Ge-doped magnetite thin films with an enhanced resistance to oxidation

Highlights: • Oxidation resistance of Fe₃O₄ thin films doped with metal elements was investigated. • Doped thin films were heat-treated at different temperatures in air. • Activation energy of the Ge-doped film was 2.5 times larger than that of the undoped film. • A heterostructure consisting of α-Fe₂O₃ and Fe₃O₄ containing Ge was formed during heat-treatment in air. The ability of metal-doped magnetite (Fe₃O₄) thin films to resist oxidation during annealing in air was investigated. The films were prepared on glass substrates by radio-frequency sputtering using a target of metal chips set on a ceramic Fe₃O₄ disk. The metal elements used in this study were Ge, Mo, W, and Mg. The films were annealed at different temperatures in air and the activation energy of oxidation was estimated. The Ge-doped film was high stable against oxidation with an activation energy of 490 KJ/mol, which was 2.5 times larger than that of undoped film. Elemental mapping using energy dispersive X-ray microscopy (EDX) and selected area electron diffraction (SAED) revealed that the Ge-doped Fe₃O₄ film was composed of a heterostructure that consisted of α-Fe₂O₃ and Fe₃O₄ containing small amount of Ge.