Microscopic environment of Fe in epitaxially stabilizedc−FeSi

Abstract

Epitaxially stabilized iron monosilicide films having the CsCl structure $(c\ensuremath{-}\mathrm{FeSi})$ have been investigated by conversion electron M\"ossbauer spectroscopy and transmission electron microscopy. The ${}^{57}\mathrm{Fe}$ M\"ossbauer parameters (isomer shift \ensuremath{\delta}, linewidth \ensuremath{\Gamma}, and quadrupole splitting \ensuremath{\Delta}) are reported and discussed in terms of the local surrounding of the Fe nucleus. High statistical accuracy and resolution allowed a detailed investigation of the effects of strain and of the structural phase transformation from the epitaxially stabilized to the bulk stable phase. The phase transformation was found to proceed in a rather surprising layer by layer mechanism with smooth interfaces between the epitaxially stabilized, the bulk stable, and a third phase. Results from a molecular-dynamics simulation at constant pressure and temperature of the structural phase transition are presented and compared with the experimental findings. The isomer shift and the electric-field gradient at the Fe nucleus in the strained $c\ensuremath{-}\mathrm{FeSi}$ and in the third phase have been calculated using the ab initio full potential linear muffin-tin orbital method. The M\"ossbauer parameters of some relevant point defects in $c\ensuremath{-}\mathrm{FeSi}$ have likewise been calculated within this framework.