MOCVD Growth of Large-Scale TMDCs and Heterostructures

Heterostructures (HSs) based on atomically thin two-dimensional transition metal chalcogenides (TMDCs) have gained increasing attention due to their chemical stability and unique interactions between materials, together with the applications in many fields such as electronics and optics Despite the advances in the fabrication of vertical HSs through multiple steps of mechanical exfoliation and transfer, this approach suffers from fabricating 2D HSs on a large scale and precious control of the size, position, and the number of layers. In this study, we studied the large-area direct growth of TMDCs and their HSs (e.g., graphene/TMDC and TMDC/TMDC)using metal-organic chemical vapor deposition. We found that two mechanisms appear in the formation of heterogeneous structures: (1) epitaxial growth within the grain and (2) selective growth on defects. The formation of a two-dimensional heterogeneous structure with unique characteristics was verified by analyzing the structural, bonding, and interaction characteristics between various types of graphene/TMDCs and TMDC/TMDC HSs. We confirmed that the 2D HSs with abrupt heterointerface were uniformly grown over large-area using SEM, TEM, Raman, and PL analysis. By analyzing how the crystallinity of TMDC grown directly on the graphene changes depending on the crystalline direction of the graphene, we confirmed the epitaxial growth tendency in the process of forming heterogeneous structures. In particular, the TMDC HSs selectively grown on graphene defects possesses ion channels comprising (i) van der Waals interlayer gaps for optimal Li+ extraction and (ii) negatively charged vertical inlets for cation attraction.