Superior Strain-Adapted Sacrificial Layer for the Synthesis of Freestanding Perovskite Oxide Films

Freestanding perovskite oxide films possess extra features of structural tunability and stacking ability when exfoliated from rigid substrates, providing potential applications in silicon-based semiconductors and flexible electronics. Well epitaxial growth on sacrificial layers is crucial to preserve fascinating physical properties in freestanding oxide membranes. However, the weak strain adaptability of sacrificial layers limits their coherent epitaxial growth on different substrates. Here, we demonstrate a simple perovskite sacrificial layer of SrMnO₃ (SMO) with superior strain adaptability, capable of being epitaxially grown on an ultrabroad spectrum of substrates with lattice constants ranging from 3.715 Å to 3.946 Å. An atomically flat SMO has been employed to synthesize diverse crack-free freestanding single-crystal perovskite oxides on a millimeter scale. The SMO sacrificial layer exhibits a high dissolution rate of 3.1 mm²/min. LaAlO₃ (LAO), SrTiO₃ (STO), SrRuO₃ (SRO), and BiFeO₃ (BFO) are typical examples and are transferred intact to silicon wafers or flexible substrates. The intrinsic ferromagnetic and ferroelectric properties are well-maintained in freestanding SRO and BFO membranes, respectively. Freestanding STO and LAO membranes can serve as transferable heteroepitaxy surfaces for perovskite oxide films, which is demonstrated by the coherent epitaxial growth of the widely used ferromagnetic La_0.7Sr_0.3MnO₃ films with a different strain state. Superior strain adaptability and ultrafast dissolution rate make SMO a prevailing sacrificial layer for synthesizing high-quality freestanding perovskite oxides with a wider range of lattice parameters.