PNNL

Abstract

Separation of electrons and holes, the fundamental process that underpins photoactivity, is traditionally accomplished by interfacing dissimilar materials to create band offsets and band-bending. Here, we report a new mechanism, whereby electron-hole separation in TiO2 is promoted by gradient structures that give rise to continuous band bending across ~10 nm large regions leading to a large functionally active volume fraction and resulting in exceptionally high photoactivity. These gradient structures form along a previously unreported transformation pathway from anatase to rutile by thermal treatment on nanoscale TiO2 and persist at room temperature. These findings suggest that interphase matter based on extended gradient structures can be designed to induce new functions not achievable using abrupt interfaces.