Several contributions of TEM on the interface science are reviewed in chronographic order. The first contribution of TEM is the observation of grain boundary dislocation. The observation of gold (113) Σ11 boundary followed, giving experimental proof of the CSL model. In silicon boundary the least dangling bond rule govern the atomic structure. In the diamond grain boundary a dangling bond may not elevate the boundary contradictory to the least dangling bond rule. Super high-resolution of the HVHRTEM enable us to determine atomic species in the grain boundary; three-fold coordinated atomic site in SiC boundary was occupied by carbon and an alike pair in the SiC boundary was shown to be a Si-Si pair. Combined use of atomic resolution HRTEM and EELSE allows us to discuss even the correlation between atomic structure and nature of the corresponding interface.
Characteristic features of the high-angle annular dark-field scanning transmission electron microscope method are described from an experimental viewpoint. Examples of experimental HAADF-STEM images are shown.
By improving coherence and brightness, HAADF-STEM enables us to obtain incoherent images with comparable resolution to HRTEM. This paper reviews imaging in the high resolution HAADF-STEM and the dynamical simulations on the basis of Bloch theory. Its capability for performing quantitative structural and compositional analysis is discussed as well. Finally the advantages and disadvantages of HAADF-STEM are presented.
Recent development of spherical aberration correction in high-resolution electron microscopy (Cs-corrected HREM) is reviewed by focusing on TEM instruments. Basis of the the previous HRTEM and new scientific elements for Cs-corrected one are summarized, and recent applications of the method to nano materials and interfaces are described through explaining its characteristic and the future prospects.
The scanning transmission electron microscope (STEM) with an annular dark-field (ADF) detector provides atomic-resolution incoherent images, whose resolution is dominated, to a good approximation, by the size of convergent electron beams. Improving a spherical aberration of microscope objective lenses has been successful in converging the beam into sub-A scale, promising a remarkably higher resolution for STEM. Here we describe the performance of aberration-corrected 300kV-STEM - the world-best STEM available today. The results clearly demonstrate that a sub-Ångstrom resolution has been indeed achieved for not only simple structures but also structurally complex systems (quasicrystals) .
A real-time defocus-image modulation processing electron microscope, which utilizes a custom designed, floating type, accelerating voltage generation system to modulate focus quickly and precisely, produced spherical aberration-free phase images with a time resolution of 1/30th second by the combination with a novel real-time image processing CCD video camera. As a result of the real-time phase reconstruction, dynamic behavior of individual atoms was successfully observed with the resolution improvement from the Scherzer limit to the information limit. It was confirmed by theoretical calculations that the spherical aberration-free phase imaging has a high potential for providing direct determination of localized atomic structures.
Two kinds of phase contrast electron microscopy, Zernike phase contrast and Hilbert differential contrast, both using phase plates, are described together with the theory of the contrast generation. Micrographs obtained by the two schemes are compared with those obtained with the scheme of defocus phase contrast most prevalent in conventional TEM. Higher contrast of unstained biological samples, without image deterioration, has been clearly demonstrated for the two phase contrast methods. As a variation of the Zernike phase contrast, complex observation is also introduced, which combines the two schemes, the conventional and the Zernike, to recover complex waves as exited from objects. It is shown that images in the complex form is the most appropriate to be corrected in image flaws arising from the spherical aberration and the defocus.
Here applications of electron crystallography to the structural analysis of membrane proteins at high resolution are described. Methods to grow two-dimensional crystals of membrane proteins for the structural analysis and the sample preparation methods for cryo-electron microscopy are discussed. About the sample preparation, we developed a new technique, in which the crystals are put between two sheets of carbon film, to reduce the beam-induced image movement by electron microscopy from tilted specimens. Two structures of the membrane proteins, a proton pump and a water channel, were shown as two examples of electron crystallographic structural analysis of membrane proteins.
A method to refine crystal structural parameters and charge density distribution using convergent-beam electron diffraction is described, which is based on the least-squares fitting between full dynamical calculations and energy-filtered intensities of two-dimensional CBED patterns. A function of parallel computation using a computer cluster was implemented to extend the applications of the method. Crystal structural parameters of the intermediate phase of hexagonal barium titanate (h-BaTiO3) was refined by the method.
This paper first summarizes principles of electron channeling X-ray microanalysis (ALCHEMI) and then describes a recent achievement in quantitative structure analysis of MgO⋅nA12O3 spinel compounds. The orientation dependent intensity variation of emitted X-rays under dynamical electron diffraction conditions is so sensitive to lattice-ion configuration in the illuminated areas that the occupation probabilities on specific positions in the crystal lattice can be determined accurately through comparison with the theoretical rocking curves. The measurements have characterized partially disordered cation configuration in MgO⋅nA12O3 crystals as a function of composition as well as irradiation-induced disordering.
In this short article the features of extended energy-loss fine structure (EXELFS) in electron energy-loss spectroscopy (EELS) associated with transmission electron microscopy (TEM) are introduced as one of the useful methods for structural analysis in a localized area. After briefly describing the principle and analysis method of EXELFS, several interesting application examples of EXELFS in materials science are presented. Finally the standing problems in EXELFS analysis and future prospects are addressed.
Electron energy-loss spectroscopy (EELS) in transmission electron microscopy (TEM) is briefly reviewed. The outline and a few experimental results of elemental and chemical analysis are shown. Recent progress in TEM-EELS, such as monochromator for high energy resolution and spectrum imaging, are also presented.
This paper reviews theoretical calculation of ELNES using first principles band structure methods. A core-hole is included in the calculation, and the matrix elements of the electric dipole transition between the ground state and the final state are computed. The satisfactory reproductions of the experimental spectra are commonly brought about by employing the sufficient large supercells. The orientation dependence of ELVES for wurtzite-A1N is discussed. The dependence was found to be much larger in K edges as compared to the L2.3 edge. The large projection dependence is predicted in O-K ELNES of SrTiO3. It was found that those spectral changes according to the position of the projection are caused by the unidirectional Ti-O-Ti bond in SrTiO3. Theoretical calculation of the low loss spectrum from SrTiO3 is also discussed.
A development of an X-ray emission spectroscopy instrument for a transmission electron microscopy to obtain a density of states of valence bands is briefly described. An example of TEM-EELS/XES analysis presented that high energy-resolution spectroscopy methods combined with transmission electron microscopy is a promising method to analyze whole electronic structures of manometer scale materials.
Dynamic behavior of magnetic domain structures and relationship between crystal structures and the magnetic domain structures in strongly correlated transition metal oxides were investigated by Lorentz electron microscopy. We found that there are interactions between magnetic domain structures and crystallographic defect structures, such as twin boundaries and antiphase boundaries. We review the characteristic magnetic domain structures in distorted perovskite-type Nd1/2Sr1/2MnO3 and double perovskite Ba2FeMoO6.
Electron holography, which visualizes a local magnetic and/or electric field, is a hopeful experimental tool in explorations of complex magnetic microstructures in advanced materials. The aim of this review article is to present the essence of electron holography and its applications to current issues about the magnetic microstructure in a perovskite-type manganite La1-xSrxMnO3, which has captured attentions of many researchers because of the peculiar magnetoresistive properties.
We describe electron holographic measurement of inner potential in crystals. When an electron wave passes through a thin crystal, the phase of the electron wave is shifted by the potential. Using electron holography, the potential can be measured from the phase shift of the electron wave. We also describe an application of this technique to dopant-profiling in semiconductor devices.