Electron Momentum Transfer Research Articles

Modeling Electron Energy Loss and Momentum Transfer in a Swift Electron Interaction with Small Polyhedral Nanoparticles

Modeling Electron Energy Loss and Momentum Transfer in a Swift Electron Interaction with Small Polyhedral Nanoparticles

Time evolution of electron distributions to bimodal steady states for electrons dilutely dispersed in theinert gases Ar, Kr, and Xe with deep Ramsauer Townsend minima in themomentum transfer cross section

The current paper considers the thermalization of an ensemble of electrons under the influence of an external electric field and dilutely dispersed in one of the inert gas moderators, Argon, Krypton or Xenon for which the electron momentum transfer cross sections have deep Ramsauer-Townsend minima. As a consequence, the steady state electron distribution functions are bimodal over a small range of external electric field strengths. The current work is directed towards the time evolution of the electron distribution function determined from the numerical solution of the Fokker-Planck equation. The kinetic theory of electrons dilutely dispersed in a heat bath of atoms at temperature T b has a very long history. The solution of the Fokker-Planck equation can be expressed as a sum of exponentials of the form where λ n are the eigenvalues of the Fokker-Planck operator. Alternatively, a finite difference algorithm is used to solve the time dependent Fokker-Planck equation to give the time dependent electron energy distribution function. We demonstrate the evolution of the initial Maxwellian into a nonequilibrium bimodal distribution which cannot be rationalized with either the Gibbs-Boltzmann entropy or the Tsallis nonextensive entropy. Instead, the time dependent approach of an initial Maxwellian to the bimodal distribution is described in terms of the Kullback-Leibler entropy. We also demonstrate the inapplicability of the Boltzmann entropy nor the Tsallis entropy for a model system with a power law momentum transfer cross section of the form, σ(x) = σ 0/x p , where is the reduced speed. This model with p = 2 is also employed to demonstrate a steady-state Kappa distribution which features prominently in space physics and other fields. For p > 2, we show distribution functions that increase without bound analogous to runaway electrons. The steady nonequilibrium distributions are interpreted as solutions of a Pearson ordinary differential equation.

Boron structure evolution in magnetic Cr2O3 thin films

B substituting O in antiferromagnetic Cr2O3 is known to increase the Néel temperature, whereas the actual B dopant site and the corresponding functionality remains unclear due to the complicated local structure. Herein, A combination of electron energy loss spectroscopy and first-principles calculations were used to unveil B local structures in B doped Cr2O3 thin films. B was found to form either magnetic active BCr4 tetrahedra or various inactive BO3 triangles in the Cr2O3 lattice, with σ∗ and π∗ bonds exhibiting unique spectral features. Identification of BO3 triangles was achieved by changing the electron momentum transfer to manipulate the differential cross section for the 1s-π* and 1s-σ* transitions. Modeling the experimental spectra as a linear combination of simulated B K edges reproduces the experimental π* / σ* ratios for 15–42% of the B occupying the active BCr4 structure. This result is further supported by first-principles based thermodynamic calculations.

The underexposed effect of elastic electron collisions in dusty plasmas

Dusty plasmas comprise a complex mixture of neutrals, electrons, ions and dust grains, which are found throughout the universe and in many technologies. The complexity resides in the chemical and charging processes involving dust grains and plasma species, both of which impact the collective plasma behavior. For decades, the orbital-motion-limited theory is used to describe the plasma charging of dust grains, in which the electron current is considered collisionless. Here we show that the electron (momentum transfer) collision frequency exceeds the electron plasma frequency in a powder-forming plasma. This indicates that the electron current is no longer collisionless, and the orbital-motion-limited theory may need corrections to account for elastic electron collisions. This implication is especially relevant for higher gas pressure, lower plasma density, and larger dust grain size and density.

Spin-lattice angular momentum transfer of localized and valence electrons in the demagnetization transient state of gadolinium

The electron–phonon scattering is one of the main microscopic mechanisms responsible for the spin-flip in the transient state of ultrafast demagnetization. Here, we present an experimental determination of the temperature-dependent electron–phonon scattering rate in Gd. Using a static x-ray emission spectroscopy method, where the reduction of the decay peak intensities when increasing the temperature is quantified, we measure independently the electron-phonon scattering rate for the 5d and the 4f electrons. We deduce the temperature dependence of scattering for the 5d electrons, while no effect on the phonon population is observed for the 4f electrons. Our results suggest that the ultrafast magnetization dynamics in Gd is triggered by the spin-flip in the 5d electrons. We also evidence the existence of a temperature threshold, above which spin-flip scattering of the 5d electrons takes place. We deduce that during the transient state of ultrafast demagnetization, the exchange energy between 5d electrons has to be overcome before the microscopic electron-phonon scattering process can occur.

Using a post-version continuum distorted wave formalism for calculation of the fully differential cross section of helium atom single ionization by proton impact

In the present work, the fully differential cross section of single ionization of helium atom is calculated by fast proton impact. The calculations are done as a four-body formalism and by using a post-version continuum distorted wave theory with considering symmetric wave functions in the both initial and final channels. The ionization is considered from the ground and $$2^{1}S$$ excited states of helium atom. In order to investigate the role of the static electronic correlations, the calculations are performed by single-parameter Hylleraas and two-parameter Silverman as the ground state of helium atom wave functions. The results of the present theory are compared with the experiment in 1MeV proton impact energy and various values of the ejected electron energy and momentum transfer in the scattering and azimuthal planes. The results show that the present theory is able to predict the binary and recoil peaks as well as the experiment for ejected electron energies and momentum transfers are discussed in this manuscript.

Nondipole effects in laser-assisted electron scattering

Laser-assisted electron scattering is often described using the electric dipole approximation for the interaction between the electron and the assisting electromagnetic field. Within the dipole approximation, theory predicts a vanishing scattering cross section for processes involving exchange of photons in critical geometries, where the electron momentum transfer vector is perpendicular to the linear polarisation of the external field. In a nonrelativistic spin-free treatment, we consider modifications of the scattering cross section by nondipole contributions to the first order in 1/c in the interaction between the laser field and the electron using the nondipole strong-field-approximation Hamiltonian (Jensen et al 2020 Phys. Rev. A 101 043408). The approach allows for an analytical solution for the wave function of a free electron in the laser field with a nondipole contribution. This wave function leads to an analytical formula for the laser-assisted scattering cross section including nondipole effects. The nondipole corrections depend on the propagation direction of the field relative to the electron momentum transfer vector. The approach gives a finite cross section in scattering geometries, where the dipole approach predicts a vanishing cross section. The theory is illustrated by application to scattering geometries similar to those considered in experiments where large deviations between experimental data and predictions based on the dipole approximation have been reported. In these scattering geometries, the nondipole strong-field-approximation approach suggests an increase in the cross section by orders of magnitude compared to results obtained within the dipole approximation.

Pushing microscopic matter in plasma with an electron beam

Manipulation of microscopic structures is routinely carried out by exploiting the light pressure of a focused laser beam. Here we use a pulsed electron beam (EB) with energy 10–14 keV and peak current 4 mA instead of a photon flux and demonstrate transport of microscopic matter over a few centimeters. Hundreds of electrically charged microspheres in diameter immersed in a radio-frequency plasma are driven into a flow with a speed of a few mm s−1 when irradiated by the EB. It is shown that the force associated with the electron momentum transfer is consistent with the observed acceleration of the microparticles (MPs) in gas at low pressure. Numerical estimates show that the electron drag force does not depend on the MP charge. The interaction of the EB is described in terms of the electron penetration depth, deposited energy and heating of the MPs, as well as the effect of the beam on the discharge. This proof of principles study has implications in dusty plasmas and beyond, in instances when MPs interact with sufficiently intense electron fluxes, and shows the potential to use an EB as a tool for displacing MPs.

Self-Passivation of 2D Ruddlesden-Popper Perovskite by Polytypic Surface PbI2 Encapsulation.

Two-dimensional Ruddlesden-Popper (2D RP) halide perovskites, C2MAn-1PbnI3n+1 (C = bulky ammonium cation; MA = methylammonium) with low n-members (n < 5), have been garnering sensational attention for photovoltaic and optoelectronic applications because of the long carrier diffusion lengths, long-term stability, and tunable bandgap. Yet, the surface modification of 2D RP under kinetic particle irradiation, such as light or electron irradiation, is ambiguous, even though it is imperative to elucidate long-stabilized conversion efficiency. Herein, we present molecular-scale observations of dynamic surface reconstruction of BA2MA2Pb3I10 (n = 3) 2D RP induced by the electron beam. The surface dynamics reveal lateral growth of polytypic PbI2 with 3R, 4H, and 2H structures at the edge and surface of the 2D perovskite, accompanied by simultaneous annihilation at the other edges. Local radiolysis occurs dominantly by the internal energy increase of electron momentum transfer, which triggers a sequential layer-by-layer degradation into PbI2. In situ observation of the polytypic PbI2 growth at the whole surface and edges of 2D RP under electron irradiation elucidates how the outer PbI2 self-passivation can protect inner 2D RP, causing longer operando stability.

A kinetic study of electron heating and plasma dynamics in microwave microplasmas

Microwave microplasmas ignited in argon are studied using a one-dimensional particle-in-cell with Monte Carlo collision (PIC-MCC) approach. One-dimensional PIC-MCC simulations are performed at specified input power densities to determine the influence of the applied frequency (ranging from 1 to 320 GHz), pressure, and total deposited power on the plasma dynamics. The frequency response study performed at a fixed input power density shows the presence of off-axis peaks in the electron number density profile at intermediate frequencies. These peaks are attributed to the interplay between the production of hot electrons by the oscillating sheath and their inability to diffuse sufficiently at higher operating pressures, thereby resulting in enhanced ionization at off-axis locations. This is confirmed by the pressure dependence study which shows that the electron number density peaks at the mid-point when the microplasma is ignited at lower pressures. As the excitation frequency is increased further, the sheath oscillation heating decreases and eventually vanishes, thereby requiring the bulk plasma to couple power to the electrons which in turn leads to an increase in electron temperature in the plasma bulk and the electron number density peak appearing at the mid-point. When the power coupled to the microplasma is decreased, the sheath oscillation at a given frequency decreases, thereby leading to higher contribution from heating in the bulk plasma which leads to the disappearance of off-axis peaks even at intermediate frequencies. The microplasma dynamics at all conditions considered in this work demonstrate the interplay between the electron momentum transfer collision frequency, the angular excitation frequency, and the plasma frequency.

Athermal recrystallization behavior of (Sn) solid-solution at an intermetallic-free Cu/Sn interface induced by room temperature electromigration

The present study, for the first time, revealed the athermal recrystallization behavior at a heterogeneous metallic interface using room temperature electromigration. The athermal recrystallization occurred within the meta-stable amorphous Cu-Sn interphase, which was formed during the early stage electromigration, for stress relaxation after further electromigration. The nano-scale polycrystalline (Sn) interphase was favorably recrystallized at the intermetallic-free Cu/Sn interface where the current crowding effect occurred. Athermal electromigration force facilitated the nucleation of Sn nuclei through the kinetic energy provided by the electron momentum transfer. The formation of the recrystallized (Sn) interphase is believed to be an intermediate material interaction product prior to further intermetallic nucleation under room temperature electromigration.

On matching the anode ring with the magnetic field in an ATON-type Hall effect thruster

In an ATON-type Hall effect thruster, a ring-shaped anode and a cusped magnetic field intersect the match between the anode shape and the field topology thus must be clarified to optimize the electron transport to the anode and consequently the design of a high-efficiency thruster. By changing the match pattern with both the change in the length of the anode ring and the axial displacement of the cusp magnetic field, this study experimentally investigated the influence of the match pattern on the discharge characteristics of an ATON-type thruster—P100—under the condition of a moderate discharge voltage. The experimental results show that there is a match pattern that always optimizes the performance of the P100 thruster. At the rated operation parameters (300 V of discharge voltage and 5 mg/s of propellant mass flow rate) and the rated magnetic field strength, the observed improvements on thrust (∼79 mN to ∼85 mN) and anode efficiency (∼46% to ∼55%) are significant. Through further theoretical analysis, this study revealed that the change in the characteristics of electron momentum and energy transfer in the near-anode region, induced by the change of the match pattern, is the basic reason. The findings of this work are instructive for both understanding the electron motion in a cusp magnetic field and guiding the design of the anode ring intersecting with a cusp magnetic field in an ATON-type Hall effect thruster.

Probing the ionization wave packet and recollision dynamics with an elliptically polarized strong laser field in the nondipole regime

We explore ionization and rescattering in strong mid-infrared laser fields in the nondipole regime over the full range of polarization ellipticity. In three-dimensional photoelectron momentum distributions (3D PMDs) measured with velocity map imaging spectroscopy, we observe the appearance of a sharp ridge structure along the major polarization axis. Within a certain range of ellipticity, the electrons in this ridge are clearly separated from the two lobes that commonly appear in the PMD with elliptically polarized laser fields. In contrast to the well-known lobes of direct electrons, the sharp ridge is created by Coulomb focusing of the softly recolliding electrons. These ridge electrons are directly related to a counterintuitive shift of the PMD peak opposite to the laser beam propagation direction when the dipole approximation breaks down. The ellipticity-dependent 3D PMDs give access to different ionization and recollision dynamics with appropriate filters in the momentum space. For example, we can extract information about the spread of the initial wave packet and the Coulomb momentum transfer of the rescattering electrons.

Conduction electrons mediating the evolution from antiferromagnetic to ferromagnetic ordering inGd(Co1−yFey)2Zn20(0≤y≤1)

${\mathrm{GdFe}}_{2}{\mathrm{Zn}}_{20}$ is a complex cagelike compound with an unusually high ferromagnetic ordering temperature (${T}_{C}=86$ K) for a very diluted ${\mathrm{Gd}}^{3+}$ magnetic sublattice, embedded in a matrix that features strong electron-electron correlations. Here, we report on a magnetic and electronic study of the substitutional intermetallic system $\mathrm{Gd}{({\mathrm{Co}}_{1\ensuremath{-}y}{\mathrm{Fe}}_{y})}_{2}{\mathrm{Zn}}_{20}$ combining magnetization measurements plus first-principles density functional theory (DFT) calculations with temperature-dependent electron spin resonance (ESR). After accounting for electron-electron correlations and itinerant molecular field effects, the ESR results indicate that the exchange interaction between the ${\mathrm{Gd}}^{3+}$ is processed via a single band of $d$-type electrons at the Fermi level and the exchange interaction is covalent in nature $[J{(0)}_{fd}l0]$ with a strong conduction electron ($ce$) momentum transfer dependence $[{J}_{fd}(q)]$. The DFT calculations support this scenario by indicating a major contribution of $d$-type $ce$ at the Fermi level and a spin polarization in $(\text{Y},\mathrm{Gd}){\mathrm{Fe}}_{2}{\mathrm{Zn}}_{20}$ wherein the most stable configuration is antiferromagnetic between ${\mathrm{Gd}}^{3+}$ and $ce$ spins. Our results demonstrate that the standard Ruderman-Kittel-Kasuya-Yosida mechanism cannot explain the ferromagnetic behavior of ${\mathrm{GdFe}}_{2}{\mathrm{Zn}}_{20}$ and a superexchangelike mechanism is proposed for this magnetic interaction. An ``extended phase diagram'' for the double substitution sequence ${\mathrm{YCo}}_{2}{\mathrm{Zn}}_{20}\ensuremath{\rightarrow}{\mathrm{GdCo}}_{2}{\mathrm{Zn}}_{20}\ensuremath{\rightarrow}{\mathrm{GdFe}}_{2}{\mathrm{Zn}}_{20}$ is presented and discussed.

CF&lt;sub&gt;4&lt;/sub&gt;, CH&lt;sub&gt;4&lt;/sub&gt;, Ar 혼합기체의 전자 평균에너지

Energy Distribution Function in pure , and mixtures of and Ar, have been analyzed over a range of the reduced electric field strength between 0.1 and 350[Td] by the two-term approximation of the Boltzmann equation (BEq.) method and the Monte Carlo simulation (MCS). The calculations of electron swarm parameters require the knowledge of several collision cross-sections of electron beam. Thus, published momentum transfer, ionization, vibration, attachment, electronic excitation, and dissociation cross-sections of electrons for , and Ar, were used. The differences of the transport coefficients of electrons in , mixtures of and Ar, have been explained by the deduced energy distribution functions for electrons and the complete collision cross-sections for electrons. The results of the Boltzmann equation and the Monte Carlo simulation have been compared with the data presented by several workers. The deduced transport coefficients for electrons agree reasonably well with the experimental and simulation data obtained by Nakamura and Hayashi. The energy distribution function of electrons in -Ar mixtures shows the Maxwellian distribution for energy. That is, has the symmetrical shape whose axis of symmetry is a most probably energy.

Einstein–Bohr recoiling double-slit gedanken experiment performed at the molecular level

SynopsisDouble-slit experiments illustrate proof for wave–particle complementarity. The essence of Einstein–Bohr's debate about wave–particle duality was whether the momentum transfer between a particle and a recoiling slit could mark the path, thus destroying the interference. We realized this recoiling double-slit gedanken experiment by resonant X-ray photoemission from molecular oxygen for geometries near equilibrium (coupled slits) and in a dissociative state far away from equilibrium (decoupled slits). Interference is observed in the former case, while the electron momentum transfer quenches the interference in the latter case.

Einstein–Bohr recoiling double-slit gedanken experiment performed at the molecular level

Double-slit experiments illustrate the quintessential proof for wave–particle complementarity. If information is missing about which slit the particle has traversed, the particle, behaving as a wave, passes simultaneously through both slits. This wave-like behaviour and corresponding interference is absent if ‘which-slit’ information exists. The essence of Einstein–Bohr's debate about wave–particle duality was whether the momentum transfer between a particle and a recoiling slit could mark the path, thus destroying the interference. To measure the recoil of a slit, the slits should move independently. We showcase a materialization of this recoiling double-slit gedanken experiment by resonant X-ray photoemission from molecular oxygen for geometries near equilibrium (coupled slits) and in a dissociative state far away from equilibrium (decoupled slits). Interference is observed in the former case, while the electron momentum transfer quenches the interference in the latter case owing to Doppler labelling of the counter-propagating atomic slits, in full agreement with Bohr's complementarity. The authors observe electron interference using the Auger electron emitted from an O2 molecule ionized by a soft X-ray photon. The interference disappears when the location of the O+ can be determined from the final state observed.

CF4, CH4, Ar 혼합기체의 전리와 부착계수

Ionization and Attachment Coefficients in pure CH<SUB>4</SUB>, CF<SUB>4</SUB> and mixtures of CF<SUB>4</SUB> and Ar, have been analyzed over a range of the reduced electric field strength between 0.1 and 350[Td] by the two-term approximation of the Boltzmann equation (BEq.) method and the Monte Carlo simulation (MCS). The calculations of electron swarm parameters require the knowledge of several collision cross-sections of electron beam. Thus, published momentum transfer, ionization, vibration, attachment, electronic excitation, and dissociation cross-sections of electrons for CH<SUB>4</SUB>, CF<SUB>4</SUB> and Ar, were used. The results of the Boltzmann equation and the Monte Carlo simulation have been compared with the data presented by several workers. The deduced transport coefficients for electrons agree reasonably well with the experimental and simulation data obtained by Nakamura and Hayashi. The energy distribution function of electrons in CF<SUB>4</SUB>-Ar mixtures shows the Maxwellian distribution for energy. That is, f(ε) has the symmetrical shape whose axis of symmetry is a most probably energy. The proposed theoretical simulation techniques in this work will be useful to predict the fundamental process of charged particles and the breakdown properties of gas mixtures.BR

Free-electron lasers with magnetized ion-wiggler

Significant progress has been made using laser ionized channels to guide electron beams in the ion focus regime in a free-electron laser. Propagation of an electron beam in the ion focusing regime (IFR) allows the beam to propagate without expanding from space-charge repulsion. The ninth-degree polynomial dispersion relation for electromagnetic and space-charge waves is derived analytically by solving the electron momentum transfer and wave equations. The variation of resonant frequencies and peak growth rates with axial magnetic field strength has been demonstrated. Substantial enhancement in peak growth rate is obtained as the axial field frequency approaches the gyroresonance frequency.

Anisotropy of the Conductivity in the Asymmetric Quantum Wells

Gorbatsevich et al. and Kibis suggested that a number of interestinggalvano-magnetic efiects could be observed in quantum structures wherethe symmetry with respect to the space coordinates inversion and time--reversal are broken simultaneously. In the paper of Kibis for example, theinflnite triangular quantum well in an external magnetic fleld was consideredand the anisotropy of electron momentum transfer due to interaction with