Inelastic scattering energy loss in CaF2 observed with soft X-ray fluorescence spectroscopy

Abstract

Abstract The advent of third-generation synchrotron radiation sources has stimulated interest in the study of X-ray emission using photon excitation. Soft X-ray fluorescence (SXF) provides a means of measuring the element and angular momentum selective valence band density of states in complex materials. Tenability of the excitation source allows a detailed investigation of the dynamical behavior of the relaxation channels and the coupling between the excitation and emission process that occurs near a resonance or an absorption edge. As an example of resonant inelastic scattering studies in solid systems by SXF spectroscopy at the insertion device beam line BL 8.0 at ALS, results from CaF 2 will be presented. When the energy of exciting photons is tuned to the Ca 2p–3d threshold absorption peak in CaF 2 , the SXF produced by recombination of the excited electrons with core holes exhibits remarkable resonances for both the 2p 3/2 and 2p 1/2 levels. When the resonant 2p–3d SXF peaks are excited, additional broad peaks appear in the spectra below the normal valence band spectrum, which are displaced from the resonant peaks by about 17 eV and track the changes in excitation energy. We identify this as evidence of a coherent, inelastic scattering process, analogous to resonant Raman scattering, in which incident photons excite a localized electronic transition and are re-radiated at an energy reduced by the energy of the excitation. Evidence is also presented which indicates that the 2p–3d absorption transitions lie about 1 eV above a weak Ca 4s absorption threshold.