Robust Strain in Freestanding Single-Crystal SrRuO₃ Membranes

Freestanding membranes provide a unique opportunity to integrate complex oxides with mature semiconductor technologies and flexible electronics. It is known that the physical functionalities of complex oxides can be modified by epitaxial strain induced by the underneath substrates. The strain release may degrade the physical properties of the freestanding oxide membranes. Here, we demonstrate that various strain states in the pristine epitaxial films can be well preserved in the freestanding single-crystal SrRuO 3 (SRO) membranes using the sacrificial layers with high lattice flexibility. Tensile and compressive strains are induced by the water-soluble sacrificial layers of Sr 3 Al 2 O 6 (SAO) and Sr 2 CaAl 2 O 6 (SCAO) on SrTiO 3 substrates, respectively. An atomically flat surface morphology and initial strain states are maintained in the freestanding SRO membranes after etching the SAO and SCAO layers in water. In light of this, the electrical and magnetic properties of the SRO membranes are comparable to those of the corresponding strained films before exfoliation but completely different from those of the fully relaxed SRO films. The robust strain in the freestanding membranes offers the ability to integrate the strain-modified functionality of complex oxides with the conventional silicon-based semiconductor or flexible electronics.