Grazing incidence X-ray diffraction has provided definite evidence for
the existence of metastable alpha-FeSi2 films (40 angstrom) grown by
molecular beam epitaxy (MBE) on Si(1 1 1) at low temperature (550-degr
ees-C) and previously suggested by a RHEED study. For thicker films (>
350 angstrom) grown on silicon by chemical beam epitaxy (CBE), alpha-
FeSi2 has also been observed in coexistence with a beta-FeSi2 layer, b
ut it disappears upon annealing.