Abstract: Freestanding single-crystalline oxide membranes provide an emerging platform for investigating novel physical properties and enabling functional integration in nanoelectronic devices. However, cracks are commonly observed in freestanding oxide membranes, limiting their potential properties and applications. Here, we report an “amorphous-fill-and-crystallize” strategy to achieve atom-by-atom crack healing (with widths up to 10 nm) in freestanding crystalline BaTiO₃ (BTO) membranes using focused electron beam irradiation. The high quality of the healed regions is confirmed through geometric phase analysis, atomic resolution electron energy loss spectroscopy mapping, and through-focus high-angle annular dark-field imaging. By employing in situ atomic-scale monitoring, we demonstrate that crack healing is dominated by interfacial bridging across the crack, with a critical bridging size of 5-6 unit cells. Furthermore, we directly observe evidence of interaction across the crack interface. Finally, we successfully extend this approach to heal cracks in freestanding La_0.67Sr_0.33MnO₃ (LSMO) membranes and fabricate a nanoscale LSMO/BTO/LSMO heterojunction. This approach provides a viable route for atomic-precision crack healing and the fabrication of functional oxide heterostructures.

Key words: Functional oxide, Crack, Healing, Interface, Electron matter interaction