Optical characteristics of an epitaxial Fe$_3$Si/Si(111) iron silicide film

The dispersion of the relative permittivity $\varepsilon$ of a $27$-nm-thick epitaxial Fe$_3$Si iron silicide film has been measured within the $E = 1.16{-}4.96$ eV energy range using the spectroscopic ellipsometry technique. The experimental data are compared to the relative permittivity calculated in the framework of the density functional theory using the GGA-PBE approximation. For Fe$_3$Si, the electronic structure and the electronic density of states (DOS) are calculated. The analysis of the frequencies corresponding to the transitions between the DOS peaks demonstrates qualitative agreement with the measured absorption peaks. The analysis of the single wavelength laser ellipsometry data obtained in the course of the film growth demonstrates that a continuous layer of Fe$_3$Si iron silicide film is formed if the film thickness achieves $5$ nm.