Strain Gradient Control in Oxide Membranes*

The successful synthesis of freestanding membranes by etching a water-soluble buffer layer [1] has provided new opportunities to investigate mechanical and electromechanical properties of a variety of materials [2]. Beyond the classical mechanics of membranes in the thin limit, another interesting topic is to study how mechanical degrees of freedom could affect the quantum nature of materials at the nanoscale. Freestanding membranes, with an extremely high tunability of strain and strain gradients compared to bulk materials, could bring us unprecedented piezoelectric and flexoelectric responses [3,4]. This could also result in the emergence of new states of matter and/or potential applications. Hence, an experimental platform to apply strain and strain gradient onto freestanding membranes, either locally or globally, is of particular interest. 

Here, I will present our investigation of realizing strain gradients on freestanding thin film oxide membranes with different geometries. Using an Atomic Force Microscope (AFM) setup, we can mechanically achieve high local strain to the point of fracture, and sample scalable Young’s modulus and fracture statistics [5,6]. We have also observed the preservation of manipulation of strain through the formation of bistable bubbles on TEM grid holes, and these bistable states can be actuated. Extreme fixed strain gradients through wrinkle formation is also investigated. 

These geometries can serve as a new general platform to access and control local strain gradients and bistable mechanical states mechanically, optically, electrically or a combination of the above.