The evolution of the facet-facet groove at grain boundaries in multi-crystalline Si during solidification was investigated by in situ observation of the melt/crystal interface. The grain boundaries changed their propagation direction without any new grain formation or grain boundaries interaction during crystal growth. We monitored the melt/crystal interface over time and carefully estimated the growth velocities on two facets. We found that the facet velocities are different in some of our experimental observations and the development of random grain boundary is strongly dependent on the facet velocities. On the basis of our experimental observations, we discussed the direction of random grain boundary during solidification by considering the growth velocities on two facets.
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