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In this contribution, we use heavy ion irradiation and photoluminescence (PL) spectroscopy to demonstrate that defects can be used to tailor the optical properties of two-dimensional molybdenum disulfide (MoS 2 ). Sonicated MoS 2 flakes were deposited onto Si/SiO 2 substrate and subjected to 3 MeV Au 2+ ion irradiation at room temperature to fluences ranging from 1 × 10 12 to 1 × 10 16 cm −2 . We demonstrate that irradiation-induced defects can control optical excitations in the inner core shell of MoS 2 by binding A 1s - and B 1s -excitons, and correlate the exciton peaks to the specific defects introduced with irradiation. The systematic increase of ion fluence produced different defect densities in MoS 2 , which were estimated using B/A exciton ratios and progressively increased with ion fluence. We show that up to the fluences of 1 × 10 14 cm −2 , the MoS 2 lattice remains crystalline and defect densities can be controlled, whereas at higher fluences (≥1 × 10 15 cm −2 ), the large number of introduced defects distorts the excitonic structure of the material. In addition to controlling excitons, defects were used to split bound and free trions, and we demonstrate that at higher fluences (1 × 10 15 cm −2 ), both free and bound trions can be observed in the same PL spectrum. Most importantly, the lifetimes of these states exceed trion and exciton lifetimes in pristine MoS 2 , and PL spectra of irradiated MoS 2 remains unchanged weeks after irradiation experiments. Thus, this work demonstrated the feasibility of engineering novel optical behaviors in low-dimensional materials using heavy ion irradiation. The insights gained from this study will aid in understanding the many-body interactions in low-dimensional materials and may ultimately be used to develop novel materials for optoelectronic applications.
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Disorder of excitons and trions in monolayer MoSe 2
The optical spectra of transition metal dichalcogenide monolayers are dominated by excitons and trions. Here, we establish the dependence of these optical transitions on the disorder from hyperspectral imaging of h-BN encapsulated monolayer MoSe 2 . While both exciton and trion energies vary spatially, these two quantities are almost perfectly correlated, with spatial variation in the trion binding energy of only ∼0.18 meV. In contrast, variation in the energy splitting between the two lowest energy exciton states is one order of magnitude larger at ∼1.7 meV. Statistical analysis and theoretical modeling reveal that disorder results from dielectric and bandgap fluctuations, not electrostatic fluctuations. Our results shed light on disorder in high quality TMDC monolayers, its impact on optical transitions, and the many-body nature of excitons and trions.
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- Award ID(s):
- 1719875
- PAR ID:
- 10411255
- Date Published:
- Journal Name:
- The Journal of Chemical Physics
- Volume:
- 157
- Issue:
- 21
- ISSN:
- 0021-9606
- Page Range / eLocation ID:
- 211101
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1063/5.0108001
