Templated epitaxy of TiO_2(B) on a perovskite

摘要

The bronze-phase TiO_2(B) has an open atomic framework that makes it a good candidate for applications in photochemical and electrochemical conversion of energy. However, the synthesis of bronze-phase TiO_2(B) thin films on perovskite substrates, such as SrTiO_3 (STO), which is one of the most conventional versatile substrates for oxide epitaxy, has been extremely challenging owing to the preferential formation of the anatase TiO_2 over TiO_2(B). The main reason is that the anatase TiO_2 has not only a smaller lattice mismatch than TiO_2(B), but also a better structural symmetry match when grown on STO. Here, we demonstrate a way to circumventing this problem by using a VO_2(B) buffer layer, yielding the growth of a high-quality single crystalline TiO_2(B) film on a (001)-oriented STO substrate. From the resulting TiO_2(B) film, we found that this film has a large optical bandgap of ～3.6 eV, which is close to the known theoretical value, the largest among TiO_2 polymorphs, and useful for developing high-power energy devices.