Microscopy and Microanalysis最新文献

Characterizing threading dislocations (TDs) in gallium nitride (GaN) semiconductors is crucial for ensuring the reliability of semiconductor devices. The current research addresses this issue by combining two techniques using a scanning electron microscope, namely electron channeling contrast imaging (ECCI) and high-resolution electron backscattered diffraction (HR-EBSD). It is a comparative study of these techniques to underscore how they perform in the evaluation of TD densities in GaN epitaxial layers. Experiments reveal that the dislocation line vectors mostly deviate from the growth direction of the film, i.e., ∦ [0001], followed by edge-type dislocations (dislocation lines || [0001]) with insignificant screw character. Furthermore, TDs from the dislocation clusters are characterized as edge- and (edge + mixed)-type TDs. By combining ECCI counting of dislocations and HR-EBSD description of geometrically necessary dislocation density type, it is possible to measure the total TD density and provide the proportion of pure (edge and screw) and mixed TDs. It has also been observed from the analyses of residual elastic strain fields and lattice rotations that it is not possible to identify individual dislocations for the spatial resolution of 50 nm in HR-EBSD. Nevertheless, ECCI and HR-EBSD can be complementarily used to count and characterize the TDs.

The challenge of imaging low-density objects in an electron microscope without causing beam damage is significant in modern transmission electron microscopy. This is especially true for life science imaging, where the sample, rather than the instrument, still determines the resolution limit. Here, we explore whether we have to accept this or can progress further in this area. To do this, we use numerical simulations to see how much information we can obtain from a weak phase object at different electron doses. Starting from a model with four phase values, we compare Zernike phase contrast with measuring diffracted intensity under multiple random phase illuminations to solve the inverse problem. Our simulations have shown that diffraction-based methods perform better than the Zernike method, as we have found and addressed a normalization issue that, in some other studies, led to an overly optimistic representation of the Zernike setup. We further validated this using more realistic 2D objects and found that random phase illuminated diffraction can be up to five times more efficient than an ideal Zernike implementation. These findings suggest that diffraction-based methods could be a promising approach for imaging beam-sensitive materials and that current low-dose imaging methods are not yet at the quantum limit.

Leeches are widely used as model organisms in scientific studies and medical treatments. Medical leeches are hematophagous parasites that usually feed on the blood of their hosts. Some leeches show deformities, usually after feeding. This causes both medical and economic losses as it reduces the effectiveness of leeches in cultivation and medical treatment. The aim of this study was to investigate the effects of morphological deformations after feeding in Hirudo verbana, Carena 1820 (Annelida, Hirudinea), an important species in medical leech treatments. For this purpose, both histopathological and scanning electron microscopy examinations of starved and fed leeches were performed. The causes of deformities in medical leeches were found to be due to overfeeding, which caused cracks on the intestinal surface and therefore deterioration of the tissues. It is also thought that the immunological agents in the fed blood destroyed the medical leech tissue in these regions. In addition, it was determined that the cellular structure of the shaped blood elements stored in the cavity after feeding was preserved for a long time (months) without deterioration. It is certain that revealing the mechanism by which this occurs will inspire the preservation of blood for a long time in blood transfusion.

The pluripotency-related T-box family transcription factor TBX3 maintains mESC self-renewal and plays a key role in the development of several tissues, including the heart, mammary glands, limbs, and lungs. However, the role of TBX3 during porcine preimplantation embryo development remains unclear. In our research, TBX3 was knocked down by injecting dsRNA to explore the function of TBX3. TBX3 expression gradually increases during early embryonic development. TBX3 knockdown resulted in decreased in the rate of four-cell and blastocyst. Depletion of TBX3 decreased the level of H3K9Ac/H3K27Ac and decreased ZGA gene expression at the four-cell stage. Furthermore, TBX3 knockdown led to a decrease in ZSACN4 protein level, DNMT1 and intracellular 5mc levels were increased, and then induced telomeres shorten and DNA damaged. Additionally, TBX3 knockdown significantly decreased histone acetylation and pluripotency genes NANOG/OCT4 expression in blastocysts. TBX3 knockdown induced apoptosis in blastocysts. Taken together, TBX3 regulate histone acetylation and play important roles in zygotic genome activation and early embryonic development in pigs.

A self-opening transfer shuttle has been designed and fabricated for the transfer of air-sensitive samples to scanning electron microscopy (SEM). Delayed push out of an airtight sample cabin sealed inside the shuttle allows the protection of the sample from air exposure during the pumping of SEM chamber. A compressed spring is employed to automatically drive the push out of the cabin. Once the cabin is fully pushed out, the sample contained inside is revealed for SEM investigation through a hollow window created on the shuttle. The O-rings that are fixed at both ends of the sample cabin not only serve as sealing parts that make the cylinder airtight but also act as resistance elements that provide sufficient friction force to slow down the push out of the sample cabin. With the advantages of self-opening without the need for external control or force, and its reasonably small size, this low-cost and easy-to-use transfer shuttle has wide compatibility with different SEMs and holds a promising application prospect in numerous research areas.

A conduction heat transfer analysis of ex situ lift-out specimen handling under cryogenic conditions (cryo-EXLO) is performed and compared with experimentally determined temperature values using a type K thermocouple. Using a finite-volume solver for heat conduction, the analysis confirms that manipulation of a specimen by a probe above a working surface cooled at liquid nitrogen (LN2) temperatures can remain below the critical vitreous temperature up to several hundreds of micrometers above the working surface, allowing for ample distance for lift out and specimen manipulation. In addition, the temperature above the cryogenic shuttle sample holder working surface remains below the vitreous temperature for several tens of minutes without adding cryogen, yielding sufficient time to complete multiple manipulations. Periodically topping off the cryogen level may allow for unlimited cryo-EXLO manipulations with this hardware and geometry.

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.