Variation Of Charge Density Research Articles

Ionic Conductance of Carbon Nanotubes: Confronting Literature Data with Nanofluidic Theory

The field of ion transport through carbon nanotubes (CNTs) is marked by a large variability of the ionic conductance values reported by different groups. There is also a large uncertainty concerning the relative contributions of channel and access resistances in the experimentally measured currents, both depending on experimental parameters (nanotube length and diameter). In this perspective article, we discuss the ionic conductance values reported so far in the case of 2 individual CNTs and compare them with standard nano-fluidic models considering both the access and channel resistances. With a view toward guiding experimentalists, we thus show in which conditions the access or the channel resistance can predominate in CNTs. We explain in particular that it is not justified to use phenomenological models neglecting the channel resistance in the case of micrometer-long CNTs. This comparison reveals that most experimental conductance values can be explained in the framework of current nanofluidic models by considering experimental variations of slip length and surface charge density and that just a few extraordinarily high values cannot be accounted for even using extreme parameter values. Finally, we discuss how to complete existing models and how to improve the statistical reliability of experimental data in the field.

Ultra Sensitive Label-Free Detection of Biomolecules Using Vertically Extended Drain Double Gate Si₀.₅Ge₀.₅ Source Tunnel FET

This work reports a vertically extended drain double gate Si0.5Ge0.5 source tunnel FET for the biomolecules detection using its electrical properties modulation in presence of biomolecules like cell, DNA, protein, etc. The reported biosensor has a dual source of Si0.5Ge0.5 and two cavities above each source-channel interface for the immobilization of biomolecules. This immobilization modulates the screening/tunneling length and energy range available for tunneling due to the dielectric constant and charge density variations of the biomolecules. The dual cavity structure increases the control of biomolecules on the source to channel tunneling probability and thus realizes an increased control on electrical performance parameters of the biosensor enabling it to have a higher sensitivity towards the biomolecules. Further, the cavity length of the reported biosensor is kept as 45 nm making it suitable for large sized biomolecules and polymers detection also. Our study demonstrates that the reported biosensor structure is resilient towards the process variations and temperature effects. Moreover, the effect of dielectric modulation and charge density modulation has also been analyzed in terms of the variation in the drive current, ON state current, threshold voltage, transconductance, and sub-threshold slope (SS). The sensitivity of the reported biosensor is also compared with the existing biosensors and it is found to be highly sensitive.

Electrochemical Impedance Imaging on Conductive Surfaces

Electrochemical impedance spectroscopy (EIS) is a powerful tool to measure and quantify the system impedance. However, EIS only provides an average result from the entire electrode surface. Here, we demonstrated a reflection impedance microscope (RIM) that allows us to image and quantify the localized impedance on conductive surfaces. The RIM is based on the sensitive dependence between the materials' optical properties, such as permittivity, and their local surface charge densities. The localized charge density variations introduced by the impedance measurements will lead to optical reflectivity changes on electrode surfaces. Our experiments demonstrated that reflectivity modulations are linearly proportional to the surface charge density on the electrode and the measurements show good agreement with the simple free electron gas model. The localized impedance distribution was successfully extracted from the reflectivity measurements together with the Randles equivalent circuit model. In addition, RIM is used to quantify the impedance on different conductive surfaces, such as indium tin oxide, gold film, and stainless steel electrodes. A polydimethylsiloxane-patterned electrode surface was used to demonstrate the impedance imaging capability of RIM. In the end, a single-cell impedance imaging was obtained by RIM.

Role of Interfacial Defects in Photoelectrochemical Properties of BiVO4 Coated on ZnO Nanodendrites: X-ray Spectroscopic and Microscopic Investigation.

Synchrotron-based X-ray spectroscopic and microscopic techniques are used to identify the origin of enhancement of the photoelectrochemical (PEC) properties of BiVO4 (BVO) that is coated on ZnO nanodendrites (hereafter referred to as BVO/ZnO). The atomic and electronic structures of core-shell BVO/ZnO nanodendrites have been well-characterized, and the heterojunction has been determined to favor the migration of charge carriers under the PEC condition. The variation of charge density between ZnO and BVO in core-shell BVO/ZnO nanodendrites with many unpaired O 2p-derived states at the interface forms interfacial oxygen defects and yields a band gap of approximately 2.6 eV in BVO/ZnO nanocomposites. Atomic structural distortions at the interface of BVO/ZnO nanodendrites, which support the fact that there are many interfacial oxygen defects, affect the O 2p-V 3d hybridization and reduce the crystal field energy 10Dq ∼2.1 eV. Such an interfacial atomic/electronic structure and band gap modulation increase the efficiency of absorption of solar light and electron-hole separation. This study provides evidence that the interfacial oxygen defects act as a trapping center and are critical for the charge transfer, retarding electron-hole recombination, and high absorption of visible light, which can result in favorable PEC properties of a nanostructured core-shell BVO/ZnO heterojunction. Insights into the local atomic and electronic structures of the BVO/ZnO heterojunction support the fabrication of semiconductor heterojunctions with optimal compositions and an optimal interface, which are sought to maximize solar light utilization and the transportation of charge carriers for PEC water splitting and related applications.

Effect of pH on Effective Slip Length and Surface Charge at Solid-Oil Interfaces of Roughness-Induced Surfaces.

Featured Application Drag reduction in many applications of micro-/nano-fluidic channel. In the development of micro/nano fluid control systems, fluid resistance has always been one of the key factors restricting its development. According to previous studies, it is found that the boundary slip effect of the solid-liquid interface can effectively reduce the resistance of the microfluid and improve the transport efficiency of the microfluid. The boundary slip length is mainly affected by surface wettability, roughness, and surface charge density. Among them, the influence mechanism of surface charge density on the boundary slip is the most complicated, and there is a lack of relevant research, and further investigation is needed. In this paper, we present research on quantification of effective slip length and surface charge density, where the roughness effect is considered. The electrostatic and hydrodynamic force data obtained from atomic force microscopy (AFM) measurements were fitted and processed for comparative analysis. We obtained the variation of surface charge density and effective slip length when different oleophobic surface samples were immersed in ethylene glycol with different pH values. The effect of pH on the surface charge density and effective slip length was investigated by their variations. The mechanism of the effect of pH on the surface charge density was discussed. The experimental results show that in the ethylene glycol solution, no matter whether the pH value of the solution increases or decreases, the charge density of the surface with the same properties decreases, and the effective boundary slip length also shows a downward trend. In deionized water, the surface charge density and effective boundary slip length decreases with the decrease of PH value.

Charge density studies of multicentre two-electron bonding of an anion radical at non-ambient temperature and pressure.

The variation of charge density of two-electron multicentre bonding (pancake bonding) between semi-quinone radicals with pressure and temperature was studied on a salt of 5,6-di-chloro-2,3-di-cyano-semi-quinone radical anion (DDQ) with 4-cyano-N-methyl-pyridinium cation (4-CN) using the Transferable Aspheric Atom Model (TAAM) refinement. The pancake-bonded radical dimers are stacked by non-bonding π-interactions. With rising pressure, the covalent character of interactions between radicals increases, and above 2.55 GPa, the electron density indicates multicentric covalent interactions throughout the stack. The experimental charge densities were verified and corroborated by periodic DFT computations. The TAAM approach has been tested and validated for atomic resolution data measured at ambient pressure; this work shows this approach can also be applied to diffraction data obtained at pressures up to several gigapascals.

Modulational instability of dust-ion-acoustic waves and associated first and second-order rogue waves in a super-thermal plasma

A proper theoretical research has been carried out to explore the modulational instability (MI) conditions of dust-ion-acoustic (DIA) waves (DIAWs) in a three-component dusty plasma system containing inertialess κ-distributed electrons, and inertial warm positive ions and negative dust grains. The nonlinear Schrödinger equation (NLSE) has been derived by employing the reductive perturbation method. The numerical analysis under consideration demonstrates two types of modes, namely, fast and slow DIA modes. The MI conditions of DIAWs and the configuration of the energetic rogue waves (RWs) associated with DIAWs in the modulationally unstable parametric regime have been rigorously changed by the variation of various plasma parameters, namely, charge, mass, temperature, and number density of the plasma species. The findings of our present investigation will be useful in understanding the criteria for the formation of electrostatic RWs in both astrophysical environments (viz., Jupiter’s magnetosphere, cometary tails, pulsar magneto-sphere, interstellar medium, Earth’s mesosphere, Saturn’s rings, etc.) and laboratory experiments.

Effect of Relative Humidity on the Surface Electric Field Intensity Characteristics under DC Voltage in a Corona Cage

The effect of relative humidity on the surface electric field (SEF) strength and a new non-contact assessment method based on space charge density were studied. The purpose of using space charge was to assess the SEF accurately, particularly after corona occurs. Space charge measurement and SEF evaluation were conducted at a relative humidity of 40% to 90%. The change law of SEF after corona occurs at different relative humidity was obtained. Results showed that under the same relative humidity, the space charge density increases with the applied voltage, while the SEF decreases with voltages after corona occurs. As the humidity condition aggravated, SEF first increases and then decreases, and the turning point is about 70%. The distribution of charge density has an opposite change trend. The variation of charge density and SEF demonstrates that the two have mutual inhibition. Meanwhile, the change formula of SEF shows that the electric field intensity on the wire surface is not constant after corona occurs. The corona discharge experiment and theoretical research can be further carried out based on the results in this paper.

Fourier Enhanced Charge Simulation Method for Electrostatic Analysis of Overhead Transmission Lines

A computationally efficient charge simulation method is developed for three-dimensional electrostatic calculations involving parallel high voltage transmission conductors near a cloud of point charges. The conductors are modeled using axial line charge density segments, each with linearly varying charge density. A typical problem involves solving for the line charge densities and point charge values given the system geometry and voltage boundary conditions. The method was developed to support ongoing research into high voltage transmission line optimization using the external electric field to link transmission capacity and switching impulse flashover. The method uses superposition and applies Fourier principles to reduce computational burden by moving portions of the problem to the spatial frequency domain. Computation time can be significantly reduced relative to an all-spatial charge simulation approach. Examples involving bundled transmission conductors show measured computation time improvement and compare space potential and electric field results to those obtained from finite element analysis.

Gravitational polarization of the quantum vacuum caused by two point-like bodies

ABSTRACT In a recent paper, quantum vacuum was considered as a source of gravity, and the simplest, phenomenon, the gravitational polarization of the quantum vacuum by an immersed point-like body, was studied. In this paper, we have derived the effective gravitational charge density of the quantum vacuum, caused by two immersed point-like bodies. Among others, the obtained result proves that quantum vacuum can have regions with a negative effective gravitational charge density. Hence, quantum vacuum, the ‘ocean’ in which all matter of the Universe is immersed, acts as a complex fluid with a very variable gravitational charge density that might include both positive and negative densities; a crucial prediction that can be tested within the Solar system. In the general case of ${N \ge {\rm{3}}}$ point-like bodies, immersed in the quantum vacuum, the analytical solutions are not possible, and the use of numerical methods is inevitable. The key point is that an appropriate numerical method, for the calculation of the effective gravitational charge density of the quantum vacuum induced by N immersed bodies, might be crucial in description of galaxies, without the involvement of dark matter or a modification of gravity. The development of such a valuable numerical method, is not possible, without a previous (and in this study achieved) understanding of the impact of a two-body system.

Control of climate on soil charge characteristics through organic matter and clay mineral distributions in volcanic soils of Mt. Kilimanjaro, Tanzania

ABSTRACT The soil cation exchange capacity (CEC), which is contributed by constant and variable charges, is a vital indicator of soil fertility and affects elemental cycling. Climate is expected to affect soil CEC by controlling soil secondary minerals and organic matter distributions. The objective of this study was to clarify the effects of climate on the charge characteristics of the soil in Mt. Kilimanjaro under diverse climatic conditions. The soils of 15 soil profiles from southeast and northwest slopes of Mt. Kilimanjaro along the elevation gradient (910–2800 m asl.) were collected. The soil physicochemical and mineralogical properties, including constant and variable charge densities, were determined. Climate data for the study site was obtained from the WorldClim database. The results showed that the contribution of the variable charge to CEC was high at the humid sites of the elevated area of the southeast slope. At the humid sites, the high content of organic matter, which was considered to be stabilized as organo-mineral complexes by nanocrystalline minerals, enlarged the soil CEC, being more evident at cool high elevation sites. On the other hand, at the dry sites on the northwest slope and low elevations of the southeast slope, the constant charge and variable charge contributed equally to the CEC. The variable charge from organo-mineral complexes was smaller due to the progressive crystallization of nanocrystalline minerals under the dry condition, and the formed crystalline clay minerals would contribute to constant charge density. Our study indicates the importance of moisture in addition to temperature as factors that influence the distribution of organic matter and crystalline clay minerals, which in turn control the soil charge characteristics. Thus, the constant charge from crystalline clay minerals should be considered in addition to the variable charge when studying the weakly weathered volcanic soils in the relatively dry regions.

Multi-floating-zone JTE for 4.5 kV SiC power devices with exponentially modulated dimensions

We propose a new multi-floating-zone junction-termination-extension (MFZ-JTE) using an exponentially modulated space and width for 4.5 kV SiC power devices to effectively spread out the electric field in reverse blocking mode and improve the tolerance against imprecise process control. A modified MFZ-JTE design with an exponential model was also proposed considering a stable patterning process. The blocking characteristics of the proposed MFZ-JTE using various exponential coefficients (α) in the model were evaluated for undesirable variations in the fabrication processes through TCAD simulations. The modified design for a 4.5 kV MFZ-JTE with α = 0.046 exhibited a low breakdown voltage deviation of 0.13% when the space variation ranged from –0.2 to +0.2 μm and 0.14% when the variation in the surface charge density at the SiO2/SiC interface was within the range of 0 to –1 × 1012 cm–3.

Charge-Plasma Based Cylindrical Nanowire FET for Low-Noise and High Sensing

A dopingless Cylindrical Nanowire Field Effect Transistor is proposed by implementing the charge plasma technique. The charge plasma technique helped in the necessary doping of the source/drain regions. The significance of using charge plasma based Nanowire FET for low-noise and higher sensing applications is investigated by analyzing the linearity parameters and compared with the Junctionless Nanowire FET. The proposed device is optimized as per the practical conditions by taking the interface trap charges into account. The interface trap charges are considered at the gate oxide-channel interface. The variation of interface trap charge (ITCs) density varies the device performance depending on the ITC polarity. The presence of ITCs can enhance device performance by tweaking the ITCs amplitude with positive polarity. The work function of the source/drain metal for the charge plasma technique is varied to get an optimized value. The higher value of source/drain metal degrades the device performance. The voltage interception point of the proposed device is greater than 5 times the actual value of the input signal. The drain current decreases drastically with the increase of source/drain work function independent of the gate bias.

A New Z-Shaped Gate Line Tunnel FET with Improved Electrostatic Performance

In this paper, we simulated a new line tunnel field-effect transistor (TFET) with a Z-shaped gate. The proposed Z-TFET generates vertical tunneling due to the presence of the front gate over the entire source region. This generates faster tunneling between the source and the channel region, providing a 3-decade improvement in drain current compared to conventional DG-TFET. The ambipolar current is also improved by 1-decade with a subthreshold swing (SS) of 40 mV/decade (reduces by 18%). Further optimization of the front and back gate is performed to investigate its impact on the analog performance of Z-TFET. The simulated results exhibit improvement in ambipolar current, reduction in OFF current by optimizing the back-gate length. This simulation work is performed in the presence of field-induced quantum confinement using the TCAD device simulator. Additional reliability issue of the structure in the presence of the interface trap charge at the semiconductor-oxide interface is properly investigated. The effect of trap charge density (Nf) and capture cross-section (σ) variation on the transfer characteristics and average SS has been examined. The proposed device can provide a higher ION/IOFF of 1013 and ION/IAMB of 107.

Electrocapillary effect in liquid films with an electrically charged interface

Abstract The electrocapillary effect is the change in interfacial tension between two immiscible liquids when subjected to an electric field across the interface. The change in interfacial tension occurs due to variations in the surface charge density of adsorbed ions or polar species at the interface. In the present work, we provide fluid mechanical insights into electrocapillarity-based dynamics of an interface between a passive air layer and a thin liquid film that has small, but finite electrical conductivity. We formulate and solve mathematical equations that model the situation in which a liquid film bounded by an air layer of controllable thickness is sandwiched between two electrode plates, and an electric field is applied across the layers. As the liquid and air have different conductivities, free charges would accumulate at the liquid–air interface to ensure that current is conserved across the layers. In our model, the interfacial tension is assumed to vary as per the classical Lippmann’s equation. The present mathematical model describes spatiotemporal variation of the film height and interfacial charge density as a function of the applied potential, air layer width, and the sensitivity of interfacial tension to the electric potential. Our results show that ultrathin liquid films (

Docking and Molecular Dynamic Simulation of Temozolomide with Carbonic Anhydrase XIII

The effect of inhibition of temozolomide, an alkylating agent widely used in cancer treatments, with carbonic anhydrase XIII protein was investigated using docking studies. The stability of temozolomide in the protein environment was assessed and analyzed by molecular dynamics simulation. The topological and charge density variations of temozolomide were studied in detail to perceive the primary insight of the pharmaceutical actions.

Synthesis and Characterization of Cationic Dendrimer‐PDMS Hybrids

A modular strategy for the synthesis of dendron-linear polymer hybrids comprised of a flexible polydimethylsiloxane (PDMS) midblock with cationic 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) dendron end groups is developed. The invention of a scalable methodology to access quaternary ammonium carboxylate building blocks and their direct use in esterification chemistry enables rapid access to cationic bis-MPA dendrons. The convergent click coupling of highly charged dendrons to hydrophobic PDMS chain-ends gives a 12-membered family of hybrids that are comprised of different dendron generations (G1-3) and quaternary ammonium alkyl chain lengths (C4 , C8 , C12 , C16 ). This provides a library of materials with variable hydrophobicity, charge density, and chain-end valency. The physical behavior of the dendron-linear PDMS hybrid copolymers significantly changes after introduction of the cationic dendron end-groups and leads to soft-solid materials as a result of inhibited chain mobility. These PDMS-dendron hybrids are expected to behave as surface-active antimicrobial additives in bulk cross-linked silicone systems.

Drain current characterization of dielectric modulated split gate TFET for bio-sensing application

This paper presents an analytical surface potential and drain current model of split gate (SG) Tunnel Field Effect Transistor (TFET) for label free detection of biomolecules e.g. protein, biotine, DNA, etc., utilizing the concept of underlap and dielectric modulation approach. A portion of the device channel is left open in between the splitted gates with a thin layer of silicon dioxide as adhesive layer. This open cavity acts as the binding site for the biomolecules to be detected which alters the effective capacitance of the region and hence modulates the device characteristic trend. The device electrostatics are developed by solving two dimensional Poisson’s equation and Young’s parabolic approximation and consequent drain current is then formulated applying Kane’s model. To assess the sensing ability of the device, both neutral and charged biomolecules with different dielectric values are immobilized within the cavity and the impact of variation in dielectric constant, charge density and height of biomolecules on device characteristics is analyzed. In addition to this, drain current sensitivity of the device is also investigated by varying the permittivity, charge density (both positive and negative) and height of the bio-species. All the analytical results are evaluated with corresponding Sentaurus TCAD simulated data to corroborate the accuracy of the derived model.

Numerical analysis of two-phase electrohydrodynamic flows in the presence of surface charge convection

The mechanism of surface charge convection (SCC) reveals inherently nonlinear coupling between the electrostatic problem and the hydrodynamic flow in the Melcher–Taylor electrohydrodynamic (EHD) model. Considering that most previous numerical models are based on decoupled leaky dielectric equations, the quantitative effect of SCC on two-phase EHD under different parameters remains unclear. In the present study, we propose a new numerical scheme to solve the two-phase EHD problems in the framework of the lattice Boltzmann method. The fully coupled equations including the Navier–Stokes equations, the Nernst–Planck equations, and the Poisson equation are solved using three well-designed lattice Boltzmann equations. The problem of droplet deformation under a uniform electric field is studied. By neglecting SCC at a small electric Reynolds number ReE ≪ 1, our model successfully reproduces previous theoretical and numerical results. When considering the SCC mechanism at finite values of ReE, the intensity of the EHD flow is reduced. Consequently, oblate droplets are predicted to be less deformed, while prolate droplets are enhanced. In addition, the SCC effect increases as the values of both ReE and the electric capillary number, Ca, increase. In addition, a sharp variation in surface charge density is observed near the equator of the droplet due to SCC.

Graphene–Ionic Liquid Interfacial Potential Drop from Density Functional Theory-Based Molecular Dynamics Simulations

Ionic liquids (IL) are promising electrolytes for electrochemical applications due to their remarkable stability and high charge density. Molecular dynamics simulations are essential for better understanding the complex phenomena occurring at the electrode-IL interface. In this work, we have studied the interface between graphene and 1-ethyl-3-methyl-imidazolium tetrafluoroborate IL, using density functional theory-based molecular dynamics simulations at variable surface charge densities. We have disassembled the electrical double layer potential drop into two main components: one involving atomic charges and the other - dipoles. The latter component arises due to the electronic polarisation of the surface and is related to concepts hotly debated in the literature, such as the Thomas-Fermi screening length, effective surface charge plane, and quantum capacitance.