Nucleation and Growth of Monolayer MoS₂ at Multisteps of MoO₂ Crystals by Sulfurization

Two-dimensional (2D) materials and their heterostructures are promising for next-generation optoelectronics, spintronics, valleytronics, and electronics. Despite recent progress in various growth studies of 2D materials, mechanical exfoliation of flakes is still the most common method to obtain high-quality 2D materials because precisely controlling material growth and synthesizing a single domain during the growth process of 2D materials, for the desired shape and quality, is challenging. Here, we report the nucleation and growth behaviors of monolayer MoS 2 by sulfurizing a faceted monoclinic MoO 2 crystal. The MoS 2 layers nucleated at the thickness steps of the MoO 2 crystal and grew epitaxially with crystalline correlation to the MoO 2 surface. The epitaxially grown MoS 2 layer expands outwardly on the SiO 2 substrate, resulting in a monolayer single-crystal film, despite multiple nucleations of MoS 2 layers on the MoO 2 surface owing to several thickness steps. Although the photoluminescence of MoS 2 is quenched owing to efficient charge transfer between MoS 2 and metallic MoO 2, the MoS 2 stretched out to the SiO 2 substrate shows a high carrier mobility of (15 cm 2 V –1 s –1 ), indicating that a high-quality monolayer MoS 2 film can be grown using the MoO 2 crystal as a seed and precursor. Our work shows a method to grow high-quality MoS 2 using a faceted MoO 2 crystal and provides a deeper understanding of the nucleation and growth of 2D materials on a step-like surface.