Epitaxy stabilised CaF 2-type ternary Co 1− xFe xSi 2 silicides on Si(1 1 1): DAFS and HRTEM measurements

Abstract

Diffraction anomalous fine structure on both Fe and Co K edges and transmission electron microscopy are used to study the crystallographic structure and morphology of thin ternary silicides films grown on Si(1 1 1). Co 1− x Fe x Si 2 layers (about 10 nm thick) have been grown by UHV–MBE in epitaxy on silicon. On either oriented or slightly mis-oriented (1 1 1) surfaces, and in situ annealed at about 925 K. In the Fe-rich part of composition, annealing at 925 K results in a phase separation into grains of two different structures, namely a CaF 2-type (as CoSi 2) and α-FeSi 2-type structures. In contrast, for Si surfaces with a very low miscut and in the Co-rich part of composition, annealing at 925 K results in an almost single phase with a CaF 2-type structure. Transmission electron microscopy images show that, even in the Co-rich part, the stress gradient generated at the step edges acts as a nucleation centre for the α-FeSi 2 phase, which is thus probably more stable than the CaF 2-type phase, stabilised by the stress on the terraces.