Multilayer formation via spinodal decomposition in TiO₂-VO₂ epitaxial films on sapphire substrates

We present multilayer formation via spinodal decomposition in rutile TiO₂-VO₂ (TVO) epitaxial films on sapphire substrates. (001)- and (101)-oriented TVO solid-solution films are grown epitaxially on TiO₂/Al₂O₃ using a pulsed laser deposition technique and annealed inside the spinodal region. X-ray diffraction measurements and scanning transmission electron microscopy (STEM) observations show that the films are phase-separated along the [001] direction and lamellar structures are formed in a parallel or slanted direction to the sapphire substrates depending on the film orientation. The results indicate the multilayer formation via spinodal decomposition in the TVO films. STEM investigations also reveal a relatively high Ti concentration in the decomposed phases, reflecting the influence of lattice deformation on the phase decomposition in the films. Our work shows that spinodal decomposition is a promising approach for the formation of a multilayer structure in TVO films and helps deepen understanding the spinodal decomposition in TVO system.