Electron Scattering Research Articles

Inelastic Electron Scattering Form Factor of Isoscalar (T = 0) and Isovector (T = 1) Particle-hole States in 12C and 16O

Inelastic longitudinal and transverse electron scattering form factors of low-lying T = 0, T = 1 particle-hole states of 12C and 16O are studied in the framework of the Tamm–Dancoff approximation (TDA). The Hamiltonian with the Michigan-three-Yukawa (M3Y) potential is diagonalized. To obtain a good agreement with the experimental data, the ground state is corrected by including the admixture from higher orbits with regard for the core polarization effects.

Cu–S-based thermoelectric compounds with a sphalerite-derived disordered crystal structure

Low lattice thermal conductivity is observed in compounds having disordered atomic configurations in their crystal structures. At temperatures above 300 ​K, a Cu–S-based semiconducting compound, Cu3.1Nb0.25Sn0.9S4, with a sphalerite-derived disordered structure, exhibits thermal conductivity less than 1 ​W ​K−1 ​m−1. In this study, we synthesized and tested the thermoelectric properties of the hole-doped derivatives, Cu3.1Nb0.25−xTixSn0.9S4 (x ​= ​0, 0.125, 0.25) and Cu3.1Ti0.1875Sn0.9S4, up to 673 ​K. The hole-carrier doping decreased the electrical resistivity, improving the power factor. Cu3.1Ti0.25Sn0.9S4 shows a dimensionless figure of merit ZT of 0.1/0.6 ​at 300/673 ​K due to its inherent low lattice thermal conductivity and improved power factor. The thermoelectric properties of the Cu3.1Nb0.25Sn0.9S4-based compounds were compared with those of Cu3SbS4-based compounds with an ordered arrangement of Cu atoms in a similar sphalerite-derived structure, showing that the disordered atomic arrangement is responsible for the enhanced scatterings of both phonons and electrons.

Nucleon momentum gap in asymmetric nuclear matter

For more than half a century, nucleons were considered to move continuously in the nuclei. Recent electron-scattering experiments indicate about 20--25% of nucleons in heavier nuclei are involved in the neutron-proton short-range correlations. Nucleons in the nuclei thus have abnormal behavior unlike those in the noninteraction fermi gas. In the neutron-rich nuclei, around the Fermi momentum, the neutron-proton short-range correlations lead to a momentum gap in the proton momentum distribution, which is circumstantially supported by the pionic experimental data. Likewise, there should also be a neutron momentum gap in the proton-rich nuclei. Nucleon momentum gap is thought to have profound and extensive implications in the studies ranging from particle physics to neutron stars as well as ultracold atomic gases.

Finite-momentum excitons and the role of electron-phonon couplings in the electronic and phonon transport properties of boron arsenide.

The emerging semiconductor boron arsenide (BAs) with high thermal conductivity has attracted much attention recently, due to its promising application to overcome the bottleneck of high-density heat generated in power electronics and optoelectronic devices. In this work, based on first-principles calculations, we find that cubic BAs possesses high intrinsic electron/hole mobilities and the ionized impurity scattering plays a more important role in carrier scattering, compared with other scattering processes. The mobilities can be significantly enhanced by 14.9% and 76.2% for electrons and holes, respectively, by strain engineering. The investigation of the optoelectronic properties of indirect semiconductor cubic BAs by considering the many-body excitonic effects reveals that the contribution from finite-momentum excitons to optical properties is larger for photon energy ranging from 2.25 eV to 3.50 eV, compared with that from zero-momentum excitons. Finally, we observe that the phonon-electron couplings to total lattice thermal conductivities are non-trivial at low temperatures. These findings provide new insight into the transport and optoelectronic properties of cubic BAs, which are beneficial for the acceleration of the application of this revolutionary thermal management material.

Electron Scattering and Ionization of Astrophysical Molecules

Electron Scattering and Ionization of Astrophysical Molecules

Electronic Structure and Resonant Inelastic X-Ray Scattering in Gata4 Se8

Electronic Structure and Resonant Inelastic X-Ray Scattering in Gata4 Se8

Excellent response to near ultraviolet light and large intervalley scatterings of electrons in 2D SnS2.

Tin disulfide (SnS2) has attracted much attention as a novel two dimensional material due to its potential applications in electronics and optoelectronics. In this work, we investigated the optical properties of ultra-thin SnS2 film samples (∼8 nm) via spectroscopic ellipsometry, and found that SnS2 maintains a relatively high imaginary part of the dielectric constant (ε2) in the range of 256-377 nm indicating high optical response. The carrier transport properties of SnS2 were investigated considering full mode-resolved electron-phonon couplings, which reveal that the intervalley scatterings between degenerate valley (peaks) states via the fifth optical branch phonons play a dominant role in electron scattering, while ZA phonons dominate the hole scattering. The calculated electron mobility is ∼50 cm2 V-1 s-1 which is close to previously reported experimental results. By considering full el-ph interactions based on the rigid-band approximation, the maximum value of the thermoelectric figure of merit zT reaches 0.43 at 700 K. Our work not only reveals the promising applications of SnS2 in the fields of electronics and optoelectronics, but also showcases the computational framework for precise calculations of thermoelectric performances.

Electron Scattering of Mass-Inverted in Graphene Quantum Dots

Electron Scattering of Mass-Inverted in Graphene Quantum Dots

Revealing the Defect-Dominated Electron Scattering in Mg3Sb2-Based Thermoelectric Materials.

The thermoelectric parameters are essentially governed by electron and phonon transport. Since the carrier scattering mechanism plays a decisive role in electron transport, it is of great significance for the electrical properties of thermoelectric materials. As a typical example, the defect-dominated carrier scattering mechanism can significantly impact the room-temperature electron mobility of n-type Mg3Sb2-based materials. However, the origin of such a defect scattering mechanism is still controversial. Herein, the existence of the Mg vacancies and Mg interstitials has been identified by synchrotron powder X-ray diffraction. The relationship among the point defects, chemical compositions, and synthesis conditions in Mg3Sb2-based materials has been revealed. By further introducing the point defects without affecting the grain size via neutron irradiation, the thermally activated electrical conductivity can be reproduced. Our results demonstrate that the point defects scattering of electrons is important in the n-type Mg3Sb2-based materials.

Absolute Differential Cross-Sections for Elastic Electron Scattering from Sevoflurane Molecule in the Energy Range from 50-300 eV.

We report the results of the measurements and calculations of the absolute differential elastic electron scattering cross-sections (DCSs) from sevoflurane molecule (C4H3F7O). The experimental absolute DCSs for elastic electron scattering were obtained for the incident electron energies from 50 eV to 300 eV, and for scattering angles from 25° to 125° using a crossed electron/target beams setup and the relative flow technique for calibration to the absolute scale. For the calculations, we have used the IAM-SCAR+I method (independent atom model (IAM) applying the screened additivity rule (SCAR) with interference terms included (I)). The molecular cross-sections were obtained from the atomic data by using the SCAR procedure, incorporating interference term corrections, by summing all the relevant atomic amplitudes, including the phase coefficients. In this approach, we obtain the molecular differential scattering cross-section (DCS), which, integrated over the scattered electron angular range, gives the integral scattering cross-section (ICS). Calculated cross-sections agree very well with experimental results, in the whole energy and angular range.

Combined Light and Electron Scattering for Exploring Proximity Effects on Hydrogen Absorption in Vanadium

We investigate proximity effects on hydrogen absorption in ultra-thin vanadium layers through combing light transmission and electron scattering. We compare the thermodynamic properties of the vanadium layers, which are based on the superlattice structure of Cr/V (001) and Fe/V (001). We find an influence of the proximity effects on the finite-size scaling of the critical temperatures, which can be explained by a variation of dead layers in the vanadium. In addition to this, the proximity effects on hydrogen absorption are also verified from the changes of excess resistivity.

Electron Scattering Cross-Section Calculations for Atomic and Molecular Iodine

Cross sections for electron scattering from atomic and molecular iodine are calculated based on the R-matrix (close-coupling) method. Elastic and electronic excitation cross sections are presented for both I and I2. The dissociative electron attachment and vibrational excitation cross sections of the iodine molecule are obtained using the local complex potential approximation. Ionization cross sections are also computed for I2 using the BEB model.

Superconducting Properties and Electron Scattering Mechanisms in a Nb Film with a Single Weak-Link Excavated by Focused Ion Beam.

Granularity is one of the main features restricting the maximum current which a superconductor can carry without losses, persisting as an important research topic when applications are concerned. To directly observe its effects on a typical thin superconducting specimen, we have modeled the simplest possible granular system by fabricating a single artificial weak-link in the center of a high-quality Nb film using the focused ion beam technique. Then, its microstructural, magnetic, and electric properties in both normal and superconducting states were studied. AC susceptibility, DC magnetization, and magneto-transport measurements reveal well-known granularity signatures and how they negatively affect superconductivity. Moreover, we also investigate the normal state electron scattering mechanisms in the Boltzmann theory framework. The results clearly demonstrate the effect of the milling technique, giving rise to an additional quadratic-in-temperature contribution to the usual cubic-in-temperature sd band scattering for the Nb film. Finally, by analyzing samples with varying density of incorporated defects, the emergence of the additional contribution is correlated to a decrease in their critical temperature, in agreement with recent theoretical results.

Total Cross Sections for Electron and Positron Scattering on Molecules: In Search of the Dispersion Relation

More than one hundred years of experimental and theoretical investigations of electron scattering in gases delivered cross-sections in a wide energy range, from few meV to keV. An analogy in optics, characterizing different materials, comes under the name of the dispersion relation, i.e., of the dependence of the refraction index on the light wavelength. The dispersion relation for electron (and positron) scattering was hypothesized in the 1970s, but without clear results. Here, we review experimental, theoretical, and semi-empirical cross-sections for N2, CO2, CH4, and CF4 in search of any hint for such a relation—unfortunately, without satisfactory conclusions.

Ab initio ultrafast spin dynamics in solids

Spin relaxation and decoherence is at the heart of spintronics and spin-based quantum information science. Currently, theoretical approaches that can accurately predict spin relaxation of general solids including necessary scattering pathways and capable for ns to ms simulation time are urgently needed. We present a first-principles real-time density-matrix approach based on Lindblad dynamics to simulate ultrafast spin dynamics for general solid-state systems. Through the complete first-principles descriptions of pump, probe and scattering processes including electron-phonon, electron-impurity and electron-electron scatterings with self-consistent electronic spin-orbit couplings, our method can directly simulate the ultrafast pump-probe measurements for coupled spin and electron dynamics over ns at any temperatures and doping levels. We first apply this method to a prototypical system GaAs and obtain excellent agreement with experiments. We find that the relative contributions of different scattering mechanisms and phonon modes differ considerably between spin and carrier relaxation processes. In sharp contrast to previous work based on model Hamiltonians, we point out that the electron-electron scattering is negligible at room temperature but becomes dominant at low temperatures for spin relaxation in n-type GaAs. We further examine ultrafast dynamics in novel spin-valleytronic materials - monolayer and bilayer WSe2 with realistic defects. We find that spin relaxation is highly sensitive to local symmetry and chemical bonds around defects. Our work provides a predictive computational platform for spin dynamics in solids, which has unprecedented potentials for designing new materials ideal for spintronics and quantum information technology.

Origin and structure of electromagnetic generator regions at the edge of the electron diffusion region

During the process of magnetic reconnection, converging magnetic fields transfer some of the stored magnetic energy into plasma energy. Simulations and spacecraft data suggest that at the edges of the electron diffusion region, “generators” can form where the local electromagnetic field gains energy from the plasma. We use a 2D Particle-in-cell (PIC) simulation and Magnetospheric Multiscale (MMS) spacecraft data to investigate the electron dynamics and energy budget of these generators. PIC simulation results suggest that these generators form where the electron population begins to remagnetize, while still not being fully frozen in to the magnetic fields. Super-Alfvénic electrons locally lose bulk kinetic energy to Hall electric fields along the outflow axis and to the out-of-plane reconnection electric field as they become remagnetized. These “partial” remagnetization regions also exhibit signatures of irreversible dissipation in MMS data, such as electron enthalpy flux and enhanced electron thermal energy density as remagnetized electrons scatter away from the neutral line within the Hall field structures of the exhaust.

Effects of Inelastic Electron Scattering on Supersmooth Sapphire Surface with Au and Pt Nanolayers

Effects of Inelastic Electron Scattering on Supersmooth Sapphire Surface with Au and Pt Nanolayers

Emergent channel over a pair of pockets in strong density waves

Different channels over which electrons scatter between parts of the Fermi surface are the key to various electronic quantum matters, such as superconductivity and density waves. We consider an effective model in higher dimensions where each of the two pockets in the original model maps to (the Landau levels of) two Dirac fermions. We discover an emergent channel when two Dirac fermions from different pairs annihilate, where the presence of a strong density wave is essential. We support our analysis with numerical calculations on model examples in the vicinity of ferromagnetic and antiferromagnetic orders. We also discuss interesting consequences on electron interaction channels that beyond-mean-field fluctuations may induce.

Elastic Scattering of Slow Electrons by Noble Gases—The Effective Range Theory and the Rigid Sphere Model

We report on an extensive semi-empirical analysis of scattering cross-sections for electron elastic collision with noble gases via the Markov Chain Monte Carlo-Modified Effective Range Theory (MCMC−MERT). In this approach, the contribution of the long-range polarization potential (∼r−4) to the scattering phase shifts is precisely expressed, while the effect of the complex short-range interaction is modeled by simple quadratic expression (the so-called effective range expansion with several adjustable parameters). Additionally, we test a simple potential model of a rigid sphere combined with r−4 interaction. Both models, the MERT and the rigid sphere are based on the analytical properties of Mathieu functions, i.e., the solutions of radial Schrödinger equation with pure polarization potential. However, in contrast to MERT, the rigid sphere model depends entirely upon one adjustable parameter—the radius of a hard-core. The model’s validity is assessed by a comparative study against numerous experimental cross-sections and theoretical phase shifts. We show that this simple approach can successfully describe the electron elastic collisions with helium and neon for energies below 1 eV. The purpose of the present analysis is to give insight into the relations between the parameters of both models (that translate into the cross-sections in the very low energy range) and some “macroscopic” features of atoms such as the polarizability and atomic “radii”.

Numerical solver for the out-of-equilibrium time dependent Boltzmann collision operator: Application to 2D materials

The Time Dependent Boltzmann equation (TDBE) is a very efficient description of a vast variety of strongly out-of-equilibrium dynamics which are becoming increasingly critical for many novel physical applications. However its applicability is greatly limited by the impractical scaling of the numerical cost with precision of its scattering integral, if addressed without any simplifying approximations (like closedness to equilibrium). In our previous works [1,2] we had proposed a numerical solver to calculate the scattering integral term in the TDBE and then improved on it [3] to include second degree momentum discretisation and adaptive time stepping. Our solver requires no close-to-equilibrium assumptions and can work with realistic band structures and scattering amplitudes. Moreover, it is numerically efficient and extremely robust against inherent numerical instabilities. While in our previous work [3] we showcased the application of our solver to 1D materials, here we showcase its applications to a simple 2D system. We show that in spite of an important increase in complexity of the scattering integrals, the 1D approach can be applied to higher dimensions. We then analyse thermalisation of a set of out-of-equilibrium initial conditions. The excitations added at higher energies were found to thermalise faster than those introduced at relatively lower energies. Also, we conclude that the thermalisation of strong out-of-equilibrium population to equilibrium values is not a simple exponential decay but rather a non-trivial function of time. Nonetheless, by fitting a double exponential function to the decay of the out-of-equilibrium population with time we were able to generate quantitative insights into the time scales involved in the thermalisations. Program summaryProgram Title: OneBandScattering-nonPerturbativeCPC Library link to program files:https://doi.org/10.17632/82bwxs5ds7.1Developer's repository link:https://github.com/MarcoBattiato/OneBandScattering-nonPerturbativeLicensing provisions: GPLv3Programming language: MATLABNature of problem: Numerical solver for the time dependent far-from-equilibrium Boltzmann scattering equation in 2D.Solution method: Ad hoc technique developed in [1,2] and here.Additional comments including restrictions and unusual features: Although extension to include a generic number of scattering legs, multiple band and multiple types of quasiparticles is straightforward, this version of the code is built for a single band electron-electron scatterings.