离子束溅射外延h-BN二维原子晶体及其与石墨烯异质结构研究

Hexagonal boron nitride (h-BN) has the same atomic structure as graphite with a small lattice mismatch, and its lamellar nature provides it an atomically flat surface. Furthermore, owing to the absence of dangling bonds and charge traps at the surface of h-BN, using h-BN as substrate for graphene is favorable for keeping its outstanding intrinsic properties such as extremely high carrier mobility. Therefore, the graphene/h-BN heterostructure has attracted great attention for high-quality graphene electronics. Besides micromechanical exfoliation, few-layer h-BN films were prepared by chemical vapor deposition (CVD) in the most experiments. However, the complex set of interrelated growth parameters governs CVD processes, and a suitable precursor is not yet available. Physical vapor deposition, a scalable, industry-compatible process, can avoid these issues. In the present project, we firstly propose to grow few-layer h-BN epitaxial films on Cu (111) or Ni (111) substrates by ion beam sputtering, and the fabrication of graphene/h-BN heterostructure is realized by combining with CVD method. The direct deposition of the heterostructure not only offers the possibility of large-area synthesis of these materials, but also results in the high quality interfaces between graphene and h-BN, which is beneficial to the carrier transport in CVD graphene. The goal of the present project is realizing the controllable fabrication of high-quality graphene/h-BN heterostructure and elucidating the mechanism of heterogeneous nucleation and growth. This project is significant from the view of both fundamental research of growth of graphene heterostructure and applications of large-area graphene-based electronics.

六角氮化硼（h-BN）与石墨烯晶格常数匹配，可实现原子级的平整度，且其表面极少存在悬挂键和电荷陷阱，有利于保持本征石墨烯极高的载流子迁移率，因此石墨烯/h-BN异质结构成为近年来的研究热点。除了机械剥离，大部分实验研究采用化学气相沉积（CVD）制备h-BN薄层，但CVD生长过程复杂，各种生长参数相互关联，且选择合适的前驱体存在困难。离子束溅射是一种成熟且应用广泛的物理气相沉积技术，目前尚未有利用离子束溅射制备h-BN的报道。我们拟采用离子束溅射在Cu或Ni单晶薄膜上外延生长h-BN二维原子晶体，并结合CVD技术制备石墨烯/h-BN异质结构。通过直接沉积的方式可以获得大面积、任意形状的样品，而且可避免转移过程引入的污染，提高石墨烯/h-BN的界面质量。通过该项目的实施，期望实现高质量石墨烯/h-BN异质结构的可控制备，探明异质结构的成核和生长机制，为大面积石墨烯电子学的应用奠定基础。

六方氮化硼（h-BN）二维原子晶体具有与石墨烯接近的晶格常数，是构建石墨烯电子器件的重要基础，石墨烯/h-BN异质结近年来备受关注。高质量的h-BN和异质结材料是其性质研究与实际应用的前提，但目前制备的h-BN单晶的尺寸仅几十微米，h-BN薄膜的质量也尚待提高。基于此，我们在h-BN二维原子晶体及其与石墨烯异质结构的可控制备和电子学应用方面展开了深入研究。我们采用离子束溅射沉积技术（IBSD），以氩离子束轰击高纯h-BN靶材，在铜箔衬底上制备了尺寸约5微米的单层及少数层h-BN单晶。利用原位离子束刻蚀对衬底进行处理，通过生长参数调控衬底表面溅射粒子的浓度，大幅降低了h-BN的成核密度，最终在多晶Ni箔衬底上制备出尺寸大于100微米的h-BN单晶。为了进一步提高h-BN单晶畴尺寸，以蓝宝石上外延生长的单晶Ni (111)薄膜为衬底，利用IBSD成功制备出单晶畴尺寸达0.6毫米的h-BN二维晶体，这也是目前报道的h-BN单晶畴的最大尺寸。结合CVD技术，我们在铜箔衬底上制备了大面积、高质量的石墨烯/h-BN异质结及h-BNC二维杂化材料，直接沉积的方式不仅可以获得大面积、任意形状的样品，而且可避免转移过程引入的污染。此外，我们将制备的少数层h-BN及石墨烯/h-BN纵向异质结应用在深紫外探测器和石墨烯/硅肖特基结太阳能电池中，获得了良好的器件性能。该项目为可控制备大面积、高质量的h-BN二维原子晶体提供了一条新的途径，为实现h-BN及石墨烯/h-BN异质结的大面积电子学应用奠定了基础，具有重要的科学意义与应用价值。基于本项目的研究成果，在Adv. Mater., Nano Energy, Small, Appl. Phys. Lett.等期刊，项目负责人作为通信作者发表标注基金资助的论文14 篇，其中SCI论文13篇；申请3项国家发明专利，授权发明专利1 项，在国际国内会议做邀请报告4次，培养研究生4名（已毕业3名，其中2人获北京市优秀毕业生、2人获中科院院长优秀奖）。