Vapour phase growth and grain boundary structure of molybdenum disulphide atomic layers

Single-layered molybdenum disulphide with a direct bandgap is a promising two-dimensional material that goes beyond graphene for the next generation of nanoelectronics. Here, we report the controlled vapour phase synthesis of molybdenum disulphide atomic layers and elucidate a fundamental mechanism for the nucleation, growth, and grain boundary formation in its crystalline monolayers. Furthermore, a nucleation-controlled strategy is established to systematically promote the formation of large-area, single- and few-layered films. Using high-resolution electron microscopy imaging, the atomic structure and morphology of the grains and their boundaries in the polycrystalline molybdenum disulphide atomic layers are examined, and the primary mechanisms for grain boundary formation are evaluated. Grain boundaries consisting of 5- and 7- member rings are directly observed with atomic resolution, and their energy landscape is investigated via first-principles calculations. The uniformity in thickness, large grain sizes, and excellent electrical performance signify the high quality and scalable synthesis of the molybdenum disulphide atomic layers. Graphene has shown many fascinating properties as asupplement to silicon-based semiconductor technologies1–4.Consequently, great effort has been devoted to the devel-opment and understanding of its synthetic processes5–8. However, graphene’s high leakage current, due to its zero bandgap energy, is not suitable for many applications in electronics and optics9,10. Recent developments in two different classes of materials