EPITAXIAL CUBIC IRON SILICIDE FORMATION ON SI(111)

Ultra-thin (3-10 monolayers (ML)) Fe films deposited on Si(111)7x7 surfaces were annealed in the 300-600-degrees-C temperature range and investigated by X-ray photoelectron diffraction (XPD), angle resolved ultraviolet photoelectron spectroscopy (ARUPS) and low-energy electron diffraction (LEED). ARUPS spectra reveal the formation of an iron-silicide film showing an increasing Si content with increasing annealing temperature. The comparison of the XPD results of these silicides to those of epitaxial CoSi2 films and to the results of single scattering calculations allows us to identify the formation of Fe silicides with a local cubic Fe environment. The orientation of the silicides with respect to the substrate is essentially of B-type. Thin enough films (< 7 ML Fe) do not show a phase transition to beta-FeSi, prior to disruption at about 600-degrees-C while thicker (approximately ML Fe) can transform from the metastable cubic silicide to the stable beta-FeSi2 phase at 550-degrees-C.