H. Hashimoto

Interpretation of atomic-resolution electron microscope images of Guiner-Preston zones in aluminium-copper alloys

Abstract Contrast calculations by the dynamical theory of electron diffraction have been performed using two kinds of models of Guiner-Preston (G.P.) (I) and (II) zones in aluminium-copper alloys, and results have been compared with high-resolution electron microscope images in the zones. Image contrast changes of the calculated images are demonstrated. The contrast is dependent both on crystal thickness and objective lens defocus, and the dependence on the latter is in good agreement with observations. The observed images of G.P. (I) zones are well understood by the copper atom monolayer model of Yoshida et al. (1976). A contrast anomaly in the observed images of G.P. (II) zones is attributed to the effect of defocus for a modified model containing shear displacements. It is proposed that the optimum imaging condition for a crystal containing lattice distortion due to G.P. zones is the tilted beam aberration free focus condition.

Effect of substitution of La by alkaline earth metal on the thermoelectric properties and the phase stability of γ-La3S4

The Seebeck coefficient, electrical resistivity, and thermal conductivity of La3−xAxS4 with the Th3P4-type structure (the γ-phase) for A=Ca, Ba, and x=0–0.8 have been measured as a function of alkaline earth metal content and temperature to determine the optimum dopant concentration and doping agent by calculating the corresponding figure of merit (Z). With an increase of x, the Seebeck coefficient and electrical resistivity increase, while the thermal conductivity decreases. The decrease of thermal conductivity is ascribed to the decrease of the electron concentration and the increase of the phonon scattering accompanying the substitution for La by an alkaline earth metal. As a result, La2.2Ca0.8S4 has a maximum value of Z of 2.3×10−4u2009°C−1 at 700u2009°C. We also have examined the long term stability of γ-La3−xAxS4. The substitution for La by alkaline earth metal of La3S4 stabilized the Th3P4-type structure at high temperature.

Improvement and application of the Fourier-transformed pattern from a small area of high resolution electron microscope images

The relation between the electron diffraction pattern and the Fourier transform pattern of the image of a crystal of varying thickness is discussed, in which weak phase object approximation and dynamic scattering object are considered. The artefacts due to the aperture used for selection of the specimen area can be eliminated by superposition of a circular aperture separated from the object plane, or by a rectangular aperture which gives the damping intensity of the image at the edge. Some examples of diffraction spots obtained by fast Fourier transform are shown.

Achievement of ultra-high resolution by 400 kV analytical atomic-resolution electron microscopy

Abstract The factors for improving the resolution of conventional electron microscopes are discussed together with the physics of the formation of electron diffraction patterns and electron microscope images, and a method for obtaining images of atoms at their correct positions. The optical features of the 400 kV Analytical Atomic-Resolution Electron Microscope (AARM) installed in Osaka University are described. Some details of the energy-selecting atom resolution microscope and an on-line image processing system attached to the AARM are also discussed.

Construction of an on-line system for FFT processing and analysis of atomic resolution microscopic images and its applications

The construction of an on-line image processing and analysis system and its applications to high resolution electron microscopy are described. The system is composed of a TV system, frame memory and microprocessor. Fast Fourier transform of atomic resolution electron microscopic images are demonstrated. Averaging the images obtained by superposing some numbers of the frames of TV pictures gives an image without random noise. After masking the area corresponding to the random noise in Fourier space, inverse Fourier transforms are carried out to get processed images without random noise. Fast Fourier transforms of the images of amorphous carbon films are analyzed to obtain the defocus values of the objective lens. It is demonstrated that the small selected area diffraction patterns can be obtained from the images of thin gold crystal containing an incoherent twin boundary and that Fourier transforms of the image of carbon film can be used for correcting the astigmatism of the objective lens.

USE OF DYNAMIC ELECTRON-SCATTERING FOR STUDYING THE POSITION OF OXYGEN-ATOMS IN SIMPLE METAL-OXIDE

Abstract A method for imaging oxygen atoms in cuprous oxide by high resolution electron microscopy (HREM) is presented. Using the dynamical theory of electron diffraction, the influence of the specimen thickness upon the imaging of oxygen atoms has been systematically investigated. The thickness dependence of the extinction of the Bragg waves reflected by planes containing cheifly light (e.g. oxygen) atoms and heavy (e.g. copper) ones has been used to obtain the optimum specimen thickness that reveals the oxygen atoms only. Using this method new suboxides of copper, including a series of hitherto unknown ones, have been analyzed and their crystal structures determined. The derived rules presented here could be also applied to the analyses of the HREM images of other oxides, carbides and nitrides of metals.

Selected‐Area Diffraction Patterns and Magnified Laue‐Diffraction Images by X‐Ray Microscopy

An ``x‐ray microscope which can take both x‐ray diffraction patterns and magnified Laue‐diffraction images of selected areas of the specimen under microscopic observation has been constructed. Resolving power of the microscope is 0.3 μ and the minimum diameter of the selected area of the specimen is about 10 μ. A decontamination device for the target is incorporated into the instrument. Some applications of the methods of x‐ray microscopy, selected‐area diffraction, and magnified Laue diffraction are described. It is shown that the selected‐area diffraction patterns are useful for the identification of the components of the specimen with complicated structure. It is also shown that the magnified Laue‐diffraction images are useful for the study of imperfections and local distortions in crystals.

Oxygen‐enhanced thermionic emission pattern of hemispherical single‐crystal LaB6

With the application of Martin’s experimental arrangement for direct observation of thermionic emission patterns from a hemispherical single‐crystal LaB6 cathode, it has been determined that oxygen‐enhanced thermionic emission does occur for the (210) plane at the rather low partial pressure of oxygen, i.e., in the 10−9‐Torr region, at sample temperatures of 1050u2009°C. For further quantitative assessment, work‐function measurements by Richardson plots were done for different crystal planes of clean surface by attaching a photomultiplier. The result clearly shows that the values of the work function increases in order from (100), (210), (110), and (111). The measurements were also extended to the oxygen‐enhanced surface of the (210) plane and it was found that the results follow, phenomenologically, the Richardson plot as well.

The combined effect of acceleration voltage and incident beam orientation on the characteristic X-ray production in thin crystals

Abstract A systematic experimental study has been carried out to determine the combined effect of acceleration voltage and incident beam orientation on the characteristic X-ray production in thin crystals. For MgAl2O4 it has been shown that the orientation dependence undergoes a reversal in character above a particular voltage, which is referred to now as the ‘inversion’ voltage. This inversion voltage has been experimentally determined to be ∼270kV for MgAl2O4 compounds with a spinel structure and is in agreement with theoretical predictions based on a highly localized scattering model for characteristic X-ray production in thin crystals. Further, in combination with theoretical calculations, this ‘inversion voltage’ behaviour has been shown to be different from the conventional critical voltage effect. From the microanalysis point of view, it has been experimentally shown that in order to obtain an analysis independent of the incident beam orientation or the acceleration voltage, it is essential to syst...

The fine structure of crossed bend contours appearing in electron microscope images of bent crystals and their energy and thickness dependence

The fine structures of crossed bend contours and zone axis patterns near the 2 ¯ 15 , 0 3 ¯ 5 , 100, 111 and 110 orientations appearing in electron microscope images of Al crystal foils were observed and their energy and thickness dependence were studied from 50 keV to 2 MeV. In the case of the 2 ¯ 15 orientation at 100 keV, contrast anomalies were observed in bright field images near the positions where three bend contours crossed. In the case of the 0 3 ¯ 5 orientation at 1 MeV, splitting of the 353 bend contour appeared at the crossing with the 200 reflection. In the case of the 100, 111 and 110 orientations, concentric ring patterns were observed at low electron energies (∼100 keV) and spot-like patterns were observed at high electron energies (∼2 MeV). Some details of these experimental results were interpreted by the many-beam dynamical theory of electron diffraction.