Vapor phase epitaxial growth of ultrathin Nonlayered-CoSe/WSe₂ heterostructure Moiré superlattices

The heterostructure moiré superlattice plays a crucial role in modulating electronic and optical properties through the formation of periodic potential patterns. However, the synthesis of ultrathin 2D heterostructures remains a significant challenge. In this work, ultrathin 2D CoSe/WSe₂ heterostructures were grown via a two-step vapor deposition route. The thickness of nonlayered hexagonal CoSe nanosheets was reduced to 1.7 nm through growth on a 0.79 nm thick WSe₂ nanosheet. Raman spectroscopy analyses indicate the formation of high-quality 2D CoSe/WSe₂ heterostructures. Selected area electron diffraction studies conclusively validate the high-quality single-crystal nature of CoSe and WSe₂ nanosheets within the resultant heterostructures. Scanning transmission electron microscopy studies show that the formed heterostructure exhibits a well-defined moiré superlattice with a periodicity of ∼ 3.96 nm. Additionally, the device based on CoSe/WSe₂ heterostructures with CoSe contacts demonstrates relatively higher on-state current and field-effect mobility compared to the WSe₂ device with Cr/Au contacts. The developed synthesis method for ultrathin CoSe/WSe₂ heterostructures provides a material platform for investigating their diverse properties.