| Project Detail |
Recent advances in the fabrication of freestanding single-crystal oxide thin films have opened up the possibility of stacking ferroelectric layers, similar to 2D van der Waals materials, and forming artificial heterostructures. This perspective offers a wealth of unique and advantageous properties that are not available in either 2D single crystals or bulk materials. The proposed research project aims at exploring the van der Waals epitaxy of ferroelectric oxides, which to date has remained largely unexplored. The project has two main goals:• First, it aims at pioneering the realization of van der Waals epitaxy of ferroelectric oxides with unexplored electrostatic boundary conditions. The project will focus on the design and characterization of stacks (i) of oppositely polarized ferroelectric membranes, (ii) of non-collinear polarized ferroelectric membranes and (iii) with arbitrary twist angles. Using a combination of atomic-scale characterization and phase-field simulations, we will reveal the mechanisms leading to the formation of topological textures and their superelastic properties, and advance the understanding of 2D van der Waals ferroelectric material systems. • Second, this project aims to contribute to the development of the 4D-STEM capabilities at Empa for orientation and strain mapping and phase imaging methods, with particular focus in differential phase contrast and ptychography for electric field mapping, ultra-high resolution and depth sectioning. For this purpose, a state-of-the-art probe aberration corrected scanning transmission electron microscope (STEM) equipped with a hybrid-pixel direct detector installed at Empas Electron Microscopy Center will be used.The research objectives will be achieved using a variety of cutting-edge imaging and spectroscopy STEM techniques, with a special focus on 4D-STEM. The work will be performed by a 4-year doctoral student working in close collaboration with the applicant. The project goals will be achieved by addressing three work packages (WPs):WP1: Innovative van der Waals ferroelectric stacks will be fabricated and samples in plan-view and cross-section configuration will be prepared for S/TEM characterization.WP2: The formation of complex polarization textures in the 2D van der Walls ferroelectric superlattices will be investigated by 4D-STEM with special emphasis on the role of ferroelectric and strain states.WP3: The domain structure of the stacks will be mimicked by phase-field simulations in order to predict the domain evolution during domain switching and to obtain an accurate description of the ferroelectric and mechanical properties of the freestanding ferroelectric stacks. In summary, this project will contribute both to scientific advancement in the emerging field of 2D van der Walls ferroelectric materials, crucial for their integration in neuromorphic computing and foldable and wearable electronic devices, and to establishing at Empa a solid 4D-STEM know-how to investigate quantum materials, ensuring that electron microscopy research in Switzerland can remain internationally competitive. |
