Observation of anisotropic interlayer Raman modes in few‐layer ReS₂

ReS₂ has recently emerged as a new member in the rapidly growing family of two‐dimensional materials. Unlike MoS₂ or WSe₂, the optical and electrical properties of ReS₂ are not isotropic due to the reduced symmetry of the crystal. Here, we present layer‐dependent Raman measurements of ReS₂ samples ranging from monolayers to ten layers in the ultralow frequency regime. We observe layer breathing and shear modes which allow for easy assignment of the number of layers. Polarization‐dependent measurements give further insight into the crystal structure and reveal an energetic shift of the shear mode which stems from the in‐plane anisotropy of the shear modulus in this material. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)