Clamping-layer-mediated strain engineering of electrical transport in freestanding nickelates membranes

Strain engineering serves as an effective approach for tuning the properties of transition metal oxides and thier heterostructures. However, conventional epitaxial approaches are foundmentally constrained by the limited choice of substrates, which restricts the ability to achieve continuous strain modulation. The emergence of freestanding oxide thin films has significantly expanded the scope of strain manipulation, allowing the application of larger tensile strains and the induction of novel functionalities. Nevertheless, current freestanding film technologies face a critical limitation: strain modulation has so far been confined to tensile strain, while the application of compressive strain remains inaccessible. To overcome this challenge, we designed a symmetric tri-layer structure composed of clamping-layer/nickelate/clamping-layer, which enables modulation of the metal-insulator transition (MIT) in freestanding NdNiO₃ (NNO) and LaNiO₃ (LNO) thin films under both tensile and compressive strain. This clamping-layer-mediated strain engineering approach can be readily generalized to other freestanding oxide systems, providing a versatile platform for manipulating the physical properties of freestanding thin films.