Microscopy (Oxford, England)最新文献

We developed a Mach-Zehnder type electron interferometer (MZ-EI) that enables simultaneous observation of interferograms created at multiple output locations on a 1.2-MV field-emission transmission electron microscope. This MZ-EI is composed of two single-crystal thin films, a lens located between the single-crystal thin films and imaging lenses. By comparing interferograms created by electron waves travelling through different beam paths, we found that the relative phase difference was caused by phase modulation passing through the single crystals and by aberrations and defocus values of the lenses. We also confirmed that the relative phase difference can be controlled using the tilted illumination method.

Scanning Transmission Electron Microscopy (STEM) enables direct determination of atomic arrangements in materials and devices. However, materials such as battery components are weak for electron beam irradiation, and low electron doses are required to prevent beam-induced damages. Noise removal is thus essential for precise structural analysis of electron-beam-sensitive materials at atomic resolution. Total square variation (TSV) regularization is an algorithm that exhibits high noise removal performance. However, the use of the TSV regularization term leads to significant image blurring and intensity reduction. To address these problems, we here propose a new approach adopting L2 norm regularization based on higher-order total variation. An atomic-resolution STEM image can be approximated as a set of smooth curves represented by quadratic functions. Since the third-degree derivative of any quadratic function is 0, total third-degree variation (TTDV) is suitable for a regularization term. The application of TTDV for denoising the atomic-resolution STEM image of CaF2 observed along the [001] zone axis is shown, where we can clearly see the Ca and F atomic columns without compromising image quality.

A new configuration for near-field ptychography using a full-field illumination with a structured electron beam is proposed. A structured electron beam illuminating the entire field of view is scanned over the specimen, and a series of in-line holograms formed in the near-field region below the specimen are collected. The structured beam is generated by a conductive film with random openings, which ensures high stability and coherence of the beam. Observation in the near-field region reduces the beam concentration that occurs in the far-field region, which contributes to accurate recording of the beam intensity with a finite dynamic range of the detectors. The use of full-field illumination prevents the accumulation of errors caused by concatenating the local structures, which is the method used in conventional reconstruction. Since all holograms are obtained from the entire field of view, they have uniform multiplicity in terms of specimen information within the field of view. This contributes to robust and efficient reconstruction for a large field of view. The proposed method was tested using both simulated and experimental holograms. For the simulated holograms, the reconstruction of the specimen transmission function was achieved with an error less than 1/3485 of the wavelength. The method was further validated using experimental holograms obtained from MgO particles. The reconstructed phase transmission function of the specimen was consistent with the specimen structure and was equivalent to a mean inner potential of 13.53±0.16 V on the MgO particle, which is in close agreement with previously reported values.

The surface sensitivity of high-resolution secondary electron (SE) imaging is examined using twisted bilayers of MoS2 stacked at an angle of 30°. High-resolution SE images of the twisted bilayer MoS2 show a honeycomb structure composed of Mo and S atoms, elucidating the monolayer structure of MoS2. Simultaneously captured annular dark-field scanning transmission electron microscope images from the same region show the projected structure of the two layers. That is, the SE images from the bilayer MoS2 selectively visualize the surface monolayer. It is noted that the SE yields from the surface monolayer are approximately three times higher than those from the second monolayer, likely attributable to attenuation when SEs emitted from the second layer traverse the surface layer. The surface sensitivity of high-resolution SE imaging is examined using twisted bilayers of MoS2 stacked at an angle of 30°. It was found that the SE images of the MoS2 bilayer visualize the surface monolayer approximately three times more intensely than the second monolayer.

In this study, we experimentally analyzed the charging phenomenon when an insulating resist film on a conductive layer formed on bulk glass is irradiated by electron beams (EBs). To quantify the charging potential induced, an electrostatic force microscope device was installed in the scanning electron microscope sample chamber, and potential distributions formed under various exposure conditions were obtained. Based on the results obtained, a model for charge accumulation within the sample, explaining positive and negative charging and their transitions, was developed. At an EB acceleration voltage of 30 kV, the following observations were made: 'global charging' could be avoided by applying -5 V to the sample. Regarding 'local charging' near the exposure area of the EB, at low exposure doses, emission of secondary electrons from the sample surface induced positive charging, while the accumulation of incident electrons within the sample induced negative charging. At exposure doses where the effects of both are balanced, the sample exhibited zero potential, revealing the appearance of the 'first zero-cross exposure dose'. At higher exposure doses, the sample transitions from negative to positive as the exposure dose increases due to the electron-beam-induced conduction, resulting in the so-called second zero-cross exposure dose. The exposure dose dependence of the charging potential distribution at various acceleration voltages was obtained. In particular, we found that at an acceleration voltage of 0.6 kV, the sample surface is not charged even when exposed to small to very large doses of EBs.

Heteroepitaxial interfaces are important because they determine the performance of devices such that career mobility is sensitive to the distribution of roughness, strain and composition at the interface. High-angle annular dark field imaging in scanning transmission electron microscopy has been utilized to capture them at an atomic scale. For precise identification of atomic column positions, a technique has been proposed to average multiple image frames taken at a high scanning rate by their positional alignment for increasing signal-to-noise ratio. However, the positional alignment between frames is sometimes incorrectly estimated because of the almost perfect periodic structure at the interfaces. Here, we developed an approach for precise positional alignment, where the images are first aligned by two consecutive images and then are aligned more precisely against the integrated image of the first alignment. We demonstrated our method by applying it to the heterointerface of Si0.8Ge0.2 (Si: silicon, Ge: germanium) epitaxial thin films on a Si substrate.

We have demonstrated localized surface plasmon (LSP)-enhanced cathodoluminescence (CL) from an atomic layer deposition-grown Al2O3/ZnO/Al2O3 heterostructure to develop a bright nanometer-scale light source for an electron beam excitation-assisted optical microscope. Three types of metals, Ag, Al and Au, were compared, and an 181-fold enhancement of CL emission was achieved with Ag nanoparticles, with the plasmon resonance wavelength close to the emission wavelength energy of ZnO. The enhanced emission is plausibly attributed to LSP/exciton coupling. However, it is also attributed to an increase in coupling efficiency with penetration depth and also to an increase in light extraction efficiency by grading the refractive indices at the heterostructure.

We investigate a one-dimensional plasmonic crystal using momentum-resolved electron energy-loss spectroscopy (EELS) and cathodoluminescence (CL) techniques, which are complementary in terms of available optical information. The plasmonic crystal sample is fabricated from large aluminum grains through the focused ion beam method. This approach allows curving nanostructures with high crystallinity, providing platforms for detailed analysis of plasmonic nanostructures using both EELS and CL. The momentum-resolved EELS visualizes dispersion curves outside the light cone, confirming the existence of the surface plasmon polaritons and local modes, while the momentum-resolved CL mapping analysis identified these surface plasmon polaritons and local modes. Such synergetic approach of two electron-beam techniques offers full insights into both radiative and non-radiative optical properties in plasmonic or photonic structures.

Cell membrane structures are supramolecular complexes that require the ordered assembly of membrane proteins and lipids. The morphology of various cell adhesion structures in multicellular organisms, such as those between epithelial cells, neural synapses and immune synapses, was initially described through electron microscopic analyses. Subsequent studies aimed to catalog their constituent proteins, which encompass transmembrane cell adhesion molecules, cytoskeletal proteins and scaffolding proteins that bind the two components. However, the diversity of plasma membrane lipids and their significance in the organization of cell adhesion structures were underappreciated until recently. It is now understood that phase separation of lipids and liquid-liquid phase separation of proteins are important driving forces for such self-assembly. In this review, we summarized recent findings on the role of lipids as scaffolds for supramolecular complexes using tight junctions in epithelial cells as an example.

Bacterial spores, known for their complex and resilient structures, have been the focus of visualization using various methodologies. In this study, we applied quick-freeze and replica electron microscopy techniques, allowing observation of Bacillus subtilis spores in high-contrast and three-dimensional detail. This method facilitated visualization of the spore structure with enhanced resolution and provided new insights into the spores and their germination processes. We identified and described five distinct structures: (i) hair-like structures on the spore surface, (ii) spike formation on the surface of lysozyme-treated spores, (iii) the fractured appearance of the spore cortex during germination, (iv) potential connections between small vesicles and the core membrane and (v) the evolving surface structure of nascent vegetative cells during germination.