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Epitaxy of Thin Ternary Co1−xFexSi2 Silicide Films on SI(111)

  • L. Khouchaf (a1), D. Berling (a1), V. Pierron-Bohnes (a2), C. Pirri (a1), S. Hong (a1), P. Wetzel (a1), G. Gewinner (a1), M. H. Tuilier (a1), S. Lefebvre (a3) and R. Cortts (a3)...

Abstract

Low-energy electron diffraction, x-ray diffraction, and x-ray absorption techniques are used to investigate the atomic structure of ternary silicides (MSi2, M = Co, Fe). 100 Å thick Co1−xFexSi2 films (with 0 ≤ × ≤ 1) were grown by codeposition onto a Si(111) substrate held at room temperature. The as-deposited films are metallic and adopt an ordered cubic structure of CsCl-type with essentially random vacancies, very similar to that of room-temperature grown FeSi2 and CoSi2 silicides. Upon annealing at 650°C, Fe-rich (x ≥ 0.85) films invariably convert into a semiconducting phase with a structure similar to the orthorhombic β-FeSi2 one. Yet, most interestingly, an almost cubic structure is preserved for x ≤ 0.85. Nevertheless, x-ray diffraction reveals a demixion into a Co rich CaF2-type silicide and a Fe-rich phase with a nearly cubic α-FeSi2 type structure. Extended x-ray absorption fine structure measurements indicate a local environment of Fe atoms similar to that in CsCl-type or α-FeSi2-type structure over the whole 0 < x < 0.85 composition range, showing that Fe does not merely substitute for Co atoms in a perfect CaF2-type CoSi2 structure, even for very low Fe content. In contrast, the local environment of Co atoms is similar to that in CoSi2 for Co-rich ternary compounds. Substantial modifications around Co sites are although observed in Fe richer silicides, suggesting that for x < 0.5, an appreciable amount of Co is incorporated in the α-FeSi2-type silicide phase.

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Epitaxy of Thin Ternary Co1−xFexSi2 Silicide Films on SI(111)

  • L. Khouchaf (a1), D. Berling (a1), V. Pierron-Bohnes (a2), C. Pirri (a1), S. Hong (a1), P. Wetzel (a1), G. Gewinner (a1), M. H. Tuilier (a1), S. Lefebvre (a3) and R. Cortts (a3)...

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