Resolving the In-Plane Anisotropic Properties of Black Phosphorus

Two-dimensional (2D) black phosphorus (BP) has recently attracted significant attention due to its favorable semiconducting properties and promise for nanoscale devices. Additionally, BP possesses distinctive anisotropic physical properties, which stem from the non-equal bond angles and bond strengths in its crystal structure along its orthogonal in-plane directions. Here, the anisotropic properties of BP are summarized, along with the methods to characterize them and the opportunities they present for novel technological applications. This survey of the progress in characterizing the anisotropy of BP will inform future efforts in BP and related anisotropic 2D nanomaterials.