Identification of iron oxide phases in thin films grown on Al2O3(0 0 0 1) by Raman spectroscopy and X-ray diffraction

We report on the identification of Fe3O4 (magnetite) and α-Fe2O3 (hematite) in iron oxide thin films grown on α-Al2O3(0001) by evaporation of Fe in an O2-atmosphere with a thickness of a few unit cells. The phases were observed by Raman spectroscopy and confirmed by X-ray diffraction (XRD). Magnetite appeared independently from the substrate temperature and could not be completely removed by post-annealing in an oxygen atmosphere as observed by X-ray diffraction. In the temperature range between 400°C and 500°C the X-ray diffraction shows that predominantly hematite is formed, the Raman spectrum shows a mixture of magnetite and hematite. At both lower and higher substrate temperatures (300°C and 600°C) only magnetite was observed. After post-annealing in an O2-atmosphere of 5×10−5mbar only hematite was detectable in the Raman spectrum.