Atomic Level Insight into the Nucleation of SnSe Thin Films Using Graphene Mask in Molecular Beam Epitaxy: ReaxFF Molecular Dynamics Simulations

The controlled growth of thin films plays a crucial role in tailoring material properties for diverse applications. Overcoming challenges in thin film fabrication, such as island growth modes and morphological irregularities, is essential for optimizing overall material and device performance. Here, we report the atomic-level investigation of the controlled nucleation of SnSe on a MgO(001) substrate through molecular beam epitaxy, using ReaxFF reactive molecular dynamics simulations. Using graphene masks for selective area nucleation, we explore the effects of mask usage and mask thickness on the morphology of the deposited SnSe material. A key finding is that a single-layer graphene mask promotes the formation of the crystalline P3̅m1 phase of SnSe₂ during nucleation. Additionally, by using multiple thermostats in our simulations we can mitigate gas-phase Sn_xSe_y clustering and ensure a more accurate representation of molecular beam epitaxy conditions. The incorporation of multiple thermostats in the simulations contributes to a deeper understanding of the nucleation mechanism. Overall, this study provides atomic-level insight into the selective area nucleation technique for thin film deposition processes.