Charge Exchange Mechanism Research Articles

Two-dimensional Cu2N–A high-performance anode material for ion batteries with excellent electrical conductivity and electrolyte wettability

Determining suitable anode materials is crucial in the advancement of lithium-ion and sodium-ion battery technologies. We propose that the two-dimensional (2D) material Cu2N holds promise as a viable anode candidate. The Cu2N monolayer exhibits a stable checkerboard lattice crystal structure, ensuring structural integrity. Its excellent metallic electronic structure facilitates efficient conductivity during battery operation. We have observed that Li/Na ions can chemically bond to Cu2N substrates via specific charge exchange mechanisms. Moreover, the Cu2N monolayer demonstrates favorable wettability and compatibility with common electrolytes used in lithium-ion and sodium-ion batteries, including solvent molecules and metal salts. Our findings indicate that the Li/Na storage capacity of the Cu2N monolayer reaches approximately 760/760 mAh/g, surpassing that of graphite anodes significantly. Notably, the Li/Na diffusion barrier on the Cu2N monolayer is merely 5/13 meV, lower than that of most other 2D anode materials. Our results underscore the potential of the Cu2N monolayer as an outstanding electrode material, offering high storage capacity, rapid charge/discharge rates, and favorable wettability with electrolytes.

Adsorption and Oxidation of NO2 on Anatase TiO2: Concerted Nitrate Interaction and Photon-Stimulated Reaction

The catalytic and photon-induced oxidation of NO2 on anatase TiO2 has been studied and compared with the surface nitrate species obtained after adsorption of HNO3. Using a combination of in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), density functional theory (DFT), and temperature-programmed desorption (TPD), it is shown that identical products are obtained in all reaction systems but that their formation rates differ significantly. The surface reaction products are identified as combinations of surface–NO3– species, where NO2 bonds to the lattice oxygen, and freely adsorbed NO3– ions. These products can be obtained either by dissociative adsorption of HNO3 or by catalytic/photocatalytic oxidation of NO2, which is facilitated by UV light. A concerted reaction mechanism is unraveled that involves reorientation of bidentate nitrate that pushes out a neighboring protonated lattice oxygen to form a surface–NO3– species and a terminal OH group. The thermal stability of these surface species has been studied by means of TPD and simultaneous in situ DRIFTS measurements that reveal a main desorption peak (m/z = 46) at around 430 °C, which is attributed to concerted nitrate desorption through pentoxide (N2O5) formation. A weaker and broader TPD peak is found at about 185 °C and is attributed to desorption of nitrate species bonded in a compressed configuration. The experimental results can be explained by the changing stability of the identified nitrate products, which depends strongly on the surface chemical environment and the surface coverage. The DFT results show that the stabilization of intermediate NO2 adsorbates and the final nitrate reaction products occurs through a bifunctional charge exchange mechanism that is mediated by the TiO2 crystal. In particular, a stable surface–NO3– and NO3– ion pair configuration has been identified. This mechanism explains both the thermal and photoinduced oxidation of NO2 and their thermal stability and different formation rates, yielding high photoinduced oxidation reaction rates. Our results provide insights into the structure and chemical stability of nitrate surface products on TiO2 particles and their formation mechanism, which is important for understanding their catalyzed transformation into the harmful compounds HONO and N2O during continued UV light illumination.

Generation and sustenance of electric fields in sandstorms

Sandstorms are frequently accompanied by the generation of intense electric fields and lightning. In a very narrow region close to the ground level, sand particles undergo a charge exchange mechanism whereby larger (resp. smaller) sized sand grains become positively (resp. negatively) charged are then entrained by the turbulent fluid motion. Our central hypothesis is that differently sized sand particles get differentially transported by the turbulent flow resulting in a large-scale charge separation, and hence a large-scale electric field. We utilize our simulation framework, comprising of large-eddy simulation of the turbulent atmospheric boundary layer along with sand particle transport and an electrostatic Poisson solver, to investigate the physics of electric fields in sandstorms and thus, to confirm our hypothesis. We utilize the simulation framework to investigate electric fields in weak to strong sandstorms that are characterized by the number density of the sand particles. Our simulations reproduce observational measurements of both mean and RMS fluctuation values of the electric field. We propose a scaling law in which the electric field scales as the two-thirds power of the number density that holds for weak-to-medium sandstorms.

Ring Current Decay During Geomagnetic Storm Recovery Phase: Comparison Between RBSP Observations and Theoretical Modeling

AbstractRing current decay during storm recovery phase may be affected by different loss processes. In this study, we have investigated the lifetimes of ring current ions (H+ and O+) of energies from 1 keV to several hundred keV at L shell from 3 to 6 during the storm recovery phase through a statistical survey. The observational data of 48 geomagnetic storms from March 2013 to May 2019 are collected based on Van Allen Probe observations. We find that (1) the observed lifetimes of H+ and O+ in general increase with L shell and (2) the lifetimes of H+ is short than that of O+ when E < ∼50 keV while the situation is reversed when E > ∼50 keV. In addition, we have made use of the charge exchange theory, combined with previous experimental results on the charge exchange cross section and two distribution models of neutral hydrogen atoms in the exosphere, so as to directly estimate the ring current ions decay caused by charge exchange mechanism only. Through the comparison between the model predictions of charge exchange lifetime and the observed lifetimes, we find that (3) the observed lifetimes are in general consistent with model results, which confirms that charge exchange is a dominant loss mechanism of ring current ions during storm recovery phase.

Interplay among work function, electronic structure and stoichiometry in nanostructured VOx films.

The work function is the parameter of greatest interest in many technological applications involving charge exchange mechanisms at the surface. The possibility to produce samples with a controlled work function is then particularly interesting, albeit challenging. We synthetized nanostructured vanadium oxide films by a room temperature supersonic cluster beam deposition method, obtaining samples with tunable stoichiometry and work function (3.7-7 eV). We present an investigation of the electronic structure of several vanadium oxide films as a function of the oxygen content via in situ Auger, valence-band photoemission spectroscopy and work function measurements. The experiments probed the partial 3d density of states, highlighting the presence of strong V 3d-O 2p and V 3d-V 4s hybridizations which influence 3d occupation. We show how controlling the stoichiometry of the sample implies control over work function, and that the access to nanoscale quantum confinement can be exploited to increase the work function of the sample relative to the bulk analogue. In general, the knowledge of the interplay among work function, electronic structure, and stoichiometry is strategic to match nanostructured oxides to their target applications.

Electrification in granular gases leads to constrained fractal growth

The empirical observation of aggregation of dielectric particles under the influence of electrostatic forces lies at the origin of the theory of electricity. The growth of clusters formed of small grains underpins a range of phenomena from the early stages of planetesimal formation to aerosols. However, the collective effects of Coulomb forces on the nonequilibrium dynamics and aggregation process in a granular gas – a model representative of the above physical processes – have so far evaded theoretical scrutiny. Here, we establish a hydrodynamic description of aggregating granular gases that exchange charges upon collisions and interact via the long-ranged Coulomb forces. We analytically derive the governing equations for the evolution of granular temperature, charge variance, and number density for homogeneous and quasi-monodisperse aggregation. We find that, once the aggregates are formed, the granular temperature of the cluster population, the charge variance of the cluster population and the number density of the cluster population evolve in such a way that their non-dimensional combination obeys a physical constraint of nearly constant dimensionless ratio of characteristic electrostatic to kinetic energy. This constraint on the collective evolution of charged clusters is confirmed both by our theory and our detailed molecular dynamics simulations. The inhomogeneous aggregation of monomers and clusters in their mutual electrostatic field proceeds in a fractal manner. Our theoretical framework is extendable to more precise charge exchange mechanisms, a current focus of extensive experimentation. Furthermore, it illustrates the collective role of long-ranged interactions in dissipative gases and can lead to novel designing principles in particulate systems.

Role of surface trapping state in the charge exchange characteristics of CdSe nanorod

The charge exchange (CE) characteristics of CdSe nanorod would be manipulated by the TBP and Li+. We employ electrochemical impedance spectroscopy (EIS) and cyclic voltammogram (CV) to scan the CE mechanism of CdSe nanorod. The EIS data shows that TBP would restrict the CE process and the Li+ would show the opposite role. The CV data confirms that the restriction behavior of CE affected by TBP is originated from the filling surface trapping state. Meanwhile, the facilitation of CE process manipulated by Li+ is coming from the creation of new trapping state and the deepening of trapping state. In comparison with TBP, Li+ would exhibit much extensive function in affecting the trapping state. Finally, the results help people to further understand the characteristics of trapping state in the charge property of nanocrystals.

Laser-stimulated deexcitation of Rydberg antihydrogen atoms

Antihydrogen atoms are routinely formed at CERN in a broad range of Rydberg states. Ground-state anti-atoms, those useful for precision measurements, are eventually produced through spontaneous decay. However given the long lifetime of Rydberg states the number of ground-state antihydrogen atoms usable is small, in particular for experiments relying on the production of a beam of antihydrogen atoms. Therefore, it is of high interest to efficiently stimulate the decay in order to retain a higher fraction of ground-state atoms for measurements. We propose a method that optimally mixes the high angular momentum states with low ones enabling to stimulate, using a broadband frequency laser, the deexcitation toward low-lying states, which then spontaneously decay to ground-state. We evaluated the method in realistic antihydrogen experimental conditions. For instance, starting with an initial distribution of atoms within the $n=20-30$ manifolds, as formed through charge exchange mechanism, we show that more than 80\% of antihydrogen atoms will be deexcited to the ground-state within 100 ns using a laser producing 2 J at 828 nm.

Double matrix effect in Low Energy Ion Scattering from La surfaces

Low Energy Ion Scattering (LEIS) has been performed on several lanthanum-based surfaces. Strong subsurface matrix effects – dependence of surface scattered He+ ion yield on the composition of subsurface layer – have been observed. The ion yield of He+ scattered by La differed by a factor of up to 2.5 for different surfaces, while only the La peak was visible in the spectra. To study these effects and enable surface quantification, He+ ion yields have been measured in a range of incident He+ energies from 1000 to 7500 eV for LaB6, La2O3, oxidized La and pure La surfaces. The investigation showed that as many as two simultaneous matrix effects are present, each one driven by a separate charge exchange mechanism. The first one is a resonant neutralization from the conduction band of La to an excited state of the He+ ion. It depends on the work function of the surface, which is lowered significantly when La interacts with O or B. The second mechanism is quasiresonant charge transfer between bound La levels and He 1s, which creates characteristic oscillations in the energy dependence of ion yields. The exact structure of the oscillations depends on small changes in binding energies of interacting La levels. This is the first time quasiresonant charge transfer is proven to be present in La. It is likely that La 5p orbitals participate in this resonance, which can be the first clear observation of a resonance between p and s orbitals in LEIS. This type of resonance was previously believed to be absent because of strong damping. We also demonstrated that despite the complex matrix effect precise measurements over a wide energy range allow quantification of the atomic composition of La-based surfaces.

The Presence of Dust and Ice Scattering in X-Ray Emissions from Comets

Abstract X-ray emissions from cometary atmospheres were modeled from first principles using the charge-exchange interaction with solar wind ions as well as coherent scattering of solar X-rays from dust and ice grains. Scattering cross-sections were interpolated over the 1 nm–1 cm grain radius range using approximations based on the optically thin or thick nature of grains with different sizes. The theoretical emission model was compared to Chandra observations of Comets ISON and Ikeya–Zhang due to their high signal-to-noise ratios and clearly defined spectral features. Comparing the observed intensities to the model showed that the charge-exchange mechanism accurately reproduced the emission spectra below 1 keV, while dust and ice scattering was negligible. Examining the 1–2 keV range found dust and ice scattering emissions to agree well with observations, while charge-exchange contributions were insignificant. Spectral features between the scattering model and observations also trended similarly over the 1–2 keV range. The dust and ice density within the cometary atmosphere n was varied with respect to grain size a as the function , with Ikeya–Zhang requiring and ISON requiring to best fit the observed spectral intensities. These grain size dependencies agreed with independent observations and simulations of such systems. The overall findings demonstrate evidence of significant scattering emissions present above 1 keV in the analyzed cometary emission spectra and that the dust/ice density dependence on grain radius a may vary significantly between comets.

Laboratory measurements compellingly supports a charge-exchange mechanism for the “Dark matter” ∼ 3.5 keV X-ray line

SynopsisThe reported observations of an unidentified X-ray line feature at ∼ 3.5 keV from galaxy clusters have driven a lively discussion about its possible dark matter origin. Motivated by this, we have investigated the X-ray spectra of highly ionized bare sulfur ions following charge exchange with residual gas in the electron beam ion trap, as a source or a contributor to this X-ray line. The X-ray feature at about 3.5 keV shows up in the experiment, which could explain the the astrophysical observations and confirm the predictions of Gu et al.

Effect of final state interaction in 3He (π−, π+) 3n reaction

The calculation of the doubly differential cross section was performed using sequential single charge exchange mechanism for the double charge exchange reaction 3He (π−, π+) 3n. The effect of the final state interaction between two active neutrons was investigated using Malfliet Tjon potential. Our results were compared with experimental results at intermediate energy range for the values 120, 180, 210 and 240 MeV. In this study, pion production was used to interpret the low energy peak that was observed on the forward angles at the incident energies of 210 and 240 MeV.

Bulk plasmon assisted electron capture process for ions travelling outside a metal surface

We obtain the interaction Hamiltonian for a charge exchange mechanism at metal surfaces in which a metal electron is captured by an ion travelling at constant velocity outside the solid while a bulk plasmon is emitted. The only work reported so far on this novel process, for the simplest case of an ion at rest, shows a transition probability in the near surface region as important as the one for the surface plasmon assisted charge exchange process. The Bohm–Pines and Fock–Tani theories provide the appropriate mathematical framework to obtain a closed analytical expression for the three-dimensional interaction potential responsible for this collective charge transfer process. Further, we show that the conservation of momentum parallel to the surface is implicitly contained in the matrix elements of such Bohm–Pines Fock–Tani Hamiltonian.

ON THE SUPPORT OF NEUTRALS AGAINST GRAVITY IN SOLAR PROMINENCES

Cool and dense prominences found in the solar atmosphere are known to be partially ionized because of their relative low temperature. In this Letter, we address the long-standing problem of how the neutral component of the plasma in prominences is supported against gravity. Using the multiple fluid approach we solve the time-dependent equations in two dimensions considering the frictional coupling between the neutral and ionized components of the magnetized plasma representative of a solar prominence embedded in a hot coronal environment. We demonstrate that given an initial density enhancement in the two fluids, representing the body of the prominence, the system is able to relax in the vicinity of magnetic dips to a stationary state in which both neutrals and ionized species are dynamically suspended above the photosphere. Two different coupling processes are considered in this study, collisions between ions and neutrals and charge exchange interactions. We find that for realistic conditions ions are essentially static while neutrals have a very small downflow velocity. The coupling between ions and neutrals is so strong at the prominence body that the behavior is similar to that of a single fluid with an effective density equal to the sum of the ion and neutral species. We also find that the charge exchange mechanism is about three times more efficient sustaining neutrals than elastic scattering of ions with neutrals.

STELLAR WIND INDUCED SOFT X-RAY EMISSION FROM CLOSE-IN EXOPLANETS

In this paper, we estimate the X-ray emission from close-in exoplanets. We show that the Solar/Stellar Wind Charge Exchange Mechanism (SWCX) which produces soft X-ray emission is very effective for hot Jupiters. In this mechanism, X-ray photons are emitted as a result of the charge exchange between heavy ions in the solar wind and the atmospheric neutral particles. In the Solar System, comets produce X-rays mostly through the SWCX mechanism, but it has also been shown to operate in the heliosphere, in the terrestrial magnetosheath, and on Mars, Venus and Moon. Since the number of emitted photons is proportional to the solar wind mass flux, this mechanism is not very effective for the Solar system giants. Here we present a simple estimate of the X-ray emission intensity that can be produced by close-in extrasolar giant planets due to charge exchange with the heavy ions of the stellar wind. Using the example of HD~209458b, we show that this mechanism alone can be responsible for an X-ray emission of $\approx 10^{22}$~erg~s$^{-1}$, which is $10^6$ times stronger than the emission from the Jovian aurora. We discuss also the possibility to observe the predicted soft X-ray flux of hot Jupiters and show that despite high emission intensities they are unobservable with current facilities.

Low-energy ion scattering: A quantitative method?

We explore under which conditions low-energy ion scattering experiments are capable of obtaining reliable quantitative results in surface composition analysis. Additionally, we elaborate on the effective information depth of this technique considering the effect of different dominant charge exchange mechanisms. Based on concrete examples, we also point out possible problems and pitfalls in the evaluation of experimental data.

Analysis of SEI on Graphite Anode in Li Ion Cell Using LiMn2O4 Spinel Cathode

Introduction We have been developing large capacity Li ion batteries for backing up of telecommunication apparatuses. Among the many types of Li ion batteries, The LiMn2O4 is convenient for replacing conventional lead-acid batteries, which have been widely used in such backup systems. This is because the LiMn2O4 has a voltage plateau, which is close to that of lead-acid batteries, due to the combination with a graphite anode. On the other hand, long calendar life of more than 10 years at full charge is also required for backup. Mn2+ ion dissolution from the LiMn2O4 cathode is well known, and we have already reported that calendar life is greatly affected by the concentration of dissolved Mn2+ ions [1]. We have postulated the degradation mechanism by charge exchange between Mn2+and intercalated Li [1]; however, the relationships between the amount of Mn deposited on the anode and that of Li consumption, which are calculated from capacity reduction, are unclear.In this study, we analyzed the solid-electrolyte-interface (SEI) on the anode to investigate the role of Mn in the degradation of Li ion batteries for backup. Experimental We used the 18650-type cylindrical Li-ion cell (capacity: about 0.7 Ah) [2]. The cathode was a Mg-doped manganese-spinel and the anode was carbon-coated graphite. We used an ethylene carbonate and dimethyl carbonate based electrolyte containing phosphazene retardant.Sample cells were charged at four voltages (4.05, 4.10, 4.15, and 4.20 V), and the environmental temperature during float charging was maintained at 50°C. The cells were discharged periodically at a current of 0.2 C (at 25°C) to evaluate their residual capacity.Degraded cells were disassembled and six different points of the anode were analyzed. The Mn content was analyzed using an inductively coupled plasma (ICP) method. We also used Li7-nuclear magnetic resonance(NMR) to identify the species on the anode. A LiCl solution of 1M was used as the standard sample. Results Figure 1 shows the lifetime of each floating charge voltage. Lifetime is defined as the duration at which the discharged capacity remains under 70% initial capacity. We found that lifetime decreased greatly between 4.15 and 4.2 V, presumably due to the phenomenon of deterioration caused by electrolyte decomposition since this test was conducted at 50°C. The lifetime at 4.05 V was slightly shorter compared with those at 4.10 and 4.15 V. The reason for this is uncertain.More than 103 times the amount of Li was observed on the degraded anode compared with that of Mg by using the ICP method. This result shows that the simple charge exchange mechanism between Mn2+ and intercalated Li will be rejected. Figure 2 shows the Li7-NMR spectrum of the anode. Two peaks were identified. One was the broad peak of which the chemical shift was -12.2 ppm. The other was that of which the chemical shift was 2.4 ppm. The area of the former was about 98%, and the latter was identified inorganic Li compound. The former may be an organic Li compound, although the chemical species remains unclear. It is known that SEI forms compact inorganic compounds, such as LiF, and organic Li compounds. The results from this study suggest that the formation of organic Li compounds is the main cause of Li consumption and that Mg deposition may accelerate organic Li compound formation. References (1) T. Tsujikawa, K. Yabuta, T. Matsushita, M. Arakawa, K. Hayashi, J. Electrochem. Soc., 158, 322 (2011).(2) T. Tsujikawa, K. Yabuta, T. Matsushita, T. Matsushima, K. Hayashi, and M. Arakawa, J. Power Sources, 189, pp. 429-434 (2009).

FP-LAPW+lo Study of Structural, Electronic, and Optical Properties of Mg1-xSrxTe Alloys

First principles total energy calculations have been performed using the full potential linear augmented plane wave plus local orbital (FP-LAPW+lo) method within density functional theory to investigate the effects of Sr-dopant on the structural, electronic, and optical properties of Mg1-xSrxTe alloys in the rock salt crystallographic phase. The generalized gradient approximation (GGA) parameterization scheme proposed by Wu and Cohen (WC) has been used for calculating the ground state structural properties, and their deviation from Vegard's law has been discussed. The Engel-Vosko (EV) GGA functional has also been employed for electronic and optical properties of the alloy systems under study, and the results of the two GGA functionals are compared. Our calculated optical bowing in the band gap for the ternary alloys is found to be mainly caused by the charge exchange mechanism. Dielectric functions, optical conductivity, and reflectivity calculations predict the use of these alloys for technologically important optical and optoelectronic devices.

The K¯NN system revisited including absorption

Abstract We present the Fixed Center Approximation (FCA) to the Faddeev equations for the K ¯ N N system with S = 0 , including the charge exchange mechanisms in the K ¯ rescattering. The system appears bound by about 35 MeV and the width, omitting two body absorption, is about 50 MeV. We also evaluate the K ¯ absorption width in the bound K ¯ N N system by employing the FCA to account for K ¯ rescattering on the NN cluster. The width of the states found previously for S = 0 and S = 1 is found now to increase by about 30 MeV due to the K ¯ N N absorption, to a total value of about 80 MeV.

Recent molecular engineering of room temperature ionic liquid electrolytes for mesoscopic dye-sensitized solar cells

Over the past decade, room temperature ionic liquids (RTILs) have been widely recognized as alternative green, tunable and robust electrolytes for mesoscopic dye-sensitized solar cells (DSCs) due to their unique properties. The negligible volatility of RTILs renders them more suitable than molecular solvents for long-term device use, while the high thermal and electrochemical stability fulfill the essential requirements for electrolyte applications. In spite of the relatively high viscosities of common RTIL iodides, the mass transport limitations can be effectively alleviated by the contribution of a Grotthous-type charge exchange mechanism. More interestingly, the physicochemical properties of RTILs can be facilely tuned by tailoring their cationic and anionic structures, which provides great feasibility for the specific designing of application-oriented RTILs. In this Feature Article, recent progress on highly efficient DSCs with RTIL electrolytes are summarized, with a special focus on the structural-dependence of the ionic diffusion property in RTIL electrolytes, as well as the charge transport and recombination kinetics at RTIL electrolytes/dye molecule/TiO2 electrodes interfaces. Furthermore, recent advances in RTIL electrolytes with iodine-free redox couples have been reviewed. Crucial issues that should be addressed in the pursuit of future developing low-cost and high-efficient RTIL electrolytes are also discussed.