ELECTRON-STATES OF INTERFACE IRON SILICIDES ON SI(111)7X7

Solid-phase epitaxy of iron silicides on Si(111)7 X 7 substrates is st udied by comparing photoemission spectroscopy of the extended states a nd core levels, and Fe L2,3 x-ray-absorption spectroscopy, for the int erface phases and the bulk stoichiometric silicides. Epitaxial growth favors the low-temperature formation of metallic tetragonal alpha-FeSi 2 which starts decomposing irreversibly into semiconducting orthorhomb ic beta-FeSi2 at above 600-degrees-C. This interface chemistry is oppo site to the bulk phase diagram where the alpha phase is the high-tempe rature stable disilicide which reversibly transforms into the beta pha se when the temperature is lowered to 950-degrees-C. No evidence of me tastable interface phases other than the bulk phases is found. The coe xistence of bulk epitaxial phases over an extended temperature range i ndicates that local properties of the interface strongly influence the silicide phase transitions.