Identification of iron oxide phases in thin films grown on Al sub(2)O sub(3)(0 0 0 1) by Raman spectroscopy and X-ray diffraction

We report on the identification of Fe sub(3)O sub(4) (magnetite) and alpha -Fe sub(2)O sub(3) (hematite) in iron oxide thin films grown on alpha -Al sub(2)O sub(3)(0 0 0 1) by evaporation of Fe in an O sub(2)-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 degree C and 500 degree 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 degree C and 600 degree C) only magnetite was observed. After post-annealing in an O sub(2)-atmosphere of 5 x 10 super(-5) mbar only hematite was detectable in the Raman spectrum.