Fast Identification of the Crystallographic Orientation of Violet Phosphorus Nanoflakes with Preferred In-Plane Cleavage Edge Orientation

Semiconducting layered violet phosphorus, the most stable phosphorus allotrope, has recently been successfully produced with large single crystal sizes and high yields. A promising anisotropy is expected by the reduced symmetry of violet phosphorus in various properties. The in-plane crystallographic anisotropy and cleavage edge orientation are especially important to the exfoliated 2D structures for their electronic, photonic, magnetic, and mechanic applications. However, the anisotropy of violet phosphorus has not been studied. Here, a fast and nondestructive way is reported to identify the crystallographic orientation of 2D violet phosphorus nanoflakes by a single polarized Raman spectrum. The 2D violet phosphorus nanoflakes have been found to have preferred in-plane cleavage edges along -[P2][P8][P2][P9]- tubular strands with <1, 1, 0> edge alignment. The b-axis (a-axis) direction has been demonstrated to be easily identified that forms an angle of 45° or 135° from the cleavage edge by the intensity of A_g mode, especially the appearance or disappearance of 491 cm^–1, under parallel configuration using polarized Raman scattering. A simple and fast method has been developed to identify the crystallographic orientation of violet phosphorus nanoflakes by a single Raman spectrum to obtain the corresponding a-axis and b-axis.