Electron Scattering Research Articles

Electron Scattering from Some Fp- Shell Nuclei with Inclusion the Effect of Short-Range Correlation

The effects of short-range correlation on elastic Coulomb (charge) form factors, charge density distributions as well as root mean square charge radii of various nuclei (for instance, 46, 48, 50Ti, 52, 54Cr, 56, 58Fe, and 72, 74, 76Ge nuclei) are examined. The one- and two body terms of the cluster expansion together with the single-particle harmonic oscillator wave functions are utilized. For the purpose of embedding these effects into the formulae of charge density and form factor we employ the correlation function of Jastrow-type. These formulae depend upon the short-range correlation parameter (which instigates from the Jastrow function) and the oscillator size parameter Both and are found by the fitting to the measured elastic form factors. It is noticed that the embedding of short-range correlation effects into the calculations of and is a requisite for the achievement of a vital change in the computed results and remarkably vital for the characterization of the measured data.

Transport properties of warm dense neon and krypton at high pressures.

The transport properties of warm dense neon (Ne) and krypton (Kr) are studied by combining self-consistent fluid variational theory (SFVT) with linear response theory (LRT). The components are determined using the SFVT, and the transport parameters, including the electrical conductivity, thermal conductivity, and thermopower, are calculated with the LRT. The relevant scattering mechanisms, including electron-ion, electron-electron, and electron-atom scatterings, are taken into account. An effective potential model in combination with the Muffin-tin model is introduced to further improve the description for electron-atom scattering, which not only includes static, exchange, and polarization interactions but also considers the plasma environmental effects. It is found that for electron-atom scattering, the influence of the plasma density is significant at lower scattering energies but the effects are different for electron-Ne and electron-Kr scattering. For electron-Kr scattering, a plasma density-dependent Ramsauer-Townsend minimum is observed. The obtained transport parameters are compared with the available experiments and other simulations. The plasma phase transition of warm dense Kr is revisited from multiple perspectives based on the numerical simulation results for the electrical conductivity and thermopower. These observations may help one to better understand the transport properties of warm dense noble gases and are an important guide for future experimental designs and theoretical developments.

Shape Resonances and Elastic Cross Sections in Electron Scattering by CF3Br and CF3I.

Trifluoroiodomethane (CF3I) is one of the most appealing candidates for applications in plasma-based technologies in view of its many interesting advantages when compared to more standard gases such as trifluorobromomethane (CF3Br). Low-energy electrons are prone to decomposing these molecules into reactive species, and knowledge on the collision cross sections is fundamental for modeling transport and reactivity in plasma environments. Despite many studies on electron collisions with the abovementioned molecules, there are conflicting results on the assignment of shape resonances and on the magnitudes of total cross sections. Here, we try to clarify these aspects by performing ab initio electron scattering calculations. We found integral cross sections in fair agreement with the most recent measurements, in contrast to previous reports. For each molecule, we found a σCX* resonance (antibonding between the carbon and the heavy halogen) at 1 eV in CF3Br and at ∼0 eV in CF3I. Furthermore, there are three shape resonances of σCF* character; two are degenerate and account for a broad feature around 6 eV and the other one appears around 9.5 eV. We also discuss the possible role of the degenerate resonance in dissociative electron attachment reactions, as well as the impact of the heavy halogen on the cross sections and on the shape resonances.

Electron and Hole Scattering by Deep Impurities in Semiconductor Heterostructures with Quantum Wells

Electron and Hole Scattering by Deep Impurities in Semiconductor Heterostructures with Quantum Wells

A Complete Cross Section Data Set for Electron Scattering by Pyridine: Modelling Electron Transport in the Energy Range 0–100 eV

Electron scattering cross sections for pyridine in the energy range 0–100 eV, which we previously measured or calculated, have been critically compiled and complemented here with new measurements of electron energy loss spectra and double differential ionization cross sections. Experimental techniques employed in this study include a linear transmission apparatus and a reaction microscope system. To fulfill the transport model requirements, theoretical data have been recalculated within our independent atom model with screening corrected additivity rule and interference effects (IAM-SCAR) method for energies above 10 eV. In addition, results from the R-matrix and Schwinger multichannel with pseudopotential methods, for energies below 15 eV and 20 eV, respectively, are presented here. The reliability of this complete data set has been evaluated by comparing the simulated energy distribution of electrons transmitted through pyridine, with that observed in an electron-gas transmission experiment under magnetic confinement conditions. In addition, our representation of the angular distribution of the inelastically scattered electrons is discussed on the basis of the present double differential cross section experimental results.

Thermodynamics and Screening in the Ising–Kondo Model

A simplification of the symmetric single‐impurity Kondo model is introduced and studied. In the Ising–Kondo model, host electrons scatter off a single magnetic impurity at the origin whose spin orientation is dynamically conserved. This reduces the problem to potential scattering of spinless fermions that can be solved exactly using the equation‐of‐motion technique. The Ising–Kondo model provides an example for static screening. At low temperatures, the thermodynamics at finite magnetic fields resembles that of a free spin‐1/2 in a reduced external field. Alternatively, the Curie law is interpreted in terms of an antiferromagnetically screened effective spin. The spin correlations decay algebraically to zero in the ground state and display commensurate Friedel oscillations. In contrast to the symmetric Kondo model, the impurity spin is not completely screened, i.e., the screening cloud contains less than a spin‐1/2 electron. At finite temperatures and weak interactions, the spin correlations decay to zero exponentially with correlation length ξ(T) = 1/(2πT).

Resolving Electron-Electron Scattering in Plasmonic Nanorod Ensembles Using Two-Dimensional Electronic Spectroscopy.

The use of two-dimensional electronic spectroscopy (2DES) to study electron-electron scattering dynamics in plasmonic gold nanorods is described. The 2DES resolved the time-dependent plasmon homogeneous line width Γh(t), which was sensitive to changes in Fermi-level carrier densities. This approach was effective because electronic excitation accelerated plasmon dephasing, which broadened Γh. Analysis of Γh(t) indicated plasmon coherence times were decreased by 20-50%, depending on excitation conditions. Electron-electron scattering rates of approximately 0.01 fs-1 were obtained by fitting the time-dependent Γh broadening; rates increased quadratically with both excitation pulse energy and frequency. This rate dependence agreed with Fermi-liquid theory-based predictions. Hot electron thermalization through electron-phonon scattering resulted in Γh narrowing. To our knowledge, this is the first use of the plasmon Γh(t) to isolate electron-electron scattering dynamics in colloidal metal nanoparticles. These results illustrate the effectiveness of 2DES for studying hot electron dynamics of solution-phase plasmonic ensembles.

Effects of Polarization Reversal on the Pitch Angle Scattering of Radiation Belt Electrons and Ring Current Protons by EMIC Waves

AbstractIn this study, we investigate the effects of polarization reversal of electromagnetic ion cyclotron (EMIC) waves at the crossover frequencies on computations of bounce‐averaged pitch angle diffusion coefficients of radiation belt electrons and ring current protons. We find that inclusion of polarization reversal can cause significant changes of H+ band‐induced particle diffusion coefficients, while scattering by the He+ band is almost unaffected. Our results show that the pure L‐mode approach, which has been widely implemented in previous studies, tends to underestimate the diffusion coefficients of ultrarelativistic (>4 MeV) electrons and overestimate those of 10–50 and >100 keV protons caused by H+ band EMIC waves. Especially for >100 keV protons, the differences in diffusion coefficients can be larger by an order of magnitude. We confirm that the polarization reversal can contribute importantly to the scattering loss of radiation belt electrons and ring current protons by H+ band EMIC waves.

Ionosphere Feedback to Electron Scattering by Equatorial Whistler Mode Waves

AbstractPlasma sheet electron precipitation, much of it driven by whistler mode waves, is critical for magnetosphere‐ionosphere coupling. This precipitation leads to a secondary electron population at low altitudes, which moves upward along magnetic field lines to the equatorial plasma sheet. We investigate observational evidence for such electron precipitation and the ionospheric feedback provided by the secondary electron outflows. Using the near‐equatorial Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission, we show that whistler mode wave bursts are accompanied by enhanced field‐aligned electrons. The properties of these electrons are not related to the whistler mode waves, as would have been expected from local wave‐particle interactions. Thus, it is unlikely that the field‐aligned electrons are formed by electron Landau resonance with whistler mode waves. This population can be the secondary electron outflows resulting from plasma sheet electron precipitation to the ionosphere. Combining THEMIS, Cluster, and Fast Auroral Snapshot Explorer (FAST) measurements, we show that this field‐aligned electron population is also observed at low altitudes, where it is associated with high‐frequency electrostatic waves. These low‐altitude waves are likely generated by the secondary electron outflows and, in turn, scatter these electrons outside of the loss cone, allowing them to be observed by the wide field‐of‐view particle instrument on the near‐equatorial THEMIS spacecraft. We discuss how this secondary electron population can subsequently alter whistler mode wave generation and propagation in the magnetosphere.

Potential Evidence of Low‐Energy Electron Scattering and Ionospheric Precipitation by Time Domain Structures

AbstractPlasma sheet electron precipitation is critical in magnetosphere‐ionosphere coupling and has long been attributed to electron scattering by whistler‐mode and electron cyclotron harmonic waves. Recent observations have revealed that time domain structures (TDSs) that appear as broadband electrostatic fluctuations may also scatter plasma sheet electrons. However, there has been no observational evidence of TDS scattering electrons into the ionosphere. This study presents potential evidence from conjugate observations between the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission and the low‐altitude Enhanced Polar Outflow Probe (e‐POP) spacecraft. During the five events presented, THEMIS observed intense electron injections accompanied by TDSs, while e‐POP captured precipitation of plasma sheet electrons with energies ∼100–325 eV over a broad pitch angle range. The observed TDSs can efficiently scatter these electrons exceeding the strong diffusion limit. Our results suggest that TDSs may contribute to plasma sheet electron scattering around times of injections.

Spin Relaxation in s-Wave Superconductors in the Presence of Resonant Spin-Flip Scatterers.

Employing analytical methods and quantum transport simulations we investigate the relaxation of quasiparticle spins in graphene proximitized by an s-wave superconductor in the presence of resonant magnetic and spin-orbit active impurities. Off resonance, the relaxation increases with decreasing temperature when electrons scatter off magnetic impurities-the Hebel-Slichter effect-and decreases when impurities have spin-orbit coupling. This distinct temperature dependence (not present in the normal state) uniquely discriminates between the two scattering mechanisms. However, we show that the Hebel-Slichter picture breaks down at resonances. The emergence of Yu-Shiba-Rusinov bound states within the superconducting gap redistributes the spectral weight away from magnetic resonances. The result is opposite to the Hebel-Slichter expectation: the spin relaxation decreases with decreasing temperature. Our findings hold for generic s-wave superconductors with resonant magnetic impurities, but also, as we show, for resonant magnetic Josephson junctions.

Electron Scattering Cross Sections for Anthracene and Pyrene.

UK molecular R-matrix calculations have been carried out for electron scattering from anthracene and pyrene. These molecules belong to the family of polycyclic hydrocarbons (PAHs) and are found in a nebula known as the Red Rectangle. Static exchange (SE), static exchange plus polarization (SEP), and close coupling (CC) approximations are used for scattering calculations. Different elastic and inelastic cross sections are computed in the present work in the energy range of 0.1-15 eV. Dissociative electron attachment cross sections are also calculated for both the molecules. Various shape, Feshbach/core-excited, and mixed resonances are detected for these molecules below 10 eV. All of the resonances detected in the present study are in agreement with the existing experimental and theoretical results. Due to the complexity of the present targets, electron collision cross sections are essentially unknown and hence most of the results are presented for the first time.

Anomalous thermal transport in metallic transition-metal nitrides originated from strong electron–phonon interactions

Metallic transition-metal nitrides (TMNs) are promising conductive ceramics for many applications, whose thermal transport is of great importance. In this article, thermal transport properties of TiN and HfN are investigated through a first-principle-based method with rigorous consideration of phonon and electron scatterings. It is found metallic TiN and HfN hold different thermal transport behaviors compared with common metals and non-metallic TMNs. Without phonon–electron scatterings, they could have extremely large phonon thermal conductivity. The phonon thermal conductivity is reduced by two orders of magnitude as the phonon–electron scatterings are considered. The nesting Fermi surfaces existing in both TiN and HfN are the main reason for the strong electron–phonon interactions. Such an effect also induces the unusual temperature-independent behavior of phonon thermal conductivity. The phonon component takes a large ratio in total thermal conductivity, as 29% for TiN and 26% for HfN at 300 K. The results for thin films are also presented, and it is shown that the phonon thermal conductivity can be efficiently suppressed by size. Our findings can provide a deeper understanding on the thermal transport in metallic TMNs as well as electron and phonon heat conduction in metals.

Energetic Electron Scattering due to Whistler Mode Chorus Waves Using Realistic Magnetic Field and Density Models in Jupiter's Magnetosphere

AbstractWe evaluate energetic electron scattering in pitch angle and energy using realistic magnetic field and density models due to whistler mode chorus waves in Jupiter's magnetosphere and study their dependences on various wave and background parameters. We calculate the bounce‐averaged diffusion coefficients by considering the latitudinal variation of total electron density and ambient magnetic field intensity, using the VIP4 internal magnetic field and CAN current sheet model. The electron phase space density evolution due to chorus waves is simulated at M shell of 10, using the central wave frequency at 0.1fce and wave amplitude of 30 pT. Under the typical values of the ratio between the plasma frequency and electron cyclotron frequency, chorus waves could cause fast pitch angle scattering loss of energetic electrons from tens to several hundred keV in several hours, and gradual acceleration of relativistic electrons at several MeV in several days. The electron pitch angle scattering at ~500 keV and the acceleration at several MeV are both enhanced using the latitudinally varying density and VIP4 + CAN magnetic field model compared to the electron evolution using the constant density and dipole magnetic field model. Our sensitivity study indicates that the electron scattering at higher energy is caused by waves at lower frequencies or in a lower‐density background plasma, and the scattering is faster for waves at smaller wave normal angles. The electron diffusion is mainly caused by waves at lower latitudes, but the waves at higher latitudes (>30°) contribute to the electron loss at higher energies (>2 MeV).

Improving the Speed and Accuracy of Large-scale Scanning Transmission Electron Microscopy (STEM) Electron Scattering Simulations

Improving the Speed and Accuracy of Large-scale Scanning Transmission Electron Microscopy (STEM) Electron Scattering Simulations

Dynes-like superconductivity in thin Al films in parallel magnetic fields

Recently, the ubiquitously applicable phenomenological Dynes formula for the tunneling density of states of superconductors has been explained by assuming that the electrons scatter on a random magnetic field due to impurities. In the original derivation, only the magnitude of the field was taken as random, but the direction of the field was assumed to be fixed. Here we show that this assumption can be relaxed, and therefore the concept of Dynes superconductivity is not restricted to systems with a preferred direction in spin space. We also address the question whether thin Al films in parallel magnetic fields can be described as Dynes superconductors.

Effect of annealing process on hot-electron energy relaxation rates in n-type modulation-doped Ga0.68In0.32N0.017As/GaAs quantum wells via deformation potential and piezoelectric scatterings

Hot electrons relax by interacting with phonons, so information about the electron-phonon interaction mechanisms are obtained by examining the cooling processes of hot electrons. In this study, the effect of annealing time on the electron temperature and energy relaxation rates in as-grown and annealed n-type modulation-doped Ga0.68In0.32N0.017As0.983/GaAs quantum well (QW) samples were investigated by comparing the relative amplitudes of Shubnikov-de Haas oscillations as a function of temperature and electric field. The samples were grown by molecular beam epitaxy (MBE) and annealed at 700 °C for 60 s and 600 s. Experiments were carried out by applying an electric field between 0.165 and 5.276 kV/m at a temperature range between 1.8 and 40 K under magnetic up to 11 T. The energy-relaxation mechanism is found to be a mixing of piezoelectric and deformation potential scatterings of hot electrons in the low-temperature regime up to 40 K electron temperature. The electron power loss by interacting with phonons is characterized with exponential term γ, which is found to be in the range from 3.42 to 4.97. The change of γ showed that the scattering mechanisms are affected by the annealing time. The piezoelectric stress constant (e14) chosen as a fit parameter in the theoretical power loss calculations, which was found between 0.129 and 0.134. The crystal quality at low temperatures has been observed to be effective on energy relaxation times.

Electron and Positron Scattering by the Formamide Molecule.

We report calculated elastic integral, differential, and momentum transfer cross sections for electron and positron collisions with the formamide (HCONH2) molecule, for impact energies up to 10 eV. We have used the Schwinger multichannel method in the static-exchange and static-exchange plus polarization approximation for collisions of electrons and the static plus polarization approximation for collisions of positrons. The Born-closure procedure was applied to account for the long-range potential due to the permanent dipole moment of formamide. We obtained the well-characterized π* shape resonance located at around 2.38 eV, which belongs to the A″ symmetry of the Cs point group. Our integral and differential cross sections for collisions of electrons were compared with the data available in the literature and showed a good qualitative agreement. To the best of our knowledge, no experimental and theoretical data are currently available for positron-formamide collision, so our present cross sections were compared with the cross sections of formic acid, which is also polar and is isoeletronic to formamide.

Three-terminal interface as a thermoelectric generator beyond the Seebeck effect

We investigate thermoelectric transport through interfaces with inelastic scatterings by developing a quantum theory, which has been extensively validated by existing theories. We find that under temperature bias, while a two-terminal conductor-insulator interface behaves only as a thermal resistor, a three-terminal conductor-insulator-conductor interface can function as an electricity generator caused by phonon-mediated electron scatterings with heat-charge current separation. Unlike conventional thermoelectrics which is a property of a bulk caused by the Seebeck effect, this thermoelectric behavior is a property of an interface driven by electron-phonon scatterings.

Electron Scattering in Liquid Water and Amorphous Ice: A Striking Resemblance.

The lack of accurate low-energy electron scattering cross sections for liquid water is a substantial source of uncertainty in the modeling of radiation chemistry and biology. The use of existing amorphous ice scattering cross sections for the lack of liquid data has been discussed controversially for decades. Here, we compare experimental photoemission data of liquid water with corresponding predictions using amorphous ice cross sections, with the aim of resolving the debate regarding the difference of electron scattering in liquid water and amorphous ice. We find very similar scattering properties in the liquid and the ice for electron kinetic energies up to a few hundred electron volts. The scattering cross sections recommended here for liquid water are an extension of the amorphous ice cross sections. Within the framework of currently available experimental data, our work answers one of the most debated questions regarding electron scattering in liquid water.