Occupied electronic states ofCaSi2and CaSi: Soft-x-ray-fluorescence spectroscopy

The Ca ${\mathit{L}}_{2,3}$ and Si ${\mathit{L}}_{2,3}$ fluorescence spectra for ${\mathrm{CaSi}}_2$ and CaSi are studied. These spectra provide s and d partial density-of-states (PDOS) information for the Ca and Si atoms. The measured PDOS’s are in good agreement with available calculations. Using monochromatized x rays to excite core electrons to localized Ca d states near threshold produces resonant recombination fluorescence peaks for the ${\mathit{L}}_3$ and ${\mathit{L}}_2$ edges of Ca in both compounds. In CaSi, with resonant excitation, inelastic Raman peaks are also observed. The energy position of the inelastic peaks indicates that the creation of the core hole shifts the Ca d states by several eV. The intensity of the resonance peaks indicates the degree of localization of the Ca d states, which is reduced by their participation in the bonding of the silicides. The empty Ca d states are found to be quite localized in CaSi, and less so in ${\mathrm{CaSi}}_2$.