Growth-Controlled Strain-Driven Epitaxial Spalling of Freestanding Oxide Membranes

Freestanding complex-oxide membranes are promising platforms for heterogeneous integration, strain engineering, and device architectures on non-native substrates. Strain-driven epitaxial spalling offers a sacrificial-layer-free route to such membranes, but its use in complex oxides has so far been explored mainly under fixed growth conditions. Here we show that the formation of freestanding LaAlO3/SrTiO3 micromembranes can be systematically controlled by tuning the pulsed-laser-deposition (PLD) conditions of the LaAlO3 stressor layer. By mapping the membrane formation yield as a function of laser fluence and oxygen background pressure, we identify a process window for reproducible high-yield spalling and correlate it with cracking behavior, membrane release, and microstructural evolution. We show that efficient spalling requires both sufficient elastic-energy accumulation and preservation of a structurally coherent early interface. Low oxygen pressure conditions during the first unit cells as well as low laser fluence during growth promote premature strain relaxation and suppress membrane formation. We also show that, within the optimized growth window, additional perovskite layers can be integrated into the LaAlO3/SrTiO3 architecture while preserving the spalling process, enabling the design of functionalized spalled membranes. We further show that complete spalling, with high-yield membrane formation, is achieved for LaAlO3 thicknesses down to 53-55 nm, substantially reducing the total membrane thickness compared with previous implementations. Finally, we demonstrate that the spalling approach can be extended to selected alternative substrates, including Ca-doped SrTiO3 and Sr2RuO4. These results establish epitaxial spalling as a growth-controlled and interface-sensitive route to structurally complex freestanding oxide micro-membranes.