Charge Buffer Research Articles

Dynamic charge exchange and delivery of the high-speed power delivery networks

In this paper, a charge exchange model is proposed to analyze the dynamic charge exchange and delivery of the highspeed power delivery networks. The power delivery network is decomposed into two parts, the charge buffer and the charge delivery path, which make the complicated dynamic charge exchange easy to understand. Based on this model, the mechanism of the dynamic charge exchange and delivery of all components in the charging hierarchy is fully demonstrated. It shows that the power planes provide a high-performance public platform for the charge exchange of all components and high-speed decoupling of the whole power delivery network.

A 6.5- $\mu \text{W}$ /MHz Charge Buffer With 7-fF Input Capacitance in 65-nm CMOS for Noncontact Electropotential Sensing

This brief presents a CMOS charge buffer with femtofarad-range input capacitance for applications in capacitive electropotential sensing. We analyze and verify a feedback mechanism to negate parasitic capacitances seen at the input of a CMOS amplifier. Measurements are presented from a prototype fabricated in 65-nm CMOS occupying an active area of 193 $ {\mu }\text{m}^{{2}}$ with an efficiency of 6.5 $ {\mu }\text{W}$ /MHz. Over-the-air measurements validate its applicability to electropotential sensing.

Ultrafine Nb2O5 Nanocrystal Coating on Reduced Graphene Oxide As Anode Materials for Sodium Ion Battery

Sodium ion battery (SIB) is a promising candidate for large-scale and practical application because of its lower costs and widespread of sodium resource.1 However, for SIBs, the intrinsic difference between sodium and lithium (ca. 55% larger and 330% heavier) lead to slower kinetics and lower energy densities.1 Nevertheless, it is reported that the enhance SIBs performance could be obtained by introducing the proper sodium host.2 For example, recent advances indicated that the ordered mesoporous Nb2O5-C delivered a reversible capacity of ~175 mA h/g and excellent cycle stability (up to 300 cycles).3 However, the low rate performance (<100 mA h/g at rate of 1A/g) cannot meet the requirements of fast charge-discharge electrochemical devices. In this work, ultrafine Nb2O5 nanocrystal/reduced graphene oxide (Nb2O5/rGO) was demonstrated as a promising anode material for sodium ion battery with high rate performance and high cycle durability. The Nb2O5/rGO was synthesized by controllable hydrolysis of niobium ethoxide and following treated at high annealing temperature in forming gas. Transmission electron microscopy (TEM) showed that ultrafine Nb2O5 nanocrystal with average particle size of 3 nm was uniformly deposited on rGO. Highly conductive rGO network and ultrafine Nb2O5 not only can enhance charge transfer and buffer the volume change during sodiation/desodiation process, but also could provide more active surface area for sodium ion storage, resulting in superior rate performance and cycle performance. XPS and XRD analyses revealed that the sodium ion storage mechanism in Nb2O5 could be accompanied with Nb5+/Nb4+ redox reaction and the ultrafine Nb2O5 nanocrystal provide more surface area to finish the redox reaction. Reference: 1. N. Yabuuchi, K. Kubota, M. Dahbi and S. Komaba, Chemical Reviews, 2014, 114, 11636-11682. 2. Y.-U. Park, D.-H. Seo, H.-S. Kwon, B. Kim, J. Kim, H. Kim, I. Kim, H.-I. Yoo and K. Kang, Journal ofthe American Chemical Society, 2013, 135, 13870-13878. 3. H. Kim, E. Lim, C. Jo, G. Yoon, J. Hwang, S. Jeong, J. Lee and K. Kang, Nano Energy, 2015, 16, 62-70.

Ultrafine Nb2O5 Nanocrystal Coating on Reduced Graphene Oxide as Anode Material for High Performance Sodium Ion Battery.

Ultrafine niobium oxide nanocrystals/reduced graphene oxide (Nb2O5 NCs/rGO) was demonstrated as a promising anode material for sodium ion battery with high rate performance and high cycle durability. Nb2O5 NCs/rGO was synthesized by controllable hydrolysis of niobium ethoxide and followed by heat treatment at 450 °C in flowing forming gas. Transmission electron microscopy images showed that Nb2O5 NCs with average particle size of 3 nm were uniformly deposited on rGO sheets and voids among Nb2O5 NCs existed. The architecture of ultrafine Nb2O5 NCs anchored on a highly conductive rGO network can not only enhance charge transfer and buffer the volume change during sodiation/desodiation process but also provide more active surface area for sodium ion storage, resulting in superior rate and cycle performance. Ex situ XPS analysis revealed that the sodium ion storage mechanism in Nb2O5 could be accompanied by Nb(5+)/Nb(4+) redox reaction and the ultrafine Nb2O5 NCs provide more surface area to accomplish the redox reaction.

Novel high voltage RESURF AlGaN/GaN HEMT with charged buffer layer

A novel reduced surface field (RESURF) AlGaN/GaN high electron mobility transistor (HEMT) with charged buffer layer is proposed. Its breakdown mechanism and on-state characteristics are investigated. The HEMT features buried Fluorine ions in the GaN buffer layer both under the Drift and the Gate region (FDG). The section of FDG under the drift region (FD) not only reduces the electric field (E-field) peak at the gate edge but also enhances the E-field in the drift region by the assisted depletion, leading to a significant improvement in breakdown voltage (BV). moreover, the section of FDG under the gate (FG) enhances the back barrier and effectively prevents electron injecting from the source to form leakage current, thus a higher BV is achieved. The BV of the proposed HEMT sharply increases to 750 V from 230 V of conventional AlGaN/GaN HEMT with the same dimensional parameters, and the specific on-resistance ($R_{\rm on,sp})$ just increases to \linebreak 1.21 m$\Omega \cdot $cm$^{2}$ from 1.01 m$\Omega \cdot $cm$^{2}$.

Effect of buffer charge on performance of air-cathodes used in microbial fuel cells

In microbial fuel cells (MFCs), buffers are typically used to improve performance by stabilizing the electrode pH and increasing the electrolyte conductivity, but the importance of the buffer net charge at current densities typical of MFCs on cathode performance has received little attention. Current production results in an electric field that drives positive ions towards the cathode, and negative ions to the anode. A series of biological buffers were selected with positive, negative, and neutral charges that had pKas ranging from 5 to 10.8. Cathodic current production using these different buffers in solutions with different pHs and conductivities was compared using linear sweep voltammetry (LSV). At lower pHs, buffers with positive charge increased cathodic current by as much as 95% within certain ranges (potential windows) of cathode potentials. No difference in cathodic current was shown in current for buffers with neutral or negative charge. The reason for this increase with the net positive charge buffers was likely due to a more stable electrode pH produced by electric field driving the positively charged ions towards the cathode. The potential window for the positively charged buffers was positively correlated to the concentration of cationic buffer in the electrolyte. At a pH higher than 9, no improvement in cathodic current was shown for buffers with positive charge, indicating at these higher pHs diffusion dominated buffer transport.

Differential influence of 7 cations on 16 non-competitive NMDA receptor blockers.

The specific binding of the NMDA receptor (NR) channel ligand [(3)H]MK-801 to rat brain membranes is sensitive to positively charged buffer ingredients as to tris(hydroxymethyl)aminomethane (Tris), to Na(+), or to protons. Here we demonstrate that 16 non-competitive NR antagonists, including 5 long-chain diamines, classical NR channel blockers and several less known compounds, differ widely in their sensitivities to cationic buffer constituents. Although chemically distinguished either as extended di-cationic or as compact mono-cationic, their sensitivities to cationic buffer ingredients did not suggest this grouping. While the di-cationic compounds are known for their sensitivity to spermine (polyamine inverse agonists), also some of the mono-cationic blockers exhibited this feature. They might share as common target a recently described negatively charged extracellular GluN1/GluN2B interface.

Chemical vapor deposition grown monolayer graphene field-effect transistors with reduced impurity concentration

We report on the restoration of the electronic characteristics of waferscale chemical vapor deposition (CVD) monolayer graphene field-effect transistors (GFETs) by reducing the impurity concentration. An optimized electropolishing process on copper foils combined with carbon-fluorine encapsulation using a suitable amorphous fluoropolymer enables reducing the surface roughness of graphene and screening out interfacial impurity scattering, which leads to an improvement in all key device metrics. The conductivity at the Dirac point is substantially reduced, resulting in an increase in the on-off current ratio. In addition, the field-effect mobility increased from 1817 to 3918 cm2/V-s, the impurity concentration decreased from 1.1 × 1012 to 2.1 × 1011 cm−2 and the electron and hole transport became more symmetric. Significantly, favorable shifts toward zero voltage were observed in the Dirac point. We postulate that the smoother surface due to electropolishing and a pool of strong dipole-dipole moments in the flouropolymer coating provide a charge buffer that relaxes the fluctuation in the electron-hole puddles. We also investigate the long-term stability in GFETs encapsulated with fluoropolymer, which exhibit a high hydrophobicity that suppresses the chemical interaction with water molecules. Open image in new window

Development of l‐histidine immobilized CIM® monolithic disks for purification of immunoglobulin G

The pseudobiospecific affinity ligand l-histidine was immobilized on epoxy, carbonyldiimidazole (CDI), and ethylenediamine (EDA) convective interaction media (BIA Separations, Slovenia) monolithic disks to obtain the histidyl affinity column for purification of immunoglobulin G (IgG). The kinetics and the mass transfer properties of the affinity columns were studied to determine the optimum buffer condition, flow rate, and concentration of IgG for maximum IgG adsorption. The binding capacities of all the three affinity columns were higher with zwitterionic buffer morpholinopropanesulfonic acid than with charged buffers such as tris-HCl and phosphate buffers, and the optimum pH was 6.5. The interaction of IgG with histidine immobilized CDI and epoxy disks was found to be predominantly driven by ionic interaction, while the interaction with EDA-histidine disk could be partially governed by multiple non-covalent forces of interaction. The maximum binding capacity (Qm ) of l-histidine immobilized on EDA-, CDI-, and epoxy-activated convective interaction media disks were 19.83 ± 0.25, 15.85 ± 0.18 and 12.11 ± 0.17 mg/ml of support, respectively, and the dissociation constant (Kd ) were calculated to be in the micromolar range for all the three histidyl monolithic columns. Purification of IgG from untreated human serum was also attempted, and the results indicate the high potential of this method for purification of total IgG from complex biological sources and also for separation of IgG1 from other subclasses.

Solar Battery Charger in CMOS 0.25 um Technology

A solar cell powered Li-ion battery charger in CMOS 0.25um is proposed. The solar battery charger consists of a DC/DC boost converter and a battery charger. The voltage generated by a solar cell is up converted from 0.65V to 1.8V, which is used as the VDD of the battery charger. In this way, the solar battery charger automatically converts solar energy to electricity and stores it directly to a Li-ion rechargeable battery. In this system, a super capacitor is needed as a charge buffer between the boost converter and the charger.

Comparison of Sn-doped and nonstoichiometric vertical-Bridgman-grown crystals of the topological insulator Bi2Te2Se

A comparative study of the properties of topological insulator Bi2Te2Se (BTS) crystals grown by the vertical Bridgeman method is described. Two defect mechanisms that create acceptor impurities to compensate for the native n-type carriers are compared: Bi excess, and light Sn doping. Both methods yield low carrier concentrations and an n-p crossover over the length of the grown crystal boules, but lower carrier concentrations and higher resistivities are obtained for the Sn-doped crystals, which reach carrier concentrations as low as 8 × 1014 cm−3. Further, the temperature dependent resistivities for the Sn-doped crystals display strongly activated behavior at high temperatures, with a characteristic energy of half the bulk band gap. The (001) cleaved Sn-doped BTS crystals display high quality Shubnikov de Haas (SdH) quantum oscillations due to the topological surface state electrons. Angle resolved photoelectron spectroscopy (ARPES) characterization shows that the Fermi energy (EF) for the Sn-doped crystals falls cleanly in the surface states with no interference from the bulk bands, which the Dirac point for the surface states lies approximately 60 meV below the top of the bulk valence band maximum, and allows for a determination of the bulk and surface state carrier concentrations as a function of Energy near EF. Electronic structure calculations that compare Bi excess and Sn dopants in BTS demonstrate that Sn acts as a special impurity, with a localized impurity band that acts as a charge buffer occurring inside the bulk band gap. We propose that the special resonant level character of Sn in BTS gives rise to the exceptionally low carrier concentrations and activated resistivities observed.

Actin Assembly at Model-Supported Lipid Bilayers

We report on the use of supported lipid bilayers to reveal dynamics of actin polymerization from a nonpolymerizing subphase via cationic phospholipids. Using varying fractions of charged lipid, lipid mobility, and buffer conditions, we show that dynamics at the nanoscale can be used to control the self-assembly of these structures. In the case of fluid-phase lipid bilayers, the actin adsorbs to form a uniform two-dimensional layer with complete surface coverage whereas gel-phase bilayers induce a network of randomly oriented actin filaments, of lower coverage. Reducing the pH increased the polymerization rate, the number of nucleation events, and the total coverage of actin. A model of the adsorption/diffusion process is developed to provide a description of the experimental data and shows that, in the case of fluid-phase bilayers, polymerization arises equally due to the adsorption and diffusion of surface-bound monomers and the addition of monomers directly from the solution phase. In contrast, in the case of gel-phase bilayers, polymerization is dominated by the addition of monomers from solution. In both cases, the filaments are stable for long times even when the G-actin is removed from the supernatant—making this a practical approach for creating stable lipid-actin systems via self-assembly.

Transfer and computation of optical topological charges via light pulse buffer memory in an electromagnetically-induced-transparency solid

We verified that optical topological charges are conserved in a two-step light-pulse storage and retrieval process based on the electromagnetically-induced-transparency (EIT) effect in a Pr${}^{3+}$:${\mathrm{Y}}_{2}{\mathrm{SiO}}_{5}$ crystal. Based on this conservation law, one could transfer topological charges from the interacting beams, which may not be overlapped in space and time domains, to the targeted output signal beam, and algebraic operations such as summation and subtraction of topological charges carried by the interacting beams were demonstrated via the EIT-assisted two-step light-pulse storage-retrieval process. The results may be useful for classical and quantum information processing based on optical topological charge buffer memory in EIT media.

Electrostatic control of peptide side-chain reactivity using amphiphilic homopolymer-based supramolecular assemblies.

Supramolecular assemblies formed by amphiphilic homopolymers with negatively charged groups in the hydrophilic segment have been designed to enable high labeling selectivity toward reactive side chain functional groups in peptides. The negatively charged interiors of the supramolecular assemblies are found to block the reactivity of protonated amines that would otherwise be reactive in aqueous solution, while maintaining the reactivity of nonprotonated amines. Simple changes to the pH of the assemblies' interiors allow control over the reactivity of different functional groups in a manner that is dependent on the pKa of a given peptide functional group. The labeling studies carried out in positively charged supramolecular assemblies and free buffer solution show that, even when the amine is protonated, labeling selectivity exists only when complementary electrostatic interactions are present, thereby demonstrating the electrostatically controlled nature of these reactions.

DNA Adsorption to and Elution from Silica Surfaces: Influence of Amino Acid Buffers

Solid phase extraction and purification of DNA from complex samples typically requires chaotropic salts that can inhibit downstream polymerase amplification if carried into the elution buffer. Amino acid buffers may serve as a more compatible alternative for modulating the interaction between DNA and silica surfaces. We characterized DNA binding to silica surfaces, facilitated by representative amino acid buffers, and the subsequent elution of DNA from the silica surfaces. Through bulk depletion experiments, we found that more DNA adsorbs to silica particles out of positively compared to negatively charged amino acid buffers. Additionally, the type of the silica surface greatly influences the amount of DNA adsorbed and the final elution yield. Quartz crystal microbalance experiments with dissipation monitoring (QCM-D) revealed multiphasic DNA adsorption out of stronger adsorbing conditions such as arginine, glycine, and glutamine, with DNA more rigidly bound during the early stages of the adsorption process. The DNA film adsorbed out of glutamate was more flexible and uniform throughout the adsorption process. QCM-D characterization of DNA elution from the silica surface indicates an uptake in water mass during the initial stage of DNA elution for the stronger adsorbing conditions, which suggests that for these conditions the DNA film is partly dehydrated during the prior adsorption process. Overall, several positively charged and polar neutral amino acid buffers show promise as an alternative to methods based on chaotropic salts for solid phase DNA extraction.

Local Electrical Properties of the 4H-SiC(0001)/Graphene Interface

Local current transport across graphene/4H-SiC was studied with nanometric scale lateral resolution by Scanning Current Spectroscopy on both graphene grown epitaxially on 4H-SiC(0001) (EG-SiC) and graphene exfoliated from highly oriented pyrolitic graphite and deposited on 4H-SiC(0001) (DG-SiC). The study revealed that the Schottky barrier height (SBH) of EG/4H-SiC(0001) is lowered by ~0.49eV. This is explained in terms of Fermi-level pinning above the Dirac point in EG due to the presence of positively charged states at the interface between Si face of 4H-SiC and carbon-rich buffer layer. Furthermore, Scanning Capacitance Spectroscopy based method allowed evaluating local electron mean free path (lgr) in graphene. lgr in EG-SiC was observed to be, on average, ~0.4 times that in DG-SiC and exhibited large point-to-point variations due to presence of laterally homogeneous positively charged buffer layer at the interface. However, lgr in graphene on SiC was observed to be larger than on standard SiO2 samples (DG-SiO2), which is explained by better dielectric screening of charged impurities and lower surface polar phonon scattering at the graphene/substrate interface.

Predicting diafiltration solution compositions for final ultrafiltration/diafiltration steps of monoclonal antibodies

Many liquid formulations for monoclonal antibodies (MAbs) require the final ultrafiltration/diafiltration step to operate at high protein concentrations, often at or above 100 g/L. When operating under these conditions, the excipient concentrations and pH of the final diafiltered retentate are frequently not equal to the corresponding excipient concentrations and pH of the diafiltration buffer. A model based on the Poisson-Boltzmann equation combined with volume exclusion was extended to predict both pH and excipient concentrations in the retentate for a given diafiltration buffer. This model was successfully applied to identify the diafiltration buffer composition required to achieve the desired pre-formulated bulk drug substance (retentate) conditions. Predictions were in good agreement with the experimental results, and reduced the number of experimental iterations needed to define the diafiltration buffer composition. Additionally, the predictive model was applied in a sensitivity analysis across ranges of protein charge, protein concentration, and diafiltration buffer pH and excipient concentration. This sensitivity analysis can facilitate the design of experiments for robustness testing, and allow for generalized predictions across classes of molecules such as MAbs.

Discrete-time charge-domain filter with charge buffer for flexible design of FIR filter

A discrete-time charge-domain filter (CDF) with wide bandwidth and high attenuation is proposed. By employing a charge buffer with timing control to move a sampled charge between capacitors, the CDF can reduce the number of pulses and select a decimation rate effectively. Measurement showed 13 MHz bandwidth and 88.86 dB attenuation in a 90 nm CMOS process.

Hofmeister effects: interplay of hydration, nonelectrostatic potentials, and ion size

The classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory of colloids, and corresponding theories of electrolytes, are unable to explain ion specific forces between colloidal particles quantitatively. The same is true generally, for surfactant aggregates, lipids, proteins, for zeta and membrane potentials and in adsorption phenomena. Even with fitting parameters the theory is not predictive. The classical theories of interactions begin with continuum solvent electrostatic (double layer) forces. Extensions to include surface hydration are taken care of with concepts like inner and outer Helmholtz planes, and "dressed" ion sizes. The opposing quantum mechanical attractive forces (variously termed van der Waals, Hamaker, Lifshitz, dispersion, nonelectrostatic forces) are treated separately from electrostatic forces. The ansatz that separates electrostatic and quantum forces can be shown to be thermodynamically inconsistent. Hofmeister or specific ion effects usually show up above ≈10(-2) molar salt. Parameters to accommodate these in terms of hydration and ion size had to be invoked, specific to each case. Ionic dispersion forces, between ions and solvent, for ion-ion and ion-surface interactions are not explicit in classical theories that use "effective" potentials. It can be shown that the missing ionic quantum fluctuation forces have a large role to play in specific ion effects, and in hydration. In a consistent predictive theory they have to be included at the same level as the nonlinear electrostatic forces that form the skeletal framework of standard theory. This poses a challenge. The challenges go further than academic theory and have implications for the interpretation and meaning of concepts like pH, buffers and membrane potentials, and for their experimental interpretation. In this article we overview recent quantitative developments in our evolving understanding of the theoretical origins of specific ion, or Hofmeister effects. These are demonstrated through an analysis that incorporates nonelectrostatic ion-surface and ion-ion dispersion interactions. This is based on ab initio ionic polarisabilities, and finite ion sizes quantified through recent ab initio work. We underline the central role of ionic polarisabilities and of ion size in the nonelectrostatic interactions that involve ions, solvent molecules and interfaces. Examples of mechanisms through which they operate are discussed in detail. An ab initio hydration model that accounts for polarisabilities of the tightly held hydration shell of "cosmotropic" ions is introduced. It is shown how Hofmeister effects depend on an interplay between specific surface chemistry, surface charge density, pH, buffer, and counterion with polarisabilities and ion size. We also discuss how the most recent theories on surface hydration combined with hydrated nonelectrostatic potentials may predict experimental zeta potentials and hydration forces.

Buffer‐trap and surface‐state effects on gate lag in AlGaN/GaN HEMTs

AbstractTwo‐dimensional simulation of turn‐on characteristics of Al‐GaN/GaN HEMTs is performed in which both buffer traps and surface states are considered. It is studied how the so‐called gate lag is affected by these factors. It is shown that gate lag due to buffer traps can occur because in the off state where the gate voltage is negative, electrons are injected into the buffer layer and captured by the traps, leading to more negatively charged buffer layer. It is also shown that gate lag due to an electron‐trap‐type surface state can occur only when electron's gate tunneling is considered (© 2010 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)