二氧化钒/石墨烯界面电子态的相变调控

Graphene, a 2D carbon material with a promising potentials in optoelectornic devices application, is always considered as the hot research topic initially. While for the pure graphene-based electronic devices fabrication, the biggest obstacle is the method lacking for stable and effective p-type doping of graphene. The recent experiment results indicate that some metallic oxide layers deposited onto the graphene surface will withdraw the electrons from graphene and induce the holes accumulating in graphene layer, resulting the p-type doping of graphene. .The main point of this project lies on the introducing the vanadium dioxide(VO2), which shows a typical metal-insulator phase transition (MIT) near its critical temperature, to act as the overlayer to adjust the electron density in graphene, thus achieving the hole doping of graphene.Simultaneously, the interaction between these two materials at the interface will be systematically investigated. The MIT modulated p-type doping of graphene across the phase transition boundary of VO2 will be investigated by high-precision angle-resolved photoelectorn spectroscopy (ARPES) technique. At the same time, the local electric field triggered VO2 phase transition induced by the resonant surface plasma (SP) in the graphene layer in nanoscale range will be detected by a precisely electrical measurement, especially for the resistivity variation of VO2, which reflects the MIT of VO2 directly. .This current project will not only clarify the electronic states and band structure at the interface, but also give a deep understanding on the interaction between the electrons and the excited surface plason. Furthermore, it will also supply a strong direction for achieving the p-type doping of graphene and realizing the applcations of VO2 material as an energy material in the future.

石墨烯材料作为有着广泛光电器件应用前景的二维碳材料，一直是人们研究的热点。然而目前制作纯粹的石墨烯基光电器件存在的最大困难在于缺乏稳定有效的p型掺杂手段。最近实验研究表明通过在石墨烯表面沉积具有大功函数的氧化物薄膜来转移石墨烯内电子，能够实现石墨烯内空穴的积累，达到p型掺杂的目的。本课题旨在引入具有典型金属绝缘体相变特征的二氧化钒作为调节石墨烯表面电荷的氧化物薄膜来实现其p型掺杂，同时深入研究其界面的相互作用。我们将利用角分辨光电子能谱原位研究在跨越二氧化钒相变温区二氧化钒的相变对石墨烯掺杂的微观调控过程,利用高精度电学测量研究界面处石墨烯面内共振等离激元局域电场对二氧化钒相变在纳米尺度上的触发调制作用。本课题的开展不仅能够深入揭示二氧化钒/石墨烯界面的电子结构和电子态以及电子和等离激元之间的相互作用机理，而且在石墨烯的p型掺杂和二氧化钒作为能源材料的应用方面有着理论上的指导意义。

本项目主要围绕二氧化钒(VO2)材料的相变调控方法以及相变机理的探索展开深入研究。利用分子束外延技术，在石墨烯和层状云母上外延生长VO2外延薄膜，并通过机械剥离得到了自支撑的柔性VO2晶态薄膜。同时项目关注界面电场对VO2薄膜相变的调控，利用离子液作为栅电极来构筑场效应晶体管结构，通过施加外加偏压在室温下实现了VO2的相变调控。同时结合原位同步辐射谱学和衍射技术，对界面电场在相变调制过程中的作用进行了原位研究。另外在在基于高质量的外延二氧化钒薄膜制备基础上，我们通过利用金属吸附驱动酸溶液的质子掺杂进入VO2材料实现温和条件下极低成本的材料加氢，发明了“点铁成氢”掺杂调控相变技术。同时理论计算给出了该现象背后的电子-质子协同掺杂机理。另外结合固态电解质在室温下外加偏压实现了VO2薄膜的多态相变过程，并据此制作了基于VO2材料的超高性能智能窗。在本课题中，我们在VO2的相变调控方法和调控机制研究方面得到了很多新颖而重要的结果，并被国内外相关领域的研究人员广泛应用。这些研究结果不仅丰富了VO2相变调控手段和相应的相变研究理论，而且有望实现高性能的VO2相变器件，进一步推动其在光电器件和节能材料方面的应用。