稲富 裕光

The microgravity experiment mission FACET (Investigation on Mechanism of Faceted Cellular Array Growth) was carried out under long duration microgravity on the International Space Station (ISS) in 2010. FACET aimed to clarify the mechanism of a faceted cellular array growth by precisely observing the phenomena at the solid/liquid interface. Phenyl salicylate / t- butyl alcohol alloy was used as a sample material instead of semiconductors or oxides. The crystal growth processes were visualized in situ using a microscope and an interferometer, especially focusing on changes in temperature and concentration in the sample. The temperature and concentration distributions in the melt during the growth were precisely measured with high spatial resolution. Negative temperature gradient as well as negative concentration gradient ahead of the S/L interface can be expected to be the driving forces of the morphological instability. It is evident that the conventional model based on the frozen temperature approximation is insufficient to explain the growth mechanism of the faceted cellular array

In_xGa_1-xSbは電子デバイスの材料として期待される三元混晶半導体の一つであるが、地上重力下では密度差対流のため均一組成のバルク結晶を得ることが困難である。一方、微小重力下では対流が抑制されるため、良質な結晶を得られることが期待される。そこで我々は混晶半導体結晶成長に関する知見を得るために、国際宇宙ステーションを利用した結晶成長実験を行ってきた。本研究では、数値解析により、界面カイネティクスがInGaSb結晶成長に及ぼす影響について検討を行った。計算結果より、カイネティクス係数が小さくなるにつれて、InGaSb結晶成長速度およびGaSb供給原料の溶解速度が小さくなるという結果が得られた。

Soret effect was investigated by experiment on the ground (1g) and in microgravity (μg) aboard ISS-JEM. Temperature gradient was given to salol -tert-butyl alcohol solution, which was packed in a quartz cell. Interference fringes generated by two-wavelength Mach-Zehnder interferometer (wavelength: 532 and 780 nm) were recorded with using a CCD camera. The moving distance after setting temperature gradient was measured. The obtained interference fringes were straight and parallel, which indicates that there was not so significant convective disturbance. The curve of time dependence of the moving distance (number of crossing interference fringes) became smooth after correction considering the thermal expansion of the quartz cell. The obtained values of Soret coefficients were similar in two experiments with using vertical and parallel interference fringes.

We performed microgravity experiments of homogeneous nucleation of iron from the vapor phase using the sounding rocket S-520-28 on December 17, 2012. The purpose is determination of a sticking probability of iron during the nucleation from the supersaturated vapor, because the sticking probability is one of the most uncertain physical quantities to understand the formation process of cosmic dust based on nucleation theories. We prepared the specially designed MachZehnder-type interferometers with an evaporation chamber and camera recording systems to fit the space and weight limitations of the rocket. Three same systems, named DUST 1 to 3, were installed into the rocket. Iron was evaporated in an argon gas and then it was cooled and nucleated to form nanoparticles. The temperature and concentration of iron vapor at the nucleation site are determined from the movement of the interference fringe. Here, we present the brief summary of the experiments and the preliminary results of the homogeneous nucleation from iron vapor under microgravity.

Si dissolution into Ge melt and crystal growth of SiGe was in-situ observed by X-ray penetration method. The rectangular shaped sandwich sample of Si (seed)/Ge/Si(feed) was used for the experiment. The penetrated X-ray intensities through the sample were recorded by rectangular shaped CdTe detector as a function of time and temperature. The experimental results demonstrate that the dissolution of Si seed was larger compared to Si feed crystal. Dissolution lengths result agreed well with numerical results. From the experimental and numerical dissolution length results. The dissolution process of Si into Ge melt was strongly influenced by gravity induced solutal convection. Moreover, the crystal growth of SiGe was clearly observed from the drastic variation of penetrated X-ray intensity near the growth interface. The growth mechanism for the observed SiGe growth process was discussed based on the penetrated X-ray intensity profile and composition profile measured by EPMA.