四维扫描透射电子显微镜技术：从材料微观结构到物性分析_冯启龙.pdf

物 理 化 学 学 报 Acta Phys.-Chim.Sin.2023,39(3),2210017(1 of 15)Received:October 13,2022;Revised:November 28,2022;Accepted:November 29,2022;Published online:December 5,2022.*Corresponding author.Email: The project was supported by the National Key Research and Development Program of China(2022YFE0113800)and the National Natural Science Foundation of China(22075250,22122505,21771161).国家重点研发计划(2022YFE0113800)及国家自然科学基金(22075250,22122505,21771161)资助项目 Editorial office of Acta Physico-Chimica Sinica Review doi:10.3866/PKU.WHXB202210017 Four-Dimensional Scanning Transmission Electron Microscopy:From Material Microstructures to Physicochemical Properties Qilong Feng,Chongzhi Zhu,Guan Sheng,Tulai Sun,Yonghe Li,Yihan Zhu*Electron Microscopy Center(Analysis and Testing Center),Frontier Interdisciplinary Research Institute,School of Chemical Engineering,Zhejiang University of Technology,Hangzhou 310014,China.Abstract:The resolution limit of scanning transmission electron microscopy(STEM)has now reached atomic resolution.Further,owing to its flexible multi-channel imaging and powerful spectral characterization abilities,STEM has shown immense promise for microscale characterization in materials sciences,life sciences,and other fields.However,the traditional STEM detector is limited by its single-pixel integral detection mechanism,due to which it can only collect scattered electrons at a specific angle.This not only results in a loss of angle-resolved information of the scattered electrons,but also reduces the dose efficiency of the incident electrons.Therefore,it is imperative that new imaging techniques are developed to achieve high-throughput,high-electron-dose-efficiency imaging.Recent advances in electron direct detection techniques and detectors with partitioned or pixelated configurations,as well as the rapidly increasing computing power and disk storage,have contributed to the rapid development of four-dimensional STEM(4D-STEM)technology.Uniquely,4D-STEM allows one to acquire structural information associated with scattered electrons.During the acquisition of 4D-STEM data,the convergent electron beam performs two-dimensional scanning on the sample plane,while a pixelated array detector with a high frame rate,wide dynamic range,and high signal-to-noise ratio collects two-dimensional diffraction data in the far field.Because these diffraction data are angle-resolved,they can be used for conventional STEM imaging as well as phase contrast imaging at the leading edge.For example,electron ptychography is used to reconstruct the sample object function from a series of diffraction patterns measured at different spatial locations.In addition,4D-STEM technology can be explored to obtain more information about the internal structure of materials,providing opportunities for the multi-scale characterization of materials.This paper introduces the basic principles of 4D-STEM imaging and summarizes a series of 4D-STEM applications ranging from the microstructural characterization of materials to the analysis of their physicochemical properties.Typical applications include virtual detector imaging as well as measurements of micro-electromagnetic fields,micro-crystal orientations,micro-strain distributions,and the local specimen thickness.In addition,electron ptychography imaging technology realized using 4D-STEM data is highly promising for low-electron-dose applications owing to its high utilization efficiency of scattered electrons.The application of 4D-STEM technology in low-electron-dose applications is discussed.Overall,with the rapid development of electron detectors and post-processing analysis software for 4D-STEM data,it is believed that the novel 4D-STEM technology will eventually completely replace traditional STEM technology.Key Words:Scanning transmission electron microscopy;Electromagnetic field distribution;Ptychography;Crystal orientation;Strain distribution;Low dose imaging 物理化学学报 Acta Phys.-Chim.Sin.2023,39(3),2210017(2 of 15)四维扫描透射电子显微镜技术：从材料微观结构到物性分析四维扫描透射电子显微镜技术：从材料微观结构到物性分析 冯启龙，朱翀之，盛冠，孙土来，李永合，朱艺涵*浙江工业大学化学工程学院，前沿交叉科学研究院，电子显微镜中心(分析测试中心)，杭州 310014 摘要摘要：扫描透射电子显微镜(Scanning transmission electron microscopy，STEM)目前已经达到了原子级分辨率，并且由于其具有灵活的多通道成像能力以及强大的与谱学分析相结合的特点，因此在材料科学、生命科学等领域展现出强大的微尺度表征能力。但传统STEM的探测器受单像素积分式探测机制的限制，使其只能收集特定角度的散射电子，这导致不仅丢失了散射电子的角分辨信息，还降低了入射电子的剂量效率，因此迫切需要发展全新成像技术来实现高通量、高电子剂量效率成像。近年来，电子探测技术和分区或像素化探测器的研发联合计算机运算、存储能力的大幅提高，推动了四维扫描透射电子显微镜技术(Four-dimensional scanning transmission electron microscopy，4D-STEM)的蓬勃发展，并为最大化、最高效挖掘散射电子信息带来希望。在采集4D-STEM数据时，会聚电子束在样品平面上进行二维扫描，与此同时使用一块具有高帧速、高动态范围以及高信噪比的像素化阵列式探测器在远场收集二维的衍射数据。因为这些衍射数据是角度解析的，所以既可以用来进行常规的STEM成像，也可以用来实现前沿的相位衬度成像。例如利用电子叠层重构(Ptychography)技术通过在不同空间位置测量的一系列衍射花样来重建样品物函数。此外，4D-STEM技术还可以被进一步挖掘从而获得更多关于材料内部结构的信息，这为材料的多尺度表征带来机会。本文从4D-STEM技术原理介绍开始，总结了4D-STEM技术从材料微观结构到物性分析方面的一系列应用。具体而言，内容包含了虚拟探测器成像、微区电磁场测量、微区晶体取向测量、微区应变分布测量以及材料局域厚度测量等材料微尺度表征方面的原理和应用。除此之外，利用4D-STEM数据实现的电子叠层重构成像技术因为具有较高的散射电子利用效率，所以在低电子剂量领域展现出极大的应用潜力，因此本文还对4D-STEM技术在低电子剂量领域的应用进行了探讨与展望。总而言之，随着电子探测器以及4D-STEM数据