2D sandwiches, artificial layered building blocks for multifunctional materials (2D-sandwich)

The possibility to create new materials bottom-up was enhanced via the stacking of atomically thin layers of two-dimensional (2D) materials with van der Waals interactions (vdWIs). Unfortunately, the downside of vdWIs is the, in general, weak electronical and mechanical interaction between the individual layers. This hinders the creation of multiferroic materials working at ambient conditions, which are despite extensive research still very scarce, from stacked layers with vdWIs. This research aims to create a new 2D building block: the 2D sandwich. This is a layered heterostructure with a strong interaction between the sandwich's individual layers mediated via an ionic or multivalent bond, whereas the interaction with other layers is still solely due to the vdWIs. As the prototype functional material, a 2D magnetoelectric multiferroic sandwich composed of layered transition metal chalcogenides, oxides or iodides will be grown using the modulated elemental reactants method. To tackle the possible sample degradation in the sandwiches, ultra-high vacuum optical surface science spectro-microscopy techniques will be developed to optically probe the 2D multiferroic sandwiches for both magnetism, ferroelectricity and the coupling between them. The concept of open samples will be introduced, facilitating the scientific community with the straightforward verification of the data and accelerate the development of this new class of 2D sandwiches. This project will provide material design strategies that can remove the stringent lattice matching criteria to stack different classes of layered materials and provide these class of layered materials with similar stacking freedom as layered materials with vdWIs. These insights will allow the interbreeding of different classes of layered quantum materials, such as complex oxides, 2D layered crystals with vdWIs, cuprate superconductors or topological insulators or semimetals.