Mössbauer characterization of gamma -FeSi2 precipitates in Si(100).

Abstract

Metastable [gamma]-FeSi[sub 2] fluorite-type was formed as precipitates in Si(100) by room-temperature [sup 57]Fe implantation, followed by ion-beam-induced epitaxial crystallization at 593 K. In spite of the cubic structure of [gamma]-FeSi[sub 2], the Moessbauer spectrum consists of two broad lines, rather than a single line. It is best described by means of a smooth distribution of electric field gradients with nearly the same isomer shift ([delta][sub IS]=0.198 mm/s) for each gradient. After thermal treatments at 773 K the distribution narrows and a finite probability occurrence frequency for zero gradient appears. As the structure of ideal [gamma]-FeSi[sub 2] consists of Si cubes alternately filled with Fe atoms, it is suggested that the distribution arises from misplacement of Fe atoms to empty Si cubes in the lattice. The dependence with thermal treatments and the evolution towards [beta]-FeSi[sub 2] are discussed.