SCANNING TUNNELING MICROSCOPY AND SPECTROSCOPY OF IRON SILICIDE EPITAXIALLY GROWN ON SI(111)

Epitaxial iron silicide films have been grown on Si(111) by solid phase epitaxy (SPE) in UHV. Structural and electronic properties have been investigated with scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). For initial Fe deposition up to 3 angstrom and annealing at 850 K, metallic gamma-FeSi2 is formed. These films exhibit a perfect (2 x 2) superstructure, which is attributed to gamma-FeSi2(111) with Si termination. SPE at higher initial iron deposition (15 angstrom) and annealing at 800 K results in epsilon-FeSi showing a (square-root 3 x square-root 3) R30-degrees superstructure. Subsequent annealing above 900 K leads to beta-FeSi2 formation. As determined by STS, beta-FeSi2 films are semiconducting with E(g) = 0.85 eV. STM topographs show that SPE produces rough silicide surfaces with beta-FeSi2(101) [and not beta-FeSi2(110)] epitaxy. The atomic structure on beta-FeSi2 terraces is complex, consisting of many anti-phase domain boundaries and defects.