Nucleation of amorphous germanium from supercooled melts

Thin germanium films on SiO₂ completely melted by pulsed laser irradiation cool rapidly by thermal conduction to the substrate until they solidify. In situ measurements indicate that the liquid is supercooled by 420-530 K with respect to the crystalline phase prior to solidification. Cross-sectional transmission electron microscopy reveals nucleation events at the Ge/SiO₂ interface. The microstructure of these events is comprised of a very fine grained (5-15 nm) polycrystalline core with much larger grains extending laterally and toward the free surface. It is believed that nucleation of the amorphous phase, which was subsequently converted to the fine-grained material, initiated solidification.