Tuning the Two-Dimensional Electron Gas at Oxide Interfaces with Ti–O Configurations: Evidence from X-ray Photoelectron Spectroscopy

A chemical redox reaction can lead to a two-dimensional electron gas at the interface between a TiO2-terminated SrTiO3 (STO) substrate and an amorphous LaAlO3 capping layer. When replacing the STO substrate with rutile and anatase TiO2 substrates, considerable differences in the interfacial conduction are observed. On the basis of X-ray photoelectron spectroscopy (XPS) and transport measurements, we conclude that the interfacial conduction comes from redox reactions, and that the differences among the materials systems result mainly from variations in the activation energies for the diffusion of oxygen vacancies at substrate surfaces.