THE FORMATION OF THE EPITAXIAL CAF2/SI(111) INTERFACE INVESTIGATED BY K-RESOLVED INVERSE PHOTOEMISSION SPECTROSCOPY

k-Resolved inverse photoemission spectroscopy (KRIPES) measurements are reported for the epitaxial system CaF2/Si(111) at low coverage, in the submonolayer range. CaF2 was deposited on H-passivated Si(111) surfaces at room temperature and subsequently annealed at 800-degrees-C. A square-root 3 x square-root 3 R30-degrees reconstruction is observed and Ca is assumed to be bonded to three Si atoms in the threefold coordinated T4 or H3 sites. KRIPES spectra show a well-resolved peak at about 1.3 eV above the Fermi level. This peak is attributed to emission from antibonding states resulting from the interaction between the Ca4s and Si3p orbitals. The energy dispersion of this interface state was recorded along the GAMMA-M' and GAMMA-K' directions of the reconstructed surface Brillouin zone. These results are interpreted in the framework of the general scheme proposed in the literature for describing the CaF2/Si(111) interface formation.