Simulation of Electron Spectra for Surface Analysis (SESSA)for quantitative interpretation of (hard) X-ray photoelectron spectra(HAXPES)

Abstract

For the interpretation of photoelectron spectra and in order to obtain quantitative information on the chemical structure of surfaces, one commonly makes a number of simplifying assumptions concerning the generation of the signal electrons, such as the neglect of photoelectron elastic scattering, and the anisotropy of photoelectron emission. While the effects of these assumptions for planar surfaces and for conventional X-ray sources has been investigated in detail in the past, the combined influence of the nanomorphology, the polarisation of the incoming beam and other processes playing a role in the photoelectron escape on the angular- and energy-distribution of emitted photoelectrons has not been clarified to date. The National Institute of Standards and Technology (NIST) Database for the Simulation of Electron Spectra for Surface Analysis (SESSA) is a unique tool for interpretation of experimental data for nanostructured surfaces as well as for experimental design with photoelectron energies between 50eV and 30keV. SESSA has recently been modified to allow a user to simulate X-ray photoelectron spectroscopy (XPS) spectra of nanostructured surfaces, such as surfaces covered with rectangular islands, nanowires, pyramids, spheres, and layered spheres. The effect of the nanomorphology on the emitted angular and energy distribution of photoelectrons is investigated and comparison is made of simulated data with experimental results. Finally, the full potential of XPS for characterising nanostructures by a consistent analysis of the angular distribution of both the photoelectron peaks and their associated inelastic loss features is explored.