Spectroscopy of extended electron energy loss fine structures for quantitative analysis of the local atomic structure in ultrathin oxide films on the surface of 3d-metals

Abstract

The work presents the theoretical description of formation processes of extended electron energy loss fine structure (EELFS) spectra. Simple analytical formulas are obtained to calculate EELFS spectra. Methods are proposed to compute amplitudes and intensities of electronic transitions of different multipolarity in electron-impact excitation of the inner shell of an atom. The corresponding test calculations are performed. We present experimental M 2,3 EELFS spectra of 3d-metals obtained from clean surfaces of Fe, Ni, and Cu and ultrathin stoichiometric oxide films of Fe2O3, NiO, and CuO as well as K EELFS spectra of oxygen from thin stoichiometric oxide films. Techniques are proposed to extract normalized oscillating parts from experimental EELFS data based on the use of calculated intensities of the corresponding electronic transitions. Atomic pair correlation functions are obtained for the objects under study from experimental EELFS data with regard to multipolarity of electron impact excitation of the atomic inner shell. Experimental results correspond well to known crystallographic data (partial interatomic distances, coordination numbers, and Debye-Waller factors).