| 1. |
- Bretscher, Hope, et al.
(author)
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Rational Passivation of Sulfur Vacancy Defects in Two-Dimensional Transition Metal Dichalcogenides
- 2021
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In: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 15:5, s. 8780-8789
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Journal article (peer-reviewed)abstract
- Structural defects vary the optoelectronic properties of monolayer transition metal dichalcogenides, leading to concerted efforts to control defect type and density via materials growth or postgrowth passivation. Here, we explore a simple chemical treatment that allows on-off switching of low-lying, defect-localized exciton states, leading to tunable emission properties. Using steady-state and ultrafast optical spectroscopy, supported by ab initio calculations, we show that passivation of sulfur vacancy defects, which act as exciton traps in monolayer MoS2 and WS2, allows for controllable and improved mobilities and an increase in photoluminescence up to 275-fold, more than twice the value achieved by other chemical treatments. Our findings suggest a route for simple and rational defect engineering strategies for tunable and switchable electronic and excitonic properties through passivation.
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| 2. |
- Li, Zhaojun, et al.
(author)
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Mechanistic insight into the chemical treatments of monolayer transition metal disulfides for photoluminescence enhancement
- 2021
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In: Nature Communications. - : Springer Nature. - 2041-1723. ; 12:1
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Journal article (peer-reviewed)abstract
- There is a growing interest in obtaining high quality monolayer transition metal disulfides for optoelectronic applications. Surface treatments using a range of chemicals have proven effective to improve the photoluminescence yield of these materials. However, the underlying mechanism for the photoluminescence enhancement is not clear, which prevents a rational design of passivation strategies. Here, a simple and effective approach to significantly enhance the photoluminescence is demonstrated by using a family of cation donors, which we show to be much more effective than commonly used p-dopants. We develop a detailed mechanistic picture for the action of these cation donors and demonstrate that one of them, bis(trifluoromethane)sulfonimide lithium salt (Li-TFSI), enhances the photoluminescence of both MoS2 and WS2 to a level double that of the currently best performing super-acid trifluoromethanesulfonimide (H-TFSI) treatment. In addition, the ionic salts used in our treatments are compatible with greener solvents and are easier to handle than super-acids, providing the possibility of performing treatments during device fabrication. This work sets up rational selection rules for ionic chemicals to passivate transition metal disulfides and increases their potential in practical optoelectronic applications. The low photoluminescence of monolayer transition metal disulfides remains a challenge for their optoelectronic application. Here the authors present an effective and green method to enhance the photoluminescence of monolayer MoS2 and WS2, and a detailed mechanistic picture of the treatments.
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