Unfolding The Challenges to Prepare Epitaxial Complex Oxide Freestanding Membranes

The possibility to prepare epitaxial complex oxide freestanding membranes has opened a whole new ground of research to investigate novel phenomena and device concepts envisaging new applications for complex oxides in next generation electronics. The use of the sacrificial layer approach emerged as one of the simplest and most versatile route to prepare complex oxide membranes. Yet, challenges remain on the synthesis level to accurately prepare and nanoengineer many complex oxide compositions, create new interfaces and exotic architectures.
Here it will be discussed the use of chemical methods to prepare high quality and ambient-stable Ca-doped Sr₃Al₂O₆ sacrificial layer [1] to deliver a series of freestanding complex oxide membranes including CoFe₂O₄, La_0.7Sr_0.3MnO₃ and BiFeO₃/ La_0.7Sr_0.3MnO₃ bilayers.
We identified that calcium doping in Sr₃Al₂O₆ has a key role on the stability of the sacrificial and define the subsequent epitaxial growth, strain and interface quality of the functional complex oxide. [2,3] Then it will also be presented a thorough study of the influence of both sacrificial and complex oxide thickness on the strain and mechanical properties of the freestanding membrane.
Finally, we demonstrate that the magnetic, electrical transport and piezoelectric properties of the CoFe₂O₄, La_0.7Sr_0.3MnO₃ and BiFeO₃/ La_0.7Sr_0.3MnO₃ membranes, respectively, are preserved when transferred on flat arbitrary substrates. [4]
Therefore, this study provides an innovative and versatile platform to synthesize transition metal oxide freestanding films and heterostructures that can be integrated in a wide variety of substrates and will empower the search for novel and enhanced properties with many technological benefits.

[1]P Salles, I Caño, R Guzman, C Dore, A Mihi, W Zhou, M.Coll Facile Chemical Route to Prepare Water Soluble Epitaxial Sr₃Al₂O₆ Sacrificial Layers for Freestanding Oxides Advanced Materials Interfaces, 8, 2001643 (2021)
[2] P Salles, R Guzmán, D Zanders, A Quintana, I Fina, F. Sanchez, W Zhou, M.Coll Bendable polycrystalline and magnetic CoFe₂O₄ membranes by chemical methods, ACS Appl. Mater. Interfaces, 14, 12845-12854 (2022)
[3] P. Salles, R. Guzman, A. Barrera, M. Ramis, J. M.Caicedo, A. Palau, W. Zhou, M. Coll On the Role of the Sr_{3− x}Ca_xAl₂O₆ Sacrificial Layer Composition in Epitaxial La_{0. 7}Sr_{0. 3}MnO₃ Membranes Advanced Functional Materials 33, 2304059(2023)
[4]P. Salles, M. Coll et al. Multifunctional epitaxial BiFeO₃ membranes for flexible applications Under evaluation (2023)