Empty electronic states of calcium silicides: An inverse-photoemission investigation in the ultraviolet photon range

Empty electronic states in calcium silicides (${\mathrm{Ca}}_2$Si, CaSi, and ${\mathrm{CaSi}}_2$) are investigated by means of inverse photoemission. We present spectra taken in the isochromat mode in the ultraviolet photon range (10–25 eV), at different photon energies. The experimental data are discussed on the basis of theoretical results obtained by self-consistent calculations performed with the Andersen linear muffin-tin orbitals (LMTO) method in the atomic-sphere approximation (ASA). A general agreement between theory and experiment is found for all silicides. However, discrepancies in the energy positions of the observed structures suggest the importance of final-state effects in inverse photoemission. The orbital origin of the spectral features is also analyzed by exploiting the photon-energy dependence of the isochromat spectra.