  The advancement in thin-film exfoliation for synthesizing oxide membranes has
opened up new possibilities for creating artificially-assembled
heterostructures with structurally and chemically incompatible materials. The
sacrificial layer method is a promising approach to exfoliate as-grown films
from a compatible material system, allowing their integration with dissimilar
materials. Nonetheless, the conventional sacrificial layers often possess
intricate stoichiometry, thereby constraining their practicality and
adaptability, particularly when considering techniques like Molecular Beam
Epitaxy (MBE). This is where easy-to-grow binary alkaline earth metal oxides
with a rock salt crystal structure are useful. These oxides, which include (Mg,
Ca, Sr, Ba)O, can be used as a sacrificial layer covering a much broader range
of lattice parameters compared to conventional sacrificial layers and are
easily dissolvable in deionized water. In this study, we show the epitaxial
growth of single-crystalline perovskite SrTiO3 (STO) on sacrificial layers
consisting of crystalline SrO, BaO, and Ba1-xCaxO films, employing a hybrid MBE
method. Our results highlight the rapid (< 5 minutes) dissolution of the
sacrificial layer when immersed in deionized water, facilitating the
fabrication of millimeter-sized STO membranes. Using high-resolution x-ray
diffraction, atomic-force microscopy, scanning transmission electron
microscopy, impedance spectroscopy, and scattering-type near-field optical
microscopy (SNOM), we demonstrate epitaxial STO membranes with bulk-like
intrinsic dielectric properties. The employment of alkaline earth metal oxides
as sacrificial layers is likely to simplify membrane synthesis, particularly
with MBE, thus expanding research possibilities.
