Vanadium dioxide is a strongly associated transition metal oxide material with a wide range of application prospects. The most notable feature is that it has four to five orders of magnitude of insulation-metal phase transition at 68°C. VO 2All kinds of photoelectric characteristics are closely related to its phase transition, but its relatively high phase transition temperature has become a major bottleneck in practical application. Through in-depth study of its phase change microscopic mechanism, it has explored effective phase change control methods to reduce phase. Variable temperature is of great significance in promoting its practical application.
Hydrogen atoms can effectively enter VO due to their small atomic radius 2The crystal lattice realizes electron doping to achieve the purpose of controlling phase transition. The method of catalytic hydrogenation using traditional high-temperature noble metals is used by the Zou Chongwen Research Group of the National Synchrotron Radiation Laboratory and the Jiangjun Research Group of the National Research Center for Microscale Materials Science at the University of Science and Technology of China. VO 2The three-phase sequential phase transition from the insulation-metal-insulation is realized in the film, and the hydrogen-induced electron-doped filling VO is revealed. 2The mechanism of conduction band energy levels (Phys. Rev. B 96, 2017, 125130). However, conventional hydrogenation doping techniques rely on conditions such as high energy-consuming temperatures and pressures, expensive precious metal catalysts, and hydrogenated The catalytic metal deposited on the surface of the material is also difficult to remove, and these adverse factors become constrained by VO 2Material hydrogenation phase change regulation and application barriers.
Recently, researchers have broken through the catalytic hydrogenation of high-temperature precious metals to regulate VO 2The traditional method of phase transformation achieves the use of metal adsorption to drive protons of acid solutions into VO 2The material achieves hydrogenation of materials at very low cost under mild conditions and invents the technique of 'hydrogen generation from point iron'.
Acid solution is easily corroded including VO 2Most of the oxides inside, so the acid can not be used as a hydrogen source in the hydrogenation treatment of oxide materials under normal temperature and pressure conditions. In the experiment, the researchers found that the metal particles with the appropriate work function and VO 2After contact with the film into the acid solution, VO 2The film is not only not corroded by the acid, but it is rapidly hydrogenated and induces a phase change. This phase change process has an extremely rapid diffusion effect, so that only a very small metal particle (1mm in diameter) can make a diameter of two inches VO 2The epitaxial film is resistant to corrosion and metallization, thereby achieving a similar 'point of iron to gold' point-of-iron hydrogenation effect. Theoretical predictions reveal the electron-proton co-doping mechanism behind this phenomenon. When the low work function metal contacts High work function VO 2When electrons spontaneously inject into VO 2Because of the electrostatic induction effect, protons in the acid are drawn into VO. 2, making VO 2Metallization and the formation of oxygen vacancies can be greatly enhanced, which can prevent the corrosion of the acid liquid. In metallized VO 2On the basis, if a lower work function metal such as Al, Zn, etc. is used, more electrons and protons can be further injected, so that the electrons are filled into the top of the new valence band to form a new insulating state, from the insulation-metal- Insulation of three phases in turn.
The electron-proton co-doping strategy is achieved by simple solution of acid, metal particles, VO 2The contact realizes the 'intrinsic insulative state-metal state-new insulative state' three-state adjustment, which can not only develop into a doping manner compatible with the conventional environment, but also have a positive influence on the research of the electronic synergy. Modification and regulation has always been the focus of physical, chemical and material science research. Doping is one of the most effective methods. Based on the principle of electron-proton co-doping, the researchers replaced the acid solution with a lithium ion solution and developed it into a solution. Electron-ion co-doping strategy, which also achieves lithium ion doping and regulates VO 2Phase transition behavior. It has been further found that this strategy can achieve more oxide materials, such as titanium dioxide (TiO2) doped hydrogenation, verifying the universality of this doping technology. Relative to traditional doping techniques tend to Using high-temperature, high-pressure and noble metal catalysis, this research institute develops a doping method that is more compatible with conventional mild environments, is easy to operate, and is extremely inexpensive. It is a development of new functional materials and devices and promotes the development of basic theory. It's all important.
Relevant research results were published in "Nature-Communications", Ph.D. candidate Chen Yuliang, visiting scholar Wang Zhaowu as the co-first author, associate researcher Zou Chongwen, and professor Jiang Jun as correspondents. The study was approved by the National Key Basic Research Development Program Youth Special projects for scientists, National Natural Science Foundation of China, Fundamental Research Funds for Central Universities, and Youth Innovation Promotion Association of Chinese Academy of Sciences.
