This review article explains about the wavelet hidden Markov model applied to noise reduction from electron holograms. This method allows for a reasonable separation of weak signal from noise, beyond the framework of the classical noise reduction using wavelet transformation. The calculations demonstrate that the noise reduction attains a significant precision improvement in the phase reconstruction from electron holograms.

A set of microscopic image/spectral intensities collected from many sampling points in a region of interest, in which multiple physical/chemical components may be spatially and spectrally entangled, could be expected to be a rich source of information about a material. To unfold such an entangled image comprising information and spectral features into its individual pure components would necessitate the use of statistical treatment based on informatics and statistics. These computer-aided schemes or techniques are referred to as blind source separation or hyperspectral image analysis, depending on their application fields, and are classified as a subset of machine learning. In this article, we briefly review our recent progress in these unfolding techniques, particularly those related to STEM, electron energy-loss spectroscopy and energy-dispersive X-ray spectroscopy. This review, which commences with the description of the basic concept, the advantages and drawbacks of the technique, presents several additional strategies to overcome existing problems and their extensions to more general tensor decomposition schemes for further flexible applications are described. For adopting the technique to datasets having a lower signal-to-noise ratio a new data treatment strategy with Poisson noise assumed is also presented.

X-ray Energy Dispersive Spectroscopy (XEDS) is widely utilized to detect elements and to measure their compositions in small areas observed in TEM/STEM. Atomic resolution element mapping by XEDS now becomes available, resulting from the considerable improvement in X-ray detection efficiency in STEM in the last decade. The present review is focused on recent achievements in location of small amounts of dopant elements in metallic compounds by XEDS element mapping, taking advantage of noise reduction processing by non-local principle component analysis (NLPCA) for Poisson noise. The first topic illustrates how effective the NLPCA processing is to this end in a trial to identify the location of 2 at % Nb doped in SrTiO₃. After discussion on the parameters for image patching and clustering, it is shown that NLPCA is quite effective to light up Nb occupying the Ti-sublattice even though the original map is noisy. The second topic is an application of the present method to Ni and Zn dopants in hexagonal η-Cu₆Sn₅ intermetallic compound, which stabilize η-phase down to room temperature, suppressing the phase transition to monoclinic η′-structure. It is disclosed that small amounts of Ni and Zn dopant atoms occupy Cu2 and Sn sites in the η-Cu₆Sn₅ structure, respectively.

All-solid-state lithium-ion batteries (LIBs) are promising candidates of next-generation secondary batteries that have the potential to overcome the problems of conventional LIBs with liquid-electrolytes. However, it is known that the Li-ion conduction resistance at the electrode/solid-electrolyte interface limits their performance. It is important to elucidate interfacial phenomena at the nanometer scale and feed it back to material design. In this paper, we use scanning transmission electron microscopy (STEM) coupled with electron energy loss spectroscopy (EELS) to dynamically observe the distribution of Li and the electronic state of transition metals in an all-solid-state LIB during the charge-discharge reactions. The distribution of Li was quantitatively observed under dynamic conditions by applying multivariate analysis. The results showed that Li ions were heterogeneously extracted/inserted during the charge/discharge reaction, and that the activity of the electrochemical reaction depended on the Li-ion concentration at the original state (as deposition). The origin of the interfacial resistance was the electrochemically inactive Co₃O₄ formed at 10–20 nm near the interface.

Electron energy-loss spectroscopy (EELS) is applied for evaluations of the dielectric properties of materials. The intensity distribution of an EELS spectrum can be interpreted as a result of dielectric response due to Coulomb interactions between incident electrons and the valence electrons in a solid. To evaluate the optical/dielectric properties of functional materials, it is important to understand the dielectric functions of the materials. In this article, the dielectric analysis using EELS is presented. First, the meaning of the dielectric function would be explained by using fundamental electromagnetic equations. After that, EELS analysis of dielectric properties of heat-shielding materials, LaB₆ and Cs_0.33WO₃ (CWO), are presented as practical examples. From the dielectric function of LaB₆ derived from EELS measurement, the properties of carrier electrons can be investigated. In the study of the dielectric properties on CWO, angled-resolved EELS (AR-EELS) measurement is conducted to investigate the anisotropic properties of plasmon oscillations of carrier electrons. AR-EELS can provide the dielectric information similar to the polarized optical measurement. Moreover, the momentum transfer dependence of the plasmon energies should reflect the conduction band structure of CWO. Therefore, AR-EELS is expected to analyze the band structure of metallic functional materials.

Correlative light-electron microscopy (CLEM) is a technique that bridges the gap in resolution between optical and electron microscopy by observing the same location of the same sample with an optical microscope and an electron microscope, and could be an important research tool in cell biology that requires the analysis of sub-organelle levels in cells. There are various methods for CLEM depending on the purpose, and recent scanning electron microscopy-based CLEM methods changed the situation dramatically. This paper reviews the overall workflow of CLEM and summarizes the works for each purpose.

DNA methylation is an important chemical modification that regulates gene expression. In this research, by applying our original protein-labeling technique, we developed a chemical probe that enhances fluorescence intensity upon binding to methylated DNA. This probe is a hybrid molecule that consists of a synthetic fluorophore and a protein and enables imaging of methylated DNA in living cells. By using this hybrid probe, we successfully imaged dynamics of methuylated DNA during mitosis.

Cathodoluminescence based on scanning transmission electron microscopy enables nanoscopic visualization of the electric field generated from a light source which produces photons through coherent processes. In this article, we mainly focus on the multipole modes of optical nanoantennas. With the angle- and polarization-resolved approach, it is possible to selectively visualize the field distribution of the degenerate modes, which cannot be resolved only by energy selection.