Atomic Level Insight into the Nucleation of SnSe Thin\nFilms Using Graphene Mask in Molecular Beam Epitaxy: ReaxFF Molecular\nDynamics Simulations

The\ncontrolled growth of thin films plays a crucial role in tailoring\nmaterial properties for diverse applications. Overcoming challenges\nin thin film fabrication, such as island growth modes and morphological\nirregularities, is essential for optimizing overall material and device\nperformance. Here, we report the atomic-level investigation of the\ncontrolled nucleation of SnSe on a MgO(001) substrate through molecular\nbeam epitaxy, using ReaxFF reactive molecular dynamics simulations.\nUsing graphene masks for selective area nucleation, we explore the\neffects of mask usage and mask thickness on the morphology of the\ndeposited SnSe material. A key finding is that a single-layer graphene\nmask promotes the formation of the crystalline <i>P</i>3̅<i>m</i>1 phase of SnSe<sub>2</sub> during nucleation. Additionally,\nby using multiple thermostats in our simulations we can mitigate gas-phase\nSn<sub><i>x</i></sub>Se<sub><i>y</i></sub> clustering\nand ensure a more accurate representation of molecular beam epitaxy\nconditions. The incorporation of multiple thermostats in the simulations\ncontributes to a deeper understanding of the nucleation mechanism.\nOverall, this study provides atomic-level insight into the selective\narea nucleation technique for thin film deposition processes.