Variation Of Charge Density Research Articles

Feedback effect of electric field force on electrification and charge structure in thunderstorm

The electrification within the thunderstorm, caused mainly by inductive and noninductive charging mechanism, can produce strong local electric field inside the thundercloud. Due to the resulting electric field force, the vertical velocity of the graupel and hail particles which are the main in-cloud charge carriers, would change. As a feedback, this variation could affect the original electrification and charge structure of the thunderstorm. In order to investigate such a feedback effect, a weather research forecasting (WRF) model coupled with explicit lightning physics including charging and discharge lightning scheme (hereafter WRF-Elec) is employed and modified in this study. We derive the formulas for calculating the mass-weighted mean terminal velocities of graupel and hail under the balance among gravity, resistance and electric field force. Then, the National Sever Storm Laboratory (NSSL) two-moment bulk microphysics scheme is modified by adding the calculating code with consideration of electric field force (EFF) acting on the fall speed of graupel and hail particles. Eventually, the two-coupled WRF-Elec is developed successfully.#br#Based on this modified WRF-Elec, sensitivity tests are conducted to quantitatively investigate the influences of EFF on the thunderstorm electrification and the corresponding charge structure in an idealized supercell case. The results show that during the rapid enhancement of the thunderstorm, the grid-scale mass-weighted mean fall speed of graupel and hail vary significantly in consideration of EFF, with the maximum values both exceeding 4 m/s, although this situation occurs within a local area and lasts a short time. The action of EFF tends to enhance the falling of graupel and weaken the falling of hail. The influences of EFF on those graupel and hail particles with smaller-size and lower number concentration are stronger, as determined by composite factors of the strength and polarity of electric field, the diameter and number concentration of graupel and hail, and their charge density and polarity as well. The adjustment of the terminal velocity of the graupel and hail in consideration of EFF, eventually results in increasing the rate of both inductive and noninductive charge separation, where the inductive charging is the much more significant one. This leads to a grid-scale total charge density variation of -0.6-1.2 nC/m3 and a redistribution of the charge structure in the thunderstorm, and correspondingly, an increase of the local vertical electric field by 5 kV/m, thus producing stronger lightning eventually. In addition, due to the effect of electric field force, the mass mixing ratio of four precipitation particles including graupel, hail, ice crystal and snow is changed in the ranges of -0.09-0.24, -0.16-0.04, -0.04-0.05, and -0.01-0.006 g/kg, respectively. Therefore, the electric field force in thunderstorm affects not only the electrification and charge structure, but also the microphysical process. Generally, the overall influence of EFF on electrification tends to be positive, and the feedback effect of EFF on the charge structure should not be neglected.

Polysaccharide based hydrogels reinforced with halloysite nanotubes via polyelectrolyte complexation

Inspired by the charge density variation, low cost and environmentally friendly clay minerals such as halloysite nanotubes (HNTs), herein we prepared nanocomposite (NC) hydrogels reinforced with HNTs via polyelectrolyte complexation (PEC) of xanthan gum and chitosan using glucuronic acid δ-galactone as acidifying agent in the aqueous media. The charge density of HNT and PEC of biopolymers can be influenced by the microstructure, physical interactions, swelling, and mechanical properties of the NC hydrogels. In vitro cell cultures of NC hydrogels on osteoblasts (MC3T3-E1) cell line showed improvement in cell proliferation than PEC hydrogels and may possibly be applied in biomedical fields such as tissue engineering.

Anomalous electrokinetics at hydrophobic surfaces: Effects of ion specificity and interfacial water structure

We study the electrokinetic transport behavior of water molecules and ions in hydrophobic graphene nanochannels with variable surface charge densities as well as the interfacial water structure based on detailed molecular dynamics simulations. The interfacial water structure, described by the water density, hydrogen bonding, diffusion, distribution of the OH bond and dipole orientations, is strikingly influenced by the surface charge sign and density. We find anomalous electrokinetic effects which are related to the distribution of counterions close to the surface, ion-specific effects and the interfacial water structure. On a negatively charged graphene layer, the attraction of Na+ ions towards the surface enhances the interfacial friction. In contrast, if the surface is positively charged, high surface charge density triggers an anomalous enhancement of electroosmotic flow, accompanied by an abrupt change of the interfacial water structure. At high surface charge densities, the mobility of the interfacial water at the positively charged surfaces is suppressed more strongly compared to the negatively charged surface. Our results reveal new electrokinetic phenomena by the comparison of negatively and positively charged surfaces.

Interaction of hydrogen with Pd- and co-decorated C24 fullerenes: Density functional theory study

In this work, we have investigated the adsorption of a hydrogen atom and molecules on the Pd and Co-decorated C24 fullerenes by means of density functional theory. The hydrogen interaction mechanism with host cages by regarding the adsorption energy and charge density variations was studied. It is found that both Pd and Co atoms have a significant role to increase the adsorption energy as an exothermal process. This energy change is strongly dependent on the electrostatic potential variations around the Pd and Co atoms doped on the C24 fullerene. Also, the HOMO-LUMO gap (Eg) for C24 fullerene varies from 1.20 to 0.76 and 0.86eV, after decorations of Co and Pd atoms, respectively. More consideration such as thermodynamics parameter, electronic density of states, and charge density analysis are discussed in the context.

Stability analysis of an electrospinning jet of polymeric fluids

The axisymmetric instability, which has a potential to cause bead formation along the fibers produced by electrospinning technique, is examined with the help of linear stability theory. The stability of a straight jet is analyzed under conditions corresponding to the electrospinning of two types of polymeric fluids, the PIB-based Boger fluid with low electrical conductivity and the highly conductive PEO solution in ethanol/water. For the former, the rheology is described by the Oldroyd-B model, suitable for unentangled polymers under weak elongational flow. On the other hand, the highly conductive polymer solution experiences a strong elongational flow due to very high axial electric force, for which the viscoelasticity is appropriately described using the eXtended Pom-Pom (XPP) model, the nonlinear rheological model for entangled polymeric systems. Contrary to previous studies, which oversimplifies the electrified jet as a cylindrical jet with uniform radius and other jet variables, we analyze the stability of the realistic non-uniform thinning jet as observed in electrospinning experiments. The stability of the thinning jet profile, obtained using the 1D slender body model, is examined by imposing non-periodic axisymmetric disturbances and constructing the spectrum of disturbance growth rate. The thinning jet is found to be relatively less unstable than the uniform jet, which is attributed to the stabilizing role of extensional stresses, in addition to the axial variation in surface charge density and electric field, present in the non-uniform deforming jet, but ignored in the analysis of the uniform jet. For both the reference fluids considered, the polymer addition renders the jet stable and thus, suppresses the bead formation during straight jet path of electrospinning. Also, the enhancement in fluid elasticity, characterized by the flow Deborah number, plays a stabilizing role for the thinning jet of Oldroyd-B fluid. However, for the XPP fluid, the fluid elasticity shows a rich behavior with a stabilizing effect for moderate values of Deborah number, attributed to stretching of polymer chain between the branch points, and a destabilizing effect for highly elastic fluids, due to strain rate softening. Increasing the strain hardening effect in the polymer solution, achieved by increasing number of arms at the branch point in the XPP molecule, tends to stabilize the electrospinning jet against axisymmetric disturbances potentially producing smooth bead-less fibers. While the instability in low conductivity fluid is driven by capillary forces, the instability in highly conductive fluid is an oscillatory conducting mode driven by the coupling of the surface charges and the axial electric field.

Low Variability in Synthetic Monolayer MoS2 Devices.

Despite much interest in applications of two-dimensional (2D) fabrics such as MoS2, to date most studies have focused on single or few devices. Here we examine the variability of hundreds of transistors from monolayer MoS2 synthesized by chemical vapor deposition. Ultraclean fabrication yields low surface roughness of ∼3 Å and surprisingly low variability of key device parameters, considering the atomically thin nature of the material. Threshold voltage variation and very low hysteresis suggest variations in charge density and traps as low as ∼1011 cm-2. Three extraction methods (field-effect, Y-function, and effective mobility) independently reveal mobility from 30 to 45 cm2/V/s (10th to 90th percentile; highest value ∼48 cm2/V/s) across areas >1 cm2. Electrical properties are remarkably immune to the presence of bilayer regions, which cause only small conduction band offsets (∼55 meV) measured by scanning Kelvin probe microscopy, an order of magnitude lower than energy variations in Si films of comparable thickness. Data are also used as inputs to Monte Carlo circuit simulations to understand the effects of material variability on circuit variation. These advances address key missing steps required to scale 2D semiconductors into functional systems.

Molecular electrostatic potential and "atoms-in-molecules" analyses of the interplay between π-hole and lone pair···π/X-H···π/metal···π interactions.

Using ab initio calculations, we analyze the interplay between π-hole interactions involving the nitro group of 1,4-dinitrobenzene and lone pair···π (lp···π), C-H···π or metal(M)···π noncovalent interactions. Moreover, we have also used 1,4-phenylenebis(phosphine dioxide) for comparison purposes. Interesting cooperativity effects are found when π-hole (F···N,P) and lp···π/C-H···π/M···π interactions coexist in the same supramolecular assembly. These effects are studied theoretically in terms of energetic and geometric features of the complexes, which are computed by ab initio methods (RI-MP2/def2-TZVP). A charge density analysis using the Bader's theory of "atoms in molecules" is carried out to characterize the interactions and to analyze their strengthening or weakening depending on the variation of charge density at critical points. The importance of electrostatic effects on the mutual influence of the interaction is studied by means of molecular electrostatic potential calculations. By taking advantage of these computational tools, the present study examines interplay of these interactions. © 2017 Wiley Periodicals, Inc.

Electric field imaging of single atoms

In scanning transmission electron microscopy (STEM), single atoms can be imaged by detecting electrons scattered through high angles using post-specimen, annular-type detectors. Recently, it has been shown that the atomic-scale electric field of both the positive atomic nuclei and the surrounding negative electrons within crystalline materials can be probed by atomic-resolution differential phase contrast STEM. Here we demonstrate the real-space imaging of the (projected) atomic electric field distribution inside single Au atoms, using sub-Å spatial resolution STEM combined with a high-speed segmented detector. We directly visualize that the electric field distribution (blurred by the sub-Å size electron probe) drastically changes within the single Au atom in a shape that relates to the spatial variation of total charge density within the atom. Atomic-resolution electric field mapping with single-atom sensitivity enables us to examine their detailed internal and boundary structures.

A dielectrically modulated electrically doped tunnel FET for application of label free biosensor

The fabrication challenges and cost of nanoscale devices have been a major concern in the field of label free biosensor. Therefore, to overcome these issues, we report for the first time a dielectrically modulated electrically doped tunnel field-effect transistor (DM-EDTFET) as a biosensor for label free detection. For this purpose, n+ drain and p+ source regions in proposed device are induced by considering polarity bias of PG-1 = +1.2 V and PG-2 = −1.2, respectively over the ultra-thin silicon body. The proposed structure is immune against doping control issues, avoids thermal budget and fabrication complexity as compared to its counterpart TFET. In DM-EDTFET, a nanogap cavity embedded within the gate dielectric is formed by etching the selected portion of gate dielectric layer towards the source side for sensing the biomolecules. The sensing ability of DM-EDTFET has been analysed in terms of variation in dielectric constant and charge density of biomolecules, and device geometry parameters at different bias conditions. To analyse the relative sensitivity, proposed DM-EDTFET is compared with MOSFET based biosensor in terms of sensing parameters. From these results, DM-EDTFET provides superior results in terms of sensitivity as compared to MOSFET based biosensor. Hence, the proposed DM-EDTFET biosensor can be a promising candidate for the development of future sensing bio-equipments.

Time-resolved whole field investigation of plasma plume-induced shock wave in liquid media of different densities

Laser-produced plasma-induced shock wave in liquid media of different densities has been experimentally studied using non-intrusive diagnostics. A time-resolved Mach–Zehnder interferometer is setup to track the shock wave and subsequent density perturbations in the medium. Two-dimensional spatial distributions for both, ambient medium density and plasma (electron) density have been obtained by employing customised inversion technique and algorithm on the recorded interferograms. It has been observed that the nature of the shock-induced density perturbation in liquid medium is significantly different as compared to that in the gaseous medium. The observed density perturbations have been correlated with the primary shock wave and stress waves reflected from within the target and travelling back in the medium. The trend in the variation of electronic charge density in the plume region has also been studied.

An assessment of strontium sorption onto bentonite buffer material in waste repository.

In the present study, changes occurring in sorption characteristics of a representative bentonite (WIn-BT) exposed to SrCl2 (0.001-0.1M) under the pH range of 1-13 were investigated. Such interaction revealed a significant variation in surface charge density and binding energy of ions with respect to bentonite, and alteration in their physicochemical properties viz., specific surface area, cation exchange capacity, thermal and mechanical behaviour were observed. The distribution coefficients (k d) calculated for sorption onto virgin (UCBT) and contaminated bentonite (CBT) indicated a greater influence of mineralogical changes occurred with variance of pH and strontium concentration. Notably, the sorption mechanism clearly elucidates the effect of structural negative charge and existence of anionic metal species onto CBT, and depicted the reason behind significant k d values at highly acidic and alkaline pH. The maximum k d of UCBT and CBT(0.001M SrCl2) were 8.99 and 2.92L/kg, respectively, at the soil pH 8.5; whereas it was 2.37 and 1.23L/kg at pH 1 for the CBT(0.1M SrCl2) and CBT(0.01M SrCl2), respectively. The findings of this study can be useful to identify the physicochemical parameters of candidate buffer material and sorption reversibility in waste repository.

Generalized Noise Study of Solid-State Nanopores at Low Frequencies.

Nanopore technology has been extensively investigated for analysis of biomolecules, and a success story in this field concerns DNA sequencing using a nanopore chip featuring an array of hundreds of biological nanopores (BioNs). Solid-state nanopores (SSNs) have been explored to attain longer lifetime and higher integration density than what BioNs can offer, but SSNs are generally considered to generate higher noise whose origin remains to be confirmed. Here, we systematically study low-frequency (including thermal and flicker) noise characteristics of SSNs measuring 7 to 200 nm in diameter drilled through a 20-nm-thick SiNx membrane by focused ion milling. Both bulk and surface ionic currents in the nanopore are found to contribute to the flicker noise, with their respective contributions determined by salt concentration and pH in electrolytes as well as bias conditions. Increasing salt concentration at constant pH and voltage bias leads to increase in the bulk ionic current and noise therefrom. Changing pH at constant salt concentration and current bias results in variation of surface charge density, and hence alteration of surface ionic current and noise. In addition, the noise from Ag/AgCl electrodes can become predominant when the pore size is large and/or the salt concentration is high. Analysis of our comprehensive experimental results leads to the establishment of a generalized nanopore noise model. The model not only gives an excellent account of the experimental observations, but can also be used for evaluation of various noise components in much smaller nanopores currently not experimentally available.

A Charge-Plasma-Based Dielectric-Modulated Junctionless TFET for Biosensor Label-Free Detection

To reduce the fabrication complexity and cost of the nanoscale devices, a charge-plasma concept is introduced for the first time to implement a dielectric-modulated junctionless tunnel field-effect transistor (DM-JLTFET) for biosensor label-free detection. The formation of p+ source and n+ drain regions in DM-JLTFET is done by the deposition of platinum (work function = 5.93 eV) and hafnium (work function = 3.9 eV) materials, respectively, over the silicon body. Furthermore, a nanogap cavity embedded within the gate dielectric is created by etching the portion of gate oxide layer toward the source end for sensing biomolecules. For this, the sensing capability of DM-JLTFET has been investigated in terms of variation in dielectric constant, charge density, length, and thickness of the cavity at different bias conditions. Finally, a comparative study between DM-JLTFET and MOSFET biosensor is investigated. The implementation of proposed device and all the simulations have been performed by using ATLAS device simulator.

Interaction Forces between Lipid Rafts.

Cellular membranes containing sphingolipids and cholesterol have been shown to self-organize into lipid rafts-specialized domains that host integral membrane proteins and modulate the bioactivity of cells. In this work, force-distance profiles between raft membranes in the liquid-ordered phase consisting of singly unsaturated 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), a complex mixture of brain sphingomyelin (BSM), and cholesterol were measured using the surface force apparatus (SFA). Two distinct force profiles were detected corresponding to uniform raft membranes and raft membranes with a higher level of topological membrane defects (heterogeneous) as corroborated by atomic force microscopy (AFM) scans. In all cases a weak, long-range electrostatic repulsion was observed with some variation in the surface charge density. The variation in electrostatic repulsion was attributed to charged lipid species primarily from the constituent lipids in the BSM mixture. The adhesion between the uniform raft membranes was comparable to our previous work with pure component, liquid-ordered POPC-DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine)-cholesterol membranes. Raft membranes with more topological defects adhered more strongly owing to hydrophobic attraction between exposed acyl chains. Even though the rafts were in the liquid-ordered phase and membrane defects were present in the contact region, the raft membranes were stable, and no structural rearrangement was observed throughout the measurements. Our findings demonstrate that liquid-ordered membranes are stable to mechanical loading and not particularly sensitive to compositional variation.

Sequential Recognition of Zinc and Pyrophosphate Ions in a Terpyridine-Functionalized Single Nanochannel.

A highly selective recognition system for zinc(II) and pyrophosphate ions is constructed using a single conical nanochannel covalently functionalized with N'-{4-[(2,2':6',2''-terpyridine)-4-yl]benzyl}ethane-1,2-diamine (TPYD). The immobilized TPYD acts as a specific coordination site for Zn2+ to form TPYD-Zn2+ complexes in preference over other metal ions, and subsequently, the resulting Zn2+ -coordinated nanochannel can be used as a selective recognition element for the pyrophosphate ion based on the coordination reaction between hydroxyl oxygen atoms of pyrophosphate and Zn2+ . Ion recognition is monitored by measuring the current-voltage curves of the solutions. The ionic current of the TPYD-functionalized system at -2.0 V undergoes a clear decrease after exposure to Zn2+ ions and is followed with an obvious increase after subsequent treatment with a pyrophosphate solution. The change of ionic current can be primarily attributed to the variation of charge density of the nanochannel. This functionalized single nanochannel might provide a simple and universal means to recognize other targets by modifying different functional molecules onto the inner surfaces of nanochannels.

Hyperbranched Copolymers Based on Glycidol and Amino Glycidyl Ether: Highly Biocompatible Polyamines Sheathed in Polyglycerols.

Functional hyperbranched polyglycerols (PGs) have recently garnered considerable interest due to their potential in biomedical applications. Here, we present a one-pot synthesis of hyperbranched PGs possessing amine functionality using a novel amino glycidyl ether monomer. A Boc-protected butanolamine glycidyl ether (BBAG) monomer was designed and polymerized with glycidol (G) through anionic ring-opening multibranching polymerization to yield a series of hyperbranched P(G-co-BBAG) with controlled molecular weights (4800-16700 g/mol) and relatively low molecular weight distributions (1.2-1.6). The copolymerization and subsequent deprotection chemistry allow the incorporation of an adjustable fraction of primary amine moieties (typically, 5-20% monomer ratio) within the hyperbranched PG backbones, thus providing potentials for varying charge densities and functionality in PGs. The copolymerization kinetics of G and BBAG was also evaluated using a quantitative in situ 13C NMR spectroscopic analysis, which revealed gradient copolymerization between the comonomers. The free amine groups within the deprotected P(G-co-BAG) copolymer were further utilized for a facile conjugation chemistry with a model molecule in a quantitative manner. Furthermore, the superior biocompatibility of the prepared P(G-co-BAG) polymers was demonstrated via cell viability assays, outperforming many existing polyamines possessing relatively high cytotoxicity. Taken together, the biocompatibility with facile conjugation chemistry of free amine groups sheathed within the framework of hyperbranched PGs holds the prospect of advancing biological and biomedical applications.

Charge Variations in Cuprate Superconductors from Nuclear Magnetic Resonance

Charge inhomogeneities in the cuprates were reported early on and have been in the focus of much research recently. Nuclear magnetic resonance (NMR) is very sensitive to local charge symmetry through the electric quadrupole interaction that must detect any static charge density variation. Recent experiments in high magnetic fields that seem to induce charge density waves in some systems have rekindled the interest in static inhomogeneities. It has long been known that excessive NMR linewidths can be observed in all cuprates, but with the exception of a few materials. However, the relation of the quadrupolar linewidths with respect to variations of the charge density in the cuprates is not understood. Here, we investigate YBa2Cu3O7 and we find even in a moderate magnetic field that below about 200 K, i.e., well above T c, a temperature dependent NMR linewidth appears that must be related to incipient static charge density variations. We argue that this establishes field induced charge density variation as a more general phenomenon in the cuprates. In view of the very recent understanding of the relation between the hole distribution in the CuO2 plane and T c, it is argued that charge density variations are ubiquitous, but appear not related to the maximum T c.

Modeling field emitter arrays using nonlinear line charge distribution

Modeling high aspect ratio field emitter arrays is a computational challenge due to the enormity of the resources involved. The line charge model (LCM) provides an alternate semi-analytical tool that has been used to model both infinite as well as finite sized arrays. It is shown that the linearly varying charge density used in the LCM generically mimics ellipsoidal emitters rather than a Cylindrical-Post-with-an-Ellipsoidal-Tip (CPET) that is typical of nanowires. Furthermore, generalizing the charge density beyond the linear regime allows for modeling shapes that are closer to a CPET. Emitters with a fixed base radius and a fixed apex radius are studied with a view to understanding the effect of nonlinearity on the tip enhancement factor and the emitter current in each case. Furthermore, an infinite square array of the CPET emitters is studied using the nonlinear line charge model, each having a height h=1500 μm and a base radius b=1.5 μm. It is found that for moderate external field strengths (0.3−0.4 V/μm), the array current density falls sharply for lattice spacings smaller than 43h. Beyond this value, the maximal array current density can be observed over a range of lattice spacings and falls gradually thereafter.

Process-Induced Variations of 10-nm Node Bulk nFinFETs Considering Middle-of-Line Parasitics

Process-induced variations of 10-nm node n-type FinFETs considering middle-of-line parasitics were investigated in terms of dc/ac performances using fully calibrated TCAD simulations. Variations of positive fixed oxide charge density at shallow trench isolation interface and source/drain (S/D) height influenced off-state and on-state performance variations, respectively, but slightly on RC delay variations. Fin width variations induced off-state performance and RC delay variations critically due to the fluctuation of short channel effects. But, fin height variations affected them slightly due to the preserved gate-to-channel controllability and the buffered effects by varying drain currents and gate capacitances in the same direction. Gate length, spacer length, and S/D length variations influenced dc/ac performance variations severely; 2-nm-length changes were barely acceptable to satisfy 10% RC delay margin. Thus, the process-induced variability parameters, including fin width, gate length, spacer length, and S/D length, should be controlled tightly under a few nanometers to reduce dc/ac performance variations of the FinFETs.

Modeling the charge density profile in thin film devices using SIMS profiling data

To obtain an insight into the degradation kinetics of thin film solar cells, we developed a theory to model the variation of total charge density across the absorber layer of CdS/CdTe thin film solar cells. The variation in total charge density has been generally ignored in the literature despite being the original reason of instability in device parameters. We used SIMS profiling data reported in the literature to track the Cu concentration across CdTe layer and it's variation under short- & open-circuit conditions. Cu migration under the stress of elevated temperature and prolonged irradiation is known to be the major degradation source in CdTe layer by increasing the charge accumulation at the junction and creating a barrier to carrier passivation. We obtained the Cu distribution functions before/after stressing the cell and imported these fitting functions in our model to calculate the real total charge density and electric field variation at both front/back regions. Our simulation indicates that stressing the cell cause charge accumulation at interface/junction of CdTe/metal and CdS/CdTe and reduces the electric field and leads to the relevant degradation trend. The depletion width is also reduced by increased Cu concentration under the stress. This model is capable to be developed to include the real distribution of vacancies, defects, doping and ions (obtained by SIMS or other spectroscopy methods) to calculate the total charge density, electric field, resistivity of solar cells stressed under various light, temperature and biasing conditions. The worsen stress condition is predicted to be the open-circuit condition.