Change In Charge State Research Articles

Structures and Chemical Bonding in NbS n 2−/−/0 (n = 3–5) Clusters: Effects of Sulfur Content and Charge States

Density functional theory and coupled cluster theory calculations are carried out to investigate the electronic and structural properties of a series of mono-niobium sulfide clusters, NbS n 2−/−/0 (n = 3–5). Generalized Koopmans’ Theorem is applied to predict the vertical detachment energies and simulate the corresponding photoelectron spectra. The evolutions of geometric and electronic structures of NbS n 2−/−/0 (n = 3–5) clusters with changes in sulfur content and charge states are illustrated. Intriguingly, diverse polysulfide ligands emerge in the corresponding sulfur-rich clusters, and distinct differences in the geometric and electronic structures influenced by charge states are exhibited, especially for the NbS 5 2−/−/0 clusters. In addition, the NbS n 2−/− are compared with the corresponding MoS n −/0 clusters. Similar structural evolution and behavior of sequential sulfidation as a function of S content are indicated for these two valence-isoelectronic systems. Molecular orbital analyses are performed to analyze the chemical bonding in these niobium sulfide clusters and to elucidate their electronic and structural evolutions.

State-of-charge-based droop control for stand-alone AC supply systems with distributed energy storage

The droop method is an advantageous technique for stand-alone AC supply systems, allowing for power sharing among various inverters with no need for communication cables. However, in stand-alone systems with multiple distributed energy storage units, the conventional droop methods are unable to control the storage unit state-of-charge (SOC) in order to change simultaneously. Existing techniques endeavor to solve this problem by changing the slope of the P–f curve however this solution compromises the power response performance. As an alternative, this paper proposes a new SOC-based droop control, whereby the P–f curve is shifted either upwards or downwards according to the battery SOC. The proposed technique makes it possible to select the time constant for the battery SOC convergence and, at the same time, to optimize the power response performance. The paper also shows how the SOC changes when the ratios between the battery capacity and the inverter rated power are different and how the proposed technique can limit the SOC imbalance. Simulation and experimental results corroborate the theoretical analysis.

DFTB3 Parametrization for Copper: The Importance of Orbital Angular Momentum Dependence of Hubbard Parameters.

We report the parametrization of a density functional tight binding method (DFTB3) for copper in a spin-polarized formulation. The parametrization is consistent with the framework of 3OB for main group elements (ONCHPS) and can be readily used for biological applications that involve copper proteins/peptides. The key to our parametrization is to introduce orbital angular momentum dependence of the Hubbard parameter and its charge derivative, thus allowing the 3d and 4s orbitals to adopt different sizes and responses to the change of charge state. The parametrization has been tested by applying to a fairly broad set of molecules of biological relevance, and the properties of interest include optimized geometries, ligand binding energies, and ligand proton affinities. Compared to the reference QM level (B3LYP/aug-cc-pVTZ, which is shown here to be similar to the B97-1 and CCSD(T) results, in terms of many properties of interest for a set of small copper containing molecules), our parametrization generally gives reliable structural properties for both Cu(I) and Cu(II) compounds, although several exceptions are also noted. For energetics, the results are more accurate for neutral ligands than for charged ligands, likely reflecting the minimal basis limitation of DFTB3; the results generally outperform NDDO based methods such as PM6 and even PBE with the 6-31+G(d,p) basis. For all ligand types, single-point B3LYP calculations at DFTB3 geometries give results very close (∼1–2 kcal/mol) to the reference B3LYP values, highlighting the consistency between DFTB3 and B3LYP structures. Possible further developments of the DFTB3 model for a better treatment of transition-metal ions are also discussed. In the current form, our first generation of DFTB3 copper model is expected to be particularly valuable as a method that drives sampling in systems that feature a dynamical copper binding site.

Transverse acceptance calculation for continuous ion beam injection into the electron beam ion trap charge breeder of the ReA post-accelerator

The ReA post-accelerator at the National Superconducting Cyclotron Laboratory (NSCL) employs an electron beam ion trap (EBIT) as a charge breeder. A Monte-Carlo simulation code was developed to calculate the transverse acceptance phase space of the EBIT for continuously injected ion beams and to determine the capture efficiency in dependence of the transverse beam emittance. For this purpose, the code records the position and time of changes in charge state of injected ions, leading either to capture or loss of ions. To benchmark and validate the code, calculated capture efficiencies were compared with results from a geometrical model and measurements. The results of the code agree with the experimental findings within a few 10%. The code predicts a maximum total capture efficiency of 50% for EBIT parameters readily achievable and an efficiency of up to 80% for an electron beam current density of 1900A/cm2.

Reversible potential-induced switching of alkyl chain aggregation in octyl-triazatriangulenium adlayers on Au(111).

In situ scanning tunneling microscopy and cyclic voltammetry studies of self-assembled octyl-triazatriangulenium monolayers on Au(111) electrode surfaces in 0.1 M HClO4 reveal a complex surface phase behavior, involving two fast, highly reversible transitions between different ordered adlayer phases: With decreasing potential, the preadsorbed (√19 × √19)R23.4° adlayer first is converted into a (7√3 × 7√3) and then into a (2√3 × 2√3)R30° phase, corresponding to a stepwise increase in the local packing density of the molecules. The (7√3 × 7√3) → (2√3 × 2√3)R30° transition is accompanied by a reorientation of the peripheral octyl chains from a more planar to a close-packed vertical arrangement. This reversible potential-induced switching between a homogeneous adlayer of small vertical extension and a Au surface partially covered by islands of a compact hydrocarbon layer is attributed to changes in the adsorbate charge state and associated changes in the intermolecular interactions.

Application of the bounds-analysis approach to arsenic and gallium antisite defects in gallium arsenide

A recently developed bounds-analysis approach has been used to interpret density-functional-theory (DFT) results for the As and Ga antisites in GaAs. The bounds analysis and subsequent processing of DFT results for the As antisite yielded levels---defined as the Fermi levels at which the defect charge state changes---in very good agreement with measurements, including the \ensuremath{-}1/0 level which is within 0.1 eV of the conduction-band edge. Good agreement was also obtained for the activation energies to transform the $\mathrm{A}{\mathrm{s}}_{\mathrm{Ga}}$ from its metastable state to its stable state. For the Ga antisite, the bounds analysis revealed that the \ensuremath{-}1 and 0 charge states are hole states weakly bound to a localized \ensuremath{-}2 charge state. The calculated levels are in good agreement with measurements.

Charge state, angular distribution, and kinetic energy of ions from multicomponent-cathodes in vacuum arc devices

We present research results on vacuum arc plasma produced with multicomponent cathode made of several different elements. The ion mass-to-charge-state spectra of the plasmas were studied by time-of-flight spectrometry. The angular distributions of different ion species were measured, and the kinetic energy of their directed (streaming) motion was determined. It is shown that the fractional composition of ions of different cathode components in the plasma flow from the cathode spot closely matches the fractional content of these components in the composite cathode. The charge states of ions of the various cathode components are determined by the average electron temperature in the cathode spot plasma. The angular distribution of lower mass ions in the plasma from a multicomponent cathode is less isotropic and broader than for the plasma from a single-component cathode of the same light element. The directed kinetic energies of the ions of the different components for plasma from a multicomponent cathode are lower for lighter elements and greater for heavier elements compared to the ion directed energy for plasmas from single-component cathodes made of the same materials. The physical processes responsible for these changes in the ion charge states in multicomponent-cathode vacuum arc plasma are discussed.

State-of-charge Stream Processing and Modeling for Electric Vehicle-Based Trips

This paper first describes how to process SoC (State of Charge) streams made up of temporal and spatial stamps, altitude, SoC reading, velocity, and the like. Collected by a probe vehicle on the same road in Jeju city, Republic of Korea, multiple times, each stream has its own initial SoC and speed. The driving distance is calculated by adding up the line segment connecting two consecutive sensor points. For each stream, we plot 1) the absolute SoC change to figure out the SoC dynamics, 2) the consumed SoC change to find the similarity between different streams, and 3) the normalized curves to build a common SoC change model. Next, the artificial neural network is exploited to trace a common pattern out of them, aiming at providing an essential basis for navigation applications supporting electric vehicles. The analysis result reveals that the model can find reasonable representative values out of different streams for each subsection, even with a simple model having just one input variable denoting the distance from the start point and one output variable denoting the SoC reading. Our model keeps the trace error less than 5 % for the duration in which the vehicle speed is the same for each stream.

Conformations of disulfide-intact and -reduced lysozyme ions probed by proton-transfer reactions at various temperatures.

Proton-transfer reactions of disulfide-intact and -reduced lysozyme ions (7+ through 14+) to 2,6-dimethylpyridine were examined in the gas phase using tandem mass spectrometry with electrospray ionization. By changing temperature of a collision cell from 280 to 460 K, temperature dependence of reaction rate constants and branching fractions was measured. Absolute reaction rate constants for the protein ions of specific charge states were determined from intensities of parent and product ions in the mass spectra. Remarkable change was observed for the rate constants and distribution of product ions. The rate constants for disulfide-intact ions changed more drastically with change of charge states and temperature than those for disulfide-reduced ions. Observed branching fractions for parent and product ions were represented by calculated reaction rate constants with a scheme of sequential process. The reaction rate constants are closely related to conformation changes with change of temperature, which are profoundly influenced by amputation of disulfide bonds.

Injection modification of multilayer dielectric layers of metal-oxide-semiconductor structures at different temperatures

The charge state change of MOS structures with multilayer dielectric films SiO2-PSG under high-field injection modification at different temperatures is studied in this article. The effect of temperature on the thermal stability of the negative charge component used to adjust the threshold voltage of MOS transistors is investigated. It is found that the performance of the high-field injection modification of MOS structures in the mode of constant current at elevated temperatures increases not only the density of the trapped negative charge but also its thermally stable component.

Multianalyte electrochemical biosensor on a monolith electrode by optically scanning the electrical double layer

Redox on an electrode is an interfacial phenomenon that modulates the charge in the electrical double layer (EDL). A novel instrument, the Scanning Electrometer for Electrical Double-layer (SEED) has been developed to measure multiple enzyme reactions on a monolith electrode due to immunospecific binding with a mixture of respective analytes. SEED quantitatively maps the local redox reaction by scanning a laser on the array of enzyme monolayer spots immobilized on the monolith electrode. SEED measures the change in local charge state of the EDL that abruptly changes due to the redox reaction. The measurement spot size defined by the size of the laser beam is ~10µm. The SEED signal is linearly proportional to the local redox current density and analyte concentration. The specificity is close to 100%. The SEED readout is compatible with microfluidics platform where the signal degrades less than 2% due to the poly(dimethyl siloxane) (PDMS) body.

Colloidal stability of carboxylated iron oxide nanomagnets for biomedical use

Magnetite nanoparticles (MNP) were synthesized and stabilized with carboxylated compounds citric acid – CA, poly(acrylic acid) – PAA, poly(acrylic acid-co-maleic acid) – PAM, humic acid – HA and gallic acid – GA (polymerizing in situ on the surface). Adsorption isotherms and bonding feature were determined and used to explain the changes in charge and aggregation states and salt tolerance of the MNPs. The thicker layer of macromolecular acids PAA, PAM and HA provides better stability at physiological pH and salt concentration compared to the CA and GA coatings. In addition, Fe(III)-CA complexation promotes the dissolution of the nanoparticles. The biocompatibility of the polyacid-coated MNPs was tested in cell proliferation experiments.

Oxygen induced transformations of the δ-Pu(111) surface

The oxides that form on metal surfaces are critical to the preservation of the material under oxidizing conditions. For the case of plutonium, oxide film properties may affect a variety of kinetic phenomena related to the corrosion of the material. To investigate the behavior of the metal–oxygen interactions critical to the formation of such passive films, electronic structure calculations were performed on the interactions between O and the δ-Pu(111) surface. By probing the relationship between structure (coordination), charge transfer (valence) and thermodynamics (reactivity), it was found that oxidation is initially a local phenomenon, but, at 1.0ML oxygen coverage, significant reconstructions that alter the phase structure of the near-surface region are induced. At this high-surface coverage the surface metal atoms are disbonded and the PuO coordination becomes four-fold as opposed to three fold. Even at this high coverage, however, the charge state more closely resembles Pu2O3 rather than PuO2. The ability for surface Pu atoms to adapt to a variety of changes in charge state and coordination provides a fundamental basis for understanding the multilayer structure of passive films formed on clean Pu surfaces. An analysis using first-principles thermodynamics also suggests that these films should develop uniformly, and not via an island or columnar growth mechanism.

Multilevel current stress technique for investigation thin oxide layers of MOS structures

In this study, a new technique of multilevel current stress for investigation thin oxide layers of MOS structures is proposed. This technique allows to investigate the generation and relaxation of positive and negative charges, accumulating in, nano-thickness gate dielectric of MOS structures under many stressing situations. The parameters characterizing the change of charge state in the thin oxide layers of MOS structures during the stress have been monitored by means of time dependence of voltage shift applied to a sample during the injection. The method takes into account the process of the MOS capacitance charging by the constant current pulse. In comparison with the conventional techniques our method is nondestructive and enables to reduce the high-field stress time while measuring the injection current-voltage characteristics of the MOS-structure. We consider this method to provide higher accuracy and to decrease the probability of dielectric breakdown. The application of present technique was carr mied out during the investigation of charge generation and relaxation, during and after high-field tunnel injection of electrons in thin thermal film of SiO2. The thin oxide layers of MOS structures after plasma and irradiation treatments also are investigated.

Evaluation of hydrophilic interaction chromatography (HILIC) versus C18 reversed-phase chromatography for targeted quantification of peptides by mass spectrometry

Hydrophilic-interaction liquid chromatography (HILIC) is a widely used technique for small polar molecule analysis and offers the advantage of improved sensitivity in mass spectrometry. Although HILIC is today frequently employed as an orthogonal fractionation method for peptides during the proteomic discovery phase, it is still seldom considered for quantification. In this study, the performances in terms of peak capacity and sensitivity of 3 HILIC columns were compared to traditional reversed phase liquid C18 column in the context of targeted quantification of proteotypic peptides using selected reaction monitoring mode (SRM). The results showed that the maximum sensitivity in HILIC chromatography was achieved by using an amide column without salt buffer and that the signal increased compared to classic reversed phase chromatography. However, the intensity improvement is quite low compared to the one obtained for small molecules. This is due on one hand to a higher matrix effect in HILIC and on the other hand to a change of charge states of peptides in organic solvent (doubly charged to monocharged). The doubly charged ions can be more readily dissociated than singly charged ions, making them ideal for SRM peptide quantification. As a result “supercharging” reagents are added to the mobile phase to shift from predominant singly charged ions to the more favorable doubly charged species. Using such optimized conditions, peptide signal is improved by a factor of between two and ten for 88% of the peptides of the 81 peptides investigated.

Dynamics of Coulomb explosion of Xe clusters in an ultrafast high-intensity laser field

Under the classical particle-dynamics simulation, Coulomb explosion of small Xe clusters in an intense femtosecond laser field and energies of the generated particles are studied. Our results show that the average kinetic energy of the generated ions increases with the cluster size. The dependence of the average kinetic energy of the product ions on the number of atoms inside Xe clusters and the change of average ions charge states from different shells of Xe561 within the interactional time are studied. The oscillation of the mass center of electrons along the direction of the laser electric field is calculated and the time evolutions of the total potential energy and the total kinetic energy of all the product particles are presented here. The total kinetic energy of Xe ions and free electrons are also calculated as functions of the interactional time.

Do Charge State Signatures Guarantee Protein Conformations?

The extent to which proteins in the gas phase retain their condensed-phase structure is a hotly debated issue. Closely related to this is the degree to which the observed charge state reflects protein conformation. Evidence from electron capture dissociation, hydrogen/deuterium exchange, ion mobility, and molecular dynamics shows clearly that there is often a strong correlation between the degree of folding and charge state, with the most compact conformations observed for the lowest charge states. In this article, we address recent controversies surrounding the relationship between charge states and folding, focussing also on the manipulation of charge in solution and its effect on conformation. 'Supercharging' reagents that have been used to effect change in charge state can promote unfolding in the electrospray droplet. However for several protein complexes, supercharging does not appear to perturb the structure in that unfolding is not detected. Consequently, a higher charge state does not necessarily imply unfolding. Whilst the effect of charge manipulation on conformation remains controversial, there is strong evidence that a folded, compact state of a protein can survive in the gas phase, at least on a millisecond timescale. The exact nature of the side-chain packing and secondary structural elements in these compact states, however, remains elusive and prompts further research.

Mechanism and kinetics of near-surface dopant pile-up during post-implant annealing

Dopant pile-up within 1-2 nm of Si/SiO2 interfaces during post-implant annealing can influence the performance of microelectronic devices using silicon-on-insulator technology or super-steep retrograde channels. Pile-up results from changes in the dopant interstitial charge state induced by band bending at the interface. But, there exists little mechanistic understanding of the specific conditions needed for pile-up or of the kinetics of temporal evolution. The present work uses continuum simulations coupled with experiments in the case of B implanted into Si to show that pile-up requires a zone near the interface wherein the Fermi level exceeds the ionization level for dopant interstitials to change their charge state. The spatial extent of pile-up corresponds closely to the width of this zone unless the annihilation probability of defects at the interface is large. The time and temperature dependences of pile-up closely track those of the free dopant interstitials concentration.

Metal–insulator transition induced by non-stoichiometry of surface layer and molecular reactions on single crystal KTaO3

In the study we present results on topography, morphology, chemical composition, electronic structure and electrical properties of the (100) surface layer of KTaO3 single crystal caused by sputtering with Ar+ ion beam with energy of 1keV. Several surface sensitive techniques, i.e. X-ray photoelectron spectroscopy (XPS), local conductivity of atomic force microscopy (LC-AFM), and Kelvin Probe Force Microscopy (KPFM) were used. The observed changes in the electronic structure were explained as a result of the chemical decomposition of the surface layer. A correlation between the electronic states which appeared in the energy gap and the changes in charge state of Ta ions was found. The activation energy related to averaged local conductivity temperature dependence was estimated from Arrhenius plot. It was also found, that variations in the local contact potential difference (LCPD) indicated changes in the chemical composition in nano-scale. The chemical reconstruction of the KTaO3 surface modified by Ar+ ion beam was deduced. This non-homogeneity corresponded to 2-D non-homogeneity of the local electric conduction (LC-AFM), which occurred within nano-areas after sputtering. Chemical reactivity of the modified surface with CO2 and O2 was observed. The reversibility of the Ar+ induced loss of oxygen non-stoichiometry was observed after the sample was exposed to various doses of O2. The successful reversibility occurred after oxidation process at high temperature, i.e. 300°C.

State of charge neural computational models for high energy density batteries in electric vehicles

Environmental concerns, increasing gasoline demand together with unpopularity of alternative energy sources to propel vehicles, have pushed on hybrid electric vehicles (HEVs) solutions. The main problem in battery management of HEVs is how to determine the battery state of charge (SOC). Estimation of SOC is an active area of research, and several approaches have been presented in the literature to monitor the SOC of a cell. At the first step, we use an optimized structure multi-layer perceptron (MLP) and an RBF neural network to determine the SOC changes of a high energy density battery in this paper. Then, a hybrid optimized structure neural model is used for SOC prediction considering the aging effect through the state of health (SOH) and discharge efficiency (DE) parameters. In this way, particle swarm optimization (PSO) algorithm is used for determining the optimum number of nodes in hidden layer(s) of MLPs. Experimental results show that the SOC estimation error by the proposed hybrid optimized structure neural model is 1.9% when compared with the real SOC obtained from a discharge test. In addition, monolithic optimized structure MLP and RBF neural models offer a good estimation of differentiated SOC.