Experimental effective attenuation length on solids for electron kinetic energies between 1 and 14 KeV: Determination of a simple practical equation

Abstract

The effective attenuation length is a fundamental parameter for the correct evaluation of XPS and AES spectra. For electron kinetic energies below 2 KeV, a large database with experimental EALs for most organic and inorganic compounds exists. In addition, several predictive equations valid in the low electron kinetic energy range are available. However, for HAXPES applications in which electron kinetic energies up to 14 KeV are used, the lack of experimental EAL data and predictive equations difficult the spectra analysis and quantification. In this work, we obtain experimental EAL values in the kinetic energy range between 1 and 14 KeV for Cu, Au, Ti, Si, Ge, TiN, SiO2, HfO2, Fe3O4, SrTiO3 and La0.7Sr0.3MnO3. The validity of the predictive equations developed for soft X-ray XPS are evaluated for high electron kinetic energies using the obtained experimental data. We find that the λfit formulae developed by Jablonski and Tougaard reproduces the experimental EAL data up to electron kinetic energies of 14 KeV within the experimental errors. Based on a fitting to the obtained experimental data for all materials used in this work we propose a simple practical equation for the evaluation of EAL for solids in the kinetic energy range between 1 and 14 KeV. The proposed equation, in comparison with the λfit predictive formulae, is only dependent on the compound effective atomic number eliminating tedious calculations based on electron inelastic mean free paths and transport mean free paths. The accuracy of the proposed practical equation reproduces within the experimental errors the experimental EALs presented in this work and the data available in the literature.