Long-term stable excitons, bound pairs of electrons and holes, in van der Waals materials were found to be handled at room temperature, paving the way to develop optoelectronic/photonic devices for future high-speed communication technology. To miniaturize and integrate such functions to achieve highly efficient excitonic devices, understanding and manipulation of exciton dynamics in the nanoscale structures is absolutely essential. Since the spatial resolution of the optical techniques, which have been mainly used in the research of this field, is limited to μm to several tens of nm, the introduction of new technology is strongly desired. Here, we demonstrate a method to probe and visualize neutral excitons using the laser-combined multiprobe scanning tunneling microscopy (STM) system. Ultrafast dynamics of excitons in the nanostructures produced in an in-plane WS2/WSe2 heterostructure, such as dynamics in the ps region of many-body effects under high density and spatial variation in the effect of local defects on lifetime, was successfully revealed with a spatial resolution of 1 nm order. This method is expected to accelerate research on exciton dynamics and the development of applications directly based on the experimental results of nanoscale.

Optical pump-probe scanning tunneling microscopy (OPP-STM) has enabled the measurement of ultrafast dynamics in real space. However, the use of a pulse picker to extract selected laser pulses to realize delay-time modulation, which efficiently suppresses the thermal expansion problems, limits the availability of time-resolved measurement. Here, we present a more applicable type of OPP-STM that we have developed. Two externally triggerable pulse lasers were used to produce pump and probe pulses, and wide-range delay-time modulation was simply realized by adjusting the timing of the pulses. The performance of this new type of OPP-STM was demonstrated by measuring the carrier dynamics in WSe2.