二维原子晶体的低电压扫描透射电子显微学研究

二维原子晶体材料,如石墨烯和过渡金属硫族化合物等,具有不同于其块体的独特性能,有望在二维半导体器件中得到广泛应用.晶体中的结构缺陷对材料的物理化学性能有直接的影响,因此研究结构缺陷和局域物性之间的关联是当前二维原子晶体研究中的重要内容,需要高空间分辨率的结构研究手段.由于绝大部分二维原子晶体在高能量高剂量的电子束辐照下容易发生结构损伤,利用电子显微方法对二维原子晶体缺陷的研究面临诸多挑战.低电压球差校正扫描透射电子显微(STEM)技术的发展,一个主要目标就是希望在不损伤结构的前提下对二维原子晶体的本征结构缺陷进行研究.在STEM下,多种不同的信号能够被同步采集,包括原子序数衬度高分辨像和电子能量损失谱等,是表征二维原子晶体缺陷的有力工具,不但能对材料的本征结构进行单原子尺度的成像和能谱分析,还能记录材料结构的动态变化.通过调节电子束加速电压和电子辐照剂量,扫描透射电子显微镜也可以作为电子刻蚀二维原子晶体材料的平台,用于加工新型纳米结构以及探索新型二维原子晶体的原位制备.本综述主要以本课题组在石墨烯和二维过渡金属硫族化合物体系的研究为例,介绍低电压扫描透射电子显微学在二维原子晶体材料研究中的实际应用.

Low voltage scanning transmission electron microscopy for two-dimensional materials

Two-dimensional (2D) materials, such as graphene and transition-metal dichalcogenide monolayers, have unique properties that are distinctly different from those of their bulk counterparts, and hopefully possess a wide range of applications in 2D semiconductor device. Structural defects are known to have profound influences on the properties of crystalline materials; thus, correlating the defect structure with local properties in 2D material is of fundamental importance. However, electron microscopy studies of 2D materials on an atomic scale have become a challenge as most of these materials are susceptible to electron beam irradiation damage under high voltage and high dose experimental conditions. The development of low voltage aberration-corrected scanning transmission electron microscopy (STEM) has made it possible to study 2D materials at a single atom level without damaging their intrinsic structures. In addition, controllable structural modification by using electron beam becomes feasible by controlling the electron beam-sample interaction. New nanostructures can be created and novel 2D materials can be fabricated in-situ by using this approach. In this article, we review some of our recent studies of graphene and transition-metal dichalcogenides to showcase the applications of low voltage aberration corrected STEM in 2D material research.