摘要
纳米结构的高精度可控加工是制约器件小型化发展的重要限制因素之一,而基于透射电子显微镜的电子辐照有望在加工精度上推动纳米加工的进程.透射电子显微镜中高能电子束不仅能用于原子结构成像,还可用于原位辐照加工.因此,基于透射电子显微镜的电子辐照效应研究既有利于从原子尺度上探索材料在电子辐照作用下的结构稳定性及结构演变规律,又有利于加深对电子辐照过程的理解,为纳米结构的高精度可控加工提供理论依据和实验基础.本文将简要介绍几种常见的电子辐照效应,并综述近年来利用透射电子显微镜在石墨烯、氮化硼、过渡金属硫族化合物等二维层状材料原位辐照方面的研究进展,为进一步研究二维材料结构稳定性和精准、可控加工低维纳米结构提供参考.
High precision fabrication of nanostructure is a primary limiting factor to devices miniaturization.Electron beam is expected to promote the process on the accuracy of fabrication.For instance,electron beam lithography has been developed to replace optical lithography to transfer patterns and has produced line width on the order of 10 nm or smaller.Furthermore,electrons can directly interact with the sample to cause changes in structure and properties,which is expected to be used for fabrication of specialized nanostructures with nanometer even sub-nanometer precision.Transmission electron microscopy（TEM） has become an indispensable tool for the study of the interaction between energetic electrons and sample.A large number of experimental studies have been carried out inside TEM where electron beam can not only be used for atomic resolution imaging but also for irradiation.These studies are conductive to understanding phenomena induced by irradiation in essence,which are the theoretical and experimental basis for controllable manipulation via electron irradiation.However,TEM images are parallel projections of three-dimensional（3D） structures onto the image plane,which tremendously increases the difficulty of atomic-structure analysis.Two-dimensional（2D） layered materials（graphene,hexagon boron nitride,transition metal dichalcogenides and so on） emerged and boomed in the past decade,which provide ideal systems to study electron irradiation effects on matter.As mono-or bi-atomic sheets,their atomic structures are accessible to image directly with atomic resolution in the advent of spherical aberration corrected TEM.The lateral resolution in TEM image,which is smaller than the bond length,leaves almost no room for uncertain interpretation.Meanwhile,the reconstruction of the lattice occurs in the 2D plane can be seen without any projection artifacts.Besides,structural changes,as they are generated under irradiation with energetic electrons,can be monitored in real time.On this basis,novel mechanisms of lattice reconstruction,which did not appear in other materials,have been discovered,such as transformations between hexagons and pentagon-heptagon pairs by in-plane 90？ rotation of C–C bonds in graphene sheet.In addition to a detailed understanding of radiation-induced structure evolution and their influence on the properties of 2D sheet,the design of new structures has become feasible.Especially,electron beams inside modern TEM can be focused onto spots less than 1 ？,which allows use of the beam as tweezers to manipulate materials even at the single atom level.In this way,sub-nanometer quasi one dimensional structures,such as nanowires,nanoribbons,nanotubes and atomic chains,have been fabricated in 2D nanosystems.Sub-5 nm nanopores can also be sculpted in 2D sheets,which is particularly suitable for chemical and biological molecule detection.Besides,2D materials can serve as substrates to study radiation-induced structural evolution of substance on their surface.This review gives a brief summary of our current knowledge about electron irradiation in the aspect of elastic scattering and inelastic scattering,and a summary of the most recent experimental results on in situ irradiation in 2D layered material systems,including atomic structural evolution under electron irradiation and controllable fabrication of nanostructures by TEM.
出处
《科学通报》
EI
CAS
CSCD
北大核心
2017年第25期2919-2930,共12页
Chinese Science Bulletin
基金
国家自然科学基金(51420105003
61274114
11327901
61601116
11674052)
国家杰出青年科学基金(11525415)
江苏省自然科学基金(BK2012024)资助
关键词
二维材料
电子辐照
透射电子显微镜
结构演变
纳米加工
2D material
electron irradiation
transmission electron microscope
structural evolution
nanofabrication
