Experimental determination of the inelastic mean free path (IMFP) of electrons in selected oxide films applying surface excitation correction

The inelastic mean free path (IMFP) of electrons was determined using elastic peak electron spectroscopy (EPES) with Cu, Si, Ag, Ni and Au reference samples. Systematic differences occurred between the experimental and calculated (TPP-2M) (Tanuma, Powell, Penn) IMFPs, which can be ascribed partly to surface losses. The experimental IMFP was deduced from the integrated elastic peak ratio of the sample and the reference. Experiments were made with the ESA 31 (ATOMKI) and DESA 100 (Staib) electron spectrometers, and covered the E = 0.2-2 keV energy range. The results were evaluated applying Monte Carlo (MC) simulation based on the NIST SRD 64/3.1 database and using the EPESWIN software of Jablonski. The surface excitation correction (surface excitation parameter (SEP)) for SiO 2 , MgO and Al 2 O 3 was determined using our new procedure applying the model of Chen and Tanuma. This correction reduced the difference between uncorrected, experimentally determined and calculated IMFPs by nearly 50%, which proves the importance of the contribution of surface excitation. The oxide layers studied are insulators. Their surface potential was determined by the energy of the Auger peak. We observed an energy shift of 1-3 eV of the Auger peak positions due to charging. The SEP material parameter resulted in a ch = 1.2 for SiO 2 and a ch = 4 for MgO and Al 2 O 3 .