Rhenium Disulfide (ReS₂)

ReS₂ is a representative Group-VII transition metal dichalcogenide. It crystallizes in a distorted 1T′ phase with a triclinic structure and space group P-1. Because the Re atoms (Re⁴⁺, d³ electronic configuration) undergo a Peierls distortion, four Re atoms cluster together to form diamond-shaped "Re₄ cluster chains," giving the lattice pronounced in-plane structural anisotropy. Its most distinctive feature is the weak interlayer coupling—even in the bulk, individual layers are nearly "decoupled" in both electronic structure and lattice vibrations, behaving almost like independent monolayers. ReS₂ possesses a near-direct bandgap of about 1.4–1.5 eV (direct/quasi-direct), which shows little variation with layer number. Its optical absorption, electrical transport, and Raman response all exhibit strong polarization dependence, giving it unique value for polarization-sensitive photodetectors and anisotropic electronic devices.