Unraveling the Intercalation-Mediated Phase Transformation and Epitaxy at the Mn/MoS ₂ Heterointerface

The integration of functional oxides with two-dimensional (2D) transition metal dichalcogenides (TMDs) is pivotal for next-generation electronics yet remains constrained by aggressive interfacial reactions and interdiffusion. Herein, we resolve the atomic-scale reaction kinetics at the Mn/MoS₂(0001) heterointerface by combining spherical aberration-corrected scanning transmission electron microscopy (STEM) with density functional theory (DFT) calculations. We identify a distinct temperature-dependent pathway that transforms destructive diffusion into precise phase engineering. At 500 °C, Mn cation intercalation serves as the primary driving force, inducing the nucleation of a metastable triclinic MnMoO₅ phase while concurrently triggering a local 2H-to-1T polymorphic transition. Crucially, this intercalation is confined to a self-limiting skin layer, evidenced by a ∼4% <i>c</i>-axis expansion. Elevating the thermal treatment to 600 °C promotes thermodynamic equilibration, facilitating the crystallization of the polar magnetic hexagonal Mn₂Mo₃O₈ phase and the reconstruction of an atomically sharp interface. These findings demonstrate a mechanism for exploiting reactive diffusion to synthesize high-quality, functional oxide/2D heterostructures with chemically distinct, sharp interfaces.