The Mechanism Of Electric Field Trigger Vanadium Dioxide Film Phase Transition

As a typical correlated oxide material, vanadium dioxide (VO2) shows a metal-insulator transition (MIT) behavior at the temperature of 340K, accompanying with a simultaneous crystal lattice transformation. Across the phase transition, the conductivity will changed with the magnitude of 3～5 orders, the magnetic property will transfer from antiferromagnetic to paramagnetic characteristics and the infrared transmittance will show a great change at the same time. Due to these specific phase transition features, VO2 has attracted great interest and shown potential applications in many field, such as the infrared laser protection, uncooled infrared detector, smart windows, memory storage and super capacitor.However, there exists a bottleneck for the practical applications of vanadium dioxide:the relatively high critical temperature Tc. Thus decreasing the Tc value of VO2 is very meaningful. Now many methods have been proposed to reduce the VO2 phase transition temperature, such as high valance metal elements doping, hydro genation, electric field induced oxygen vacancy, the interface strain, ion implantation and voltage regulation. Although high valance metal elements doping and interface strain can effectively reduce the Tc value, it is irreversible and difficult to achieve continuously phase control. Hydrogenation process is reversible, but H-doped VO2 is not stable in the air for a long time. Applying electric field by ion liquid to produce oxygen vacancies in VO2 crystal will inevitably degrade the quality of VO2 film. By using the voltage to control the Tc can not only realize continuous and reversible phase modulation, it will also not damage the quality of the film, which has caused great interest.Although the voltage regulation of the vanadium dioxide phase transition behavior is increasingly becoming research hotspots, the mechanism of phase transition regulation has not yet been determined, there is a great deal of controversy between electric field and joule heat induced mechanism. Therefore we will explain the mechanism of phase transition regulation from a new angle in this paper. We also study the vanadium dioxide composite material systems to extent its application area, and the main research contents of this paper include:(1) High quality film of vanadium dioxide single crystal film was grown on sapphire substrate with OMBE method, and studied delayed characteristic of the voltage regulate vanadium dioxide phase transition process. From the perspective of thermodynamic equilibrium, we also studied the relationship in voltage, location temperature and time, and gave out a direct evidence of joule heat mechanism.(2) Vanadium dioxide thin film, ferromagnetic Ni film and antiferromagnetic NiO film were grown on sapphire substrate with OMBE method to build multilayer membrane structure, and we found that the phase transition behavior of vanadium dioxide affect the coercivity of ferromagnetic material, which can extent the application of vanadium dioxide in electromagnetic material.(3) Vanadium dioxide film was grown on n-GaN substrate by OMBE method, and applied external voltage/current on n-GaN substrate which has good conductivity performance to continuously regulate the phase transition process of vanadium dioxide.