STRUCTURAL COMPOSITION DEPENDENCE OF AMORPHOUS SILICON-IRON PREPARED BY ION-IMPLANTATION AND BY COEVAPORATION - A MOSSBAUER STUDY

The structural evolution of amorphous Si(1-x)Fe(x) with composition has been investigated. Implanted specimens with iron concentrations below and above x = 0.2, where a structural transformation was previously reported for evaporated samples, have been studied by conversion-electron Mossbauer spectroscopy. Applying the model of Miedema and van der Woude for the isomer shift, a consistent description of our results and of those available from the literature (both from ion-implanted and coevaporated specimens) is given, which covers a wide composition range (0.001 less-than-or-equal-to x less-than-or-equal-to 0.750). It was concluded that three differentiated regions exist: a silicon-rich one where iron bears a strong covalent character in a continuous random network structure; an intermediate region where the covalent character decreases continuously at the iron sites, which are here proposed to have a local structure like the one existing in the intermetallic compound FeSi; and finally an iron-rich region where covalent effects are absent, supporting a dense-random-packing description of the amorphous structure.