\omega ^2 + v_0 ^2 )} .$$ Here k is the Boltzmann constant, T is the plasma temperature in the absence of a field, m and e are the electronic charge and mass, & is the mean fraction of energy transferred to a heavy particle by an electron on collision,ω is the frequency of field variation, ν0 is the electron-ion collision frequency in the absence of a field. In weak electromagnetic fields (E≪Ep) the plasma maintains thermodynamic equilibrium, and the electrical conductivity of the plasma is independent of the field. In strong electric fields (E≫Ep) there is a sharp difference of electron temperature and the voltage-current characteristics of the plasma become nonlinear. The question of nonequilibrium electrical conductivity has been fairly fully studied [3–5] as regards monatomic gas plasmas like argon and potassium mixtures. It was shown in [3] that for the plasmas which were considered the dependence of the electrical conductivity on the electric field with no magnetic field present could be satisfactorily described by a power function of the absolute current density, i.e., σ =c∣j∣ γ , where c is a function of the atomic temperature. This function has also been confirmed experimentally for an argon-potassium plasma for a temperature of the order of 0.2 eV and a pressure of the order of 1 atm. [3]. In the following we consider electromagnetic phenomena in a dense plasma with an electrical conductivity of the type σ =c∣j∣γ when it is in motion in a traveling magnetic field. It is assumed that the plasma parameters and limits of variation of the independent quantities (j, Te) are such that the function σ =c∣j∣γ is stable [4]. In addition the plasma is taken as having the properties of an ideal incompressible fluid. These last assumptions together with the assumption that the gradients of static pressure and pondermotive forces are only in the direction of plasma motion allow us to commence from the equations of electrodynamics.