Two-dimensional (2D) Janus transition metal dichalcogenides (Janus 2D TMD) are specific planar materials with different top and bottom termination layers. This new class of materials thus exhibits broken structural symmetry in the out-of-plane direction, predicted to result in exotic new properties, such as vertical piezoelectricity, Rashba spin splitting and unexpected exciton behavior. However, fabrication of Janus 2D TMD is an extremely challenging task, owing to the need of an epitaxial atomic replacement within classical 2D TMD. This project is designed to achieve chalcogenide exchange within classical TMDs by two novel approaches. In the first approach, we will utilize an electron beam as tool to alter the top layer, allowing its selective selenization/sulfurization. In the second approach, we aim to utilize increased reactivity in the van der Waals gap to allow for selective chalcogenide exchange within the gap.

Keywords
electron microscopy, 2D materials, in-situ, Janus