Structural changes in metastable silicide layers were investigated, as a function of composition, by means of inelastic energy electron diffraction and photo-electron diffraction techniques. Silicides which were grown onto Si(111), by Fe and Si co-deposition onto room-temperature Si(111) substrates, were found to be epitaxial for compositions which ranged from FeSi to FeSi2. The use of Fe 2p3/2 and Si 2p polar scans along the high-symmetry [12¯1] and [1¯21¯] directions of the substrate, as well as inelastic medium-energy electron diffraction, showed that the Fe and Si atoms were located in very similar cubic lattices. The experimental data clearly revealed a lattice parameter decrease in going from FeSi to FeSi2. Experimental profiles for FeSix, where x was between 1 and 2, were reproduced theoretically by assuming a CsCl-type FeSix structure in which randomly distributed Fe vacancies were progressively formed when the composition changed from FeSi to FeSi2.

S.Hong, C.Pirri, P.Wetzel, D.Bolmont, G.Gewinner: Applied Surface Science, 1995, 90[1], 65-74