How a trapeziform flake of monolayer WS2 formed on SiO2(1 0 0)? A first-principle study

The two-dimensional (2D) transitional-metal dichalcogenides (TMDCs) have attracted widespread attention due to their unique properties. Single crystal substrates have been previously reported for regulating the orientation as well as tailoring the structure of 2D TMDCs. However, the underlying growth mechanism is still not fully understood and the controlled growth is hard to achieve due to inadequate theoretical guidance. Therefore, we investigate the growth process and growth mechanism of monolayer WS on SiO(1 0 0) by the first-principle calculations. Considering the effect of temperature and pressure, the WS is confirmed to be the most dominant precursor for monolayer WS on SiO(1 0 0) in the chemical vapor deposition growth. The density of states of WS on SiO(1 0 0) reveals the predominant interaction between W and O. The anisotropic diffusion energy barrier of WS on SiO(1 0 0) explores that the x direction growth is preferential. The 0° and 60° are two dominant growth directions for the controlled monolayer WS. Therefore, the WS grows into trapezoidal shape and merges into a monolayer WS. We can offer a theoretical support for growing highly aligned monolayer WS and contribute to a deep understanding of the growth mechanism which is instructive for further experiment.