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1. Direct Visualization of the Earliest Stages of Crystallization

   https://doi.org/10.1017/S1431927621000441  

   Singh, Manish Kumar; Ghosh, Chanchal; Miller, Benjamin; Carter, C. Barry (January 2021, Microscopy and Microanalysis)

   null (Ed.)

   Investigating the earliest stages of crystallization requires the transmission electron microscope (TEM) and is particularly challenging for materials which can be affected by the electron beam. Typically, when imaging at magnifications high enough to observe local crystallinity, the electron beam's current density must be high to produce adequate image contrast. Yet, minimizing the electron dose is necessary to reduce the changes caused by the beam. With the advent of a sensitive, high-speed, direct-detection camera for a TEM that is corrected for spherical aberration, it is possible to probe the early stages of crystallization at the atomic scale. High-quality images with low contrast can now be analyzed using new computing methods. In the present paper, this approach is illustrated for crystallization in a Ge 2 Sb 2 Te 5 (GST-225) phase-change material which can undergo particularly rapid phase transformations and is sensitive to the electron beam. A thin (20 nm) film of GST-225 has been directly imaged in the TEM and the low-dose images processed using Python scripting to extract details of the nanoscale nuclei. Quantitative analysis of the processed images in a video sequence also allows the growth of such nuclei to be followed. 

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2. Focused ion beam milling and MicroED structure determination of metal-organic framework crystals

   https://doi.org/10.1016/j.ultramic.2023.113905  

   Bardin, Andrey A.; Haymaker, Alison; Banihashemi, Fateme; Lin, Jerry Y.S.; Martynowycz, Michael W.; Nannenga, Brent L. (March 2024, Ultramicroscopy)

   We report new advancements in the determination and high-resolution structural analysis of beam-sensitive metal organic frameworks (MOFs) using microcrystal electron diffraction (MicroED) coupled with focused ion beam milling at cryogenic temperatures (cryo-FIB). A microcrystal of the beam-sensitive MOF, ZIF-8, was ion-beam milled in a thin lamella approximately 150 nm thick. MicroED data were collected from this thin lamella using an energy filter and a direct electron detector operating in counting mode. Using this approach, we achieved a greatly improved resolution of 0.59 Å with a minimal total exposure of only 0.64 e−/A2. These innovations not only improve model statistics but also further demonstrate that ion-beam milling is compatible with beam-sensitive materials, augmenting the capabilities of electron diffraction in MOF research. 

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3. High-Resolution Conductivity Mapping with STEM EBIC

   https://doi.org/10.31399/asm.cp.istfa2022p0251  

   Hubbard, William A; Chan, Ho Leung; Regan, B. C. (October 2022, International Symposium for Testing and Failure Analysis)

   Abstract Modern electronic systems rely on components with nanometer-scale feature sizes in which failure can be initiated by atomic-scale electronic defects. These defects can precipitate dramatic structural changes at much larger length scales, entirely obscuring the origin of such an event. The transmission electron microscope (TEM) is among the few imaging systems for which atomic-resolution imaging is easily accessible, making it a workhorse tool for performing failure analysis on nanoscale systems. When equipped with spectroscopic attachments TEM excels at determining a sample’s structure and composition, but the physical manifestation of defects can often be extremely subtle compared to their effect on electronic structure. Scanning TEM electron beam-induced current (STEM EBIC) imaging generates contrast directly related to electronic structure as a complement the physical information provided by standard TEM techniques. Recent STEM EBIC advances have enabled access to a variety of new types of electronic and thermal contrast at high resolution, including conductivity mapping. Here we discuss the STEM EBIC conductivity contrast mechanism and demonstrate its ability to map electronic transport in both failed and pristine devices. 

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4. Accounting for electron-beam-induced warping of molecular nanocrystals in MicroED structure determination

   https://doi.org/10.1107/S2052252524012132  

   Vlahakis, Niko; Clauss, Arden; Rodriguez, Jose A (March 2025, IUCrJ)

   High-energy electrons induce sample damage and motion at the nanoscale to fundamentally limit the determination of molecular structures by electron diffraction. Using a fast event-based electron counting (EBEC) detector, we characterize beam-induced, dynamic, molecular crystal lattice reorientations (BIRs). These changes are sufficiently large to bring reciprocal lattice points entirely in or out of intersection with the sphere of reflection, occur as early events in the decay of diffracted signal due to radiolytic damage, and coincide with beam-induced migrations of crystal bend contours within the same fluence regime and at the same illuminated location on a crystal. These effects are observed in crystals of biotin, a series of amino acid metal chelates, and a six-residue peptide, suggesting that incident electrons inevitably warp molecular lattices. The precise orientation changes experienced by a given microcrystal are unpredictable but are measurable by indexing individual diffraction patterns during beam-induced decay. Reorientations can often tilt a crystal lattice several degrees away from its initial position before irradiation, and for an especially beam-sensitive Zn(II)-methionine chelate, are associated with dramatic crystal quakes prior to 1 e⁻ Å⁻²electron beam fluence accumulates. Since BIR coincides with the early stages of beam-induced damage, it echoes the beam-induced motion observed in single-particle cryoEM. As with motion correction for cryoEM imaging experiments, accounting for BIR-induced errors during data processing could improve the accuracy of MicroED data. 

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5. Pushing the limits of high-resolution polymer microscopy using antioxidants

   https://doi.org/10.1038/s41467-020-20363-1  

   Kuei, Brooke; Gomez, Enrique D. (January 2021, Nature Communications)

   Abstract High-resolution transmission electron microscopy (HRTEM) has been transformative to the field of polymer science, enabling the direct imaging of molecular structures. Although some materials have remarkable stability under electron beams, most HRTEM studies are limited by the electron dose the sample can handle. Beam damage of conjugated polymers is not yet fully understood, but it has been suggested that the diffusion of secondary reacting species may play a role. As such, we examine the effect of the addition of antioxidants to a series of solution-processable conjugated polymers as an approach to mitigating beam damage. Characterizing the effects of beam damage by calculating critical doseD_Cvalues from the decay of electron diffraction peaks shows that beam damage of conjugated polymers in the TEM can be minimized by using antioxidants at room temperature, even if the antioxidant does not alter or incorporate into polymer crystals. As a consequence, the addition of antioxidants pushes the resolution limit of polymer microscopy, enabling imaging of a 3.6 Å lattice spacing in poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3″′-di(2-octyldodecyl)-2,2′;5′,2″;5″,2″′-quaterthiophene-5,5″′-diyl)] (PffBT4T-2OD). 

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