Spatial Distribution Of Electrons Research Articles

The plasma environment inside geostationary orbit: A Van Allen Probes HOPE survey.

The two full precessions in local time completed by the Van Allen Probes enable global specification of the near‐equatorial inner magnetosphere plasma environment. Observations by the Helium‐Oxygen‐Proton‐Electron (HOPE) mass spectrometers provide detailed insight into the global spatial distribution of electrons, H+, He+, and O+. Near‐equatorial omnidirectional fluxes and abundance ratios at energies 0.1–30 keV are presented for 2 ≤ L ≤ 6 as a function of L shell, magnetic local time (MLT), and geomagnetic activity. We present a new tool built on the UBK modeling technique for classifying plasma sheet particle access to the inner magnetosphere. This new tool generates access maps for particles of constant energy for more direct comparison with in situ measurements, rather than the traditional constant μ presentation typically associated with UBK. We present for the first time inner magnetosphere abundances of O+ flux relative to H+ flux as a function of Kp, L, MLT, and energy. At L = 6, the O+/H+ ratio increases with increasing Kp, consistent with previous results. However, at L < 5 the O+/H+ ratio generally decreases with increasing Kp. We identify a new “afternoon bulge” plasma population enriched in 10 keV O+ and superenriched in 10 keV He+ that is present during quiet/moderate geomagnetic activity (Kp < 5) at ~1100–2000 MLT and L shell 2–4. Drift path modeling results are consistent with the narrow energy and approximate MLT location of this enhancement, but the underlying physics describing its formation, structure, and depletion during higher geomagnetic activity are currently not understood.

On the calculation of the energies of dissociation, cohesion, vacancy formation, electron attachment, and the ionization potential of small metallic clusters containing a monovacancy

In terms of the model of stable jellium, self-consistent calculations of spatial distributions of electrons and potentials, as well as of energies of dissociation, cohesion, vacancy formation, electron attachment, and ionization potentials of solid clusters of Mg N , Li N (with N ≤ 254 ) and of clusters containing a vacancy (N ≥ 12) have been performed. The contribution of a monovacancy to the energy of the cluster and size dependences of its characteristics and of asymptotics have been discussed. Calculations have been performed using a SKIT-3 cluster at Glushkov Institute of Cybernetics, National Academy of Sciences, Ukraine (Rpeak = 7.4 Tflops).

Extraction dynamics of electrons from magneto-optically trapped atoms

Pulsed photoionization of laser-cooled atoms in a magneto-optical trap (MOT) has the potential to create cold electron beams of few meV bandwidths and few ps pulse lengths. Such a source would be highly attractive for the study of fast low-energy processes like coherent phonon excitation. To study the suitability of MOT-based sources for the production of simultaneously cold and fast electrons, we study the photoionization dynamics of trapped Cs atoms. A momentum-microscope-like setup with a delay-line detector allows for the simultaneous measurement of spatial and temporal electron distributions. The measured patterns are complex, due to the Lorentz force inducing spiral trajectories. Ray-tracing simulations reproduce the main features. We find that the production of electron bunches with bandwidths of a few meV is straightforward; however, pulses in the ps-range are more demanding and require beam blanking or partial blocking.

Ab initio study of the structure and electronic properties of magnesium and calcium nitrates and their crystal hydrates

The crystal structures and electronic properties of magnesium and calcium nitrates, magnesium nitrate hexahydrate, and calcium nitrate tetrahydrate are studied at the density functional theory level by a hybrid functional in the basis set of localized atomic orbitals using the CRYSTAL14 program code. Atomic structural parameters, atomic charges, bond populations, energy and electron spatial distributions are calculated. The mainly electrostatic nature of interactions between nitro groups and water molecules is shown. The spectrum of the density of states of crystal hydrates, in comparison with nitrates, contains additional bands due to the presence of water. In the spectra of unoccupied states a gap is observed: the anionic gap is ~6.5 eV and the cationic gap is ~8.8 eV.

STRUCTURE, ELECTRON AND OSCILLATORY PROPERTIES OF ZINC NITRATE AND ITS CRYSTAL HYDRATES

Within the generalized gradient aproximation of the Density Functional Theory (DFT) with the PBE exchange-correlation functional in the basis of localized atomic orbital of CRYSTAL14 program code, the study is conducted to evaluate the structural, electronic and oscillatory properties of zinc nitrate and its crystal hydrates Zn(NO3)2 • nH2O (n = 2,4,6), with its tested method using the zinc oxide. The first-principle structural study is performed at the full optimization of the lattice distance and atomic positions for the zinc nitrate in the cubic lattice and that of crystal hydrates - in monoclinic lattice. Elastic properties of the nitrate are studied and the mechanical stability is approved using the Born criteria. Electronic properties of rated structures are assessed by energetic (energy-band picture, full and partial density of states) and spatial electron distribution (electronic and deformation density, population density of atomic membranes and density of their overlapping). Crystal hydrates show the electrostatic pattern of nitrogroup interaction and water molecules, availability of localized valence bands and areas of vacant state of anion and cation origin. Oscillatory properties are studied by calculation of frequencies and intensity of IR-active normal long-wave oscillation. In crystal hydrates, the appearance of additional oscillation frequency O-H in terms of nitrate 3000 cm-1 above the IR-spectrum in water molecules and within the area 1200÷1600 cm-1 - of hybrid with nitrogroups.

Proposal for a Nanoscale Superconductive Memory

Energy efficiency is a key issue for modern high performance computing. Superconductive digital electronics has already demonstrated superior performances in terms of speed and energy dissipations. However, there is still the open issue of the realization of effective submicron scale superconductive memories. Superconducting nanowires represent the state-of-the-art of single-photon detectors. Their technology has also been used to realize three-terminal active devices, where the output response is triggered by a current pulse. The combination of the electrothermal mechanism of the nanowire and the magnetic coupling with a suitable material can be used for the realization of a nanowire-based memory device scalable to nanoscale. The principle of operation and material requirements are presented here. In particular, the feasibility of the proposed device using EuS as magnetic material and NbN as nanowire is discussed. By using a physical model of the nanowire dynamics, in terms of the spatial distribution of electron and phonon temperatures, the feasibility of the proposed device has been verified, through numerical simulations. The device configurations considered have the specific goal of realizing reliable and high-speed read and write operations, with the possibility of scalability to nanoscale.

Separation of geminate electron-hole pairs at donor-acceptor interfaces in the approximation of prescribed diffusion

It is generally believed that electrons and holes in organic solar cells are generated by dissociation of excitons at the interface between donor and acceptor materials in the form of geminate, coulombically bound electron-hole pairs. The further motions of electrons and holes are restricted to the acceptor material and donor material, respectively. Using the method of prescribed diffusion, we solve the Smoluchowski equation describing evolution of the spatial distribution of electrons and holes. The separation probability of electron-hole pairs is found as a function of an initial intrapair separation and external electric field.

Circuit model for functionally integrated injection laser modulators

This paper proposes a circuit model for injection lasers with functionally integrated optical-radiation modulators. This model takes into account the design and structural features of the functionally-integrated injection laser modulators (FIILMs), as well as the effect exerted by the spatial distributions of electrons, holes, and photons in the FIILMs’ active region on the behavior of the physical processes there.

Two-dimensional numerical simulation of a continuous needle-like argon electron-beam plasma

The fluid-Poisson equations coupled with the Monte Carlo method were used to simulate the spatio-temporal behavior of a needle-like argon electron-beam plasma. Based on the Monte Carlo simulation, three coupled parameters characterizing the electron beam propagation for initial energies above several keV were expressed using a universal dimensionless shape function given in terms of the beam range multiplied by a normalized coefficient. Therefore, a single run of the Monte Carlo code was sufficient for the simulations over a wide range of conditions. The spatial potential as a function of space and time was studied from the fluid-Poisson equations. The results indicate that the time evolution of the spatial potential was influenced by the presence of the slowed-down electrons and the flying beam electrons, whereas the potential in quasi-equilibrium was mainly determined from the spatial distribution of the secondary electron. The potential in quasi-equilibrium was positive near the beam entrance and most negative along the tip of the beam range, which was a result of ambipolar diffusion. When the enclosing boundary surfaces were moved within the beam range, the potential was nearly positive everywhere. The calculation on the diffusion-drift flux indicated that the net current of the secondary electrons flowing back to the incident plane in quasi-equilibrium balanced the incident beam current, which was the so-called return current in the three-dimensional space.

Mobility Modulation and Suppression of Defect Formation in Two-Dimensional Electron Systems by Charge-Transfer Management

Electron mobility is one of the most-debated key attributes of low-dimensional electron systems emerging at complex oxide heterointerfaces. However, a common understanding of how electron mobility can be optimized in these systems has not been achieved so far. Here, we discuss a novel approach for achieving a systematic increase in electron mobility in polar/nonpolar perovskite interfaces by suppressing the thermodynamically required defect formation at the nanoscale. We discuss the transport properties of electron gases established at interfaces between SrTiO3 and various polar perovskites [LaAlO3, NdGaO3, and (La,Sr)(Al,Ta)O3], allowing for the individual variation of epitaxial strain and charge transfer among these epitaxial interfaces. As we show, the reduced charge transfer at (La,Sr)(Al,Ta)O3/SrTiO3 interfaces yields a systematic increase in electron mobility, while the reduced epitaxial strain has only minor impact. As thermodynamic continuum simulations suggest, the charge transfer across these interfaces affects both the spatial distribution of electrons and the background distribution of ionic defects, acting as major scatter centers within the potential well. Easing charge transfer in (La,Sr)(Al,Ta)O3/SrTiO3 yields an enlarged spatial separation of mobile charge carriers and scattering centers, as well as a reduced driving force for the formation of ionic defects at the nanoscale. Our results suggest a general recipe for achieving electron enhancements at oxide heterostructure interfaces and provide new perspectives for atomistic understanding of electron scattering in these systems.

Spatial distribution of electrons near the Fermi level in the metallic LaB6 through accurate X-ray charge density study

Charge densities of iso-structural metal hexaborides, a transparent metal LaB6 and a semiconductor BaB6, have been determined using the d > 0.22 Å ultra-high resolution synchrotron radiation X-ray diffraction data by a multipole refinement and a maximum entropy method (MEM). The quality of the experimental charge densities was evaluated by comparison with theoretical charge densities. The strong inter-octahedral and relatively weak intra-octahedral boron-boron bonds were observed in the charge densities. A difference of valence charge densities between LaB6 and BaB6 was calculated to reveal a small difference between isostructural metal and semiconductor. The weak electron lobes distributed around the inter B6 octahedral bond were observed in the difference density. We found the electron lobes are the conductive π-electrons in LaB6 from the comparison with the theoretical valence charge density. We successfully observed a spatial distribution of electrons near the Fermi level from the X-ray charge density study of the series of iso-structural solids.

Stability of Excess Electrons Introduced by Ti Interstitial in Rutile TiO2(110) Surface

The surface chemistry of rutile TiO2(110) has long been ascribed to surface bridging oxygen vacancies (VO) and accompanying excess electrons. However, recently there has been debate whether titanium interstitials (Tiint), a subsurface defect, participates in the surface reactions of TiO2(110). We used a combination of ab initio molecular dynamics and static density functional theory calculations to systematically investigate the spatial distribution of excess electrons introduced by Tiint. We found that these excess electrons form polarons and that the most stable structure had one polaron located at the Tiint site, and the other three at second-layer Ti sites below five-coordinate Ti sites. This behavior of Tiint providing excess electrons to the near-surface region is similar to that of VO, which suggests that Tiint may contribute to the surface chemical reactions of TiO2(110).

Hexacyanometallates for sodium-ion batteries: insights into higher redox potentials using d electronic spin configurations.

A fundamental understanding of anomalous redox mechanisms in hexacyanometallate compounds, compared with conventional NaMO2 systems (M: transition metals), is presented based on first-principles calculations and experimental validations. From theoretical calculations, we identified low-spin and high-spin states of Fe ions coordinated by the cyanide group (-CN) with the same oxidation state (Fe2+) in Na2Fe2(CN)6. Considering the site dependency of d electronic spin configurations based on the crystal field theory (CFT) of transition metals (TMs), we calculated the thermodynamic mixing energy using Na2Fe2(CN)6 and Na2Mn2(CN)6 for obtaining a thermodynamically stable phase of Na2FeMn(CN)6. The phase stabilities of Na2Fe2-xMnx(CN)6 among many atomic configurations and lattice parameters originating from octahedral structures (i.e., Fe(CN)6 and Mn(NC)6) are highly dependent on the electronic structures of TMs with spin states. From partial density of states (PDOS) and spatial electron distributions, it was observed that Fe2+ in the low-spin state (t) and Mn2+ in the high-spin states (t and e) in the stable phase lead to higher redox potentials (∼3.55 V vs. Na/Na+) with the removal of Na+ as compared to that of Na2Fe2(CN)6. In addition, lattice parameters from x = 0 to x = 1 in Na2Fe2-xMnx(CN)6 are increased due to the larger ionic radius of Mn2+ in the high-spin states. On the other hand, Fe2+ in the high-spin states (t and e) and Mn2+ in the low-spin state (t) in the most unstable phase of Na2FeMn(CN)6 would have lower redox potentials. Based on the fundamental correlation between redox potentials and CFT with spin configurations of TMs, we suggest a material design concept for intercalation compounds with higher energy densities for rechargeable battery systems.

Pulsed electron‐nuclear double resonance diagnostics of Ce3+ emitters in scintillating garnets

Pulsed electron paramagnetic resonance (EPR) and pulsed electron‐nuclear double resonance (ENDOR) techniques have been applied to study the environment of luminescent Ce3+ ions in garnet based scintillator powders and ceramics. The presence of aluminum and gallium isotopes with large nuclear magnetic and quadrupole moments in the nearest neighborhood of the Ce3+ ion allows for the use of the hyperfine and quadrupole interactions with these ions for determination of the unpaired electron spatial distribution and the definition of the electric field gradient at the aluminum and gallium sites. Pulsed EPR and ENDOR techniques made it possible to study the coherent properties of the Ce3+ spin system in garnet powders and ceramics, which is important for spin manipulation on Ce3+ centers.

Electronic structure and spatial distribution of the spin density of shallow nitrogen donors in the SiC lattice

The discovery of unique magnetooptical properties of paramagnetic centers in silicon carbide, which make it possible to control spins of small arrays of centers of atomic sizes to single centers at room temperatures, using the techniques of optical detection of the magnetic resonance, posed a number of problems, among which one of the main ones is the creation of conditions under which spin relaxation effects are minimized. As studies of properties of spin nitrogen-vacancy centers in diamond showed, the main contribution to spin relaxation is made by the interaction with nitrogen donors, being a major impurity in diamond. A similar problem exists for silicon carbide, since nitrogen donors are also basic background impurities. The objective of this work is to study the spatial distribution of the spin density of nitrogen donors in two basic silicon carbide polytypes, i.e., 4H-SiC and 6H-SiC, to use this information for minimizing the interaction of nitrogen donors with paramagnetic centers in silicon carbide. The results of the study are analyzed by magnetic resonance methods; the spin density distribution on the nearest coordination spheres of nitrogen donors occupying carbon sites in silicon carbide is determined. It is concluded that paramagnetic centers in the 4H-SiC polytype, including silicon vacancies, can be more stable to the interactions with unpaired donor electrons, since electrons are not localized on the coordination sphere closest to the paramagnetic center in this case.

High-latitude F region large-scale ionospheric irregularities under different solar wind and zenith angle conditions

A numerical model is used to study systematically the evolution of large scale irregularities depending on the IMF Bz and By components, solar zenith angle (seasonal and daily variation), solar and geomagnetic activity. The model enables to reproduce the 3-D distribution of electron density over the high-latitude F region ionosphere in the altitude range between 130 and 640km. Since the convection electric field driven by changes in solar wind conditions has an important effect on the high-latitude ionosphere, the rotation of the IMF vector in the Y–Z plane causes a significant redistribution of the ionospheric plasma. Under the southward IMF conditions the plasma density is enhanced over a large portion of the near-pole ionosphere as a tongue of ionization, while the northward IMF leads to a considerable depletion and occurrence of the polar hole. The IMF By polarity is crucial for the shift and extension of the tongue of ionization to the dusk or dawn side. Particle precipitation also plays a role through a localized increase of the electron density mostly within the auroral oval and more pronounced auroral peak. The solar zenith angle, especially its seasonal variation, is the strongest regular factor influencing the electron density magnitude and spatial distribution. In winter, when the polar ionosphere is in darkness, large variations associated with different solar wind condition are more prominent. The daily variation of the zenith angle considerably modifies the Ne within a particular pattern. At a given time, the combined action of the IMF, solar zenith angle, level of solar and geomagnetic activity produces a complicated ionospheric response which can be considered as a superposition of different effects. Quantitative estimates of the ionospheric response to each factor are presented.

Particle dynamics in the electron current layer in collisionless magnetic reconnection

Particle dynamics in the electron current layer in collisionless magnetic reconnection is investigated by using a particle-in-cell simulation. The electron motion and velocity distribution functions are studied by tracking self-consistent trajectories. New classes of electron orbits are discovered: figure-eight-shaped regular orbits inside the electron jet, noncrossing regular orbits on the jet flanks, noncrossing Speiser orbits, and nongyrotropic electrons in the downstream of the jet termination region. The properties of a super-Alfvénic outflow jet are attributed to an ensemble of electrons traveling through the Speiser orbits. The noncrossing orbits are mediated by the polarization electric field near the electron current layer. The noncrossing electrons are found to be non-negligible in number density. The impact of these new orbits to electron mixing, spatial distribution of energetic electrons, and observational signatures is presented.

Experimental study of the spatial distributions of relativistic electron beams reflected and refracted by a thin foil

Photographs of cross sections of an electron beam scattered from thin foils have been obtained on a dosimetric film. The procession of images makes it possible to obtain the spatial distribution of particles both reflected from a foil and passed through it. The spatial distribution of electrons incident on aluminum, copper, and lead foils, as well as on bimetallic foils composed of aluminum and lead layers and of aluminum and copper layers, has been measured. The effect of the material and thickness of the foil, as well as of the angle between the initial beam trajectory and the target plane, on the spatial distribution of electrons has been studied. The effect of the sequence of the metal layers in bimetallic foils on the distribution of beams has been analyzed. A 7.4-MeV microtron has been used as a source of electrons.

Separation of angular and energy relaxations of nonequilibrium electrons in a solid

We demonstrate that the collision integral of the kinetic equation for the interaction of hot electrons with phonons can be split into substantially different parts that correspond to elastic and inelastic collisions. In particular, this applies to electrons with energies of about 1 eV that propagate in semiconductors. The difference in the characteristic energy and momentum relaxation times makes it possible to separate the angular and energy relaxation processes. If the differential cross section of elastic scattering depends, not on the scattering angle, but on the directions of incident and scattered electrons (which is observed, e.g., for the interaction of an electron with piezoelectric lattice vibrations in AIIIBV compounds), the Laplacian in the equation that describes the spatial and energy distributions of electrons can be replaced by an elliptical operator; i.e., the electron diffusion turns out to be anisotropic.

Capacitance, the Next of Kin to Chemical Softness and Density of States, an Unexpected Perk of Being the “Middle Child”

The capacitance characterizes abilities of various systems to store energy in the form of energy density of electric field. The spatial distribution of electrons exhibits a nonuniform relationship with external potential of atomic nuclei as a consequence of shielding or bonding, and other localized or delocalized charges. Respectively, the stored system energy is affected through thermodynamic displacement. Considering the general resemblance of capacitance definition with two other physical quantities used in the field of chemical physics, the chemical softness or the density of states, it is important to uniquely express this function in nanoscale materials to characterize phenomena resulting from confinement of few electrons generally characterized by density distribution. The exact fundamental linkages and differences between these functions have to be recognized to deal with unintuitive quantum mechanical effects related to the design, development, and comprehending the working principle of nanoscale...