Electron Scattering Research Articles

Rydberg electron-atom scattering in forbidden regions of negative kinetic energy

Scattering of a Rydberg electron by ground-state atoms (scatterers) located in its classically forbidden region can be viewed as electron-atom scattering with negative incident energy. We propose a treatment of this unusual case of scattering in the context of long-range molecular potentials arising from the interaction of a Rydberg electron with ground state atoms. We describe a treatment leading to proper equivalents of scattering lengths and phase shifts for negative incident energies, which becomes advantageous when a Rydberg atom is penetrated by more than one scatterer and the Rydberg electron scatters back and forth between the atoms in the classically allowed and forbidden regions. We apply this approach to Cs and Rb samples, and find evidence for a resonance-like feature for their 3S1 states.

Elastic Magnetic Electron Scattering from odd-A Nuclei

Magnetic form factors from odd-A spherical and deformed nuclei corresponding to elastic electron scattering are calculated in the plane-wave Born approximation. The nuclear structure of the target is described within a deformed self-consistent mean-field calculation with effective interactions of Skyrme type and pairing correlations in the BCS approximation. We focus our attention to stable nuclei where experimental information is available. It is shown that the deformed formalism improves the agreement with experiment in deformed nuclei, while reproducing equally well spherical nuclei by taking properly the spherical limit of the deformed model. Effects of the collective rotation and nucleon-nucleon correlations are also studied. These results demonstrate the ability of the method to address electron scattering from unstable nuclei to be measured in future experiments on electron-ion beam colliders.

Investigation of Nanometer- and Submicron-Size Dispersed Phases in Titanium Pseudo- β -Alloys using Scattering and Diffraction of Neutrons, Electrons, and X-Ray Radiation

The size and volume fraction of fine particles of secondary β -phase formed during hardening heat treatment of pseudo-β-titanium alloy VT22 are determined using low-angle scattering of neutrons, x-ray diffractometry, electron back-scatter diffraction, and transmission microscopy combined with x-ray spectral microanalysis. Based on comprehensive use of experimental data obtained by methods of different restriction levels analysis is conducted for the size, shape, elemental composition, and volume content of fine particles obtained after different versions of hardening heat treatment. Activation of β -phase decomposition energy due to low-temperature aging is determined.

On the Inoculation and Phase Formation of Zr<sub>47.5</sub>Cu<sub>45.5</sub>Al<sub>5</sub>Co<sub>2</sub> and Zr<sub>65</sub>Cu<sub>15</sub>Al<sub>10</sub>Ni<sub>10</sub> Bulk Metallic Glass Matrix Composites

Bulk metallic glass matrix composites have emerged as new potential material for structural engineering applications owing to their superior strength, hardness and high elastic strain limit. However, their behaviour is dubious. They manifest brittleness and inferior ductility which limit their applications. Various methods have been proposed to overcome this problem. Out of these, introduction of foreign particles (inoculants) during solidification have been proposed as most effective. In this study, an effort has been made to delimit this drawback. A systematic tale has been presented which explain the evolution of microstructure in Zr47.5Cu45.5Al5Co2 and Zr65Cu15Al10Ni10 bulk metallic glass matrix composites with varying percentage of ZrC inoculant as analysed by secondary electron and back scatter electron imaging of as cast unetched samples. A support is provided to hypothesis that inoculation remain successful in promoting phase formation and crystallinity and improve toughness.

Low-Energy Electron Scattering from Dimethyl Ether.

Low-energy (0.1 to 15 eV) R-matrix calculation is performed for dimethyl ether molecule. Electronic excitation and momentum transfer cross section for low energies are reported for the first time. Present differential cross sections show good agreement with previous data in terms of shape but are significantly higher in magnitude. Apart from low energies, we have also performed high-energy calculation (11-5000 eV) using spherical complex optical potential formalism. To deal with the molecular nature of the present target, we have applied an effective potential method in our computation for the first time. Good consistency can be seen at the overlapping energies of the two calculations.

Modified Drude model for small gold nanoparticles surface plasmon resonance based on the role of classical confinement

In this paper, we study the effect of restoration force caused by the limited size of a small metallic nanoparticle (MNP) on its linear response to the electric field of incident light. In a semi-classical phenomenological Drude-like model for small MNP, we consider restoration force caused by the displacement of conduction electrons with respect to the ionic positive background taking into account a free coefficient as a function of diameter of nanoparticle (NP) in the force term obtained by the idealistic Thomson model in order to adjust the classical approach. All important mechanisms of the energy dissipation such as electron-electron, electron-phonon and electron-NP surface scatterings and radiation are included in the model. In addition a correction term added to the damping factor of mentioned mechanisms in order to rectify the deficiencies of theoretical approaches. For determining the free parameters of model, the experimental data of extinction cross section of gold NPs with different sizes doped in the glass host medium are used and a good agreement between experimental data and results of our model is observed. It is shown that by decreasing the diameter of NP, the restoration force becomes larger and classical confinement effect becomes more dominant in the interaction. According to experimental data, the best fitted parameter for the coefficient of restoration force is a third order negative powers function of diameter. The fitted function for the correction damping factor is proportional to the inverse squared wavelength and third order power series of NP diameter. Based on the model parameters, the real and imaginary parts of permittivity for different sizes of gold NPs are presented and it is seen that the imaginary part is more sensitive to the diameter variations. Increase in the NP diameter causes increase in the real part of permittivity (which is negative) and decrease in the imaginary part.

Stationary-state Electron Scattering Using a Complex Injecting Potential

We simulated stationary electron scattering by solving the time-dependent Schrodinger equation with a complex injecting potential (CIP). The calculated electron transmission probabilities through o...

Scattering of Dirac electrons from a skyrmion: Emergence of robust skew scattering

We study electron scattering from a closed magnetic structure embedded in the top surface of a topological insulator (TI). Outside the structure there is a uniform layer of ferromagnetic insulator (FMI), leading to a positive effective mass for the Dirac electrons. The mass inside can be engineered to be negative, leading to a skyrmion structure. The geometric shape of the structure can be circular or deformed, leading to integrable or chaotic dynamics, respectively, in the classical limit. For a circular structure, the relativistic quantum scattering characteristics can be calculated analytically. For a deformed structure, we develop an efficient numerical method, the multiple multipole method, to solve the scattering wavefunctions. We find that anomalous Hall effect as characterized by strong skew scattering can arise, which is robust against structural deformation due to the resonant modes. In the short (long) wavelength regime, the resonant modes manifest themselves as confined vortices (excited edge states). The origin of the resonant states is the spin phase factor of massive Dirac electrons at the skyrmion boundary. Further, in the short wavelength regime, for a circular skyrmion, a large number of angular momentum channels contribute to the resonant modes. In this regime, in principle, classical dynamics are relevant, but we find that geometric deformations, even those as severe as leading to fully developed chaos, have little effect on the resonant modes. The vortex structure of the resonant states makes it possible to electrically ``charge'' the skyrmion, rendering feasible to manipulate its motion electrically. In the long wavelength regime, only the lowest angular momentum channels contribute to the resonant modes, making the skew scattering sharply directional. These phenomena may find applications for information storage and in Hall devices based on dynamic skyrmion.

Combined Scattering of Radiation Belt Electrons by Low‐Frequency Hiss: Cyclotron, Landau, and Bounce Resonances

AbstractLow‐frequency hiss is known to play an important role in the precipitation of radiation belt electrons by cyclotron, Landau, and bounce resonances. To investigate the potential combined scattering effect caused by these resonant processes, we analyze the resonant conditions and develop a full relativistic test particle code to quantify the net pitch angle scattering efficiency. It is indicated that the three resonance processes can coexist to scatter electrons at different energies and pitch angles, with the net pitch angle scattering rates up to ~10−3 s−1 for low‐frequency hiss ~175 pT at L = 4.5. Comparisons with the quasi‐linear theory results demonstrate that the cyclotron resonance is mainly responsible for the pitch angle scattering of electrons < ~ 80°, while both Landau and bounce resonances can affect the scattering of near‐equatorially mirroring electrons and their combined diffusion produces smaller scattering coefficients compared to quasi‐linear theory calculations.

Direct Evidence of the Pitch Angle Scattering of Relativistic Electrons Induced by EMIC Waves

AbstractIn this study, we analyze an electromagnetic ion cyclotron (EMIC) wave event of rising tone elements recorded by the Van Allen Probes. The pitch angle distributions of relativistic electrons exhibit a direct response to the two elements of EMIC waves: at the intermediate pitch angle, the fluxes are lower; and at the low pitch angle, the fluxes are higher than those when no EMIC was observed. In particular, the observed changes in the pitch angle distributions are most likely to be caused by nonlinear wave‐particle interaction. The calculation of the minimum resonant energy and a test‐particle simulation based on the observed EMIC waves support the role of the nonlinear wave‐particle interaction in the pitch angle scattering. This study provides direct evidence for the nonlinear pitch angle scattering of electrons by EMIC waves.

Effect of Environment on the Scattering of Electrons by a Junction of Different Topological Materials

AbstractThe studies of electron transport through a junction of topological materials in the literature so far ignore the coupling of a topological material to its surrounding environment. Here, the dynamics of an open system through a stochastic Hamiltonian are simulated to investigate the influence of the environment on the scattering of electrons by a junction of different topological materials, such as a Dirac–Weyl magnetic junction and a topological insulator. It is found that, although the detrimental effect of the environment is inevitable, the Landauer conductance can be enhanced via adjusting the system–environment coupling strength. This result supplies the possibilty of changing the transport feature of topological materials by modulating the surrounded environment. It is also demonstrated that a non‐Hermitian Hamiltonian can be used to replace the stochastic Hamiltonian for this study, when the system and the environment coupling are weak.

Experimental methods in chemical engineering: Transmission electron microscopy—TEM

AbstractThanks to an accelerating voltage in the range of 30 to 300 kV, an electron beam can pass through a thin specimen and form an image with sub‐Ångström spatial resolution. When impinging on a thin crystalline specimen, the fast electrons scatter and diffract. The transmitted electron pattern depends on the local thickness, density, crystal structure, and chemical nature of the sample. The transmission electron microscope (TEM) shapes the incoming electron beam using magnetic lenses onto the specimen and, using a different set of magnetic lenses, focuses the projected electron pattern to a camera. The final image magnification and contrast are controlled using the parameters from the electron gun, apertures positioned along the optical path, and magnetic lenses. With this combination of lens and aperture, TEM offers two possible modes of operation: (a) imaging, including high‐resolution electron microscopy to reveal the size, shape, crystallinity, and morphology of materials; and (b) diffraction, to determine the crystalline nature of a region of interest of a thin film, particle, or collection of particles. Chemical engineers have taken advantage of both of these modes to analyze their samples and inform their research. A bibliometric study conducted using the WoS database places TEM as one of the preferred microscopy tools to study advanced materials such as thin films, nanomaterials, and composites used in particular for the development of applications related to energy storage and conversion (catalysis, photocatalysis, electrochemistry, and batteries) and environment (adsorption, waste‐water treatment, and filtration).

Electron Scattering in Conventional Cell Flask Experiments and Dose Distribution Dependency

Electron beam therapy (EBT) is commonly used for treating superficial and subdermal tumors. Previous cellular radiosensitivity research using EBT may be underestimating the contribution from flask wall scattering and the corresponding dose distribution. Single cell suspensions of Chinese hamster ovary (CHO) cells were plated on flasks and irradiated with 3, 4, 7, 9, and 18 MeV energy electron beams from two different institutions, and the spatial locations of surviving colonies were recorded. Gafchromic film dosimetry and Monte Carlo simulations were carried out to determine the spatial electron scattering contribution from the flask walls. Low electron irradiation resulted in an uneven surviving colony distribution concentrated near the periphery of the flasks, while spatial colony formation was statistically uniform at energies above 7 MeV. Our data demonstrates that without proper dosimetric corrections, studies using low energy electrons can lead to misinterpretations of energy dependent cellular radiosensitivity in culture vessels, and radiotherapeutic applications.

Alternative Approach for the Determination of Mean Free Paths of Electron Scattering in Liquid Water Based on Experimental Data.

Mean free paths of low-energy electrons in liquid water are of importance for modeling many physicochemical processes, but neither theoretical predictions nor experimental results have converged for these parameters. We therefore introduce an approach to determine elastic and inelastic mean free paths (EMFP, IMFP) based on experimental data. We show that ab initio calculations of electron scattering with water clusters converge with cluster size, thus providing access to condensed-phase scattering. The results are used in Monte Carlo simulations to extract EMFP and IMFP from recent liquid-microjet experiments that determined the effective attenuation length (EAL) and the photoelectron angular distribution (PAD) following oxygen 1s-ionization of liquid water. For electron kinetic energies from 10 to 300 eV, we find that the IMFP is noticeably larger than the EAL. The EMFP is longer than that of gas-phase water and the IMFP is longer compared to latest theoretical estimations, but both EMFP and IMFP are much shorter than suggested by experimental measurements of integral cross sections for amorphous ice.

Elastic Scattering of Electrons by Helium Atoms in Born Approximation

Elastic scattering phenomena arising in electron-helium scattering are dominant processes. The determination of accurate elastic differential cross sections for electron-helium scattering has a considerable importance. An accurate calculation of the plane-wave first Born exchange amplitude of electrons elastic scattering by helium atoms is reported. The direct and exchange amplitudes are calculated analytically from the Hartree-Fock orbital wave functions by using a variational method. The forms of these wave functions are very suitable for analytical calculations and powerful to generalize to more complex atomic systems. The interaction potential is modelled by the static Coulomb interaction between the incident electron and the atomic system. The differential cross sections are calculated at intermediate energies taking into account the exchange effects. We have established in the high energies region, by neglecting the exchange effects, the analytical expressions of the total and momentum transport cross sections suitable for the calculation of the plasma transport properties. A very compact form of the Born amplitude has been proposed as a finite series of Gaussian functions, which represents a major tool in the calculations of differential cross sections of two-electron atomic systems. Numerical results are used to analyze the contribution of the exchange amplitude to the differential cross sections at intermediate and high energies. The differential cross sections are calculated for the energy range 30-400 eV. We find good agreement in high energy domain scattering with experimental results and other sophisticated calculations without using any adjustable parameter.

Scattering of Energetic Electrons by Heat-flux-driven Whistlers in Flares

Abstract The scattering of electrons by heat-flux-driven whistler waves is explored with a particle-in-cell simulation relevant to the transport of energetic electrons in flares. This simulation is initiated with a large heat flux produced by using a kappa distribution of electrons with positive velocity and a cold return current beam. This system represents energetic electrons escaping from a reconnection-driven energy-release site. This heat-flux system drives large-amplitude oblique whistler waves propagating both along and against the heat flux, as well as electron acoustic waves. While the waves are dominantly driven by the low-energy electrons, including the cold return current beam, the energetic electrons resonate with and are scattered by the whistlers on timescales of the order of a hundred electron cyclotron times. Peak whistler amplitudes of and angles of ∼60° with respect to the background magnetic field are observed. Electron perpendicular energy is increased, while the field-aligned electron heat flux is suppressed. The resulting scattering mean-free-paths of energetic electrons are small compared with the typical scale size of energy-release sites in flares, which might lead to the effective confinement of energetic electrons required for the production of very energetic particles.

Scattering of Electrons from (Curium, Europium and Ytterbium) Atoms at Energy range (10 - 10000) eV

This study covers the calculation of the differential cross sections (DCS’s), total cross sections(TCS’s), momentum transfer cross sections (MTCS’s) and spin polarization parameters S(Ɵ),T(Ɵ),U(Ɵ) for electron scattered by [Curium (Cm) ,Europium(Eu) and Ytterbium(Yb)] atoms. The aim of such calculations is to represent the interaction between electron and target atoms in the range (10- 10000) eV by using optical potential. The theoretical method was conducted based on the combination of the static potential with the polarization potential at long distances and the correlation potential of Perdew - Zunger at short distances. Overall, the results show a close agreement when compared to the experimental and theoretical findings that reported by the others.

Composite super-moiré lattices in double-aligned graphene heterostructures.

When two-dimensional (2D) atomic crystals are brought into close proximity to form a van der Waals heterostructure, neighbouring crystals may influence each other's properties. Of particular interest is when the two crystals closely match and a moiré pattern forms, resulting in modified electronic and excitonic spectra, crystal reconstruction, and more. Thus, moiré patterns are a viable tool for controlling the properties of 2D materials. However, the difference in periodicity of the two crystals limits the reconstruction and, thus, is a barrier to the low-energy regime. Here, we present a route to spectrum reconstruction at all energies. By using graphene which is aligned to two hexagonal boron nitride layers, one can make electrons scatter in the differential moiré pattern which results in spectral changes at arbitrarily low energies. Further, we demonstrate that the strength of this potential relies crucially on the atomic reconstruction of graphene within the differential moiré super cell.

Emergence of electron-phonon coupling in a dual topological insulator BiTe

A versatile van der Waals epitaxy of BiTe, a newly discovered dual TI and a predicted higher order topological insulator (HOTI) thin film on muscovite mica is demonstrated using pulsed laser deposition. Topographic, structural and XPS analyses confirm the chemical homogeneity and high crystalline quality with large-area coverage with atomically smooth surface. The magneto transport data reveals weak anti-localization and electron-electron interaction driven insulating ground state with n-type character. An elaborate thickness, temperature and magnetic field dependence of transport data indicates a transition from coupled, partially coupled and fully decoupled surface states wherein 3D electron-electron and electron-phonon scatterings play significant role in dephasing mechanism, unlike 2D electron-electron dephasing in most TIs. Also from the fitting of the resistivity upturn we found that the coulomb screening factor (F) in thicker samples turns out to be negative which indicates the presence of the electron phonon coupling in those samples.

Study of Charge Density Distributions and Elastic Electron Scattering Cross Sections for some Stable Nuclei

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