Figure 1.

Crystal structures of C-BN-BN-C quadrilayers: (a,d) top and side view of AB-AA${}^{\prime }$-AB stacking. (b,e) the same for AB-AA${}^{\prime }$-AB${}^{\prime }$ stacking; (c,f) top and side view of the 21.8${}^{\circ }$ twisted case T-AA${}^{\prime }$-T. In the side views, the stacked atoms are circled in black, whereas the red dots indicate the vertical alignment of one atom in the upper layer with the center of the hexagon in the bottom layer.