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.