Freestanding Oxide Membranes for Epitaxial Ferroelectric Heterojunctions

Since facile routes to fabricate freestanding oxide membranes were previously established, tremendous efforts have been made to further improve their crystallinity, and fascinating physical properties have been also reported in heterointegrated freestanding membranes. Here, we demonstrate our synthetic recipe to manufacture highly crystalline perovskite SrRuO₃ freestanding membranes using new infinite-layer perovskite SrCuO₂ sacrificial layers. To accomplish this, SrRuO₃/SrCuO₂ bilayer thin films are epitaxially grown on SrTiO₃ (001) substrates, and the topmost SrRuO₃ layer is chemically exfoliated by etching the SrCuO₂ template layer. The as-exfoliated SrRuO₃ membranes are mechanically transferred to various nonoxide substrates for the subsequent BaTiO₃ film growth. Finally, freestanding heteroepitaxial junctions of ferroelectric BaTiO₃ and metallic SrRuO₃ are realized, exhibiting robust ferroelectricity. Intriguingly, the enhancement of piezoelectric responses is identified in freestanding BaTiO₃/SrRuO₃ heterojunctions with mixed ferroelectric domain states. Our approaches will offer more opportunities to develop heteroepitaxial freestanding oxide membranes with high crystallinity and enhanced functionality.