Freestanding Oxide Membranes for Epitaxial Ferroelectric Heterojunctions

Abstract

Since facile routes to fabricate freestanding oxide membraneswerepreviously established, tremendous efforts have been made to furtherimprove their crystallinity, and fascinating physical properties havebeen also reported in heterointegrated freestanding membranes. Here,we demonstrate our synthetic recipe to manufacture highly crystallineperovskite SrRuO3 freestanding membranes using new infinite-layerperovskite SrCuO2 sacrificial layers. To accomplish this,SrRuO3/SrCuO2 bilayer thin films are epitaxiallygrown on SrTiO3 (001) substrates, and the topmost SrRuO3 layer is chemically exfoliated by etching the SrCuO2 template layer. The as-exfoliated SrRuO3 membranes aremechanically transferred to various nonoxide substrates for the subsequentBaTiO(3) film growth. Finally, freestanding heteroepitaxialjunctions of ferroelectric BaTiO3 and metallic SrRuO3 are realized, exhibiting robust ferroelectricity. Intriguingly,the enhancement of piezoelectric responses is identified in freestandingBaTiO(3)/SrRuO3 heterojunctions with mixed ferroelectricdomain states. Our approaches will offer more opportunities to developheteroepitaxial freestanding oxide membranes with high crystallinityand enhanced functionality.