(color online) (a) Top view of a 3 × 3 phosphorene supercell, the zigzag and armchair chiralities are along the x and y directions, respectively. (b) Enlarged single unit cell of phosphorene. The top and bottom phosphorus atoms are marked separately as P1 and P2. Reproduced from Ref. [65] with permission from AIP Publishing. (c) Phonon dispersion relation of monolayer phosphorene along the path passing through high-symmetry k-points. The acoustic and optical phonon branches are denoted in different colors. The upper inset denotes the high-symmetry k-points in the Brillouin zone and the lower inset depicts the vibration direction of flexural phonons. Reproduced from Ref. [91] with permission from the Royal Society of Chemistry.