Polarized Raman Investigation of 1T'-Phase Tungsten Disulfide Atomic Layers Grown by Chemical Vapor Deposition

Phase engineering is currently a prominent topic in 2D materials research. In particular, metastable 1T'-phase WS₂ has attracted considerable interest owing to its unique properties, including spin-Hall insulating states, superconductivity, and catalytic activity in hydrogen evolution reaction (HER). The 1T'-phase WS₂ possesses a monoclinic structure, which suggests the presence of anisotropic properties; however, these characteristics have not yet been thoroughly explored. In this study, polarized Raman spectroscopy investigations of 1T'-phase WS₂ are performed to examine its anisotropic behavior and establish a method to identify its principal crystallographic axes. Combined with transmission electron microscopy measurements and density functional theory calculations, the irreducible representations of the Raman peaks are successfully assigned and it is revealed that the anisotropy of the $A_g^6$ peak at ≈406.8 cm^-1 can be used to determine the principal axis, corresponding to the direction of the W─W zigzag chain in 1T'-phase WS₂. Understanding the anisotropic properties of 1T'-phase WS₂ is essential for controlling its performance in future applications.