Centimeter-Scale CVD Growth of Highly Crystalline Single-Layer MoS Film with Spatial Homogeneity and the Visualization of Grain Boundaries.

MoS monolayer attracts considerable attention due to its semiconducting nature with a direct bandgap which can be tuned by various approaches. Yet a controllable and low-cost method to produce large-scale, high-quality, and uniform MoS monolayer continuous film, which is of crucial importance for practical applications and optical measurements, remains a great challenge. Most previously reported MoS monolayer films had limited crystalline sizes, and the high density of grain boundaries inside the films greatly affected the electrical properties. Herein, we demonstrate that highly crystalline MoS monolayer film with spatial size up to centimeters can be obtained via a facile chemical vapor deposition method with solid-phase precursors. This growth strategy contains selected precursor and controlled diffusion rate, giving rise to the high quality of the film. The well-defined grain boundaries inside the continuous film, which are invisible under an optical microscope, can be clearly detected in photoluminescence mapping and atomic force microscope phase images, with a low density of ∼0.04 μm. Transmission electron microscopy combined with selected area electron diffraction measurements further confirm the high structural homogeneity of the MoS monolayer film with large crystalline sizes. Electrical measurements show uniform and promising performance of the transistors made from the MoS monolayer film. The carrier mobility remains high at large channel lengths. This work opens a new pathway toward electronic and optical applications, and fundamental growth mechanism as well, of the MoS monolayer.