Suppression of Metal-Insulator Transition in VO₂ by Interfacial Oxygen Migration

Oxygen defects are essential building blocks for designing functional oxides with remarkable properties, ranging from electrical and ionic conductivity to magnetism and ferroelectricity. Oxygen defects therefore can profoundly alter crystal and electronic structures and enables emergent phenomena. In this work, we achieved tunable metal-insulator transition (MIT) in oxide heterostructures by inducing interfacial oxygen vacancy migration. We chose VO_2-x as a model system due to its near room temperature metal-insulator transition temperature. We found that depositing a TiO₂ capping layer on an epitaxial VO2 thin film can effectively suppress the MIT in VO₂. We systematically studied the TiO₂/VO₂ heterostructures by structural and transport measurements, resonant inelastic x-ray scattering, X-ray photoelectron spectroscopy, and first principles calculations and found that that oxygen vacancy migration from TiO₂ to VO₂ is responsible for the suppression of MIT. Our findings underscore the importance of the interfacial oxygen “diode” effect in determining electronic structure and functionality, and provide new pathways of designing oxide heterostructures for novel ionotronics and computing devices.