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

The heterostructure moire 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 moire superlattice with a periodicity of similar to 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.