Mobile Ionic Charge Research Articles

Charge Transport Properties of a Protic Ionic Liquid studied by Dielectric Spectroscopy

Three simple models including the Debye type model, Cole-Cole type model and Einstein-Smoluchowski model are used to determine the number density ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> , charge carrier density) and the mobilities (μ) of the charge carriers separately from the dielectric spectroscopy. By comparing them, the Cole-Cole type model appears to evaluate charge transport properties very well while the Debye type model doesn’t work for a complex ionic system. The temperature dependence of the mobility exhibits a Vogel-Fulcher-Tammann (VFT) behavior, while the number density of mobile charges is almost insensitive to the temperature. However, the fraction of available (mobile) charge carriers is found to be surprisingly low (~6 % at 25 °C), which can be attributed to charge immobilization in molecular aggregates. A subtle step in the mobility and (mobile) charge density around -10 °C is discussed in terms of a “hidden” phase transition possibly affecting the molecular organization in such aggregates. Increasing the fraction of mobile ionic charges by preventing aggregation would be an effective strategy to enhance σ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DC</sub> of the protic ionic liquid trioctylammonium methanesulfonate ([TOA][OMs]).

The relationship between ionic-electronic coupling and transport in organic mixed conductors.

Organic mixed ionic-electronic conductors (OMIECs) directly convert between ionic and electronic charge through electrochemical (de)doping, enabling a wide range of applications in bioelectronics, neuromorphic computing, and energy storage and conversion. While both ionic and electronic transport are individually well characterized, their combined transport has been difficult to describe self-consistently. We use in situ measurements of electrochemical (de)doping of an archetypal OMIEC to inform a quasi-field drift-diffusion model, which accurately captures experimentally measured ion transport across a range of potentials. We find that the chemical potential of holes, which is modulated by changes in doping level, represents a major driving force for mixed charge transport. Using numerical simulations at device-relevant time scales and potentials, we find that the competition between hole drift and diffusion leads to diffuse space charge regions despite high charge densities. This effect is unique to mixed conducting systems where mobile ionic charges can compensate the accumulation or depletion of electronic charge, thereby screening electrostatic driving forces.

Driftfusion: an open source code for simulating ordered semiconductor devices with mixed ionic-electronic conducting materials in one dimension

The recent emergence of lead-halide perovskites as active layer materials for thin film semiconductor devices including solar cells, light emitting diodes, and memristors has motivated the development of several new drift-diffusion models that include the effects of both electronic and mobile ionic charge carriers. In this work we introduce Driftfusion, a versatile simulation tool built for modelling one-dimensional ordered semiconductor devices with mixed ionic-electronic conducting layers. Driftfusion enables users to model devices with multiple, distinct, material layers using up to four charge carrier species: electrons and holes plus up to two ionic species. The time-dependent carrier continuity equations are coupled to Poisson’s equation enabling transient optoelectronic device measurement protocols to be simulated. In addition to material and device-wide properties, users have direct access to adapt the physical models for carrier transport, generation and recombination. Furthermore, a discrete interlayer interface approach circumvents the requirement for boundary conditions at material interfaces and enables interface-specific properties to be introduced.

Mobile ions determine the luminescence yield of perovskite light-emitting diodes under pulsed operation

The external quantum efficiency of perovskite light-emitting diodes (PeLEDs) has advanced quickly during the past few years. However, under pulsed operation, an operation mode which is important for display and visible light communication, the performance of PeLEDs changes a lot and requires in-depth understanding to facilitate these applications. Here, we report the response of PeLEDs under pulsed operation in the range of 10 Hz to 20 kHz. Beyond transient effects in the low frequencies, we find that for higher frequencies (>500 Hz) the transient electroluminescence intensity depends strongly on the duty cycle. This feature is much more pronounced and of different origin than that in conventional LEDs. We rationalise our experimental observations using a mathematical model and assign these features to the effect of mobile ionic charges in the perovskite. Our work also provides important implications for the operation of PeLEDs under the steady state, where accumulation of mobile ions at the interfaces could be beneficial for high electroluminescence yields but harmful for the long-term stability.

Study of mobile ionic charges by thermally stimulated currents in 4H-SiC MOS capacitors with thick SiO2 layers

Thick oxides deposited on 4H-SiC epilayers to form Metal-Oxide-Semiconductor capacitors have been studied by Capacitance-Voltage (C-V) and Thermally Stimulated Ionic Current (TSIC) measurements. The very negative flatband voltage VFB in regards to the theoretical value indicates the presence in the oxide of a large number of positive charges. Positive mobile charges are responsible for a large part of this unusual VFB, as shown by the hysteresis cycle on C-V characteristics. Four traps have been detected at the gate/oxide interface and three at the oxide/SiC interface. One of them is similar to a trap already detected in MOS 3C-SiC and 6H-SiC structures. The others seem rather different. Dependences of the detrapping energy of mobile ions in these traps have been determined. Secondary Ion Mass Spectroscopy analyses have shown the presence of K+ and Na+ ions in the oxide in concentrations that agree well with the values obtained by TSIC measurements.

Multiscale modeling of the ionic conductivity of acceptor doped ceria

The ionic conductivity of acceptor doped ceria is strongly influenced by grain boundaries and interfaces, with most experiments showing a conductivity decrease in these regions. Classical models explain this observation by the formation of space charge layers, that are depleted of mobile ionic charge carriers. However, some experiments demonstrate an increase in ionic conductivity and recent models show that the space charge layers can also be enriched in mobile ionic species. Because of these discrepancies, it is still not certain whether nanocrystalline or thin film ceria can offer superior ionic conductivity or not. Recently, we have demonstrated by means of Monte Carlo simulations that the ionic conductivity in space charge layers can indeed exceed the bulk value. In this work, we combine these Monte Carlo simulations with a continuum model to predict charge carrier concentration profiles. This multiscale approach allows for a realistic prediction of the grain boundary ionic conductivity.

Identification of recombination losses and charge collection efficiency in a perovskite solar cell by comparing impedance response to a drift-diffusion model.

Interpreting the impedance response of perovskite solar cells (PSCs) is significantly more challenging than for most other photovoltaics. This is for a variety of reasons, of which the most significant are the mixed ionic-electronic conduction properties of metal halide perovskites and the difficulty in fabricating stable, and reproducible, devices. Experimental studies, conducted on a variety of PSCs, produce a variety of impedance spectra shapes. However, they all possess common features, the most noteworthy of which is that they have at least two features, at high and low frequency, with different characteristic responses to temperature, illumination and electrical bias. The impedance response has commonly been analyzed in terms of sophisticated equivalent circuits that can be hard to relate to the underlying physics and which complicates the extraction of efficiency-determining parameters. In this paper we show that, by a combination of experiment and drift-diffusion (DD) modelling of the ion and charge carrier transport and recombination within the cell, the main features of common impedance spectra are well reproduced by the DD simulation. Based on this comparison, we show that the high frequency response contains all the key information relating to the steady-state performance of a PSC, i.e. it is a signature of the recombination mechanisms and provides a measure of charge collection efficiency. Moreover, steady-state performance is significantly affected by the distribution of mobile ionic charge within the perovskite layer. Comparison between the electrical properties of different devices should therefore be made using high frequency impedance measurements performed in the steady-state voltage regime in which the cell is expected to operate.

Interfacial traps and mobile ions induced flatband voltage instability in 4H-SiC MOS capacitors under bias temperature stress

Bias temperature stresses (BTSs) are critical factors that cause severe threshold voltage (Vth) instability in silicon carbide (SiC) metal-oxide-semiconductor (MOS) devices. In this work, we studied the behavior of flatband voltage (Vfb) instability in 4H-SiC MOS capacitors under various BTSs from low temperature (LT) to high temperature (HT) considering the combined effects of interfacial traps and mobile ions. Results showed that nitrogen and nitrogen–hydrogen plasma passivation improved the Vfb instability. The initial sweeping gate voltage determined the direction of Vfb shift. BTSs from LT to HT induced different capacitance–voltage hysteresis characteristics. The Vfb shift was further separated according to the contribution of the interface trapped, oxide trapped, and mobile ionic charges. At LT, the charge trapping dominated the shift behavior. The interface trap density was also extracted by another high-frequency and quasi-static method, which was the same as the separated interface trap density at 100 K, confirming the separation correctness of Vfb shift. At room temperature, charge trapping and mobile ions with very weak mobility contributed to the Vfb shift. At HT, mobile ions that counteracted the charge-trapping effect determined the Vfb shift, although the additional traps were activated in the interface and oxide. Physical models of Vfb instability under different temperature stresses were proposed. Finally, we chose the 100 K, 273 K, and 423 K to analyze gate bias stresses and stress time induced Vfb instabilities as well as their mechanisms.

Identifying Dominant Recombination Mechanisms in Perovskite Solar Cells by Measuring the Transient Ideality Factor

The ideality factor determined by measuring the open circuit voltage (VOC) as function of light intensity is often used as a means to identify the dominant recombination mechanism in solar cells. However, applying this Suns-VOC technique to perovskite cells is problematic since the VOC evolves with time in a way which depends on the previously applied bias (Vpre), the light intensity, and the device architecture/processing. Here we show that the dominant recombination mechanism in two structurally similar CH3NH3PbI3 devices containing either mesoporous Al2O3 or TiO2 layers can be identified from the signature of the transient ideality factor following application of a forward bias, Vpre, to the device in the dark. The transient ideality factor, is measured by monitoring the temporal evolution of VOC at different light intensities. The initial values of the transient ideality were consistent with corresponding photoluminescence vs intensity as well as electroluminescence vs current density measurements. Time-dependent simulations of the measurement on modelled devices, which include the effects of mobile ionic charge, show that Shockley Read Hall (SRH) recombination through deep traps at the charge collection interfaces is dominant in both devices. Using transient photovoltage measurements superimposed on the evolving VOC of bifacial devices we further show that the charge collection interface extends throughout the mesoporous TiO2 layer, consistent with a transient ideality signature corresponding to SRH recombination in the bulk of the film. This information could not be inferred from an ideality factor determined from only steady-state VOC values. The method we have developed will be useful for identifying performance bottlenecks in new variants of perovskite devices by comparison with the transient ideality signatures we have predicted for a range of possible recombination schemes.

Ionic conductivity of space charge layers in acceptor doped ceria

The ionic conductivity of acceptor doped ceria is strongly influenced by grain boundaries and interfaces. Most experiments show a decrease in ionic conductivity and an increase in electronic conductivity in these regions. Classical models explain this observation by the formation of space charge layers that are depleted of mobile ionic charge carriers and enriched in small polarons. However, some experiments demonstrate an increase in ionic conductivity and recent models show that the space charge layers can also be enriched in mobile ionic species. Because of these contradictions, it is still not clear whether nanocrystalline or thin film ceria can offer superior ionic conductivity or not. To aid this debate, we calculate the ionic conductivity of yttrium doped ceria in regions of net charge density using kinetic Monte Carlo simulations. Through an appropriate choice of the charge densities, these calculations allow to demarcate the possible conductivity gains from space charge layers.

Evidence for ion migration in hybrid perovskite solar cells with minimal hysteresis.

Ion migration has been proposed as a possible cause of photovoltaic current–voltage hysteresis in hybrid perovskite solar cells. A major objection to this hypothesis is that hysteresis can be reduced by changing the interfacial contact materials; however, this is unlikely to significantly influence the behaviour of mobile ionic charge within the perovskite phase. Here, we show that the primary effects of ion migration can be observed regardless of whether the contacts were changed to give devices with or without significant hysteresis. Transient optoelectronic measurements combined with device simulations indicate that electric-field screening, consistent with ion migration, is similar in both high and low hysteresis CH3NH3PbI3 cells. Simulation of the photovoltage and photocurrent transients shows that hysteresis requires the combination of both mobile ionic charge and recombination near the perovskite-contact interfaces. Passivating contact recombination results in higher photogenerated charge concentrations at forward bias which screen the ionic charge, reducing hysteresis.

Chemical diffusion and defect chemistry of grain boundaries in n-type barium titanate ceramics

Conductivity relaxation experiments have been performed on n-type barium titanate ceramics, co-doped with Y (donor) and Mn (acceptor), as a function of temperature (700–900°C) and oxygen partial pressure (0.001–1.0bar) by employing the van der Pauw technique. The chemical diffusion process owing to a change of the oxygen partial pressure in the surrounding atmosphere can be described by fast transport of oxygen vacancies along the grain boundaries (mainly core regions) and slow diffusion of cation vacancies into adjacent bulk regions (including space charge layers). A careful analysis of the experimental conductivity relaxation experiments allows the determination of the chemical diffusion coefficient for oxygen along grain boundary core regions with typical values in the range of 10−8 to 10−9cm2s−1 and an activation energy of 0.9eV (900>T/°C>700). Furthermore, the partial pressure dependence of the electronic conductivity can be interpreted by means of a defect chemical model involving grain boundary core regions where Mn is segregated and oxygen vacancies are the decisive mobile ionic charge carriers.

Ferroelectric domain freezing and charge conduction in proton-irradiated K(H0.36D0.64)2PO4

We have studied the effects of proton irradiation in K(H0.36D0.64)2PO4 single crystals by employing impedance spectroscopy. Frequency-dependent dielectric loss measurements allowed us to investigate changes in the domain wall dynamics of a proton-irradiated crystal with a ferroelectric phase transition temperature raised by 5 K. Thus, the increase caused by proton irradiation in the activation energy of the domain freezing in the direction of the hydrogen bonds was found to be significantly greater than in the case of KH2PO4. Furthermore, the temperature dependence of the power-law exponent n in the frequency-dependent electrical conductivity in the proton-conducting systems manifested changes arising from the proton irradiation in the interactions between the mobile ionic (proton) charges and their environments.

The Poisson–Boltzmann equation and the charge separation phenomenon at the silica-water interface: A holistic approach

The Poisson Boltzmann equation is known for its success in describing the Debye layer that arises from the charge separation phenomenon at the silica/water interface. However, by treating only the mobile ionic charges in the liquid, the Poisson Boltzmann equation accounts for only half of the electrical double layer, with the other half, the surface charge layer, being beyond its computational domain. In this work, we take a holistic approach to the charge separation phenomenon at the silica/water interface by treating, within a single computational domain, the electrical double layer that comprises both the mobile ions in the liquid and the surface charge density. The Poisson Nernst Planck equations are used as the rigorous basis for our methodology. The holistic approach has the advantage of being able to predict surface charge variations that arise either from the addition of salt and acid to the liquid, or from the decrease of the liquid channel width to below twice the Debye length. As the electrical double layer must be overall neutral, we use this constraint to derive both the form of the static limit of the Poisson Nernst Planck equations, as well as a global chemical potential that replaces the classical zeta potential as the boundary value for the PB equation, which can be re-derived from our formalism. We present several predictions of our theory that are beyond the framework of the PB equation alone, e.g., the surface capacitance and the so-called pK and pL values, the isoelectronic point at which the surface charge layer is neutralized, and the appearance of a Donnan potential that arises from the formation of an electrical double layer at the inlet regions of a nano-channel connected to the bulk reservoir. All theory predictions are shown to be in good agreement with the experimental observations.

IJARCCE - Computer and Communication Engineering

Enough aptitude ability addressable memory (CAM) is a key element in wide variety of applications. A designing impoverish inskilfulness of such systems is the complexities of scaling MOS transistors. Converges of choice technologies, which are well-matched regarding CMOS processing may allow extension of Moore's law for a precedent-setting years. This mix provides a newheadway predisposition for the stumbling-block and modeling of memristor based CAM (MCAM) using a combination of MOS devices to form a core of a memory or logic cell that forms the building block of the CAM manufacture. The non labiledescription and the nanoscale geometry rack up fro concord of the memristor increases the peignoir council with CMOS processing technology , provides for the new approaches towards power management through disabling CAM blocks without loss of stored data, reduces power indulgence, and has scope for speed improvement as the technology matures. The memristor behaves as a switch, greatly breath a air. Putting, whimper like the transistor, it is a unite decreed instead of three-terminal device and does not need power to retain either of its two states. A memristor unsteadiness its partizan between two values and this achieved via the movement of mobile ionic charge within an oxide layer. This applicability influences the architecture of CAM systems, there is no loss of stored data even if the power supply of CAM blocks are disabled.Sake, memristor- based CAM cells have the potential for major saving in power dissipation.

Electrokinetics at Aqueous Interfaces without Mobile Charges

We theoretically consider the possibility of using electric fields in aqueous channels of cylindrical and planar geometry to induce transport in the absence of mobile ionic charges. Using the Navier-Stokes equation, generalized to include the effects of water spinning, dipole orientation and relaxation, we show analytically that pumping of a dipolar liquid through an uncharged hydrophobic channel can be achieved by injecting torque into the liquid, based on the coupling between molecular spinning and fluid vorticity. This is possible using rotating electric fields and suitably chosen interfacial boundary conditions or transiently by suddenly switching on a homogeneous electric field. A static electric field, however, does not induce a steady state flow in channels, irrespective of the geometry. Using molecular dynamics (MD) simulations, we confirm that static fields do not lead to any pumping, in contrast to earlier publications. The pumping observed in MD simulations of carbon nanotubes and oil droplets in a static electric field is tracked down to an imprudent implementation of Lennard-Jones interaction truncation schemes.

Performance of perovskite-related oxide cathodes in contact with lanthanum silicate electrolyte

The cathodic performance of selected mixed-conducting electrodes, including perovskite-type SrMn 0.6Nb 0.4O 3 − δ , Sr 0.7Ce 0.3Mn 0.9Cr 0.1O 3 − δ and Gd 0.6Ca 0.4Mn 0.9Ni 0.1O 3 − δ , and Ruddlesden–Popper La 2Ni 0.5Cu 0.5O 4 + δ , LaSr 2Mn 1.6Ni 0.4O 7 − δ , La 4Ni 3 − x Cu x O 10 − δ ( x = 0–0.1) and La 3.95Sr 0.05Ni 2CoO 10 − δ , was evaluated in contact with apatite-type La 10Si 5AlO 26.5 solid electrolyte at 873–1073 K and atmospheric oxygen pressure. The electrochemical activity of porous nickelate-based layers was found to correlate with the concentration of mobile ionic charge carriers and bulk oxygen transport, thus lowering in the series La 4Ni 2.9Cu 0.1O 10 − δ > La 4Ni 3O 10 − δ > La 3.95Sr 0.05Ni 2CoO 10 − δ and decreasing on copper doping in K 2NiF 4-type La 2Ni 1 − x Cu x O 4 − δ . The relatively high overpotentials of nickelate-based cathodes, varying in the range − 240 to − 370 mV at 1073 K and current density of − 200 mA/cm 2, are primarily associated with surface diffusion of silica from La 10Si 5AlO 26.5, which partially blocks the electrochemical reaction zone. As compared to the intergrowth nickelate materials, the manganite-based electrodes exhibit substantially worse electrochemical properties, in correlation with the level of oxygen-ionic and electronic conduction in Mn-containing phases. The effects of cation interdiffusion between the cell components as a performance-deteriorating factor are briefly discussed.

Metal-Insulator-Gap-Insulator-Semiconductor Structure for Sensing Devices

We report on the use of sensing devices that have a metal-insulator-gap-insulator-semiconductor structure. We have used capacitance-voltage measurements from a metal-insulator-gap-insulator-semiconductor sensing device to characterize different pH solutions and deoxyribonucleic acid (DNA) solutions. Hysteresis in the capacitance-voltage curves results from mobile ionic charges in the solutions and the influence of changes on the sensing surface condition. As the pH decreases in the pH range of 2.7 to 7.0, the flatband voltage shift toward the negative voltage increases. The differences in the flatband voltage shift in capacitance-voltage curves are related to the mobile ionic charge density in solutions with different pH values or DNA molecules.

Preparation and electrical properties of Cr 2O 3 gate insulator embedded with Fe dot

We investigated the electrical properties of a metal (Au)/insulator (magneto-electric materials: Cr 2O 3)/magnetic materials (Fe)/tunnel layer (Cr 2O 3)/semiconductor (Si) capacitor. This capacitor shows the typical capacitance–voltage ( C– V) properties of an Si-MIS capacitor with hysteresis depending on the Fe dispersibility which is determined by the deposition condition. The C– V curve of the only sample having a 0.5 nm Fe layer was seen to have a hysteresis window with a clockwise trace, indicating that electrons have been injected into the ultra-thin Fe layer. The samples having Fe layers of other thicknesses show a counterclockwise trace, which indicates that the film has mobile ionic charges due to the dispersed Fe. These results indicated that the charge-injection site, which works as a memory, in the Cr 2O 3 can be prepared by Fe insertion, which is deposited using well-controlled conditions. The results also revealed the possibility of an MIS capacitor containing both ferromagnetic materials and an ME insulating layer in a single system.

Metal-Insulator-Gap-Insulator-Semiconductor structure for Biological Sensors

A metal-insulator-gap-insulator-semiconductor sensing device has been characterized in different pH solutions and with different single strand DNA solutions by capacitance-voltage measurements. The capacitance-voltage curves show the difference from pH and the difference from DNA base by hysteresis and flat band voltage shift due to mobile ionic charge in the solution. As the pH decreases, the flat band voltage shift increases in the pH range of 2.7 to 7.0. The hysteresis in the capacitance-voltage curves shows the influence of ionic charge in the solutions and the change of the sensing surface condition. The difference of the flat band voltage shift in the capacitance-voltage curves is related to the mobile ionic charge in the solutions due to pH or DNA molecules.