Ion Drift Research Articles

Antiphase Boundaries Constitute Fast Cation Diffusion Paths in SrTiO3 Memristive Devices

AbstractResistive switching in transition metal oxide‐based metal‐insulator‐metal structures relies on the reversible drift of ions under an applied electric field on the nanoscale. In such structures, the formation of conductive filaments is believed to be induced by the electric‐field driven migration of oxygen anions, while the cation sublattice is often considered to be inactive. This simple mechanistic picture of the switching process is incomplete as both oxygen anions and metal cations have been previously identified as mobile species under device operation. Here, spectromicroscopic techniques combined with atomistic simulations to elucidate the diffusion and drift processes that take place in the resistive switching model material SrTiO3 are used. It is demonstrated that the conductive filament in epitaxial SrTiO3 devices is not homogenous but exhibits a complex microstructure. Specifically, the filament consists of a conductive Ti3+‐rich region and insulating Sr‐rich islands. Transmission electron microscopy shows that the Sr‐rich islands emerge above Ruddlesden–Popper type antiphase boundaries. The role of these extended defects is clarified by molecular static and molecular dynamic simulations, which reveal that the Ruddlesden–Popper antiphase boundaries constitute diffusion fast‐paths for Sr cations in the perovskites structure.

The effect of brine salinity and oil components on dynamic IFT behavior of oil-brine during low salinity water flooding: Diffusion coefficient, EDL establishment time, and IFT reduction rate

Dynamic behavior of fluid-fluid interactions can potentially affect the performance of any enhanced oil recovery (EOR) process including low salinity water flooding. In this work, dynamic interfacial tension (IFT) of crude-oil/brine system is measured in a wide range of salinity of sea water (SW), from 50-time diluted sea water (SW50D) to 2-time concentrated sea water (SW2C). Contrary to the most of published IFT trends in the literature, for the system under investigation here, as the brine salinity increases the crude-oil/brine IFT reduces, which cannot be explained using the existing theories. The lack of a physical model to explain the observed phenomena was the motivation to develop a new model based on a drift-diffusion theory. This theory considers a current of oil polar molecules toward the oil-water interface which is caused by electrostatic attraction from aqueous ions (drift) and a resistance against this current caused by concentration gradient (diffusion). After applying this model to measured dynamic IFT data, the IFT reduction rate, and electrical double layer (EDL) establishment time are calculated. Then, these matching parameters set as criteria to explain the mechanisms behind the dynamic behavior of crude oil-saline water interfacial tension.For further investigation of the involved mechanisms which are responsible for the macroscopic behavior of crude-oil/brine dynamic IFT, the role of oil components is also examined using the IFT reduction rate and EDL establishment time. Although the obtained results show the asphaltene molecules play a vital role in the dynamic IFT behavior, the concentration of n-heptane, in the model oil containing n-heptane and toluene, is essential to capture the IFT behavior of the crude oil. Increasing n-heptane fraction in the model oil to the amount which exist in the crude oil, results in longer EDL establishment time which is in agreement with the crude oil sample.

Dual frequency DBD: influence of the amplitude and the frequency of applied voltages on glow, Townsend and radiofrequency DBDs

To study dual frequency Townsend glow and radio frequency DBDs in an Ar/NH3 Penning mixture, different voltages are applied on each electrode of a plane/plane DBD. The one which has the higher amplitude and frequency, V H, determines the discharge regime. The other one, which has a lower amplitude and frequency, V L, is more similar to a bias voltage. V H frequency ranges from 50 kHz to 13.56 MHz and V L frequency from 1 kHz to 2 MHz. The amplitude of V L is always kept lower than the breakdown voltage. The discharge behavior is characterized by space and phase resolved optical emission spectroscopy and Fourier transform of the plasma induced light intensity. When the frequencies of two voltages are close to each other, V L higher than 150 V increases the discharge light intensity. In glow and Townsend discharges, this increase is attributed to the enhancement of the plasma density, due to the ions drift from the plasma bulk to the cathode, which produces a higher secondary electron emission. For the radiofrequency discharge, the enhancement of the light intensity is attributed to an enhancement of the positive space charge due to the higher voltage amplitude.When the frequencies of two voltages are very different, e.g. for V L between 1 and 100 kHz and a 5.5 MHz α-RF discharge, the behavior largely depends on V L amplitude. Above some low frequency (LF), the discharge tends to extinguish when V L amplitude is at its maximum. This is explained by a diminution of the plasma density resulting from the ion drift to the cathode due to V L. When V L is very high, it enhances the discharge intensity. This discharge amplification is associated with a transition from α to γ RF mode, which only occurs when the two voltages have the same polarity. Whatever the RF discharge mode, γ or α, the discharge is diffuse. To determine the interest of LF-RF dual frequency DBD for the PECVD, SiOx coatings, made with a single and a dual LF-RF frequency DBDs, are compared. It is concluded that the ɣ dual frequency removes OH functions from the material lattice and densifies the layer.

Interface reactions between water and ionic wind generated by d.c. corona discharge in nitrogen

This work investigated the interface reactions between water and ionic wind from a positive d.c. corona discharge in nitrogen. The effects of drift ions and active neutral species were investigated on their production of hydrogen peroxide in water. Both positive drift ions and active neutral species were found to produce hydrogen peroxide in water. 1 mol positive drift ions can produce 0.13 mol hydrogen peroxide under atmospheric pressure; a reduced gas pressure increased the production of hydrogen peroxide, with 1 mol ions producing 0.29 mol hydrogen peroxide at 100 torr. The gas pressure has little effect on the production of hydrogen peroxide by active neutral species. The drift positive ions acted as ion anode on water surface, reacting with water to produce hydrogen, oxygen, and hydrogen peroxide. The adsorbed form of OH and O produced at the interface can synergistically work to react with the OH scavengers in water. Both HO2 and H2O2 from the discharge were transported to water to produce the liquid phase hydrogen peroxide.

Ion drift instability in a strongly coupled collisional complex plasma

We investigate the low-frequency wave mode associated with heavy particles and its instability in a collisional complex plasma with drifting ions. The effect of the ion drift on the sound velocity of this mode is discussed. The general condition of the instability is derived for subthermal ion drifts, taking into account strong coupling of the particle component. As a general tendency, strong coupling effects reduce the sound velocity and facilitate the occurrence of the ion drift instability. A wide parameter range is considered from the weakly collisional to strongly collisional regimes for the ion and particle components. The chosen plasma parameters are representative to the PK-4 experiment, currently operational on board the International Space Station.

Understanding the Stability of MAPbBr3 versus MAPbI3: Suppression of Methylammonium Migration and Reduction of Halide Migration.

Solar cells based on metal halide perovskites often show excellent efficiency but poor stability. This degradation of perovskite devices has been associated with the migration of mobile ions. MAPbBr3 perovskite materials are significantly more stable under ambient conditions than MAPbI3 perovskite materials. In this work, we use transient ion drift to quantify the key characteristics of ion migration in MAPbBr3 perovskite solar cells. We then proceed to compare them with those of MAPbI3 perovskite solar cells. We find that in MAPbBr3, bromide migration is the main process at play and that contrary to the case of MAPbI3, there is no evidence for methylammonium migration. Quantitatively, we find a reduced activation energy, a reduced diffusion coefficient, and a reduced concentration for halide ions in MAPbBr3 compared to MAPbI3. Understanding this difference in mobile ion migration is a crucial step in understanding the enhanced stability of MAPbBr3 versus MAPbI3.

Dynamics of Auroral Precipitation Boundaries Associated With STEVE and SAID

AbstractUsing Defense Meteorological Satellite Program (DMSP) and National Oceanic and Atmospheric Administration (NOAA) satellite observations and ground‐based observations by the THEMIS all‐sky imagers (ASIs) and SuperDARN radars, we determine how the equatorward boundary locations of ring current ions and plasma sheet electrons at pre‐midnight relate to occurrence of strong thermal emission velocity enhancement (STEVE) and intense subauroral ion drifts (SAID) during substorms. We found that the STEVE events are associated with a sharper gradient of electron precipitating flux, lower precipitating ion flux, and a narrower (<1°) latitudinal gap between the equatorward boundaries of trapped ring current ions and precipitating plasma sheet electrons and narrower region‐2 field‐aligned currents (FACs) than for the non‐STEVE events. The narrow gap of the particle boundaries contains intense SAID, higher upflow velocity, lower trough density, and slightly higher electron temperature than those for the non‐STEVE events. The non‐STEVE substorms have much wider gaps between the trapped ions and precipitating electrons, and subauroral polarization streams (SAPS) do not show intense SAID. These results indicate that subauroral flows and downward FACs for the STEVE events can only flow within the latitudinally narrow subauroral low‐conductance region between the ion and electron boundaries, resulting in intense SAID and heating. During the non‐STEVE events, the SAPS flows can flow in the latitudinally wide region without forming intense SAID.

Magnetospheric Conditions for STEVE and SAID: Particle Injection, Substorm Surge, and Field‐Aligned Currents

AbstractTo understand magnetosphere‐ionosphere conditions that result in thermal emission velocity enhancement (STEVE) and subauroral ion drifts (SAID) during the substorm recovery phase, we present substorm aurora, particle injection, and current systems during two STEVE events. Those events are compared to substorm events with similar strength but without STEVE. We found that the substorm surge and intense upward currents for the events with STEVE reach the dusk, while those for the non‐STEVE substorms are localized around midnight. The Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellite observations show that location of particle injection and fast plasma sheet flows for the STEVE events also shifts duskward. Electron injection is stronger and ion injection is weaker for the STEVE events compared to the non‐STEVE events. SAID are measured by Super Dual Auroral Radar Network during the STEVE events, but the non‐STEVE events only showed latitudinally wide subauroral polarization streams without SAID. To interpret the observations, Rice Convection Model (RCM) simulations with injection at premidnight and midnight have been conducted. The simulations successfully explain the stronger electron injection, weaker ion injection, and formation of SAID for injection at premidnight, because injected electrons reach the premidnight inner magnetosphere and form a narrower separation between the ion and electron inner boundaries. We suggest that substorms and particle injections extending far duskward away from midnight offer a condition for creating STEVE and SAID due to stronger electron injection to premidnight. The THEMIS all‐sky imager network identified the east‐west length of the STEVE arc to be ~1900 km (~2.5 h magnetic local time) and the duration to be 1–1.5 h.

Structure of Nonlinear Small-Scale Waves in the Plasma of the D Layer of the Ionosphere

The conditions for the existence of spatially periodic flat nonlinear small-scale plasma and electric field structures with a characteristic size L on the order of several meters are found at altitudes of the D layer of the ionosphere. It is shown that for their description it is necessary to abandon the approximation of plasma quasineutrality, to take into account the presence of ions of both signs and electrons, the slow motion of these structures with respect to a neutral gas with the velocity $$U \ll {{V}_{ \pm }},$$ significantly lower than the ion drift velocity V±, and also take into account the difference in temperature of electrons and ions in the strong electric field. The structure of nonlinear waves in the plasma and its changes depending on the wave velocity U and other parameters of the plasma and geomagnetic field are calculated. The formation of such structures leads to the disruption of the radio communication and can be used as an ionospheric precursor of earthquakes.

First-Principles Collision Cross Section Measurements of Large Proteins and Protein Complexes.

Rotationally averaged collision cross section (CCS) values for a series of proteins and protein complexes ranging in size from 8.6 to 810 kDa are reported. The CCSs were obtained using a native electrospray ionization drift tube ion mobility-Orbitrap mass spectrometer specifically designed to enhance sensitivity while having high-resolution ion mobility and mass capabilities. Periodic focusing (PF)-drift tube (DT)-ion mobility (IM) provides first-principles determination of the CCS of large biomolecules that can then be used as CCS calibrants. The experimental, first-principles CCS values are compared to previously reported experimentally determined and computationally calculated CCS using projected superposition approximation (PSA), the Ion Mobility Projection Approximation Calculation Tool (IMPACT), and Collidoscope. Experimental CCS values are generally in agreement with previously reported CCSs, with values falling within ∼5.5%. In addition, an ion mobility resolution (CCS centroid divided by CCS fwhm) of ∼60 is obtained for pyruvate kinase (MW ∼ 233 kDa); however, ion mobility resolution for bovine serum albumin (MW ∼ 68 kDa) is less than ∼20, which arises from sample impurities and underscores the importance of sample quality. The high resolution afforded by the ion mobility-Orbitrap mass analyzer provides new opportunities to understand the intricate details of protein complexes such as the impact of post-translational modifications (PTMs), stoichiometry, and conformational changes induced by ligand binding.

Novel ion drift tube for high-performance ion mobility spectrometers based on a composite material

Ion mobility spectrometers (IMS) are able to detect pptV-level concentrations of substances in gasses and in liquids within seconds. Due to the continuous increase in analytical performance and reduction of the instrument size, IMS are established nowadays in a variety of analytical field applications. In order to reduce the manufacturing effort and further enhance their widespread use, we have developed a simple manufacturing process for drift tubes based on a composite material. This composite material consists of alternating layers of metal sheets and insulator material, which are connected to each other in a mechanically stable and gastight manner. Furthermore, this approach allows the production of ion drift tubes in just a few steps from a single piece of material, thus reducing the manufacturing costs and efforts. Here, a drift tube ion mobility spectrometer based on such a composite material is presented. Although its outer dimensions are just 15 mm × 15 mm in cross section and 57 mm in length, it has high resolving power of Rp = 62 and detection limits in the pptV-range, demonstrated for ethanol and 1,2,3-trichloropropane.

Three-dimensional cross-field flows at the plasma-material interface in an oblique magnetic field

This article describes experimental evidence that the magnetic presheath is a fully three-dimensional structure modified by ion–neutral collisions. Velocity distributions of both ions and neutrals, obtained via laser-induced fluorescence, show that cross field ion drifts do not result from entrainment of ions in a flowing neutral background. Ion flows parallel to E×B arise and accelerate to as much as 0.2cs within several ion gyroradii of the boundary surface, where cs is the sound speed. Within measurement resolution, the onset of the E×B aligned flow occurs at the same distance to the surface that ions begin to deflect from travel along magnetic field lines. Collisional fluid and particle-in-cell simulations of the boundary region are compared to the experimental measurements. We find that, in contrast to the classical collisionless Chodura model, collisional effects between the ions and the non-flowing neutral population are essential to quantitatively predict the observed ion drift velocities. No momentum coupling between ions and neutrals, separable from noise and other effects, is observed in either signal. We discuss several explanations and implications of this observation.

MMS Observations of Intense Whistler Waves Within Earth's Supercritical Bow Shock: Source Mechanism and Impact on Shock Structure and Plasma Transport

AbstractThe properties of whistler waves near lower‐hybrid frequencies within Earth's quasi‐perpendicular bow shock are examined using data from the Magnetospheric Multiscale (MMS) mission. These waves appear as right‐hand polarized wave packets propagating upstream obliquely to the magnetic field and shock normal with phase speeds from a few hundred up to 1,600 km/s. The wavelengths are near the ion inertial length scale (λ∼ 0.3–1.3 λi). Detailed analysis finds characteristics consistent with the modified two‐stream instability mechanism driven by the reflected ion and electron drift. Correlations between wave and electron anisotropy variations reveal that the whistlers are affecting electron dynamics and thus their perpendicular and parallel temperatures. The electron signatures are explainable via the interaction of magnetized electrons in the whistler induced nonmonotonic magnetic fields. These waves have intense magnetic fields (δB/B∘∼ 0.1–1) and carry sizable currents that are a significant fraction of the thermal current (|J/Jvte|∼ 0.1–0.5). The whistler‐induced currents and the electron anisotropies are sufficiently large to respectively excite high‐frequency (HF) electrostatic (>100 Hz) and HF whistler waves (f∼ 0.1–0.5 fce). Energy dissipation J·E from whistlers at 30 Hz and below range from a few thousandths to few hundredths of μW/m3. Comparisons reveal that plasma energy is converted to wave energy in the foot, whereas wave energy gets dissipated into the plasma in the ramp, where irreversible heating occurs. These observed features are indicative of an intricate coupling between small‐scale interaction processes and larger‐scale structure transpiring within the layer. Such a characterization is only made possible now with the MMS high‐time‐resolution measurements.

THE IMS PARADOX: A PERSPECTIVE ON STRUCTURAL ION MOBILITY-MASS SPECTROMETRY.

Studies of large proteins, protein complexes, and membrane protein complexes pose new challenges, most notably the need for increased ion mobility (IM) and mass spectrometry (MS) resolution. This review covers evolutionary developments in IM-MS in the authors' and key collaborators' laboratories with specific focus on developments that enhance the utility of IM-MS for structural analysis. IM-MS measurements are performed on gas phase ions, thus "structural IM-MS" appears paradoxical-do gas phase ions retain their solution phase structure? There is growing evidence to support the notion that solution phase structure(s) can be retained by the gas phase ions. It should not go unnoticed that we use "structures" in this statement because an important feature of IM-MS is the ability to deal with conformationally heterogeneous systems, thus providing a direct measure of conformational entropy. The extension of this work to large proteins and protein complexes has motivated our development of Fourier-transform IM-MS instruments, a strategy first described by Hill and coworkers in 1985 (Anal Chem, 1985, 57, pp. 402-406) that has proved to be a game-changer in our quest to merge drift tube (DT) and ion mobility and the high mass resolution orbitrap MS instruments. DT-IMS is the only method that allows first-principles determinations of rotationally averaged collision cross sections (CSS), which is essential for studies of biomolecules where the conformational diversities of the molecule precludes the use of CCS calibration approaches. The Fourier transform-IM-orbitrap instrument described here also incorporates the full suite of native MS/IM-MS capabilities that are currently employed in the most advanced native MS/IM-MS instruments. © 2020 John Wiley & Sons Ltd. Mass Spec Rev.

Assimilation of GNSS Measurements for Estimation of High‐Latitude Convection Processes

AbstractGeomagnetic storms produce significant electrodynamics at midlatitudes. Strong ion convection can affect thermospheric neutral wind motion. The converse is also true, such that both fields and winds can drive ionospheric plasma movement. This work adjusts a background modeled high‐latitude electrostatic potential to estimate the storm time electric field based on data‐derived plasma densities and measurements of neutral wind. Electron densities are derived from global navigation satellite system (GNSS) total electron content measurements using Ionospheric Data Assimilation Four‐Dimensional (IDA4D). These are input to Estimating Model Parameters from Ionospheric Reverse Engineering (EMPIRE) to estimate electric potential corrections to the background Weimer 2000 potential model. The EMPIRE basis functions for electric potential are spherical harmonics in dipole magnetic colatitude and longitude, enforced to be constant along a magnetic field line. For the 17 March 2015 storm, EMPIRE electric potential produces westward zonal ion drifts that more closely agree with incoherent scatter radar (ISR) measurements made at Millstone Hill than the background Weimer 2000 model alone, when electric potential and meridional neutral winds are both corrected. Additionally ingesting northward line‐of‐sight neutral wind measurements from a Fabry‐Perot interferometer at Millstone Hill makes little difference in the agreement between zonal ion drift predictions and measurements. Estimation of only electric potential reduces the agreement between the assimilated prediction of the field‐perpendicular zonal drifts and ISR measurements significantly.

A method to determine the electric field of liquid argon time projection chambers using a UV laser system and its application in MicroBooNE

Liquid argon time projection chambers (LArTPCs) are now a standard detector technology for making accelerator neutrino measurements, due to their high material density, precise tracking, and calorimetric capabilities. An electric field (E-field) is required in such detectors to drift ionization electrons to the anode where they are collected. The E-field of a TPC is often approximated to be uniform between the anode and the cathode planes. However, significant distortions can appear from effects such as mechanical deformations, electrode failures, or the accumulation of space charge generated by cosmic rays. The latter effect is particularly relevant for detectors placed near the Earth's surface and with large drift distances and long drift time. To determine the E-field in situ, an ultraviolet (UV) laser system is installed in the MicroBooNE experiment at Fermi National Accelerator Laboratory. The purpose of this system is to provide precise measurements of the E-field, and to make it possible to correct for 3D spatial distortions due to E-field non-uniformities. Here we describe the methodology developed for deriving spatial distortions, the drift velocity and the E-field from UV-laser measurements.

Direct detection of gas-phase mercuric chloride by ion drift - Chemical ionization mass spectrometry

Mercury is a persistent environmental pollutant that enters the atmosphere mostly in elemental form (Hg0) and leaves in oxidized form. The atmospheric oxidation mechanism of Hg0 is inadequately constrained because of the limited direct experimental knowledge of molecular identities of gaseous oxidized mercury (GOM), severely hindering the evaluation of mercury deposition to the terrestrial and aqueous environment. Here we present the development and testing of a direct approach for laboratory detection of GOM, using the ion drift - chemical ionization mass spectrometry (ID-CIMS). In this approach, GOM reacts in an ion drift tube with an appropriate reagent ion to form well-defined product ions, which are detected by a quadrupole mass spectrometer equipped with a counting electron multiplier. We used HgCl2 as GOM surrogate, along with SF6−, CO3−, and NO3−⋅HNO3 as reagent ions, which were selected based on quantum chemical evaluations of several possible reaction mechanisms, including charge transfer, ion transfer, and ion-molecule clustering. All three reagent ions react with HgCl2 through one or more of the above mechanisms, providing a sensitivity sufficient for laboratory studies of atmospheric mercury chemistry. To make direct sampling of atmospheric GOM possible, the sensitivity must be improved, primarily through the use of the ambient pressure chemical ionization.

Effect of bootstrap current on the onset of neoclassical tearing mode

The effect of bootstrap current perturbation on the onset of neoclassical tearing modes (NTMs) is studied numerically based on two-fluid equations, using externally applied resonant magnetic perturbations (RMPs) as triggers. With increasing the bootstrap current density, a larger RMP is found to be required to excite the NTM’s onset when the bi-normal electron fluid velocity is in the ion drift direction, being contrary to the conventional understanding that the bootstrap current perturbation is always destabilizing. For the electron fluid velocity in the electron drift direction, however, the opposite results are found.

Coupled Drift Ion Acoustic Shock waves with trapped electrons in Quantum Magnetoplasma

Coupled drift ion acoustic shock waves are studied in inhomogeneous, dissipative quantum magnetoplasmas in the presence of adiabatically trapped electrons. We have derived a nonlinear Burgers like evolution equation having a fractional nonlinearity. The quantum magnetohydrodynamics model (QMHD) has been employed to derive this nonlinear equation (2 + 1) (two spatial and one temporal) dimensions. Nonlinear analysis of the equation is carried out to show that it admits shock solutions. These shock structures are numerically investigated by using parameters of neutron stars where quantum effects are expected to dominate the dynamics of the system. These results show significant dependence on the physical parameters namely inhomogeneity, number density, ambient magnetic field, collisional frequency and the angle of propagation.

Characterisation & modelling of perovskite-based synaptic memristor device

Neuromorphic computing architectures are required to execute several operations such as forgetting and learning behaviours with high-speed data processing. Due to the rapid advancement in technology, various transistor-based devices like field-effect transistor (FET), complementary metal-oxide-semiconductor (CMOS), etc. have the limitation to perform efficiently with a higher density of integration in combination with lower energy consumption. Consequently, there is a strong necessity for creating new devices with fast information storage, high-speed data processing, high density of integration, and low operating energy. Memristors are emerging as promising candidates as the next-generation technology which contains all the above-mentioned properties. According to previous literature, a nanoscale memristive device based on methylammonium lead iodide perovskite (CH3NH3PbI3) can be fabricated and characterised as a low power synaptic device. This study proposes the behavioural modelling of a perovskite-based synaptic memristor device with Glass/indium tin oxide (ITO)/SnO2/CH3NH3PbI3/Au structure for SPICE simulation in neuromorphic applications. We report an in-depth analysis of the physical model behind the creation of the p-i-n structure, induced by the ion drift in the perovskite layer. Furthermore, a SPICE Model is proposed to reproduce the observed behaviour of fabricated Glass/ITO/SnO2/CH3NH3PbI3/Au device and is able to mimic the neuromorphic learning and remembering process, similar to biological synapses. The proposed SPICE model will foster the potential of perovskite based synaptic devices by enabling large-scale circuit-level simulations thus allowing designers to explore the potential of this new device, for example in power-on-chip approaches and in an artificial neural network.