Electrical Capacitance Measurements Research Articles

Changes in Ion Transport across Biological Membranes Exposed to Particulate Matter.

The cells of living organisms are surrounded by the biological membranes that form a barrier between the internal and external environment of the cells. Cell membranes serve as barriers and gatekeepers. They protect cells against the entry of undesirable substances and are the first line of interaction with foreign particles. Therefore, it is very important to understand how substances such as particulate matter (PM) interact with cell membranes. To investigate the effect of PM on the electrical properties of biological membranes, a series of experiments using a black lipid membrane (BLM) technique were performed. L-α-Phosphatidylcholine from soybean (azolectin) was used to create lipid bilayers. PM samples of different diameters (<4 (SRM-PM4.0) and <10 μm (SRM-PM10) were purchased from The National Institute of Standards and Technology (USA) to ensure the repeatability of the measurements. Lipid membranes with incorporated gramicidin A (5 pg/mL) ion channels were used to investigate the effect of PM on ion transport. The ionic current passing through the azolectin membranes was measured in ionic gradients (50/150 mM KCl on cis/trans side). In parallel, the electric membrane capacitance measurements, analysis of the conductance and reversal potential were performed. Our results have shown that PM at concentration range from 10 to 150 μg/mL reduced the basal ionic current at negative potentials while increased it at positive ones, indicating the interaction between lipids forming the membrane and PM. Additionally, PM decreased the gramicidin A channel activity. At the same time, the amplitude of channel openings as well as single channel conductance and reversal potential remained unchanged. Lastly, particulate matter at a concentration of 150 μg/mL did not affect the electric membrane capacity to any significant extent. Understanding the interaction between PM and biological membranes could aid in the search for effective cytoprotective strategies. Perhaps, by the use of an artificial system, we will learn to support the consequences of PM-induced damage.

Freestanding lipid bilayer tensiometer for the study of mechanosensitive ion channels

Mechanical forces modify the cell membrane potential by opening mechanosensitive ion channels. We report the design and construction of a lipid bilayer tensiometer to study channels that respond to lateral membrane tension, [Formula: see text] , in the range 0.2 to 1.4 [Formula: see text] (0.8 to 5.7 [Formula: see text] ). The instrument consists of a black-lipid-membrane bilayer, a custom-built microscope, and a high-resolution manometer. Values of [Formula: see text] are obtained from the determination of the bilayer curvature as a function of applied pressure by means of the Young-Laplace equation. We demonstrate that [Formula: see text] can be determined by calculating the bilayer radius of curvature from fluorescence microscopy imaging or from measurements of the bilayer's electrical capacitance, both yielding similar results. Using electrical capacitance, we show that the mechanosensitive potassium channel TRAAK responds to [Formula: see text] , not curvature. TRAAK channel open probability increases as [Formula: see text] is increased from 0.2 to 1.4 [Formula: see text] but open probability never reaches 0.5. Thus, TRAAK opens over a wide range of [Formula: see text] , but with a tension sensitivity about one-fifth that of the bacterial mechanosensitive channel MscL.

Effect of CuO/rGO and ZnO/rGO Hybrid Additional Layers on Supercapacitor Performance

Increasing the specific electrical capacitance of supercapacitors has been received great attention from both researchers and industry. Herein, how to achieve this by coating the surface of reduced graphene oxide (rGO) with copper(II) oxide (CuO) and zinc oxide (ZnO) is reported. The CuO/rGO and ZnO/rGO hybrid layers were prepared via chemical reactions between graphene oxide (GO) and salts of copper and zinc, respectively. The crystallographic structures and surface morphologies of composite materials were studied by using X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. Cyclic voltammetry (CV) and electrical capacitance measurements were used to analyze the electrochemical properties of the composites. The results show that CuO and ZnO increased the specific electrical capacitance of rGO, while the composite CuO/rGO and ZnO/rGO materials have good chemical stability with a higher specific electrical capacity (465.73 F×g−1) than CuO/rGO (167.52 F×g−1), ZnO/rGO (185.48 F×g−1), rGO (113.50 F×g−1), and annealed graphite (53.12 F×g−1). The mechanism of increasing the specific capacitance depending on whether the composite CuO/rGO and ZnO/rGO materials act as a pseudocapacitor and/or an electrical double-layer capacitor is elucidated.&#x0D; HIGHLIGHTS&#x0D; &#x0D; One challenging problem for supercapacitor improvement is increasing its specific electrical capacitance&#x0D; CuO/rGO and ZnO/rGO hybrid layers were prepared using graphene oxide and copper and zinc salts&#x0D; The composite CuO/rGO and ZnO/rGO materials have better chemical stability with a higher specific electrical capacity than CuO/rGO, ZnO/rGO, rGO, and annealed graphite&#x0D; &#x0D; GRAPHICAL ABSTRACT

Quadrature phase shifter for the measurement systems of testing of electrical insulation

Quadrature phase shifters are widely used in practice of development of measurement systems intended for the measurements of dielectric dissipation factor and electrical capacitance. This article presents the examples of implementation of phase shifters intended to obtain the value of phase shift equal to 90º for the applying in measurement systems of monitoring and diagnosing the technical condition of electrical insulation. The developed solutions are based on applying of the analog signal multiplier implemented in the AD633 integrated circuit. The required value of phase shift is provided by adding a pre-shifted at a certain angle input harmonic signal to a signal with the reduced amplitude and the opposite initial phase. The article is also focused on the development of schematic solutions which can be used in order to remove the undesirable for many practical applications discrepancy between the amplitudes of the input and the output signals. This alignment of amplitudes is provided by the detection of their average rectified values with subsequent multiplication of their ratio by the shifted at 90º signal with the reduced amplitude. The designed schematic solutions imply the applying of analog circuits which contain the input phase shifter, low pass filter, voltage summing amplifier, two detectors of average rectified values, three analog multipliers and one voltage divider.

Impact damage detection in glass fibre reinforced polymers via electrical capacitance measurements on integrated carbon fibre bundles

Impact damages are critical for fibre reinforced polymers, as they can lead to large delaminations that strongly influence the structural integrity of the components. Therefore, reliable detection of impact damages through structural health monitoring is desired. This paper demonstrates a method for the detection and size estimation of impact damages in glass fibre reinforced polymers using capacitance measurements on integrated carbon fibre bundles. Therefore, individual rovings of glass fibre fabrics are replaced by carbon fibre rovings. After infusion of the laminate, the electrical capacitance is measured between the carbon fibre bundles. Damage in the form of matrix cracks or delaminations results in incorporated air that changes the permittivity of the material and, therefore, can be detected as a capacitance decrease. Considering the magnitude of capacitance decrease, a size estimation of the impacts is possible. Consequently, the presented method can be used for in-situ monitoring of damages in glass fibre reinforced polymers.

ACE2-based capacitance sensor for rapid native SARS-CoV-2 detection in biological fluids and its correlation with real-time PCR

The spread of the SARS-CoV-2 and its increasing threat to human health worldwide have necessitated the development of new technological tools to combat the virus. Particular emphasis is given to the development of diagnostic methods that monitor the spread of the virus rapidly and effectively. In this study, we report the development and testing of an antibody-free biosensor, based on the immobilization of ACE2 protein on the surface of gold interdigitated electrode. When the sensor was used in laboratory conditions for targeting the virus’ structural spike protein, it showed a limit of detection [LOD] of 750 pg/μL/mm2. Thereafter, the response of the sensor to swab and saliva samples from hospitalized patients was examined. The virus presence in the samples was confirmed by electrical effective capacitance measurements executed on the biosensor, and correlated with real-time PCR results. We verified that the biosensor can distinguish samples that are positive for the virus from those that are negative in a total of 7 positive and 16 negative samples. In addition, the biosensor can be used for semi-quantitative measurement, since its measurements are divided into 3 areas, the negative samples, the weakly positive and the positive samples. Reproducibility of the experiments was demonstrated with at least 3 replicates and stability was tested by keeping the sensor standby for 7 days at 4 °C before repeating the experiment. This work presents a biosensor that can be used as a fast-screening test at point of care detection of SARS-CoV-2 since it needs less than 2 min to provide results and is of simple operation.

Calcium ion effect on phospholipid bilayers as cell membrane analogues

Ion attachment can modify stability and structure of phospholipid bilayers. Of particular importance is the interaction of phospholipids with divalent cations, such as calcium ions playing an important role in numerous cellular processes.The aim of our study was to determine effects of calcium ions on phospholipid membranes employing two cell membrane analogues, liposomes and planar lipid bilayers, and for the first time the combination of two instrumental setups: gas-phase electrophoresis (nES GEMMA instrumentation) and electrical (capacitance and resistance) measurements. Liposomes and planar lipid bilayers consisted of phosphatidylcholine, cholesterol and phosphatidylethanolamine. Liposomes were prepared from dried lipid films via hydration while planar lipid bilayers were formed using a Mueller-Rudin method. Calcium ions were added to membranes from higher concentrated stock solutions.Changes in phospholipid bilayer properties due to calcium presence were observed for both studied cell membrane analogues. Changes in liposome size were observed, which might either be related to tighter packing of phospholipids in the bilayer or local distortions of the membrane. Likewise, a measurable change in planar lipid bilayer resistance and capacitance was observed in the presence of calcium ions, which can be due to an increased rigidity and tighter packing of the lipid molecules in the bilayer.

Electrical capacitance measurements to assess European Corn Borer infestation in maize

The European Corn Borer (ECB), Ostrinia nubilalis, is an agricultural pest which bores small holes in the rind of maize stalks and then proceeds to consume the pith. Because most of the damage to the stalk is internal, it is difficult to quantify the damage to an individual stalk without time-consuming, manual examination. This work focused on determining the feasibility of detecting internal damage using non-destructive, electrical measurements. Laboratory experiments and numerical simulation studies predicted changes in capacitance of stalks due to hollow core ECB damage. A guarded probe device to measure electrical impedance from 500 Hz to 100 kHz was designed and constructed for data collection. A field test with the measurement device was conducted and frequency-swept impedance measurements were taken on field-grown plants with and without ECB damage. Field measurements demonstrated that statistically significant capacitance changes associated with ECB damage could be detected in agreement with numerical simulations of stalk damage. Numerical, laboratory, and field test results all supported the hypothesis that electrical impedance measurements, in particular, capacitance, provide a promising new avenue for ECB damage evaluation. While further research will be needed to further refine this concept, this measurement approach is non-destructive, thus allowing measurements to be performed without sacrificing the infested plants.

The decreasing of the influence of parasitic inductance of tested object on the accuracy of its electrical capacitance measurement

This paper gives a description of measurement technique which can be used in practice of carrying out estimation of electrical capacitance of tested object with substantial stray inductance. Electrical capacitance is determined as a ratio of mean value of discharge current to the mean value of time derivative, taken from voltage on unknown capacitance. The decreasing of deleterious impact of stray inductance on accuracy of measurements is achieved by proper selection of the duration of analyzed signals. In proposed technique the duration is limited by instants of time that correspond to the maximum value of discharge current and to the termination of transient. The accuracy of described method for electrical capacitance estimation is affected by noisy components of obtained oscillograms. This deleterious impact can be alleviated by smoothing of time dependence by applying of least square method. Another reason for lost of accuracy is associated with possible influence of skin-effect in conductive elements of discharge circuit, which can cause time dependence of resistance and inner inductance of conductive parts of tested object and discharge circuit. Described technique, however, is based on taking into consideration independent on time parameters of equivalent lamped discharge circuit. Nevertheless, the example of practical implementation has shown that described approach allows to partially mitigate the influence of stray inductance on carried out measurements of electrical capacitance, as the value of relative error turned out to be equal to 2.04%

Skin Viability and Microvascular Function Under Localised Applications of Heat and Pressure

Soft tissue pressure injuries are localised injuries to surface and deep tissue, caused by sustained compression of skin and muscle between a bony area of the body, and for example, a hospital mattress or medical device. Prolonged cell deformation is known to reduce the structural integrity of the cell cytoskeleton, leading to cascade of cell death, inflammation, oedema and oxidative stress, factors that are likely exacerbated by inadequate blood flow and oxygen delivery. Numerous secondary factors are thought to accelerate this cascade, including systemic hypoxia and changes in tissue temperature. By examining the responses of various skin viability markers, both during and after the application of temperature and pressure stimuli, the present study aims to expand understanding of the secondary factors affecting pressure ulcer onset and progression. In the present study, a custom skin deformation device, with an area of 33cm2, was used to apply a combination of pressures (6, 20 and 40mmHg) and temperatures (23, 33, 38°C) at the sacrum of four healthy volunteers (data collection ongoing). A laser doppler flowmetry probe, embedded into the skin deformation device, was used to measure baseline skin blood flow, skin blood flow under pressure, and reactive hyperaemia (RH) on pressure release. All measurements were calculated as a percentage of heat-induced maximal cutaneous vascular conductance (%CVCmax). Changes in stratum corneum and epidermal hydration were calculated using the difference in tissue electrical capacitance (corneometry) measurements before and after skin deformation. The results indicated a significant difference in loaded skin blood flow between the pressures of 6-20mmHg (p=0.045), and 6-40mmHg (p=0.018), decreasing from 30.5 ± 9.1 %CVCmax to 21.8 ± 9.0 %CVCmax and 17.5 ± 6.7 %CVCmax respectively. Furthermore, there was a significant increase (p=0.030) from 16.9 ± 8.2 %CVCmax to 29.8 ± 5.4 %CVCmax in loaded skin blood flow, between the temperatures of 28-38°C. Finally, blood flow saw a significant (p=0.005) increase on pressure release, from a loaded average of 19.7 ± 8.2 %CVCmax to an unloaded average of 29.0 ± 12.0 %CVCmax, however there was no significant effect of pressure level or temperature on reactive hyperemia. Changes in stratum corneum hydration between 28-33°C (p=0.044), and 28-38°C (p=0.019), increased from 20.8 ± 11.3% to 38.8 ± 12.7% and 48.5 ± 15.5% respectively. Differing pressures and temperatures had no significant effect on epidermal hydration. Initial indications from the present study suggest low local tissue temperature reduces tissue blood flow under pressure, thereby potentially reducing oxygen transport to, and metabolites away from, areas of loaded tissue. However, increased local temperature results in greater moisture accumulation on the surface layer of the cutaneous tissues, potentially resulting in a lower structural integrity. On balance, a neutral skin temperature may be best to balance the harmful effects pressure on tissue viability, but further investigation is required to fully understand the influence of temperature on each aspect of the pressure injury cascade, including cell cytoskeleton integrity, inflammation, and oedema, as well as blood flow dynamics, oxygen delivery, cell metabolism and oxidative stress.

Novel volumetric analysis technique for characterizing the solubility and diffusivity of hydrogen in rubbers

We introduce a volumetric analysis technique to characterize the solubility of hydrogen dissolved in polymers and its diffusion coefficient by electrical capacitance measurement electrodes to determine the water level in graduated cylinders. This new and simple technique measures the volume of hydrogen released from rubber inside a graduated cylinder after a sample is exposed to high-pressure hydrogen and subsequent decompression. A diffusion analysis program is utilized to determine the total uptake (C0) and diffusivity (D) of hydrogen, which are used to calculate the solubility (S) and permeability (P). This method is applied to spherical rubber samples of nitrile butadiene rubber (NBR), ethylene propylene diene monomer (EPDM), and fluoroelastomer (FKM), which are potential sealing materials for H2 energy infrastructures. C0 follows Henry's law for all samples. No sample size and pressure dependence is observed for S, whereas an appreciable size dependence for the three rubbers is detected for D. The uncertainty is evaluated by considering uncertainty factors that affect the measurement. The correlation between D and density of rubber is found. The developed method can be utilized as a standard test for the transport properties versus pressure of various polymer membranes regardless of the sample shapes and size.

Capacitance measurements on integrated conductors for detection of matrix cracks in GFRP

For the reliable and cost-efficient application of glass fibre polymer composites in structural applications, knowledge of the damage state of the material during operation is necessary. Within this work, a structural health monitoring method based on in-situ electrical capacitance measurements is presented, which enables damage monitoring in glass fibre reinforced polymers. For this purpose, individual glass fibre rovings in a non-crimp fabric were replaced by carbon fibre rovings at regular intervals. Additionally, specimens with solid or stranded copper conductors were manufactured to gain insights into the influences of conductor material and composition. The modified fabrics were implemented as 90 ∘ layers of [0/904]s glass fibre polymer cross-ply laminates. To monitor the progressive damage, conductive rovings were contacted, forming the capacitor walls of interleaved capacitors. Carbon fibre conductors show higher sensitivity of the capacitance to crack formation than solid or stranded copper conductors. Capacitance decrease measured in-situ during tensile tests on specimens with carbon fibre conductors shows a high correlation with crack initiation, further crack formation and speed of crack evolution. An analytical model can describe the correlation based on the assumptions of an ideal plate capacitor. Thus, the structural health monitoring method developed in this work can reveal in-situ knowledge of the material damage state.

Brillouin zone center phonon modes in ZnGa2O4

Infrared-active lattice mode properties of melt-grown high-quality single bulk crystals of ZnGa2O4 are investigated by combined spectroscopic ellipsometry and density functional theory computation analysis. The normal spinel structure crystals are measured by spectroscopic ellipsometry at room temperature in the range of 100 cm–1–1200 cm–1. The complex-valued dielectric function is determined from a wavenumber-by-wavenumber approach, which is then analyzed by the four-parameter semi-quantum model dielectric function approach augmented by impurity mode contributions. We determine four infrared-active transverse and longitudinal optical mode pairs, five localized impurity mode pairs, and the high frequency dielectric constant. All four infrared-active transverse and longitudinal optical mode pairs are in excellent agreement with results from our density functional theory computations. With the Lyddane–Sachs–Teller relationship, we determine the static dielectric constant, which agrees well with electrical capacitance measurements performed on similarly grown samples. We also provide calculated parameters for all Raman-active and for all silent modes and, thereby, provide a complete set of all symmetry predicted Brillouin zone center modes.

Simultaneous and rapid quantification of microalga biomolecule content using electrochemical impedance spectroscopy.

Lipids, proteins, and carbohydrates are the major constituents found in microalga cells, in varying proportions, and these biomolecules find applications in different industries. During microalga cultivation, to efficiently manipulate, control, and optimize the productivity of a specific compound for a specific application, real-time monitoring of these three cell components is essential. In this study, a method using measurement of electrical capacitance was developed to simultaneously determine the lipid, protein, and carbohydrate content of microalga cells without the requirement for any pre-processing steps. The marine microalga Nannochloropsis oculata was cultivated under nitrogen starvation conditions to induce lipid accumulation over a period of 22 days. The correlation between the electrical capacitance of the microalga culture and the intracellular biomolecule content (determined by standard techniques) was investigated, enabling subsequent deduction of microalga intracellular content from electrical capacitance of the culture. The accuracy and precision of the technique were proven by validating an independent sample. The main advantage of the proposed technique is its capability of quantifying microalga composition within a few minutes, significantly faster than currently available conventional techniques.

Modeling of oil–water separation efficiency in three-phase separators: Effect of emulsion rheology and droplet size distribution

The multi-fluid Eulerian multiphase model coupled with the inhomogeneous population balance model is applied to predict the gas, oil, and water separation behavior and emulsion destabilization in a high-pressure horizontal three-phase separator. The population balance model is applied to predict the evolving droplet size distribution due to droplet coalescence in the crude oil emulsion. The effect of water fraction on the emulsion viscosity was incorporated to predict the existence of the dense packed layer or zone (DPZ) – a high water-fraction emulsion layer formed at the interface between the oil and water phases. The novel emulsion viscosity model incorporates a dependence on the local droplet size. Parameter estimation for the droplet coalescence kernel in the population balance equation is determined from experimental measurements of emulsion separation kinetics. A proportional integral derivative (PID) controller logic is used to maintain the gas/oil and oil/water interface levels by automatically adjusting the oil and water outlet pressure, respectively. The pilot separator experimental measurements include inlet and outlet flowrates and density, and electrical capacitance measurement of the vertical water concentration profile. The CFD model determines the flow patterns, phase distributions and the dispersed water droplet size distribution in the emulsion in the separator. The model results are in good agreement with the data for the separation efficiency from the water flow rate in and out of the separator, the phase distributions and the DPZ at different flow rates and water fractions. This study demonstrates the importance in multiphase separator design and troubleshooting of including the influence of water fraction on emulsion viscosity and the droplet size distribution with droplet coalescence phenomena. The methodology presented has significant advantages over previously published methods and improves on the value and potential impact toward research and industry practice.

Root capacitance measurements allow non-intrusive in-situ monitoring of the seasonal dynamics and drought response of root activity in two grassland species

Background and aimsIn this study, the potential of non-intrusive root electrical capacitance (CR) measurements for monitoring the seasonal changes and drought response of root activity was tested on two grassland species in a climate change experiment.MethodsCR was detected between a ground electrode inserted into the soil and a plant electrode attached to the stem of the perennial grass Stipa borysthenica and the biennial herb Crepis rhoeadifolia in control and drought plots throughout two growing seasons. A pilot study revealed that CR was strongly correlated with root biomass for a given time and soil water content. The effect of changing soil water content on the measured CR value was accounted for by means of species-specific experimental calibrations.ResultsRoot activity (CR) was found to peak at the flowering stage in late spring (S. borysthenica) or early summer (C. rhoeadifolia). Both the natural shortage of rainfall and the experimental summer drought reduced root activity in both species. Stipa borysthenica displayed great plasticity in root activity, including quick post-treatment recovery during the rainy autumn. The changes observed in root activity were similar to those previously recorded using conventional root investigation techniques (i.e. destructive, minirhizotron, ingrowth core) in temperate grasslands.ConclusionsRoot capacitance measurements proved to be adequate for monitoring root activity in situ in natural grassland. The method could be particularly useful in studies where plant injury or soil disturbance need to be avoided.

Electromagnetic Characteristics of Shape Memory Spring

Electric impedance is widely used in imaging and detection techniques. The applications range from non-destructive testing, structural health monitoring, and geophysical imaging to medical imaging. The frequency of the signal used for the measurement ranges from less than 1 Hz to about 1 GHz. This paper addresses the measurement and evaluation of the phase dependent electrical resistance, inductance, capacitance, and impedance of a shape memory alloy (SMA) spring (BMX 150, Toki Corporation). The material characteristics can be obtained by means of their electromechanical impedance. Experimental procedures are implemented and the electrical characteristics are obtained for a wide range of frequency. The electrical resistance, inductance, impedances of the austenite and martensite phase are determined, also the quality factor of the Bio Metal coil to be (9.465 – 9.95) Ω and (10.358 – 10.8) Ω, (0.458 – 0.38) μH and (0.458 – 0.36) μH and, (9.47 – 10.24) Ω and (10.36 – 11.11) Ω respectively for the frequency range of 100 kHz - 1MHz. The quality factor of the Bio Metal ranges between 0.03 and 0.2 during heating and, 0.028 and 0.022 during the cooling phase. The experimental results herein show that an equivalent circuit of the SMA spring is a series resistor-inductor circuit with a parasitic capacitance effect. The electromagnetic behaviour of SMA is determined using a finite element tool.

New Type of Thermal Moisture Sensor for in‐Textile Measurements

The measurement of moisture in textile materials worn on or near the skin can be performed for a variety of reasons, for example, to analyze the amount of perspiration in clothing, wound fluid in bandages or even urine in diapers or bed sheets. Conventional moisture measurement methods, such as electrical resistance or capacitance measurement, can be susceptible to cross sensitivities to electrical fields or ionic impurities, often occurring in measurements close to the human body. The very reliable gravimetric methods are too bulky and difficult to be integrated in portable and online measurements. In this paper, the authors present a “transient heat moisture sensor” (THMS) which is small and comparatively easy to integrate into textiles. The authors describe the measurement principle and present a sensor element manufactured with thin film technologies. The analytical description of the sensor fits to both, experimental data and the result of first numerical analysis (COMSOL Multiphysics). The authors demonstrate how to limit the sensors spatial sensitivity to a thin layer of textile without being influenced by the adjacent environment by proper timing of the signal readout.

Role of sintering temperature on microstructure and nonlinear electrical properties of 0.1 mol.% Nb2O5 added ZnO–V2O5 varistor ceramics

The effect of sintering temperature on the microstructure, density and nonlinear electrical properties of 0.1 mol% Nb2O5 added ZnO–V2O5 varistor ceramics had been investigated. Density measurement, scanning electron microscopy (SEM), X-ray diffraction (XRD) pattern analysis characterized the sintered samples. The electric current and capacitance measurements of the varistor samples were done in varying voltage over a wide range. Image analysis by SEM shows an increase in the average grain size from 2.8 to 7.2 µm when the sintering temperature increases from 850 to 975 °C. The varistor sample, sintered at 850 °C, exhibits breakdown field of 4258 V/cm with nonlinear exponent value of 24. Degradation in breakdown field (1440 V/cm) and nonlinear exponent (9) have been observed with an increase in sintering temperature up to 975 °C. Barrier height estimated from the electric field–current density (E–J) and the capacitance–voltage (C–V) measurements follow an inverse relationship with sintering temperature.

Dynamics of Charge Distribution in Sandwich-Type Light-Emitting Electrochemical Cells Probed by the Stark Effect

A sandwich-type structure composed of thin films of functional materials is the dominant architecture of organic optoelectronic devices. During device operation, injected or inside-generated electrical charges arrange in a specific spatial distribution. This distribution affects the electric field profile throughout the layers and has a fundamental impact on charge transport and recombination/separation processes. However, probing of the charge distribution is challenging because the hidden active layers are experimentally not directly accessible. Here, we study the temporal evolution of organic salt-based light-emitting electrochemical cells and demonstrate that electroabsorption spectroscopy in combination with electrical capacitance measurements enables the determination of the distribution of the injected, uncompensated electronic charge inside these devices. For constant-voltage operating conditions and over a period of hours, the Stark effect signal intensity and the capacitance increase steadily, but to a different extent. We demonstrate that this difference sensitively depends on the position and distribution width of injected mobile electrons. Estimates show a substantial spreading over the active layer of the injected electron density with time, screening the electric field behind the charge peak.