Microscopy and Microanalysis最新文献

Mitochondrial division is a fundamental biological process essensial for cellular functionality and vitality. The prevailing hypothesis that dynamin related protein 1 (Drp1) provides principal control in mitochondrial division, in which it also involves the endoplasmic reticulum (ER) and the cytoskeleton, does not account for all the observations. Therefore. the hypothesis may be incomplete. Our previous study in HeLa cells led to a new hypothesis of mitochondrial division by budding. To follow-up our previous study, we employed in situ cryo-electron tomography to visualize mitochondrial budding in the intact healthy monkey kidney cells (BS-C-1 cells). Our findings reaffirm single and multiple mitochondrial budding, consistent with our observations in HeLa cells. Notably, the budding regions vary significantly in diameter and length, which may represent different stages of budding. More interestingly, neither rings nor ring-like structures, nor the wrapping of ER tubes was observed in the budding regions, suggesting mitochondrial budding is independent from Drp1 and ER. Meanwhile, we uncovered direct interactions between mitochondria and large vesicles that are distinct from small mitochondrial-derived vesicles and extracellular mitovesicles. We propose that these interacting vesicles may have mitochondrial origins.

We introduce a new approach to the numerical simulation of Scanning Transmission Electron Microscopy images. The Lattice Multislice Algorithm takes advantage of the fact that the electron waves passing through the specimen have limited bandwidth and therefore can be approximated very well by a low-dimensional linear space spanned by translations of a well-localized function. Just like in the PRISM algorithm recently published by C. Ophus, we utilize the linearity of the Schrödinger equation but perform the approximations with functions that are well localized in real space instead of Fourier space. This way, we achieve a similar computational speedup as PRISM, but at a much lower memory consumption and reduced numerical error due to avoiding virtual copies of the probe waves interfering with the result. Our approach also facilitates faster recomputations if local changes are made to the specimen such as changing a single atomic column.

In catalysis research, the amount of microscopy data acquired when imaging dynamic processes is often too much for nonautomated quantitative analysis. Developing machine learned segmentation models is challenged by the requirement of high-quality annotated training data. We thus substitute expert-annotated data with a physics-based sequential synthetic data model. We study environmental scanning electron microscopy (ESEM) data collected from isopropanol oxidation to acetone over cobalt oxide as an example. Upon applying a temperature program during the reaction a phase transition occurs, reducing the catalyst selectivity toward acetone. This is accompanied on the micrometer ESEM scale by the formation of cracks between the pores of the catalyst surface. We aim to generate synthetic data to train a neural network capable of semantic segmentation (pixel-wise labeling) of this ESEM data. This analysis will lead to insights into this phase transition. To generate synthetic data that approximates this transition, our algorithm composes the ESEM images of the room-temperature catalyst with dynamically evolving synthetic cracks satisfying physical construction principles, gathered from qualitative knowledge accessible in the ESEM data. We mimic the surface crack growth propagation along surface paths, avoiding close vicinity to nearby pores. This physics-based approach results in a lowered rate of false positives compared to a random approach.

Atom probe tomography (APT) enables three-dimensional chemical mapping with near-atomic scale resolution. However, this method requires precise sample preparation, which is typically achieved using a focused ion beam (FIB) microscope. As the ion beam induces some degree of damage to the sample, it is necessary to apply a protective layer over the region of interest (ROI). Herein, the use of redeposition, a (frequently considered negative) side effect of FIB sputtering, is explored as a technique for targeted surface coatings in site-specific, near-surface APT investigations. In addition, the concept of "self-coating" is presented, which is the application of a capping layer using material from the same, or a similar, sample. It is shown to provide a pathway for high-quality coatings, as well as a method of minimizing the field evaporation threshold difference at the cap-sample interface, thus greatly reducing the likelihood of premature fractures. In situ redeposition surface coatings are shown to be versatile, with four materials used in the coating and analysis of two Si-based semiconductors and a Fe-Mn alloy. Several factors are discussed, such as the specimen yield, the capping layer quality, and the ease of ROI identification, all of which demonstrate its effectiveness in routine sample preparation workflows.

Barleria is a palaeotropical genus of herbs, shrubs, and rarely climbers or trees. We investigated the karyotypes and male meiosis of 12 and 13 species, respectively, for the first time. Mitotic metaphases revealed two chromosome counts, 2n = 40 and 2n = 44. Chromosomes had median (m), submedian (sm), and subterminal (st) region centromeres. The total haploid chromosome length (TCL) ranged from 78.95 µm (Barleria sahyadrica) to 37.80 µm (B. nitida). Dispersion index differentiated the species into two groups, one with lower (3.40-4.79) and the other with higher (6.63-12.87) values. Principal component analysis based on six karyological parameters, namely base number (x), 2n, TCL, coefficient of variation of chromosome length, coefficient of variation of centromeric index, and mean centromeric asymmetry, exhibited three clusters. Cluster I included species of the subgenus Barleria. Cluster III had species of the subgenus Prionitis section Somalia. Cluster II comprised species of the subgenus Barleria and the subgenus Prionitis section Prionitis (B. sahyadrica). Pollen grains were oblate spheroidal or distinctly three-lobed, tri-brevicolporate with honey-combed tectum. Our analyses revealed karyological relationships among the investigated species and also provide raw data to breeders interested in horticultural applications of Barleria for accomplishing interspecific hybridization.

The present communication aims at demonstrating the wealth of information accessible by 1D-atom probe experiments using pulsed field desorption mass spectrometry (PFDMS), ultimately combined with video-field ion microscopy, while subjecting metallic samples to elevated gas pressures and studying surface reaction kinetics. Two case studies are being presented here: (a) the microkinetics of nickel tetracarbonyl (Ni(CO)4) formation through reaction of carbon monoxide with nickel and (b) the nitric oxide decomposition and reaction with hydrogen on platinum at variable steady electric fields mimicking electrocatalytic conditions. In both cases, surface areas with 140-150 atomic sites of the stepped Ni (001) and Pt (111) sample surfaces were probed. Under (a), we demonstrate variable repetition frequencies of field pulses to inform kinetic and mechanistic details of the surface reaction while under (b), we reveal the occurrence of field-induced processes impacting the surface reaction mechanism of nitric oxide with hydrogen and therefore opening new pathways not available under purely thermal conditions (in the absence of electric fields). Some aspects of PFDMS technical achievements will be discussed as they may provide clues for designing dynamic atom probe tomography instrumentation.

Reflection electron energy loss spectroscopy (REELS) has played a pivotal role in allowing researchers to explore the characteristics of various bulk materials. This study presents results for the low-loss region of REELS with a new cylindrical lens spectrometer integrated into a low-voltage scanning electron microscope. The operational principles and implementation of the spectrometer are explained through comparisons between electron optical simulations and experimental results. Notably, the analysis shows the ability to distinguish samples in film and bulk forms. Graphene and graphite, despite their identical elemental composition and crystalline structure, are found to have distinct energy spectra as indicated by plasmon peaks. Furthermore, the study explores the bandgap measurement of SiO2 at low-energy conditions of 2.5 keV, highlighting the proposed instrument's advantages in the measurement without the harmful effect of Cherenkov loss. Additionally, this method reaffirms the capability to measure multiple plasmon peaks from the energy spectra of bulk gold samples, thus introducing a pioneering avenue in energy spectrum measurement. Leveraging the compact size and simple experimental setup of the spectrometer for REELS, the method enables the measurement of energy spectra of both bulk- and film-formed samples under low electron energy conditions, marking a significant advancement in the field.

Tuneable phase plates for free electrons are a highly active area of research. However, their widespread implementation, similar to that of spatial light modulators in light optics, has been hindered by both conceptual and technical challenges. A specific technical challenge involves the need to minimize obstruction of the electron beam by supporting films and electrodes. Here, we describe numerical and analytical mathematical frameworks for three-dimensional stacks of phase plates that can be used to provide near-arbitrary electron beam shaping with minimal obstruction.

Recent work in ultra-high temperature in situ electron microscopy has presented the need for accurate, contact-free temperature determination at the microscale. Optical measurement based on thermal radiation (pyrometry) is an attractive solution but can be difficult to perform correctly due to effects, such as emissivity and optical transmission, that must be accounted for. Here, we present a practical guide to calibrating and using a spectral pyrometry system, including example code, using a Czerny-Turner spectrometer attached to a transmission electron microscope. Calibration can be accomplished using a thermocouple or commercial heated sample holder, after which arbitrary samples can be reliably measured for temperatures above ∼600∘C. An accuracy of 2% can be expected with the possibility of sub-second temporal resolution and sub-Kelvin temperature resolution. We then demonstrate this capability in conjunction with traditional microscopic techniques, such as diffraction-based strain measurement for thermal expansion coefficient, or live-video sintering evolution.

A detailed analysis of ptychography for three-dimensional (3D) phase reconstructions of thick specimens is performed. We introduce multi-focus ptychography, which incorporates a 4D-STEM defocus series to enhance the quality of 3D reconstructions along the beam direction through a higher overdetermination ratio. This method is compared with established multi-slice ptychography techniques, such as conventional ptychography, regularized ptychography, and multi-mode ptychography. Additionally, we contrast multi-focus ptychography with an alternative method that uses virtual optical sectioning through a reconstructed scattering matrix (S-matrix), which offers more precise 3D structure information compared to conventional ptychography. Our findings from multiple 3D reconstructions based on simulated and experimental data demonstrate that multi-focus ptychography surpasses other techniques, particularly in accurately reconstructing the surfaces and interface regions of thick specimens.