Formation and evolution of body-centered orthorhombic mesophase in TiO ₂ thin films

A new mesophase orientation has been established in TiO₂ thin films formed by self-assembling of a poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) triblock copolymer (Pluronic F127). They were then characterized by using scanning electron microscopy, transmission electron microscopy, small-angle X-ray scattering, and X-ray diffraction. This new mesophase was identified and indexed as a body-centered orthorhombic mesophase structure with the (001) plane parallel to the substrate. It may well originate from a body-centered tetragonal structure, orienting with the square base perpendicular to the substrate. The mesophase then underwent a uniaxial contraction in the direction normal to the substrate upon drying and thermal treatment. As a result, the in-plane parameters were preserved whereas the out-of-plane parameters were markedly reduced by heating.