Spatial Distribution Of Ions Research Articles

Steadily Decreasing Power Loss of a Double Schottky Barrier Originating from the Dynamics of Mobile Ions with Stable Interface States

A general aging model of the double Schottky barrier was proposed to unveil the long-term aging behaviors of $\mathrm{Zn}\mathrm{O}$ varistor ceramics, especially for those ones with steadily decreasing power loss. For those samples, the barrier height and electrical properties were even enhanced rather than commonly deteriorated, which were beyond the classic ion migration model. In this paper, inspired by the unique reversible aging of them, interface states are proposed to remain stable in those samples. The major mobile ions, which have been in debate, are further identified to be ${\mathrm{Zn}}_{i}^{\ensuremath{\cdot}}$ ions. Based on these assumptions, a quantitative dynamic ion migration-diffusion model is proposed. The calculated power loss steadily decreases with aging time, which well supported our proposal. When the interface states are not combined with those mobile ions, the formation of a ``U-shape'' ion spatial distribution in depletion layers is found to be responsible for the unique aging phenomena, i.e., a reduction in the depletion layer and interfacial charge, a rise in the depletion layer width, and an increase in the barrier height. However, continuously increasing power loss would be generated if the mobile ions combined with the interface states. Therefore, a general mechanism on the aging of the double Schottky barrier is unveiled that it is a competition process between consumption of the interface states and the dynamics of mobile ions in depletion layers.

Study of the critical angle of channeling of active metal ions through thin aluminum films

The spatial distributions of ions (K+, Na+) passed through thin polycrystalline and single-crystalline Al films with the thickness from 180 to 600 Angstrem and critical channeling angles have been studied. The ion energies have been varied within the range E0=10-30 keV. It has been shown that an increase in the energy of the primary ion beam leads to a decrease in the width of the maxima of the angular distribution, which is associated with a decrease in the critical channeling angle psicr. It has been found that the value psicr does not exceed 4-50 for axial channeling and 9-100 for planar channeling Keywords: critical angle, passage of ions, angular distribution, channeling, spatial distribution.

Ion density and phase space density distribution of planetary ions Na+, O+ and He+ in Mercury’s magnetosphere

Photo-ionization of Mercury’s tenuous exosphere contributes to the heavy ion population in the Hermean environment. Observations with the MESSENGER Fast Imaging Plasma Spectrometer (FIPS) have revealed the ion density and spatial distribution of the three most abundant planetary ions or ion groups around Mercury: The Na+-group (mass-per-charge ratio m/q=21–30amu/e), O+-group (m/q=16–20amu/e) and He+. We developed a test-particle model coupled to a neutral exosphere model and two different models of the magnetosphere to simulate the ion density distribution of Na+, He+ and O+. We compare the modeled ion density distribution at aphelion for northward interplanetary magnetic field (IMF) with FIPS observations from the entire orbital phase (23 March 2011 to 30 April 2015). Our model reproduces several observed features but the average ion density is up to 18x too high. However, we find that the discrepancy is less than 3x for other solar wind and exosphere conditions. Comparison with previous simulation studies of the Na+ ion density and magnetic field line resonance observations give an average Na+ density which is on the same order as our estimate. Finally, we model the phase space density (PSD) distribution in four different regions. We find that in three out of four regions only a fraction of the PSD distribution can typically be observed by FIPS. This is mainly due the obstruction of the field-of-view caused by the spacecraft’s sun shield, which blocks plasma with a high vx/vz ratio from entering the instrument.

Osmotic Transport at the Aqueous Graphene and hBN Interfaces: Scaling Laws from a Unified, First-Principles Description.

Osmotic transport in nanoconfined aqueous electrolytes provides alternative venues for water desalination and "blue energy" harvesting. The osmotic response of nanofluidic systems is controlled by the interfacial structure of water and electrolyte solutions in the so-called electrical double layer (EDL), but a molecular-level picture of the EDL is to a large extent still lacking. Particularly, the role of the electronic structure has not been considered in the description of electrolyte/surface interactions. Here, we report enhanced sampling simulations based on ab initio molecular dynamics, aiming at unravelling the free energy of prototypical ions adsorbed at the aqueous graphene and hBN interfaces, and its consequences on nanofluidic osmotic transport. Specifically, we predicted the zeta potential, the diffusio-osmotic mobility, and the diffusio-osmotic conductivity for a wide range of salt concentrations from the ab initio water and ion spatial distributions through an analytical framework based on Stokes equation and a modified Poisson-Boltzmann equation. We observed concentration-dependent scaling laws, together with dramatic differences in osmotic transport between the two interfaces, including diffusio-osmotic flow and current reversal on hBN but not on graphene. We could rationalize the results for the three osmotic responses with a simple model based on characteristic length scales for ion and water adsorption at the surface, which are quite different on graphene and on hBN. Our work provides fundamental insights into the structure and osmotic transport of aqueous electrolytes on 2D materials and explores alternative pathways for efficient water desalination and osmotic energy conversion.

Impact of electrostatic doping on carrier concentration and mobility in InAs nanowires

We fabricate dual-gated electric double layer (EDL) field effect transistors based on InAs nanowires gated with an ionic liquid, and we perform electrical transport measurements in the temperature range from room temperature to 4.2 K. By adjusting the spatial distribution of ions inside the ionic liquid employed as gate dielectric, we electrostatically induce doping in the nanostructures under analysis. We extract low-temperature carrier concentration and mobility in very different doping regimes from the analysis of current–voltage characteristics and transconductances measured exploiting global back-gating. In the liquid gate voltage interval from −2 to 2 V, carrier concentration can be enhanced up to two orders of magnitude. Meanwhile, the effect of the ionic accumulation on the nanowire surface turns out to be detrimental to the electron mobility of the semiconductor nanostructure: the electron mobility is quenched irrespectively to the sign of the accumulated ionic species. The reported results shine light on the effective impact on crucial transport parameters of EDL gating in semiconductor nanodevices and they should be considered when designing experiments in which electrostatic doping of semiconductor nanostructures via electrolyte gating is involved.

Изучение критического угла каналирования ионов активных металлов через тонкие пленки алюминия

The spatial distributions of ions (K+, Na+) passed through thin polycrystalline and single-crystalline Al films with the thickness from 180 to 600 Å and critical channeling angles have been studied. The ion energies have been varied within the range E0 = 10-30 keV. It has been shown that an increase in the energy of the primary ion beam leads to a decrease in the width of the maxima of the angular distribution, which is associated with a decrease in the critical channeling angle ψcr. It has been found that the value ψcr does not exceed 4-50 for axial channeling and 9-100 for planar channeling.

Simple model for the electric field and spatial distribution of ions in a microdroplet.

It is well established that the chemistry in microdroplets has been found to be radically different from reactions in bulk, particularly in the case of water. It has also been established that there is a threshold size for microdroplets to behave differently than droplets near the 10 µm diameter range. We present a three-dimensional electrostatic treatment in the spirit of the Gouy-Chapman model for double layers at interfaces. Our treatment predicts a strong concentration of charged molecules toward the surface of the droplet. As the droplet size deceases, the majority of the volume of the liquid experiences a large DC electric field. Such electric fields are highly unusual in a conducting fluid such as water. We believe that this unique environment helps to explain the reaction rate acceleration and new chemistry that have been observed in microdroplets compared to bulk phase.

Mass spectrometry imaging technology and its application in medicinal plants research

As an important molecular imaging technology, mass spectrometry imaging(MSI) converts the ionic strength, mass-charge ratio and coordinates of ionized molecules in specific areas recorded by mass spectrometer into a pixel model by special imaging analysis software, and reconstructs the spatial ion distribution image of the compounds tested. It has the advantages of simple sample preparation, high sensitivity and no need for labeling. In recent years, MSI technology has been widely used in medicine, pharmacy, botany and other fields. Among them, the application of MSI technology in the research of medicinal plants provides a new technical idea for clarifying the pharmacological mechanism, improving the curative effect, tracking the distribution of toxic components, and makes an important contribution to the further development and utilization of medicinal plants. This review summarizes the research results of MSI technology in recent years for identification of medicinal plants, distribution of metabolites, pathway of active ingredient synthesis, medicinal safety and plant defense, and discusses the advantages and disadvantages of different research methods. Finally, the advantages and practical obstacles of MSI technology in medicinal plant research are briefly pointed out, and the prospects for the future development of MSI technology and medicinal plant research are also prospected.

Bridging electrostatic properties between nanoscopic and microscopic highly charged droplets

The chemical reaction mechanisms within electrosprayed droplets are still unknown. The location of ions provides insight into theses mechanisms. We demonstrate the convergence of ion spatial distributions in aqueous droplets using molecular dynamics. This convergence allows one to extrapolate the simulation results from nanoscopic dimensions to larger ones, which are still inaccessible to atomistic modeling. The surface excess charge and electric field are also computed. We find that the surface excess charge layer is approximately 1.5 nm–1.7 nm thick and that ≈55%-24% (from smaller to larger droplets) of the total number of ions reside in this layer.

The effects of the position of the ether oxygen atom in pyrrolidinium-based room temperature ionic liquids on their physicochemical properties.

Room temperature ionic liquids (RTILs) containing ether oxygen atoms have been investigated for a gamut of science and technology applications owing to their superior physicochemical properties. However, the effect of the position of the ether oxygen atom in the side chain on their physicochemical properties is not clearly understood. This study investigates, using both experimental and computational approaches, the effect of ether oxygen atoms on the physicochemical properties of RTILs consisting of bis(trifluoromethylsulfonyl)amide (TFSA-) with 1-methyl-1-propylpyrrolidinium (MPP+), 1-butyl-1-methylpyrrolidinium (BMP+), 1-methoxymethyl-1-methylpyrrolidinium (MOMMP+), 1-ethoxymethyl-1-methylpyrrolidinium (EOMMP+), and 1-methoxyethyl-1-methylpyrrolidinium (MOEMP+). The viscosity of the RTILs containing the ether oxygen atom was lower than that of the alkyl analogues. Moreover, the viscosity of EOMMPTFSA was lower than that of MOEMPTFSA, albeit EOMMPTFSA and MOEMPTFSA have the same molecular weight with ether oxygen atoms at different positions. Ab initio calculations reveal that the number of methylene groups between nitrogen and oxygen atoms in the cation structure profoundly impacts the local stable structure of the cation. Furthermore, we discussed the relationship between the transport properties and the spatial distribution of ions obtained by MD simulations. This result will be valuable in the design of functionalized RTILs, via the judicious tuning of the conformational flexibility of ether oxygen atoms in related ionic liquids.

Non-radioactive electron source with nanosecond pulse modulation for atmospheric pressure chemical ionization.

Ion mobility spectrometers (IMSs) are well-known instruments for fast and ultrasensitive trace gas detection. In recent years, we introduced a compact nonradioactive electron source providing a defined current of free electrons with high kinetic energy at atmospheric pressure for initiating a chemical gas phase ionization of the analytes identical to radioactive sources. Besides its nonradioactivity, one major advantage of this electron source is its controlled electron emission current even in pulsed mode. By optimizing the geometric parameters and developing faster control electronics, we now achieve electron pulses with extremely short pulse widths down to 23 ns. This allows us to kinetically control the formation of reactants and analyte ions by chemical gas phase ionization (e.g., reducing discrimination processes caused by competing ionization), enhancing the analytical performance of the IMS. However, this paper concentrates on the pulsed electron source. For its characterization, we developed a measurement setup, which allows the detection of nanosecond electron pulses with amplitudes of only a few nanoamperes. Furthermore, we investigated the spatial ion distribution in the ionization region depending on several operating parameters, such as the kinetic electron energy or the ionization time.

Where Do the Ions Reside in a Highly Charged Droplet?

Aqueous droplets in atmospheric and electrosprayed aerosols are charged due to presence of multiple ionic species. We examine the ion spatial distribution and the surface electric field in aqueous charged nanodrops by using atomistic modeling and analytical theory. We find that in nanoscopic liquid drops the concentration of simple ions is higher in the outer droplet shells, reduces gradually toward the drop center, and dies-off toward the vapor-droplet interface. The behavior of the ion spatial distribution is supported by a general analytical theory that takes into account a fluctuating droplet interface, an effective screening length of the charges and the finite size of a solvated ion. We compute the electric potential and the electric field near the droplet surface using a multipole expansion. We emphasize the significance of the fluctuations of the normal component of the electric field in ion evaporation via the Born model. In the presence of a highly charged peptide, we find that the peptide is situated mainly in the droplet interior and occasionally near the droplet surface. The simple ions are mainly near the droplet surface. The study provides insight into droplet chemistry and electrospray ionization mass spectrometry findings.

Motional states of laser cooled Yb ions in an optimized radiofrequency trap

Efficient cooling of trapped ions is one of the key problems in the development of optical clocks and quantum sensors, in quantum computations, and many other fields. We numerically analyze the motion of linear Yb+ crystals and optimized trapping potential to achieve a uniform spatial distribution of ions. Using a compact robust laser system we demonstrate Doppler cooling of a 174Yb+ isotope in a quadrupole Paul trap. This is an important step towards laser cooling of 171Yb+ ions, which will be used in single-ion optical clocks and for the realization of high-fidelity quantum gates.

Groundwater Chemical Characteristics and Analysis of Their Controlling Factors in an Alluvial Fan of Jianjiang River

The Jianjiang alluvial fan is one of the frontal alluvial fan clusters in the Longmen Mountains of the Chengdu Plain. In order to study the groundwater chemical characteristics and controlling factors, we collected 30 groups of groundwater samples on site in May 2018. Descriptive statistical analysis, Piper diagrams, ArcGIS spatial analysis, ion-scale coefficients, and other methods were used to analyze the chemical types and ion spatial distribution characteristics. The main factors controlling the chemical evolution processes of the groundwater and the main sources of ions are discussed. The northeast area of the alluvial fan contains mostly weakly acidic waters, accounting for 13.33%, the rest being weakly alkaline. Groundwater chemical types included HCO3·SO4-Ca, HCO3-Ca, HCO3·SO4-Ca·Mg, and HCO3·SO4-Ca·Na, and all groundwater was freshwater. The main ion spatial variation coefficient were between 0.22 and 0.91, and the variability was moderate. The chemical evolution processes of groundwater was mainly controlled by leaching, and human activities have certain influence. The effect of evaporation and concentration, and atmospheric rainfall, and alternating cation adsorption were not obvious.

Unsupervised segmentation of mass spectrometric ion images characterizes morphology of tissues.

MotivationMass spectrometry imaging (MSI) characterizes the spatial distribution of ions in complex biological samples such as tissues. Since many tissues have complex morphology, treatments and conditions often affect the spatial distribution of the ions in morphology-specific ways. Evaluating the selectivity and the specificity of ion localization and regulation across morphology types is biologically important. However, MSI lacks algorithms for segmenting images at both single-ion and spatial resolution.ResultsThis article contributes spatial-Dirichlet Gaussian mixture model (DGMM), an algorithm and a workflow for the analyses of MSI experiments, that detects components of single-ion images with homogeneous spatial composition. The approach extends DGMMs to account for the spatial structure of MSI. Evaluations on simulated and experimental datasets with diverse MSI workflows demonstrated that spatial-DGMM accurately segments ion images, and can distinguish ions with homogeneous and heterogeneous spatial distribution. We also demonstrated that the extracted spatial information is useful for downstream analyses, such as detecting morphology-specific ions, finding groups of ions with similar spatial patterns, and detecting changes in chemical composition of tissues between conditions.Availability and implementationThe data and code are available at https://github.com/Vitek-Lab/IonSpattern.Supplementary information Supplementary data are available at Bioinformatics online.

Calcium carbonate precipitation in compacted bentonite using electromigration reaction method and its application to estimate the ion activity coefficient in the porewater

ABSTRACT In the safety assessment of radioactive waste disposal, it is critical to understand the porewater chemistry in compacted bentonite in order to predict long-term migration behavior of radionuclides in the engineered barrier. This study estimates the activity coefficients of dissolved ions in the porewater of compacted bentonite from the concentrations of ions at which CaCO3 precipitation occurred. Solutions containing CaCl2 and NaHCO3 were introduced under electrical potential gradient from the opposite sides of the compacted Na-bentonite packed at the dry density of 1.0kg/dm3. After the electromigration, the spatial distribution of ions along the compacted bentonite sample was determined. Sequential extraction method was developed to distinctly determine the concentrations of free ions in the porewater and in solid phase in bentonite. The results show that the exchangeable Na+ ions were progressively replaced by the incoming Ca2+ ions, and the compacted bentonite sample can be divided into three zones: Ca-, Ca-/Na-, and Na-bentonite zones. Precipitates of CaCO3 were observed both in Ca- and Ca/Na-bentonite zones. The experimentally determined activity coefficients were at least smaller by a factor of 3 compared to the theoretical approximation calculated using PHREEQC code assuming dilute-solution conditions with no electrostatic interactions between ions and bentonite surface.

Size effect on electric-double-layer capacitances of conducting structures

The charge storage in an electrical double-layer capacitor is dependent on the accumulation of ions on the interface between electrolyte and conducting material and the spatial distribution of ions in electrolyte. In this work, we study the effect of local curvature on the concentration of ions on the interface between electrolyte and electrode from the framework of thermodynamics and incorporate the concentration of ions on the interface in the analysis of the spatial distribution of ions for symmetric binary electrolytes. Semi-analytical results of the integral electrical-double-layer capacitances per unit area under the condition of large Debye-Hückel constant are obtained for spherical particle and cylindrical rod, which reveal the contribution of interface energy between the conducting material and the electrolyte to the storage of charge. For spherical cavity and cylindrical pore at small electric potential, the solution of the electric potential for linearized Poisson-Boltzmann equation is used in the calculation of the integral electrical-double-layer capacitances per unit area, which are dependent on the sizes of the cavity and pore and independent of the interface energy between the conducting material and the electrolyte. For spherical cavity and cylindrical pore at large electric potential, the integral double-layer capacitances are dependent on the interface energy.

Imaging the source of high-harmonics generated in atomic gas media.

We report the application of the time gated ion microscopy technique in accessing online the position of the source of harmonics generated in atomic gas media. This is achieved by mapping the spatial extreme-ultraviolet (XUV)-intensity distribution of the harmonic source onto a spatial ion distribution, produced in a separate focal volume of the generated XUV beam through single photon ionization of atoms. It is found that the position of the harmonic source depends on the relative position of the harmonic generation gas medium and the focus of the driving infrared (IR) beam. In particular, by translating the gas medium with respect to the IR beam focus different "virtual" source positions are obtained online. Access to such online source positioning allows better control and provides increased possibilities in experiments where selection of electron trajectory is important. The present study gives also access to quantitative information which is connected to the divergence, the coherence properties and the photon flux of the harmonics. Finally, it constitutes a precise direct method for providing complementary experimental info to different attosecond metrology techniques.

Acceleration of carbon ions to high energies by a multi-PW laser

Extreme Light Infrastructure (ELI) is a large-scale European project, still in the development stage, offering parameters of laser drivers required for multiple applications (femtosecond pulse duration, ultra-relativistic laser intensities ∼ 1022 - 1023 W/cm2), however studies of ion acceleration in the given intensity regime are still in the very early stages and require a deeper understanding of the processes occurring during laser-matter interactions to maximize the efficiency of ion acceleration. The purpose of this work is a numerical examination of the properties of carbon ion beams produced during the interaction of an ultra-intense laser beams (of intensities ∼ 1021 – 1023 W/cm2 and pulse duration order of femtoseconds, predicted to be available at ELI-NP, Romania) with C12 target. The dependence of ion beam parameters, such as intensity, energy spectrum, maximum and average ion energy and spatial distribution of ion charge density, on laser pulse parameters (mainly intensity) and the target thickness is investigated. The possibility of generation of high intensity, GeV energy ion beams in the foregoing conditions is demonstrated. The obtained results can be useful for research in high energy-density physics, nuclear physics or medical applications of ion beams.

IDPM: an online database for ion distribution in protein molecules

BackgroundInteractions between ions and proteins have been extensively studied, yet most of the studies focus on the ion binding site. The binding mechanism for many ion binding sites can be clearly described from high resolution structures. Although knowledge accumulated on a case-by-case basis is valuable, it is also important to study the ion-protein interaction statistically. From experimentally determined structures, it is possible to examine the ion distribution around each amino acid. Such distributions can reveal relation between ions and amino acids, so it is desirable to carry out a systematic survey of ‘ion-amino acid’ pairing interaction and share the information with a publicly available database.ResultsThe survey in the Protein Data Bank (PDB) revealed that approximately 40% of molecules records contain at least one ion. To reduce the bias resulted from protein redundancy, the statistics were extracted from a non-redundant dataset by excluding the proteins with similar sequences. Based on the structures of protein molecules and the location of ions, the statistical distributions of ions around each proteinogenic amino acid type were investigated and further summarized in a database. To systematically quantify the interactions between ions and each amino acid, the positions of ions were mapped to the coordinate system centered at each neighboring amino acid. It was found that the distribution of ions follows the expected rules governed by the physicochemical interactions in general. Large variations were observed, reflecting the preference in ‘ion-amino acid’ interactions. The analysis program is written in the Python programming language. The statistical results and program are available from the online database: ion distribution in protein molecules (IDPM) at http://liulab.csrc.ac.cn/idpm/.ConclusionThe spatial distribution of ions around amino acids is documented and analyzed. The statistics can be useful for identifying ion types for a given site in biomolecules, and can be potentially used in ion position prediction for given structures.