Surface and interface properties of epitaxial iron oxide thin films deposited on MgO(001) studied by XPS and Raman spectroscopy

Epitaxial Fe3O4(001) thin films, 5 nm and 25 nm in thickness, have been pre pared on MgO(001) substrates by evaporating iron in the presence of oxygen. The XPS and Raman spectroscopy spectra obtained for the as-deposited films confirm the growth of magnetite, as previously observed with reflection hi gh energy electron diffraction, low-energy electron diffraction and AES, Th e films were annealed in dry air at 400-600 K, For the 25 mm thick him the transformation Fe3O4 --> gamma Fe2O3 is observed at 500 K, in good agreemen t with the results obtained for bulk magnetite, For the 5 nm thick film ann ealed at 600 K, Mg/Fe interdiffusion occurs at the interface and a modifica tion in the chemical environment of magnesium is observed on the XPS Mg 2p spectrum. The Raman spectrum of this film is peculiar and cannot be assigne d to gamma Fe2O3 or alpha Fe2O3. A new phase, probably the inverse spinel ( MgxFe1-x)Fe2O4, is formed. Copyright (C) 2000 John Wiley & Sons, Ltd.