Sodium-Mediated Low-Temperature Synthesis of Monolayers of Molybdenum Disulfide for Nanoscale Optoelectronic Devices

Monolayers of molybdenum disulfide are of vital importance in the fabrication of optical and nanoelectronic devices. The development of thin and low-cost devices has increased the demand for synthesis processes. Usually, the synthesis of molybdenum disulfide monolayers requires temperatures of approximately 800 degrees C, which is a drawback for the applications mentioned above. Here, we propose a route using the atmospheric pressure chemical vapor deposition technique to grow monolayers of MoS2 at 550 degrees C mediated by using sodium as a catalyst. We produced single crystals and polycrystalline films by controlling the NaNO3/MoO3 catalyst/precursor ratio and the growth time. Using first-principles calculations, we determined that sodium was the nucleation site of the growth process. The precursor's ratio is crucial to decrease the formation energy and the synthesis temperature. First-principles calculations and experiments showed that the ideal precursor ratio was 0.3 and that the synthesis temperature should be decreased by 250 degrees C. We investigated the monolayers with optical microscopy, high-resolution scanning transmission electron microscopy, Xray photoelectron spectroscopy, atomic force microscopy, Raman spectroscopy, photoluminescence spectroscopy, and transport experiments. The optical and electrical performances were comparable to those of monolayers grown at higher temperatures. We believe that a low-temperature synthesis recipe is essential to drive the fabrication of nanoscale optoelectronic devices.