Epitaxially grown single-crystalline SrTiO3 membranes using a solution-processed, amorphous SrCa2Al2O6 sacrificial layer

Abstract

Water-soluble sacrificial layers based on epitaxially grown, single crystalline (Ca, Sr, Ba)₃Al₂O₆ layers are widely used for creating free-standing perovskite oxide membranes. However, obtaining these sacrificial layers with intricate stoichiometry remains a challenge, especially for molecular beam epitaxy (MBE). In this study, we demonstrate the hybrid MBE growth of epitaxial, single crystalline SrTiO₃ films using a solution processed, amorphous SrCa₂Al₂O₆ sacrificial layer onto SrTiO₃ (001) substrates. Prior to the growth, oxygen plasma exposure was used to first create the crystalline SrCa₂Al₂O₆ layer with well-defined surface crystallinity. Utilizing reflection high energy electron diffraction, X-ray diffraction, and atomic force microscopy, we observe an atomic layer-by-layer growth of epitaxial, single crystalline SrTiO₃ films on the SrCa₂Al₂O₆ layer with atomically smooth surfaces. The SrCa₂Al₂O₆ layer was subsequently dissolved in deionized water to create free-standing SrTiO₃ membranes that were transferred onto a metal-coated Si wafer. Membranes created with Sr-deficiency revealed ferroelectric-like behavior measured using piezo-force microscopy whereas stoichiometric films retained paraelectric-like behavior. These findings underscore the viability of using ex situ deposited amorphous SrCa₂Al₂O₆ for epitaxial, single crystalline growth, as well as the importance of point defects in determining the ferroic properties in membranes.