We report an excellent growth behavior of a high-κ dielectric on ReS 2, a two-dimensional (2D) transition metal dichalcogenide (TMD). The atomic layer deposition (ALD) of an Al 2 O 3 thin film on the UV-Ozone pretreated surface of ReS 2 yields a pinhole free and conformal growth. In-situ half-cycle X-ray photoelectron spectroscopy (XPS) was used to monitor the interfacial chemistry and ex-situ atomic force microscopy (AFM) was used to evaluate the surface morphology. A significant enhancement in the uniformity of the Al 2 O 3 thin film was deposited via plasma-enhanced atomic layer deposition (PEALD), while pinhole free Al 2 O 3 was achieved using a UV-Ozone pretreatment. The ReS 2 substrate stays intact during all different experiments and processes without any formation of the Re oxide. This work demonstrates that a combination of the ALD process and the formation of weak S–O bonds presents an effective route for a uniform and conformal high-κ dielectric for advanced devices based on 2D materials. View Full-Text