石墨烯纳米带的边缘效应及器件应用研究

Graphene Nanoribbons (GNRs) have attracted much interest because of their unique one-dimensional structures with open edges and tunable bandgaps. However, so far, common synthetic methods such as plasma etching and oxidative unzipping of carbon nantoubes inevitably create a lot of defects on the edges of GNRs, leading to low temperature transport characteristics dominated by defects rather than the intrinsic properties of GNRs. This has also limited the device applications of GNRs. Recently, we were able to synthesize high-quality GNRs by sonication-assisted unzipping of carbon nanotubes. Many GNRs exhibit well-difined, atomically smooth edges which provide an ideal testbed for many theoretical predictions. In this project, we propose to take advantage of our high-quality GNR samples, systematically study the electron transport in GNR quantum dots and quantum wires and make high-performance GNR devices. We will reveal the effect of quantum confinement and open edges on GNR properties (such as bandgap and conductivity) and transport phenomena (such as Coulomb blockade and excited states). We will explore the new physics introduced by the open edges such as the magnetic edge states widely predicted by theories. We will investigate the transport signature of the edges states, and realize spin-polarized transport. Finally, we will fabricate high mobility and high on/off ratio GNR field-effect transistors and pn junctions, and study their potential applications in future electronics.

石墨烯纳米带以其独特的一维结构、开放性边缘和可控带隙成为石墨烯物理和器件研究的前沿和热点。然而常用的物理刻蚀以及氧化展开碳管方法不可避免地在制备过程中引入大量边缘缺陷，导致了纳米带在输运研究中无法表现出理论预测的本征性质，极大的限制了纳米带在器件方面的应用。最近，申请人与合作者通过超声展开碳管，实现了边缘平滑的纳米带。本项目拟利用申请人在石墨烯纳米带合成上的优势，完善现有的合成技术，系统研究石墨烯纳米带量子线及量子点的低温电子输运性质与高性能电子器件。揭示纳米带的量子尺寸效应与边缘对其物理性质（禁带宽度、电导率等）及输运现象（库伦阻塞、电子激发态等）的影响；实验上探索规则边缘引入的磁性边缘态与自旋极化输运，并在此基础上研究外场对电子/自旋输运的量子调控规律；实现高迁移率、高开关比的场效应器件以及纳米带pn结器件，为石墨烯纳米带在集成电路中的应用提供器件基础。

本项目基于申请人在石墨烯纳米带合成方面的优势，研究了高质量纳米带的低温电子输运性质与电子器件，揭示了高磁场下尺寸、缺陷等对边缘态电子输运的影响规律。同时，紧跟国际前沿，开展了二维过渡金属硫族化合物电子器件研究，在MoS2等高性能晶体管方面取得了众多具有国际影响力的成果。共发表了19篇论文，包括Nature Comm., PRL, Adv. Mater.等高水平论文，完成了项目的预期目标。主要成果如下：1. 利用超声化学方法打开多壁纳米碳管，制备出宽度分布在10-30nm的双层石墨烯纳米带，该纳米带晶体管的载流子迁移率最高可以达到2500cm2/Vs，电子自由程最高可以达到50nm，并首次在20nm以下的准一维体系中观测到量子霍尔效应。2.发现环境气体吸附在MoS2中引入大量表面态，发明原位真空退火技术，提高迁移率50-100倍，被国际上广泛采用。发现MoS2中存在大量硫空位缺陷，提出并验证了电子的跃迁输运机制，为提高迁移率指明了方向。使用硫醇界面修饰方法及高k介质的屏蔽作用，将单层MoS2晶体管室温迁移率提高至150cm2/Vs，是目前报道的最高纪录。在研究过程中，发展了一套理论模型，系统揭示了二维层状半导体材料的微观电子散射机制。