Dependence of core-level XPS spectra on iron silicide phase

Core-level and valence-band XPS spectra for Fe3Si, FeSi, and FeSi2 were collected from the surfaces of polycrystalline silicides. The clean surfaces were prepared by mechanically fracturing the bulk polycrystalline silicides in a spectrometer under ultra-high vacuum, and then the chemical shifts and spectral shapes characteristic of each iron silicide phase were investigated in detail. The Fe 2p spectra for these samples exhibited positive chemical shifts as compared to those of elemental Fe, and the shifts observed for FeSi2 were slightly larger than the others. The spectral shapes of the Fe 2p3/2 spectra had asymmetric shapes, decreasing in magnitude with increasing Si content. The Fe 3s spectra for Fe3Si exhibited multiple splitting due to the exchange interaction between the 3s core and the 3d unfilled shell; such splitting was not found in the other silicide phases. In comparing the valence band spectra of these silicides, the spectral intensity at the Fermi edge was found to be notably higher for Fe3Si. Similar results were obtained from theoretical consideration of the partial density of state (PDOS) using a first-principle calculation method. These features affect the asymmetric spectral shape of the Fe 2p spectra for Fe3Si.