Hard X-ray Photoelectron Spectroscopy Study of Electron Spectral Structure beyond the Known Signal Electron Peak

Abstract

HAXPES (hard X-ray photoelectron spectroscopy) is a powerful emerging instrument in surface analysis. It extended the photoelectron energy range up to 15,000 eV and opened the possibility to study much thicker films, buried layers and bulk electronic properties. In order to study these features, data for the electron IMFP (inelastic mean free path) at these energies is needed. To date, only calculated IMFP are available at energies above 5,000 eV and therefore experimental validation of these calculations are essential. In this paper, a new approach for using the HAXPES spectra is presented. This approach, treats the attenuated part of the electron spectrum as a whole to calculating the average electron energy loss. This average electron energy loss is the result of inelastic collisions in the material and hence, carry with it information about the electron transport poses. Carbon layers with thicknesses between 20 and 75 nanometer deposited over copper substrate were used to test this approach at the Spanish beam-line (Spline) in the ESRF (European synchrotron radiation facility). The measured results showed good agreement with the predictions of the multiple inelastic scattering theory. In addition, an algorithm for the experimental evaluation of electron IMFP, using the measured energy loss, is proposed.