Emergent Strain Engineering of Freestanding Oxide Membranes
Freestanding membranes have driven a profound evolution of strain engineering by fundamentally overcoming the substrate clamping effect. This structural degree of freedom enables the introduction of spatially complex, reversible, and giant strain fields into the membranes via mechanical manipulations such as stretching, bending, and interfacial twisting, ultimately facilitating the modulation of diverse physical properties. This review systematically discusses recent experimental and theoretical advances in the field, highlighting the modulation of physical properties via uniaxial/biaxial strain, strain gradients, and oxide twist. These mechanical strain strategies substantially broaden the range of achievable material properties, furthermore provide fundamentally new pathways for realizing unconventional mechanical behaviors, inducing emergent polar topological structures, and exploring correlated electronic states. Finally, this review summarizes current methodologies for implementing emergent strain engineering of oxide membranes, delves into the profound impacts of spatially complex strain on the fundamental physical properties of freestanding oxides, and offers a forward-looking perspective on the tremendous opportunities and challenges in this rapidly evolving field.