Atomic Lift-Off of Wafer-Scale Single-Crystalline Gold Membranes Enables Buried-Interface Epitaxy for Flexible Oxide Electronics

Flexible oxide electronics require inorganic semiconductors that maintain high-performance under bending, yet scalable approaches to wafer-scale single-crystalline (SC) oxide films and, critically, atomically sharp metal/oxide contacts remain limited. Here, we introduce a buried-interface epitaxy strategy based on atomic lift-off of epitaxial metal films to create atomically defined SC metal/oxide heterostructures in flexible architectures. We fabricate 2-in. freestanding SC Au(111) membranes and employ film-flipping to expose the originally buried Au/Si epitaxial interface as an intrinsically atomically flat growth surface. This converts conventional surface deposition into interface deposition, enabling wafer-scale epitaxial Cu2O(111)/Au with a flat interface. The interface-deposited flexible Cu2O exhibits nearly 2-fold higher carrier mobility and photocurrent, while maintaining stable transport under bending. Flexible Cu2O photocathodes further exhibit 1.6 times higher full-angle light harvesting and 5.6 times higher photocurrent-to-mass metrics compared with rigid counterparts. This work establishes freestanding SC metals as transferable epitaxial templates for flexible oxide electronics and energy devices.