Microscopy and Microanalysis最新文献

In the scanning transmission electron microscope, both phase imaging of beam-sensitive materials and characterization of a material's functional properties using in situ experiments are becoming more widely available. As the practicable scan speed of 4D-STEM detectors improves, so too does the temporal resolution achievable for both differential phase contrast (DPC) and ptychography. However, the read-out burden of pixelated detectors, and the size of the gigabyte to terabyte sized data sets, remain a challenge for both temporal resolution and their practical adoption. In this work, we combine ultra-fast scan coils and detector signal digitization to show that a high-fidelity DPC phase reconstruction can be achieved from an annular segmented detector. Unlike conventional analog data phase reconstructions from digitized DPC-segment images yield reliable data, even at the fastest scan speeds. Finally, dose fractionation by fast scanning and multi-framing allows for postprocess binning of frame streams to balance signal-to-noise ratio and temporal resolution for low-dose phase imaging for in situ experiments.

Atom probe tomography data are composed of a list of coordinates of the reconstructed atoms in the probed volume. The elemental identity of each atom is derived from time-of-flight mass spectrometry, with no local chemical information readily available. In this study, we use a data processing technique referred to as field evaporation energy loss spectroscopy (FEELS), which analyzes the tails of mass peaks. FEELS was used to extract critical energetic parameters that are related to the activation energy for atoms to escape from the surface under intense electrostatic field and dependent of the path followed by the departing atoms. We focused our study on pure face-centered cubic metals. We demonstrate that the energetic parameters can be mapped in two-dimensional with nanometric resolution. A dependence on the considered crystallographic planes is observed, with sets of planes of low Miller indices showing a lower sensitivity to the field. The temperature is also an important parameter in particular for aluminum, which we attribute to an energetic transition between two paths of field evaporation between 25 and 60 K close to (002) pole. This paper shows that the information that can be retrieved from the measured energy loss of surface atoms is important both experimentally and theoretically.

Scanning ion microscopy applications of novel focused ion beam (FIB) systems based on ultracold rubidium (Rb) and cesium (Cs) atoms were investigated via ion-induced electron and ion yields. Results measured on the Rb+ and Cs+ FIB systems were compared with results from commercially available gallium (Ga+) FIB systems to verify the merits of applying Rb+ and Cs+ for imaging. The comparison shows that Rb+ and Cs+ have higher secondary electron (SE) yields on a variety of pure element targets than Ga+, which implies a higher signal-to-noise ratio can be achieved for the same dose in SE imaging using Rb+/Cs+ than Ga+. In addition, analysis of the ion-induced ion signals reveals that secondary ions dominate Cs+ induced ion signals while the Rb+/Ga+ induced signals contain more backscattered ions.

The levels of nicotinamide adenine dinucleotide (NADH) dehydrogenase [ubiquinone] iron-sulfur protein 2 (NDUFS2, a subunit of NADH dehydrogenase) decrease in aged tissues, and these reductions may be partly associated with age-related conditions such as Parkinson's disease. Aging leads to many mitochondrial defects, such as biogenesis disruption, dysfunction, defects in the mitochondrial membrane potential, and production of reactive oxygen species, that may be highly related to NDUFS2 expression. The relationship between NDUFS2 and postovulatory oocyte aging in pigs remains unknown. In this study, we investigated changes in NDUFS2 expression during postovulatory aging (POA). Furthermore, NDUFS2 was knocked down via dsRNA microinjection at the MII stage to evaluate the effects on mitochondrial-related processes during POA. The mRNA expression of NDUFS2 decreased significantly after 48-h aging compared with that in fresh oocytes. NDUFS2 knockdown (KD) significantly impaired the maintenance of oocyte morphology and blastocyst development of embryos after POA. The levels of PGC1α (mitochondrial biogenesis-related proteins) decreased significantly after NDUFS2 KD, while the level of GSNOR, a protein denitrosylase, was reduced by NDUFS2 KD after 48 h of aging. These data suggest that NDUFS2 is vital for maintaining the oocyte quality during POA in pigs.

As hydrogen is touted as a key player in the decarbonization of modern society, it is critical to enable quantitative hydrogen (H) analysis at high spatial resolution and, if possible, at the atomic scale. H has a known deleterious impact on the mechanical properties (strength, ductility, toughness) of most materials that can hinder their use as part of the infrastructure of a hydrogen-based economy. Enabling H mapping including local hydrogen concentration analyses at specific microstructural features is essential for understanding the multiple ways that H affect the properties of materials including embrittlement mechanisms and their synergies. In addition, spatial mapping and quantification of hydrogen isotopes is essential to accurately predict tritium inventory of future fusion power plants thus ensuring their safe and efficient operation. Atom probe tomography (APT) has the intrinsic capability to detect H and deuterium (D), and in principle the capacity for performing quantitative mapping of H within a material's microstructure. Yet, the accuracy and precision of H analysis by APT remain affected by complex field evaporation behavior and the influence of residual hydrogen from the ultrahigh vacuum chamber that can obscure the signal of H from within the material. The present article reports a summary of discussions at a focused workshop held at the Max-Planck Institute for Sustainable Materials in April 2024. The workshop was organized to pave the way to establishing best practices in reporting APT data for the analysis of H. We first summarize the key aspects of the intricacies of H analysis by APT and then propose a path for better reporting of the relevant data to support interpretation of APT-based H analysis in materials.

It is important to understand the carbide distribution around high-energy sites such as dislocations and grain boundaries in martensitic steels as they have a major influence on the alloy performance. The aim of this study is to characterize fine ε carbides precipitated in low-carbon lath martensitic steel using the ultrawide field-of-view (FoV) CAMECA Invizo 6000 atom probe. We demonstrate the advantages of the wide FoV and determine the optimum conditions for analysis, by comparing the results such as the background noise and the C++/C+ charge state ratio (CSR) between voltage-pulsed and laser-pulsed modes. Increasing the laser pulse energy decreased the background noise and the CSR, where 70 pJ laser pulse energy produced a comparable mass-to-charge ratio spectrum to that recorded in voltage-pulsed mode, with the bulk compositions of C, Si, and Mn closest to that measured using voltage-pulsed mode. Increasing laser pulse energies to above 300 pJ decreased the bulk carbon content, with a more diffuse distribution of carbon around the carbides. This paper outlines some of the important experimental considerations when performing quantitative study of carbide precipitation in low-carbon martensitic steels using the Invizo 6000, considerations that can also be applied to other ferrous and non-ferrous alloy systems.

The biocompatibility and resorption characteristics of β-tricalcium phosphate (β-TCP, Ca3(PO4)2) have made it a coveted alternative for bone grafts. However, the underlying mechanisms governing the biological interactions between β-tricalcium phosphate and osteoclasts remain elusive. It has been speculated that the composition at grain boundaries might vary and affect β-TCP resorption properties. Atom probe tomography (APT) offers a quantitative approach to assess the composition of the grain boundaries, and thus advance our comprehension of the biological responses within the microstructure and chemical composition at the nanoscale. The precise quantitative analysis of chemical composition remains a notable challenge in APT, primarily due to the influence of measurement conditions on compositional accuracy. In this study, we investigated the impact of laser pulse energy on the composition of β-TCP using APT, aiming for the most precise Ca:P ratio and consistent results across multiple analyses performed with different sets of analysis conditions and on two different instruments.

Magnetic dopants in three-dimensional topological insulators (TIs) offer a promising avenue for realizing the quantum anomalous Hall effect (QAHE) without the necessity for an external magnetic field. Understanding the relationship between site occupancy of magnetic dopant elements and their effect on macroscopic property is crucial for controlling the QAHE. By combining atomic-scale energy-dispersive X-ray spectroscopy (EDS) maps obtained by aberration-corrected scanning transmission electron microscopy (AC-STEM) and novel data processing methodologies, including semi-automatic lattice averaging and frame registration, we have determined the substitutional sites of Mn atoms within the 1.2% Mn-doped Sb2Te3 crystal. More importantly, the methodology developed in this study extends beyond Mn-doped Sb2Te3 to other quantum materials, traditional semiconductors, and even electron irradiation sensitive materials.

Abamectin is one of the most widely used pesticides due to its strong insecticidal and anthelmintic activities. Melatonin is a neurohormone with potent antioxidant, anti-apoptotic, and anti-inflammatory effects. This study aimed to investigate the potential ameliorative effects of melatonin against abamectin-induced testicular toxicity in rats. Twenty-four rats were divided into four groups: control group (1 mL/kg/day corn oil), melatonin-treated group (10 mg/kg/day), abamectin-treated group (0.5 mg/kg/day), and melatonin plus abamectin-treated group. Test substances were administered via oral gavage once daily for 28 days. While MDA and 8-OHdG levels increased in the testicular tissue of rats treated with abamectin, SOD, CAT, GPx, and GST enzyme activities decreased significantly. While interleukin-17 levels, TNF-α, and caspase3 expression increased in the testicular tissue, acetylcholinesterase activity decreased. At the same time, serum gonadotropins (luteinizing and follicle-stimulating hormones) and testosterone levels decreased. Light microscope examinations of testicular tissues revealed severe histopathological changes, such as atrophic hyalinized seminiferous tubules, basement membrane irregularity, degeneration, spermatogenic cell loss, and necrosis. Electron microscopy examinations revealed large vacuoles in Sertoli and spermatogenic cells, swelling and vacuolization in mitochondria, lysosomal structures, and increased pyknotic nuclei. In contrast, melatonin supplementation significantly ameliorated abamectin-induced testicular toxicity in rats through antioxidant, antiapoptotic, and anti-inflammatory mechanisms.

Heat shock proteins (HSPs) are induced in response to stressful stimuli and play an important role in cell repair and protection. This study, using immunohistochemistry, aimed to determine whether HSPs are induced in the cerebellum of rats subjected to hyperthermia during postnatal development (PND). The results showed that unlike HSP27 and HSP70, HSP60 and HSP90 were constitutively expressed in the cerebellum of rats. However, hyperthermia induced HSP27 in the white matter (WM) and HSP70 in the Bergmann glial cells, the internal granule layer (IGL), and the WM. In the WM, HSP27 induction was only observed on days PND20, PND25, and PND30, and HSP27 expression was higher on day PND30 compared with days PND20 and PND25 (p < 0.001). In the Bergmann glial cells, HSP70 induction was only observed on days PND5, PND10, and PND20, and HSP70 expression was greater on days PND5 and PND10 compared with day PND20 (p < 0.001). In the IGL and the WM, HSP70 expression was higher on days PND20, PND25, and PND30 compared with days PND5 and PND10 (p < 0.001). These findings indicate that unlike HSP60 and HSP90, HSP27 and HSP70 have different expression patterns in the cerebellum of rats after hyperthermia during PND.