Ze Hua

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.

The development of nanostructured LiFePO4 (LFP) electrodes represents a prominent research direction in the Li-ion battery field, owing to its intrinsic advantages such as high theoretical capacity and excellent structural stability. Studying the electrochemical reaction mechanisms at the atomic scale by in situ TEM is essential; however, the mechanisms of ion migration on LFP have not yet been fully elucidated. We report atomic-scale in situ TEM studies of delithiation and lithiation in multi-particle LFP coupled to a Li-rich garnet (LLZNO) solid electrolyte. During delithiation, LFP converts to a metastable L0.5FP via a periodicity-doubling mechanism (every second layer) accompanied by the emergence of a solid-solution zone, and we directly observe interparticle Li+ transport that drives reversible LFP–L0.5FP–LFP cycles. Conversely, under reductive bias, lithiation proceeds by an interface-dominated crystalline–amorphous transformation, identifying amorphization as a primary particle-level failure pathway. Tracking the structural evolution of LiFePO4 at the atomic scale during (de)lithiation provides key insights into its kinetic limitations and phase stability, which is essential for optimizing its electrochemical performance.

Due to complex thermodynamic and kinetic mechanism, phase engineering in nanomaterials is often limited by restricted phases and small-scale synthesis, hindering material diversity and scalability. Here, we demonstrate the exploration to unlock the stoichiometry as a degree of freedom for phase engineering in the Pd-Te binary compound. By reducing diffusion rates, we effectively engineer the stoichiometry of the reactants. We visualize the kinetic process, showing the stoichiometry transition from Pd₁₀Te₃ to PdTe₂ through a sequential multi-step nucleation process. In total, five distinct phases are identified, demonstrating the potential to enhance phase diversity by fine-tuning stoichiometry. By controlling spatially uniform nucleation and halting the phase transition at precise points, we achieve stoichiometry-controllable wafer-scale growth. Notably, four of these phases exhibit superconducting properties. Our findings offer insights into the mechanism of phase transition through stoichiometry engineering, enabling the expansion of the phase library in nanomaterials and advancing scalable applications.

Understanding the physical and chemical processes at the interfaces of metals and topological insulators is crucial for the development of the next generation of topological quantum devices. Here, we report the discovery of robust superconductivity in Pd/Bi₂Se₃ bilayers fabricated by sputtering Pd on the surface of Bi₂Se₃. Through transmission electron microscopy measurements, we identify that the observed interfacial superconductivity originates from the diffusion of Pd into Bi₂Se₃. In the diffusion region, Pd chemically reacts with Bi₂Se₃ and forms a layer of PdBiSe, a known superconductor with a bulk transition temperature of 1.5 K. Our work provides a method for the introduction of superconductivity into Bi₂Se₃, laying the foundation for the development of sophisticated Bi₂Se₃-based topological devices.