Synthesis of Crystalline Materials with High Quality Under Short‐Time Microgravity
Synthesis of Crystalline Materials with High Quality Under Short‐Time Microgravity
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短时微重力下高质量晶体材料的合成
DOI：
10.1002/9780470294574.ch25
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发表时间：
2008
期刊：
影响因子：
--
通讯作者：
K. Ikezawa
中科院分区：
文献类型：
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作者：
T. Okutani;H. Minagawa;H. Nagai;Y. Nakata;Masa;Y. Ito;T. Tsurue;K. Ikezawa
微重力（μg）提供了一个独特的环境，液体和固体物质均匀分散，但没有热对流。当金属或合金的熔体冷却到μg以下时，很容易发生过冷。随后，当熔体在μg下单向快速冷却凝固时，由于熔体均匀且结晶速度远大于lg，凝固熔体中很少形成核。对Ge和InSb熔体在10−4g、10−3g、1.2 s的μg环境下进行了凝固实验。微重力环境是通过日本微重力中心（JAMIC）的490米自由落体设施、HNIRI的10米自由落体塔和13米的落体管获得的。用光学显微镜（OM）和透射电镜（TEM）观察了锗在μg中的固化产物，发现固化产物中几乎没有缺陷。而在1g凝固的产物中存在较多的晶界和层错。用压缩后的In - Sb粉末混合物在μg下固化，得到了原子比在52:48 ~ 46:54之间的高质量InSb单晶，在pg下固化后的InSb在近红外区的光学吸光度比用浮区法生产的InSb单晶高10% ~ 30%。在非化学计量组成的InSb中观察到杂质半导体的性质。滴管实验结果表明，高质量的微重力环境、单向凝固的应力释放和快速冷却是制备高质量结晶材料的重要条件。
Microgravity (μg) provides a unique environment with homogeneous dispersion of liquid and solid substances but no thermal convection. When melts of metals or alloys are cooled under μg, it is easy to achieve supercooling. Subsequently, when the melts are solidified unidirectionally by rapid cooling under μg, nuclei seldom form in the solidifying melts because the melts are homogeneous and the rate of crystallization is much greater than in lg because of supercooling. Solidification experiments of Ge and InSb melts were conducted in a μg environment of 10−4g for 10 seconds and 10−3g for 1.2 seconds. The microgravity environments were obtained using the Japan Microgravity Center's (JAMIC's) 490m free‐fall facility, HNIRI's 10m free‐fall drop tower, and a 13m drop tube. Observations of the Ge solidified in μg using an optical microscope (OM) and a transmission electron microscope (TEM) revealed very few defects in the solidified products. In contrast, many grain boundaries and stacking faults were found in the products solidified in 1g. A high‐quality InSb single crystal with an atomic ratio between 52:48 and 46:54 was produced by solidifying a melt of compressed In‐Sb powder mixture under μg. The optical absorbance of the InSb solidified under pg in the near infrared region was found to be 10% to 30% greater than that of commercial single crystal InSb produced by the floating zone method. The properties of impurity semiconduction were observed in the InSb with non‐stoichiometric compositions. The results of the drop‐tube experiments showed that a high‐quality microgravity environment, the relief of stress by unidirectional solidification, and rapid cooling are very important for producing high‐quality crystalline materials.