Theoretical Study On The Growth Of Two-dimensional Transition-metal Dichalcogenides Films

Two-dimensional(2D)materials have become a hot research topic for researchers and industry in recent years due to their amazing properties in electronic,optical,mechanical,chemical,and thermal aspects.In particular,transition metal dihalides(TMDs)have become a very popular 2D material because of their distinctive physical properties,such as ideal band gaps and high optical absorption coefficients,which may have applications in multiple fields.Experimentally,researchers have found some special properties exhibited by 2D materials,which are often closely related to their morphology.This inspires us to synthesize 2D materials with specific properties by controlling their growth morphology.Chemical vapor deposition(CVD)is a common method of 2D material synthesis.Recently,researchers have observed special long strip-shaped TMDs when using CVD to prepare TMDs,and these long strip-shaped TMDs have been found to exhibit excellent advantages in electrocatalytic and optoelectronic applications.However,the essential conditions for the formation of such specially shaped TMDs and the microscopic growth mechanism have not been thoroughly studied yet,which is related to the experimental realization of the targeted synthesis of specific shapes and the precise regulation of material properties.Therefore,it is a very important issue to understand the growth mechanism of TMDs with specific morphologies from a theoretical point of view.To solve this problem,a kinetic Monte Carlo(kMC)model for the growth of TMDs is developed in this paper.We abstract from experimental phenomena to find the physical mechanism behind them and effectively simplify the complex growth events.This simplification makes the model more general and saves the time cost in simulation and provides the possibility of growth simulation of materials at a large scale.Based on the simulations of the kMC model,we successfully reproduce several key phenomena in the experiments,such as the formation of classical triangular TMDs,the growth of long strip TMDs with controlled orientation,and the aspect ratio regulation of long strip TMDs.This indicates that our model successfully reflects the main physical processes of the actual growth.Moreover,by analyzing the kinetic growth process,we reveal two determining factors leading to the formation of these long strip-like TMDs,the lattice mismatch caused by the difference between the lattice symmetry of the TMDs and the symmetry of the substrate,and the suitable interaction strength between the TMDs and the substrate.In addition,using the phase diagram of the system obtained from the simulation,we found that the interaction strength,substrate cell aspect ratio,and cell size can be adjusted to obtain long stripes of TMDs,and the aspect ratio of TMDs can also be controlled to precisely regulate their properties.In this paper,the physical mechanism of the growth of long strip TMDs is explored through theoretical model simulations.The results deepen the theoretical understanding of the formation and growth control of TMDs and may inspire new ideas for the development of new materials with special properties,which is of great significance to further promote the development of two-dimensional materials.