Synthesis of Si–Ge Alloy by Rapid Cooling in Short-Duration Microgravity

Abstract

We solidified Si–Ge alloys by rapid cooling in short-duration microgravity. When the Si–Ge melt was solidified by contact with the copper chill block (cooling rate; 100 K/s), the samples solidified in microgravity and on the ground had large grains (about 0.2 mm diameter), and were segregated. When we splat-solidified Si–Ge melt on the copper chill block by using argon gas pressure (4×105 Pa), the solidified sample contained less Ge than the starting material because of the heterogeneity of the Ge component in the melt. When we splat-solidified the Si–Ge melt in microgravity, we obtained a layer with a fine structure (less than 1 µm diameter) on the side contacting the copper chill block because of the high cooling rate (>5000 K/s). A 100-µm-thick layer with fine structure was obtained by doping with P; this layer was much thicker than that in the nondoped sample. The thermal conductivity of the sample splat-solidified in microgravity was lower than that of the arc-melted sample.