Department of Physics, University of Oxford, Parks Road, Oxford, OX1 3PU, UK.
Center for Nanochemistry, Beijing Science and Engineering Center for Nanocarbons, Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, Beijing, 100871, P. R. China.
Adv Mater. 2017 Jul;29(27). doi: 10.1002/adma.201606741. Epub 2017 May 8.
Graphene has demonstrated great potential in new-generation electronic applications due to its unique electronic properties such as large carrier Fermi velocity, ultrahigh carrier mobility, and high material stability. Interestingly, the electronic structures can be further engineered in multilayer graphene by the introduction of a twist angle between different layers to create van Hove singularities (vHSs) at adjustable binding energy. In this work, using angle-resolved photoemission spectroscopy with sub-micrometer spatial resolution, the band structures and their evolution are systematically studied with twist angle in bilayer and trilayer graphene sheets. A doping effect is directly observed in graphene multilayer system as well as vHSs in bilayer graphene over a wide range of twist angles (from 5° to 31°) with wide tunable energy range over 2 eV. In addition, the formation of multiple vHSs (at different binding energies) is also observed in trilayer graphene. The large tuning range of vHS binding energy in twisted multilayer graphene provides a promising material base for optoelectrical applications with broadband wavelength selectivity from the infrared to the ultraviolet regime, as demonstrated by an example application of wavelength selective photodetector.
石墨烯由于其独特的电子特性，如大载流子费米速度、超高载流子迁移率和高材料稳定性，在新一代电子应用中显示出巨大的潜力。有趣的是，通过在不同层之间引入扭转角，可以进一步在多层石墨烯中设计电子结构，在可调谐的结合能处产生范霍夫奇点（vHS）。在这项工作中，我们使用具有亚微米空间分辨率的角分辨光发射谱，系统地研究了双层和三层石墨烯片层中扭转角的能带结构及其演化。在宽的扭转角范围内（从 5°到 31°），我们直接观察到了在石墨烯多层系统中的掺杂效应以及双层石墨烯中的 vHS，其可调谐能量范围很宽，超过 2eV。此外，我们还在三层石墨烯中观察到了多个 vHS（在不同的结合能处）的形成。在扭曲的多层石墨烯中，vHS 结合能的大范围可调谐为从红外到紫外波段的宽带波长选择性光电应用提供了有前景的材料基础，如波长选择性光探测器的应用实例所示。
