Crystallographic Pathways to Tailoring Metal-Insulator Transition through Oxygen Transport in VO₂

The metal-insulator (MI) transition of vanadium dioxide (VO₂) is effectively modulated by oxygen vacancies, which decrease the transition temperature and insulating resistance. Oxygen vacancies in thin films can be driven by oxygen transport using electrochemical potential. This study delves into the role of crystallographic channels in VO₂ in facilitating oxygen transport and the subsequent tuning of electrical properties. A model system is designed with two types of VO₂ thin films: (100)- and (001)-oriented, where channels align parallel and perpendicular to the surface, respectively. Growing an oxygen-deficient TiO₂ layer on these VO₂ films prompted oxygen transport from VO₂ to TiO₂. Notably, in (001)-VO₂ film, where oxygen ions move along the open channels, the oxygen migration deepens the depleted region beyond that in (100)-VO₂, leading to more pronounced changes in metal-insulator transition behaviors. The findings emphasize the importance of understanding the intrinsic crystal structure, such as channel pathways, in controlling ionic defects and customizing electrical properties for applications.