Self-organized vertical multilayer structures in spinodally decomposed TiO₂-VO₂ films on glass substrates

In this study, we investigated the formation of vertical multilayer structures via phase separation in TiO₂-VO₂ films on glass substrates. A key point for the formation is to utilize the anisotropy in the spinodal decomposition of the system. Solid-solution films of Ti_0.3V_0.7O₂ were grown on quartz glass substrates using pulsed laser deposition and annealed inside the spinodal region. X-ray diffraction, scanning transmission electron microscopy (STEM) measurements showed that spinodal decomposition occurs along the c-axis, and multilayer structures composed of alternating stacking of Ti- and V-rich phases were formed in the annealed film. In addition, STEM observations revealed that the multilayer structures were aligned vertically on the surface to the glass substrates. In resistivity measurements the annealed film showed a metal-insulator transition with the transition temperature lower than Ti_xV_1-xO₂ bulk due to the strain effect induced by the coherent interface between Ti- and V-rich phases. The overall results clearly show that vertical multilayer structures were formed via spinodal decomposition along the c-axis direction in the Ti_0.3V_0.7O ₂ film on the glass substrates. Our study indicates that anisotropy in the spinodal decomposition is an effective approach for the formation of self-organized vertical multilayer structures in Ti_0.3V_0.7O ₂ films on glass substrates, and provides useful guidelines for generating self-organized novel nanostructures on amorphous substrates in oxide films.