Synthesis of iron oxide films by reactive magnetron sputtering assisted by plasma emission monitoring

Iron oxide films were synthesized by pulsed-DC magnetron sputtering from a metallic target in Ar and O-2 gas mixtures. Plasma emission monitoring was implemented to accurately control the metal-to-oxygen ratio in the coating through the chemical state of the iron target. The intensity of the Fe* emission line was maintained at a given value (setpoint) by regulating the introduced oxygen flow rate. In addition, the oxidation rate of the growing film was adjusted by controlling the oxidation-to-deposition rate ratio as a function of the position of the substrates relative to the magnetron axis. The iron oxide films were characterized by X-ray diffraction, UV-VIS spectrophotometry, electrical measurement and vibrating sample magnetometry. In addition to the crystallization of pure hematite and magnetite phases, both phases coexist in a transition domain for a short range of setpoint depending on the oxidation-to-deposition rate ratio. The electrical, optical and magnetic behaviors of the FeOx films suggest that the relative proportion of phases can be tailored in this range. The FeOx film behaviors can then be tuned from the hematite semi-conductor properties to the semi-metallic magnetite properties.