The role of the substrate on the structure of reactive sputtered Co3O4: From polycrystalline to highly oriented films

We report a systematic study of the substrate's influence on the structure of Co3O4 thin films grown by direct current reactive magnetron sputtering. Three different substrates have been simultaneously loaded to the deposition chamber and held at 620 K during growth: amorphous fused silica (a-SiO2), LaAlO3 (001), and α-Al2O3 (0001). Samples were characterized using atomic force microscopy, Raman spectroscopy, and high-resolution X-ray using synchrotron radiation (HR-XRD). Raman spectra showed bands corresponding to modes of Co3O4. The θ-2θ (HR-XRD) scans confirmed only the presence of the cubic spinel Co3O4 phase with its texture reliant on the sample substrate used. Rocking curves indicate that α-Al2O3 favors (111) Co3O4 film orientation (smaller mosaic spread). High-resolution 3-D Reciprocal Space Map analysis covering both (0006) α-Al2O3 and the (222) Co3O4 reflections have shown out-of-plane strain (0.1905%) and presented an in-plane isotropic intensity distribution of the film reciprocal lattice point, indicating no preferred mosaic direction. The substrate epitaxy governs the structure and morphology of the three samples, going from a rather flat, but polycrystalline textured Co3O4 film on a-SiO2, to a flat highly oriented strained film on α-Al2O3 and a rough highly textured and strained film on LaAlO3.