Medium energy electron diffraction and X-ray photoelectron diffraction study of pseudomorphic Fe silicides grown on Si(111) Evidence of Fe vacancy formation

The structural evolution of metastable Fe silicide layers versus composition has been investigated by means of inelastic medium energy electron diffraction and photoelectron diffraction. These silicides grown on Si(111) by Fe and Si co-deposition onto room temperature Si(111) substrate are found to be epitaxial over a wide composition range from FeSi to FeSi2. Fe2p3/2 and Si2p polar scans measured along high symmetry [121] and [121] directions of the substrate as well as inelastic medium energy electron diffraction show that Fe and Si atoms are located in a very similar cubic lattice. Experimental data clearly show the lattice parameter decrease versus Fe content decrease from FeSi to FeSi2. Single scattering calculations have been performed for FeSix silicides with CsCl-type structure. Experimental profiles of FeSix (1 < x < 2) are very well reproduced in the calculations by assuming a CsCl-type FeSix structure in which randomly distributed Fe vacancies are progressively formed when the composition evolves from FeSi to FeSi2.