Energy Of Emitted Electrons Research Articles

Doubly differential cross sections for ionization in proton collisions with atomic hydrogen: Energy and angular distribution of emitted electrons

Doubly differential cross sections for ionization in proton collisions with atomic hydrogen: Energy and angular distribution of emitted electrons

Modeling the Photoelectric Effect on Photocells Using Python

To simulate the laboratory work «Study of the Photoelectric Effect with External Photoelectric Effect» in Python, a program was developed that models the interaction of light with the surface of the metal and measures the kinetic energy of emitted electrons depending on the frequency of light. The program uses the matplotlib library to visualize the results and includes various blocks, such as library imports, definition of constants, functions for calculating kinetic energy and plotting graphs, as well as interactive widgets for changing parameters and observing results in real time.

Studies on electron acceleration from modulated surface at grazing angle laser interaction

Surface plasmon (SP) based electron acceleration has been investigated during the interaction of short, ultra-intense (I > 1019 W/cm2) laser pulse with periodically modulated solid target. Laser contrast conditions are required to preserve the structural integrity of the target. Two dimensional (2D) particle-in-cell (PIC) simulations report emission of energetic (~ 78 MeV) electron bunches along grating surface for grazing incident of laser pulse at an optimum angle 4° with respect to target surface. The energy and flux of emitted electrons for grazing laser incidence were found to be strongly enhanced as compared to the incident angles satisfying the resonant condition for surface plasma wave’s excitation.

Theoretical triple differential cross sections for ionization of N 2 and CH 4 molecules by electron impact

We present the angular distribution of electron emission by calculating the triple differential cross sections for (e, 2e) process on N 2 and CH 4 by using the three-body formalism of molecular first Born approximation (MFBA), two-Coulomb wave (M2CW), and three-Coulomb wave (M3CW) models, respectively. In these models, a Coulomb distorted wave is considered for the motion of the incident electron. We have considered the continuum-continuum correlation effect by choosing the final state as the three-Coulomb and two-Coulomb wave functions in M3CW and M2CW models, whereas the ejected electron is affected by a single centre field of the target in the MFBA model. In the M2CW model, the interaction between scattered electron-residual target ion has been described as a plane wave. The distinguishing feature among the three models has been noted in the TDCS as a strong binary peak with and without a recoil peak for several electron emission energies at fixed scattering angle. In the case of N 2 molecule, the TDCS shows oscillatory behaviour with the variation of the electron emission angle. The positions of the binary peak obtained by our theoretical models are well established by the experimental findings, but a large deviation is found in the region of the recoil peak. The contributions of TDCS for different molecular orbitals of the molecules to the spectrum of angular distributions at different electron emission energies have also been analyzed. Finally, a comparison is made with the measurement in coplanar asymmetry geometry. Overall, good agreement was found between experiments and M3CW theory.

Electron emission from deep traps in HfO2 under thermal and optical excitation

The ratio between the energies of optical and thermal ionization depends on the defect nature and the strength of the interaction of trapped electrons with phonons. Knowing this ratio for a certain type of defect allows one to predict, e.g., thermal emission energies from the optically measured values. We present the results of direct empirical extraction of the ratio between optical and thermal electron emission energies for HfO2 bulk electron traps combined with theoretical analysis of the physical mechanism of electron transitions from the trapped state to the mobility edge. We show that, by applying different excitation mechanisms, we affect the same deep traps inside the HfO2 band gap; i.e., these traps are both optically and thermally active and are likely to have similar nature. The extracted empirical optical/thermal ionization energy ratio of 2.2±0.3 is in good agreement with the polaronic nature of the probed electron traps, as shown by the results of theoretical calculations. Our results provide experimental and theoretical methodologies for consistently linking thermal and optical ionization energies of electron traps and describing their distributions in the band gap of amorphous oxides, and can help improve modeling frameworks for reliability issues related to oxide traps. Published by the American Physical Society 2024

Classical-trajectory model for ionizing proton-ammonia molecule collisions: the role of multiple ionization

We use an independent electron model with semi-classical approximation to electron dynamics to investigate differential cross sections for electron emission in fast collisions of protons with ammonia molecules. An effective potential model for the electronic orbitals is introduced, and utilized in the context of the classical-trajectory Monte Carlo (CTMC) approach for single-electron dynamics. Cross sections differential in electron emission angle and energy are compared with experimental data. Compared to previous scattering-theory based quantum-mechanical results the time-dependent semi-classical CTMC approach provides results of similar quality for intermediate and high ionized electron energies. We find some discrepancies in the total cross sections for q-fold ionization between the present model and independent-atom-model calculations. The double ionization cross sections are considerably larger than recent experimental data which are derived from coincidence counting of charged fragments. The calculated triple ionization cross sections exceed the experimental coincidence data for q = 3 by several orders of magnitude at intermediate energies.

A Critical Analysis of Target Ionization and Projectile Electron Loss in Neutral– and Ion–Atom Collisions

Electron removal (target ionization and/or projectile electron loss) in neutral–atom collisions is theoretically studied for the impact of H0, He0 and He+ beams on noble gases (He, Ne and Ar). These reactions are investigated theoretically within the Continuum Distorted Wave-Eikonal Initial State model. New features have been included in the theoretical model: (i) a scaled projectile charge depending on its velocity and charge, (ii) a dynamic projectile-effective-charge depending on the momentum transfer, and (iii) a dynamic target-effective-charge depending on the kinematics of the emitted electron. The energy and angular spectra of emitted electrons from the target and from the projectile are calculated and compared with the available experimental data. Also, the influence of each one of the corrections on the resulting spectra will be studied.

Ionization of uracil molecule in collisions with 2.5-MeV/u Si12+ ions

The energy and angular distribution of electron emission from a RNA base molecule, uracil (C 4 H 4 N 2 O 2), are investigated in collisions with 2.5-MeV/u Si12+ ions under high perturbation strength. The absolute double differential cross sections (DDCS) are measured using electron spectroscopy for emission angles between 20° to 160° in the electron energy range 1-620 eV. The single differential cross sections (SDCS) are evaluated by integrating the DDCS over emission angles or energies. The measured cross sections (DDCS and SDCS) are compared with the state-of-the-art continuum distorted wave-eikonal initial state (CDW-EIS) theoretical model. The DDCS obtained by the CDW-EIS is found to provide better agreement with the measurements in the backward angles. With an increase in perturbation strength from 0.5 to 1.19 a.u., the DDCS is found to increase by 10 times in comparison to the earlier reported uracil data for 3.5-MeV/u bare C-ions [Phys. Rev. A 87, 032716 (2013)]. The significant enhancement in the TCS is found for the total cross section in case of Si12+ ions over that predicted by a scaling law as derived for lower charge state projectiles. The forward-backward angular asymmetry is found to increase monotonically with the velocity of emitted electrons and shows very good agreement with the model. For a comparative study, the DDCS is also measured for oxygen molecule using same ion impact, which is found to be about ten times lower than that for the uracil. The forward-backward angular asymmetry for oxygen is found to be almost the same as uracil.

Novel low-macroscopic-field emission cathodes for electron probe spectroscopy systems

The current state of electron probe methods [including energy loss spectroscopy of inelastically scattered electrons (EELS)] is considered. The analysis concerning the issues of their application, challenges, and limitations is performed. Particular attention is paid to the fundamental limitations and the means to overcome those during electron probe methods’ subsequent development for the study of composite nanostructured materials. It is emphasized that the emitted electron energy spectrum dispersion (or electron energy distribution function width) is one of the main factors limiting a further increase in EELS energy resolution, although the use of direct detection sensors and monochromators allows one to approach the physical limit of this method. Novel low-macroscopic-field electron emitters are synthesized and investigated. Their properties are analyzed and compared with previously obtained specimens. Both energy and temporal resolutions of an EEL system utilizing the suggested cathodes are estimated. The comparison of its characteristics with the corresponding parameters of classical facilities is performed. The obtained results indicate the possibility to achieving a significant growth in energy and temporal resolutions as well as a decrease in the detection threshold of chemical elements with trace concentrations while maintaining relatively high emission current density values.

Calculation of Energy and Angular Distributions of Electrons Produced in Intermediate-Energy p + H2 Collisions

We extend the two-centre wave-packet convergent close-coupling approach to doubly differential ionisation in proton collisions with H2 to intermediate projectile energies. The results for the doubly differential cross section at projectile energies from 48 to 200 keV are presented as a function of the energy and angle of emitted electrons. We consider a wide range of emission angles from 10 to 160∘, and compare our results to experimental data, where available. Excellent agreement between the presented results and the experimental data was found, especially for emission angles less than 130∘. For very large backward emission angles our calculations tended to slightly overestimate the experimental data when energetic electrons are ejected and the doubly differential cross section is very small. This discrepancy may be due to the large uncertainties in the experimental data in this region and the model target description. Overall, the present results show significant improvement upon currently available theoretical results and provide a consistently accurate description of this process across a wide range of incident energies.

4H-SiC Schottky barrier diodes as radiation detectors: A role of Schottky contact area

Large-area SiC Schottky barrier diodes can significantly improve the sensitivity in radiation detection due to the increased interacting SiC volume. In this work, we tested a large SiC detector with an area of 1 × 1 cm2. Extensive electrical characterization was performed at temperatures ranging from 150 K to 390 K, demonstrating the impact of barrier inhomogeneities on the electrical performance of the diode. Forward current-voltage (I-V) measurements of the diodes revealed two distinct regions caused by Schottky barrier inhomogeneity present throughout the entire temperature range. The barrier heights in the low- and high-current forward voltage regions were extracted from Richardson plots corrected for the Gaussian distribution of barrier heights, yielding values of 1.52 eV and 1.79 eV, respectively. Deep-level transient spectroscopy (DLTS) revealed only one deep-level defect, Z1/2, with an activation energy for electron emission of 0.67 eV, which was assigned to the known carbon vacancy. The DLTS study showed no correlation between electrically active defects and barrier inhomogeneity. An excellent energy resolution of 3.2 % was measured using a large area 241Am radiation source, consistent with values for small area SiC detectors that exhibited no barrier height inhomogeneities. The impact of temperature on the alpha particle radiation response was determined within a temperature range of 200 K to 390 K.

Triple differential cross sections for single ionization of an atom by bare ion impact

We present triple differential cross sections (TDCSs) for single ionization of atoms by proton and highly charged bare ions impact by means of the three-body formalism of the first Born, two-Coulomb wave and three-Coulomb (3C) wave (3CW) methods, respectively. The TDCS has been calculated both in the scattering and perpendicular planes. The purpose of this work is to investigate the validity of different methods as well as the role of interaction between projectile and residual-target-ion in the final state for weak perturbation strength with low electron emission energy at several momentum transfers. By comparing our calculations with experimental data, overall, the 3CW predicts better agreement with experiments than other calculations in the scattering plane. In the perpendicular plane, all calculations deviate from experimental data with increasing transverse momentum transfer for p − He collision. At low momentum transfer, the location of binary peak obtained by the first Born approximation calculation is well established with the experiment for proton impact. On the other hand, the 3CW model is in much better agreement with experiments, both in absolute values and peak position for highly charged impact. Finally, the strong influence of the internuclear Coulomb distortion on TDCS has been observed at low and intermediate momentum transfer.

Neutrino-induced reactions on 18O and implications of 18O mixture in water Cherenkov detectors on supernova neutrino events

Neutrino-nucleus reaction cross sections on 18O are evaluated by shell-model calculations and compared with those on 16O. Important contributions from Gamow-Teller transitions are noticed for 18O (νe, e−) 18F in contrary to the case for 16O, where spin-dipole transitions are dominant contributions. Calculated cross sections for 18O (νe, e−) 18F are shown to be larger than for 16O at low neutrino energies below 20 MeV in natural water with the 0.205% admixture of 18O due to the lower threshold energy (1.66 MeV) for 18O than that for 16O (15.42 MeV). The resulting electron spectra, that is, the cross sections as functions of emitted electron energy Te, are also shown to be quite different, reflecting the different threshold energies. The electron spectra from (νe, e−) reactions on 18O and 16O in water Cherenkov detectors for supernova neutrino detection are investigated for both the cases with and without the neutrino oscillation and compared with those of the neutrino-electron scattering. It has been shown that the contribution from 18O (0.205% mixture) enhances the rates from 16O by 60% for the case without the oscillation and by 20-30% for the case with the oscillation below Te =20 MeV. For the case with the neutrino oscillation, the event rates for 18O and 16O become comparable to those of the neutrino-electron scattering. However, their rates at low energy (Te< 20 MeV) are much lower than those of the neutrino-electron scattering, which is important for the pointing accuracy to the supernova direction.

Doubly differential cross sections for ionisation in proton–helium collisions at intermediate energies: energy and angular distribution of emitted electrons

Using the two-centre wave-packet convergent close-coupling approach, we continue our study of the proton–helium collision system. This method uses a correlated two-electron wave function to describe the helium target and discretises the continuum using wave-packet pseudostates. The cross section differential in the electron-emission energy and emission angle is calculated for incident-projectile energies in the intermediate range from 70 to 300 keV, where coupling between various channels and electron–electron correlation effects are important. We also apply an alternative, simpler approach that reduces the target to an effective single-electron system. Overall, the present results from both methods agree well with the available experimental data. This positions both implementations of the two-centre wave-packet convergent close-coupling approach well to further study other doubly differential, as well as fully differential, cross sections of single ionisation in proton–helium collisions.Graphical abstract

Two-injection Scenario for the Hard X-Ray Excess Observed in Mrk 421

An interesting result that was recently reported for Mrk 421 is the detection of a significant excess at hard X-ray energies, which could provide useful information to investigate particle acceleration and emission mechanisms in the relativistic jet. Considering a two-injection scenario, we develop a self-consistent one-zone leptonic model to understand the origin of the hard X-ray excess in Mrk 421 during the period of extremely low X-ray and very high-energy flux in 2013 January. In the model, two populations of mono-energetic ultra-relativistic electrons are injected into the emission region, which is a magnetized plasmoid propagating along the blazar jet. We numerically calculate the emitting electron energy distribution by solving a kinetic equation that incorporates both shock acceleration and stochastic acceleration processes. Moreover, we infer analytic expressions relating the electrons’ acceleration, cooling, escape, and injection to the observed spectra and variability. In particular, for the injection luminosity, we derive a new approximate analytical expression for the case of continual injection with a mono-energetic distribution. Based on a comparison between the theoretical predictions and the observed SED, we conclude that the hard X-ray excess that was observed in Mrk 421 may be due to the synchrotron radiation emitted by an additional electron population, which is co-spatial with an electron population producing simultaneous optical/UV, soft X-ray, and γ-ray emissions. Therefore, stochastic acceleration may play a major role in producing the observed X-ray spectrum.

Deep-level traps in as-grown and electron-irradiated homo-epitaxial n-GaN layers grown by MOVPE

The results of junction spectroscopy measurements on deep-level defects in MOVPE (Metal–Organic Vapor-Phase Epitaxy) n-GaN samples grown on highly doped Ammono-GaN and subjected to 1.5 MeV electron irradiation are compared with the published results for epi-GaN materials grown by other techniques. It is found that in addition to the commonly observed deep-level traps in n-type GaN, such as E1 (0.25 eV) and E3 (0.59 eV), 1.5-MeV electron irradiation introduces two other electron traps, EE1 and EE2, with electronic levels at about 0.14 and 0.98 eV below the conduction band edge (EC), respectively. In the case of the EE1 level, a strong influence of the electric field (E) on the electron emission rate (eem) is observed. This suggests a donor type character of this trap level. Further, we have observed that strong electric field, as high as 2 × 105 V/cm, results in lowering the activation energy of electron emission from the EE1 level down to the value of 0.095 eV. The strong eem(E) dependence for the EE1 trap can explain the wide variation in electronic signatures of this trap reported in previous publications. The analysis of the EE1 trap concentrations in the electron irradiated samples allowed us to estimate the average production rate of this trap by 1.5 MeV electrons as 0.125 cm−1 for n-GaN material grown on Ammono-GaN substrate. A series of DLTS measurements with different filling pulse lengths revealed a complexity of the EE1 trap level structure, since at least three emission signals with different capture and emission rates have been separated within the broad EE1 emission signal. Possible origins of the detected deep-level traps are discussed.

A comprehensive analysis of electron emission from a-Si:H/Al2O3 at low energies

Recently developed microchannel plates (MCPs) based on amorphous silicon offer potential advantages with respect to glass based ones. In this context, secondary electron emission (SEE) at very low energies below 100 eV has been studied for relevant materials for these novel devices. The aim of this work was to quantify the low energy electron emission—secondary emission and elastic scattering—from amorphous silicon and alumina and the dependence of the emission energy distribution on the primary electron energy, which was previously unknown. Secondary emission and energy distribution were both modelled and measured using equipment particularly designed for this energy range. The effects of roughness, angle of incidence and surface composition were analysed. We show crossover energies as well as the angular dependence of electron emission from amorphous silicon and alumina, with a maximum experimental emission yield value of 2 and 2.8, respectively, at an incident angle of 75∘. A parameterization for the energy dependence of the emission energy spectrum at low energies was derived. This extensive analysis is fundamental for a comprehensive understanding of the performance of amorphous silicon-based MCP detectors. It provides a complete model for SEE for a detailed description of the detector operation. The present results thus set the basis for a simulation framework, which is an essential element to increase the performance of these detectors and enable further developments.

Experimental evidence for large negative electron affinity from scandium-terminated diamond

Two Sc–diamond (100) and (111) surfaces have the highest negative electron affinity for a metal adsorbed onto bare diamond measured to date, as well as being thermally stable up to 900 °C.

Формирование плазмы в атмосфере азота импульсным электронным пучком вблизи диэлектрической мишени при форвакуумных давлениях

Features of the processes of beam plasma formation near a dielectric (aluminum oxide ceramic) target being irradiated by an intense pulsed electron beam in the forevacuum pressure range (4–15 Pa) have been investigated. It has been established that the density of the beam plasma near the irradiated dielectric target is higher than in the case of "free" propagation of the electron beam. The observed increase in plasma density depends on the emission current (electron beam current), gas pressure, and accelerating voltage. The influence of the dielectric target on the beam plasma density is due to emission of electrons from the target surface and the uncompensated negative potential on the target surface, which determines the energy of emitted electrons. An increase in gas pressure leads to a smaller increase in the beam plasma density due to a decrease in the absolute value of the negative potential. Varying the electron beam current and accelerating voltage provide to control the beam plasma density.

Near-Monochromatic Tuneable Cryogenic Niobium Electron Field Emitter.

Creating, manipulating, and detecting coherent electrons is at the heart of future quantum microscopy and spectroscopy technologies. Leveraging and specifically altering the quantum features of an electron beam source at low temperatures can enhance its emission properties. Here, we describe electron field emission from a monocrystalline, superconducting niobium nanotip at a temperature of 5.9K. The emitted electron energy spectrum reveals an ultranarrow distribution down to 16meV due to tunable resonant tunneling field emission via localized band states at a nanoprotrusion's apex and a cutoff at the sharp low-temperature Fermi edge. This is an order of magnitude lower than for conventional field emission electron sources. The self-focusing geometry of the tip leads to emission in an angle of 3.7°, a reduced brightness of 3.8×10^{8} A/(m^{2} sr V), and a stability of hours at 4.1nA beam current and 69meV energy width. This source will decrease the impact of lens aberration and enable new modes in low-energy electron microscopy, electron energy loss spectroscopy, and high-resolution vibrational spectroscopy.