Evolution of Structural and Electrical Properties of Oxygen-Deficient VO₂ under Low Temperature Heating Process

Structural stability and functional performances of vanadium dioxide (VO₂) are strongly influenced by oxygen vacancies. However, the mechanism of metal-insulator transition (MIT) influenced by defects is still under debate. Here, we study the evolution of structure and electrical property of oxygen-deficient VO₂ by a low temperature annealing process (LTP) based on a truss-structured VO₂ nanonet. The oxygenation process of the oxygen-deficient VO₂ is greatly prolonged, which enables us to probe the gradual change of properties of the oxygen-deficient VO₂. A continuous lattice reduction is observed during LTP. No recrystallization and structural collapse of the VO₂ nanonet can be found after LTP. The valence-band X-ray photoelectron spectroscopy (XPS) measurements indicate that the oxygen deficiency strongly affects the energy level of the valence band edge. Correspondingly, the resistance changes of the VO₂ films from 1 to 4.5 orders of magnitude are achieved by LTP. The effect of oxygen vacancy on the electric field driven MIT is investigated. The threshold value of voltage triggering the MIT decreases with increasing the oxygen vacancy concentration. This work demonstrates a novel and effective way to control the content of oxygen vacancies in VO₂ and the obvious impact of oxygen vacancy on MIT, facilitating further research on the role of oxygen vacancy in structure and MIT of VO₂, which is important for the deep understanding of MIT and exploiting innovative functional application of VO₂.