In-situ High Pressure Polarized Raman Spectroscopy of Rhenium Disulfide

Pressure engineering is known as an efficient, continuous and reversible technique capable of tuning material structure, as well as its electrical, optical, and other physical properties. Raman spectroscopy is used to perform efficient and non-destructive analysis of material structure, and is compatible with the application of external tuning fields. In this work, we combine in-situ pressure engineering and polarized Raman spectroscopy to study the pressure-induced evolution of 18 Raman-active modes in ReS2 crystal. We find that the ReS2 undergoes a structural transformation from 1T' to a distorted-1T' phase at 3.04 GPa, followed by an intralayer deformation of Re4 clusters occurring at 14.24 GPa. Interlayer transitions from disordered to ordered stacking in different in-plane directions are observed at 22.08 GPa and 25.76 GPa when the laser is polarized in different directions, which reflects the pressure-enhanced in-plane anisotropy, i.e. the anisotropy of ReS2 crystal becomes more prominent under high pressure. Our findings demonstrate the effectiveness of pressure in tuning material properties, and shed light on potential applications of ReS2 crystals in anisotropic optical and optoelectronic devices.