Microscopy and Microanalysis最新文献

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.

We report a large-angle rocking beam electron diffraction (LARBED) technique for electron diffraction analysis. Diffraction patterns are recorded in a scanning transmission electron microscope (STEM) using a direct electron detector with large dynamical range and fast readout. We use a nanobeam for diffraction and perform the beam double rocking by synchronizing the detector with the STEM scan coils for the recording. Using this approach, large-angle convergent beam electron diffraction (LACBED) patterns of different reflections are obtained simultaneously. By using a nanobeam, instead of a focused beam, the LARBED technique can be applied to beam-sensitive crystals as well as crystals with large unit cells. This paper describes the implementation of LARBED and evaluates the performance using silicon and gadolinium gallium garnet crystals as test samples. We demonstrate that our method provides an effective and robust way for recording LARBED patterns and paves the way for quantitative electron diffraction of large unit cell and beam-sensitive crystals.

Paclitaxel, a chemotherapeutic drug, induces sensorimotor peripheral neuropathy. Carvedilol, a nonselective β-adrenoreceptor blocker, has been shown to exert antioxidant activity. Platelet-rich plasma (PRP) has supra-physiological levels of growth factors (GFs), enhances biosynthesis of antioxidant enzymes, and suppresses oxidative stress. This study compared the ameliorative effects of carvedilol and PRP on paclitaxel-induced femoral neuropathy. Eighty-eight adult male albino rats were equally randomized into four groups: group I served as the control; group II received paclitaxel (16 mg/kg intraperitoneally, weekly); group III received carvedilol (10 mg/kg daily, orally) concomitant with paclitaxel; and group IV received PRP (0.5 mL/kg subcutaneously, twice weekly) concomitant with paclitaxel. After 5 weeks, femoral nerve conduction velocity was measured, and blood samples were collected to assess catalase and superoxide dismutase levels. All animals were sacrificed, and gene expression of miR-21 was quantified. Tissue sections were stained with hematoxylin and eosin and toluidine blue. Then, the ultrathin sections were examined by transmission electron microscopy. Both carvedilol and PRP reversed paclitaxel-induced changes in the peripheral nerve, but PRP demonstrated a stronger antioxidant effect and a more pronounced presence of GFs, as evidenced by electron microscopy. PRP may represent a promising therapeutic approach for paclitaxel-induced neuropathy.

Amorphous thin films grown by magnetron co-sputtering exhibit changes in atomic structure with varying growth and annealing temperatures. Structural variations influence the bulk properties of the films. Scanning nanodiffraction performed in a transmission electron microscope (TEM) is applied to amorphous Tb17Co83 (a-Tb-Co) films deposited over a range of temperatures to measure relative changes in medium-range ordering (MRO). These measurements reveal an increase in MRO with higher growth temperatures and a decrease in MRO with higher annealing temperatures. The trend in MRO indicates a relationship between the growth conditions and local atomic ordering. By tilting select films, the TEM measures variations in the local atomic structure as a function of orientation within the films. The findings support claims that preferential ordering along the growth direction results from temperature-mediated adatom configurations during deposition, and that oriented MRO correlates with increased structural anisotropy, explaining the strong growth-induced perpendicular magnetic anisotropy found in rare earth-transition metal films. Beyond magnetic films, we propose the tilted FEM workflow as a method of extracting anisotropic structural information in a variety of amorphous materials with directionally dependent bulk properties, such as films with inherent bonding asymmetry grown by physical vapor deposition.

The production of plutonium-238 through irradiation of neptunium-237 (237Np) target materials for the use in radioisotope thermoelectric generators is paramount for continued deep space exploration. This work employs scanning electron microscopy to analyze 237Np materials coupled with a well-developed image analysis framework (Morphological Analysis for Material Attribution, or MAMA) to determine the degree of micron-scale homogeneity in the materials. This work demonstrated how the quantification of particle characteristics can validate production materials and affirm the qualitative similarities observed in micrographs. The 237Np oxide particle analysis determined that the materials from five production runs were quantitatively homogenous (significant at α = 0.05) in particle area, circularity, equivalent circular diameter, and ellipse aspect ratio, with two of the sampling dates having statistically significant different means for one of the four characteristics. These metrics not only confirm general homogeneity of the material but also expand the application of MAMA workflows to 237Np materials, demonstrating the utility of MAMA analysis for a wider breadth of nuclear materials than previously reported. In the open literature, this study is the first time that these microanalytical techniques were applied to 237Np materials to this degree.

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.

In the field of quantum materials, understanding anomalous behavior under charge degrees of freedom through bond formation is of fundamental importance, with two key concepts: Dimerization and charge order at different cation sites. The coexistence of both dimerization and charge ordering is unusually found in NaRu2O4, even in its metallic state at room temperature. Our work unveils the origin of the interplay of these effects within metallic single-crystalline NaRu2O4. Employing advanced transmission electron microscopy techniques, we probe the lattice order of NaRu2O4 as a function of temperature and provide direct microscopic evidence of a Peierls-type transition. This transition is accompanied by a pronounced dimerization of the ruthenium chains, resulting in a distinctive twofold superstructure along the b axis below the critical transition temperature of ∼535 K, coinciding with a charge order. In situ heating experiments confirm the reversibility of this first-order phase transition, and periodic lattice displacement maps depict atomic-scale displacements linked to dimerization.

There is still room for improvement in the isolation and purification techniques for extracellular vesicles (EVs), particularly in the separation of exosomes (small EVs) from other membrane vesicles such as microvesicles and apoptotic bodies. Furthermore, it is crucial to establish preparation methods that preserve the intrinsic properties of EVs in this context. In this study, we focus on the isolation and preparation of small EVs, exosomes, from the culture supernatant of a human cell line. We discuss the sequential use of regenerated cellulose membranes with different molecular weight cutoffs, based on direct evaluation by transmission electron microscopy, and examine the challenges of characterizing biological membrane vesicles, small EVs, identified during this process.

A new method for dark field imaging is introduced, which uses scanned electron diffraction (or 4DSTEM-4-dimensional scanning transmission electron microscopy) datasets as its input. Instead of working on simple summation of intensity, it works on a sparse representation of the diffraction patterns in terms of a list of their diffraction peaks. This is tested on a thin perovskite film containing structural ordering resulting in additional superlattice spots that reveal details of domain structures, and is shown to give much better selectivity and contrast than conventional virtual dark field imaging. It is also shown to work well in polycrystalline aggregates of CuO nanoparticles. In view of the higher contrast and selectivity, and the complete exclusion of diffuse scattering from the image formation, it is expected to be of significant benefit for characterization of a wide variety of crystalline materials.

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.