STRUCTURAL AND ELECTRONIC-PROPERTIES OF PSEUDOMORPHIC FESI1+X FILMS ON SI(111)

Epitaxial FeSi1+x (0 less-than-or-equal-to x less-than-or-equal-to 1) films were grown on Si(111) by MBE at room temperature (RT). They were characterized in situ by RHEED, UPS, XPS and STM and ex situ by TEM. Kikuchi band and TEM analysis revealed that FeSi has the simple cubic CsCl structure with a lattice constant close to half the Si one. This phase which does not occur in the equilibrium Fe-Si phase diagram can be stabilized epitaxially on Si(111) through a favourable interface st ructure. UPS spectra display a distinct Fermi edge indicating that FeS i is metallic. Upon annealing, films thicker than approximately 15 ang strom exhibit a phase transformation to the stable bulk epsilon-FeSi p hase, which can be either epitaxial or heavily twinned. In thinner fil ms the Si content was observed to increase up to 1:2 without any chang e of symmetry.