Van der Waals growth of monolayer transition metal dichalcogenide superconductors on ultra-flat graphene

Abstract Two-dimensional (2D) superconductors have desirable physical properties and a wide range of potential applications. However, many 2D superconducting materials have poor structural integrity and performance at thicknesses down to monolayer. Therefore, they are still hardly exploited in large-scale practical applications. In this study, we demonstrate a growth strategy based on the two-step vapor deposition process and van der Waals (vdW) ultra-flat graphene as a buffer layer, and thereafter realize the wafer-scale monolayer transition metal dichalcogenide (TMD) films, especially for 2D TMD superconductors. By comparing different non-vdW and vdW growth substrates, we demonstrate that ultra-flat graphene films provide an atomically smooth surface and effectively isolates oxygen-dangling bonds, and finally promote the superconducting behaviours of monolayer NbSe2 and TaS2 films. This growth strategy could also be extended to other wafer-scale TMD films and be of both fundamental and technological significance in the development of wafer-scale monolayer TMD-based devices.