Evidence of a lamellar microstructure in β-FeSi₂ thin films grown on Si(111) by solid-phase epitaxy: a transmission electron microscopy analysis

Thin films of β-FeSi₂, grown on Si(111) by the technique of solid-phase epitaxy (SPE) in ultra-high vacuum (UHV) conditions, were analysed by transmission electron microscopy (TEM). The expected epitaxies, β-FeSi₂(101)/Si(111) and β-FeSi₂(110)/ Si(111), were detected for film thicknesses smaller than ~250 Å. The present analysis reveals an unusual microstructure: the films are composed of very thin lamellae (5–30 Å) of both orientations induced by planar defects. Such lamellar films are strained, with a parameter shift estimated to be about 0.4%. For these films, grain sizes in the μm range were obtained and the interface roughness increased with increasing film thickness. An unexpected film orientation, β-FeSi₂(100)/Si(111), was also found.