Study on the optical properties of ReS 2 flakes by unpolarized and polarized optical contrast measurements

In-plane anisotropic two dimensional (2D) layered materials, such as ReS2, offer one more degree of freedom than isotropic 2D materials to deliver various physical properties. Optical properties of ReS2 flakes are dependent on the layer number (N) from monolayer to multilayer. Here, taking ReS2 flakes with an anisotropic-like (AI) stacking order as an example, we probed their optical properties by optical contrast (OC) measurements. The N-dependent and angular-dependent characteristics of ReS2 flakes were demonstrated respectively by unpolarized and polarized OC curves. The results facilitate further study on out-of-plane and in-plane complex refraction index properties of ReS2 flakes.