Microscopy and Microanalysis最新文献

A DigitalMicrograph® script RAPID-DM (RAtio method Pattern InDexing) has been developed, which allows instant on-site indexing of zone axis electron diffraction patterns of cubic lattices using the Rn ratio principle. In addition to indexing spot electron diffraction patterns, the program is also capable of indexing Kikuchi patterns taken from or near a zone axis. Both cases are demonstrated by examples for silicon. The program has a guided workflow and requires only three user-defined lines or Kikuchi bands for indexing. RAPID-DM has been extensively tested and verified to work reliably with both calibrated and noncalibrated zone axis patterns and allows the user to easily evaluate whether the material under examination is cubic, pseudo-cubic, or neither. For calibrated patterns, the program provides an average value of the cubic lattice parameter, which can serve for phase identification in connection with a structural database or it can simply be used to verify the material under investigation. In its current state, the developed script has proved to be a valuable add-on to the DigitalMicrograph® platform in the authors' service laboratory, as it greatly simplifies on-site crystallographic analysis of electron diffraction patterns of steels, alloys, and ceramics, which frequently form cubic or pseudo-cubic structures.

Irradiation produces a distribution of defect sizes in materials, with the smallest defects often below one nanometer in size and approaching the scale of a single unit cell in metals. While high-resolution scanning transmission electron microscopy (STEM)-based imaging can directly image structures at this level, techniques such as four-dimensional STEM (4D-STEM) enable characterization of materials across large fields of view, capturing a more representative volume that can be valuable for quantifying defects, their distributions, and the associated strain fields. Here we present a combined HRSTEM and 4D-STEM approach to study the model system of He bubble implantation in an Au thin film. The present work is of general interest for the study of materials in extreme environments, as it demonstrates an effective way to characterize even the tiniest sub-nanometer sized He bubbles in addition to larger irradiation defects.

Due to the apparent width/diameter broadening common for sub-10 nm features, scanning electron microscopy faces many challenges for nanometrology in silicon-based and emerging carbon nanotube (CNT)-based technologies. The influence of beam size (σbeam), landing energy (LE), and charging on the apparent diameter of CNTs (WCNT) is investigated here. Experiments show WCNT increases with increasing σbeam, decreases with increasing LE, and shows little variation between conductive Si and insulating SiO2/Si substrates. Monte Carlo simulations show WCNT remains unchanged with σbeam smaller than ∼1/6 of CNT diameters (dCNT) but begins to increase once σbeam becomes larger, and WCNT varies little with increasing LE if σbeam is fixed. These results suggest (1) σbeam is decisive in the WCNT broadening; (2) the effect of LE is attributed to the change in σbeam instead of the width of interaction volume; and (3) the contribution of charging is minimal with the contrast separation method. We also notice that increasing the LE beyond 3 keV makes CNT almost invisible. This is attributed to the too-small ratio of electron-CNT interaction volume to the electron-substrate interaction volume. Testing LEs ranging from 0.3 to 10 keV, we find optimal balancing of WCNT and visibility in the 0.5-1.0 keV range.

Atom probe tomography (APT) provides a unique, three-dimensional map of elemental and isotopic distributions over a wide range of materials with near-atomic scale resolution and is particularly strong at analyzing buried interfaces within materials. However, it is much more difficult to apply atom probe to the analysis of nanoscale surface films, such as those formed during alloy passivation, where unique challenges persist for sample preparation and data collection. Here, we present sample preparation strategies involving the deposition of a <100 nm capping layer that enables reliable characterization of thin passive films ∼2-5 nm thick formed on binary and multiprincipal element alloys via APT. Several capping layer materials (Pt, Ti, and Ni/Cr bilayer) and deposition methods are contrasted. Our results indicate a sputtered Ni/Cr bilayer enables the characterization of the entire passive film and concentration profiles that can easily be interpreted to clearly distinguish base alloy/passive film/capping layer interfaces. Lastly, we highlight ongoing challenges and opportunities for this experimental approach.

Among neurodegenerative diseases, Parkinson's disease (PD) is the second most common disorder. It is marked by the degeneration of dopaminergic neurons and depletion of dopamine. The mesenchymal stem cells (MSCs)-derived exosomes hold a promise for addressing neurodegeneration-associated neurological disorders owing to their distinctive immunomodulatory and regenerative properties. The investigation explored the therapeutic potential of MSCs-derived exosomes to mitigate the pathological changes in the cerebellar cortex in a rat model of PD. Thirty rats were divided into control, PD, and PD-BM-MSCs-derived exosomes groups. For 5 weeks, rodents were administered a subcutaneous injection of 2 mg/kg/day of rotenone to induce a PD model. The PD group exhibited a substantial increase in relative cerebellar mRNA HOTAIR, BAX, and caspase 3 gene expression, along with a concomitant decrease in relative cerebellar miRNA-221 gene expression. Light and transmission electron microscopy also depicted marked degenerative changes in the cerebellar cortex. The immune expression of glial fibrillary acidic protein and ionized calcium-binding adaptor molecule-1 markedly increased, while synaptophysin expression markedly decreased. Interestingly, all changes showed a significant regression following treatment with exosomes derived from BM-MSCs. In conclusion, BM-MSCs-derived exosomes may be a promising PD intervention strategy.

Correlative imaging is a powerful tool for revealing information on cell-type structures and their biochemistry, with the potential to inform healthier food choices and improved dietary recommendations. Determination of plant structures and their structural biochemistry advances our understanding of specific structures designed to store different biomolecules within cells and tissues. Compared to the classical biochemical separation techniques, the key advantage of sequential correlative imaging techniques is in relating spatial plant (micro)structures to their biochemistry in a nondestructive manner. Sequential imaging reported here comprises six methodologies on a single sample, a cross-section of a Tartary buckwheat (Fagopyrum tataricum) grain, namely, bright-field and autofluorescence microscopy, fluorescence microspectroscopy, MeV-secondary ion mass spectrometry, micro-particle-induced X-ray emission, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, and laser ablation-inductively coupled plasma-mass spectrometry. Results confirm that the stepwise addition of the desired information across several classes of biomolecules and several spatial scales informs the quality and safety of plant-based produce across scales. Therefore, a viable workflow is proposed, enabling sequential spatial analysis of grain and highlighting plant structures' in situ specificity. The advantages and disadvantages of the selected methodologies were critically evaluated.

The understanding of protein structure and interactions remains a fundamental challenge in modern biology. While X-ray and electron-based techniques have provided atomic-level protein configurations, they require numerous molecules for averaged views and lack detailed compositional information crucial for biochemical activity. Atom probe tomography (APT) emerges as a promising tool for biological material analysis, though its capabilities for examining biomolecules in their native, hydrated state remain largely unexplored. We present systematic analyses of amino acids in frozen aqueous solutions using two different nanoporous metal supports across various analysis conditions. Our methodology employs a complete cryogenic workflow, including drop-casting, inert gas glovebox freezing, and specimen transfer via a cryogenically cooled ultra-high vacuum shuttle to both focused ion beam microscopy and atom probes. Using water molecular ion ratios as electrostatic field condition indicators, we investigate amino acid fragmentation and behavior. We evaluate the critical factors for successful biomolecular analysis: support material selection, cryogenic specimen preparation, and optimal data acquisition parameters. This work establishes guidelines for cryogenic APT analysis of biomolecules, advancing the technique's application in biological sciences.

Leucine-rich repeat kinase 2 (LRRK2) is a multidomain protein known for its involvement in neurodegenerative disorders, particularly Parkinson's disease, where it is considered one of the most common genetic contributors. LRRK2 plays multiple roles in cellular signaling, protein trafficking, and cytoskeletal dynamics. In present study, using mouse as the mammalian model, we reported its important roles in early embryo development. We showed that LRRK2 accumulated around nucleus before two-cell stage but distributed in the cytoplasm of blastomeres after four-cell stage. Loss of LRRK2 activity induced two-cell to four-cell transition defects, indicating the failure of zygotic genome activation during embryo development. We showed the mitochondria dysfunction after LRRK2 inhibition, since the mitochondria distribution, intensity, ATP production, and mitochondria number were all altered. This might further induce the evaluated ROS level for the occurrence of oxidative stress. Besides, we also observed that the cortex and cytoplasmic actin in the blastomere of embryos were decreased, which further linked with mitochondria. In summary, we showed that LRRK2 activity is essential for actin-based mitochondria distribution and function, which further controls the occurrence of oxidative stress for mouse early embryo development.

Burnup estimation in nuclear fuels is vital for evaluating fuel performance, transportation, and safe fuel storage. Accurate assessments of burnup from service period and spent fuels involve tracking the consumption of fissile isotopes of uranium (U) offering a direct insight into energy changes within the fuels especially for thermal spectrum reactors. In current approach, mass spectroscopic technique in atom probe tomography (APT) is utilized for accurate quantification of U isotopes. Quantification of U peaks in mass spectrum is performed on asymmetric shapes due to delayed signals, known as thermal tails, particularly for poorly conducting samples analyzed in laser mode. In this study, we introduce a novel quantification tool for isotopic analysis from APT datasets by developing a fitting algorithm based on shapes of the peaks. A MATLAB-based dynamic peak fitting toolbox is developed and designed to adapt to various peak shapes, ensuring accurate quantification of U isotopes. The effectiveness of this approach is demonstrated in standard Ni-Cr sample, depleted and enriched U samples, and U-based fuels with different burnup levels. The viability of this approach for isotopic quantification is demonstrated on both metallic and ceramic fuels.

Neutral atoms originating from liquid metal ion sources are an often-overlooked source of contamination and damage in focused ion beam microscopy. Beyond ions and single atoms, these sources also generate atom clusters. While most studies have investigated charged clusters, here we demonstrate that neutral clusters are also formed. These neutral clusters bypass the electrostatic beam blanking system, allowing them to impinge on samples even when the ion beam is blanked. We investigate this phenomenon using thin (≤20 nm) freestanding membranes of hexagonal boron nitride, silicon, and silicon nitride as targets. Randomly dispersed nanopores that form upon neutral cluster exposure are revealed. The average nanopore diameter is ∼2 nm with a narrow size distribution, suggesting that the atom clusters have a preferred size. Various electron microscopy techniques are used to characterize the nanopores, including high-resolution transmission electron microscopy, multislice ptychography, and electron energy-loss spectroscopy. Finally, we show how electron irradiation in the transmission electron microscope can be used to both remove any amorphous material that may clog the pores and to controllably grow the pores to specific sizes. Tunable nanopores such as these are interesting for nanofluidic applications requiring size-selective membranes.