Raman spectroscopy in black phosphorus

In this article, we review the current status of Raman spectroscopy in orthorhombic black phosphorus (BP) (for simplicity, henceforth, referred to as BP). BP is a layered semiconductor crystal that recently regained interest because it can be exfoliated down to the single layer, thus exhibiting 2‐D properties. First, we briefly review the crystalline structure and the phonon dispersion relations in BP. Then, the symmetries of the Raman‐active modes are discussed in the light of group theory, and the scattering configurations for observing the different phonon modes are presented. Polarized Raman spectroscopy results are discussed and reveal unusual angular dependence features, which can be ascribed to the linear dichroism and to the complex nature of the electron–phonon matrix elements. Edge phonon effects originated from rearrangements of the atomic terminations are also discussed. Subsequently, Raman modes that emerge from interlayer interaction and that are only visible in the few‐layer regime are presented and discussed. Finally, we outline new perspectives to BP Raman spectroscopy in directions that remain partially or totally unexplored and that can provide potentially important outcomes to problems such as defects, oxidation, doping, strain, stacking order and other BP‐like 2‐D materials. Copyright © 2017 John Wiley & Sons, Ltd. Black phosphorus (BP) is an emergent 2D layered crystal that can be exfoliated down to the monolayer regime. It exhibits an orthorhombic structure which leads to highly anisotropic physical properties. In this work, we review the basic concepts of Raman spectroscopy in BP, covering from bulk to few‐layer and monolayer BP crystals, where new features appear in the spectra. We emphasize the anomalous angular dependence of spectra measured by polarized Raman spectroscopy and the presence of edge phonons due to the rearrangement of atoms near the crystal termination.