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Sandhya Susarla1 2 Luiz Tizei2 Alberto Zobelli2 Odile Stephan2 Pulickel Ajayan1

1, Rice University, Houston, Texas, United States
2, Laboratoire de physique des solides, Université Paris-Sud, Orsay, , France

Transition metal dichalcogenide (TMD) heterostructures, both lateral and vertical, create atomically thin p-n junctions that have potential application as photodetectors, LED and solar cells.1,2 The type of interface of TMD heterostructures is critical for all these applications and gives rise to interesting phenomena like ultrafast charge transfer and strong interlayer coupling.3,4 At present, all these effects are probed by photoluminescence (PL), Raman spectroscopy and pump probe spectroscopy at a micronic resolution. Using electron beam spectroscopy in a scanning transmission electron microscope (STEM) instead of optical light spectroscopy can improve the spatial resolution limit up to 1 nm by which the interesting effects happening at the atomic scale could easily be observed in correlation with structural and morphological information.5 In the present work, two electron spectroscopic techniques, Cathodoluminescence (CL) and low loss electron energy loss spectroscopy (EELS) in STEM mode have been used to probe the optical properties such as band gap and exciton states at the interface of laterally confined MoS2/WS2 heterostructure. The optical properties were observed in both absorption and emission, allowing the determination of possible Stoke shifts at high spatial resolution.
Keywords: low loss EELS, Cathodoluminescene, STEM, lateral heterostructures
References:
1. Novoselov, K. S., Mishchenko, A., Carvalho, A., Neto, A. H. C. & Road, O. 2D materials and van der Waals heterostructures. Science (80-. ). 353, (2016).
2. Liu, Y. et al. Van der Waals heterostructures and devices. Nat. Rev. Mater. 1, 16042 (2016).
3. Hong, X. et al. Ultrafast charge transfer in atomically thin MoS2/WS2 heterostructures. Nat Nano 9, 682–686 (2014).
4. Fang, H. et al. Strong interlayer coupling in van der Waals heterostructures built from single-layer chalcogenides. Proc. Natl. Acad. Sci. U. S. A. 111, 6198–202 (2014).
5. Kociak, M. & Zagonel, L. F. Cathodoluminescence in scanning transmission electron microscope. Ultramicroscopy 177, 14–19 (2017).

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