In situ observation of multiple parallel (1 1 1) twin boundary formation from step-like grain boundary during Si solidification

The formation of multiple parallel twin boundaries at grain boundary grooves during Si solidification was investigated using an in situ observation system. Twin boundaries were repeatedly generated at a crystal/melt interface from a step-like grain boundary during solidification. The growth velocity of the micro-facet at the grain boundary groove accelerated and decelerated, which resulted in the nucleation of a twin and the development of a step-like structure at the grain boundary. The undercooling for multiple parallel twin formation as estimated based on experimental observation and the result was further discussed by comparison with previous studies.