Electron inelastic mean free path in solids as determined by electron Rutherford back-scattering

Energetic electrons scattering elastically over large angles from atoms lose energy depending on the mass of the scattering atom. If the energy of the incident electron is large enough, 10's of keV, this energy loss can be measured with high resolution electron spectrometers, allowing the separation of heavy and light elements. This technique is in many ways analogous to Rutherford back-scattering (RBS), with electrons employed as the scattering particle rather than ions. We refer to these measurements as electron Rutherford back-scattering (ERBS). We present ERBS data for a simple two-layer system (gold on carbon). It is shown that this method can be used to determine the inelastic mean free path of electrons in carbon. We obtain a value of 350 ± 50 Å for 40 keV electrons in amorphous carbon. A comparison of the ERBS results is made with traditional RBS results from the same film. A consistent interpretation of both measurements using calculated differential elastic cross sections was not obtained.