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Materials Science

Title: Role of the short range order on the self- and impurity diffusion of group 14 (IVB) elements with a different degree of complexity
Principle investigator: Toshio Itami(Japan Aerospace Exploration Agency)
Co-investigator: Tadahiko Masaki   Japan Aerospace Exploration Agency
Kozo Hoshino   Hiroshima University
Shin'ichi Takeda   Kyushu University
Takashi Kamiyama   Hokkaido University
Misako Uchida   Ishikawajima-Harima Heavy Industries Co., Ltd.

Salient Points and Brief Summary of the theme
In the present study, the diffusion coefficients in liquid germanium, whose group number in the periodic table is the same as that of silicon, the most important industrial material, are accurately measured in microgravity aboard the International Space Station (ISS).

Constituent atoms in liquids are continuously moving and their migrations are influenced by frequent collisions among them. At present, it is hardly possible to directly observe such complex atomic motion in melts. The diffusion coefficient is a measure of the average migration distance of these atoms in a given time. Therefore, it is possible to obtain important information about atomic motion by accurately measuring the diffusion coefficient. Generally, two kinds of liquids are caused to contact each other and the development of atomic mixing with the lapse of time is investigated to measure diffusion coefficients in melts. However, in previous studies, it was difficult to accurately measure this development in melts of metals and semiconductors because convection caused by even small temperature differences in such melts at high temperatures spoils this development. Microgravity suppresses convection and enables us to accurately measure the diffusion coefficient in high-temperature melts. The present experiment employs a mirror furnace with an X-ray observation system. Directly observing the liquid state of a diffusion sample during diffusion experiments by an X-ray image assures the successful performance of the diffusion experiments for high-temperature melts.

The obtained result from the present experiment not only contributes acquiring new fundamental information about atomic motion in melts but also provides precious information for applications to improve the homogeneity of impurity concentrations in semiconductor materials, which is important for producing high-quality semiconductor crystals.

Before diffusion
During diffusion
After diffusion
(Separated state of liquid diffusion column)(Formation of liquid diffusion column)(Sectioning of liquid diffusion column)


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Last Updated : October 1, 2003

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