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High-resolution transmission electron microscopy of AlAs/GaAs/AlGaAs multilayer heterostructure

Nishio K., Kątcki J., Shiojiri M.

Electron Technology

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1999

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Vol. 32, No. 4

348-353

EN

A multilayer heterostructure of GaAs/AlAs/GaAs/AlGaAs/GaAs, which was prepared by molecular beam epitaxy at the Institute of Electron Technolgy was analysed by high-resolution transmission electron microscpoy (HRTEM) with the aid of image simulation and image processing. In spite of specimen damage during ion-milling Tem specimen preparation, columns of Ga and As atoms in the GaAs and columns of Al and As atoms in the AlAs were positioned in the (110) HRTEM images. The average and the variance of the widths of AlAs, GaAs, and AlGaAs layers were estimated from a small-ange scattering image reconstructed from the HRTEM image.

2

Magnetization and structure of Fe-Al powders.

Fujii M., Saito K., Wakayama K., Kawasaki M., Yoshioka T., Isshiki T., Nishio K., Shiojiri M.

Inżynieria Materiałowa

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1998

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R. XIX, nr 4

860-863

EN

A few micrometers-sized Fe1-xAlx (x=0.35-0.42) powders prepared by atomizing method have the B2 structure and are paramegnetic. The powder milled for several hours is magnetized and has a spontaneous magnetization as great as 100 emu/g. The milled powder particles become flakes, which are composed of lamellae expanding parallel to the (110) plane and having heavily distorted lattice. High-resolution transmission electron microscopy and electron diffraction revealed that structures appear in very thin areas within the lamellae. These superlattices indicate the creation of large number of antiphase boundaries, which induce ferromagnetism. When the milled powder is heated at 100-400 degrees centigrade the magnetization decreases to a few tens emu/g, the lamella structures being kept.

3

High-resolution electron microscopy and cathodoluminescence scanning electron microscopy of SrTiO3-based ceramics elucidating their varistor property.

Shiojiri M., Isshiki T., Nishio K., Saijo H., Nomura T., Hitomi A., Sato S.

Inżynieria Materiałowa

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1998

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R. XIX, nr 4

779-784

EN

Semiconductive SrTiO3-based ceramics practically used as varistors and capacitors have been investigated using HRTEM, EDX and CLSEM. They were produced with and without an additonal reducing treatment at Po2=10 raising to a 12th power Pa in the sintering process at Po2=10 raising to a -8 power Pa, followed by reoxidizing process in the air. (Sr0.35Ba0.35Ca0.30)1.026TiO3 varistors produced without the additional heat-treatment are composed of well-developed crystalline grains with facet boundaries, having a low varistor coefficient (alpha<4). CL revealed that the grain, particularly near varistor surface, has high conductive inside containing oxygen vacancies and less-conductive boundary layer without the oxygen vacancies. The boundary layers may work as the double Shottky barriers. The additional reducing treatment forms a lot of oxygen vacancies in the grains of the varistors and damaged the crystallinity near the grain boundaries. The damaged regions easily introduce oxygen atoms into the grains during the reoxydizing process. The additional treatment, hence, produces thick boundary layers and consequently gives rise to high varistor coefficient (alpha>4), which is favourable for practical use. (Sr0.94Ba0.01Ca0.05)0.99TiO3 capacitors were also produced without the additional reducing treatment. Their grains have the facet boundary structure. The dielectric boundary layer and semiconductive inside of the grain are also observed. The boundary layer is as thin as a few ten nanometers, which cause the ceramic a high capacitance.

4

Investigations of materials in random-system by quantitative high-resolution transmission electron microscopy and electron diffraction

Shiojiri M., Endoh H., Saijo H., Isshiki T., Nishio K.

Electron Technology

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1998

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Vol. 31, No. 2

189-192

EN

A detail of our project, "analysis of materials in random system by accurate measurement of high-resolution transmission electron microscopy (HRTEM) contrast and electron diffraction (ED) intensity" is reviewed. The main method is quantitative HRTEM and ED using an imaging plate (IP) recording and processing system, with the aid of the simulation and compresion. X-ray and neutron diffraction and cathodoluminescence scanning microscopy are also used as complementary methods. We have been making investigations on: 1) the local atomic configuration in cellular random system such as BaTi₂₋xSnFe₄O₁₁ and Fe-Al alloys, and the relation between their structure and magnetic properties; 2) the distribution of atoms at the heterointerfaces in multilayers such as GaAs/GaInP/Al-GaInP and GaAs/AlGaAs, and in polymorphic Zn(Mg)Se; 3) the site of doped Y atoms in BaTiO₃; 4) the structure and crystallization of elements and metal oxides in topological random system.

5

In situ obsevations of solid-solid reaction : decomposition of barium titanyl oxylate and formation of barium titanate

Isshiki T., Nishio K., Shiojiri M., Noguchi H., Deguchi Y., Yamamoto H.

Electron Technology

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1998

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Vol. 31, No. 2

202-207

EN

The thermal decomposition of BaTiO(C₂O₄)₂ 4H₂O and formation of BaTiO₃ were investigated by thermogravimetric analysis (TGA), differential thermal analysis combined with mass-spectroscopy (DTA-MS), high-temperature X-ray diffraction (XRD), and in situ scanning electron microscopy (SEM) and transmission electron microscopy (TEM). TGA and DTA-MS showed that the dehydration occurred in a temperature range of 25 ÷ 240°C, followed by the decomposition of BaTiO(C₂O₄)₂ 4H₂O to BaCO₃, TiO₂, CO and CO₂ in a range of 240 ÷ 470°C. A porous structure showing the escape of CO and CO₂ gases was observed in an SEM image of a specimen at 400°C. Only diffuse peaks appeared in XRD charts in 200 ÷ 500°C, indicating that the BaCO₃ and TiO₂ are amorphous and/or micro-crystalline. XRD also disclosed that hexagonal BaTiO3 crystallites were formed by the solid-state reaction of the BaCO₃ and TiO₂ in range of 500 ÷ 650°C and then transformed to cubic crystals above 650°C. The direct formation of cubic BaTiO₃ crystals also occurred as a retareded reaction of the BaCO₃ and TiO₂ above 730°C.