"A Journey through Flatlands: Interfaces, Defects, and Modified Functionalities in Van der Waals Materials"
Van der Waals solids are materials with strong covalent bonding in a 2D plane but only weak interlayer interactions. This allows their isolation into single two-dimensional molecular sheets, that may be used as ‘building blocks’ to assemble new materials by ‘stacking’ or by growing of dissimilar 2D materials on top of each other. The combination of diverse materials with atomic precision opens new technological paradigms for synthesis of heterostructure materials as well as enabling fundamental studies of interactions between dissimilar materials at the nanoscale. Importantly, because of the atomic-scale dimensions of 2D materials their properties are easily manipulated by external fields, interfaces, and environments and thus allow for manipulation of their properties. This makes van der Waals materials interesting for diverse problems ranging from semiconducting devices to the study of many body physics in reduced dimensions. Moreover, interest in 2D materials has also come from energy related applications in electrochemistry, such as electrocatalysts or batteries. Thus, in recent years, 2D materials have been discovered as decisive nanomaterials for a wide range of fundamental and applied problems. While the field was initiated by mechanical exfoliation of single layers from bulk materials this approach has limited applicability. To enable the study and manipulation of advanced 2D materials, direct growth methods need to be developed. In this talk, I present examples of van der Waals epitaxy of monolayers and heterostructures with the goal of identifying new functionalities in the monolayer limit and to better understand the role of interface interactions for controlling the properties of van der Waals heterostructures. Finally, we also explore the potential of crystal modifications in these material systems for inducing new functionalities.