Material dependence of electron inelastic mean free paths at low energies

Abstract

We present and discuss electron inelastic mean free path (IMFP) data for aluminum and gold in the 50–200 eV range. These elements serve as examples of IMFP calculations that have been made for 50–2000 eV electrons in 31 materials (27 elements and 4 compounds). Substantial differences are found in the shapes of the IMFP versus energy curves for Al and Au and these can be understood in terms of the different inelastic scattering mechanisms in the two metals. The minimum IMFP value occurs at 40 eV in aluminum and at 120 eV in gold, a result which is consistent with the trends expected from free-electron IMFP calculations. This result differs, however, from that expected from the Seah and Dench attenuation length formula which shows essentially no material dependence at low energies. We have extended a general formula derived earlier to describe the calculated IMFPs over the 200–2000 eV energy range to give the IMFP dependences on material and energy from 50 to 2000 eV.