Structural properties of iron oxynitride films obtained by reactive magnetron sputtering
Résumé
Iron oxynitride films were prepared by magnetron sputtering of an iron target in Ar–N2–O2 reactive mixtures using a nitrogen flow rate of 2 sccm and a constant argon pressure of 0.3 Pa. The oxygen flow rate varied from 0 to 2 sccm. The thickness of the films deposited on silicon (100) and glass substrates ranged from 0.5 to 2 µm. In order to determine the chemical composition of the films, Rutherford backscattering spectrometry was used. Whatever the iron, nitrogen and oxygen contents, this study revealed that the film composition was homogeneous along the film depth. The films were characterized by several complementary experimental techniques, such as x-ray diffraction, x-ray photo-electron spectroscopy and 57Fe Mössbauer spectrometry, which gave the most accurate information about the short-range order of iron atoms. Due to their different spatial scale efficiency, the analysis by both 57Fe transmission and conversion electron Mössbauer spectrometry and x-ray diffraction allowed us to characterize both the structural and microstructural nature of these films. The study of the films by x-ray diffraction indicated an evolution of the structure from iron nitride ε-Fe2N or ζ-Fe2N to an fcc intermediate phase and finally to an oxide-like Fe2(O,N)3. The hyperfine structure observed on the Mössbauer spectra for the intermediate phase showed the presence of a phase of iron oxynitride Fe1.06O0.35N0.65 which is consistent with the x-ray diffraction results.