Fig. 2: Crystal structures of group-V elemental 2D layers.

a Schematics of top views and side views (along x- and y-horizontal directions) of atomic crystal structures of α and β phase group-V elemental 2D materials (Vene). b Calculated average binding energies of α and β allotropes of all group-V elemental 2D materials, from which the related stability and composability can be acknowledged. c, d SAED images of α- and β-bismuthene, presenting one pseudo-cubic structure with four-fold symmetry in α-Vene and another hexagonal structure with typical six-fold symmetry in β-Vene, respectively. Images of a and b used with permission from John Wiley and Sons²². Images of c and d used with permission from John Wiley and Sons⁴³.