Structure and stability. (a) Atomic structure of 2D antimonene and its isoelectronic counterparts in the three typical phases α, β, and c, with constituents A (B) in light (dark) purple representing In (I), Sn (Te), and Sb (Sb) atoms, respectively. The corresponding space group is given under each structure. (b) Cohesive energy difference ΔE_coh between α, β phases and c phase, here the cohesive energy of the c phase as a reference is set to be zero, α and β lie either at the bottom or on top of the rectangle.