Electric Charge Transfer Research Articles

Electric field induced tunable bistable conductance switching and the memory effect of thiol capped CdS quantum dots embedded in poly(methyl methacrylate) thin films

Experimental results on conductivity switching and appearance of hysteresis in the current–voltage characteristics of thiol (benzyl mercaptan)-capped CdS quantum dots (QDs) embedded in a poly(methyl methacrylate) (PMMA) matrix are presented in this manuscript. The dependence of switching behavior has been studied under different conditions such as sample cell temperature, scan speed of voltage, illumination of light of various intensities, film thickness, size of thiol-capped CdS QDs etc. The voltage at which the conductivity switching occurs i.e. threshold voltage (Vth) appearing in the current–voltage characteristic curve, decreases with the increasing sample cell temperature and also with increasing intensity of photoexcitations but Vth increases with the increasing scan rate of voltage and size of thiol-capped CdS QDs. Between forward and reverse bias sweeps, the switching events exhibit hierarchy of hysteresis loops. The area within the hysteresis loops decreases with increasing sample cell temperature and ultimately disappear at higher temperatures. The switching events can be tuned by changing the external parameter (experimental conditions) such as sample cell temperature, scan speed of bias voltage, irradiation of light, size of thiol-capped CdS QDs etc. The switching mechanism and appearance of hysteresis have been attributed to an electric field-induced charge transfer from the polymer to the thiol-capped CdS QDs. The nanocomposites of PMMA and thiol-capped CdS nanocrystallites may be suitable for polymer based memory devices.

Magnetic nano-oscillator driven by pure spin current

With the advent of pure-spin-current sources, spin-based electronic (spintronic) devices no longer require electrical charge transfer, opening new possibilities for both conducting and insulating spintronic systems. Pure spin currents have been used to suppress noise caused by thermal fluctuations in magnetic nanodevices, amplify propagating magnetization waves, and to reduce the dynamic damping in magnetic films. However, generation of coherent auto-oscillations by pure spin currents has not been achieved so far. Here we demonstrate the generation of single-mode coherent auto-oscillations in a device that combines local injection of a pure spin current with enhanced spin-wave radiation losses. Counterintuitively, radiation losses enable excitation of auto-oscillation, suppressing the nonlinear processes that prevent auto-oscillation by redistributing the energy between different modes. Our devices exhibit auto-oscillations at moderate current densities, at a microwave frequency tunable over a wide range. These findings suggest a new route for the implementation of nanoscale microwave sources for next-generation integrated electronics.

Instantaneous impedance evaluation of dissolution of AISI 304 stainless steel during intergranular corrosion

PurposeThe purpose of this paper is to focus on diversification between electrical parameters determined on the basis of instantaneous impedance measurements within the activation and reactivation scan of dissolution of sensitized AISI 304 stainless steel during a proceeding intergranular corrosion process.Design/methodology/approachThe investigations were carried out by means of dynamic electrochemical impedance spectroscopy (DEIS). DEIS measurements were conducted “on‐line” while the samples were polarized in agreement with a measurement procedure presented in the ASTM G108‐94 standard, in order to guarantee conditions equivalent with the DL‐EPR tests performed on AISI 304 stainless steel.FindingsPerformed researches revealed the advantages of the DEIS technique over standard double‐loop electrochemical potentiokinetic reactivation (DL‐EPR) tests in the field of intergranular corrosion investigations. Application of the DEIS technique made it possible to trace instantaneous changes in the examined system's impedance versus potential during the intergranular corrosion process. The form of recorded DEIS spectra and obtained distribution of measurement frequencies within the reactivation potential range were equivalent to those obtained for pure iron dissolution in sulfuric acid medium. As a result, instantaneous changes of electrical double layer capacitance and charge transfer resistance as a function of potential have been obtained in the range of activation and reactivation scans.Originality/valueThe paper provides information regarding diversification between the electrical double layer capacitance and the charge transfer resistance determined for sensitized AISI 304 stainless steel with respect to polarization conditions during the standard DL‐EPR test, which were obtained in order to evaluate the susceptibility to intergranular corrosion.

Mangiferin binding to serum albumin is non-saturable and induces conformational changes at high concentrations

The binding interaction between mangiferin (MGF), which a natural xanthone isolated from mangoes, and bovine serum albumin (BSA) was studied with absorbance and fluorescence spectroscopy, cyclic voltammetry and molecular modeling. The data were analyzed to assess the binding mechanism, effect of pH and ionic strength, conformational changes in the protein and electrical charge transfer involved. The MGF–BSA complex exhibited positive cooperativity with a 1:1 stoichiometry (Kd=0.38mmolL−1) for the first binding site and a non-saturable binding at high ligand concentrations. Furthermore, the data also suggest an increase in drug bioavailability in the acidic region and relatively low ionic strength values, which are close to physiological levels. The data suggest a specific electrostatic interaction together with hydrophobic effects and H-bonding displayed in MGF binding to the BSA IIA subdomain. Synchronous fluorescence spectra indicate that there are conformational changes in the polypeptide backbone upon ligand binding. Cyclic voltammetry indicates that there is an irreversible charge transfer between MGF and BSA that is modulated by diffusion on the electrode surface, where two electrons are transferred. These results can help the knowledge of the pharmacokinetic activities of natural or chemical xanthone-based drugs.

Synthesis of TiO2 nanoparticles using novel titanium oxalate complex towards visible light-driven photocatalytic reduction of CO2 to CH3OH

TiO2 nanoparticles (NPs) with controlled crystalline structure and morphology were synthesized by a facile hydrothermal method using a novel titanium oxalate complex. The structure, morphology, and spectral properties of the synthesized TiO2 NPs were characterized by X-ray diffraction, Raman spectroscopy, scanning/transmission electron microscopy, and UV–vis diffuse reflectance spectroscopy. The titania phases of anatase, rutile, or brookite can be easily tuned by tailoring the solution pH during reaction. Highly ordered flower-like rutile could be obtained with oxalic acid additive. The synthesized TiO2 catalysts showed excellent visible light absorption and remarkable photocatalytic activity for CO2 reduction to CH3OH under both UV–vis and visible light irradiation, mainly due to doped carbon and nitrogen. Bicrystalline anatase–brookite composite afforded maximum CH3OH yield, attributed mainly to the unique electrical band structures and efficient charge transfer between the two crystalline phases.

Modeling electrically active viscoelastic membranes.

The membrane protein prestin is native to the cochlear outer hair cell that is crucial to the ear's amplification and frequency selectivity throughout the whole acoustic frequency range. The outer hair cell exhibits interrelated dimensional changes, force generation, and electric charge transfer. Cells transfected with prestin acquire unique active properties similar to those in the native cell that have also been useful in understanding the process. Here we propose a model describing the major electromechanical features of such active membranes. The model derived from thermodynamic principles is in the form of integral relationships between the history of voltage and membrane resultants as independent variables and the charge density and strains as dependent variables. The proposed model is applied to the analysis of an active force produced by the outer hair cell in response to a harmonic electric field. Our analysis reveals the mechanism of the outer hair cell active (isometric) force having an almost constant amplitude and phase up to 80 kHz. We found that the frequency-invariance of the force is a result of interplay between the electrical filtering associated with prestin and power law viscoelasticity of the surrounding membrane. Paradoxically, the membrane viscoelasticity boosts the force balancing the electrical filtering effect. We also consider various modes of electromechanical coupling in membrane with prestin associated with mechanical perturbations in the cell. We consider pressure or strains applied step-wise or at a constant rate and compute the time course of the resulting electric charge. The results obtained here are important for the analysis of electromechanical properties of membranes, cells, and biological materials as well as for a better understanding of the mechanism of hearing and the role of the protein prestin in this mechanism.

Pickering emulsion fabrication and enhanced supercapacity of graphene oxide-covered polyaniline nanoparticles

Polyaniline/graphene oxide (PANI/GO) composites in a novel structure consisting of PANI nanoparticles covered by GO nanosheets are synthesized by means of Pickering emulsion polymerization for the first time. The Fourier transform infrared (FTIR) spectra indicate the main combination mode of the PANI/GO composite includes hydrogen bonding and π–π interactions between PANI and GO. The TGA and SEM results indicate the PANI/GO composite has better morphology stability than that of pure PANI. And thus the specific capacitance and cycling stability of the PANI/GO composite have been remarkably enhanced. The improved electrochemical performance may be attributed to the GO sheets not only improve the stability of the PANI nanoparticles, but also increase electronic conductivity and reduce electrical charge transfer resistance of the PANI/GO electrode.

Growth of long and aligned multi-walled carbon nanotubes on carbon and metal substrates

Well aligned, long and dense multi-walled carbon nanotubes (CNT) can be grown on both carbon fibres and any metal substrates compatible with the CNT synthesis temperature. The injection-CVD process developed involves two stages, including fibre pretreatment by depositing a SiO2-based sub-layer from an organometallic precursor followed by CNT growth from toluene/ferrocene precursor mixture. Carbon substrates, as well as metals, can easily be treated with this process, which takes place in the same reactor and does not need any handling in between the two stages. The aligned CNT carpets obtained are similar to the ones grown on reference quartz substrates. The CNT growth rate is fairly high (ca. 30 μm min−1) and it is possible to control CNT length by varying the CNT synthesis duration. The thickness of the SiO2-based sub-layer can be varied and is shown to have an influence on the CNT growth. This layer is assumed to play a diffusion barrier layer role between the substrate and the iron based catalyst nanoparticles producing CNT. The CNT anchorage to the carbon fibres has been checked and good overall adhesion proved, which is in favour of a good transfer of electrical charge and heat between the nanotubes and fibre.

Discussion on Hetero Charge Accumulation in Polyimide Film by Quantum Chemical Calculation

The hetero charge accumulated in Polyimide film, which was increased with increasing applied electric field, was observed by PEA equipment. In order to explain the mechanism of hetero charge accumulation depending on electric field, we proposed a new model combined Fermi-Dirac function (the electron-hole pair generation probability between band gap (about 2.5eV) of HOMO and LUMO under thermally equilibrium condition, which was obtained by Quantum Chemical Calculation) and Pool-Frenkel effect (the electron-hole pair generating probability affected by local electric field). In the process of electric charge transfer, the electron carrier is stayed at deep trap site (the molecular part of one benzene ring with imide groups) and the hole carrier is able to drift between shallow trap sites (the molecular part of ether bond between two benzene rings). From the different transfer properties between electron and hole, we could explain the mechanism of hetero charge accumulation in Polyimide film under high electric stress.

Faradaic impedance simulation of mediator-type enzyme-functional electrode

Theoretical equation of Faradaic impedance ( Z F) of a mediator-type enzyme-functional electrode is derived by introducing a new theoretical model in which the diffusion of mediator and substrate, enzymatic reaction and electrode reaction are considered. The typical Faradaic impedance spectrum describes the locus of the semicircle in the Nyquist plot, due to the electric double layer capacitance and charge transfer resistance of the mediator on the electrode surface. The finite diffusion impedance is also observed whose locus shows straight line of 45° to real axis and converges on real axis in the low frequency limit. In the present paper, the behaviors of the Faradaic impedance are discussed by changing in the simulation parameters including the electrode potential, diffusion coefficients, and enzymatic reaction constant.

Injection and transport of electric charge in a metal/copolymer structure

The dynamical processes of the electric charge injection and transport from a metal electrode to the copolymer are investigated by using a nonadiabatic dynamic approach. The simulations are performed within the framework of an extended version of the one-dimensional Su-Schrieffer-Heeger (SSH) tight-binding model. It is found that the electric charge can be injected into the copolymer by increasing the applied voltage. For different structures of the copolymer, the critical voltage biases are different and the motion of the injected electric charge in the copolymer varies obviously. For the copolymer with a barrier-well-barrier configuration, the injected electric charge forms a wave packet due to the strong electron-lattice interaction in the barrier, then comes into the well and will be confined in it under a weak electric field. Under a medium electric field, the electric charge can go across the interface of two homopolymers and enter into the other potential barrier. For the copolymer with a well-barrier-well configuration, only under strong enough electric field can the electric charge transfer from the potential well into the barrier and ultimately reach a dynamic balance.

Modelling of electroreduction of porous oxides in molten salt

A numerical model has been used to investigate the role of porosity, as well as the initial metallic content, in the kinetics of the direct electroreduction process. Equations of electrical charge transfer, interfacial reactions, and diffusion of oxygen in cathode are solved for a model system, with different levels of porosity. The results show that the overall reaction kinetics is an outcome of the interplay between oxygen diffusion and charge transfer. It has been found that increasing the porosity up to certain level accelerates the reduction process, resulting in lower reduction times, while further increase of porosity may lead to imperfect reduction. The numerical results thus imply existence of an optimum porosity level for real systems. Also, analysis of metal/oxide mixtures suggests that addition of metallic particles to the cathode has a positive effect only on the initial reduction rate.

Controlled enhancement of spin-current emission by three-magnon splitting

Spin currents--the flow of angular momentum without the simultaneous transfer of electrical charge--play an enabling role in the field of spintronics. Unlike the charge current, the spin current is not a conservative quantity within the conduction carrier system. This is due to the presence of the spin-orbit interaction that couples the spin of the carriers to angular momentum in the lattice. This spin-lattice coupling acts also as the source of damping in magnetic materials, where the precessing magnetic moment experiences a torque towards its equilibrium orientation; the excess angular momentum in the magnetic subsystem flows into the lattice. Here we show that this flow can be reversed by the three-magnon splitting process and experimentally achieve the enhancement of the spin current emitted by the interacting spin waves. This mechanism triggers angular momentum transfer from the lattice to the magnetic subsystem and modifies the spin-current emission. The finding illustrates the importance of magnon-magnon interactions for developing spin-current based electronics.

Jump Mechanism of Electric Charge Transfer in Gallium Arsenide Exposed to Polyenergy Implantation with H+Ions

The article presents the experimental results on electric conductivity investigations of gallium arsenide, exposed to polyenergy implantations with H ions, depending on alternating current frequency (50 Hz ÷ 5 MHz), testing temperature (liquid nitrogen temperature ÷373 K) and the temperature of 15 min isochronous annealing (293÷ 663 K). It has been found that the obtained dependences σ(Tp, f) result from a jump mechanism of electric charge transfer between the radiation defects that form in the process of ion implantation. Correlations between annealing of various types of radiation defects and conductivity characteristics σ(Tp, f) have also been discussed.

Effect of membrane mechanics on charge transfer by the membrane protein prestin

Prestin was found in the membrane of outer hair cells (OHCs) located in the cochlea of the mammalian inner ear. These cells convert changes in the membrane potential into dimensional changes and (if constrained) to an active electromechanical force. The OHCs provide the ear with the mechanism of amplification and frequency selectivity that is effective up to tens of kHz. Prestin is a crucial part of the motor complex driving OHCs. Other cells transfected with prestin acquire electromechanical properties similar to those in the native cell. While the mechanism of prestin has yet to be fully understood, the charge transfer is its critical component. Here we investigate the effect of the mechanics of the surrounding membrane on electric charge transfer by prestin. We simulate changes in the membrane mechanics via the corresponding changes in the free energy of the prestin system. The free energy gradient enters a Fokker-Planck equation that describes charge transfer in our model. We analyze the effects of changes in the membrane tension and membrane elastic moduli. In the case of OHC, we simulate changes in the longitudinal and/or circumferential stiffness of the cell's orthotropic composite membrane. In the case of cells transfected with prestin, we vary the membrane areal modulus. As a result, we show the effects of the membrane mechanics on the probabilistic characteristics of prestin-associated charge transfer for both stationary and high-frequency conditions. We compare our computational results with the available experimental data and find good agreement with the experiment.

Asymmetry of Polarization Reversal and Current-Voltage Characteristics of Pt/PZT-Film/Pt:Ti/SiO2/Si-Substrate Structures

The characterization of the asymmetries of bipolar charge-voltage and current-voltage loops of polarization reversal and unipolar current-voltage curves for Pt/PZT-film/Pt:Ti/SiO2/Si-substrate systems was performed in the dynamic mode. The asymmetry of local deformation-voltage loops was observed by piezoresponse force microscopy. The comparison of the dependences of introduced asymmetry factors for the bipolar charge-voltage and current-voltage loops and unipolar current-voltage curves on drive voltage indicates the interconnection of ferroelectric and electrical space charge transfer asymmetries.

Influence Assessment of Supply Gas Condition and Separator Structure on In-Plane Temperature Distribution and Power Generation Performance of Single Cell of PEFC

To clarify the mechanism of coupling phenomena such as heat, mass and electric charge transfer in a single-cell polymer electrolyte fuel cell (PEFC), we have measured in-plane temperature distribution in a single-cell PEFC by thermograph under power generation. We have investigated the influence of relative humidity and flow rate of supply gas and gas channel pitch of separator on in-plane temperature distribution and power generation performance. As a result, when the stoichiometric ratio of gas flow rate is set over 1.00 regardless of relative humidity of supply gas, the lower and higher temperature region is observed near the inlet and outlet of cell, respectively. This is caused by the convention heat transfer by excess oxygen flow in gas channel at the cathode. Total voltage is increased and the temperature in observation area is decreased with decreasing the gas channel pitch of separator regardless of relative humidity of supply gas under the experimental condition in this study.

Simulation of the dynamic (frequency-dependent) permeability and electrical conductivity in porous materials based on the concept of an ensemble of pores

The class of models of porous media based on the concept of an ensemble of pores with a certain distribution of the main geometrical parameters (e.g., pore size) is studied. The case of the saturation of the pore space with a single-phase multicomponent fluid mixture is studied with and without taking into account the transfer of electric charges. Transfer laws are derived from the condition of decreasing free energy. The hydrodynamic connectivity of pores (and electrical conductivity) is described by two kernels: one kernel describes the connectivity of pores in space, and the other describes the connectivity of pores in the elementary macrovolume. The frequency dependences of the dynamic permeability determined in laboratory experiments and the electrical conductivity of the porous medium were determined using the concept of an ensemble of pores. The relationship between the models considered and relaxation filtration models is established.

Identification and selection of unconstrained controls in power systems propelled by heat and mass transfer

This investigation provides an approach towards identification, selection or construction of certain unconstrained controls called Carnot variables which are particularly suitable for easy determining of power limits in various power systems. Applying these controls we develop a unified analysis of how various transfer phenomena (heat, mass and electric charge transfer) effect power limits in various energy converters, such as thermal, chemical and radiation engines and fuel cells. We present diverse pseudo-Carnot structures for converters’ efficiencies and apply them in estimating irreversible power limits in steady state systems. Power limits are determined for steady thermal systems propelled by differences of temperatures and for steady chemical systems driven by differences of chemical potentials. Radiation engines are treated as systems described by Stefan–Boltzmann equations. We show that both chemical and electrochemical energy generators (fuel cells) satisfy similar principles of modeling and apply similar schemes of power evaluation as thermal machines. Based on a systematic application of Carnot controls (as variables which satisfy identically the internal entropy constraint) we construct, in fact, a methodologically novel, coherent approach to the family of power systems. Such approach has the virtue of reducing the number of controls and is superior to the traditional approach, which works with an enlarged number of traditional constrained controls. We believe that, because of its formal lucidity, the new approach also improves our understanding of the role of various energy transfer phenomena in power systems.

Modelling of electromagnetic processes in system 'welding arc–evaporating anode' Part 2 – model of arc column and anode metal

A mathematical model of electromagnetic processes occurring in the 'arc column–anode region–evaporating anode' system is suggested. Electric charge transfer processes in the multicomponent plasma of the electric arc and in the bulk of the metallic anode are described using the Ohm's law and charge conservation law generalised for a case of discontinuity of the electric field potential at the boundary between the arc plasma and the anode surface. A procedure was developed for finding the numerical solution of the stated problem by the shock capturing method, allowing modelling of the electromagnetic processes in the 'welding arc–evaporating anode' system in the presence of a reverse potential jump in the anode region (negative anode drop). Results of modelling of the said processes for gas metal arc and plasma transferred arc welding of steel in an inert gas (Ar) atmosphere are given.