Interfacial Robustness in Fe₂TiO₅/ZnO Core-Shell Nanodendrites Revealed by STXM-Ptychography for Enhanced...

The atomic configuration and spatially resolved electronic structure of epitaxially grown core-shell Fe₂TiO₅/ZnO/SnO₂ heterojunction nanodendrites are systematically investigated using synchrotron-based X-ray absorption spectroscopy, scanning transmission X-ray microscopy combined with Ptychography, and complementary structural characterization techniques. Fe and Ti K-edge extended X-ray absorption fine-structure analyses reveal pronounced interfacial tensile strain at the Fe₂TiO₅/ZnO interface, manifested by elongation of nearest-neighbor Fe-O and Ti-O bonds, and contraction of next-nearest-neighbor Fe-Fe/Ti (Ti-Ti/Fe) distances. High-resolution transmission electron microscopy and spatially resolved scanning transmission X-ray microscopy-Ptychography further uncover abundant oxygen-related defects in the surface/shell region, which induce partial reduction of Ti⁴⁺ to Ti³⁺ and establish a distinct valence gradient across the heterojunction nanodendrites. The resulting valence gradient intrinsically establishes an interfacial built-in electric field, which drives directional charge separation and suppresses carrier recombination. Furthermore, Fe/Ti L₃- and O K-edge Ptychography-XANES (X-ray absorption near-edge structure) measurements reveal interfacial electron hopping between the Ti³⁺ and Fe³⁺ 3d states mediated by O 2p orbitals via a superexchange interaction, enabling more efficient electron transport across the interface. The cooperative interplay of interfacial strain, defect-induced valence modulation, built-in electric field formation, and superexchange-assisted electron transport markedly enhances carrier extraction efficiency and interfacial kinetics, leading to improved photoelectrochemical performance. These findings establish interfacial strain and valence-state engineering as effective design strategies for advanced heterojunction photoelectrodes in solar-driven energy conversion.