Epitaxial Single-Crystal Growth of Transition Metal Dichalcogenide Monolayers via Atomic Sawtooth Au Surface

Two-dimensional (2D) layered materials such as graphene, transition metal dichalcogenides (TMDs), and hexagonal boron nitride have attracted attention due to their distinctive physical and chemical properties. Therefore, many applications such as high-performance field-effect transistors, atomically thin pn diodes, and Coulomb drag transistors have been investigated. However, such applications are currently only available with a lateral size of up to a few tens of micrometers. Therefore, the growth of single-crystal 2D materials is highly desired to manifest intrinsic physical and chemical properties over the whole region. While wafer-scale single-crystal hexagonal boron nitride film has been successfully grown on liquid Au and vicinal Cu surfaces, an ideal growth platform for diatomic transition metal dichalcogenides has not been established to date. Here, we report the single-crystal growth of monolayer TMD films on atomic sawtooth Au substrates. The atomic sawtooth Au surface, which has periodic atomic step-edges and terraces, is simply prepared by one-step solidification of liquid Au. The atomic step-edges provoke the anisotropic adsorption energy of the TMD cluster, eventually leading to the growth of coherently aligned TMD grains over the whole region. The aligned TMD grains are merged without producing grain boundaries and form the single-crystal TMD films. Furthermore, the growth of several TMD monolayer films, including WS₂, WSe₂, MoS₂, the MoSe₂/WSe₂ heterostructure, and W_1−xMo_xS₂ alloys is demonstrated, indicating that the atomic sawtooth surface could be employed as a universal growth template. This strategy provides a general avenue for the single-crystal growth of diatomic van der Waals heterostructures on a wafer scale, to further facilitate the applications of TMDs in post-silicon technology.