Electronic Doping Of Vanadium Dioxide

Because of electronic correlation,strongly correlated oxides show many wonderful physical properties,such as metal-insulator transition?MIT?,superconductivity,and magnetic order.As a typical transition metal oxide,vanadium dioxide?VO₂?shows a dramatic metal-insulator transition near 68? accompanying structure phase transition,infrared switch effect,and magnetic transition at same time,which makes VO₂ an ideal physical model for studying electronic correlation as well as a potential candidate in fields of temperature switch,laser protection,smart window and micro-machine.However,the theoretical mechanism of VO₂ MIT is debating between Peierls transition and Mott transition.On the other hand,the relatively high transition temperature is an intrinsic barrier of applications of VO₂.Recently,a lot of research have proven that electronic doing can adjust properties of correlated oxides effectively.Here,we dope electrons into VO₂ by three ways.The electron-doped VO₂ is explored systematically from aspects of physical properties,crystal structure,band structure,and electronic states by using advanced electronic transport measurement,optical spectrum,characterizations of synchrotron radiation and theoretical calculation for trying to unveil transition mechanism as well as transition feature.The main research and results are summarized as follows:1.VO₂ field-effect transistor with solid or liquid dielectrics may suffer leakage current,breakdown,or chemical doping,which complexes the mechanism of controlling phase transition.Furthermore,applying electric field by external source is not convenient in certain scenarios.Hence,we introduce triboelectric filed as a novel electronic doping by contact-separation of triboelectric dielectrics,which can induce 10¹⁰-10¹¹ cm^-2 electron density in VO₂ channel.The in-situ resistance measurement at different temperatures suggests this electron density is able to adjust transition feature strongly in phase transition region.Finite elements analysis stimulates the induction of electron in VO₂ channel,and first-principle calculation confirms the mechanism about this kind of electrostatic doping.2.Compared with solid dielectric,liquid dielectric or electrolyte have been proved that can accomplish higher doping concentration and nonvolatile chemical doing.The VO₂ films with different preferred directions are deposited by molecular beam epitaxy.The Li can be charged/discharged into VO₂ by gating lithium electrolyte.The gating effect is nonvolatile and strongly influenced by crystal directions.Synchrotron radiation characterization confirms that Li doping has changed crystal structure of VO₂ as well as increased the occupancy of t2%orbital,which is responsible for the metallic state formation as proved by first-principle calculation.Dynamic simulation suggests Li+ diffusion along[001]has lowest energy barrier.3.Low work function metal as an isolated electron source and acid liquid as an isolated proton source,for the first time,a synergetic doping effect of electron-proton is observed by immersing VO₂ into acid with contacting a metal particle on its surface at room temperature and pressure.The synergetic doping is so powerful that makes VO₂ be anticorrosion and switch between triple states.Various characterizations and theoretical calculation confirm the synergetic mechanism arising from the perfect cooperation of work function difference,proton breaking electrostatic screen,and electronic doping anticorrosion.This synergetic effect can be also extended to electron-ion synergy.