Reactive Force Field for P/Sn/I System: Atomistic Insight into the Early Stage of Black Phosphorus and Phosphorene Synthesis Process

Black phosphorus and its two dimensional counterpart, phosphorene, are typically synthesized through chemical vapor transport using Sn and I2 additives. Chemical vapor deposition synthesis of phosphorene and allotropes is still yet not well understood. Investigating the atomistic mechanisms underlying phosphorus transport and early stage processes is difficult experimentally. In this study, a reactive force field for the PSnI system was developed and applied using ReaxFF based molecular dynamics to explore the early stage phase of the pre nucleation relevant to BP-phosphorene growth. The force field parameters were trained on a comprehensive quantum mechanical dataset covering bond dissociation, angle and torsion profiles, and tin condensed phase equation of state and cluster formation energies, showing strong agreement in both gas and condensed phases. We demonstrate that iodine and density together control phosphorus recombination. Under low density, atomic phosphorus dominates with minimal clustering. Adding I2 greatly increases P-P recombination, promotes the formation of PxIy motifs, and transient SnxPyIz compounds. Higher density systems favor the formation of larger Px clusters and support the development of ternary SnxPyIz compounds that grow by capturing transported phosphorus. At the highest density, the system produces condensed, Hittorf like phosphorus structures at the edges of SnxPyIz clusters, along with BP-like hexagons stabilized by iodine that may act as nucleation seeds. These results offer an atomistic view of transport and early stage steps in BP synthesis and provide a practical reactive model for studying growth conditions and additive effects in BP phosphorene vapor synthesis.