Amorphous alloy thin films from molecular precursors. Evidence of structure and stoichiometry from crystallization and effects of precursor ligand structure on stoichiometry

Abstract

(CO)3H4 at low low pressure has been studied by using the techniques of X-ray diffraction and Mbsbauer spectroscopy. The resulta unambiguously show that the films are iron rich in terms of the ideal stoichiometry of Fe/B = 3, signifying some loss of boron during film formation. The iron-main group atom phase that crystallizes from the amorphous film is orthorhombic Fe,B1,Cx, with x for the specific film examined lying between 0.3 and 0.4. The cleavage of CO is postulated to account for the overall Fe/B ratio of 3, formation of the mixed boride/carbide phase and the presence of B203 in the film. That is, the boron sequesters the oxygen atom as B203, whereas the carbon atom replaces boron so lost in Fe3B to form the Fe3B1,C,phase. Deposition of films from a closely related precursor, HFe3(CO)laH2, have also been examined.Most of the boron is lost during deposition even at the lowest substrate temperature. Crystallization of these amorphous films requires higher temperatures and yields a-Fe and a phase indistinguishable from orthorhombic Fe3C. Decomposition during sublimation with the production of Fe(CO), accounts for the qualitatively different behavior of HFe3(CO)loBH2.