Abstract
The excitonic states of transition metal dichalcogenide (TMD) monolayers are heavily influenced by their external dielectric environment and depend on the substrate used. In this work, various wide band gap dielectric materials, namely hexagonal boron nitride (h-BN) and amorphous silicon nitride (Si3N4), under different configurations as support or encapsulation material for WS2 monolayers, are investigated to disentangle the factors contributing to inhomogeneous broadening of exciton absorption lines in TMDs using electron energy loss spectroscopy in a scanning transmission electron microscope. In addition, monolayer roughness in each configuration was determined from tilt series of electron diffraction patterns by assessing the broadening of diffraction spots by comparison with simulations. From our experiments, the main factors that play a role in linewidth broadening can be classified, in increasing order of importance, by monolayer roughness, surface cleanliness, and substrate-induced charge trapping. Furthermore, because high-energy electrons are used as a probe, electron-beam-induced damage on bare TMD monolayers is also revealed to be responsible for irreversible linewidth increases. h-BN not only provides clean surfaces of TMD monolayers and minimal charge disorder, but can also protect the TMD from irradiation damage. This work provides a better understanding of the mechanisms by which h-BN remains, to date, the most compatible material for 2D material encapsulation, facilitating the realization of intrinsic material properties to their full potential.
Original language | English |
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Article number | 074005 |
Journal | Physical Review Materials |
Volume | 6 |
Issue number | 7 |
DOIs | |
State | Published - Jul 2022 |
Externally published | Yes |
Funding
This project has been funded in part by the National Agency for Research under the program of future investment TEMPOS-CHROMATEM (Reference No. ANR-10-EQPX-50), MAGMA Research Grant No. ANR-16-CE09-0027, and the JCJC grant SpinE (Reference No. ANR-20-CE42-0020), by the National Key Technologies R&D Program of China (Grant No. 2018YFA0306100), and by the European Union's Horizon 2020 research and innovation program under Grant Agreements No. 823717 (ESTEEM3) and No. 101017720 (EBEAM). This work has been supported by Region Île-de-France in the framework of DIM SIRTEQ. F.S. acknowledges support by the China Scholarship Council. A.A. and B.J.C. acknowledge support by the Alexander von Humboldt Foundation. A.A. acknowledges funding from DFG Grant No. AR 1128/1 and NM-ICPS of the DST, Government of India through the I-HUB Quantum Technology Foundation (Pune, India). C.M. would like to acknowledge support through Royal Society University Research Fellowship No. UF160539 and the Research Fellow Enhancement Award No. 2017 (RGF/EA/180090) by the Royal Society UK. K.W. and T.T. acknowledge support from the Elemental Strategy Initiative conducted by MEXT, Japan (Grant No. JPMXP0112101001) and JSPS KAKENHI (Grants No. 19H05790, No. 20H00354, and No. 21H05233). The authors acknowledge S. Rohart for AFM measurements on thin films.