High-Throughput Characterization of (FeCo_1-)₃O₄ Thin-Film Composition Spreads

Thin-film continuous composition spreads of Fe-Co-O were fabricated by reactive cosputtering from elemental Fe and Co targets in reactive Ar/O₂ atmosphere using deposition temperatures ranging from 300 to 700 °C. Fused silica and platinized Si/SiO₂ strips were used as substrates. Ti and Ta were investigated as adhesion layer for Pt and the fabrication of the Fe-Co-O films. The thin-film composition spreads were characterized by high-throughput electron-dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, atomic force microscopy, scanning electron microscopy, and optical transmission spectroscopy. The Fe-content ranged from 28 to 72 at. %. The spinel phases Fe₂CoO₄ and FeCo₂O₄ could be synthesized and stabilized at all deposition temperatures with a continuous variation in spinel composition in between. The dependence of the film surface microstructure on the deposition temperature and the composition was mapped. Moreover, the band gap values, ranging from 2.41 eV for FeCo₂O₄ to 2.74 eV for Fe₂CoO₄, show a continuous variation with the composition.