In Situ Tem Study On Metal-Insulator Transition Of Vanadium Dioxide And Its Modulation

Vanadium dioxide（VO₂）is widely studied for its metal-insulator transition（MIT）at near room temperature.The MIT is accompanied by changes in electronic,optical properties and volume.In this study,using advanced electron microscopy,two key issues in MIT of VO₂ that are associated to the transition mechanism of MIT and the modulation of MIT are investigated.The micro/nanowires of VO₂ was synthesized,based on which the fundamental transition mechanisms as well as the strain engineering of the MIT were then pursued.Some new approaches to modulate the MIT of VO₂ was developed.The“Synthesis-Research”process was carried out as a complete project.The main achievements are following:（1）The micro/nanowires of VO₂ was synthesized by physical vapor transportation method.A series of experiment platform for in situ heating and electric testing of VO₂ at different scales in TEM and light microscopy were built up.（2）The transition mechanism of the MIT was studied.The MIT can be triggered with current,where the decoupling that electronic transition preceded structural transition was observed.Under an electric field of 10⁷ V/m without current flowing the nanowire,no MIT was observed.It is inferred that the Joule heat of current plays a key role in electrically triggered MIT of VO₂.（3）The strain engineering of the MIT was performed.By bending the nanowire,the tensile/compress strains along the axial direction of the nanowire were applied so as to modify the transition temperature,the metal-insulator domain structure as well as the electric transport property of the nanowire.（4）By in situ lithiation of the VO₂ nanowire in TEM,the M₂ phase of the VO₂ was stabilized to room temperature,which is a new strategy to stabilize the M₂.The strain introduced after the Li ions were inserted into the vanadium-oxygen octahedron channels in lattice of VO₂ is considered to stabilize the M₂.（5）The controllable preferential nucleation of the MIT in VO₂ was realized by electron irradiation in TEM.The electron irradiation can reduce the transition temperature of VO₂ from 68°C even to room temperature by creating oxygen vacancies that were arising from the Auger decaying of oxygen atom in the irradiated zone.