Interface structure and stabilization of metastable B2-FeSi/Si(111) studied withlow-energy electron diffraction and density functional theory

Abstract

We present a combined experimental and theoretical investigation of the interfacebetween a B2-type FeSi film and Si(111). Using an ultra-thin B2-FeSi film grownon Si(111), the interface is still reached by electrons, so quantitative low-energyelectron diffraction (LEED) could be applied to determine the bonding geometryexperimentally. As a result, the local configuration at the shallow buriedinterface is characterized by near-substrate Fe atoms being 8-fold coordinatedto Si atoms and by the silicide unit cell being rotated by 180° withrespect to the Si unit cell (B8 configuration). The interface energetics wereexplored by total-energy calculations using density functional theory (DFT). TheB8-type interface proves to be the most stable one, consistent with theexperimental findings. The atomic geometries obtained experimentally (LEED)and theoretically (DFT) agree within the limits of errors. Additionally, thecalculations explain the stabilization of the B2 phase, which is unstable as bulkmaterial: the analysis of the elastic behaviour reveals a reversed energy hierarchyof B2 and the bulk stable B20 phase when epitaxial growth on Si(111) is enforced.