Junction Electrodes Research Articles

Simulation of Electric Field in Co-Field Treatment Chamber Using FEM

The technique of pulsed electric field is used for killing microbes causing food spoilage. This paper presents the calculation of electric field in co-field treatment chamber with the elliptic insulator type by the finite element method. The chamber diameter is 5 mm, and the insulator gap is 6 mm. The length of high-voltage electrode and the height of insulator were varied. The results show that too short voltage electrode length can generate high electric field spot at the junction of electrode and insulator. Increasing insulator height by 0.01 mm can decrease the maximum of the electric field by 1 percent. The results suggest that the dimensions of electrode and insulator are important to investigate the electric field for eliminating microbes.

Stimulating the Comfort of Textile Electrodes in Wearable Neuromuscular Electrical Stimulation.

Textile electrodes are becoming an attractive means in the facilitation of surface electrical stimulation. However, the stimulation comfort of textile electrodes and the mechanism behind stimulation discomfort is still unknown. In this study, a textile stimulation electrode was developed using conductive fabrics and then its impedance spectroscopy, stimulation thresholds, and stimulation comfort were quantitatively assessed and compared with those of a wet textile electrode and a hydrogel electrode on healthy subjects. The equivalent circuit models and the finite element models of different types of electrode were built based on the measured impedance data of the electrodes to reveal the possible mechanism of electrical stimulation pain. Our results showed that the wet textile electrode could achieve similar stimulation performance as the hydrogel electrode in motor threshold and stimulation comfort. However, the dry textile electrode was found to have very low pain threshold and induced obvious cutaneous painful sensations during stimulation, in comparison to the wet and hydrogel electrodes. Indeed, the finite element modeling results showed that the activation function along the z direction at the depth of dermis epidermis junction of the dry textile electrode was significantly larger than that of the wet and hydrogel electrodes, thus resulting in stronger activation of pain sensing fibers. Future work will be done to make textile electrodes have similar stimulation performance and comfort as hydrogel electrodes.

Stationary Josephson current as a tool to detect charge density waves in high-[formula omitted] oxides

Nonmonotonic and even sign-changing dependences on the temperature and the doping level were predicted for the stationary Josephson tunnel current Ic between superconductors with d-wave order parameter symmetry and partial gapping by charge density waves (CDWs). The junction electrodes were considered in the framework of the two-dimensional electron spectrum appropriate to high-Tc cuprates. The non-trivial behavior can be observed for certain relative electrode orientations. Hence, Ic-measurements in wide ranges of doping and temperature may serve as an indicator of CDW existence.

Electronic and thermal properties of Biphenyl molecules

Transport properties of a single Biphenyl molecule coupled to two contacts are studied. We characterise this system by a tight-binding Hamiltonian. Based on the non-equilibrium Green’s functions technique with a Landauer–Büttiker formalism the transmission probability, current and thermoelectrical power are obtained. We show that the Biphenyl molecule may have semiconductor behavior for certain values of the electrode–molecule–electrode junctions and different values of the angle between the two rings of the molecule. In addition, the density of states (DOS) is calculated to compare the bandwidths with the profile of the transmission probability. DOS allows us to explain the asymmetric shape with respect to the molecule’s Fermi energy.

A First Principle Study of the Massive TMR in Magnetic Tunnel Junction Using Fe<sub>3</sub>Al Heusler Alloy Electrodes and MgO Barrier

The massive tunnel magnetoresistane (TMR) is expected when Fe3Al Heusler alloy are used for magnetic electrodes in magnetic tunnel junction (MTJ). We demonstrate the Fe3Al/MgO/Fe3Al MTJ, which have good lattice matching interfaces. The electronic and transport properties of these system are systematically investigated by first principle calculation. The electronic band structure of Fe3Al Heusler alloy and MgO are represented for discussion spin filtering effect. Besides, the transmission conductance is calculated to study the spin tunneling effect. We found that the massive TMR is clearly achieved at zero-bias condition, and the TMR is decreased when the finite bias are applied. Thus, among ferromagnetic materials, the Fe3Al Heusler alloy will be good alternative to bcc-Fe based electrodes with MgO barrier for the MTJs beyond.

Magnetotransport properties of a few-layer graphene-ferromagnetic metal junctions in vertical spin valve devices

Magnetotransport properties were studied for the vertical spin valve devices with two junctions of permalloy electrodes and a few-layer graphene interlayer. The graphene layer was directly grown on the bottom electrode by chemical vapor deposition. X-ray photoelectron spectroscopy showed that the permalloy surface fully covered with a few-layer graphene is kept free from oxidation and contamination even after dispensing and removing photoresist. This enabled fabrication of the current perpendicular to plane spin valve devices with a well-defined interface between graphene and permalloy. Spin-dependent electron transport measurements revealed a distinct spin valve effect in the devices. The magnetotransport ratio was 0.8% at room temperature and increased to 1.75% at 50 K. Linear current-voltage characteristics and resistance increase with temperature indicated that ohmic contacts are realized at the relevant interfaces.

Glucose sensor based on conducting polyaniline nanowire electrode junction

In the present investigation, a glucose sensor based on conducting polyaniline nanowire electrode junction (CPNEJ) has been reported. The CPNEJ platform was modified by glucose oxidase by cross-linking in the presence of glutaraldehyde. The signal transduction mechanism of the sensor is based on the change in micro electrode junction conductance as a result of glucose oxidation induced change in the polymer redox state. Small size of CPNEJ sensor causes to regenerate enzyme naturally without need of redox mediators, as a result it consumes minimum amount of oxygen and also gives very fast response. This sensor exhibited good linear response range from 1 mM to 20 mM of glucose concentration with excellent sensitivity of 12 μA/mM.

Conducting polyaniline nanowire electrode junction

In this paper, a synthesis of conducting polyaniline nanowires electrode junction (CPNEJ) has been reported. Conducting polyaniline nanowires electrode junction on Si / SiO 2 substrate (having 3 μm gap between two gold microelectrodes) is prepared. Polyaniline nanowires with diameter (ca. 140 nm to 160 nm) were synthesized by one step electrochemical polymerization using galvanostatic (constant current) technique to bridge this gap. The surface morphology of CPNEJ was studied by scanning electron microscope (SEM). The synthesized CPNEJ is an excellent platform for biosensor applications.

Is Molecular Rectification Caused by Asymmetric Electrode Couplings or by a Molecular Bias Drop?

We investigate possible causes of molecular rectification in electrode–molecule–electrode junctions. By using a simple model and simulated conductance histograms, we show that a molecular bias drop is responsible for rectification; conversely, asymmetric molecule–electrode couplings do not directly result in rectification. Instead, the degree of coupling (a)symmetry can be observed in the line shapes of the conductance histograms used to experimentally assess the current–voltage properties of such molecular junctions. More coupling asymmetry leads to less positively skewed histogram peaks.

Correlation between amplitude of spin accumulation signals investigated by Hanle effect measurement and effective junction barrier height in CoFe/MgO/n+-Si junctions

Correlation between the amplitude of the spin accumulation signals and the effective barrier height estimated from the slope of the log (RA) - tMgO plot (RA: resistance area product, tMgO: thickness of MgO tunnel barrier) in CoFe/MgO/n+-Si junctions was investigated. The amplitude of spin accumulation signals increases with increasing effective barrier heights. This increase of the amplitude of spin accumulation is originated from the increase of the spin polarization (PSi) in Si. The estimated absolute values of PSi using three-terminal Hanle signals are consistent with those estimated by four-terminal nonlocal-magnetoresistance (MR) and two-terminal local-MR. To demonstrate large spin accumulation in Si bulk band and enhance the local-MR through Si channel, these results indicate that the increase of the effective barrier height at ferromagnet/(tunnel barrier)/n+-Si junction electrode is important.

STATE OFCoANDMnIN HALF-METALLIC FERROMAGNETCo2MnSiEXPLORED BY MAGNETIC CIRCULAR DICHROISM IN HARD X-RAY PHOTOELECTRON EMISSION AND SOFT X-RAY ABSORPTION SPECTROSCOPIES

The half-metallic Heusler compound Co2MnSi is a very attractive material for spintronic devices because it exhibits very high tunnelling magnetoresistance ratios. This work reports on a spectroscopic investigation of thin Co2MnSi films as they are used as electrodes in magnetic tunnel junctions. The investigated films exhibit a remanent in-plane magnetization with a magnetic moment of about 5 μBwhen saturated, as expected. The low coercive field of only 4 mT indicates soft magnetic behavior. Magnetic dichroism in emission and absorption was measured at the Co and Mn 2p core levels. The photoelectron spectra were excited by circularly polarized hard X-rays with an energy of 6 keV and taken from the remanently magnetized film. The soft X-ray absorption spectra were taken in an induction field of 4 T. Both methods yielded large dichroism effects. An analysis reveals the localized character of the electrons and magnetic moments attributed to the Mn atoms, whereas the electrons related to the Co atoms contribute an itinerant part to the total magnetic moment.

Electrical transport properties of nanocrystalline nonstoichiometric nickel ferrite at and above room temperature

The electrical transport properties of chemically prepared nanocrystalline nonstoichiometric nickel ferrite followed by high energy ball milling have been reported. The dc conductivity of the samples shows semiconducting behavior. The adiabatic small polaron model is most suitable for analyzing the dc conductivity at higher temperature, whereas at lower temperature Schnakenberg acoustical one phonon assisted hopping model is suitable. The frequency dependent conductivity has been described by power law σ/(f)∝fs and a maximum has been observed in the temperature behavior of ‘s’. The dielectric properties of the samples have been explained in terms of electric modulus vector. Both dc and ac activation energy have been measured for different samples. The metallic electrode and semiconductor junction formed Schottky diode and the diode parameters have been extracted from the capacitance–voltage characteristics.

Void Detection in Dielectric Films Using a Floating Network of Substrate-Embedded Electrodes

A sensor is developed for simple, in situ characterization of dielectric thermal interface materials (TIMs) at bond line thicknesses less than 100 μm. The working principle is based on the detection of regions of contrasting electric permittivity. An array of long, parallel electrodes is flush-mounted into each opposing substrate face of a narrow gap interface, and exposed to the gap formed between the two surfaces. Electrodes are oriented such that their lengthwise dimension in one substrate runs perpendicular to those in the other. A capacitance measurement taken between opposing electrodes is used to characterize the interface region in the vicinity of their crossing point (junction). The electric field associated with each electrode junction is numerically simulated and analyzed. Criteria are developed for the design of electrode junction geometries that localize the electric fields. The capacitances between floating-ground electrodes in the electrode sensor configuration employed give rise to a nontrivial network of interacting capacitances which strongly influence the measured response at any junction. A generalized solution for analyzing the floating network response is presented. The technique is used to experimentally detect thermal grease spots of 0.2 mm to 1.8 mm diameter within a 25 μm interface gap. It is necessary to use the generalized solution to the capacitance network developed in this work to properly delineate regions of contrasting permittivity in the interface gap region using capacitance measurements.

Activation behavior and dielectric relaxation of nanocrystalline zinc ferrite

We report the ac conductivity and dielectric relaxation studies of nanocrystalline zinc ferrite prepared by the ball milling. The real part of the complex ac conductivity is found to follow the universal dielectric response σ′(f)∝Tnfs and values of both s and n show an anomalous behavior. Both the magnitude of the temperature exponent ‘n’ and thermal activation energy for ac conduction strongly depends on frequencies. The dielectric constant exhibits strong temperature dependence at higher temperature and lower frequencies. The dielectric properties of the samples have been analyzed in terms of electric modulus vector. The complex impedance has also been modeled by an ideal equivalent circuit consisting of grain and grain boundary resistances and capacitances. Considering the formation of Schottky diode at the metallic electrode and semiconductor junction, the diode parameters like built in voltage and space charge density have been extracted from the capacitance-voltage characteristics.

A Proposal to Apply Effective Acceptor Level for Representing Increased Ionization Ratio of Mg Acceptors in Extrinsically Photon-Recycled GaN

An effective acceptor level (EAeff) for representing the increased ionization ratio in extrinsically photon-recycled p-type GaN is proposed. EAeff at 300 K in the range of 0.1360.145 eV is found to reproduce current/voltage characteristics of transmission-line-model patterns formed with GaN p-n junction epitaxial layers and electrode spacing of 320 μm when the p-n diode current flowing through an 80×100-μm electrode is 90 mA. When EAeff is decreased from 0.160 eV to 0.145 eV, the on-resistance of 18×100-μm GaN bipolar transistors is predicted to be reduced by more than 50%.

Nonequilibrium Ionic Response of Biased Mechanically Controllable Break Junction (MCBJ) Electrodes.

Novel experimental techniques allow for the manipulation and interrogation of biomolecules between metallic probes immersed in micro/nanofluidic channels. The behavior of ions in response to applied fields is a major issue in the use of these techniques in sensing applications. Here, we experimentally and theoretically elucidate the behavior of background currents in these systems. These large currents have a slowly decaying transient response, as well as noise that increases with ionic concentration. Using mechanically controllable break junctions (MCBJ), we study the ionic response in nanogaps with widths ranging from a few nanometers to millimeters. Moreover, we obtain an expression for the ionic current by solving time-dependent Nernst–Planck and Poisson equations. This expression shows that after turning on an applied voltage, ions rapidly respond to the strong fields near the electrode surface, screening the field in the process. Ions subsequently translocate in the weak electric field and slowly relax within the diffusion layer. Our theoretical results help to explain the short- and long-time behavior of the ionic response found in experiments, as well as the various length scales involved.

Mathematical Model of Solid Food Pasteurization by Ohmic Heating: Influence of Process Parameters

Pasteurization of a solid food undergoing ohmic heating has been analysed by means of a mathematical model, involving the simultaneous solution of Laplace's equation, which describes the distribution of electrical potential within a food, the heat transfer equation, using a source term involving the displacement of electrical potential, the kinetics of inactivation of microorganisms likely to be contaminating the product. In the model, thermophysical and electrical properties as function of temperature are used. Previous works have shown the occurrence of heat loss from food products to the external environment during ohmic heating. The current model predicts that, when temperature gradients are established in the proximity of the outer ohmic cell surface, more cold areas are present at junctions of electrodes with lateral sample surface. For these reasons, colder external shells are the critical areas to be monitored, instead of internal points (typically geometrical center) as in classical pure conductive heat transfer. Analysis is carried out in order to understand the influence of pasteurisation process parameters on this temperature distribution. A successful model helps to improve understanding of these processing phenomenon, which in turn will help to reduce the magnitude of the temperature differential within the product and ultimately provide a more uniformly pasteurized product.

Carbon tips for all-carbon single-molecule electronics.

We present here an exhaustive ab initio study of the use of carbon-based tips as electrodes in single-molecule junctions. Motivated by recent experiments, we show that carbon tips can be combined with other carbon nanostructures, such as graphene, to form all-carbon molecular junctions with molecules like benzene or C60. Our results show that the use of carbon tips can lead to relatively conductive molecular junctions. However, contrary to junctions formed with standard metals, the conductance traces recorded during the formation of the all-carbon single-molecule junctions do not exhibit clear conductance plateaus, which can be attributed to the inability of the hydrogenated carbon tips to form chemical bonds with the organic molecules. Additionally, we explore here the use of carbon tips for scanning tunneling microscopy and show that they are well suited for obtaining sample images with atomic resolution.

Anomalous Effect of Flow Rate on the Electrochemical Behavior at a Liquid|Liquid Interface under Microfluidic Conditions

We have investigated the oxidation of ferrocene at a flowing organic solvent|aqueous electrolyte|solid electrode junction in a microfluidic setup using cyclic voltammetry and fluorescent laser scanning confocal microscopy. At low flow rates the oxidation current decreases with increasing flow, contrary to the Levich equation, but at higher flow rates the current increases linearly with the cube root of the flow rate. This behavior is explained using a simple model postulating a smallest effective width of the three-phase junction, which after fitting to the data comes to be ca. 20 μm. The fluorescence microscopy reveals mixing of the two phases close to the PDMS cover, but the liquid|liquid junction is stable close to the glass support. This study shows the importance of the solid|liquid|liquid junctions for the behavior of multiphase systems under microfluidic conditions.

Strain on field effect transistors with single–walled–carbon nanotube network on flexible substrate

We have systematically analyzed the effect of strain on the electrical properties of flexible field effect transistors with a single-walled carbon nanotube (SWCNT) network on a polyethersulfone substrate. The strain was applied and estimated at the microscopic scale (<1 μm) by using scanning electron microscope (SEM) equipped with indigenously designed special bending jig. Interestingly, the strain estimated at the microscopic scale was found to be significantly different from the strain calculated at the macroscopic scale (centimeter-scale), by a factor of up to 4. Further in-depth analysis using SEM indicated that the significant difference in strain, obtained from two different measurement scales (microscale and macroscale), could be attributed to the formation of cracks and tears in the SWCNT network, or at the junction of SWCNT network and electrode during the strain process. Due to this irreversible morphological change, the electrical properties, such as on current level and field effect mobility, lowered by 14.3% and 4.6%, respectively.