Structure and Strength of Grain Boundaries in Si Bicrystals with ⟨111⟩ Twist Misorientations

Abstract

In order to determine the relationship between structure and strength of grain boundaries in Si, bicrystals with ⟨111⟩ twist boundaries were prepared from 6 N high-purity Si single crystals by press-joining, and their fracture strength was measured by 3-point bending test and the structure was observed by TEM. The results obtained are as follows. (1) The fracture strength depends on the twist angle in a similar manner as predicted theoretically by Inomata et al. without any consideration of the relaxation of boundary structure. However, the observed misorientation-dependence is much weaker than the prediction. (2) The measured grain-boundary energy depends on the twist angle in the same way as the fracture strength. (3) The boundary extension is too small to be observed. These results are compared with those of covalent-bonded SiC and refractory metal Mo, and the cause of the boundary extension observed in SiC and Si₃N₄ is discussed.