Surface-diffusion-limited growth of atomically thin WS2 crystals from core–shell nuclei

Abstract

Atomically thin transition metal dichalcogenides (TMDs) have recently attracted great attention since the unique and fascinating physical properties have been found in various TMDs, implying potential applications in next-generation devices. The progress towards developing new functional and high-performance devices based on TMDs, however, is limited by the difficulty in producing large-area monolayer TMDs due to a lack of knowledge of the growth processes of monolayer TMDs. In this work, we have investigated the growth processes of monolayer WS₂ crystals using a thermal chemical vapor deposition method, in which the growth conditions were adjusted in a systematic manner. It was found that, after forming WO₃–WS₂ core–shell nanoparticles as nucleation sites on a substrate, the growth of three-dimensional WS₂ islands proceeds by ripening and crystallization processes. Lateral growth of monolayer WS₂ crystals subsequently occurs by the surface diffusion process of adatoms toward the step edge of the three-dimensional WS₂ islands. Our results provide understanding of the growth processes of monolayer WS₂ by using chemical vapor deposition methods.