Nb-doped coherent TiO2/LaAlO3 interfaces: Segregation mechanism and improved photocatalytic performance

Elemental doping at coherent interfaces is very difficult and rarely used to improve the interfacial properties since coherent interfaces have low interfacial energies and lack open space for trapping dopant atoms. Exploring universally applicable strategies for elemental doping at coherent interfaces represents an important progress in interface science and engineering. In this study, Nb atoms are successfully doped at coherent (001) LaAlO₃/anatase-TiO₂ interfaces, which enhances greatly the efficiency of photocatalytic hydrogen production from water. Transmission electron microscopy investigations reveal that both LaO- terminated and AlO₂-terminated LaAlO₃/anatase-TiO₂ interfaces can trap two layers of Nb atoms, which accompanies with the formation of La vacancies between them. First-principles calculations suggest that Nb atoms segregate at the interfaces under the action of potential gradient, which increases significantly the strength of the built-in electric field in TiO₂, thereby facilitating the separation of photogenerated carriers and improving the photocatalytic performance. The H₂ production of the Nb doped coherent interface is about 4 times that of the pristine coherent interface. Since potential gradient widely exists at various interfaces including the coherent ones, elemental doping by potential gradient should be an universally applicable fabrication method for tuning the properties of interfaces and heterostructures.