Abstract
The dynamic behavior of the solid-liquid interface and crystal defect during the melt growth of a Bi thin foil (99.9% purity) has been observed using a transmission electron microscopy and a TV–VTR imaging system. The (11\bar1) film was partially melted and regrown by cooling at a rate of 8.3×10−3 to 2.7×10−1 K/s. The growing interface was concave toward the melt when the cooling rate was low and it became nearly straight when the cooling rate was high. Moreover, three types of the interface movement were observed during the melt growth; (a) a back-and-forth oscillation at the slow cooling rate, (b) a step-wise oscillation at the intermediate cooling rate and (c) a steady advancement at the high cooling rate. The oscillatory interface motion was found to be caused by a small fluctuation of temperatures during cooling. No facet growth was seen at any cooling rate against expectation.
In the melt-grown crystals various kinds of defects were observed; (1) short and long dislocations and dislocation loops, (2) lineage defects probably composed of a dislocation array, (3) circular voids and (4) triangular defects unidentified. The formation and behavior of these defects during the melt growth and subsequent cooling processes were explained and their density and size were estimated. Among the defects introduced in crystals the following three were most dominant; short dislocations 0.1 μm in average length, dislocation loops 0.05 μm in average diameter and circular voids 0.03 μm in average diameter.
