Formation process of β-FeSi2 from amorphous Fe-Si synthesized by ion implantation: Fe concentration dependence

P>Formation processes of beta-FeSi2 from amorphous Fe-Si layers have been investigated using transmission electron microscopy (TEM). Si(111) substrates were irradiated with 120 keV Fe ions at -150 degrees C to fluences of 1.0 x 1017 and 4.0 x 1017 cm-2. An amorphous Fe-Si layer embedded in an amorphous Si was formed in the low-fluence sample, whereas an amorphous Fe-Si surface layer on an amorphous Si was obtained in the high-fluence one. The amorphous Fe-Si layers were crystallized to beta-FeSi2 after thermal annealing at 800 degrees C for 2 h. Cross-sectional and plan-view TEM observations revealed that, prior to the formation of beta-FeSi2, the amorphous Fe-Si layers crystallized to alpha-FeSi2 in the low-fluence sample and to epsilon-FeSi in the high-fluence one. The absence of metastable gamma-FeSi2 which is considered as a precursor of epitaxially grown beta-FeSi2 on Si was attributed to the instability of gamma-phase in an amorphous matrix.