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

Abstract

Epitaxial Fe3O4(001) thin films, 5 nm and 25 nm in thickness, have been prepared 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 high energy electron diffraction, low-energy electron diffraction and AES. The films were annealed in dry air at 400-600 K. For the 25 nm thick film the transformation Fe3O4→γFe2O3 is observed at 500 K, in good agreement with the results obtained for bulk magnetite. For the 5 nm thick film annealed at 600 K, Mg/Fe interdiffusion occurs at the interface and a modification 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 assigned to γFe2O3 or αFe2O3. A new phase, probably the inverse spinel (MgxFe1-x)Fe2O4, is formed.