Lateral Rutile/Anatase Biphase TiO₂ Superlattice: Its Step-Assisted Controllable Growth and Interfacial Structure

Rutile/Anatase (R/A) biphase TiO₂ has superior photocatalytic performance than its single-phase counterpart due to the effect of interface band alignment. However, two crucial issues remain unresolved: First, the controllable growth of epitaxial R/A TiO₂ with unburied interfaces is extremely challenging. Second, the direction of electron flow is full of controversy since the atomic and electronic structures of the R/A interface have not been experimentally obtained. Here a controllable growth of lateral R/A biphase TiO₂ superlattice on stepped LaAlO₃ substrates is demonstrated. The R-TiO₂ nucleates at the steps of substrate while the A-TiO₂ grows on the terraces. It is revealed that the R/A interface has a built-in electric field and a reduced band gap. Photogenerated electrons flow toward A-TiO₂ due to its higher electron affinity. The lateral R/A biphase TiO₂ superlattice exhibits outstanding water-splitting performance and may find applications in other fields. The strategy of step-assisted growth of lateral biphase superlattice should be applicable for other compounds with polymorphs.