Coexistence of Both Localized Electronic States and Electron Gas at Rutile TiO₂ Surfaces

Abstract

Localized electron polarons formed through the coupling of excess electrons and ionic vibrations play a key role in the functionalities of materials. However, the mechanism of the coexistence of delocalized electrons and localized polarons remains underexplored. Here, the discovery of high‐mobility 2D electron gas at the rutile TiO2 surfaces through argon ion irradiation induced oxygen vacancies is reported. Strikingly, the electron gas forms localized electronic states at lower temperatures, resulting in an abrupt metal–insulator transition. Moreover, it is found that the low‐temperature conductivity in the insulating state is dominated by excess free electrons with a high mobility of ≈103 cm2 V−1 s−1, whereas the carrier density is dramatically suppressed with decreasing temperature. Remarkably, it reveals that the application of an electric field can lead to a collapse of the localized states, resulting in a metallic state. These results reveal the strongly correlated/coupled nature between the localized electrons and high‐mobility electrons and offer a new pathway to probe and harvest the exotic electron states at the complex oxide surfaces.

Facet-Dependent Interfacial Charge Transfer between T-Phase VS2 Nanoflakes and Rutile TiO2 Single Crystals

“…Rutile TiO 2 (termed as r-TiO 2 ) has been extensively studied as a prototypical representative of functional TMO owing to the attractive physicochemical properties 28,29 and wide range applications in photocatalysis, medicine, sensors, etc. 30 optoelectronic devices.…”

“…Rutile TiO 2 (termed as r-TiO 2 ) has been extensively studied as a prototypical representative of functional TMO owing to the attractive physicochemical properties , and wide range applications in photocatalysis, medicine, sensors, etc. − Its hybridization with metallic 2D T-VS 2 can be potentially applied in photoelectrochemical processes as well as optoelectronic devices. Therefore, in this work, we have developed an ambient-pressure CVD method to directly grow high-quality few-layer T-VS 2 flakes on the atomically flat r-TiO 2 single crystals and to construct the model system of VS 2 /TiO 2 with an ideal interface structure.…”