Atomic Structure of Vertical and In-Plane Heterostructures Formed by Two- Dimensional MoS2 and ReS2

Since the advent of graphene in 2004, there has been tremendous progress in the field of two-dimensional (2D) materials. Examples include the discovery of monolayer direct bandgap semiconductors such as MoS2 and WS2, as well as the integration of multiple 2D materials into heterostructures in various geometries (e.g. vertical and in-plane) [1]. Briefly, vertical heterostructures are obtained by stacking different 2D materials on top of each other with only van der Waals forces present between the layers, whereas lateral heterostructures contain 2D materials that are stitched in their basal plane via covalent bonds. These vertical and in-plane heterostructures are ideal candidates to study layer-layer interactions in 2D materials, often leading to improved performance in targeted applications such as optoelectronics [2]. However, the performance of heterostructures is highly dependent on the structure and quality of the interface between the layers [3]. For example, 2D materials that are mechanically stacked on top of each other to prepare vertical heterostructures are prone to contamination at the interface, which originates from the transfer process. Moreover, control over the relative orientation of the layers is also difficult [3]. This can be mitigated by directly growing vertical heterostructures using chemical vapor deposition (CVD), a process that has better control over the interface and relative epitaxy.