Nanoscale ultrafast dynamics in molecular/TMD heterostructure imaged by time-resolved photoemission electron microscopy

Advancements in synthesizing and constructing organic-inorganic 2D van der Waals heterostructures have enabled modular design of novel properties due to the extensive chemical tunability of molecular building blocks. However, these heterostructures and interfaces can have considerable spatial variation, which modifies electronic structure and interfacial charge transfer on the nanoscale and determines functionality. To establish a nanoscale morphology-property relationship as well as understand how Moiré superlattice impacts charge transfer, we investigated an atomically thin perylene diimide (PDI) film deposited on polycrystalline single layer MoS₂ using photoemission electron microscopy (PEEM) with spatial resolution as good as 25 nm. We were able to image molecular orientation of PDI crystals and calculate the relative angles with respect to MoS₂ domains. We mapped out spatially-evolving excited state lifetimes from time- and energy-resolved PEEM. Statistical analysis shows that the nanoscale variation in the excited state dynamics can be attributed to the non-epitaxial PDI growth, which introduces distinct lattice mismatch that structurally modifies interlayer coupling. Our results provide insights on structural variations underpinning the twist angle dependent electronic properties and promote a molecular framework for desired optoelectronic applications.