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

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...     

Phase retrieval from local measurements: Improved robustness via eigenvector-based angular synchronization

We improve a phase retrieval approach that uses correlation-based measurements with compactly supported measurement masks [30]. Our approach admits deterministic measurement constructions together with a robust, fast recovery algorithm that consists of solving a system of linear equations in a lifted space, followed by finding an eigenvector (e.g., via an inverse power iteration). Theoretical reconstruction error guarantees from [30] are improved as a result for the new and more robust reconstruction approach proposed herein. Numerical experiments demonstrate robustness and computational efficiency that compete with other approaches on large problems. Along the way, we show that this approach also trivially extends to phase retrieval problems based on windowed Fourier measurements.     

X‐Ray Scattering and Imaging Studies of Electrode Structure and Dynamics

We will review structures and dynamics of electrode interfaces studied in situ using x‐ray scattering and imaging techniques. The examples cover single‐crystal and nanocrystal structures relevant to electrocatalytic activities, anodic oxidation and corrosion, aqueous dissolution reactions, surface reconstructions, and surface modifications by under potential deposition. The x‐ray techniques include the widely used traditional surface x‐ray scattering, such as crystal truncation rods and x‐ray reflectivity, as well as recently developed resonance surface scattering, coherent surface x‐ray photon correlation spectroscopy, coherent x‐ray Bragg diffraction imaging, and surface ptychography. Results relevant to various electrochemical phenomena will be highlighted.