Ionization by impact electrons in solids: Electron mean free path fitted over a wide energy range

Abstract

We propose a simple formula for fitting the electron ionization mean free paths in solids both at high and at low electron energies. The free-electron-gas approximation used for predicting electron mean free paths is no longer valid at low impact energies ͓͑E − E F ͒ Ͻ 50 eV͔, as the band structure effects become significant at those energies. Therefore, we include the results of band structure calculations in our fit. Finally, we apply the fit to nine elements and two compounds.

Impact of hollow-atom formation on coherent x-ray scattering at high intensity

“…An important damage mechanism characteristic of extended molecular systems is impact ionization by (quasi-)free electrons [28,34,48,67,68]. For an x-ray pulse much shorter than inner-shell decay lifetimes, impact ionization by Auger electrons is irrelevant for the formation of electronic damage during the pulse.…”

“…Shake-up and shake-off processes [64][65][66] also make a small contribution to electronic damage and are not included in our model. We also neglect impact ionization [28,34,48,67,68], i.e., secondary ionization in molecules induced by photoelectrons and/or Auger electrons via (e,2e) processes. We will discuss a straightforward strategy to reduce impact ionization in Sec.…”

Simple model of bulk and surface excitation effects to inelastic scattering in low-energy electron beam irradiation of multi-walled carbon nanotubes

“…[23][24][25] and stimulated field-emission devices [26][27][28][29] using SEM or EBL, as well as in the quantitative interpretation of spectroscopic data from surface-sensitive techniques, such as X-ray photoelectron spectroscopy (XPS), Auger-electron spectroscopy (AES) and reflection-electron-energy-loss spectroscopy (REELS). 30,31 Finally, inelastic scattering of low-energy electrons is also important in understanding irradiation effects by high-energy ion beams [32][33][34] or from various X-ray sources 35,36 due to the role of secondary electron cascades in the spatial distribution of energy absorption in the material.…”

X-ray induced optical reflectivity

“…1, 2 X-ray absorption by a deep core electron produces an energetic photoelectron and typically one or more Auger electrons (or a fluorescence photon) that lose their energy by strong inelastic scattering with valence electrons, leaving behind multiple core holes. 3,4 The increase in conduction electrons and valence holes causes an abrupt change in optical reflectivity, which makes the x-ray pump optical probe technique a valuable tool for characterizing the dynamical response of the material as well as the temporal characteristics of the incident x-ray pulse. 5,6 Optical pump optical probe studies have long been used to observe dynamical responses in a variety of materials, especially with the advent of high power femtosecond lasers.…”

“…To estimate this, we consider the conditions described by Krupin et al 10 for XFEL pulses of 50-150 fs at 500-2000 eV, with a pulse energy of 1 mJ deposited in a 0.6 mm 2 spot size. Assuming a GaAs target, 800 eV photons with a ∼0.6 micron attenuation length, and that all of the x-ray energy ultimately goes into electron-hole pair creation at ∼10 eV per pair, 3 the induced conduction electron density is a durbin@purdue.edu 2158-3226/2012/2(4)/042151/7 C Author(s) 2012 2, 042151-1 2 × 10 21 cm −3 , or 1% of the valence electron density. While this corresponds to an extremely high doping level in a semiconductor, it is less than what is experimentally observed to create a metallic transition or irreversible damage in GaAs using optical laser pulses.…”