Releasing the epitaxial oxide heterostructures from substrate constraints
leads to the emergence of various correlated electronic phases and paves the
way for integrations with advanced semiconductor technologies. Identifying a
suitable water-soluble sacrificial layer, compatible with the high-quality
epitaxial growth of oxide heterostructures, is currently the key to the
development of large-scale freestanding oxide membranes. In this study, we
unveil the super-tetragonal Sr4Al2O7 (SAOT) as a promising water-soluble
sacrificial layer. The distinct low-symmetric crystal structure of SAOT enables
a superior capability to sustain epitaxial strain, thus allowing for broad
tunability in lattice constants. The resultant structural coherency and
defect-free interface in perovskite ABO3/SAOT heterostructures effectively
restrain crack formations during the water-assisted release of freestanding
oxide membranes. For a variety of non-ferroelectric oxide membranes, the
crack-free areas can span up to a few millimeters in length scale. These
compelling features, combined with the inherent high-water solubility, make
SAOT a versatile and feasible sacrificial layer for producing high-quality
freestanding oxide membranes, thereby boosting their potential for innovative
oxide electronics and flexible device designs.Comment: 5 figures and SI, it is the second version of this manuscrip