fig3

Figure 3. Crystal structures of (A) graphene (planar) and (B) BP (puckered orthorhombic). Reproduced with permission^[88]. Copyright 2022, Elsevier; (C) Modeled mono-, bi-, and tri-layer BP structures, illustrating the stacking of puckered layers. Reproduced with permission^[91]. Copyright 2015, Springer Nature; (D) Top view of single-layer BP (phosphorene), showing bond angles (96.3° and 102.1°) and the anisotropic lattice directions (zigzag vs. armchair). Reproduced with permission^[93]. Copyright 2015, National Academy of Sciences; (E) Evolution of BP bandgap with sample thickness, showing the thickness-dependent bandgap change. Reproduced with permission^[88]. Copyright 2022, Elsevier. BP: Black phosphorus.