IRON ENVIRONMENT IN PSEUDOMORPHIC IRON SILICIDES EPITAXIALLY GROWN ON SI(111)

Pseudomorphic iron-silicide phases grown on Si(111) have been studied by means of low-energy electron-diffraction, x-ray photoelectron-diffraction, and surface extended x-ray-absorption fine-structure experiments at the Fe K edge (7110 eV). These silicides have been epitaxially grown by codeposition of Fe and Si onto a room-temperature Si(111) substrate with silicide stoichiometry ranging from FeSi to FeSix (x2). In all cases, they were found to be epitaxial as attested to by a (1×1) low-energy electron-diffraction pattern observed after room-temperature deposition. X-ray-absorption measurements reveal that Fe atoms are coordinated with eight Si atoms for all metastable silicides with bond lengths of 2.342.37 and with Fe atoms with bond lengths in the 2.682.75- range. Fe-Si and Fe-Fe bond lengths as well as coordination numbers are found to increase with Fe contents within the silicide. These experiments confirm the formation of an epitaxial cubic and metastable CsCl-type FeSi upon deposition of Fe and Si in the 1:1 ratio onto a room-temperature Si(111) substrate. Furthermore, all data recorded from FeSi2 grown at room temperature or annealed at high temperature, are consistent with CsCl-derived or -derived FeSi2 structures. Finally, the present data are inconsistent with the formation of a CaF2-type FeSi2 structure. © 1995 The American Physical Society.