Transition Metal Dichalcogenide (TMD) monolayers can be stacked to form heterostructures (HS), representing an opportunity to create new materials which combine and tailor the electronic and optical properties of the constituent layers. TMD HS with Type II band alignment, the conduction band minimum and valence band maximum reside in different layers, resulting in Interlayer Charge Transfer (ICT) following optical excitation of an intralayer exciton. ICT refers to two processes - Interlayer Hole Transfer (IHT) and Interlayer Electron Transfer (IET) - which both proceed on ultrafast timescales. Standard ultrafast spectroscopic techniques, such as ultrafast transient absorption, are unable to clearly resolve the sub-100 fs timescales of ICT due to the inverse relationship of pump spectral selectivity and pump pulse duration. To unambiguously resolve the sub-100 fs timescales of ICT we perform Two-Dimensional Electronic Spectroscopy (2DES) on a large-area WS2/MoS2 HS with a 22 fs instrument response function. 2DES affords simultaneously high frequency and temporal resolution, allowing us to resolve ultrafast IHT and IET from the same measurement which we fit to reveal time scales of 34 ± 14 and 69 ± 9 fs, respectively. These measurements are compared to control experiments on the constituent monolayers WS2 and MoS2. 2DES is a promising technique for resolving sub-100 fs dynamics such ICT as demonstrated here, but is also well suited for further disentangling different energy and charge transfer processes on the sub-ps timescale.

Disentangling of interlayer electron and hole transfer dynamics in a large area TMD heterostructures using two-dimensional electronic spectroscopy

ACS Spring 2022

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