Layer Rotation-Angle-Dependent Excitonic Absorption in van der Waals Heterostructures Revealed by Electron Energy Loss Spectroscopy.

Pranjal Kumar Gogoi, Yung-Chang Lin, Ryosuke Senga, Hannu-Pekka Komsa, Swee Liang Wong, Dongzhi Chi, Arkady V Krasheninnikov, Lain-Jong Li, Mark B H Breese, Stephen J Pennycook, Andrew T. S. Wee, Kazu Suenaga

Research output: Contribution to journalArticlepeer-review

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Heterostructures comprising van der Waals (vdW) stacked transition metal dichalcogenide (TMDC) monolayers are a fascinating class of two-dimensional (2D) materials. The presence of interlayer excitons, where the electron and the hole remain spatially separated in the two layers due to ultrafast charge transfer, is an intriguing feature of these heterostructures. The optoelectronic functionality of 2D heterostructure devices is critically dependent on the relative rotation angle of the layers. However, the role of the relative rotation angle of the constituent layers on intralayer absorption is not clear yet. Here, we investigate MoS2/WSe2 vdW heterostructures using monochromated low-loss electron energy loss (EEL) spectroscopy combined with aberration-corrected scanning transmission electron microscopy and report that momentum conservation is a critical factor in the intralayer absorption of TMDC vdW heterostructures. The evolution of the intralayer excitonic low-loss EEL spectroscopy peak broadenings as a function of the rotation angle reveals that the interlayer charge transfer rate can be about an order of magnitude faster in the aligned (or anti-aligned) case than in the misaligned cases. These results provide a deeper insight into the role of momentum conservation, one of the fundamental principles governing charge transfer dynamics in 2D vdW heterostructures.
Original languageEnglish (US)
Pages (from-to)9541-9550
Number of pages10
JournalACS nano
Issue number8
StatePublished - Jul 29 2019

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