Mechanism of Alkali Metal Compound-Promoted Growth of Monolayer MoS2: Eutectic Intermediates

Monolayer MoS2, processing flexibility and remarkable physical properties derived from its direct bandgap feature, has been endowed to be one of the potential materials for practical applications such as integrated circuits and logic devices. Recently, a facile CVD method using alkali metal compounds as promoters attracted a lot of attention. Here, we systematically investigated the mechanism of alkali metal compound-promoted growth of monolayer MoS2 by CVD and proposed a eutectic intermediate model. In the presence of alkali metal compounds, large monolayer MoS2 was obtained, regardless of the anions. However, nonalkali metal compounds did not promote the growth of monolayer MoS2. We proposed that the formation of eutectic intermediates, containing alkali metal molybdates and molybdenum oxides, played a crucial role in promoting the growth of monolayer MoS2. It is because the low melting point of eutectic intermediates could facilitate their mobility, favoring less nuclei and lateral growth. The proposal of the eutectic intermediates model could not only contribute to growing ultralarge monolayer MoS2 and other 2D materials but also inspire new ideas about growing 2D materials based on low melting point and high mobility of eutectic intermediates.