Lateral Interfaces between Monolayer MoS Edges and Armchair Graphene Nanoribbons on Au(111).

The realization of electronic devices based on heterostructures of metallic, semiconducting, or insulating two-dimensional materials relies on the ability to form structurally coherent and clean interfaces between them, vertically or laterally. Lateral two-dimensional heterostructures that fuse together two different materials in a well-controlled manner have attracted recent attention, but the methods to form seamless interfaces between structurally dissimilar materials, such as graphene and transition-metal dichalcogenides (TMDCs), are still limited. Here, we investigate the structure of the lateral interfaces that arise between monolayer MoS flakes on Au(111) and two families of armchair graphene nanoribbons (GNRs) created through on-surface assisted Ullmann coupling using regular organobromine precursors for GNR synthesis. We find that parallel alignment between the GNR armchair edge and MoS leads to van der Waals bonded nanoribbons, whereas a perpendicular orientation is characterized by a single phenyl-group of the GNR covalently bonded to S on the edge. The edge-on bonding is facilitated by a hydrogen treatment of the MoS, and temperature control during growth is shown to influence the nanoribbon width and the yield of covalently attached nanoribbons. Interestingly, the temperatures needed to drive the intramolecular dehydrogenation during GNR formation are lowered significantly by the presence of MoS, which we attribute to enhanced hydrogen recombination at the MoS edges. These results are a demonstration of a viable method to make laterally bonded graphene nanostructures to TMDCs to be used in further investigations of two-dimensional heterostructure junctions.