Extended energy loss fine structure measurement above shallow and deep core levels of 3d transition metals

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Abstract
The authors present a systematic investigation of surface structure of 3d transition metals through electron energy loss fine structure (EELFS) measurements, above the edges of shallow and deep core levels in the reflection mode. Fine structures above these edges, similar to those measured in X-ray absorption spectra and transmission energy loss spectra, extend for several hundred eV from the threshold. From the Fourier analysis of these features they obtained the radial distribution function around the excited atom. They discuss the EELFS analysis (Fourier transformations, backscattering amplitudes and phase shifts) above the M2,3 edges of Cu, Ni, Co, Fe and Ti metals. The experimental NiM2.3 phase shift is compared with recent theoretical calculations of shallow core levels and the discrepancy observed is ascribed to possible Fano-interference relaxation effects. They present a direct comparison between the EELFS spectrum of the TiL2.3 edge with the EXAFS spectrum obtained with synchrotron radiation. This comparison gives the most convincing evidence that the dipole (q equivalent to 0 AA-1, Delta l=+or-1) is the predominant term in the inelastic cross-section even when low primary beam energies are used and high energy loss are involved. Finally the surface sensitivity of the present technique is shown through the modification of surface-EELFS features above the FeM2,3 edge during the early stages of oxidation.