High-resolution x-ray-photoemission study of metastable Fe silicide core-electron states.

Abstract

The core-electron states of metastable pseudomorphic Fe silicides, epitaxially grown on Si(111), have been measured by monochromatized x-ray photoemission. These silicides have been grown by molecular-beam epitaxy with composition ranging from FeSi up to ${\mathrm{FeSi}}_{2}$. Si 2p and Fe 2${\mathit{p}}_{3/2}$ core lines have been compared to those measured on both polycrystalline and epitaxially grown stable \ensuremath{\beta}-${\mathrm{FeSi}}_{2}$ and \ensuremath{\varepsilon}-FeSi layers. Metastable silicide related Si 2p and Fe 2${\mathit{p}}_{3/2}$ core line binding-energy shifts, with respect to \ensuremath{\beta}-${\mathrm{FeSi}}_{2}$ or clean Si(111), have been interpreted as arising from electron charge transfer from Si to Fe, in agreement with recent calculations. Si 2p and Fe 2${\mathit{p}}_{3/2}$ binding energies as well as line-shape evolutions, over a wide composition range, give strong support to a model with a nearly cubic structure, evolving from FeSi to ${\mathrm{FeSi}}_{2}$, in which Fe atoms are randomly distributed over the Si cages.