Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “electron scattering”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Monte Carlo Simulation of Electron Interactions in an MeV-STEM for Thick Frozen Biological Sample Imaging

A variety of volume electron microscopy techniques have been developed to visualize thick biological samples. However, the resolution is limited by the sliced section thickness (>30–60 nm). To preserve biological samples in a hydrated state, cryo-focused ion beam scanning electron microscopy has been developed, providing nm resolutions. However, this method is time-consuming, requiring 15–20 h to image a 10 μm thick sample with an 8 nm slice thickness. There is a pressing need for a method that allows the rapid and efficient study of thick biological samples while maintaining nanoscale resolution. The remarkable ability of mega-electron-volt (MeV) electrons to penetrate thick biological samples, even exceeding 10 μm in thickness, while maintaining nanoscale resolution, positions MeV-STEM as a suitable microscopy tool for such applications. Our research delves into understanding the interactions between MeV electrons and frozen biological specimens through Monte Carlo simulations. Single elastic scattering, plural elastic scattering, single inelastic scattering, and plural inelastic scattering events have been simulated. The electron trajectories, the beam profile, and the intensity change of electrons in each category have been investigated. Additionally, the effects of the detector collection angle and the focal position of the electron beam were investigated. As electrons penetrated deeper into the specimen, single and plural elastic scattered electrons diminished, and plural inelastic scattered electrons became dominant, and the beam profile became wider. Even after 10 μm of the specimen, 42% of the MeV electrons were collected within 10 mrad. This confirms that MeV-STEM can be employed to study thick biological samples.

electron specimen interaction↗
DOE OSTI2023

Substrate effects on spin relaxation in two-dimensional Dirac materials with strong spin-orbit coupling

Understanding substrate effects on spin dynamics and relaxation is of key importance for spin-based information technologies. However, the key factors that determine such effects, in particular for materials with strong spin-orbit coupling (SOC), have not been well understood. Here we performed first-principles real-time density-matrix dynamics simulations with SOC and the electron phonon and electron-impurity scattering for spin lifetimes (τ s ) of supported/free-standing germanene, a prototypical strong SOC 2D Dirac material. We show that the effects of different substrates on τ s can surprisingly differ by two orders of magnitude. We find that substrate effects on τ s are closely related to substrate-induced modifications of the SOC-field anisotropy, which changes the spin flip scattering matrix elements. We propose a new electronic quantity, named spin-flip angle θ ↑↓ , to characterize spin relaxation through intervalley spin-flip scattering. We find that $τ^{-1}_s$ is approximately proportional to the averaged value of sin 2 (θ ↑↓ /2), which serves as a guiding parameter of controlling spin relaxation.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Quasielastic lepton scattering and back-to-back nucleons in the short-time approximation

Understanding quasielastic electron- and neutrino-scattering from nuclei has taken on new urgency with current and planned neutrino oscillation experiments, and with electron scattering experiments measuring specific final states, such as those involving nucleon pairs in “back-to-back” configurations. Accurate many-body methods are available for calculating the response of light (A ≤ 12) nuclei to electromagnetic and weak probes, but they are computationally intensive and only applicable to the inclusive response. In the present work we introduce a novel approach, based on realistic models of nuclear interactions and currents, to evaluate the short-time (high-energy) inclusive and exclusive response of nuclei. The approach accounts reliably for crucial two-nucleon dynamics, including correlations and currents, and provides information on back-to-back nucleons observed in electron and neutrino scattering experiments. We demonstrate that in the quasielastic regime and at moderate momentum transfers both initial- and final-state correlations, and two-nucleon currents are important for a quantitatively successful description of the inclusive response and final state nucleons. Finally, the approach can be extended to include relativistic—kinematical and dynamical—effects, at least approximately in the two-nucleon sector, and to describe the response in the resonance-excitation region.

6 ≤ A ≤ 19↗
DOE OSTI2022

Anomalous electrical transport behavior in the vicinity of the first-order magnetostructural transition in the giant magnetocaloric Gd 4 ScGe 4

Here, magnetic, specific heat, and electrical transport measurements of Gd 4 ScGe 4 single crystals reveal sharp, discontinuous, nearly anhysteretic first-order magnetostructural transformation at $T_C$ = 63 K. The electrical resistivity exhibits two distinct regions where it increases with decreasing temperature: between $T_C$ and 120 K, as well as below 3 K; electronic transport remains conventionally metallic at all other measured temperatures, up to 325 K. The dispersion of charge carriers due to electron-paramagnon scattering is the likely reason for the observed anomalous transport above $T_C$. Additionally, the existence of intermediate lattice states near the transition recognized by the spike in the interslab Ge-Ge distances is expected to reduce the mean free path of the electrons contributing to the unusual behavior of the electrical resistivity between $T_C$ and 120 K. Beyond conventional electronic and lattice terms, the third component of likely magnetic origin contributes to the low-temperature heat capacity; the presence of spin waves may be responsible for the increased electron-magnon scattering below 3 K. Minor magnetocrystalline anisotropy is observed with the b axis as the easy magnetization axis in Gd 4 ScGe 4 . A negative deviation from linearity in the temperature dependence of the inverse magnetic susceptibility is detected below 150 K.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Control of quantum electrodynamical processes by shaping electron wavepackets

Fundamental quantum electrodynamical (QED) processes, such as spontaneous emission and electron-photon scattering, encompass phenomena that underlie much of modern science and technology. Conventionally, calculations in QED and other field theories treat incoming particles as single-momentum states, omitting the possibility that coherent superposition states, i.e., shaped wavepackets, can alter fundamental scattering processes. Here, we show that free electron waveshaping can be used to design interferences between two or more pathways in a QED process, enabling precise control over the rate of that process. As an example, we show that free electron waveshaping modifies both spatial and spectral characteristics of bremsstrahlung emission, leading for instance to enhancements in directionality and monochromaticity. The ability to tailor general QED processes opens up additional avenues of control in phenomena ranging from optical excitation (e.g., plasmon and phonon emission) in electron microscopy to free electron lasing in the quantum regime.

42 ENGINEERING↗
DOE OSTI2021

Quantization effects in semiconductor nanostructures and singlet fission in molecular chromophores for photovoltaics and solar fuels

Hot carriers in semiconductors are electrons and/or holes that have energies greater than carriers that reside at the top and bottom of the conduction and valence bands, respectively; the latter carriers are in equilibrium with the lattice and have a temperature equal to the lattice (ambient) temperature. Hot carriers are created in semiconductors upon the absorption of photons with energies greater than the bandgap. The excess energy above the bandgap energy is in the form of kinetic energy. The hot carriers can cool to the lattice temperature via electron–phonon scattering and establish separate Boltzmann distributions for electrons and holes at the band edges. Thus, upon cooling, the excess kinetic energy of the hot carriers is transformed into heat and is unavailable to be converted into electrical or chemical free energy in a solar photon-converting cell. This hot-carrier cooling process significantly limits the maximum possible power conversion efficiency (PCE) of the free energy of solar photons into electrical free energy or chemical free energy in chemical bonds of fuels. However, if hot-carrier cooling can be slowed such that the hot carriers can be extracted before cooling to create higher photovoltages, or utilized to create additional electron-hole pairs through carrier multiplication, then beneficial use can be made of the excess energy of hot carriers and the maximum thermodynamic PCE can be dramatically increased. Quantization effects in semiconductor nanostructures, unique properties of some bulk semiconductors, and exciton multiplication in both semiconductors and molecular chromophores that undergo singlet fission have shown a path forward for potential dramatic increases in the PCEs of solar photons into electricity and solar fuels. The status, history, and future promise of the science and technology of these future approaches for different types of photovoltaic cells and cells for solar fuels will be discussed.

14 SOLAR ENERGY↗
DOE OSTI2024

FEFF analysis of americium oxides

The Am N 4,5 (4d 3/2 and 4d 5/2 ) and Am O 4,5 (5d 3/2 and 5d 5/2 ) x-ray absorption spectroscopy (XAS) of americium sesquioxide (Am 2 O 3 ) and americium dioxide (AmO 2 ) has been evaluated with FEFF, a Green's function–based, multiple scattering code. Taking guidance from the intermediate coupling model (ICM), applicable to local and nonmagnetized samples, it is possible to completely reconstruct the experimental results for the N 4,5 spectra, including the observed differences between the Am 2 O 3 and the AmO 2 cases. Although complicated by a more asymmetric line shape and difficult background variations, the FEFF analysis confirms the absence of core hole angular momentum coupling in Am O 4,5 spectroscopy.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Quantum efficiency, photoemission energy spectra, and mean transverse energy of ultrananocrystalline diamond photocathode

The quantum efficiency and mean transverse energy of electrons emitted from a cathode determine the quality of beams generated from photoinjectors. The nitrogen-incorporated ultrananocrystalline diamond, (N)UNCD, is a new class of robust semiconductor photocathodes, which has been considered in photoinjectors for high peak current extraction. In this work, we measure the spectral response in quantum efficiency, photoemission energy spectra, and mean transverse energy of the (N)UNCD photocathode using a photoemission electron microscope. The observed quantum efficiency was comparable to that of copper photocathodes. Photoemission spectra showed the evidence of scattering of electrons before emission. This relaxation of electrons due to scattering is also observed in the spectral response of the mean transverse energy. The mean transverse energy is limited to ∼70 meV at the threshold. We attribute this to the physical and chemical roughness of the (N)UNCD photocathode and, hence, smoother films will be required to further reduce the mean transverse energy obtained from the (N)UNCD photocathode.

Kachwala, A. (ORCID:0000000301756478)↗
DOE OSTI2021

A laser inverse Compton scattering diagnostic to study runaway electron dynamics during tokamak disruptions

The goal is to design a new diagnostic based on laser inverse Compton scattering (LICS) to study the dynamics of runaway electron formation and their subsequent loss during triggered disruptions in DIII-D. It is known that better measurements of the runaway electron population, throughout the evolution of a disruption, is critical for mitigating the impact of energetic electron beams especially in high plasma current discharges such as those in reactor relevant burning plasmas. The goal of the LICS approach being designed for DIII-D is to measure the timeresolved spatial profile and energy distribution of the runaway electrons while they are in the core of the tokamak plasma. During the last year, a code was developed to simulate the signals from a new laser scattering diagnostic for DIII-D, which will measure the relativistic electron population expected in DIII-D after disruptions triggered by argon pellet injection.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Deeply virtual Compton scattering off the neutron

The three-dimensional structure of nucleons (protons and neutrons) is embedded in so-called generalized parton distributions, which are accessible from deeply virtual Compton scattering. In this process, a high-energy electron is scattered off a nucleon by exchanging a virtual photon. Then, a highly energetic real photon is emitted from one of the quarks inside the nucleon, which carries information on the quark's transverse position and longitudinal momentum. By measuring the cross-section of deeply virtual Compton scattering, Compton form factors related to the generalized parton distributions can be extracted. Here, we report the observation of unpolarized deeply virtual Compton scattering off a deuterium target. From the measured photon-electroproduction cross-sections, we have extracted the cross-section of a quasifree neutron and a coherent deuteron. Due to the approximate isospin symmetry of quantum chromodynamics, we can determine the contributions from the different quark flavours to the helicity-conserved Compton form factors by combining our measurements with previous ones probing the proton's internal structure. These results advance our understanding of the description of the nucleon structure, which is important to solve the proton spin puzzle. The internal structure of the neutron has now been probed by highly energetic photons scattering off it. Combined with previous results for protons, these measurements reveal the contributions of quark flavours to the nucleon structure.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2026

Collisional stopping power of ions in warm dense matter

Here, a model for the collisional stopping of ions on free electrons in warm dense matter is developed and explored. It is based on plasma kinetic theory, but with modifications to address the warm dense matter regime. Specifically, it uses the Boltzmann-Uehling-Uhlenbeck kinetic equation to incorporate effects of Fermi degeneracy of electrons. The cross section is computed from quantum scattering of electrons and ions occurring via the potential of mean force derived from an average atom model, which incorporates effects of strong Coulomb correlations. Predictions from this model show comparable accuracy to results from time-dependent density functional theory calculations for deuterium near solid density and a temperature of several electronvolts, at a fraction of the computational cost. Further, the model captures the transition of a plasma from the classical limit to the degenerate limit, including qualitative behaviors of solid state theory.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Interfacing electron and neutrino quasielastic scattering cross sections with the spectral function in GENIE

Progress in neutrino-nucleus cross section models is being driven by the need for highly accurate predictions for the neutrino oscillation community. These sophisticated models are being developed within a microscopic description of the nucleus with the goal of encompassing all reaction modes relevant for the accelerator neutrino program. The disconnect between these microscopic models and the event generators that will be used in the next generation of experiments represents a critical obstacle that must be overcome in order to precisely measure the neutrino oscillation parameters. To this end we have developed a hadron tensor interface for lepton-nucleus quasielastic (QE) scattering within the GENIE event generator as a proof of principle, with the broader goal of creating an efficient pipeline for incorporating advanced theoretical models in event generators. As a demonstration of this interface we have implemented the spectral function model into GENIE by connecting theorist provided fortran code through the hadron tensor interface. The spectral function model offers a more complete description of the nuclear ground state, as well as the ability to provide quantifiable theoretical uncertainties. Finally, we validate this implementation and compare its predictions against data and against QE models already available in GENIE.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Study of deeply virtual Compton scattering at the future electron-ion collider

This study presents the impact of future measurements of deeply virtual Compton scattering (DVCS) with the ePIC detector at the electron-ion collider (EIC), currently under construction at Brookhaven National Laboratory. The considered process is sensitive to generalized parton distributions (GPDs), the understanding of which is a cornerstone of the EIC physics program. Our study marks a milestone in the preparation of DVCS measurements at EIC and provides a reference point for future analyses. In addition to presenting distributions of basic kinematic variables obtained with the latest ePIC design and simulation software, we examine the impact of future measurements on the understanding of nucleon tomography and DVCS Compton form factors, which are directly linked to GPDs. We also assess the impact of radiative corrections and background contribution arising from exclusive π 0 production.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Influence of temperature, doping, and amorphization on the electronic structure and magnetic damping of iron

Hybrid magnonic quantum systems have drawn increased attention in recent years for coherent quantum information processing, but too large magnetic damping is a persistent concern when metallic magnets are used. Their intrinsic damping is largely determined by electron-magnon scattering induced by spin-orbit interactions. In the low scattering limit, damping is dominated by intra-band electronic transitions, which has been theoretically shown to be proportional to the electronic density of states at the Fermi level. In this work, we focus on body-centered-cubic iron as a paradigmatic ferromagnetic material. We comprehensively study its electronic structure using first-principles density functional theory simulations and account for finite lattice temperature, boron (B) doping, and structure amorphization. Our results indicate that temperature induced atomic disorder and amorphous atomic geometries only have a minor influence. Instead, boron doping noticeably decreases the density of states near the Fermi level with an optimal doping level of 6.25%. In addition, we show that this reduction varies significantly for different atomic geometries and report that the highest reduction correlates with a large magnetization of the material. Furthermore, this may suggest materials growth under external magnetic fields as a route to explore in experiment.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Surface conduction and reduced electrical resistivity in ultrathin noncrystalline NbP semimetal

The electrical resistivity of conventional metals such as copper is known to increase in thin films as a result of electron-surface scattering, thus limiting the performance of metals in nanoscale electronics. Here, in this study, we find an unusual reduction of resistivity with decreasing film thickness in niobium phosphide (NbP) semimetal deposited at relatively low temperatures of 400°C. In films thinner than 5 nanometers, the room temperature resistivity (~34 microhm centimeters for 1.5-nanometer-thick NbP) is up to six times lower than the resistivity of our bulk NbP films, and lower than conventional metals at similar thickness (typically about 100 microhm centimeters). The NbP films are not crystalline but display local nanocrystalline, short-range order within an amorphous matrix. Our analysis suggests that the lower effective resistivity is caused by conduction through surface channels, together with high surface carrier density and sufficiently good mobility as the film thickness is reduced. These results and the fundamental insights obtained here could enable ultrathin, low-resistivity wires for nanoelectronics beyond the limitations of conventional metals.

42 ENGINEERING↗