Speaker
Description
Two-dimensional (2D) van der Waals materials and their heterostructures with molecular materials are a highly promising class of materials due to their low dimensional nature and highly tuneable electronic properties that lead to rich charge and spin carrier dynamics. Beyond chemical tunability, their optoelectronic properties can be dynamically modified on ultrafast timescales through the formation of transient charge-separated states. [1]
In this work, we investigate hybrid heterostructures consisting of metal phthalocyanine (MPc) molecular films deposited on bulk transition metal dichalcogenides (TMDCs), specifically a FePc monolayer on WSe$_2$. Interfacial interaction leads to an altered energy level alignment in the electronic band structure, with the FePc HOMO sitting in between the spin-split valence states of WSe$_2$. Additionally, the distinct orbital character of the iron centre induces a long-range ordering of the molecular layer, resulting in a localisation of molecular bands in momentum space.
Building on this, we explore the optically induced ultrafast charge carrier dynamics using time- and angle-resolved photoemission spectroscopy (trARPES) in a VIS-pump, XUV-probe scheme. This approach enables us to simultaneously track excited electron populations and the corresponding hole dynamics on femtosecond timescales. By disentangling intra- and interlayer processes via their distinct momentum-space signatures, we reveal the temporal evolution of charge transfer across the FePc/WSe$_2$ interface, demonstrating how transient charge separation leads to ultrafast modifications of the interfacial energy-level alignment.
[1] B. Arnoldi et al., Nat.Commun. 15, 3573 (2024)