Mechanism of substrate-induced anisotropic growth of monolayer WS2 by kinetic Monte Carlo simulations

Abstract

Controlled anisotropic growth of two-dimensional materials provides an approach for the synthesis of large single crystals and nanoribbons, which are promising for applications as low-dimensional semiconductors and in next-generation optoelectronic devices. In particular, the anisotropic growth of transition metal dichalcogenides induced by the substrate is of great interest due to its operability. To date, however, their substrate-induced anisotropic growth is typically driven by the optimization of experimental parameters without uncovering the fundamental mechanism. Here, the anisotropic growth of monolayer tungsten disulfide on an ST-X quartz substrate is achieved by chemical vapor deposition, and the mechanism of substrate-induced anisotropic growth is examined by kinetic Monte Carlo simulations. Results show that, besides the variation of substrate adsorption, the chalcogen to metal (C/M) ratio is a major contributor to the large growth anisotropy and the polarization of undergrowth and overgrowth; either perfect isotropy or high anisotropy can be expected when the C/M ratio equals 2.0 by properly controlling the linear relationship between gas flux and temperature.WS 2 : anisotropic growth on quartzThe anisotropic growth of WS2 is governed by the chalcogen to metal ratio. A team led by Gaofeng Wang at Hangzhou Dianzi University established a substrate-sensitive kinetic Monte Carlo (kMC) model that accounts for the local substrate effects on adsorption, desorption, and diffusion processes, to study the growth anisotropy in atomically thin transition metal dichalcogenides. Using the representative case of chemical vapor deposition growth of monolayer WS2 on ST-X quartz, the physical mechanism of substrate-induced anisotropic growth was investigated using first-principles calculations to obtain the energy parameters for modeling the kinetic events, followed by kinetic quantum Monte Carlo simulations within the kMC framework. The driving force of the anisotropic growth behavior was found to be the chalcogen to metal ratio, which could be controlled by tailoring the gas flux and temperature.