Thickness–dependent and Wavelength–dependent Dichroic Response of Layered Rhenium Sulfide

Anisotropic two-dimensional (2D) materials, particularly transition metal dichalcogenides (TMDs), are promising candidates for next-generation optical sensors due to their unique responses to polarized light. Rhenium disulfide (ReS₂) possesses distinctive directional characteristics owing to its in-plane structural anisotropy. This anisotropy manifests in the differential absorption of light, which varies depending on the polarization direction. A thorough comprehension of the effects of flake thickness and incident wavelength on this anisotropic behavior continues to be an area of ongoing research. This study examines the sensitivity of ReS₂ flakes to light polarization through comprehensive absorption measurements across various polarization angles, controlled using a polarizer. The dichroic factor, defined as the ratio of maximum absorption (parallel to the crystal b-axis) to minimum absorption (perpendicular to the crystal b-axis), was subsequently calculated. The dichroic factor exhibits a decreasing trend as the flake thicknesses increase. Within the range of 9 to 197 nm, the dichroic factor decreased by approximately 54%, indicating that thinner layers are more susceptible to polarization manipulation. Angular absorption measurements conducted at diverse wavelengths indicate an enhanced dichroic factor at longer wavelengths. This phenomenon is attributed to more pronounced polarization dependence near band-edge excitation. These findings offer new insights into the wavelength and thickness-dependent anisotropy of ReS₂, supporting its potential application in polarization-sensitive and wavelength-tunable photodetectors.