MOSSBAUER CHARACTERIZATION OF GAMMA-FESI2 PRECIPITATES IN SI(100)

Metastable -FeSi2 fluorite-type was formed as precipitates in Si(100) by room-temperature Fe57 implantation, followed by ion-beam-induced epitaxial crystallization at 593 K. In spite of the cubic structure of -FeSi2, the Mössbauer 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 (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 -FeSi2 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 -FeSi2 are discussed. © 1995 The American Physical Society.