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

Published online by Cambridge University Press:  10 February 2011

L. Khouchaf
Affiliation:
LPSE - FST, Université de Haute Alsace, CNRS, F-68093 Mulhouse -, France
D. Berling
Affiliation:
LPSE - FST, Université de Haute Alsace, CNRS, F-68093 Mulhouse -, France
V. Pierron-Bohnes
Affiliation:
GEMM - IPCMS, Université Louis Pasteur, CNRS, F-67037 Strasbourg -, France
C. Pirri
Affiliation:
LPSE - FST, Université de Haute Alsace, CNRS, F-68093 Mulhouse -, France
S. Hong
Affiliation:
LPSE - FST, Université de Haute Alsace, CNRS, F-68093 Mulhouse -, France
P. Wetzel
Affiliation:
LPSE - FST, Université de Haute Alsace, CNRS, F-68093 Mulhouse -, France
G. Gewinner
Affiliation:
LPSE - FST, Université de Haute Alsace, CNRS, F-68093 Mulhouse -, France
M. H. Tuilier
Affiliation:
LPSE - FST, Université de Haute Alsace, CNRS, F-68093 Mulhouse -, France
S. Lefebvre
Affiliation:
LURE, Université de Paris-Sud, CNRS, F-91405 Orsay -, France
R. Cortts
Affiliation:
LURE, Université de Paris-Sud, CNRS, F-91405 Orsay -, France
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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.

Type
Research Article
Copyright
Copyright © Materials Research Society 1998

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