Electron inelastic mean free path and stopping power modelling in alkali halides in the 50 eV–10 keV energy range

Abstract

A model for calculating the electron inelastic mean free path and stopping power in insulators in the 50 eV–10 keV energy range is presented. Both valence and core electron contributions have been considered. The valence part has been estimated following the dielectric theory modified to include the energy gap; the core contribution has been evaluated on the basis of the classical binary encounter theory. Inelastic mean free path and stopping power calculations based on this model have been performed for several alkali halides: LiF, NaCl, KCl and CsI. They are compared to existing experimental data and Penn model’s predictions for the mean free path and to Bethe’s values for the stopping power; a fair agreement is found for incident electron energies higher than 100-200 eV.

Inelastic Electron Interactions in the Energy Range 50 eV to 10 keV in Insulators: Alkali Halides and Metal Oxides

“…Unfortunately, we have no data to determine any IMFP dependence on atomic number of the alkali metal for a given halide. Comparing the KI and CsI [39] IMFPs does not show any relevant difference over the whole energy range considered. These conclusions are also consistent with the tight-binding model [2].…”

“…In the case of LiF, there is a clear separation between collective valence-band excitation and interband transitions and hence the plasmon excitation is beyond any doubt. Using the dielectric function (4) for LiF with the fitting parameters given in [39], we estimated the plasmon inverse IMFP to be 70% of the total inverse IMFP. Our estimate agrees with the 60% contribution of the plasmon decay to the SEE spectrum as estimated in [56].…”

“…It would be preferable to use an OLF that could be confirmed by EELS measurements. Indeed, in the case of KC1, where the experimental OLF and EELS are very close, the error is less [39]. Despite other sources of uncertainties noted above, the inaccuracy of the experimental OLF or EELS data is assumed to be the main source of errors when one calculates the IMFP.…”

“…Despite other sources of uncertainties noted above, the inaccuracy of the experimental OLF or EELS data is assumed to be the main source of errors when one calculates the IMFP. In Table5, we summarize the calculated mean ionization potentials 7 for the materials presented in this article and those considered in our previous publication [39], together with the accepted data [32] for this quantity or estimated values using the adopted rules for its calculation in the case of compound materials. One can see that the agreement is quite good except for BeO.…”

Material characterization and modification using helium lon microscopy : various examples

“…Moreover, we do not observe a significant difference in shape between the PSF function and the curve obtained from SRIM. This is because of the short electron mean free path of only 1-2 nm in NaCl [153,154]. Unfortunately, we do not have experimental data for radial distances smaller than 40 nm.…”