Anisotropic Wet Etching of WSe₂ and MoS₂ for Twist-Angle Extraction of Heterobilayers

We focus on the formation of hexagonal holes in WSe2 and MoS2 multilayers by anisotropic wet etching. It is found that anisotropic wet etching occurs for a high H2O2 concentration in an etchant and large thicknesses of WSe2 and MoS2. Furthermore, photoexcited carriers accelerate the anisotropic wet etching of the WSe2 multilayers. It is found that the oxidation process at the edges of WSe2 crystals significantly impacts anisotropic wet etching, and photoexcited carriers facilitate the WSe2 oxidation reaction with H2O2. We also demonstrate that anisotropic wet etching can be used to determine the twist angle in WSe2/MoS2 heterobilayers. The photoluminescence intensities of the infrared interlayer exciton are proportional to the twist angle in the heterobilayers. These results suggest the potential for exploiting the orientation-dependent phenomena of transition metal dichalcogenides.