Electrical Transport Platform for Strongly Corrugated Complex Oxide Membranes

Within the conventional framework of thin film synthesis, stabilization of high quality single crystalline films requires a substrate with the correct lattice symmetry and reasonable lattice constant matching. The use of a water-soluble oxide buffer layer, however, has alleviated this requirement such that one can lift off an epitaxially grown film from the substrate and transfer it in freestanding membrane form onto an arbitrary platform [1]. Free from epitaxial constraints, some oxide membranes bonded to elastic substrates have been mechanically stretched up to large tensile strain states [2,3]. Another fascinating, though relatively unexplored, aspect of freestanding membranes is that they can accommodate a high degree of bending or buckling out-of-plane with respect to their original two-dimensional basal plane. Conceptually similar three-dimensional microstructures have been fabricated in polycrystalline films to provide new functionalities [4,5]. In this study, we present a unique experimental methodology to process single crystalline oxide membranes in a corrugated morphology and package them into electrical transport devices. A variety of corrugated geometries are realized by bonding membranes onto elastomers and applying compressive force in a controlled fashion. With large compression, the radii of curvature at the peaks and troughs become smaller than a micrometer – the regime where the membrane thickness is a few percent in size compared to the bending radii and the amplitude of out-of-plane protrusions becomes comparable or larger than the corrugation period. In addition, we introduce our approach of enhancing the mechanical stability of corrugated membranes in a shape-preserving fashion and depositing micro-scale electrodes without any lithography. Employing these techniques, we investigate the evolution of electrical transport response in a magnetic metal as the degree of corrugation intensifies. We furthermore note that the spatial gradation of the lattice constant is expected in corrugated membranes and would generate a substantial strain gradient, which has shown potential to induce significant modifications in physical properties [6-8]. The technical developments presented herein will help explore interesting strain gradient effects as well as open new device functionalities.

References
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[8] W. Peng et al., Nat. Phys. 20, 450 (2024)