Naoto Sumida

Some Applications of an Ultra-High Voltage Electron Microscope on Materials Science

Fundamental problems for application of a 3 MV-class electron microscope have been examined at 2 MV on various materials such as aluminum, copper, 18-8 type stainless steel and gold as follows: (a) The maximum observable thickness of these specimens at 2 MV is generally 12~13 times larger than those at 0.1 MV. And thus, it is expected that processes of various phenomena in most materials can be continuously observed as same as in bulk specimens by the electron microscopy. (b) The anomalous transmission of electrons clearly occurs at the symmetry position of 111 reflections at 2 MV even in aluminum. (c) Total amount of secondary defects due to electron irradiation damage strongly depends not only on the order of reflections but also on deviation from the Bragg condition. When the anomalous transmission at the symmetry position occurs, the amount of defects shows the maximum value at the symmetry position of reflections. (d) Utility of capsules are examined on determination of the liquid structure and oxidizing processes of aluminum.

Dislocation Multipoles in Slightly Deformed Cu–10 at%Al Single Crystals

Structures of dislocation multipoles of the primary slip system in slightly deformed Cu–Al single crystals have been investigated by electron microscopy. They are closely related to the operation of the secondary slip systems, especially the cross one. The multipoles are divided into many blocks by shifting along operated cross slip planes, and various types of the multipoles including elongated dislocation loops and zigzag dislocation lines are formed. Formation processes of these multipoles are discussed.

Electron Microscope Study of the Anomalous Transmission of Electrons in Aluminum up to 3 MV

The anomalous transmission of electrons in aluminum has been examined over the voltage range 0.5 to 3 MV by electron microscopy. The anomalous transmission begins to appear at about 1 MV at the symmetry position of 111 reflections, and at about 2 MV in a case of 200 reflections. The degree of anomalous transmission increases with increasing accelerating voltage up to 3 MV. The experimental results are compared with those of 18/8 type stainless steel, and discussed in terms of the axial and planar channeling parameters of electrons proposed by Fujimoto et al. The anomalous transmission phenomenon in these metals shows good correlation with the planar channeling parameter, and is also related to the axial one when the same systematic set of reflections is used.

Diffraction Contrast of Thickness Fringes in High Voltage Electron Microscope Images

The diffraction contrast of bend contours in several different f.c.c. and b.c.c. metals has been observed under the various reflecting conditions in the voltage range 0.5 to 3 MV by electron microscopy. The micrographs taken under various observing conditions are arranged in the order of the value of the interaction parameter, αp, which is correlated with the number of the bound states of the incident electron in a crystal potential, and the relation between the contrast of these images and the values of αp is discussed. The result shows that the contrast is well determined by the interaction parameter in spite of differences in materials, the order of reflections and accelerating voltages.

The Effect of Reflecting Condition on the Secondary Defect Formation in Copper by Electron Irradiation

Defect formation in copper by the electron irradiation has been studied at room temperature with a 3 MV-class electron microscope. The density of interstitial loops formed during electron irradiation strongly depends on the reflecting condition of the specimen and it decreases with increasing order of reflection. For example, the density at the symmetry position of the 111 systematic reflection is the highest compared with that at each Bragg position of the systematic reflections. The formation rate of primary defects at each position of the 111 systematic reflection has been estimated from the density of interstitial loops. The results show that the formation rate at the symmetry position is about 2.5 and 3 times larger than that at first and second Bragg positions, respectively.

Structural Analyses of Fractional Monolayer (GaAs)m/(AlAs)n Superlattices by X-ray Resonant/Off-Resonant Scattering

The structure of (GaAs)m/(AlAs)n superlattices with a period length of a fractional number in monolayer (ML) units, which is fabricated by shutter control in molecular beam epitaxy (MBE) growth, is studied by X-ray diffraction (XRD) analysis using synchrotron radiation. Satellite peaks originating from the fractional superlattice (SL) periods, 1.69 monolayers (ML), are clearly observed in XRD profiles. XRD simulation, which is based on the model of modulated composition distribution, can reproduce the satellite peak positions. We also measure X-ray resonant scattering at the Ga K-edge and estimate the atomic composition in the SL region.

Growth of GaNAs/GaAs Multiple Quantum Well by Molecular Beam Epitaxy Using Modulated N Radical Beam Source

GaNAs/GaAs multiple quantum well (MQW) structures have been grown on GaAs(001) substrates by molecular beam epitaxy (MBE) using modulated N radical beam source under optimized conditions, wherein the amount of N2 gas flow, RF-power and shutter sequence are systematically controlled. Clear and flat GaNAs/GaAs interfaces were observed in the cross-sectional transmission electron microscopy (TEM) measurements. Fine MQW structures originating from the precise control of the modulated N radical beam have been demonstrated as clear satellite peaks from the X-ray diffraction (XRD) measurements and sharp photoluminescence (PL) peaks. The step-like behaviors in the absorption spectra which reflect the density of state in two-dimensional systems, were clearly observed for all MQW samples.

Anomalous Transmission of Electrons at High Energy

The relation between the Bloch waves and the anomalous transmission in the high energy electron diffraction is studied and it is shown that the Bloch waves of electrons bound loosely by crystal potential mainly contribute to the diffraction contrast in the Kikuchi patterns and electron micrographs. An experiment is carried out to observe the bend contours of thin gold, tungsten and molybdenum crystals by a high voltage electron microscope and it is found that the position of the anomalous transmission changes from the symmetry position to the first Bragg one at the energies corresponding to the same value of an interaction parameter which is correlated with the number of the bound state of the incident electron in the planar potential.

Internal Stress Field in Ultrafine Grained Aluminium Fabricated by Accumulative Roll-Bonding

Internal stress field in a severely deformed aluminium with ultrafine grained microstructure has been studied by convergent-beam electron diffraction (CBED) technique in transmission electron microscopy (TEM). A commercial purity aluminium (99.1%Al) sheet was highly strained by the accumulative roll-bonding (ARB) process to evolve an ultrafine grained structure. Higher-order Laue zone (HOLZ) lines in the incidence disk of the ] 12 1 [ zone axis have been observed at various positions within an identical ultrafine grain. The key finding is that the HOLZ line pattern taken from the vicinity (~50nm) of the grain boundary (lamellar boundary) looses ) 1 1 0 ( mirror symmetry, whereas the pattern from the grain centre has the symmetry. The former and the latter represent the existence of a large non-hydrostatic stress field and a small internal stress field, respectively. The magnitude of the internal stress becomes larger with approaching to a grain boundary.

Enantiomorph identification in organic crystals by electron diffraction

The convergent-beam electron diffraction (CBED) method we proposed recently for enantiomorph identification has successfully been applied to some amino acid crystals such as glutamic acid and threonin. Enantiomorph identification (either left-handed or right-handed form) can readily be made within the framework of the proposed method by noting the asymmetric intensity distribution of Bijvoet pairs of reflections in the CBED pattern taken along an appropriate zone-axis orientation. Although the proposed method usually requires only a single CBED pattern, some effort to eliminate the ambiguity of 180°-rotation of the CBED pattern about the incident beam is needed for enantiomorph identification for these organic crystals because of the lack of HOLZ (higher-order Laue zone) reflection disks.