二维层状材料合成与结构演变的原位透射电镜研究

Two dimensional (2D) layered materials with their rich unique properties are promising for application in 2D semiconductor devices. However, the controlled synthesis and understanding to unearth their structure-property relationships is still at an early stage and this is limiting their application. Electron microscopy techniques allow nanomaterials to be fabricated in situ through electron beam irradiation (from the imaging electrons). Such in situ electron microscopy investigations facilitate exploration of the intrinsic structure-property relationships of nanomaterials, in particular 2D nanomaterials. In this work we aim to (1) Deposit the precursor material, ex situ, on a 2D layer (Graphene, h-BN, etc.) which also serves as a support. Then, novel 2D hetero-layered materials (both laterally and vertically stacked) can be fabricated through in-situ electron beam irradiation. (2) The dynamic structure evolution of 2D layered materials under external stimuli will be explored. The ideal and ultimate goal is to understand the growth mechanism and monitor the structure evolution. This will help enable the controlled design and engineering of 2D layered materials at the atomic scale. Various external stimuli such as electron beam irradiation, thermal activation and electrical activation can be used to manipulate and tune the structure and performance of 2D hetero-layered materials, in situ. This proposal will provide new routes for investigating the atomic structure and local properties of 2D layered materials. It will also provide the bright future for its wide range of applications by experimental and theoretical studies.

二维层状纳米材料以其独特的性能有望在二维半导体器件中得到广泛应用。然而，二维层状材料的可控生长和对其结构-性能本征联系的认知不足，仍然是限制其应用的难点。原位电子显微镜技术可在原子尺度上通过成像电子束辐照诱导生长纳米材料，通过研究材料的动态结构演变规律，为揭示其结构-性能相关性提供了一个全新的途径。本项目拟从两个方面展开研究：（1）利用电子束辐照石墨烯、氮化硼等基层表面上的前驱体，诱导其生长出新的二维层状材料，并与基层构筑出纵向或侧向二维异质结；（2）研究二维异质结在电子束下的动态结构演变，解析其生长机制和结构演变规律，结合原位电、热等技术手段，在原子尺度上对二维层状材料进行可控设计与加工，最终实现对其结构-性能的有效调控。本项目的开展有望在原子尺度上探究二维层状材料的原子结构和局域物性开辟新的途径，并为其广泛应用打下实验与理论基础。

石墨烯独特的单原子厚二维结构特征以及它呈现出来的独特的物理化学性能，极大的激发了人们探索和制备新型二维层状材料的兴趣。虽然有理论研究认为超过45种金属元素有望形成单原子层厚的二维纳米结构，然而，这些材料的合成方法和条件仍然是个挑战，它们是否可以像石墨烯一样能够稳定存在，也缺少实验上的证据。此外，二维层状材料生长机制仍未盖棺定论，如何实现对二维层状纳米材料的可控制备，解析其生长机制，仍然是材料科学研究的热点和难点。本项目采用电子束辐照技术，通过对电子束的工作方式及能量、剂量、束斑尺寸等精确控制，将石墨烯表面上的金属原子簇诱发形成了自支撑的二维金属原子膜，并进一步研究了这些二维金属原子膜，以及金属原子与石墨烯基底在电子束辐照下的动态结构演变过程，解析其演变规律和反应机制。具体工作包括：（1）利用电子束辐照，在单层石墨烯边缘处制备得到仅有一个原子厚的二维金原子纳米带；（2）是利用原位电子束辐照在石墨烯表面或纳米孔中形成单原子层厚的二维金、银、铜原子膜，并进一步研究了这些新型二维纳米材料在电子束下的动态结构演变过程及规律；（3）是研究了原位电子束辐照下，金属（金，铬）原子在石墨烯晶格中/孔洞边缘处形成的掺杂缺陷及稳定性。