The fabrication of freestanding complex oxide membranes: Can we avoid using water?

Recent advances in fabricating scalable two-dimensional or freestanding functional materials have shown promise for their use in modern silicon-based electronics and future technologies. A growing interest is in creating freestanding complex oxide membranes using new methods like epitaxial lift-off and mechanical exfoliation to enhance their quality and integrity. Despite these advances, it remains challenging to consistently produce high-quality freestanding oxide membranes on a large scale for practical use. This perspective paper provides an overview of release-and-transfer techniques for fabricating freestanding single-crystalline complex oxide layers, which are initially grown epitaxially. Specifically, we systematically explore the advantages and disadvantages of water-assisted exfoliation of freestanding oxide layers, which have been widely adopted using a water-soluble sacrificial layer in recent years. Furthermore, we compare this approach with other methods to navigate future directions in oxide layer transfer technology, considering material selections, fabrication processes, and functionalization strategies. Graphical abstract: Seeking a water-free epitaxial lift-off process: (1) Growth: An epitaxial film is grown on a sacrificial layer placed on a single-crystal substrate (top left). (2) Release: The film is released from the substrate without using a water-based sacrificial layer (top right). (3) Transfer: The film is transferred onto a new platform (bottom right). (4) Support Removal: A polymer support is removed from the film (bottom left).