Energy spectra of electrons reflected from layered targets

Here we consider backscattering of electrons with an initial energy from 10 keV to several MeV by plane-parallel sandwich targets. Using invariance principles, we obtain a formula describing the changes in the energy spectra of electrons reflected into a given solid angle. These changes occur with increasing thickness of films of different materials on substrates of finite and infinite thickness. We present methods for calculating the reflection and transmission function used in the above calculation. Repeating this method for each layer gives the spectra of electrons backscattered by multilayer targets. Comparison with experimental data shows that the theory developed adequately describes the process of electron backscattering. Our results indicate that the spectroscopy of nonelastically reflected electrons could be very useful forin situ nondestructive express analysis of depth profiles of multicomponent materials.     

Energy spectra of light ions backscattered from random solids

A scheme for the calculation of energy spectra of ions backscatterred from random solids is proposed for the energy region where multiple collisions dominate. Calculations are performed for light ion bombardment of heavy targets, which is a case of special interest for the plasma-well interaction in fusion reactors. Examples of spectra obtained for protons incident on a Cu target are presented. A maximum in the spectra is found in accordance with measurements. The position of the maximum seems to vary slowly with the initial ion energy.     

Features of bremsstrahlung from relativistic electrons in solid targets

It has been shown that the classical Bethe-Heitler result can be inapplicable for describing the bremsstrahlung spectrum of relativistic electrons in real solid targets.     

Energy and angular distributions of backscattered electrons from collisions of 5 keV electrons with thick Al,Ti, Ag,W and Pt targets

The energy and angular distributions of backscattered electrons produced under the impact of 5 keV electrons with thick Al, Ti, Ag, W and Pt targets are measured. The energy range of backscattered electrons is considered between E _B = 50 eV and 5000 eV. The angle of incidence α and take-off angle θ are chosen to have values α = 0 and 10 and θ = 100, 110 and 120 respectively. The measured energy spectra are compared with the available theoretical models for α = 0 and 10. The elastic peak intensity of backscattered electrons is found to be a function of angle of incidence, take-off angle and atomic number of the target material. The considered theories are reasonably in good agreement with experiment for the energy spectra of the backscattered electrons having their reduced energies ∈ (= E _B/E ₀) in the range of 0.20 to 1.00.      

Energy spectra of secondary electrons ejected by ions from foils

Secondary electron spectra in the energy range below 3.5 keV arising from the passage of α-particles and fission products through thin carbon and gold foils are presented and compared to gas target spectra and theoretical calculations which include the slowing down and the angular scattering of the electrons in the foil. A good agreement between the calculation and the experimental results is found. The shape of fission product induced electron spectra differs systematically from that of light ion induced spectra. Total yields and mean energies of the secondary electrons are derived from the spectra.     

Energy spectra of electrons in plasma accelerators

The acceleration of electrons in the fast (relativistic) plasma wave, generated, e.g., by intense laser pulse in an underdense plasma, is studied theoretically and numerically. The analytical method, developed to describe the energy spectrum of electrons accelerated in one-dimensional (1-D) plasma wave of an arbitrary form, predicts the “bunching” of electrons in the energy space for linear (harmonic) plasma wave in contrast to the nonlinear one. The results of one- and two-dimensional (2-D) numerical simulations of the resonant and nonresonant electron bunch acceleration are presented and discussed     

Energy spectra of electrons in a crystal

The characters are given for the irreducible nonequivalent weighted corepresentations for all possible types of coequivalent weights for groups D₂h, D_4h, and D₆h.     

Energy spectra and charge fractions for keV hydrogen and helium backscattered from silicon

Energy spectra and charge fractions for hydrogen and helium backscattered from silicon targets are reported. The primary energy of the incident particle varies from 5 to 15 keV. The backscattered energy distributions are measured down to 500 eV and the results are compared to a Monte-Carlo computer simulation. Good agreement is found between the theoretical model and the experimental data. Charge fractions are measured by differentiating between scattered ions and neutrals. For hydrogen, neutralization occurs primarily at the surface for the backscattered particles and no depth effects are found. Helium shows a large peak in the ion yield for surface scattering with a much reduced ion yield for particles scattered from within the solid.     

Energy spectra of electrons and depressed potential collector in gyrotrons

Energy distributions of electrons after their interaction with RF field in the gyrotron with the output power 1 MW and frequency 140 GHz are calculated. The energy spectra evolution is studied for the cases when velocity spread, pitch-factor, beam current and cyclotron frequency change. The efficiency of one- and two stage energy recovery systems are investigated.     

利用渡越辐射研究超热电子在固体靶中的输运过程

为了探索超热电子的输运过程，在100 TW掺钛蓝宝石飞秒激光器上利用光学CCD相机和OMA光学多道分析仪，分别在靶背表面法线方向测量了光发射空间分布图案和光谱. 实验测量结果显示，光发射空间分布图案呈圆盘状，在圆盘中明亮而强的光信号呈局部化分布，该现象表明，超热电子在输运的过程中存在成丝效应，引起严重的不稳定性；光发射光谱在3倍频和3/2倍频附近出现尖峰，分别是3次谐波和3/2次谐波，这一现象归因于超热电子束在传输的过程中产生的微束团而引起的相干渡越辐射(CTR)；光发射光强随靶厚度的增加而减小. 关键词： 超热电子 相干渡越辐射 输运 不稳定性     

Energy calculation of electrons in solid solutions of isovalent substitution

In the given paper the dependence of the electron energy on the concentration of isoelectronic impurity in solid solutions is discussed. The algorithm of calculation of the electron energy in substitutional isoelectronic solutions with the prescribed error of the approximation theory is found.     

Site-specific recoil diffraction of backscattered electrons in crystals

A novel diffraction effect in high-energy electron backscattering is demonstrated: the formation of element-specific diffraction patterns via nuclear recoil. For sapphire (Al(2)O(3)), the difference in recoil energy allows us to determine if an electron scattered from aluminum or from oxygen. The angular electron distribution obtained in such measurements is a strong function of the recoiling lattice site. These element-specific recoil diffraction features are explained using the dynamical theory of electron diffraction. Our observations open up new possibilities for local, element-resolved crystallographic analysis using quasielastically backscattered electrons in scanning electron microscopy.     

Argon L x-ray spectra from collisions of argon ions with various solid state targets

Spectral measurements have been made of Ar-L-shell X-rays produced by Ar ions incident on various solid state targets. Different spectra have been observed for targets with Z < 18 and Z > 18 respectively. The data are discussed within the framework of the electron promotion model of Barat and Lichten.     

Control of strong-laser-field coupling to electrons in solid targets with wavelength-scale spheres

Irradiation of a planar solid by an intense laser pulse leads to fast electron acceleration and hard x-ray production. We have investigated whether this high field production of fast electrons can be controlled by introducing dielectric spheres of well-defined size on the target surface. We find that the presence of spheres with a diameter slightly larger than half the laser wavelength leads to Mie enhancements of the laser field which, accompanied by multipass stochastic heating of the electrons, leads to significantly enhanced hard x-ray yield and temperature.     

Energy and momentum relaxation of electrons in bulk and 2D GaN

We present our experimental and theoretical studies regarding the energy and momentum relaxation of hot electrons in n-type bulk GaN and AlGaN/GaN HEMT structures. We determine the non-equilibrium temperatures and the energy relaxation rates in the steady state using the mobility mapping technique together with the power balance conditions as described by us elsewhere [N. Balkan, M.C. Arikan, S. Gokden, V. Tilak, B. Schaff, R.J. Shealy, J. Phys.: Condens. Matter 14 (2002) 3457]. We obtain the e–LO phonon scattering time of 8 fs and show that the power loss of electrons due to optical phonon emission agrees with the theoretical prediction. The drift velocity–field curves at high electric fields indicate that the drift velocity saturates at approximately 3×10⁶ cm/s for the two-dimensional structure and 4×10⁶ cm/s for the bulk material at 77 K. These values are much lower than those predicted by the existing theories. A critical analysis of the observations is given with a model taking into account of the non-drifting non-equilibrium phonon production.     

Energy spectra of electrons in crystals part 6. Associated corepresentations

A study is reported for the conditions under which time reversal for associated weighted representations lead to associated weighted corepresentations.