Programming heterophase structure in two-dimensional palladium telluride by reaction diffusion

Two-dimensional heterophase structures integrate distinct crystalline phases to enable novel electronic and quantum functionalities through atomic-scale interfaces, yet their controlled synthesis remains challenging due to difficulties in stabilizing metastable phases and achieving atomically defined interfaces. Here, we presented a reaction-diffusion-based approach for the spatially controlled fabrication of Pd-Te heterostructures with tailored phase compositions. By designing a vertical Pd/Te architecture and precisely regulating the Pd:Te ratio, we suppressed undesired in-plane diffusion and achieved selective phase formation through solid-state reactions. By employing an in situ optical-monitoring chemical vapor deposition strategy and subsequently characterizing the samples by aberration-corrected scanning transmission electron microscopy after the reaction, we revealed that interfacial diffusion-driven by local stoichiometric deviations-triggered phase transformations and interface migration. This process was quantitatively described via Fick’s law. We demonstrated the synthesis of patterned heterophase structures with atomically sharp interfaces and diverse geometries. Our work elucidates the complex diffusion mechanism and validates reaction diffusion as a novel, feasible strategy for the fabrication of heterophase structures, thereby providing a fresh pathway for advancing phase engineering.