Probing exciton dispersions of freestanding monolayer WSe2 by momentum resolved electron energy loss spectroscopy

Abstract

Momentum resolved electron energy-loss spectroscopy was used to measure the dispersions of excitons in a free-standing monolayer of WSe2. Besides the parabolically dispersed valley excitons, a sub-gap dispersive exciton was observed at specific q values for the first time. The simultaneous STEM-ADF imaging of the local probed areas suggests that this sub-gap exciton is attributed to the prolific Se vacancies.

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• Nano-optics of transition metal dichalcogenides and their van der Waals heterostructures with electron spectroscopies
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