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Information transfer of a 1-MV field-emission transmission electron microscope (TEM) was improved by reducing mechanical vibrations and improving the stability of an acceleration voltage. The resulting mechanical stability was estimated from lattice fringes with an obtained spacing of 19.6 pm under achromatic conditions. This value corresponds to a vibration amplitude of <19.6 pm. The stability of the acceleration voltage was improved by reducing thermal noises in the power supply. As a result, 39.2-pm-spacing linear lattice fringes were obtained under chromatic conditions. This indicates that 25.5 nm-1 information transfer was accomplished in the 1 MV field-emission TEM. [ABSTRACT FROM AUTHOR]

This paper reviews the basics of electron holography as an introduction of the holography part of this special issue in Microscopy. We discuss the general principle of holography and interferometry regarding measurements and analyses of phase distributions, first using the optical holography. Next, we discuss physical phenomena peculiar to electron waves that cannot be realized by light waves and principles of electromagnetic field detection and observation methods. Furthermore, we discuss the interference optical systems of the electron waves and their features, and methods of reconstruction of the phase information from electron holograms, which are essential for realization of practical electron holography. We note that following this review application of electron holography will be discussed in detail in the papers of this special issue. [ABSTRACT FROM AUTHOR]

Lorentz microscopy has opened the door to observing a single quantized magnetic flux line (i.e. a vortex) and its dynamic behavior inside a superconductor in real time. It resulted from the efforts of Dr Akira Tonomura and his collaborators, who developed a field emission electron microscope and advanced the technologies used for visualizing vortices (e.g. a low-temperature specimen stage and a magnetic-field application system). They used a 1-MV field emission transmission electron microscope with an electron beam that can penetrate thick specimens of high-temperature superconductors (Bi2Sr2CaCu2O8+δ and YB2C3O7−δ) to reveal the flux-line features inside materials and their interactions with defects. This memorial paper reviews the results of research in the area of vortex matter physics. [ABSTRACT FROM PUBLISHER]

Essentially, all optics is wave optics, be it with light, X-rays, neutrons or electrons. The information transfer from the object to the image can only be understood in terms of waves given by amplitude and phase. However, phases are difficult to measure: for slowly oscillating waves such as sound or low-frequency electromagnetic waves, phases can be measured directly; for high frequencies this has to be done by heterodyne detection, i.e. superposition with a reference and averaging over time. In optics, this is called interferometry. Because interference is mostly very difficult to achieve, phases have often been considered ‘hidden variables’ seemingly pulling the strings from backstage, only visible by their action on the image intensity. This was almost the case in conventional Electron Microscopy with the phase differences introduced by an object. However, in the face of the urgent questions from solid state physics and materials science, these phases have to be determined precisely, because they encode the most dominant object properties, such as charge distributions and electromagnetic fields. After more than six decades of very patient advancement, electron interferometry and holography offer unprecedented analytical facilities down to an atomic scale. Akira Tonomura has prominently contributed to the present state. [ABSTRACT FROM PUBLISHER]

Phase-shifting electron holography (PS-EH) is an interference transmission electron microscopy technique that accurately visualizes potential distributions in functional materials, such as semiconductors. In this paper, we briefly introduce the features of the PS-EH that overcome some of the issues facing the conventional EH based on Fourier transformation. Then, we present a high-precision PS-EH technique with multiple electron biprisms and a sample preparation technique using a cryo-focused-ion-beam, which are important techniques for the accurate phase measurement of semiconductors. We present several applications of PS-EH to demonstrate the potential in organic and inorganic semiconductors and then discuss the differences by comparing them with previous reports on the conventional EH. We show that in situ biasing PS-EH was able to observe not only electric potential distribution but also electric field and charge density at a GaAs p–n junction and clarify how local band structures, depletion layer widths and space charges changed depending on the biasing conditions. Moreover, the PS-EH clearly visualized the local potential distributions of two-dimensional electron gas layers formed at AlGaN/GaN interfaces with different Al compositions. We also report the results of our PS-EH application for organic electroluminescence multilayers and point out the significant potential changes in the layers. The proposed PS-EH enables more precise phase measurement compared to the conventional EH, and our findings introduced in this paper will contribute to the future research and development of high-performance semiconductor materials and devices. [ABSTRACT FROM AUTHOR]

Electron holography was invented for correcting aberrations of the lenses of electron microscopes. It was used to observe the atomic arrangements in crystals after decades of research. Then it was combined with a hardware aberration corrector to enable high-resolution and high-precision analysis. Its applications were further extended to magnetic observations with sub-nanometer resolution. High-resolution electron holography has become a powerful technique for observing electromagnetic distributions in functional materials. [ABSTRACT FROM AUTHOR]

We have developed an amplitude-division type Mach-Zehnder electron interferometer (MZ-EI). The developed MZ-EI is composed of single crystals corresponding to amplitude-division beam splitters, lenses corresponding to mirrors and an objective aperture. The spacings and azimuth angles of interference fringes can be controlled by single crystal materials and their orientations and by diffraction spots selected by the objective aperture. We built the MZ-EI on a 1.2-MV field-emission transmission electron microscope and tested its performance. Results showed that interference fringes were created for various spacings and azimuth angles, which demonstrates the practicability of the MZ-EI as an amplitude-division type electron interferometer. [ABSTRACT FROM AUTHOR]

Phase-shifting electron holography (PS-EH) using a transmission electron microscope (TEM) was applied to visualize layers with different concentrations of carriers activated by Si (at dopant levels of 1019, 1018, 1017 and 1016 atoms cm−3) in n -type GaN semiconductors. To precisely measure the reconstructed phase profiles in the GaN sample, three electron biprisms were used to obtain a series of high-contrast holograms without Fresnel fringes generated by a biprism filament, and a cryo-focused-ion-beam (cryo-FIB) was used to prepare a uniform TEM sample with less distortion in the wide field of view. All layers in a 350-nm-thick TEM sample were distinguished with 1.8-nm spatial resolution and 0.02-rad phase-resolution, and variations of step width in the phase profile (corresponding to depletion width) at the interfaces between the layers were also measured. Thicknesses of the active and inactive layers at each dopant level were estimated from the observed phase profile and the simulation of theoretical band structure. Ratio of active-layer thickness to total thickness of the TEM sample significantly decreased as dopant concentration decreased; thus, a thicker TEM sample is necessary to visualize lower carrier concentrations; for example, to distinguish layers with dopant concentrations of 1016 and 1015 atoms cm−3. It was estimated that sample thickness must be more than 700 nm to make it be possible to detect sub-layers by the combination of PS-EH and cryo-FIB. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editor discusses various reports within the issue on topics including Dr. Akira Tonomura, electron holography and Lorentz microscopy.

The coherency of a 1.2-MV transmission electron microscope was evaluated through illumination semiangles calculated from lengths over which Fresnel fringes can be observed. These lengths were determined from the diameters of circular holes fully filled with Fresnel fringes, i.e. this method allows lengths to be accurately measured even if micrographs are subjected to distortions. The smallest illumination semiangle of 4.0 × 10−9 rad was obtained for a circular hole with a diameter of 191 μm. In addition, electron beam brightness was estimated to be approximately 3 × 1014 A/m2·sr from the obtained illumination semiangle values and current densities. The results provide us with essential information that can be referred to in future electron holography studies aimed at detecting weak electromagnetic fields in materials. [ABSTRACT FROM AUTHOR]

The research on flux line lattices and pancake vortices in superconducting materials, carried out within a long and fruitful collaboration with Akira Tonomura and his group at the Hitachi Advanced Research Laboratory, led us to develop a mathematical framework, based on the reciprocal representation of the magnetic vector potential, that enables us to simulate realistic phase images of fluxons. The aim of this paper is to review the main ideas underpinning our computational framework and the results we have obtained throughout the collaboration. Furthermore, we outline how to generalize the approach to model other samples and structures of interest, in particular thin ferromagnetic films, ferromagnetic nanoparticles and p–n junctions. [ABSTRACT FROM PUBLISHER]

A dual-axis 360° rotation specimen holder was developed for use in reconstructing the three-dimensional (3D) distribution of a magnetic field using a combination of electron holography and tomography. Pillar-shaped specimens are used to obtain accurate reconstruction without a missing angle. The holder’s rotation rod can be turned >360°; the pillar is set ±45° to the azimuth for both x- and y-axis rotation. Two rotation series of holograms in individual axes are recorded for vector field tomography. The two vector components of the magnetic field are reconstructed directly from the two series of holograms, and the remaining component is calculated using Maxwell’s equation, div B = 0. As a result, all 3D magnetic fields are reconstructed. [ABSTRACT FROM AUTHOR]

Methods of controlled electron interference in k-space on the diffraction plane by means of an electron biprism invented during the Tonomura Electron Wavefront Project are briefly reviewed. The results presented show the partial coherence of self-interfered diffusely scattered electrons, elastically scattered and inelastically scattered, found outside and in between the Bragg diffracted beams often referred to as thermal diffuse scattering (TDS) of electrons. The interference fringes formed in the TDS intensity have been used to calculate a mean displacement of the atom of u ∼ 12 pm in Aluminum in the direction perpendicular to the Bragg planes. [ABSTRACT FROM PUBLISHER]

High-resolution study of the giant viruses presents one of the latest challenges in cryo-electron microscopy (EM) of viruses. Too small for light microscopy but too large for easy study at high resolution by EM, they range in size from ∼0.2 to 2 μm from high-symmetry icosahedral viruses, such as Paramecium burseria Chlorella virus 1, to asymmetric forms like Tupanvirus or Pithovirus. To attain high resolution, two strategies exist to study these large viruses by cryo-EM: first, increasing the acceleration voltage of the electron microscope to improve sample penetration and overcome the limitations imposed by electro-optical physics at lower voltages, and, second, the method of 'block-based reconstruction' pioneered by Michael G. Rossmann and his collaborators, which resolves the latter limitation through an elegant leveraging of high symmetry but cannot overcome sample penetration limitations. In addition, more recent advances in both computational capacity and image processing also yield assistance in studying the giant viruses. Especially, the inclusion of Ewald sphere correction can provide large improvements in attainable resolutions for 300 kV electron microscopes. Despite this, the study of giant viruses remains a significant challenge. [ABSTRACT FROM AUTHOR]

An automated hologram acquisition system for big-data analysis and for improving the statistical precision of phase analysis has been upgraded with automated particle detection technology. The coordinates of objects in low-magnification images are automatically detected using zero-mean normalized cross-correlation with preselected reference images. In contrast with the conventional scanning acquisitions from the whole area of a microgrid and/or a thin specimen, the new method allows efficient data collections only from the desired fields of view including the particles. The acquisition time of the cubic/triangular nanoparticles that were observed was shortened by about one-fifty eighth that of the conventional scanning acquisition method because of efficient data collections. The developed technology can improve statistical precision in electron holography with shorter acquisition time and is applicable to the analysis of electromagnetic fields for various kinds of nanoparticles. [ABSTRACT FROM AUTHOR]

An image identification method was developed with the aid of a deep convolutional neural network (CNN) and applied to the analysis of inorganic particles using electron holography. Despite significant variation in the shapes of α-Fe2O3 particles that were observed by transmission electron microscopy, this CNN-based method could be used to identify isolated, spindle-shaped particles that were distinct from other particles that had undergone pairing and/or agglomeration. The averaging of images of these isolated particles provided a significant improvement in the phase analysis precision of the electron holography observations. This method is expected to be helpful in the analysis of weak electromagnetic fields generated by nanoparticles showing only small phase shifts. [ABSTRACT FROM AUTHOR]

In this study, a noise-reduction technique for series low-dose electron holograms using tensor decomposition is demonstrated through simulation. We treated an entire dataset of the series holograms with Poisson noise as a third-order tensor, which is a stack of 2D holograms. The third-order tensor, which is decomposed into a core tensor and three factor matrices, is approximated as a lower-rank tensor using only noise-free principal components. This technique is applied to simulated holograms by assuming a p-n junction in a semiconductor sample. The peak signal-to-noise ratios of the holograms and the reconstructed phase maps have been improved significantly using tensor decomposition. Moreover, the proposed method was applied to a more practical situation of time-resolved in situ electron holography by considering a nonuniform fringe contrast and fringe drift relative to the sample. The accuracy and precision of the reconstructed phase maps were quantitatively evaluated to demonstrate its effectiveness for in situ experiments and low-dose experiments on beam-sensitive materials. [ABSTRACT FROM AUTHOR]

A phase imaging method that measures the phase shift existing at a dislocation's core is described. The method uses the interference of two symmetrically diffracted beams on the optic axis by means of an electron biprism. Each diffracted beam carries half the phase of the dislocation core. When combined, the entire phase shift of the dislocation core is obtained. [ABSTRACT FROM AUTHOR]

In this paper, we review the current state of phase plate imaging in a transmission electron microscope. We focus especially on the hole-free phase plate design, also referred to as the Volta phase plate. We discuss the implementation, operating principles and applications of phase plate imaging. We provide an imaging theory that accounts for inelastic scattering in both the sample and in the hole-free phase plate. [ABSTRACT FROM AUTHOR]

Ptychography is a coherent diffractive imaging technique that can determine how an electron wave is transmitted through an object by probing it in many small overlapping regions and processing the diffraction data obtained at each point. The resulting electron transmission model describes both phase and amplitude changes to the electron wave. Ptychography has been adopted in transmission electron microscopy in recent years following advances in high-speed direct electron detectors and computer algorithms which now make the technique suitable for practical applications. Its ability to retrieve quantitative phase information at high spatial resolution makes it a plausible alternative or complement to electron holography. Furthermore, unlike off-axis electron holography, it can provide phase information without an electron bi-prism assembly or the requirement of a minimally structured region adjacent to the region of interest in the object. However, it does require a well-calibrated scanning transmission electron microscope and a well-managed workflow to manage the calibration, data acquisition and reconstruction process to yield a practical technique. Here we detail this workflow and highlight how this is greatly assisted by acquisition management software. Through experimental data and modelling we also explore the similarities and differences between high-resolution ptychography and electron holography. Both techniques show a dependence of the recovered phase on the crystalline orientation of the material which is attributable to dynamical scattering. However, the exact nature of the variation differs reflecting fundamental expectations, but nonetheless equally useful information is obtained from electron holography and the ptychographically determined object transmission function. [ABSTRACT FROM AUTHOR]

A phase retrieval technique based on a transport of intensity equation (TIE) is one of the defocus series reconstruction techniques in microscopy. Since it does not require any dedicated devices like a biprism, and only three defocus images are enough to retrieve phase information, it has been applied to observe magnetic fields, magnetic domains, electrostatic potentials and strains. It is also used to improve image resolution by correcting spherical aberration. This technique is simple and easy to use, but some artifacts often appear in the retrieved phase map. One should pay careful attention to the experimental conditions and the algorithms and boundary conditions used to solve the TIE. This paper reviews the principle of the TIE method, the algorithms used to solve it and application results in materials science. [ABSTRACT FROM AUTHOR]

We describe small-angle electron diffraction (SmAED) and Lorentz microscopy using a conventional transmission electron microscope. In SmAED, electron diffraction patterns with a wide-angular range on the order of 1 × 10−2 rad to 1 × 10−7 rad can be obtained. It is demonstrated that magnetic information of nanoscale magnetic microstructures can be obtained by Fresnel imaging, Foucault imaging and SmAED. In particular, we report magnetic microstructures associated with magnetic stripes and magnetic skyrmions revealed by Lorentz microscopy with SmAED. SmAED can be applied to the analysis of microstructures in functional materials such as dielectric, ferromagnetic and multiferroic materials. [ABSTRACT FROM AUTHOR]

We investigate the effect that recording off-axis electron holograms on pixelated detectors, such as charge-coupled devices (CCD) and direct-detection devices (DDD), can have on measured amplitudes and phases. Theory will be developed for the case of perfectly uniform interference fringes illuminating an imperfect detector with gain variations and pixel displacements. We will show that both these types of defect produce a systematic noise in the phase images that depends on the position of the holographic fringes with respect to the detector. Subtracting a reference hologram from the object hologram will therefore not remove the phase noise if the initial phases of the two holograms do not coincide exactly. Another finding is that pi-shifted holograms are much less affected by gain variations but show no improvement concerning geometric distortions. The resulting phase errors will be estimated and simulations presented that confirm the theoretical developments. [ABSTRACT FROM AUTHOR]

This review examines methods of magnetic flux density measurements from the narrow grain boundary (GB) regions, the thickness of which is of the order of nanometers, produced in Nd–Fe–B-based sintered magnets. Despite of the complex crystallographic microstructure and the significant stray magnetic field of the sintered magnet, recent progress in electron holography allowed for the determination of the intrinsic magnetic flux density due to the GB which is embedded in the polycrystalline thin-foil. The methods appear to be useful as well for intensive studies about interface magnetism in a variety of systems. [ABSTRACT FROM AUTHOR]

Lensless Fourier transform holography has been developed. By treating Bragg diffraction waves as object waves and a transmitted spherical wave as a reference wave, these two waves are interfered and recorded as holograms away from the reciprocal plane. In this method, reconstruction of holograms requires only one Fourier transform. Application of this method to analyze vortex beams worked well and their amplitude and phase distributions were obtained on the reciprocal plane. By combining the conventional holography with the developed lensless Fourier transform holography, we can reconstruct and analyze electron waves from the real to reciprocal space continuously. [ABSTRACT FROM AUTHOR]

Transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) enable the visualization of three-dimensional (3D) microstructures ranging from atomic to micrometer scales using 3D reconstruction techniques based on computed tomography algorithms. This 3D microscopy method is called electron tomography (ET) and has been utilized in the fields of materials science and engineering for more than two decades. Although atomic resolution is one of the current topics in ET research, the development and deployment of intermediate-resolution (non-atomic-resolution) ET imaging methods have garnered considerable attention from researchers. This research trend is probably not irrelevant due to the fact that the spatial resolution and functionality of 3D imaging methods of scanning electron microscopy (SEM) and X-ray microscopy have come to overlap with those of ET. In other words, there may be multiple ways to carry out 3D visualization using different microscopy methods for nanometer-scale objects in materials. From the above standpoint, this review paper aims to (i) describe the current status and issues of intermediate-resolution ET with regard to enhancing the effectiveness of TEM/STEM imaging and (ii) discuss promising applications of state-of-the-art intermediate-resolution ET for materials research with a particular focus on diffraction contrast ET for crystalline microstructures (superlattice domains and dislocations) including a demonstration of in situ dislocation tomography. [ABSTRACT FROM AUTHOR]

We try to improve the limit of the phase estimation of the interference fringe at low electron dose levels in electron holography by a noise reduction method. In this paper, we focus on unsupervised approaches to apply it to electron beam-sensitive and unknown samples and describe an overview of denoising methods used widely in image processing, such as wiener filter, total variation denoising, nonlocal mean filters and wavelet thresholding. We compare the wavelet hidden Markov model (WHMM) denoising that we have studied so far with the other conventional noise reduction methods. We evaluate the denoise performance of each method using the peak signal-to-noise ratio between noise-free and the target holograms (noisy or denoised holograms) and the root mean-square error (RMSE) between the true phase of the fringe and the measured phase by the discrete Fourier transform phase estimator. We show the denoised holograms for simulation and experimental data by using each noise reduction method and then discuss evaluation indexes obtained from these denoised holograms. From experimental results, it can be seen that the WHMM denoising can reduce the RMSE of fringe phase to about 1/4.5 for noisy simulation holograms and it has stable and good performance for noise reduction of observed holograms with various image qualities. [ABSTRACT FROM AUTHOR]

An automated acquisition system for collecting a large number of electron holograms, to improve the statistical precision of phase analysis, was developed. A technique for shifting the electron beam in combination with stage movement allows data to be acquired over a wide area of a TEM-specimen grid. Undesired drift in the hologram position, which may occur during the hologram acquisition, can be corrected in real time by automated detection of the interference-fringe region in an image. To demonstrate the usefulness of the developed automated hologram acquisition system, gold nanoparticles dispersed on a carbon foil were observed with a 1.2-MV atomic resolution holography electron microscope. The system could obtain 1024 holograms, which provided phase maps for more than 500 nanoparticles with a lateral resolution of 0.14 nm, in just 1 h. The observation results revealed an anomalous increase in mean inner potential for a particle size smaller than 4 nm. The developed automated hologram acquisition system can be applied to improve the precision of phase measurement by averaging many phase images, as demonstrated by single particle analysis for biological entities. Moreover, the system makes it possible to study electrostatic potential of catalysts and other functional nanoparticles at atomic resolution. [ABSTRACT FROM AUTHOR]

The correlation of electron counts from two detectors illuminated by a coherent electron beam is analyzed by associating the path of the electron beam through the lenses with the direct Coulomb interaction between two individual electrons. This is shown to lead to a full statistical description of the electron counts. The dominant contribution to the correlation is found to be due to the trajectory displacement caused by the repulsive Coulomb interaction between the first anode and the cathode tip, and the correlation of electron counts is found to depend on the amount of defocusing on the shift of the virtual source for two electrons within the correlation time. The Coulomb scatterings, which altered the direction of two neighbor electrons, occur during the acceleration, leading to a significant decrease in the electron density. The Coulomb potential with no screening will then cause large-angle scattering of nearest-neighbor electrons within the correlation time. These results are consistent with those obtained by a previous experiment. [ABSTRACT FROM AUTHOR]

The innate electric potentials in biased p- and n-type GaAs compound semiconductors and the built-in potential were successfully measured with high accuracy and precision by applying in situ phase-shifting electron holography to a wedge-shaped GaAs specimen. A cryo-focused-ion-beam system was used to prepare the 35°-wedge-shaped specimen with smooth surfaces for a precise measurement. The specimen was biased in a transmission electron microscope, and holograms with high-contrast interference fringes were recorded for the phase-shifting method. A clear phase image around the p–n junction was reconstructed even in a thick region (thickness of ~700 nm) at a spatial resolution of 1 nm and precision of 0.01 rad. The innate electric potentials of the unbiased p- and n-type layers were measured to be 12.96 ± 0.17 V and 14.43 ± 0.19 V, respectively. The built-in potential was determined to be 1.48 ± 0.02 V. In addition, the in situ biasing measurement revealed that the measured electric-potential difference between the p and n regions changed by an amount equal to the voltage applied to the specimen, which indicates that all of the external voltage was applied to the p–n junction and that no voltage loss occurred at the other regions. [ABSTRACT FROM AUTHOR]

We developed a novel sample preparation method for transmission electron microscopy (TEM) to suppress superfluous electric fields leaked from biased TEM samples. In this method, a thin TEM sample is first coated with an insulating amorphous aluminum oxide (AlOx) film with a thickness of about 20 nm. Then, the sample is coated with a conductive amorphous carbon film with a thickness of about 10 nm, and the film is grounded. This technique was applied to a model sample of a metal electrode/Li-ion-conductive-solidelectrolyte/ metal electrode for biasing electron holography. We found that AlOx film with a thickness of 10 nm has a large withstand voltage of about 8 V and that double layers of AlOx and carbon act as a 'nano-shield' to suppress 99% of the electric fields outside of the sample. We also found an asymmetry potential distribution between high and low potential electrodes in biased solid-electrolyte, indicating different accumulation behaviors of lithium-ions (Li+) and lithium-ion vacancies (VLi-) in the biased solid-electrolyte. [ABSTRACT FROM AUTHOR]

In this study, we report on phase retrieval by the maximum likelihood method with conjugate gradient method (CG-MAL) using through-focus images in Lorentz transmission electron microscopy (LTEM). The method was evaluated using 32 simulated and experimentally obtained through-focus images of magnetic bubbles; these images were collected under a defocus range from approximately -3mm to 3 mm. Consequently, we obtained the magnetic domain structures of the magnetic bubbles in both the simulation and the LTEM experiment. Furthermore, the CG-MAL method showed better convergence behavior than other iterative phase retrieval methods. Therefore, the method can also be widely and effectively applied to the observation of magnetic domain structures other than magnetic bubbles when highly defocused through-focus images are used. [ABSTRACT FROM AUTHOR]

Higher order geometrical aberration correctors for transmission electron microscopes are essential for atomic-resolution imaging, especially at low-accelerating voltages. We quantitatively calculated the residual aberrations of fifth-order aberration correctors to determine the dominant aberrations. The calculations showed that the sixth-order threelobe aberration was dominant when fifth-order aberrations were corrected by using the double-hexapole or delta types of aberration correctors. It was also deduced that the sixth-order three-lobe aberration was generally smaller in the delta corrector than in the double-hexapole corrector. The sixth-order three-lobe aberration was counterbalanced with a finite amount of the fourth-order three-lobe aberration and 3-fold astigmatism. In the experiments, we used a low-voltage microscope equipped with delta correctors for probe- and image-forming systems. Residual aberrations in each system were evaluated using Ronchigrams and diffractogram tableaux, respectively. The counterbalanced aberration correction was applied to obtain high-resolution transmission electron microscopy images of graphene and WS2 samples at 60 and 15 kV, respectively. [ABSTRACT FROM AUTHOR]

In this study, a function for the correction of coma aberration, 3-fold astigmatism and real-time correction of 2-fold astigmatism was newly incorporated into a recently developed real-time wave field reconstruction TEM system. The aberration correction function was developed by modifying the image-processing software previously designed for auto focus tracking, as described in the first article of this series. Using the newly developed system, the coma aberration and 3-fold astigmatism were corrected using the aberration coefficients obtained experimentally before the processing was carried out. In this study, these aberration coefficients were estimated from an apparent 2-fold astigmatism induced under tilted-illumination conditions. In contrast, 2-fold astigmatism could be measured and corrected in real time from the reconstructed wave field. Here, the measurement precision for 2-fold astigmatism was found to be ±0.4 nm and ±2°. All of these aberration corrections, as well as auto focus tracking, were performed at a video frame rate of 1/30 s. Thus, the proposed novel system is promising for quantitative and reliable in situ observations, particularly in environmental TEM applications. [ABSTRACT FROM AUTHOR]

The achievement of a fine electron probe for high-resolution imaging in scanning transmission electron microscopy requires technological developments, especially in electron optics. For this purpose, we developed a microscope with a fifth-order aberration corrector that operates at 300 kV. The contrast flat region in an experimental Ronchigram, which indicates the aberration-free angle, was expanded to 70 mrad. By using a probe with convergence angle of 40 mrad in the scanning transmission electron microscope at 300 kV, we attained the spatial resolution of 40.5 pm, which is the projected interatomic distance between Ga-Ga atomic columns of GaN observed along [212] direction. [ABSTRACT FROM AUTHOR]

To improve the reliability of silicon carbide (SiC) electronic power devices, the characteristics of various kinds of crystal defects should be precisely understood. Of particular importance is understanding the correlation between the surface morphology and the near surface dislocations. In order to analyze the dislocations near the surface of 4H-SiC wafers, a dislocation analysis protocol has been developed. This protocol consists of the following process: (1) inspection of surface defects using low energy scanning electron microscopy (LESEM), (2) identification of small and shallow etch pits using KOH low temperature etching, (3) classification of etch pits using LESEM, (4) specimen preparation of several hundred nanometer thick sample using the in-situ focused ion beam micro-sampling® technique, (5) crystallographic analysis using the selected diffraction mode of the scanning transmission electron microscope (STEM), and (6) determination of the Burgers vector using multi-directional STEM (MD-STEM). The results show a correlation between the triangular terrace shaped surface defects and an hexagonal etch pit arising from threading dislocations, linear shaped surface defects and elliptical shaped etch pits arising from basal plane dislocations. Through the observation of the sample from two orthogonal directions via the MD-STEM technique, a basal plane dislocation is found to dissociate into an extended dislocation bound by two partial dislocations. A protocol developed and presented in this paper enables one to correlate near surface defects of a 4H-SiC wafer with the root cause dislocations giving rise to those surface defects. [ABSTRACT FROM AUTHOR]

A method for generating electron lattice beams carrying vortices using nanofabricated polygonal slits in a transmission electron microscope is proposed. Experimental and simulation study of the intensity of the beams verified their Bessel beam-like nearly nondiffracting behavior. Phase analysis using a diffractive imaging method found arrays of quantized vortices, forming an electron beam lattice with cylindrical intensity distribution in the propagation direction. Such vortex lattice beams may be used in a variety of applications including nanofabrication, particle manipulation or a new electron imaging method. [ABSTRACT FROM AUTHOR]

All-solid-state Li-ion batteries having incombustible solid electrolytes are promising energy storage devices because they have significant advantages in terms of safety, lifetime and energy density. Electrochemical reactions, namely, Li-ion insertion/extraction reactions, commonly occur around the nanometer-scale interfaces between the electrodes and solid electrolytes. Thus, transmission electron microscopy (TEM) is an appropriate technique to directly observe such reactions, providing important information for understanding the fundamental solid-state electrochemistry and improving battery performance. In this review, we introduce two types of TEM techniques for operando observations of battery reactions, spatially resolved electron energy-loss spectroscopy in a TEM mode for direct detection of the Li concentration profiles and electron holography for observing the electric potential changes due to Li-ion insertion/ extraction reactions. We visually show how Li-ion insertion/extractions affect the crystal structures, electronic structures, and local electric potential during the charge- discharge processes in these batteries. [ABSTRACT FROM AUTHOR]

We report a method for acquiring Foucault images and small-angle electron diffraction patterns in external magnetic fields using a conventional transmission electron microscope without any modification. In the electron optical system that we have constructed, external magnetic fields parallel to the optical axis can be controlled using the objective lens pole piece under weak excitation conditions in the Foucault mode and the diffraction mode. We observe two ferromagnetic perovskite-type manganese oxides, La0.7Sr0.3MnO3 (LSMO) and Nd0.5Sr0.5MnO3, in order to visualize magnetic domains and their magnetic responses to external magnetic fields. In rhombohedral-structured LSMO, pinning of magnetic domain walls at crystallographic twin boundaries was found to have a strong influence on the generation of new magnetic domains in external applied magnetic fields. [ABSTRACT FROM AUTHOR]

An atomic resolution phase map, which enables us to observe charge distribution or magnetic properties at an atomic scale, has been pointed out to be retrieved by transport of intensity equation (TIE) when taking two atomic-resolved transmission electron microscope (TEM) images of small defocus difference. In this work, we firstly obtained the atomic-resolved phase maps of an exfoliated molybdenum disulfide sheet using spherical aberration-corrected transmission electron microscope. We successfully observed 60° grain boundary of mechanically exfoliated monolayer molybdenum disulfide sheet. The relative phase shift of a single molybdenum atomic column to the column consisting of two sulfur atoms was obtained to be about 0.01 rad on average, which was about half lower than the simulated TIE phase map, indicating that the individual atomic sites can be distinguished qualitatively. The appropriate condition for retrieving atomic-resolved TIE phase maps was briefly discussed. [ABSTRACT FROM AUTHOR]