Review Article
Four-Dimensional Scanning Transmission Electron Microscopy (4D-STEM): From Scanning Nanodiffraction to Ptychogra- phy and Beyond by C Ophus, Microsc Microanal | doi: 10.1017/S14319276190000497 Scanning transmission electron microscopy (STEM)
is a flexible characterization tool used for many different imaging and spectroscopic measurements. Te development of high-speed direct electron detectors has facilitated the widespread introduction of four-dimensional (4D)-STEM experiments, where a full 2D image of the STEM probe is recorded over a 2D grid of probe positions. Tese datasets are oſten extremely large, requiring both a large amount of digital storage and efficient computational analysis methods. However, tackling these challenges is worthwhile because of the large amount of structural information that can be recorded for a sample over many different length scales. In this paper, we review 4D-STEM experiments including mapping (of phase, orientation, and strain), virtual diffrac- tion imaging, measurements of medium range order, posi- tion-averaged convergent beam electron diffraction, phase contrast imaging methods such as contrast ptychography, scanning confocal electron microscopy, structured phase plates, and others. We also discuss associated topics such as precession electron diffraction, computational analysis, electron scattering simulation, and detector development for 4D-STEM.
A simulated 4D-STEM dataset for a nanoparticle resting on an amorphous car- bon substrate. The probes along the outer edge have passed only through the substrate, and therefore scatter weakly, so most of the intensity remains in the central beam. The probes passing through the nanoparticle show Bragg diffrac- tion patterns, which can be used to measure the local crystal orientation and deformation.
Techniques and Biological Applications
Nanoindentation Properties and Finite Element Analysis of the Rostrum of Cyrtotrachelus buqueti Guer (Coleoptera: Curculionidae) by LH Li, C Guo, S Xu, YP Ma, and ZW Yu, Microsc Microanal | doi: 10.1017/S1431927619000242 Nanoindentation measurements and finite element
analysis of mechanical properties of the rostrum of the outstanding driller weevil Cyrtotrachelus buqueti Guer are reported. Nanoindentation tests were used to mea- sure the Young’s modulus and hardness of the rostrum, with results for the “dry” samples being 13.89 ± 0.75 GPa and 0.37 ± 0.04 GPa, respectively. The values for “fresh” samples showed no clear difference from those of the “dry” ones. Moreover, field observations were conducted to determine the motion behavior of the rostrum. Micro- computed tomography (9 μm slices) was employed to obtain structural information about the rostrum, and a 3D model of the rostrum was created using the MIMICS design program. It was concluded that the rostrum of Cyr- totrachelus buqueti Guer provides an ideal biological tem- plate for the design of lightweight tube-shaped structures, which can be used in automobiles, aircraft, robotic arms, and other tube-like structures.
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The weevil Cyrtotrachelus buqueti Guer is an outstanding driller that is able to effectively chew holes into and suck on bamboo. During the feeding process, the rostrum is subject to great pressure and high torque that changes with movement. These mechanical properties make it an ideal model to inspire new lightweight designs for long tubular structures.
doi:10.1017/S1551929519000609
www.microscopy-today.com • 2019 July
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