NANOscientific

A study on the morphological, mechanical and electrostatic properties of transferred single crystalline La₀.₇ Sr₀.₃ MnO₃ freestanding membranes

Martí Ramis¹, Markos Paradinas¹, José Manuel Caicedo², Pol Sallés³, Roger Guzman¹, Mariona Coll¹

¹ Institut de Ciència de Materials de Barcelona (ICMAB CSIC) Campus UAB, Bellaterra, Barcelona 08193, Spain
² Catalan Institute of Nanoscience and Nanotechnology (ICN2) Campus UAB, Bellaterra, Barcelona 08193, Spain
³ European Synchrotron Radiation Facility | ESRF · Div ision of Experiments, Grenoble 38000, France

The remarkable properties of complex oxides, including colossal magnetoresistance, superconductivity or multiferroicity, arise from the interplay between multiple degrees of freedom such as spin, charge, orbit and lattice. Releasing single-crystalline oxide films from their growth substrates enables new ways to control and study these couplings, potentially unlocking emergent phenomena for novel applications. For instance, engineering topographical patterns in freestanding membranes can yield unique mechanical responses and strain-driven effects at the nanoscale, paving the way for smart, flexible surfaces [1].

In this study, we fabricate single-crystalline LSMO membranes on polymeric sheets substrates using a sacrificial layer technique [2,3]. By systematically tuning the membrane thickness from 4 nm to 100 nm, we examine its impact on wrinkle formation, mechanical behaviour, local strain distribution and the modulation of surface potential. In particular, we correlate the structure and morphological characteristics of the surfaces with their mechanical and electrostatic responses by combining different AFM methods.

The amplitude and periodicity of LSMO wrinkles, formed upon transfer to suitable elastomeric substrate due to the release of accumulated stress, are found to depend on the film thickness. As the thickness increases, the wrinkle amplitude grows and the wavelength become longer. The mechanical properties are also influenced by the film thickness, and a localized study of the wrinkled membrane reveals that corrugation plays a direct role. Those variation of the film conformation are related to changes on the local strain within the LSMO lattice where the larger the strain the stiffer the LSMO membrane. The atomic-resolution analysis of the structure by Transmission Electron Microscopy (TEM) shows that thicker membranes exhibited more structural defects and a relaxed structure overall, whereas the thinnest membrane displayed a defect-free microstructure with enhanced tetragonality and pronounced vertical strain gradients. Additionally, mapping the electrostatic forces of such membranes by Electrostatic Force Microscopy (EFM) and Kelvin Probe Force Microscopy (KPFM) it enabled to correlate the formation of large strain gradients with a variation in surface potential between wrinkle peaks and valleys.

The ability to fabricate topographical patterns in single-crystalline complex oxide membranes offers a versatile and straightforward platform for strain engineering. Combined with advanced characterization techniques this approach enables a deeper understanding of the interplay between morphology, strain, mechanical and electrostatic properties. Such insights are crucial for the rational design of novel functional materials.

References:
[1] S. S. Raj, R. M. Mathew, et al. Chemistry Select 7, e202200714 (2022)
[2] P. Salles, M. Coll et al. Adv. Mater. Interfaces 8, 2001643 (2021)
[3] P. Salles, M. Coll et al. Adv. Funct. Mater., 33, 2304059 (2023)