Complex-oxide materials exhibit a vast range of functional properties desirable for next-generation electronic, spintronic, magnetoelectric, neuromorphic, and energy conversion storage devices1–4. Their physical functionalities can be coupled by stacking layers of such materials to create heterostructures and can be further boosted by applying strain5–7. The predominant method for heterogeneous integration and application of strain has been through heteroepitaxy, which drastically limits the possible material combinations and the ability to integrate complex oxides with mature semiconductor technologies. Moreover, key physical properties of complex-oxide thin films, such as piezoelectricity and magnetostriction, are severely reduced by the substrate clamping effect. Here we demonstrate a universal mechanical exfoliation method of producing freestanding single-crystalline membranes made from a wide range of complex-oxide materials including perovskite, spinel and garnet crystal structures with varying crystallographic orientations. In addition, we create artificial heterostructures and hybridize their physical properties by directly stacking such freestanding membranes with different crystal structures and orientations, which is not possible using conventional methods. Our results establish a platform for stacking and coupling three-dimensional structures, akin to two-dimensional material-based heterostructures, for enhancing device functionalities8,9.
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Acknowledgements The team at MIT and the University of Wisconsin-Madison acknowledge support primarily by the Defense Advanced Research Projects Agency (DARPA) (award number 027049-00001, W. Carters and J. Gimlett). The work at University of Wisconsin-Madison is also supported by the Army Research Office through grant W911NF-17-1-0462. C.A.R. and J.B. acknowledge support from the SMART Center sponsored by NIST and SRC. J.A.R. and S. Subramanian acknowledge support from NSF CAREER award 1453924. J.H.L. acknowledges support from a National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (number 2018R1D1A1B07050484). The work at Cornell University is supported by the National Science Foundation (Platform for the Accelerated Realization, Analysis and Discovery of Interface Materials (PARADIM)) under Cooperative Agreement Number DMR-1539918. J.K. thanks the Masdar Institute/Khalifa University, the LG Electronics R&D Center, Amore Pacific, the LAM Research Foundation, Analogue Devices, and Rocky Mountain Vacuum Tech for general support. We are grateful to J. Li for assistance with the TEM measurements. We especially thank R. Bliem and B. Yildiz of MIT for early help in preparation of STO films.
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