Morphology of the asymmetric iron–silicon interfaces

• Exhaustive study of the Fe silicide formation at interfaces of (Fe/Si) multilayers.
• Thickness = 1.4 nm and roughness = 0.6 nm are found for the Si-on-Fe interface.
• First time that the Fe 1s HAXPES spectra of a multilayered system is recorded.
• The c-Fe1−xSi sublayer is identical in both Si-on-Fe and Fe-on-Si interfaces.
• The asymmetry is caused only by the ferromagnetic silicide Fe1−xSix sublayer.

A systematic study of the iron–silicon interfaces formed upon preparation of (Fe/Si) multilayers has been performed by combination of modern and powerful techniques. Samples were prepared by thermal evaporation under ultrahigh vacuum onto a Si(1 0 0) substrate. The morphology of these films and their interfaces was studied by a combination of scanning transmission electron microscopy, X-ray reflectivity, angle resolved X-ray photoelectron spectroscopy and hard X-ray photoelectron spectroscopy. The Si-on-Fe interface thickness and roughness were determined to be 1.4(1) nm and 0.6(1) nm, respectively. Moreover, determination of the stable phases formed at both Fe-on-Si and Si-on-Fe interfaces was performed using conversion electron Mössbauer spectroscopy on multilayers with well separated Si-on-Fe and Fe-on-Si interfaces. It is shown that while a fraction of Fe remains as α-Fe, the rest has reacted with Si, forming the paramagnetic c-Fe1−xSi phase and a ferromagnetic Fe rich silicide (DO3 type phase). We conclude that the paramagnetic c-Fe1−xSi silicide sublayer is identical in both Si-on-Fe and Fe-on-Si interfaces, whereas an asymmetry is revealed in the composition of the ferromagnetic silicide sublayer.