Hisamitsu Endoh

Direct Observation of Fine Structure within Images of Atoms in Crystals by Transmission Electron Microscopy

Fine structure of the electron microscopic images of the atoms in crystals formed by the zero-aberration lens and a real lens is discussed by the theories of electron diffraction and image formation. The observed image of rows of gold atoms having such fine inner structure is shown,

Direct Observations of the Arrangement of Atoms around Stacking Faults and Twins in Gold Crystals and the Movement of Atoms Accompanying Their Formation and Disappearance

Two types of imaging methods in high resolution transmission electron microscopy, which give the images of atoms at the atomic positions in crystals containing defects, are presented. Using one of the methods, atomic arrangements of partial dislocations, intrinsic and extrinsic stacking faults, sessile dislocations formed by the interaction of two partial dislocations, and coherent and incoherent twin boundaries in gold thin crystals have been observed. Dynamic observations using TV systems have been carried out on the movement of atoms accompanying the formation, the movement and disappearance of stacking faults and twins, and their interaction.

A metastable phase in thermal decomposition of Ca-deficient hydroxyapatite.

We investigated the microstructural changes on an atomic length scale during thermal decomposition process of Ca-deficient hydroxyapatite (Ca-def HAp) by high-resolution transmission electron microscopy (HRTEM). Ca-def HAp was prepared by hydrolysis of α-tricalcium phosphate. The Ca-def HAp had a whisker-like morphology 2–5 μm in length and 0.1 μm in diameter that was elongated along c-axis. Thicker planer defects parallel to the (100) plane of the HAp matrix were observed as precipitation in the sample annealed at 700 and 800 °C by HRTEM observation. Thickness of the precipitation was about 10 nm and the boundaries between the precipitation and HAp matrix was coincident. The periodicity in the precipitation was parallel to the (100) plane of the HAp matrix and measured to be 1.42 nm. Since the precipitation was observed only in the sample annealed at a narrow temperature range of 700–800 °C, it was regarded as a metastable phase formed on the thermal decomposition process. Absorption peaks in IR spectra of annealed Ca-def HAp containing the metastable phase appeared at 744 and 3538 cm−1 due to non-stoichiometric HAp with high Ca/P molar ratio. Furthermore, the results of energy dispersive X-ray spectroscopy showed that the metastable phase had higher Ca/P molar ratio than that of the matrix and stoichiometric HAp. Therefore, the metastable phase could be identified as Ca-rich metastable phase. The presence of Ca-rich metastable phase was confirmed to be associated with the thermal decomposition process.

Atomic Structure Images Formed by Plasma-Loss Electrons

Two kinds of energy filtered atomic structure images of Si crystal in (011) orientation formed by no-loss and plasma-loss electrons were photographed using the energy analyzer of a sector type magnet which was attached to the bottom of a high resolution electron microscope. The behavior of plasma-loss electrons in the crystal was discussed on the basis of the dynamical theory of electron diffraction. The contrast of the crystal lattice image formed by the plasma-loss electrons was calculated and compared with the observed image.

Transmission electron microscopic studies on an initial stage in the conversion process from α-tricalcium phosphate to hydroxyapatite

The microstructural changes in the initial stage of a conversion process of α-tricalcium phosphate [α-Ca 3 (PO 4 ) 2 ] (a-TCP) to hydroxyapatite [Ca 1 0 (PO 4 ) 6 (OH) 2 ] (HAp) by the hydrolysis method were investigated by transmission electron microscopy (TEM). To investigate the microstructural changes that take place during the conversion process, we prepared two types of α-TCP specimens for TEM: α-TCP powder and sintered α-TCP thin film. According to our results, the microstructural changes can be summarized as follows. At first, the surface of the α-TCP was covered with an amorphous calcium phosphate layer, resulting from hydration or the dissolution of α-TCP. Subsequently, the nucleation of HAp occurred on the amorphous layer, and then dendritic structures appeared on the layer. Thereafter, the dendritic structures would grow into needlelike fine HAp crystals.

Theoretical and observed electron microscope images of impurity atoms in thin crystals formed by L-shell ionization electrons

Abstract Theoretical electron microscope images and electron diffraction patterns of aluminum and silicon crystals formed by electrons that have undergone losses at the inner shells of an aluminum or a silicon atom are discussed. The inelastic scattering factors for AlL 1 and SiL 3 ionizations are derived by the program of modified hydrogenic L-shell cross section. By embedding the inelastic event in a multi-slice computation for elastic scattering the intensity distribution of electron waves at the bottom surfaces of the crystals are derived. Then the contrast of the electron microscope images and intensity distribution of electron diffraction patterns are obtained by taking into account the spherical aberration of the lens and the coherence of the electron waves. It is concluded that bright spots appear at individual atomic columns containing atoms that have undergone inner-shell ionizations. 200 kV electron microscope images of Al-1.2wt%Si crystals containing precipitated Si crystals are recorded by using 119 ± 2.5 eV loss electrons, corresponding to the losses at inner shells of AlL i and SiL 2,3 . From these images have been subtracted the images of the same area formed by using 88 ± 2.5 eV electrons (background of EELS). The obtained image contrast is discussed in the light of calculated results. We conclude that bright spots appearing in the images of Si single crystals and in Al matrices thinner than 15 nm are the images of individual atomic columns containing Si atoms.

Atomic resolution electron microscope images formed by SiL3-ionization electrons

Abstract Contrast of energy-filtered electron microscope images with atomic resolution of Si atoms producing SiL 3 -ionization electrons in a Si crystal is discussed. The localization width of the inelastic scattering potential is deduced from the inelastic scattering factor for SiL 3 -ionization, which is based on a program for a modified hydrogenic L-shell cross section. The image contrast at the bottom surfaces of the Si crystals containing a single inelastic scattering layer at the top, middle and bottom layers showed diffuse, sharp and very sharp image contrast, i.e. top-bottom effect is predominant. Similar images of an atom which scattered electrons inelastically with a very small energy loss in an aluminum crystal were calculated and it is noted that the atomic structure of aluminum is observed.

Characterization of thin film materials by 400 kV electron microscope images and with an energy filter

Abstract Characterization of thin film materials by the contrast of high resolution electron microscope images and by the images of electrons that excite the core electrons of the specimen is discussed. Using current high resolution electron micrographs, which are produced by partially coherent waves, the best focus for obtaining the atomic structure images of three crystals, MgO/MgAl 2 O 4 /Al 2 O 3 , has been found using pseudo AFF conditions. Three kinds of electron microscope images of ThO 2 crystal, formed by the zero-loss, plasma-loss and O 4,5 core-loss electrons, are shown. Three similar images of a Si crystal, which precipitated in an Al crystal, are also shown, and the contrast mechanism of core-loss electron images is discussed by deriving the inelastic scattering factors of Si and Al crystals and using multi-slice elastic image contrast calculations. It is noted that the individual spot contrast in Si core-loss images of a small crystal is due to the images of Si atoms in a single atomic column when the thickness is less than 10 nm.

Growth of dendritic and needle tungsten oxide crystals studied by high-resolution electron microscopy

Abstract Needle crystals of β-WO 2.90 and λ-WO 2.72 are produced by heating α-WO 3 powder in a vacuum apparatus under various air pressures. Whether β-or λ-tungsten oxide is produced depends on the specimen temperature rather than on the air pressure. The initial stages of the growing process of dendritic or needle crystals have been observed using a high-resolution electron microscope. It is found that bumps which are formed on the surface of a mother needle crystal are necessary for the growth of dendrite crystals. When no bumps are formed on the surface, single needle crystals grow. The needle axis is the b -axis on both β- and ω-tungsten oxides which belong to the same monoclinic system. In this study no amorphous drops have been observed on top of any needle crystal.

Study of the Commensurate Superstructure in 4Hb–TaS2 by High Resolution Electron Microscopy

The commensurate superstructures caused by CDW in 4Hb–TaS2 have been investigated by a high resolution electron microscope at room temperature. It was found that the two types of √13a × √13a superstructures, which rotated ±13.9° from a-axis in 00.1 plane, coexist in the same region, not in same layers but in different layers which have octahedral coordination. The two types of superstructure occur with different probabilities whose ratio depends on the samples. It was also observed that these superstructures were not greatly affected by dislocations in the crystal.