Iron silicide formation at different layers of (Fe/Si)3 multilayered structures determined by conversion electron Mössbauer spectroscopy

Abstract

The morphology and the quantitative composition of the Fe-Si interface layer forming at each Fe layer of a (Fe/Si)3 multilayer have been determined by means of conversion electron Mössbauer spectroscopy (CEMS) and high-resolution transmission electron microscopy (HRTEM). For the CEMS measurements, each layer was selected by depositing the Mössbauer active 57Fe isotope with 95% enrichment. Samples with Fe layers of nominal thickness dFe = 2.6 nm and Si spacers of dSi = 1.5 nm were prepared by thermal evaporation onto a GaAs(001) substrate with an intermediate Ag(001) buffer layer. HRTEM images showed that Si layers grow amorphous and the epitaxial growth of the Fe is good only for the first deposited layer. The CEMS spectra show that at all Fe/Si and Si/Fe interfaces a paramagnetic c-Fe1−xSi phase is formed, which contains 16% of the nominal Fe deposited in the Fe layer. The bottom Fe layer, which is in contact with the Ag buffer, also contains α-Fe and an Fe1−xSix alloy that cannot be attributed to a single phase. In contrast, the other two layers only comprise an Fe1−xSix alloy with a Si concentration of ≃0.15, but no α-Fe.