Two-dimensional bilayer MoS2 flakes with variable size of the upper layer grown by chemical vapor deposition

Abstract

Bilayer transition-metal dichalcogenides, particularly twisted bilayer, provide a promising platform for the exploration of novel fundamental properties and applications in valleytronics and twistronics. Here, we report the growth of two-dimensional (2D) bilayer molybdenum disulfide (MoS2) flakes with varied upper-layer size by a conventional space-confined chemical vapor deposition. The area ratio of upper layer/bottom layer of these bilayer flakes at the difference locations along the gas-flow direction is estimated to be 5% (S1), 35% (S2), 73% (S3), and 100% (S4), respectively. The detailed layer number and optical properties of these samples have been evaluated by AFM, Raman, and PL characterizations. Furthermore, the evolution of area ratio of upper layer/bottom layer is unveiled by the energy and precursors concentration variation along the gas flow direction during the narrow space. Our results provide a feasible approach for the fabrication of 2D bilayer TMDCs crystals that can accelerate the performance study and promising applications.