Fig. 1.

a Crystal structure of monolayer BP. The zigzag and armchair directions are represented by the green coordinates. The dash dot lines frame the unit cell of the BP; adapted with permission [44]. Copyright 2019 Elsevier. b Structures of three predicted polymorphs of phosphorene. Adapted with permission [45]. Copyright 2015 Nature Publishing Group. c AFM image; d Raman spectra of monolayer and bulk BP; reproduced with permission [23]. Copyright 2014, American Chemical Society; HR-TEM e, f SAED for few-layer 2D BP. Reproduced with permission [47]. Copyright 2015, American Chemical Society; g schematics of phosphorene nanoribbons model where n is the neck width and W is the nanoribbon width. Top two are zigzag nanoribbons with nanoholes in the middle and near the edge, while the bottom one is armchair nanoribbon. Computed bandgap structure for zigzag and armchair nanoribbons is shown on the top and bottom, respectively. Reproduced with permission [64]. Copyright 2020 Royal Society of Chemistry