Depth profiling of charging effect of Si nanocrystals embedded in SiO2: a study of charge diffusion among Si nanocrystals

Si nanocrystal (nc-Si) embedded in SiO2 thin film is synthesized with low-energy Si ion implantation. Depth profiling of the charging effect of the nc-Si is determined from X-ray photoemission measurement. It is observed that there is a strong correlation between the depth profile of the charging effect and the nc-Si depth distribution. The charging effect is found to decrease with the increase of nc-Si concentration and to vanish when a densely stacked nanocrystal layer is formed. The phenomenon is attributed to the charge diffusion among the nanocrystals. The charge diffusion in the nanocrystal layer may have an important implication for nanocrystal flash memory. When such a layer is used as the charge-storage layer in the memory cells, the stored charges could be lost due to the rapid charge diffusion among the nc-Si if a single defect exists in the tunneling oxide, causing a reliability problem in data retention.     

The charging of a liquid dielectric upon its flow past a flat-plate

The charging of a liquid dielectric upon its flow past a flat-plate is considered. Analytical expressions for the density distribution of electric charge and charging current are derived. The dependences of the current and charge density distribution on the system parameters are investigated. The effect of the electric field that emerges owing to charge separation on the charging process is taken into account. Consideration of the electric field is shown to lead to lower values of the electric charge density and charging current. As the Debye number decreases, the charge density also decreases. The charging current increases with an increase in the Debye number.     

Quantized Double‐Layer Charging of Iron Oxide Nanoparticles on a‐Si:H Controlled by Charged Defects in a‐Si:H

Sequential single‐electron charging of iron oxide nanoparticles encapsulated in oleic acid/oleyl amine envelope and deposited by the Langmuir‐Blodgett technique onto Pt electrode covered with undoped hydrogenated amorphous silicon film (a‐Si:H) is reported. Quantized double‐layer charging of nanoparticles is detected by cyclic voltammetry as current peaks and the charging effect can be switched on/off by the excess of negative/positive charged defect states in the a‐Si:H layer. The particular charge states in a‐Si:H are created by the simultaneous application of a suitable bias voltage and illumination before the measurement.     

Continuum Field Charging of Dielectric Spheroids

Classical continuum theory for field charging is applied in an analysis of the ionic charging of spheroidal dielectrics. Assuming that the particle orientation is fixed during the charging process, the saturation charge and charging rate are determined as functions of the orientation and aspect ratio of spheroids. For spheroids of small dielectric constants the saturation charge becomes the largest when the electric field is directed perpendicular to the major axis of the spheroid. For an ensemble of randomly oriented spheroids the average saturation charge can be approximated as the arithmetic average of the saturation charges for the spheroid with the electric field directed along the three principal axes of the spheroid. In addition, the ensemble average of the dimensionless charging rate of randomly oriented spheroids of moderate axial ratio approximates the dimensionless charging rate of a sphere. Copyright 2000 Academic Press.     

Surface charging behaviors of electrocatalytic interfaces with partially charged chemisorbates

The surface charge is a key concept in electrochemistry. Mathematically, the surface charge is obtained from a spatial integration of the volume charge along a particular direction. Ambiguities thus arise in choosing the starting and ending points of the integration. As for electrocatalytic interfaces, the presence of chemisorbates further complicates the situation. In this minireview, I adopt a definition of the surface charge within a continuum picture of the electric double layer. I will introduce surface charging behaviors of firstly ordinary electrochemical interfaces and then electrocatalytic interfaces featuring partially charged chemisorbates. Particularly, the origin of nonmonotonic surface charging behaviors of electrocatalytic interfaces is explained using a primitive model. Finally, a brief account of previous studies on the nonmonotonic surface charging behavior is presented, as a subline of the spectacular history of electric double layer.     

Mechanism of charging and supercharging molecules in electrospray ionization

The origin of the extent of charging and the mechanism by which multiply charged ions are formed in electrospray ionization have been hotly debated for over a decade. Many factors can affect the number of charges on an analyte ion. Here, we investigate the extent of charging of poly(propyleneimine) dendrimers (generations 3.0 and 5.0), cytochrome c, poly(ethylene glycol)s, and 1,n-diaminoalkanes formed from solutions of different composition. We demonstrate that in the absence of other factors, the surface tension of the electrospray droplet late in the desolvation process is a significant factor in determining the overall analyte charge. For poly(ethylene glycol)s, 1,n-diaminoalkanes, and poly(propyleneimine) dendrimers electrosprayed from single-component solutions, there is a clear relationship between the analyte charge and the solvent surface tension. Addition of m-nitrobenzyl alcohol (m-NBA) into electrospray solutions increases the charging when the original solution has a lower surface tension than m-NBA, but the degree of charging decreases when this compound is added to water, which has a higher surface tension. Similarly, the charging of cytochrome c ions formed from acidified denaturing solutions generally increases with increasing surface tension of the least volatile solvent. For the dendrimers investigated, there is a strong correlation between the average charge state of the dendrimer and the Rayleigh limiting charge calculated for a droplet of the same size as the analyte molecule and with the surface tension of the electrospray solvent. A bimodal charge distribution is observed for larger dendrimers formed from water/m-NBA solutions, suggesting the presence of more than one conformation in solution. A similar correlation is found between the extent of charging for 1,n-diaminoalkanes and the calculated Rayleigh limiting charge. These results provide strong evidence that multiply charged organic ions are formed by the charged residue mechanism. A significantly smaller extent of charging for both dendrimers and 1,n-diaminoalkanes would be expected if the ion evaporation mechanism played a significant role.     

Discrete electrostatic charge transfer by the electrophoresis of a charged droplet in a dielectric liquid

We have experimentally investigated the electrostatic charging of a water droplet on an electrified electrode surface to explain the detailed inductive charging processes and use them for the detection of droplet position in a lab-on-a-chip system. The periodic bouncing motion of a droplet between two planar electrodes has been examined by using a high-resolution electrometer and an image analysis method. We have found that this charging process consists of three steps. The first step is inductive charge accumulation on the opposite electrode by the charge of a droplet. This induction process occurs while the droplet approaches the electrode, and it produces an induction current signal at the electrometer. The second step is the discharging of the droplet by the accumulated induced charge at the moment of contact. For this second step, there is no charge-transfer detection at the electrometer. The third step is the charging of the neutralized droplet to a certain charged state while the droplet is in contact with the electrode. The charge transfer of the third step is detected as the pulse-type signal of an electrometer. The second and third steps occur simultaneously and rapidly. We have found that the induction current by the movement of a charged droplet can be accurately used to measure the charge of the droplet and can also be used to monitor the position of a droplet under actuation. The implications of the current findings for understanding and measuring the charging process are discussed.     

Quantized double-layer charging of highly monodisperse metal nanoparticles

We describe unprecedented resolution of electrochemically observed quantized double layer (QDL) charging, attained with use of reduced solution temperatures and with an annealing procedure that produces hexanethiolate monolayer protected gold clusters (C6 MPCs) with a high level of monodispersity in charging capacitance, C(CLU). The spacing DeltaV = e/C(CLU) on the electrochemical potential axis between one electron changes in the electronic charge of nanoscopic metal particles is determined by their effective capacitance C(CLU). The high monodispersity of the C6 MPCs with Au(140) cores facilitates (a) detailed rotated disk and cyclic voltammetric measurements, (b) simulation of QDL waveshapes based on assumed reversible, multivalent redox-like behavior, (c) determination of nanoparticle diffusion rates, and (d) observation of as many as 13 changes in the MPC charge state, from MPC(6-) to MPC(7+). The single electron QDL charging peaks are quite evenly spaced (DeltaV constant) at potentials near the MPC potential of zero charge, but are irregularly spaced at more positive and negative potentials. The irregular spacing is difficult to rationalize with classical double layer capacitance ideas and is proposed to arise from a correspondingly structured (e.g., not smooth) density of electronic states of the nanoparticle core, resulting from its small HOMO/LUMO gap and incipiently molecule-like behavior.     

Quantized spectroelectrochemical behaviour of monolayer-protected gold cluster films assessed by reflectance spectroelectrochemical quartz crystal microbalance

The spectral changes occurring in multilayer films of hexanethiolate monolayer-protected Au₁₄₇ clusters (C6–Au₁₄₇ MPCs) as a consequence of quantized MPC core charging have been investigated in aqueous solutions using a multiresponse technique, UV–vis reflectance spectroelectrochemical quartz crystal microbalance (SEQCM). The joint technique, a combination of UV–vis near-normal incidence reflectance spectroelectrochemistry and electrochemical quartz crystal microbalance, has enabled us to follow both reflectance and gravimetric changes taking place in the MPC film concurrently with each single electron transfer event. Reversible film reflectance drops were observed upon anodic MPC charging, which were linearly dependent on the MPC charge state. The values of the formal potential and number of electrons transferred in each charging step, determined from the potential dependence of the reflectance changes, proved that the spectral features were induced by the discrete charging of the MPCs. Simultaneously, the gravimetric signal monitored with EQCM yielded values of the number of MPC-bound electrolyte ions as a function of the MPC redox state, both during voltammetric and potential step charging of the MPC films. Additionally, the dynamics of electron transfers in these multilayer MPC films has been investigated by electrochemical impedance spectroscopy (EIS). Thus, the film capacitance, the resistance to charge transfer, and the electron-transfer rate constant for MPC oxidation have been estimated.     

Characterization of mineral oxide charging in apolar media

This paper presents an investigation of the charging behavior of mineral oxide particles dispersed in apolar media. There are a growing number of applications that seek to use electrostatic effects in apolar media to control particle movement and improve aggregation stability. Progress is limited, however, by incomplete knowledge of the mechanism(s) of particle charging in these systems. It has been shown in a number of cases that the acid-base properties of both the particles and the surfactants used to stabilize charge play key roles. A mechanism for acid-base charging has previously been established for mineral oxides in aqueous systems, where the surface hydroxyl groups act as proton donors or receivers depending on the pH of the surrounding solution. In water, the pH at which the surface charge density is zero, i.e., the point of zero charge (PZC), can be used to characterize the acid-base nature of the mineral oxide particles. The current work explores the possible extension of this charging behavior to apolar systems, with the key difference that the surface hydroxyl groups of the mineral oxides react with the surfactant molecules instead of free ions in solution. The apolar charging behavior is explored by measuring the electrophoretic mobility of a series of mineral oxides dispersed in a solution of Isopar-L and AOT, a neutral surfactant in water. The electrophoretic mobility of the particles is found to scale quantitatively, with respect to both sign and magnitude, with their aqueous PZC value. This provides support for the theory of acid-base charging in apolar media and represents a method for predicting and controlling particle charge of mineral oxides dispersed in apolar media.     

Electrophoresis of randomly charged particles

The technique of "rotational electrophoresis" has been developed recently to measure the charge nonuniformity on Brownian particles in a suspension. Measurements of the angular velocity in electrophoresis are interpreted with electrokinetic theory to give a standard deviation of zeta potential among N regions on a particle. A key question is how various molecular mechanisms of charging could lead to charge nonuniformity on a length scale of O (100 nm). Simple statistical physics is used to show that although Poisson charging with univalent charges cannot explain recent measurements showing significant charge nonuniformity, random charging with multivalent charges can better explain the data. In addition, the result shows that a small number of charged "visualization" molecules can be adsorbed to a particle without impacting the experimental technique of rotational electrophoresis.     

Free energy of charge transfer and intraprotein electric field: method of calculation depends on the charge state of protein at a given structure.

Free energy of charge transfer presents a basic characteristic of reactions such as protonation, oxido-reduction and similar. Evaluation of this quantity requires calculation of charging energy. Proteins are structured dielectrics, and a consistent incorporation of their structure into calculation of intraprotein electric field results in expression for charging energy of an active group in protein, which is essentially different from that for a simple dielectric. An algorithm for semi-continuum calculation of relevant free energies is described. First of the two components of charging energy in protein, energy of the medium response to charge redistribution in reactants, should be always calculated as the charging energy by the charge redistribution using the static dielectric constant of protein. The second term is interaction energy of the charge redistribution with the 'frozen' electric field of the system before reaction. Charges of protein groups, at which the protein structure has been determined, are often different from those before reaction of charge transfer, so is the corresponding intraprotein field. The field is expressed through either both the optical and static dielectric constants of protein or only optical one depending on whether the charges of protein groups before reaction and upon structural analysis are the same or not. Proper allowance for difference in charges of reacting groups before reaction and upon structural analysis of protein is thermodynamically necessary and quantitatively important. The expression for activation free energy for charge transfer in proteins is derived in the form presenting explicitly an invariant contribution of protein structure.     

Ligand heterogeneity on monolayer-protected gold clusters

This paper describes the effects of oxidative electronic charging of the Au cores of the monolayer-protected clusters (MPCs), Au140(S(CH2)5CH3)53 and Au38(SCH2CH2Ph)24, on nuclear magnetic resonance (NMR) spectra of their monolayer ligand shells. Previously unresolved fine structure in the 13C NMR hexanethiolate methyl and C5 methylene resonances is seen in spectra of solutions of monodisperse Au140(S(CH2)5CH3)53 MPCs, reflecting magnetically inequivalent ligand sites. Incremented increases in positive cluster core charge, effected by electrochemical charging, cause the spectral fine structure of the methyl resonance to coalesce, becoming a single peak at the Au140(3+) charge state. The spectral changes are reversible; charging back to the original core charge state regenerates the methyl 13C resonance fine structure. Adding an equimolar quantity of a Au(I) thiolate complex, Au(I)[SCH2(C6H4)C(CH3)3], to an uncharged Au140(S(CH2)5CH3)53 MPC solution in d2-methylene chloride causes partial spectral coalescence. 13C NMR spectra of Au38(SCH2CH2Ph)24 MPCs exhibit roughly comparable spectral changes upon positive core charging to the '0', '+1', and '+2' states. The NMR results indicate that exchange between magnetically inequivalent sites occurs at rates of 100 to 400 s(-1), a rate believed to be too fast to be accountable by actual exchanges of ligands between different sites on the Au core. We also describe changes in core electronic spectra of Au140(S(CH2)5CH3)53 induced by positive charging, measured using spectroelectrochemistry.     

The unpredictability of electrostatic charging

Capricious charges: the electrostatic charging that occurs when two surfaces come into contact is familiar to everyone, and has been known for millennia. Nonetheless, the scientific understanding of the phenomenon is poor, and it is not possible to reliably predict which surface will charge positively and which will charge negatively. Recent work shows why electrostatic charging may never be predictable.     

Effect of rubbing load on nanoscale charging characteristics of human hair characterized by AFM based Kelvin probe

The manageability and feel of human hair is significantly affected by its surface charge. Understanding and developing ways to control charge build up is hence highly beneficial. Previous studies have looked at static charging characteristics of hair on a macroscale. In this study, static charging characteristics of hair are studied on the nanoscale with an AFM. Hair is charged by rubbing a control area on its surface with an AFM tip, to which a small voltage bias is applied. The resulting charge distribution is characterized by measuring the surface potential of the control area in situ with AFM based Kelvin probe microscopy. The rubbing load is progressively increased, and the effect of this increase on the charge build up is assessed. Virgin, damaged and conditioner treated hair samples are studied for a better understanding of charge build up and dissipation. Relevant mechanisms are discussed.     

应用于AGV自动导引车的快速充电系统

设计建立一种用于AGV自动导引车镍氢动力蓄电池的快速充电系统,该系统在充电过程中能实时监测蓄电池组的各个运行参数,完成数据运算并逻辑判断、控制充电过程至其结束,并利用去极化放电脉冲提高充电效率.     

Unlocking Charge Transfer Limitations for Extreme Fast Charging of Li-Ion Batteries

Extreme fast charging (XFC) of high-energy Li-ion batteries is a key enabler of electrified transportation. While previous studies mainly focused on improving Li ion mass transport in electrodes and electrolytes, the limitations of charge transfer across electrode–electrolyte interfaces remain underexplored. Herein we unravel how charge transfer kinetics dictates the fast rechargeability of Li-ion cells. Li ion transfer across the cathode–electrolyte interface is found to be rate-limiting during XFC, but the charge transfer energy barrier at both the cathode and anode have to be reduced simultaneously to prevent Li plating, which is achieved through electrolyte engineering. By unlocking charge transfer limitations, 184 Wh kg⁻¹ pouch cells demonstrate stable XFC (10-min charge to 80 %) which is otherwise unachievable, and the lifetime of 245 Wh kg⁻¹ 21700 cells is quintupled during fast charging (25-min charge to 80 %).     

Modifying the charge state distribution of proteins in electrospray ionization mass spectrometry by chemical derivatization

Electrospray ionization (ESI) of denatured proteins produces a broad distribution of multiply-charged ions leading to multiple peaks in the mass spectrum. We investigated changes in the positive-mode ESI charge state distribution produced by several chemical modifications of denatured proteins. Capping carboxylic acid groups with neutral functional groups yields little change in charge state distribution compared with unmodified proteins. The results indicate that carboxyl groups do not play a significant role in the positive charging of denatured proteins in ESI. The modification of proteins with additional basic sites or fixed positive charges generates substantially higher charge states, providing evidence that the number of ionizable sites, rather than molecular size and shape, determines ESI charging for denatured proteins. Fixed charge modification also significantly reduces the number of protons acquired by a protein, in that the charge state envelope is not increased by the full number of fixed charges appended. This result demonstrates that Coulombic repulsion between positive charges plays a significant role in determining charge state distribution by affecting the gas-phase basicity of ionizable sites. Addition of fixed-charge moieties to a protein is a useful approach for shifting protein charge state distributions to higher charge states, and with further work, it may help limit the distribution of protein ions to fewer charge states.     

In-situ Study of Charge and Discharge of Ni-MH Battery Using the Combined Method of Electrochemistry and Microcalorimetry

An apparatus to study the battery system has been set up. The thermal effects of charge and discharge of Ni-MH batteries have been studied. The calorimetric measurements indicate that the net heat dissipation during charging is larger than that during discharging. It is observed that the ratio of heat dissipation to charging energy varies with charging capacity, and almost 90 percent of charging energy is lost as heat dissipation near the end of the charging process at 97.7 mA. A jump of thermal curve near the end of discharge due to a secondary electrode reaction has been observed.This revised version was published online in November 2005 with corrections to the Cover Date.     

Super-stoichiometric charge neutralization in particle-polyelectrolyte systems

The adsorption of poly(vinylamine) (PVA) on poly(styrene sulfate) latex particles is studied, and its consequences on the charging behavior and suspension stability are investigated. The adsorption process is assessed by batch depletion experiments and time-resolved electrophoretic mobility measurements. The adsorption of PVA appears to be basically irreversible. The rate of adsorption decreases with decreasing polymer dose. At low polymer dose, the polymer coverage corresponds to the amount of the polyelectrolyte added, while at high polymer dose, the polymer coverage saturates the surface. Stability ratios are determined by dynamic light scattering, and strongly depend on the polymer dose and salt level. The aggregation is rapid near the isoelectric point (IEP), and it slows down when moving away from it. The charge neutralization is highly nonstoichiometric with charging ratios (CR) larger than unity, meaning that several charges on an adsorbed polyelectrolyte chain are necessary to neutralize a single charge on the particle surface. By comparing the IEP for particles and polyelectrolytes of different charge densities, we find a strong dependence of the CR on the mismatch between the average distances between individual charges on the surface and on the polyelectrolyte. A simple model is proposed to explain this trend.