Wide Range Of Electron Energies Research Articles

Electron impact excitation of Ca XX: collision strengths and rate coefficients

Collision strengths for all transitions belonging to states up to the n=5 level of Ca XX are calculated in a wide electron energy range below 520 Ryd. These are obtained from the standard R-matrix program for all partial waves with L<or=12 and the no-exchange R-matrix program for 12<L<or=40. The resonances are delineated in the threshold energy region and collision strengths are tabulated at a few representative energies above threshold. These have also been integrated over a Maxwellian distribution of electron velocities to calculate the effective collision strengths. The results so obtained are tabulated for all transitions in an electron temperature range of log Te=5.0-7.2 K.

Deep-level defects and numerical simulation of radiation damage in GaAs solar cells

Abstract A review of the deep-level defects observed in both electron- and proton-irradiated GaAs solar cells is presented. Studies of the effects of periodic and continuouss thermal annealing on the radiation-induced electron and hole traps and the recombination parameters in GaAs solar cells were made for a wide range of electron and proton energies, fluence, annealing temperature and annealing time. A refined model for numerical simulations of the displacement damage was developed for computing the defect density and the cell parameters in the electron- and proton-irradiated GaAs solar cells. excellent agreement was obtained between the calculated values and the experimental data for the proton-irradiated GaAs solar cells.

Low-voltage scanning electron microscopy: A surface sensitive technique

The advancements in electron optics have made it possible to cover a wide electron energy range without significant degradation in the imaging quality of a scanning electron microscope. The secondary electron emission and the surface sensitivity are enhanced when using low voltages. The addition of an energy dispersive x-ray spectrometer with a thin window allows the detection of low energy emission lines, thus making the technique comparable, or at least complementary to surface techniques such as Auger electron and x-ray photoelectron spectroscopies. In this paper, aspects of low-voltage SEM are discussed and factors affecting the secondary electron images are examined. The surface sensitivity is evaluated and is compared to Auger electron spectroscopy. Study cases from the printed circuit board manufacturing area are presented.

Ionization of Tiq+, Crq+ and Niq+ Ions by Electron Impact

The cross sections and corresponding rate coefficients averaged over a Maxwellian velocity distribution for direct ionization of Tiq+ and Niq+ with 1 ⩽ q ⩽ 10 and all stages of Crq+ ions were calculated using the Born-Oppenheimer approximation with orthogonalized wavefunctions. For each ion the ionization of electrons from two outer shells was taken into account. The numerical data are approximated in a wide range of electron energy and temperature by analytical formulas containing two fitting parameters. The tables of these parameters are given together with the error of analytical approximation. The results of calculations are compared with recommended data.

A computer program for the free-free and bound-free Gaunt factors of Rydberg systems

A computer code for the calculation of the quantum mechanical free-free and bound-free Gaunt factors of Rydberg system is described. FORTRAN sources are given which are numerically stable for a wide range of photon and electron energies. Temperature averaged values of the free-free Gaunt factors are also computed for a Maxwellian electron distribution.

Combined apparatus for x-ray photoelectron spectroscopy and extended x-ray absorption fine structure method using synchrotron radiation

A combined apparatus for Synchrotron Radiation (SR) was designed and developed in order to analyze the structure and properties of the solid surface. Two kinds of analyses; x-ray photoelectron spectroscopy (XPS) and x-ray absorption spectroscopy (XAS), are available using a 180° hemispherical electrostatic analyzer and/or other detection systems. High resolution XPS spectra were achieved with high signal-to-background ratio over a wide electron energy range up to 2600 eV using a monochromatized x ray (2600 eV) from SR. XAS spectra were obtained in two modes of total electron yield and Auger electron yield. The two modes described are complementary.

Cross Sections and Rate Coefficients for Inelastic Electron Collisions with Carbon and Oxygen Ions

The cross sections and rate coefficients (averaged over a Maxwellian distribution) for excitation and ionization of hydrogen-, helium, lithium- and beryllium-like ions of carbon and oxygen are calculated in the Coulomb-Born-Exchange approximation. The numerical data are approximated in a wide range of electron energies and temperatures by analytic formulae containing two fitting parameters. These parameters are tabulated. The error of analytic approximation is given also and the numerical data of this work are compared with the numerical results of the most advanced theoretical calculations.

The energy dependence of electron inelastic mean free paths

AbstractAn analysis has been made of the dependence on electron energy of calculated inelastic mean free paths (IMFPs) for aluminum, copper, silver, and gold from four recent sources of data. The analysis was made using Fano plots which clearly show differences in energy dependences. In addition, the slopes of linear regions in the Fano plots can be compared with values calculated from experimental optical data and with values obtained from Fano plots made with experimental attenuation length (AL) data. It was found that the slopes of the Fano plots using IMFPs from calculations of Powell and Penn agreed well with the optical results; there was generally good agreement for the IMFPs of Ashley et al., but the slopes using the IMFP data of Szajman et al. exceeded the optical values by 9–40%. The slopes in the Fano plots using AL data for Al, Cu, and Au exceeded the optical values by 29–54 %; this result is similar to those found in other analyses and indicates that the electron energies for these AL measurements were not high enough to be in the asymptotic Bethe region. Analysis of the optical data also showed that a lower limit for the electron energy range over which the Fano plots could be expected to be linear (with their asymptotic slopes) was about 400 eV for Al and about 1000 eV for Cu, Ag, and Au. More extensive AL measurements over a wide electron energy range are needed to determine the shapes of the Fano plots for different types of materials.

Electron-impact excitation of He-like ions: Mg XI.

The collision strengths for the electron-impact excitation of inelastic transitions in Mg xi have been calculated by use of the R-matrix method. Eleven lowest LS target states 1${s}^{2}$ ${}^{1}$S, 1s2s ${}^{1}$,3S, 1s2p ${}^{1}$,3P\ifmmode^\circ\else\textdegree\fi{}, 1s3s ${\mathrm{}}^{1}$,3S, 1s3p ${\mathrm{}}^{1}$,3P\ifmmode^\circ\else\textdegree\fi{}, and 1s3d ${\mathrm{}}^{1}$,3D are included in the expansion of the total wave function. These target states are represented by accurate configuration-interaction wave functions. The lower partial-wave (L\ensuremath{\le}8) results obtained in the R-matrix method are supplemented by higher partial waves obtained in the close coupling with exchange terms omitted (L=9\char21{}15), Coulomb-Born (L=16\char21{}36), and Coulomb-Bethe (Lg36) approximations. Rydberg series of resonances converging to n=2 and 3 thresholds are considered in the calculations. Results are obtained over a wide electron energy range (97.66\char21{}350.0 Ry) and are compared, where possible, with the previously available five-state Coulomb-exchange distorted-wave approximation results of Bednell. These collision strengths are then integrated with the assumption of a Maxwellian distribution of electron energies to obtain effective collision strengths for temperatures between ${10}^{5}$ and 4\ifmmode\times\else\texttimes\fi{}${10}^{7}$ K.

Weight functions for integral conversion electron mössbauer spectroscopy (ICEMS)

Weight functions for ICEMS, computed from Monte Carlo simulation of electron transport, are tested for scaling properties. It is shown that energy scaling holds with high accuracy for a wide range of materials and electron energies. Mass scaling from iron to other materials is shown to be adequate except for low atomic number materials.

Processes of annealing and defect generation in semiconductors irradiated by supercurrent electron beam

Abstract The positron annihilation method (PA), Rutherford back scattering of channeled ions (RBSCI) and measurements of minority charge carrier lifetimes (MCCLT) combined have been used to investigate the processes of annealing and defect generation in semiconducting crystals affected by supercurrent electron beam (SEB). We used silicon samples phosphorous doped in the process of their growing (N≃1.7-1016cm−3), or boron doped (N≃2.3·xs1017cirr3) and implanted by phosphorous ions (D≃5.1014cm−2) of 30 keV energy as well as GaAs samples tellurium doped (N=2.6 1016cm−3) or implanted by Te ions (D≃3.1013cm−2 and 1.2-1016cm−2) of 75 keV energy. Dependences of PA parameters and X minimum yield on the SEB energy density within the wide electron energy range have been obtained. The dependences have three regions: 1. Plateau when the beam effect cannot be detected by any of the methods used (the density being ⩽ 0.250 Joule/cm2 for vacancy type defects and 0.4 Joule/cm2 for interstitial atoms); (2) The annealing st...

Versatile temperature controller for the investigation of surface phenomena

The design, construction, and performance of a stable temperature controller specifically built for surface studies is described. The controller can be operated either manually as an independent unit or automatically while interfaced to a digital signal analyzer, a computer, or an external programmer. Problems arising from the magnetic field generated by sample heating current are eliminated, allowing detailed studies of surface phenomena by electron spectroscopies over a wide range of temperatures and electron energies.

Distribution of the excitation density in electron-beam-pumped semiconductor lasers

The Monte Carlo method is used to calculate the spatial distribution of the density of the absorbed energy and the dimensions of the excited region in GaAs and CdS semiconductor lasers excited by beams of electrons of energies from 10 keV to 20 MeV. The results of the calculations are used to derive an approximate analytic expression convenient for the determination of the distribution of the density of the absorbed energy with depth in the material in a wide range of electron energies. A considerable reduction in the maximum value of the density of the absorbed energy of the pump electrons occurs when the electron beam diameter is small. This is one of the reasons for the increase in the lasing threshold (expressed in terms of the pump current density) on reduction in the size of the electron beam used to excite a laser.

Design of a passive magnetic shunt for the extraction of electron beams from a photon tagging spectrometer

A method is described in which a passive magnetic shunt is used to provide clean extraction of primary electron beams from a photon tagging spectrometer. For a wide range of magnetic fields and incident electron energies, the point at which the primary beam leaves the system can be very well localized. The design, fabrication and testing of the magnetic shunt are described.

Virtual photon spectrum in second-order Born approximation

We have evaluated expressions for E1 and M1 virtual photon spectra for relativistic electron scattering in second order Born approximation and included the effects of finite nuclear size and charge. The scattering amplitude can be evaluated analytically provided the elastic and inelastic form factors contain only poles. We have observed that the virtual photon spectrum is insensitive to details of both form factors over a wide range of electron energy and depends only on the nuclear rms radius and transition radius. The integral over the physical momentum transfer is performed numerically. We have evaluated spectra for electric dipole and magnetic dipole radiation for electron energies in the range 10--200 MeV and compared with distorted wave calculations. Except for low energy and high Z, our results compare well. A range-of-validity plot is given for each multipole, distinguishing regions of electron energy and mass number where the second order calculation is adequate and also those where the first order term alone would be sufficient and where the conventional long wavelength limit is applicable. Comparison with data on the excitation of the 16.3 MeV isobaric analog state in /sub 40//sup 90/Zr yields excellent agreement with no adjustable parameters.

Backscattering in electron beam therapy for energies between 3 and 35 MeV

Whenever a heterogeneity is present in an electron beam treatment field during radiotherapy, there is the possibility of tissue overdosage at the tissue-heterogeneity interface due to electrons backscattered from the heterogeneity. Measurements of this effect were made in a polystyrene phantom using a purpose-built thin-window parallel-plane ionisation chamber. Materials of various atomic numbers were used as scatterers and the investigations were made over a wide range of electron energies. Electron backscatter factor (EBF), defined as the ratio of dose at the interface surface with and without the scatterer present, was found to increase with increasing atomic number and decrease with increasing beam energy. Both of these relationships were found to be non-linear. The EBF dependence on the scatterer thickness was also investigated. All data in this work were expressed in relation to the beam energy incident on the scatterer in preference to the nominal beam energy set on the accelerator. This approach enables the dose enhancement at an interface to be predicted from a knowledge of the heterogeneity (atomic number and thickness), its depth in tissue and the beam energy being used for treatment. The results of this work were compared with the published data and an explanation is offered to account for the difference.

Cross sections and rates for direct electron-impact ionization of sodiumlike ions

Cross sections and rate coefficients for the direct electron-impact ionization of sodiumlike ions have been calculated in a distorted-wave Born exchange approximation. For higher charge states the cross section is dominated by inner-shell ionization of the $2{p}^{6}$ subshell. Analytic fits to the data allow rapid calculation of cross sections and rate coefficients over a wide range of incident electron energies. The importance of electron-impact excitation to autoionizing states is discussed.

Spectroscopic diagnostics of CF4-O2 plasmas during Si and SiO2 etching processes

The emission intensities in the range of 2000–8000 Å of CF, CF2, O, F, CO, CO+, and CO2 produced in CF4/O2 radio-frequency discharges, operated at 1 Torr of pressure and 50 W of power input, have been used to follow the etching process of Si and SiO2, as a function of the CF4/O2 feed composition. The addition of small amounts of nitrogen or argon to the plasma mixtures has permitted the determination of the effect of the oxygen addition to the gas feed on the electron densities of the plasma for a wide range of electron energies. The relative concentration profiles of F and O, as well as of CO and CO2, have been determined with this technique, as a function of the oxygen content in the feed. The important role played by atomic F as active etchant for both Si and SiO2 substrates has been confirmed.

A secondary electron spectroscopy and electron energy loss spectroscopy study of the interaction of oxygen with a polycrystalline aluminum surface

The interaction of oxygen with a polycrystalline aluminum sample has been studied using electron energy loss spectroscopy (ELS) and secondary electron spectroscopy (SES) over a wide range of primary electron energies (30 ⩽ E p ⩽ 250 eV). The use of low primary electron energies enables the detection of interband transitions previously unobserved in reflexion energy loss spectroscopy. For E p > 100 eV, the ELS spectrum is dominated by the plasmon loss structures while for E p below the plasmon excitation threshold only single electron transitions appear. The fine structure in the clean aluminum SES spectrum is attributed to plasmon decay into single electron excitations. For oxygen covered aluminum it may be due to electron scattering on the O 2p and O 2s oxygen induced orbitals.

Design considerations and performance of an analytical stem

A VG Microscope HB5 has been modified in collaboration with the manufacturers. The major modifications are the addition of three post specimen lenses, a second condenser lens and a z-lift on the specimen stage. The requirements of the various parts of the microscope are reviewed and the compromises made necessary their interaction are discussed. The performance of the double condenser system, the z-lift stage and the high excitation objective lens are discussed briefly. A more detailed discussion of the expected performance of the post-specimen optics is given and preliminary experimental results are presented. The discussion is in two parts. The first part considers the recording of diffraction patterns and the use of detectors in the diffraction plane. The major effect is the distortion introduced by the lens system. By a suitable choice of operating conditions, this can be minimised. The second part considers the use of an electron spectrometer. Large chromatic effects can occur if a wide range of electron energies is involved. Provided that the correct lens configuration is used, these may prove to be an advantage since it is possible to produce an increase in collection efficiency with increasing energy loss. Finally, the effect of using an electron spectrometer with lower aberrations in conjunction with the post-specimen lenses is considered briefly.