3D architectures of single-crystalline complex oxides

Controlling the structure of a material over a wide range of scales has been extensively pursued because the structure dictates its function. Here, we explore the formation of 3D structures at almost a millimetre scale using single-crystal complex oxides, which has been challenging because of the brittle nature of oxides. Our scheme is to release epitaxial oxide thin film heterostructures from the rigid substrate in order to utilise the elastic epitaxial strain as a driving force for self-shaping the flexible free-standing membrane in a controlled manner. Using an epitaxial free-standing LaAlO 3 /SrTiO 3 membrane as a model system, we were able to create various 3D forms, such as cylindrically-rolled, spherically-bent, and helically-twisted structures, where the inversion-symmetry is broken by the strain gradient via flexoelectric effects. Our results will provide opportunities not only to broaden the application of functional oxides toward flexible electronics, but also to discover new functionalities driven by 3D architectures at various scales. We proposed 3D architectures of complex oxides as a way to derive novel properties: various 3D shapes were formed by self-shaped free-standing membranes, and curvature-induced polarization in an otherwise nonpolar material was observed.