Microscopy (Oxford, England)最新文献

Accurately deriving the momentum-transfer dependence of the dielectric function ε(q, ω) using angle-resolved electron energy-loss spectroscopy (AR-EELS) is necessary for evaluating the average electron-hole distance, i.e., the exciton size, in materials. Achieving accurate exciton-size evaluations will promote the comprehension of optical functionality in materials such as photocatalysts. However, for amorphous materials, it is difficult to accurately derive ε(q, ω) because the elastic scattering intensity originating from the amorphous structure and the inelastic scattering intensity associated with the elastic scattering overlap in the EELS spectrum. In this study, a method to remove these overlapping intensities from the EELS spectrum is proposed to accurately derive the ε(q, ω) of an amorphous material. Amorphous SiO2 (am-SiO2) was subjected to AR-EELS measurements, and ε(q, ω) of am-SiO2 was derived after removing the intensity due to the amorphous structure using the proposed method. Thereafter, the exciton absorption intensity and the exciton size were evaluated. Applying the proposed method, the exciton absorption intensity was considerably suppressed in the q-region after 1.0 Å-1, where the elastic and inelastic scattering intensities originating from the amorphous structure are dominant. The exciton size evaluated was 2 nm (1 nm), consistent with the theoretically predicted size of ~1 nm. Therefore, the proposed method is effective for deriving accurate ε(q, ω), facilitating exciton-size evaluation for amorphous materials using AR-EELS.

Immunoelectron microscopy is a technique for analyzing molecular localization at the ultrastructural level. In the pre-embedding immunoelectron microscopy, samples are immunolabeled with extremely small gold particles. Gold enhancement then enlarges the gold particles to an easily visible size. During the examination of the optimal conditions, we found that phosphate buffer accelerates the enhancement reaction. Furthermore, disodium hydrogen phosphate was identified as responsible for this effect. Disodium hydrogen phosphate enabled the gold labeling of deep regions within thick tissue samples. In conclusion, our method is useful for increasing the sensitivity, especially in the deeper region of the sample.

High-quality thin lamellae are essential for state-of-the-art scanning transmission electron microscopy (S/TEM) analyses. While the preparation of S/TEM lamellae using focused ion beam (FIB-) scanning electron microscopy (SEM) has been established since the early 21st century, two critical factors have only recently been addressed: precise control over lamella thickness and a systematic understanding of FIB-induced damage. This study conducts an experimental investigation and simulation to explore how the intensities of backscattered and secondary electrons (BSEs and SEs, respectively) depend on lamellae thickness for semiconductor (Si), insulator (Al2O3), and metallic (stainless-steel) materials. The BSE intensity shows a simple linear relationship with the lamella thickness for all materials below a certain thickness, whereas the relationship between the SE intensity and thickness is more complex. In conclusion, the BSE intensity is a reliable indicator for accurately determining lamella thickness across various materials during FIB thinning processing, while the SE intensity lacks consistency due to material and detector variability. This insight enables the integration of real-time thickness control into S/TEM lamella preparation, significantly enhancing lamella quality and reproducibility. These findings pave the way for more efficient, automated processes in high-quality S/TEM analysis, making the preparation method more reliable for a range of applications.

X-ray microscopy using computed tomography is an excellent 3D imaging instrument. Three-dimensional X-ray microscopy (3DXRM) is a nondestructive imaging technique used to inspect internal and external structures in units of submicrometers or less. The 3DXRM, although attractive, is mostly used as an observation instrument and is limited as a measurement system in quantitative evaluation and quality control. Calibration is required for use in measurement systems such as coordinate measurement systems, and specific standard samples and evaluation procedures are needed. The certified values of the standard samples must ideally be traceable to the International System of Units (SI). In the 3DXRM measurement system, line structures (LSs) are fabricated as prototype standard samples to conduct magnification calibration. In this study, we evaluated the LS intervals using calibrated cross-sectional scanning electron microscopy (SEM). A comparison of the evaluation results between SEM and 3DXRM for the LS intervals provided the magnification calibration factor for 3DXRM and validated the LSs, whereby the interval methods and feasibility of constructing an SI traceability system were evaluated using the calibrated SEM. Consequently, a magnification calibration factor of 1.01 was obtained for 3DXRM based on the intervals of the LSs evaluated by SEM. A possible route for realizing SI-traceable magnification calibration of 3DXRM has been presented.

The spatial coherence and the axial brightness of a cold field emission gun, a Schottky field emission gun and a lanthanum hexaboride thermionic gun are precisely measured. By analyzing the Airy pattern from a selected area aperture, various parameters including the spatial coherence length are determined. Using the determined coherence length, the axial brightness of the field emission guns is estimated using the equation which we previously derived based on the discussion of the Wigner function of an electron beam. We also make some extensions in the method to be applicable to the measurements of the thermionic gun, which has anisotropic intensity distribution in most cases unlike the field emission guns. Not only conventional average brightness but also the axial brightness measured for the three kinds of emitters are compared accurately and precisely without being influenced by the measurement conditions.

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.

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.

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.

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.