Observation of rapid solidification of deeply undercooled Si melts using electrostatic levitation

Abstract

Pure Si samples with diameters of about 1.7 mm were undercooled down to 317 K while electrostatically levitated. The crystal growth velocities were measured as a function of undercooling and the appearance of the solid/liquid interface was observed by means of a high-speed camera. The results were compared with those reported previously for larger Si droplets using an electromagnetic levitator. In this study, nucleation was triggered at a given undercooling using needle darting and particle interspersing. As a new finding, the transition of growth mechanism from a single plate to multi-plate crystal was observed at the undercooling of 80 K. Transitions from plate-like crystal to coarse faceted dendrite and from coarse to fine faceted dendrite hardly depended on the sample size.