SI-RICH P(2X2) SURFACE RECONSTRUCTION OF EPITAXIAL FLUORITE-TYPE IRONSILICIDE LAYERS ON SI(111)

Thin epitaxial metastable iron silicide overlayers with probably the C aF2-structure were grown on Si(111) by either solid-phase epitaxy or a layer-by-layer growth technique. After annealing in the 500-550-degre es-C temperature range, a strong Si segregation at the surface is obse rved in ion scattering spectroscopy experiments. In LEED these layers are characterized by a sharp p(2 x 2) pattern, which is shown to be du e to a reconstruction of the Si-rich surface. Angle-resolved ultraviol et photoelectron spectroscopy (ARUPS) reveals a characteristic surface electronic state with the same 2 x 2 periodicity in reciprocal space as the surface reconstruction. At the GAMMABAR point, the surface stat e is located at 1.85 eV binding energy in a relative gap of the calcul ated bulk electronic structure of fluorite-type FeSi2.