Internal Charge Distribution Research Articles

Design of microstructure and performance testing of high-pressure ZnO grain boundary layer

Abstract This paper firstly constructs the microstructure of the ZnO grain boundary layer of a high voltage system fits: microstructure characteristics of the ZnO varistor and conductive mechanism of the ZnO varistor. The ZnO structure can be seen as an irregular three-dimensional mesh composed of ZnO grain-high resistance grain boundary layer-ZnO grain. Then the electric field distribution of the ZnO grain boundary layer is calculated by Poisson’s equation, and the relationship curve of the space charge distribution inside the ZnO grain boundary with time is further simulated. Finally, the ZnO grain boundary performance is tested based on the bipolar carrier transport model with a double Schottky barrier, and the results show that the negative charge density at the grain boundary interface gradually decreases from 5×1025m−3 to 4.2452×1025m−3 and the initial charge value in the grain boundary region is 0m−3, and the negative charge at the grain boundary interface gradually decreases, and the negative charge in the grain boundary region gradually increases. In this study, the internal space charge distribution, Schottky barrier height and grain boundary leakage current are systematically investigated, which provides important theoretical support for the in-depth research on the conductivity mechanism, aging mechanism and performance improvement related to ZnO varistors.

An impedance flow cytometry with integrated dual microneedle for electrical properties characterization of single cell

Electrical characteristics of living cells have been proven to reveal important details about their internal structure, charge distribution and composition changes in the cell membrane, as well as the extracellular context. An impedance flow cytometry is a common approach to determine the electrical properties of a cell, having the advantage of label-free and high throughput. However, the current techniques are complex and costly for the fabrication process. For that reason, we introduce an integrated dual microneedle-microchannel for single-cell detection and electrical properties extraction. The dual microneedles utilized a commercially available tungsten needle coated with parylene. When a single cell flows through the parallel-facing electrode configuration of the dual microneedle, the electrical impedance at multiple frequencies is measured. The impedance measurement demonstrated the differential of normal red blood cells (RBCs) with three different sizes of microbeads at low and high frequencies, 100 kHz and 2 MHz, respectively. An electrical equivalent circuit model (ECM) was used to determine the unique membrane capacitance of individual cells. The proposed technique demonstrated that the specific membrane capacitance of an RBC is 9.42 mF/m−2, with the regression coefficients, at 0.9895. As a result, this device may potentially be used in developing countries for low-cost single-cell screening and detection.

Anisotropic strain induced fracture of Ni(OH)2 nanosheet electrodes for supercapacitors through a charge-ordered mixed-valent intermediate

Beta nickel hydroxide (β-Ni(OH)2) is a popular electrode material for manufacturing Ni-H batteries and pseudocapacitors. The cycle stability of β-Ni(OH)2 electrodes is limited owing to their volumetric changes during charge–discharge process, in which, internal charge distribution of β-Ni(OH)2 changes with the external swelling. In this paper, β-Ni(OH)2 nanosheets synthesized by HCl etching have been taken as an example to investigate details of the morphology and structure variations during capacity fading of these electrodes. The findings shows that the β-Ni(OH)2 nanosheets form a wrinkled surface and become fractured after the charge–discharge cycles. Fractured nanoparticles with diameters around 10 nm could be collected by the polyaniline coating on the β-Ni(OH)2 nanosheets. Charge-ordering of Ni2+/Ni3+ has been observed in β-Ni(OH)2 nanosheet via a sluggish cyclic voltammetry cycling. Although the charge-ordering state may lower the strain penalty involved in charging-discharging, the increased anisotropic strain in the β-Ni(OH)2 finally leads to the fracture and capacity fading of the nanosheet electrodes.

Semiconductor to half-metal transition in magnetic Ce cation incorporated A-site-ordered quadruple perovskite CeMn3Mn4O12

The charge degree of freedom of A-site cation as well as B-site cation plays a significant role in determining the internal charge distribution and gives rise to fascinating physical properties in perovskite oxides. Here, we discuss the magnetic couplings and electronic structures of rare-earth Ce cation incorporated A-site-ordered quadruple perovskite CeMn3Mn4O12 via first-principles calculations. This report demonstrates that the A site Ce is magnetic cation with quantity of 4 f electrons, which is quite different from the nonmagnetic Ce4+ usually found in isostructural compounds. As a result, not only the A′ and B site manganese sublattices but also the A site cerium sublattice is involved in the complex magnetic interactions. In the low-temperature phase, CeMn3Mn4O12 is ferrimagnetic with the Ce(↓)-Mn1(↑)-Mn2(↓)-Mn3(↑)-Mn4(↑)-Mn5(↓) type, in which the effective magnetic couplings are generated from A-site Ce sublattice as well as the antiparallel arrangement within both the A and B site manganese sublattices. The analysis of electronic structure reveals the valence distribution is Ce3+Mn3+3Mn3+4O2-12 where both the oxidation state of Ce and Mn is +3. Nevertheless, ferromagnet is the most favorable in energy with a large saturated magnetic moment at the high-temperature phase. Interestingly, the electronic structure undergoes a semiconducting to half-metallic transition accompanying with the phase transformation. The present results offer a new strategy to realizing the tunable charge distribution via variable valence A site cation in A-site-ordered quadruple perovskites and thus open an avenue to modulate these materials with exotic properties.

Origin of the giant persistent photoconductivity in LaAlO3/SrTiO3 heterostructures probed by noise spectroscopy

• The origin of the giant persistent photoconductivity in LaAlO 3 /SrTiO 3 heterostructures is explained by the photo-induced valence change in oxygen vacancies. • The change in the ionization state distribution is successfully probed by the noise spectroscopy technique. • The noise spectra correlate the ionization state distribution and the charge trapping behavior of oxygen vacancies. • The neutralization of the ionized oxygen vacancies near the LaAlO 3 /SrTiO 3 interface hinders the fast and complete charge relaxation, resulting in the strong persistent photoconductivity. LaAlO 3 /SrTiO 3 (LAO/STO) heterostructures have shown a strong persistent photoconductivity (PPC) at room temperature. The abnormally strong PPC has attracted immense research interest due to its possible applications in optically-tunable electronic devices. Despite its promise, the fundamental understanding of the PPC in the LAO/STO heterostructures is still elusive. Herein, we report that the giant PPC originates from the photo-induced valence change in oxygen vacancies near the LAO/STO interface. Our spectral analysis of the photocurrent and the model-fitting study consistently show that the ionized oxygen vacancies near the interface are neutralized during the electron relaxation process. They hinder the complete relaxation of the photoexcited electrons by the deeply-located oxygen vacancies and result in the strong PPC. The change in the ionization state distribution of the oxygen vacancies is probed by the persistent noise behavior at the frequency between 1 kHz and 20 kHz regime. These results provide insight into the role of oxygen vacancies in influencing the internal charge distribution and triggering the PPC phenomena in complex oxide heterostructures.

Analysis and Optimization of Organic Tandem Solar Cells by Full Opto-Electronic Simulation

This paper reports on the analysis and optimization of high-efficiency organic tandem solar cells via full opto-electronic device simulation on continuum level and using a hopping model for the explicit description of the charge recombination junction. Inclusion of the electrical sub-cell interconnection allows for a rigorous assessment of the impact of the internal charge distribution and associated built-in fields as well as quasi-Fermi level profiles on the measured device characteristics. It enables the direct evaluation of the external quantum efficiency in a simulation that follows closely the measurement protocol, and sheds light on complications related to the dependence of the band profile on the illumination conditions. The study also points at fingerprints of insufficient junction quality in the electrical characteristics of the tandem device. After studying the impact of key electrical parameters such as, carrier mobility, lifetime and interface hopping rate, onto the device characteristics, the latter are optimized not only optically, but also electronically, adding in both cases an increasing number of layers to the parameters of the global optimization procedure. An improvement of 2% absolute power conversion efficiency by using the full opto-electronic optimization as compared to optical optimization only is found.

Study on the output performance of the proton exchange membrane fuel cells using print circuit board

This paper presents a proton exchange membrane fuel cell (PEMFC) using anode and cathode printed circuit boards (PCBs) to load the membrane electrode assembly (MEA). A three-dimensional CFD-electrochemical model of the PCB-based PEMFC is developed and used to calculate the internal species, charge, and water distribution. The effects of the shape of the inlet opening, the opening ratio and the relative humidity of the air on the output performance of the PEMFC are investigated. To validate the simulation model, the output performance of the PEMFC is tested under the same operating conditions. The results show that circular and rounded rectangular openings show better PEMFC output performance than U-shaped openings, and the output performance of PEMFC is improved as the opening ratio of the inlet openings and the relative humidity of air increase. The results will provide specific reference values for the design of PCB-based planar PEMFC stacks.

Radiating composite stars with electromagnetic fields

We derive the junction conditions for a general spherically symmetric radiating star with an electromagnetic field across a comoving surface. The interior consists of a charged composite field containing barotropic matter, a null dust and a null string fluid. The exterior atmosphere is described by the generalised Vaidya spacetime. We generate the boundary condition at the stellar surface showing that the pressure is determined by the interior heat flux, anisotropy, null density, charge distribution and the exterior null string density. A new physical feature that arises in our analysis is that the surface pressure depends on the internal charge distribution for generalised Vaidya spacetimes. It is only in the special case of charged Vaidya spacetimes that the matching interior charge distribution is equal to the exterior charge at the surface as measured by an external observer. Previous treatments, for neutral matter and charged matter, arise as special cases in our treatment of composite matter.

Ultrasensitive bio-detection using single-electron effect

Single-electron devices are capable of detecting changes of the electric field caused by the presence of one single electron in their environment. These devices are optimized to identify the material that is in close contact with them based on the material's internal charge distribution or dipole moment. As an important practical use, they present the possibility of detecting bacteria, viruses, or pathogens. However, their practical use is hampered by their nano-meter size, which is normally an order of magnitude smaller than that of detected species, their very complex fabrication techniques, their cryogenic operational temperature, and the problem of bringing the said species in contact with the single-electron structure. In this document, a large scaled room temperature single-electron structure is introduced, and its ability to distinguish liquids based on their internal dipole moments is demonstrated. The device is a Schottky junction made of PtSi, as the metal contact, and the walls and surfaces of the porous Si, as the semiconductor. The reverse bias current-voltage (IV) characteristic of this device is sensitive to 1 ppm change in the dipole moment of the liquid entering its pores. The simple fabrication, easy testing procedure, high sensitivity, and fast response can make this device an optimized testing kit to identify the given bacteria, viruses, or pathogens dissolved in liquids.

A molecular shift register made using tunable charge patterns in one-dimensional molecular arrays on graphene

The ability to tune the electronic properties of molecular arrays is an important step in the development of molecule-scale electronic devices. However, control over internal device charge distributions by tuning interactions between molecules has proved challenging. Here, we show that gate-tunable charge patterning can occur in one-dimensional molecular arrays on graphene field-effect transistors. One-dimensional molecular arrays are fabricated using an edge-templated self-assembly process that allows organic molecules (F4TCNQ) to be precisely positioned on graphene devices. The charge configurations of the molecular arrays can be reversibly switched between different collective charge states by tuning the graphene Fermi level via a back-gate electrode. Charge pinning at the ends of the molecular arrays allows the charge state of the entire array to be controlled by adding or removing an edge molecule and changing the total number of molecules in an array between odd and even integers. Charge patterns altered in this way propagate down the array in a cascade effect, allowing the array to function as a charge-based molecular shift register. An extended multi-site Anderson impurity model is used to quantitatively explain this behaviour. One-dimensional molecular arrays on graphene field-effect transistors can be reversibly switched between different periodic charge states by tuning the graphene Fermi level via a back-gate electrode and by manipulating individual molecules, allowing them to function as a nanoscale shift register.

Impact of molecular weight on polyelectrolyte multilayer assembly and surface properties

Polyelectrolyte multilayers (PEMs) are a versatile category of materials due to their ability to modify surface properties for applications ranging from protective coatings to improved cell adhesion. Polyelectrolyte choice, including its structure and molecular weight (MW), is known to greatly influence PEM assembly and surface properties. In this work, poly(acrylic acid)/poly-l-lysine PEMs using three pairs of MWs (1.8k/15–30k, 100k/120k, and 250k/275k) were studied to determine the effects of their MWs on PEM assembly, topography and surface energy. PEMs assembly was monitored in a quartz crystal microbalance with dissipation, resulting in masses of 3.90 ± 0.87 µg/cm2, 10.80 ± 4.189 µg/cm2, and 30.04 ± 13.68 µg/cm2 for 10 bilayers of low, medium, and high MW pairs, respectively. The low MW PEM was more rigid. Low and high MW PEMs exhibited higher roughness than medium MW, caused by polyelectrolyte stripping. Surface energy remained constant with bilayer count in the low and high MW PEMs, but steadily increased in the medium MW PEM. Differences between medium MW PEMs from low and high MW systems indicate that, while PEM properties change with MW, they are not monotonically correlated and are instead related to changes in internal charge distributions and the resultant stripping that may occur.

Surface functionalization of GeC monolayer with F and Cl: Electronic and optical properties

Abstract In this work, we systematically investigate the electronic and optical properties of surface-functionalized GeC monolayer with F and Cl using density functional theory. Our calculations indicate that the surface functionalization of the GeC with F and C atoms leads to the disruption of the planar structure of the GeC monolayer and the surface-functionalized GeC monolayer has a low-bucking structure. At equilibrium, all four configurations of surface-functionalized GeC monolayer with F and Cl, i.e., F–GeC–F, F–GeC–Cl, Cl–GeC–F, and Cl–GeC–Cl, are direct semiconductors. Their band gaps vary from 2.839 eV to 3.175 eV which are calculated using Heyd–Scuseria–Ernzerhof (HSE) hybrid functional. Compared to the other configurations, the formation energy of F–GeC–F is the smallest, − 9 . 097 eV , which implies that this configuration is the most likely to occur. We also used the Mulliken population analysis to estimate the internal charge distribution and transferred charge in the systems. The functionalization of the surface leads to the shifting the first optical gap of the material. The fully chlorination of GeC causes its absorption coefficient to increase significantly, up to 14 . 912 × 1 0 4 cm−1 at the incident light energy of 13.173 eV. Besides, surface-functionalized GeC monolayer with F and Cl strongly absorbs light in the near ultraviolet region. Our calculation results provide detailed information on how to change the electronic and optical properties of monolayer GeC by surface functionalization, which has promising applications in opto-electronic devices.

Effect of internal charge distribution on the electrophoretic mobility of poly(N-isopropylacrylamide) based core-shell microgel particles

The electrophoretic mobility of poly(N-isopropylacrylamide) and poly(N-isopropylacrylamide-co-acrylic acid) copolymer particles, as well as different core-shell microgel particles (neutral core with charged shell and charged core with neutral shell) was investigated as function of microgel swelling. The swelling of the microgels were varied with increasing the temperature. To interpret the experimental results, we used scaling arguments to show that due to the strong hydrodynamic interactions the inner part of the microgel particles are non-draining in low ionic strength media and only the outmost thin shell of the microgel contributes actively to the electrophoretic mobility. We found that the experimental results were in good agreement with the prediction of this model, while we found physical inconsistencies when the experiments were analysed in terms of the draining models often used in the literature.

Charged nanorods at heterogeneously charged surfaces.

We study the spatial and orientational distribution of charged nanorods (rodlike counterions) as well as the effective interaction mediated by them between two plane-parallel surfaces that carry fixed (quenched) heterogeneous charge distributions. The nanorods are assumed to have an internal charge distribution, specified by a multivalent monopolar moment and a finite quadrupolar moment, and the quenched surface charge is assumed to be randomly distributed with equal mean and variance on the two surfaces. While equally charged surfaces are known to repel within the traditional mean-field theories, the presence of multivalent counterions has been shown to cause attractive interactions between uniformly charged surfaces due to the prevalence of strong electrostatic couplings that grow rapidly with the counterion valency. We show that the combined effects due to electrostatic correlations (caused by the coupling between the mean surface field and the multivalent, monopolar, charge valency of counterions) as well as the disorder-induced interactions (caused by the coupling between the surface disorder field and the quadrupolar moment of counterions) lead to much stronger attractive interactions between two randomly charged surfaces. The interaction profile turns out to be a nonmonotonic function of the intersurface separation, displaying an attractive minimum at relatively small separations, where the ensuing attraction can exceed the maximum strong-coupling attraction (produced by multivalent monopolar counterions between uniformly charged surfaces) by more than an order of magnitude.

Coulomb excitation of the deuteron in peripheral collisions with a heavy ion

We develop an ab initio, non-perturbative, time-dependent Basis Function (tBF) method to solve the nuclear structure and scattering problems in a unified manner. We apply this method to a test problem: the Coulomb excitation of a trapped deuteron by an impinging heavy ion. The states of the deuteron system are obtained by the ab initio nuclear structure calculation implementing a realistic inter-nucleon interaction with a weak external trap to localize the center of mass and to discretize the continuum. The evolution of the internal state of the deuteron system is directly solved using the equation of motion for the scattering. We analyze the excitation mechanism of the deuteron system by investigating its internal transition probabilities and observables as functions of the exposure time and the incident speed. In this investigation, the dynamics of the Coulomb excitation are revealed by the time evolution of the system's internal charge distribution.

A Low-Cost Tiny-Size Successive Approximation ADC for Applications Requiring Low-Resolution Conversion with Moderate Sampling Rate

The required silicon die area of successive approximation analog-to-digital converters (SA-ADCs) increases rapidly with ADC resolution. In particular, a main design challenge for SA-ADCs is the number of unit capacitors required for the internal charge distribution capacitive-array digital-to-analog converter (DAC), which increases exponentially with a monotonic increase in the number of the output bits. Therefore, the overall performance of the final design is affected by the huge die area and, in turn, the switching energy of the capacitive-array DAC. In this article, a tiny-size MOSFET-only SA-ADC topology is proposed for those applications which require a low-resolution and moderate to high sampling-rate analog-to-digital converters prior to digital processing units. To this end, the widely used metal–insulator–metal (MIM) capacitors of mixed-signal CMOS technologies are replaced with area-efficient MOS capacitors available in every technology. The effectiveness of this implementation is validated through successful simulation of a 5-bit 20 MS/s MOSFET-only SA-ADC in a low-cost 0.18-µm digital CMOS technology. The ADC consumes a total power of 76.88 µW from a 1.2-V voltage supply, while it occupies a die size of only 190 µm2. This area is roughly 40% lower than 310 µm2, the die area of an equivalent design based on MIM capacitors.

Self-organizing layers from complex molecular anions

The formation of traditional ionic materials occurs principally via joint accumulation of both anions and cations. Herein, we describe a previously unreported phenomenon by which macroscopic liquid-like thin layers with tunable self-organization properties form through accumulation of stable complex ions of one polarity on surfaces. Using a series of highly stable molecular anions we demonstrate a strong influence of the internal charge distribution of the molecular ions, which is usually shielded by counterions, on the properties of the layers. Detailed characterization reveals that the intrinsically unstable layers of anions on surfaces are stabilized by simultaneous accumulation of neutral molecules from the background environment. Different phases, self-organization mechanisms and optical properties are observed depending on the molecular properties of the deposited anions, the underlying surface and the coadsorbed neutral molecules. This demonstrates rational control of the macroscopic properties (morphology and size of the formed structures) of the newly discovered anion-based layers.

Nonlocal electrostatics in ionic liquids: The key to an understanding of the screening decay length and screened interactions.

Screened electrostatic interactions in ionic liquids are investigated by means of exact statistical mechanical analysis combined with physical arguments that enhance the transparency and conceptual accessibility of the analysis and results. The constituent ions and immersed particles in the liquid can have arbitrary shapes and any internal charge distributions. The decay of the screened electrostatic potential and the free energy of interaction in ionic liquids can be exponentially damped oscillatory (like in molten simple salts) as well as plain exponential and long-ranged (like in dilute electrolyte solutions). Both behaviors are in agreement with the exact statistical mechanical analysis and reasons for their appearances are investigated. Exact but surprisingly simple expressions for the decay parameter κ of the screened electrostatics are obtained, which replace the classical expression for the Debye-Hückel parameter κDH (the reciprocal Debye length). The expressions are applicable both for cases with plain exponential and oscillatory behaviors. The key importance of nonlocal electrostatics is thereby demonstrated explicitly. Dielectric properties of ionic liquids and other electrolytes are investigated, in particular the static dielectric function ϵ̃(k) and some effective relative permittivities (Ereff and Er∗), which take roles that the dielectric constant εr has for polar liquids consisting of electroneutral molecules. The dielectric constant in the latter case, which is the limit of ϵ̃(k) when the wave number k → 0, can be expressed solely in terms of dipolar features of the molecules. In contrast to this, the effective dielectric permittivities of ionic liquids have contributions also from quadrupolar, octupolar, and higher multipolar features of the constituent ions. The "dielectric constant" of electrolytes does not exist since ϵ̃(k)→∞ when k → 0, a well-known effect of perfect screening. The effective relative permittivities, Ereff, and Er∗ of ionic liquids are obtained from the non-diverging part of ϵ̃(k), but not as a k → 0 limit. Influences of ion associations, especially pairing, are investigated for screened electrostatics and these permittivities. A general, multipolar expansion of ϵ̃(k) is derived and used to analyze dielectric properties of ionic liquids and other electrolytes.

A novel approach for electrical circuit modeling of Li-ion battery for predicting the steady-state and dynamic I–V characteristics

A novel approach for electrical circuit modeling of Li-ion battery is proposed in this paper. The model proposed in this paper is simple, fast, not memory intensive and does not involve any look-up table. The model mimics the steady-state and dynamic behavior of battery. Internal charge distribution of the battery is modeled using two RC circuits. Self-discharge characteristic of the battery is modeled using a leakage resistance. Experimental procedure to determine the internal resistance, leakage resistance and the value of RC elements is explained in detail. The variation of parameters with state of charge (SOC) and magnitude of current is presented. The internal voltage source of the battery model varies dynamically with SOC to replicate the experimental terminal voltage characteristics of battery. The accuracy of model is validated with experimental results.

Electron Transport Models and Precision Measurements With the Constant Voltage Conductivity Method

Recent advances are described in the techniques, resolution, and sensitivity of the constant voltage conductivity (CVC) method and the understanding of the role of charge injection mechanisms and the evolution of internal charge distributions in associated charge transport theories. These warrant reconsideration of the appropriate range of applicability of this test method to spacecraft charging. We conclude that under many (but not all) common spacecraft charging scenarios, careful CVC tests provide appropriate evaluation of conductivities down to ≈ 10-22 (Ωcm)-1, corresponding to decay times of many years. We describe substantial upgrades to an existing CVC chamber, which improved the precision of conductivity measurements by more than an order of magnitude. At room temperature and above and at higher applied voltages, the ultimate instrument conductivity resolution can increase to ≈ 4·10-22 (Ωcm)-1, corresponding to decay times of more than a decade. Measurements of the transient conductivity of low-density polyethylene using the CVC method are fit very well by a dynamic model for the conductivity in highly disordered insulating materials over more than eight orders of magnitude in current and more than six orders of magnitude in time. Current resolution of the CVC system approaches fundamental limits in the laboratory environment set by the Johnson thermal noise of the sample resistance and the radiation-induced conductivity from the natural terrestrial background radiation dose from the cosmic ray background.