electron dose
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2022 ◽  
pp. 1-9
Author(s):  
Tiarnan Mullarkey ◽  
Jonathan J. P. Peters ◽  
Clive Downing ◽  
Lewys Jones

In the scanning transmission electron microscope, fast-scanning and frame-averaging are two widely used approaches for reducing electron-beam damage and increasing image signal noise ratio which require no additional specialized hardware. Unfortunately, for scans with short pixel dwell-times (less than 5 μs), line flyback time represents an increasingly wasteful overhead. Although beam exposure during flyback causes damage while yielding no useful information, scan coil hysteresis means that eliminating it entirely leads to unacceptably distorted images. In this work, we reduce this flyback to an absolute minimum by calibrating and correcting for this hysteresis in postprocessing. Substantial improvements in dose efficiency can be realized (up to 20%), while crystallographic and spatial fidelity is maintained for displacement/strain measurement.


2021 ◽  
pp. 1-7
Author(s):  
Hiroyasu Katsuno ◽  
Yuki Kimura ◽  
Tomoya Yamazaki ◽  
Ichigaku Takigawa

Low electron dose observation is indispensable for observing various samples using a transmission electron microscope; consequently, image processing has been used to improve transmission electron microscopy (TEM) images. To apply such image processing to in situ observations, we here apply a convolutional neural network to TEM imaging. Using a dataset that includes short-exposure images and long-exposure images, we develop a pipeline for processed short-exposure images, based on end-to-end training. The quality of images acquired with a total dose of approximately $5$ $e^{-}$ per pixel becomes comparable to that of images acquired with a total dose of approximately $1{,}000$ $e^{-}$ per pixel. Because the conversion time is approximately 8 ms, in situ observation at 125 fps is possible. This imaging technique enables in situ observation of electron-beam-sensitive specimens.


2021 ◽  
Author(s):  
Cathryn Barbagallo

Abstract A newly installed superficial x-ray unit was found to produce enhanced electron dose at the skin surface. ACPSEM guidelines suggest using nail varnish within the treatment cones as a method to reduce this dose. In this study, a 3D PLA sleeve was produced and used as an alternative to the nail varnish. Further, plastic wrap was also investigated for its anecdotal recommendations to reduce dose. It was found that a 1 mm printed sleeve, inserted into the treatment cone sufficiently reduced the enhanced dose to within approximately 3% of the dose measured with a Farmer-type chamber. The use of plastic wrap also reduced the enhanced dose, but impracticalities in its use make it non-viable for routine clinical use.


2021 ◽  
Vol 12 (4) ◽  
pp. 57
Author(s):  
Stefanie Riedel ◽  
Daniel Ward ◽  
Radmila Kudláčková ◽  
Karolina Mazur ◽  
Lucie Bačáková ◽  
...  

Biological hydrogels are highly promising materials for bone tissue engineering (BTE) due to their high biocompatibility and biomimetic characteristics. However, for advanced and customized BTE, precise tools for material stabilization and tuning material properties are desired while optimal mineralisation must be ensured. Therefore, reagent-free crosslinking techniques such as high energy electron beam treatment promise effective material modifications without formation of cytotoxic by-products. In the case of the hydrogel gelatin, electron beam crosslinking further induces thermal stability enabling biomedical application at physiological temperatures. In the case of enzymatic mineralisation, induced by Alkaline Phosphatase (ALP) and mediated by Calcium Glycerophosphate (CaGP), it is necessary to investigate if electron beam treatment before mineralisation has an influence on the enzymatic activity and thus affects the mineralisation process. The presented study investigates electron beam-treated gelatin hydrogels with previously incorporated ALP and successive mineralisation via incubation in a medium containing CaGP. It could be shown that electron beam treatment optimally maintains enzymatic activity of ALP which allows mineralisation. Furthermore, the precise tuning of material properties such as increasing compressive modulus is possible. This study characterizes the mineralised hydrogels in terms of mineral formation and demonstrates the formation of CaP in dependence of ALP concentration and electron dose. Furthermore, investigations of uniaxial compression stability indicate increased compression moduli for mineralised electron beam-treated gelatin hydrogels. In summary, electron beam-treated mineralized gelatin hydrogels reveal good cytocompatibility for MG-63 osteoblast like cells indicating a high potential for BTE applications.


2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Shulin Chen ◽  
Changwei Wu ◽  
Bo Han ◽  
Zhetong Liu ◽  
Zhou Mi ◽  
...  

AbstractUnderstanding the atomic structure and structural instability of organic-inorganic hybrid perovskites is the key to appreciate their remarkable photoelectric properties and understand failure mechanism. Here, using low-dose imaging technique by direct-detection electron-counting camera in a transmission electron microscope, we investigate the atomic structure and decomposition pathway of CH3NH3PbI3 (MAPbI3) at the atomic scale. We successfully image the atomic structure of perovskite in real space under ultra-low electron dose condition, and observe a two-step decomposition process, i.e., initial loss of MA+ followed by the collapse of perovskite structure into 6H-PbI2 with their critical threshold doses also determined. Interestingly, an intermediate phase (MA0.5PbI3) with locally ordered vacancies can robustly exist before perovskite collapses, enlightening strategies for prevention and recovery of perovskite structure during the degradation. Associated with the structure evolution, the bandgap gradually increases from ~1.6 eV to ~2.1 eV. In addition, it is found that C-N bonds can be readily destroyed under irradiation, releasing NH3 and HI and leaving hydrocarbons. These findings enhance our understanding of the photoelectric properties and failure mechanism of MAPbI3, providing potential strategies into material optimization.


2021 ◽  
Vol 7 (32) ◽  
pp. eabd9887
Author(s):  
Kenji Takada ◽  
Mari Morita ◽  
Takane Imaoka ◽  
Junko Kakinuma ◽  
Ken Albrecht ◽  
...  

Microscopic observation of single molecules is a rapidly expanding field in chemistry and differs from conventional characterization techniques that require a large number of molecules. One of such form of single-molecule microscopy is high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), which is especially suitable for coordination compounds because of its atomic number–dependent contrast. However, to date, single-molecule observations using HAADF-STEM has limited to simple planar molecules. In the present study, we demonstrate a direct structural investigation of nonplanar dendronized polynuclear Ir complexes with subnanometer resolution using Ir as an atomic label. Decreasing the electron dose to the dendrimer complexes is critical for the single-molecule observation. A comparison with simulated STEM images of conformational isomers is performed to determine the most plausible conformation. Our results enlarge the potential of electron microscopic observation to realize structural analysis of coordination macromolecules, which has been impossible with conventional methods.


2021 ◽  
Vol 27 (S1) ◽  
pp. 1066-1067
Author(s):  
Eric Van Cappellen ◽  
Christian Maunders ◽  
Ingrid Kieft ◽  
Maarten Bischoff ◽  
Felix Van Uden ◽  
...  
Keyword(s):  

2021 ◽  
Vol 11 (Suppl_1) ◽  
pp. S20-S20
Author(s):  
Timur Baymukhametov ◽  
Olesya Kravchenko ◽  
Zhanna Afonina ◽  
Konstantin Vassilenko

Background: The ribosome is a molecular machine that translates mRNAs into proteins. In eukaryotes, ribosome consists of small (40S) and large (60S) subunits. Translation in eukaryotes is a complicated molecular process that involves the formation of various molecular complexes consisting of ribosomal subunits and protein factors. Cryo-EM approaches such as single particle analysis are widely used for structural analysis of components and intermediates of the translation machinery. However, the process of translation in plants is still poorly characterized at a structural level. Here, we present the structure of Triticum aestium small ribosomal subunit obtained at sub 3 resolution that can be used for further structural studies of the translation process in plants. Methods: The structures of the 40S subunits purified from wheat germ extract were obtained using high-resolution single particle cryo-EM. For cryo-EM sample preparation were used Quantifoil R 1.2/1.3 grids coated with an additional 2 nm amorphous carbon film were glow-discharged for 30 seconds at 15 mA using PELCO easiGlow (Ted Pella). 3 µL of the sample were applied onto the grids, blotted for 3 sec at 10°C and 100% humidity, and plunge-frozen in liquid ethane using Vitrobot Mark IV (Thermo Fisher). Cryo-EM data were collected using a Cs-corrected Titan Krios (Thermo Fisher) transmission electron microscope, equipped with a Falcon II direct electron detector. Data were acquired with defocus range of -0.6 to -2.0 at a nominal magnification of 75,000x, giving a calibrated pixel size of 0.86 Å/pixel. The micrographs were recorded as movie stacks. The exposure time for each stack was 1.6 s, corresponding to a total electron dose of ~84 e-/Å2 fractionated into 32 frames (~2.6 e-/Å2 per single frame). A total of 5521 movie stacks was collected. Raw cryo-EM data preprocessing was performed with Warp software (Tegunov et al., 2019). All further data processing steps were performed using the cryoSPARC v3.2.0 software (Punjani et al., 2017). Results: For final cryo-EM map refinement, 140,000 particles were used resulting in 2.7 Å resolution estimated using an FSC=0.143 gold-standard threshold. The obtained structural data clearly demonstrate the peculiarities of the spatial organization of the 40S ribosomal subunit, like the motility of the head relative to the body revealed by 3D variability analysis. Conclusion: The resulting structure was solved at a significantly higher resolution compared to the previously published structure of a plant ribosome (Armache et al., 2010) and will be used as a reference for further studies of translation initiation in plants.


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