不同应变的褶皱结构对石墨烯电学性质的调控研究

Recently, much effort has been spent on control of graphene wrinkles motivated by the fact that wrinkles-induced lattice deformations can generate effective electric and pseudomagnetic fields on the propagating Dirac fermions, which strongly modify the electronic spectra and properties of graphene. Therefore, strain engineering, which usually induces lattice distortions in graphene, becomes a powerful method for tuning the electronic properties of this ultimate thin film. The strain can not only induce pseudomagnetic field controlling the carrier behavior, but also can modulate the band structure of graphene effectively. According to theory, a band gap can indeed be generated by applying a large strain beyond 20%. The experimental study on the effect of the wrinkles with large strain on the electronic properties of graphene is an urgent task to be faced. And, it is of great significance that the Landau quantization of pseudomagnetic fields been evidenced by transport measurements directly, especially in the application of electronic devices. In this proposal, we will investigate the effects of the wrinkles-induced strain on the electronic properties of graphene, and establish the relationship between the surface curvature of the wrinkles and the produced pseudomagnetic field. It is expected to realize a zero-field quantum Hall effect in strained graphene by transport measurements. This project also focuses on large strained wrinkles and its unusual electrical properties. These efforts may pave the way for the realization of graphene-based electronic devices, and promote the development of nanoelectronic devices.

通过在石墨烯中引入褶皱结构产生的应变可以有效调控石墨烯的电学性质，为控制石墨烯中载流子的行为开辟了新的领域—“应变工程”。应变不仅可以诱导产生赝磁场调控载流子的行为，而且可以有效调控石墨烯的能带结构。理论研究表明应变大于20%的褶皱结构可以使石墨烯能带结构打开带隙，较大应变的石墨烯褶皱结构的实验研究是目前面临的主要任务。通过输运手段测量赝磁场作用下的朗道量子化现象对石墨烯在电子器件的应用意义重大。本项目基于应变工程的最新进展，在石墨烯中通过衬底的变化获得不同应变的褶皱结构，建立褶皱结构表面曲率与产生赝磁场大小之间的关系，为褶皱结构调控赝磁场的大小提供参考和依据，采用输运手段测量零磁场下褶皱结构的量子霍尔效应，着重研究较大应变褶皱结构特殊的电学性质。本项目能够为实现以石墨烯为基础的电子器件的利用开辟道路，从实质意义上推动纳米电子器件的发展。

石墨烯作为理想的二维纳米材料，其独特的六角蜂窝状晶格结构赋予了石墨烯极高的载流子迁移率、特殊的能带结构，如何有效调控石墨烯的电学性质是实现石墨烯纳米电子学器件应用的重要前提。本课题利用化学气相沉积法在不同金属衬底表面成功制备了大面积石墨烯薄膜及单晶，并在金属衬底和非金属衬底表面获得了不同应变的石墨烯褶皱结构，详细研究了褶皱结构对石墨烯光学、电学性质的调控。项目基本按照原计划进行并做了些微调，获得的研究成果如下：.（1）通过化学气相沉积法实现了石墨烯在多种不同金属衬底表面的可控制备。.（2）利用金属衬底与石墨烯热膨胀系数的差异成功在金属衬底表面制备了具有不同应变的石墨烯褶皱结构；证实了通过将单分散颗粒引入到非金属衬底表面能够在非金属衬底表面获得具有应变的石墨烯褶皱结构。.（3）具有较大应变的双层石墨烯褶皱结构表现出朗道量子化和谷极化行为，证实了应变和褶皱结构表面大的曲率能够导致双层有转角石墨烯产生带隙，产生的赝磁场达到90T左右，推断出单、双层褶皱结构观测赝磁场的朗道能级量子化的判断依据，此外应变还能够增加双层有转角石墨烯的层间耦合强度，使费米面附近范霍夫奇点的距离减小。.（4）直径为500nm的单分散金颗粒引入的应变导致石墨烯的拉曼特征峰G与2D峰发生红移，并使G峰劈裂为G+、G-，证明应变破坏了碳原子的双重简并光学声子模E2g，通过该方式引入的应变较小，颗粒顶点处引入的应变量最大仅为0.18 %。.（5）采用化学气相沉积法，成功实现了类石墨烯二维层状材料MoS2、MoSe2的可控制备，探究了其生长机制；理论研究了缺陷和应变对单层MoSe2、WSe2的电学及磁学性质的影响。采用化学气相沉积法通过调控加热温度和生长温度实现了类石墨烯狄拉克材料三维拓扑绝缘体Bi2Se3纳米线及其Cu掺杂的可控制备。研究了二维半导体氧化物Cu2O薄膜退火自组装机理，实现了二维MoO2纳米片的可控制备及带隙调控。