Controllable Synthesis of Large-Area MoSe2 Monolayer Films and Bilayer Crystals

Two-dimensional transition-metal dichalcogenides (TMDs) have attracted significant attention due to their unique layer-dependent electronic properties. Yet the growth of large-area TMDs with controllable layers has remained challenging. In this paper, we report the robust synthesis of large-area monolayer MoSe2 films using confined chemical vapor deposition. The size of monolayer MoSe2 films can reach approximately 1 cm. We systematically investigated the influence of growth temperature, gas flow, the Se/Mo ratio, and sodium chloride on the synthesis process. Additionally, we propose a method for growing bilayer AA and AB-stacked MoSe2. Bilayer MoSe2 nanoribbon, twisted bilayer MoSe2, and substrate-mediated aligned bilayer MoSe2 are also produced. Distinct optical properties observed in the Raman and photoluminescence spectra of bilayer MoSe2 indicate different interlayer interactions. Our study enhances the understanding of the synthesis mechanisms behind monolayer and bilayer TMD materials and provides insights into controlling interlayer interaction in few-layer TMDs.