In-plane heterojuctions formed from two monolayer semiconductors represent the finest control of electrons in condensed matter and have attracted significant interest. Various device studies have shown the effectiveness of such structures to control electronic processes, illustrating their potentials for electronic and optoelectronic applications. However, information about the physical mechanisms of charge carrier transfer across the junctions is still rare, mainly due to the lack of adequate experimental techniques. Here we show that transient absorption measurements with high spatial and temporal resolution can be used to directly monitor such transfer processes. We studied MoS2-MoSe2 in-plane heterostructures fabricated by chemical vapor deposition and lithographic patterning followed by laser-generated vapor sulfurization. Transient absorption measurements in reflection geometry revealed evidence of exciton transfer from MoS2 to MoSe2. By comparing the experimental data with a simulation, we extracted an exciton transfer velocity of 104 m s-1. These results provide valuable information for understanding and controlling in-plane carrier transfer in two-dimensional lateral heterostructures for their electronic and optoelectronic applications.
Keywords: electron transfer; transient absorption; transition metal dichalcogenide; two-dimensional material; van der Waals interface.