Fe-sulicides were formed by annealing MBE-deposited thin 57Fe layers with thicknesses between 20 Å and 60 Å on (7x7) reconstructed Si(111) substrates. During the growth the substrate was held at room temperature. The silicide formation upon annealing in the temperature range of 200°C to 900°C was studied in-situ with RH-EED. Samples were studied with in-situ CEMS (Conversion Electron Mossbauer Spectroscopy) as well as with ex-situ CEMS after covering with Ag to prevent oxidation. RBS/Channeling was used to study the epitaxial quality and the structure of these layers.
Using the 57Fe nuclear probe, it is shown that silicide formation occurs at the interface already at room temperature. Metastable silicides with cubic structure are observed in the low temperature annealing range, and characterized by their Mossbauer parameters. At higher temperatures stable ε-FeSi and β-FeSi2 are formed.