Spatial Distribution Of Electrons Research Articles

Quantum shell effects in compressed mesoscopic system

This article demonstrates the nontrivial manifestation of quantum shell effects in a compressed mesoscopic system. It is shown that there are two spatial scales in the distribution of degenerate electrons in a spherical well. The first scale is the Fermi length ∼h/pF. By the quantum shell effect, the authors mean the existence of the new spatial scale, which is the order of the system size and much larger than the first scale. The theoretical analysis for the large amount of free electrons (N ≲ 109) in an infinite spherical well demonstrates what causes the appearance of the spatial nonuniformity and gives the analytical expression for the electron distribution function. These results are confirmed by a numerical summation of exact solutions for the electron wave functions in an infinite potential well. It is shown that an analogous effect for the spatial distribution of electrons exists in a compressed hydrogen gas bubble of submicron size (<0.1 μm). The numerical simulation of the electron distribution was carried out by the Density Functional Theory method. The consequence of this effect is the nontrivial dynamics of the compressible cold gas bubble. This system can be realized in the thermonuclear experiments. The limiting factors of the analyzed effect are considered: symmetry of the system, electron temperature, and curvature of the system boundary.

Structure and Properties of Ice Phase States

The structure, equation of state, mechanical and vibrational properties of single crystals of ices II, VIII, XI and ice in a previously predicted phase bct-4 are studied within the Hartree-Fock method using the density functional theory (B3LYP hybrid functional) with localized Gaussian atomic orbitals as implemented in the “CRYSTAL14” software package. Calculated lattice parameters, elastic moduli of single crystals, and mechanical parameters of polycrystalline samples are shown to meet the criteria of mechanical stability. Parameters of the Vinet equation of state are obtained. Energy band widths and Mulliken atomic charges are determined using obtained energy and spatial distribution of electrons. The frequencies of long-wave vibrations are calculated and vibrational spectra are constructed.

Electric Field Distribution Characteristics and Space Charge Motion Process in Transformer Oil Under Impulse Voltage

The electric field and space charge dynamics characteristics in oil under impulse voltage are key factors to the transformer insulation design, which are mainly obtained through simulation, falling short of experimental verifications. Applying the Kerr electro-optic method, the present paper carried out an actual measurement for the electric field characteristics in transformer oil under impulse voltage and managed to obtain their correlations with an electrode material, voltage amplitude, and wave-front time, respectively. First, it was found that, under impulse voltage and in pure transformer oil, the aluminum electrode had the largest amount of charge injection, followed by stainless steel and then copper, which was attributed to the different work functions of metal elements in electrodes. Second, with the increase of voltage amplitude, the effect of the space charge on the intermediate electric field of the oil gap was first enhanced, then weakened, and eventually enhanced. Third, as the wave-front time was prolonged, the peak of electric field in transformer oil showed a downward trend. For instance, the peak value of the electric field was reduced by 17.6 % when the wave-front time was increased from 0.5 μs to 40.0 μs. The reason is that when the wave-front time is longer, the amount of injected charge grows larger and the weakening effect becomes stronger. Fourth, a charge dynamic motion model in transformer oil under impulse voltage was established to demonstrate its spatial-temporal effects on the electric field. Besides, this paper has clarified the source of the negative and positive charges in the transformer oil under impulse voltage by using the theories of field emission and field ionization. Moreover, the variation of electron mobility over-voltage amplitude, wave-front time, and spatial distribution was worked out to present the quantitative results of its motion process.

Study of Local Charge Accumulation in ZrO2(Y) Films with Au Nanoparticles by Kelvin Probe Force Microsсopy

The time dynamics of the spatial distribution of electrons locally injected from the probe of an atomic force microscope into thin (less than 10 nm) ZrO2(Y) films with embedded Au nanoparticles on Si substrates is studied via Kelvin probe force microscopy. The profiles of the film surface potential induced by the injection of a countable number (several tens) of electrons into Au nanoparticles, as a function of the time elapsed after injection, are measured and analyzed.

The synergistic effect of non-metal doping or defect engineering and interface coupling on the photocatalytic property of g-C3N4: First-principle investigations

The light response range, redox potential, and consequently, the photo-reactivity of a semiconductor photocatalyst for solar-to-hydrogen are intrinsically dominated by its electronic structure. Introducing chemical impurities, structural defects, and construction of heterostructures have been considered as the widely adopted strategies to modify the electronic structures of two-dimensional photocatalyst. Up to now, however, the synergetic effect of these strategies on the photocatalytic property of photocatalyst remains unknown. In our work, using first-principles calculations, we systemically studied the effect of non-metal (sulfur) doping, vacancy engineering and interface coupling, as well as their synergetic effect on the electronic structure of g-C3N4. Results indicate that the introduction of doped S atom or C (N)-vacancy in g-C3N4 could extend the light response range by narrowing the band gap or creating gap states, while the coupling effect at interface of g-C3N4/MoS2 is able to tune the band edge potentials of g-C3N4. Incorporation of these strategies, a g-C3N4 with appropriate band gap and suitable band edge potentials can be obtained. Moreover, we also found that these modification strategies can influence the spatial electron distribution corresponded to the band edges, which would be beneficial to inhibiting the recombination of photogenerated electron-hole pairs. Therefore, incorporating doping or defect engineering with interface coupling should be an experimentally attainable way to improve the photo-reactivity of 2D semiconductors for overall photocatalytic water splitting.

Rotamer Modelling of Cu(II) Spin Labels Based on the Double-Histidine Motif

Spin labels attached to two residues of a protein chain have less conformational flexibility than those attached to a single residue and thus lead to a narrower spatial distribution of the unpaired electron. The case of Cu2+ labels based on the double-histidine (dHis) motif is of particular interest, as it combines the advantage of precise localization of the unpaired electron with a labelling scheme orthogonal to the more common cysteine-based labelling. Here, we introduce an approach for in silico spin labelling of a protein by dHis motifs and Cu2+ complexes of iminodiacetic acid or nitrilotriacetic acid. We discuss a computerized scan for native histidine pairs that might be prone to bind such Cu2+ complexes and spin-labelling site pair scans that can identify suitable double mutants for labelling. Predicted distance distributions between two Cu2+ labels are compared to experimental distance distributions. We also test the hypothesis that elastic network modelling of conformational transitions with Cu2+-dHis labels can provide more accurate structural models than with nitroxide labels.

Microwave and Hard X-Ray Observations of the 2017 September 10 Solar Limb Flare

Abstract We report the first science results from the newly completed Expanded Owens Valley Solar Array (EOVSA), which obtained excellent microwave (MW) imaging spectroscopy observations of SOL2017-09-10, a classic partially occulted solar limb flare associated with an erupting flux rope. This event is also well-covered by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) in hard X-rays (HXRs). We present an overview of this event focusing on MW and HXR data, both associated with high-energy nonthermal electrons, and we discuss them within the context of the flare geometry and evolution revealed by extreme ultraviolet observations from the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory. The EOVSA and RHESSI data reveal the evolving spatial and energy distribution of high-energy electrons throughout the entire flaring region. The results suggest that the MW and HXR sources largely arise from a common nonthermal electron population, although the MW imaging spectroscopy provides information over a much larger volume of the corona.

The Determination and Application of the Point Spread Function in the Scanning Electron Microscope.

A method is presented to determine the spatial distribution of electrons in the focused beam of a scanning electron microscope (SEM). Knowledge of the electron distribution is valuable for characterizing and monitoring SEM performance, as well as for modeling and simulation in computational scanning electron microscopy. Specifically, it can be used to characterize astigmatism as well as study the relationship between beam energy, beam current, working distance, and beam shape and size. In addition, knowledge of the distribution of electrons in the beam can be utilized with deconvolution methods to improve the resolution and quality of backscattered, secondary, and transmitted electron images obtained with thermionic, FEG, or Schottky source instruments. The proposed method represents an improvement over previous methods for determining the spatial distribution of electrons in an SEM beam. Several practical applications are presented.

One- and two-photon absorption spectra of dibenzoterrylene

Dibenzoterrylene (DBT) has garnered interest as a potential single photon source (SPS). To have a better grasp of any possible limitations of using DBT for this application, a better understanding of its optical properties is needed. We use a configuration interaction (CI) strategy to calculate the many body wavefunctions of DBT, and we use these wavefunctions to calculate its optical properties. We calculate the linear absorption spectrum and the spatial distributions of electrons involved in several bright transitions. We also calculate the two-photon absorption spectrum of DBT and show that there are several excited states that are bright due to two-photon absorption. Except at high photon energies, we predict that there are no competing optical processes regarding the use of DBT as a SPS. Our calculations provide details of the optical properties of DBT that are interesting in general, and useful for considering optical applications of DBT.

Inhomogeneous Spatial Distribution of Electrons in a Compressed Gas Bubble of Submicron Size

The inhomogeneous spatial distribution of the macroscopic amount of electrons (N <109) in a spherical potential well is considered. It is shown that the electron distribution has two spatial scales. The first scale is the Fermi length. By effect, we mean the existence of the second scale, which is related with the radius of the potential well and much larger than the first scale. Two systems are considered: a system of free electrons in a spherical well and electrons in a compressed gas bubble. Based on the analysis of the distribution function of a system of free semiclassical electrons, we demonstrate the cause of the appearance of the spatial heterogeneity. This result is confirmed by a numerical summation of exact solutions of the wave functions of electrons in an infinite potential well. It is shown that there is an analogous effect for the spatial distribution of electrons in compressed hydrogen gas bubble of submicron size (<0.1 μm). This system can be realized in the thermonuclear experiments. Numerical simulation of the electron distribution was carried out by the DFT method. The limiting factors of the effect are considered. The aim of problem considered in the article deals with the analysis of possible physical processes occurring in the thermonuclear experiments.

Passivated Codoping Can Improve the Solar-to-Hydrogen Efficiency of Graphitic Carbon Nitride

Passivated codoping has never been reported to enhance the solar-to-hydrogen activity of g-C3N4, although it is an effective approach for other materials. In this letter, we use many-body Green’s function theory to analyze the electronic structures, optical absorption spectra, and spatial distribution of electron–hole pair of the doped g-C3N4. Our results suggest that the passivated codoping, such as B+O, could not only extend absorption toward visible range but also promote the separation of photogenerated hole and electron to different parts of g-C3N4. Improvement of photocatalytic activity can be realized only when the n-type and p-type dopants reside in different tris-triazine units of g-C3N4. This manifests the important role of codoping microstructure on solar-to-hydrogen efficiency. These results could provide a guideline for the design of more efficient artificial photocatalysts.

Transient Radiation Imaging Based on a ZnO:Ga Single-Crystal Image Converter

A ZnO:Ga single crystal with an applicable size of φ40 × 1 mm was prepared using the hydro-thermal method. The crystal exhibits good crystallinity and scintillation properties with a 63.94-arcsec full-width at half-maximum (FWHM) in the X-ray rocking curve (XRC) spectrum, 8% luminous non-uniformity, emission at 389 nm in the X-ray excited luminescence spectrum, fast response and 5.5% BGO luminous intensity. Furthermore, an X-ray pinhole imaging system of nanosecond temporal resolution with a ZnO:Ga single-crystal image converter was established to diagnose the cathode electron emission spatial distribution of an intense current diode. Results for shutter times of 4 μs and 5 ns were obtained, which directly represent the cathode electron spatial distribution throughout the entire pulse duration and during a certain moment of the pulse, respectively. The results demonstrate that the large ZnO:Ga single crystal can diagnose the spatial distribution of cathode electron emission in an intense current diode with high temporal resolution and provide new solutions for high-temporal-resolution diagnosis of a pulse radiation field.

Aluminum and gallium nuclei as microscopic probes for pulsed electron-nuclear double resonance diagnostics of electric-field gradient and spin density in garnet ceramics doped with paramagnetic ions

The presence of aluminum and gallium isotopes with large nuclear magnetic and quadrupole moments in the nearest environment of impurity ions Mn2+ and Ce3+ in garnets made it possible to use hyperfine and quadrupole interactions with these ions to determine the spatial distribution of the unpaired electron and the gradient of the electric field at the sites of aluminum and gallium in the garnet lattice. High-frequency (94 GHz) electron spin echo detected electron paramagnetic resonance and electron-nuclear double resonance measurements have been performed. Large difference in the electric field gradient and quadrupole splitting at octahedral and tetrahedral sites allowed identifying the positions of aluminum and gallium ions in the garnet lattice and proving that gallium first fills tetrahedral positions in mixed aluminum-gallium garnets. This should be taken into account in the development of garnet-based scintillators and lasers. It is shown that the electric field gradient at aluminum nuclei near Mn2+ possessing an excess negative charge in the garnet lattice is ca. 2.5 times larger than on aluminum nuclei near Ce3+.

Study of electron transport in the functionalized nanotubes and their impact on the electron transfer in the active site of horseradish peroxidase

Electrochemical characterization of functionalized carbon nanotubes (f-CNT) including carboxyl (CNT-COOH), amine (CNT-NH2) and hydroxyl (CNT-OH) functional groups were studied using differential pulse voltammetry (DPV). The current-voltage (I-V) curves were obtained from each system and the effect of f-CNT on redox interaction of horseradish peroxidase (HRP) immobilized on the electrode surface was investigated. The non-equilibrium Green's function (NEGF) combined with density functional theory (DFT) were used to study the transport properties of f-CNT. Additionally, the effect of the number of functional groups on transport properties of CNT, I-V characteristics, electronic transmission coefficients and spatial distribution of f-CNTs have been calculated and analyzed. The results showed that the carboxyl derivative has larger transmission coefficients and current value than other f-CNTs. Then, the effect of functional groups on the electron transport in heme group of HRP is discussed. Finally, the effect of a covalent bond between active site amino acids and amine functional group of CNT was investigated and discussed.

Tunable electric properties of bilayer InSe with different interlayer distances and external electric field

Using density functional theory we explore the band structure of bilayer Indium selenide (InSe), and we find that the van der Waals interaction has significant effects on the electric and optical properties. We then explore the tuning electronic properties by different interlayer distances and by an external vertical electric field. Our results demonstrate that the band gaps of bilayer InSe can be continuously tuned by different interlayer coupling. With decreasing interlayer distances, the tunable band gaps of bilayer decrease linearly, owing to the enhancement of the interlayer interaction. Additionally, the band structure of bilayer InSe under external vertical fields is discussed. The presence of a small external electric field can make a new spatial distribution of electron–hole pairs. A well separation based on the electrons and holes, localized in different layers can be obtained using this easy method. These properties of bilayer InSe indicates potential applications in designing new optoelectronic devices.

Experimental study on secondary electron emission characteristics of Cu.

Secondary electron emission (SEE) of a surface is the origin of the multipacting effect which could seriously deteriorate beam quality and even perturb the normal operation of particle accelerators. Experimental measurements on secondary electron yield (SEY) for different materials and coatings have been developed in many accelerator laboratories. In fact, the SEY is just one parameter of secondary electron emission characteristics which include spatial and energy distribution of emitted electrons. A novel experimental apparatus was set up in China Spallation Neutron Source, and an innovative method was applied to obtain the whole characteristics of SEE. Taking Cu as the sample, secondary electron yield, its dependence on beam injection angle, and the spatial and energy distribution of secondary electrons were achieved with this measurement device. The method for spatial distribution measurement was first proposed and verified experimentally. This contribution also tries to give all the experimental results a reasonable theoretical analysis and explanation.

Energy Characteristics of Small Metal Clusters Containing Vacancies

Self-consistent calculations of spatial distributions of electrons, potentials, and energies of dissociation, cohesion, vacancy formation, and electron attachment, as well as the ionization potential of solid Al N , Na N clusters (N ≥ 254), and clusters containing a vacancy (N ≥ 12) have been performed using a model of stable jellium. The contribution of a monovacancy to the energy of the cluster, the size dependences of the characteristics, and their asymptotic forms have been considered. The calculations have been performed on the SKIT-3 cluster at the Glushkov Institute of Cybernetics, National Academy of Sciences of Ukraine (Rpeak = 7.4 Tflops).

Anisotropic spin-density distribution and magnetic anisotropy of strained La1\u2212xSrxMnO3 thin films: angle-dependent x-ray magnetic circular dichroism

Magnetic anisotropies of ferromagnetic thin films are induced by epitaxial strain from the substrate via strain-induced anisotropy in the orbital magnetic moment and that in the spatial distribution of spin-polarized electrons. However, the preferential orbital occupation in ferromagnetic metallic La1−xSrxMnO3 (LSMO) thin films studied by x-ray linear dichroism (XLD) has always been found out-of-plane for both tensile and compressive epitaxial strain and hence irrespective of the magnetic anisotropy. In order to resolve this mystery, we directly probed the preferential orbital occupation of spin-polarized electrons in LSMO thin films under strain by angle-dependent x-ray magnetic circular dichroism (XMCD). Anisotropy of the spin-density distribution was found to be in-plane for the tensile strain and out-of-plane for the compressive strain, consistent with the observed magnetic anisotropy. The ubiquitous out-of-plane preferential orbital occupation seen by XLD is attributed to the occupation of both spin-up and spin-down out-of-plane orbitals in the surface magnetic dead layer.

NiSx Quantum Dots Accelerate Electron Transfer in Cd0.8Zn0.2S Photocatalytic System via an rGO Nanosheet “Bridge” toward Visible-Light-Driven Hydrogen Evolution

Minimizing the charge transfer barrier to realize fast spatial separation of photoexcited electron–hole pairs is of crucial importance for strongly enhancing the photocatalytic H2 generation activity of photocatalysts. Herein, we propose an electron transfer strategy by reasonable design and fabrication of high-density NiSx quantum dots (QDs) as a highly efficient cocatalyst on the surface of Cd0.8Zn0.2S/rGO nanosheet composites. Under visible-light irradiation, the formation of a two-dimensional (2D) Cd0.8Zn0.2S/rGO nanohybrid system with 2 wt % NiSx loading gave a prominent apparent quantum efficiency (QE) of 20.88% (435 nm) and H2 evolution rate of 7.84 mmol g–1 h–1, which is 1.4 times higher than that of Pt/Cd0.8Zn0.2S/rGO. It is believe that the introduced rGO nanosheets and NiSx QDs obviously improved the interfacial conductivity and altered the spatial distribution of electrons in this nanoarchitecture. Thus, the synergistic effects of interfacial junctions result in a regulated electron transporta...

Spatial distribution of topological surface state electrons in Bi2Te3 probed by low-energy Na+ ion scattering

${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ is a topological insulator whose unique properties result from topological surface states in the band gap. The neutralization of scattered low-energy ${\mathrm{Na}}^{+}$, which is sensitive to dipoles that induce inhomogeneities in the local surface potential, is larger when scattered from Te than from Bi, indicating an upwards dipole at the Te sites and a downwards dipole above Bi. These dipoles are caused by the spatial distribution of the conductive electrons in the topological surface states. This result demonstrates how this alkali ion scattering method can be applied to provide direct experimental evidence of the spatial distribution of electrons in filled surface states.