C.J. Tung

Electron inelastic mean free paths and energy losses in solids II: Electron gas statistical model☆☆☆

Abstract A statistical model for the calculation of inelastic mean free paths and energy losses of electrons in solids is described. Results for the application of the model to the six solid media Al, Au, Ag, Cu, Ni, and Si are presented. Agreement between calculated mean free paths and experimental attenuation lengths indicates that the statistical model provides a useful method in the little-studied electron energy range from a few tens of electron volts to 10 keV.

Electron inelastic mean free paths and energy losses in solids: I. Aluminum metal

Abstract Inelastic mean free paths and energy losses in aluminum metal are calculated for electrons with energies from a few eV to 10 4 eV above the Fermi level. We have represented the contribution from excitations of the valence electrons by using an electron gas model. The effect of damping in the electron gas on the mean free path and energy loss is included within the context of the Mermin-Kliewer-Fuchs model of the electron gas dielectric function. The influence of core polarizability and local field corrections are discussed briefly. The contributions to the mean free path and energy loss of electrons from ionization of inner shells have been evaluated from atomic models. Comparisons are made with experimental data taken over a wide range of energies.

Surface excitation parameters of low-energy electrons crossing solid surfaces

The surface excitation parameter, which describes the influence of surface excitations by electrons for the vacuum side in electron spectroscopies, has been calculated for electrons of 200-2000 eV energies crossing surfaces of Cu, Ag, Au, Fe, Pd, Ni, MgO and SiO 2 , These calculations were performed for both incident and escaping electrons by the use of dielectric response theory. Spatially varying differential inverse mean free paths for surface excitations as a function of electron distance from the surface were found. The results showed that small differences existed in the surface excitation parameter among different metals but large differences occurred between metals and semiconductors or insulators, Calculated surface excitation parameters were fitted very well to a simple formula, i.e. P. = aE -b , where P. is the surface excitation parameter and E is the electron energy.

ELECTRON INELASTIC MEAN FREE PATHS FOR PLASMON EXCITATIONS AND INTERBAND-TRANSITIONS

Abstract Both plasmon excitations and interband transitions are important in the response of valence bands to fast electrons. An extended Drude dielectric function was established to describe such a response in solids of complex band structures. Parameters in this function were determined by a fit of the imaginary part of the function to experimental optical data. The real part of the dielectric function and the energy-loss function were also checked with experimental data to confirm critical-point energies in the interband transitions and plasmon energies in the collective excitations. In addition, sum-rules about the imaginary part of the dielectric function and the energy-loss function, respectively, were applied to assure the accuracy of these functions. Electron inelastic mean free paths in several solids were calculated and compared to available experimental and theoretical data.

Calculations of mean free paths and stopping powers of low energy electrons (⩽ 10 keV) in solids using a statistical model

A statistical model is described and employed to calculate inverse mean free paths and stopping powers for electrons of energies from a few eV to 10 keV above the Fermi level in Al, Si, Ni, Cu, Ag, and Au. Brief tables of mean free paths and stopping powers for these solids are presented. In some cases graphical displays of inverse mean free paths and stopping powers are also included. The calculations based on this model are discussed and compared with previous work.

Electron Slowing-Down Spectra in Solids'

Some theoretical methods used to describe the interaction of electrons with metals, semiconductors, and insulators are reviewed. Calculations of electron slowing-down spectra using these methods are presented for Al, Cu, Cr, Si, and Al

Inelastic Interactions of Electrons with Polystyrene: Calculations of Mean Free Paths, Stopping Powers, and CSDA Ranges

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Survey of computed tomography scanners in Taiwan: Dose descriptors, dose guidance levels, and effective doses

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Analyses and applications of single scan dose profiles in computed tomography

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Determination of guidance levels of dose for diagnostic radiography in Taiwan

. Experimental electron slowing-down spectra for these materials are also presented and comparisons with theoretical calculations are discussed. 40 refs. (auth)