2D Vacancy Confinement in Anatase TiO₂ for Enhanced Photocatalytic Activities

Abstract

Light‐driven energy conversion devices call for the atomic‐level manipulation of defects associated with electronic states in solids. However, previous approaches to produce oxygen vacancy (V_O) as a source of sub‐bandgap energy levels have hampered the precise control of the distribution and concentration of V_O. Here, a new strategy to spatially confine V_O at the homo‐interfaces is demonstrated by exploiting the sequential growth of anatase TiO₂ under dissimilar thermodynamic conditions. Remarkably, metallic behavior with high carrier density and electron mobility is observed after sequential growth of the TiO₂ films under low pressure and temperature (L‐TiO₂) on top of high‐quality anatase TiO₂ epitaxial films (H‐TiO₂), despite the insulating properties of L‐TiO₂ and H‐TiO₂ single layers. Multiple characterizations elucidate that the V_O layer is geometrically confined within 4 unit cells at the interface, along with low‐temperature crystallization of upper L‐TiO₂ films; this 2D V_O layer is responsible for the formation of in‐gap states, promoting photocarrier lifetime (≈300%) and light absorption. These results suggest a synthetic strategy to locally confine functional defects and emphasize how sub‐bandgap energy levels in the confined imperfections influence the kinetics of light‐driven catalytic reactions.