摘要:

The incident angle dependence of ion-induced kinetic electron emission (KEE) from Cu is calculated in the energy range from 100 eV to 1 MeV, using a Monte Carlo simulation of transport of incident ions (H+and Xe+) and recoiling target atoms and a semiempirical theory of KEE. The calculated results are in good agreement with the experimental data and reveal dominant effects of backscattering ions and recoiling target atoms on the deviation from the inverse cosine law for light and heavy ion impacts, respectively.

ISSN:1042-0150    

DOI:10.1080/10420159408219776

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A review is given on single-electron mechanisms, which dominate the electronic energy transfer processes of light ions in gases and solids. In the case of gas targets, it will be shown that it is possible to perform highly accurate ab-initio stopping power calculations which cover the range of incident energies from a few eV/u up to the Bethe regime. First principle calculations are applied to the stopping of p, H+, H0, He2+and Li3+in H and He gas targets. The resulting discrepancies to experimental data are about 10% or less and can be attributed to two-electron processes. Strong deviations from the usually assumed velocity proportionality at low incident energies as well as pronounced Z1dependencies are found and will be discussed. Furthermore, it will be shown that neither a single-harmonic-oscillator model nor local-density electron-gas approaches allow for a reliable prediction of the impact parameter dependence of the mean energy transfer. In the case of solids, perturbation theory is applied to the stopping of low energy ions in alkaline metals. These calculations include Bloch wavefunctions of Wigner-Seitz type obtained from a Hartree-Fock-Slater calculation and allow for a prediction of the mean energy loss under channelling conditions. Results of the most widely used free-electron gas approximation will be compared to data of our more complete treatment. Additionally, simple scaling laws for the stopping of light ions in gases and solids may be extracted from our results.

ISSN:1042-0150    

DOI:10.1080/10420159408219777

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A Monte Carlo code is described which simulates angle resolved Auger electron energy spectra from highly charged ion surface interaction. The combined effect of the Doppler spread of laboratory emission energy and electron scattering by the solid, together with the broad inherent line width, is found to have considerable influence on the spectral lines. As a new feature, low or high energy shoulders can appear. By comparison between simulated and measured spectra information on the kinematic and electronic state of the projectile ions in the moment of electron emission can be extracted. The standard method of spectrum analysis, which is based on the assumption of direct escape of the electrons, is evaluated with respect to the simulated spectra.

ISSN:1042-0150    

DOI:10.1080/10420159408219778

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Resonant loss and capture transition rates, distances of neutralization and total number of neutralized protons are calculated for different bound states (n = 2 to n = 6) of 25 keV protons scattered by an A1(111) surface. Due to the importance that the orientation of the orbital shows when these quantities are calculated, the perturbation introduced in the atomic levels by the image potential is analyzed for the level n = 2. First order perturbation theory and the specular reflection model with the surface plasmon pole approximation are used. The linear coefficient of the plasmon dispersion relation is calculated as a function of the distance from the jellium edge to the image plane. The transition rates and the equilibrium populations of the new eigenstates are presented as a function of the velocity of the protons, and compared with the results obtained for the unperturbated states.

ISSN:1042-0150    

DOI:10.1080/10420159408219779

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Computer simulation studies of the energy distribution of transmitted ions such as alpha-particles, He-, and B-ions through crystalline silicon, using the enhanced binary-collision cascade simulator MARLOWE, will be reviewed. The enhancement includes an additional electronic-energy loss (EEL) model which takes into account explicitly both the target electron density variation via the structure factors and the electron density of the projectile. Investigations of the stopping power for He ions and protons in silicon, at intermediate- and high-energies, based on the adapted EEL model and a velocity-dependent effective charge will be presented. The overall agreement between the calculated and experimentally determined stopping power data and the simulated and measured transmission spectra will be demonstrated. Effects of energy-loss straggling, core-electron contribution to the energy loss at high-energies and charge-state effects at low energies on the transmission spectra will also be discussed.

ISSN:1042-0150    

DOI:10.1080/10420159408219780

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Computer simulations using molecular dynamics (MD) have become the standard tool to describe the dynamics of energetic collision cascades. However, several problems concerning the physical description within MD schemes still remain open. One of the most challenging is the fact that MD simulations describe the thermal behavior of an insulator, neglecting the conductivity due to electrons. In this work we review some of the relevant ideas proposed to incorporate this effect.

ISSN:1042-0150    

DOI:10.1080/10420159408219781

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

When high-energy electrons penetrate crystalline matter, the successive processes of photon emission and pair production form an electromagnetic shower. If the incident electrons are directed along the crystal axis, the cross section for photon emission is drastically enhanced because electrons in ‘channeling’ states feel a strong electric field continuously. Experiments designed to detect this effect were performed at CERN. The results showed an anomalous peak in the energy loss spectrum of the emerging electrons. In this paper, we report results of a Monte-Carlo simulation of shower formation in a Germanium crystal. Our results agree with the experimental data more quantitatively than previous simulations. We simulated a shower formation by incident photons as well.

ISSN:1042-0150    

DOI:10.1080/10420159408219782

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Electron emission statistics (ES) of proton-induced electron emission from Au at keV energy are investigated by applying a Monte Carlo model to describe the transport of electrons. Apparent deviations of ES from Poisson distributions are found in the same manner as experimental ES: larger probabilities for no electron emission and for emission of 2 or more electrons. At low energy, electron cascades produce an important deviation from the Poisson distribution, in addition with deviations due to the backscattering of incident ions.

ISSN:1042-0150    

DOI:10.1080/10420159408219783

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The interaction of small energetic clusters of metal atoms with surfaces has been investigated by molecular dynamics computer simulations. A wide variety of cluster-solid combinations have been studied so that the effects of the energy, size, and angle of incidence of the cluster, and the relative elastic properties of the cluster and substrate could be elucidated. ‘Soft landings’ were also investigated. From these studies, a mechanism map for cluster-solid interactions is developed. The results have particular importance for cluster beam deposition of thin films. The simulations are fully dynamical and 3-dimensional; they employ embedded-atom method potentials, which have been modified for interactions at close separations. A scheme for reducing the CPU time that is required for these and other simulations of radiation effects is described.

ISSN:1042-0150    

DOI:10.1080/10420159408219784

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The time-evolution Monte Carlo simulation code DYACAT is applied in order to investigate the depth profiles of big cluster impacts on amorphous targets, using three different cluster-target combinations. For (Ag), cluster impacts on A1, the recoil A1 atoms clear the way for the cluster Ag atoms coming afterwards. The projected range of an (Ag)500cluster is about four times larger than that of a monoatomic ion. In the case of the (Al)ncluster impacts on Ag, the clearing-the-way effect is not so large if n < 100, and the frontrunners are the cluster atoms in the lower part of the cluster. In the case of the (D)<ncluster impacts on Ag, there is no clearing-the-way effect. The projected range of a big (D)ncluster is slightly less than that of the monoatomic ion due to the enhanced energy removal at the surface.

ISSN:1042-0150    

DOI:10.1080/10420159408219785

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor