Stacking and Twisting of Freestanding Complex Oxide Thin Films

The integration of dissimilar materials in heterostructures has long been a cornerstone of modern materials science - seminal examples are the two-dimensional (2D) materials and van der Waals heterostructures. Recently, new methods have been developed, which enable the realization of ultra-thin freestanding oxide films approaching the 2D limit. Oxides offer new degrees of freedom, due to the strong electronic interactions, especially the 3d orbitals, which give rise to rich exotic phases. Inspired by this progress, we have developed a new platform for assembling ultra-thin freestanding oxide thin films with different materials and orientations into artificial stacks with heterointerfaces. We show that the oxide stacks can be tailored by controlling the stacking sequences as well as the twist angle between the constituent layers with atomically sharp interfaces, leading to distinct moiré patterns in the transmission electron micrographs of the full stacks. Stacking and twisting has been recognized as a key degree of structural freedom in 2D materials but until now has never been realized for oxide materials. Our approach opens unexplored avenues for fabricating artificial 3D oxide stacking structure with freestanding membranes across a broad range of complex oxide crystal structures with functionalities not available in conventional 2D materials. This article is protected by copyright. All rights reserved.