**3.2 Defect lines**

Another defect observed in BN 2D material is *defect lines*, which form due to the difference in polarities of h-BN. This difference in polarity results in the convergence of N-terminated edges from domains with 60° rotation differences. These defects are observed when h-BN epilayers grow on lattice-matched substrates like Cu (111) or Ni (111). However, in situ observation of such defect lines is not detected yet. Therefore, determining adatom species migration during this defect needs further detailed study [51].

**Figure 5.**

*Two types of B-N bonds are zigzag BN nanoribbon and armchair BN nanoribbon with their defects [46].*
