Exciton Dynamics in Suspended Monolayer and Few-Layer MoS<sub>2</sub> 2D Crystals

Shi, Hongyan; Yan, Rusen; Bertolazzi, Simone; Brivio, Jacopo; Gao, Bo; Kis, András; Jena, Debdeep; Xing, Huili Grace; Huang, Libai

doi:10.1021/nn303973r

Cited by 744 publications

(919 citation statements)

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“…While they hypothesized that at such short time scale the initially generated excitons may not be thermalized, recent measurements with femtosecond resolution showed that thermalization for ∼3 eV excitation occurs in less than 1 ps. 18 For this reason, the signal observed in ref 21 can be attributed to the intrinsic radiative decay time of the A exciton at 4 K. This is confirmed by the work from Lagarde et al, 22 who recently measured the timeresolved PL of monolayer MoS 2 excited resonantly at the A exciton and observed a PL decay time of 4.5 ps, in excellent agreement with our computed value.…”

supporting

confidence: 91%

“…They tentatively attribute the 2 ps time to exciton trapping at defects, the 75 ps to hot carrier thermalization, and the 0.85 ns to radiative A exciton recombination. 18 We obtain an effective radiative lifetime of 0.82 ns at room temperature, which is in excellent agreement with the 0.85 ns decay signal observed experimentally. This result indicates that the room-temperature radiative lifetime is of order 1 ns at room temperature and corresponds to the longer PL decay component observed in time-resolved PL experiments.…”

supporting

confidence: 88%

“…21,22 Room-temperature transient absorption experiments by Shi et al 18 on suspended monolayer MoS 2 show a triexponential decay signal with time constants of 2 ps, 75 ps, and 0.85 ns. They tentatively attribute the 2 ps time to exciton trapping at defects, the 75 ps to hot carrier thermalization, and the 0.85 ns to radiative A exciton recombination.…”

mentioning

confidence: 98%

“…The energies of the bright and dark excitons with A and B character are shown in Figure 2b. The bright and dark exciton character stems, respectively, from dipole-allowed and dipoleforbidden transitions at K. Because exciton thermalization occurs on a faster (∼500 fs) 18,20 time scale than radiative recombination in monolayer TMDs, the radiative recombination of the bright A exciton is the main process contributing to PL. 12 In the W-based monolayers, we find a rich series of mostly dark excitons 38 at energies between the A and B peaks (A * excitons in Figure 2b) made up by holes from the VBM and electrons from the CBM and the band above the CBM.…”

mentioning

confidence: 99%

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Exciton Radiative Lifetimes in Two-Dimensional Transition Metal Dichalcogenides

Palummo¹,

2015

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Light emission in two-dimensional (2D) transition metal dichalcogenides (TMDs) changes significantly with the number of layers and stacking sequence. While the electronic structure and optical absorption are well understood in 2D-TMDs, much less is known about exciton dynamics and radiative recombination. Here, we show firstprinciples calculations of intrinsic exciton radiative lifetimes at low temperature (4 K) and room temperature (300 K) in TMD monolayers with the chemical formula MX 2 (X = Mo, W, and X = S, Se), as well as in bilayer and bulk MoS 2 and in two MX 2 heterobilayers. Our results elucidate the time scale and microscopic origin of light emission in TMDs. We find radiative lifetimes of a few picoseconds at low temperature and a few nanoseconds at room temperature in the monolayers and slower radiative recombination in bulk and bilayer than in monolayer MoS 2 . The MoS 2 /WS 2 and MoSe 2 /WSe 2 heterobilayers exhibit very long-lived (∼20−30 ns at room temperature) interlayer excitons constituted by electrons localized on the Mo-based and holes on the W-based monolayer. The wide radiative lifetime tunability, together with the ability shown here to predict radiative lifetimes from computations, hold unique potential to manipulate excitons in TMDs and their heterostructures for application in optoelectronics and solar energy conversion. KEYWORDS: Monolayer materials, transition metal dichalcogenides, luminescence, radiative lifetime, excitons, optoelectronics T wo-dimensional (2D) transition metal dichalcogenides (TMDs) are promising materials for ultrathin electronic, optoelectronic, photocatalytic, and photovoltaic devices. 1−8 Out of approximately 40 existing TMDs, 9,10 some have received particular attention due to their semiconducting nature and tunable band gap. In particular, group 6 monolayer TMDs with chemical formula MX 2 (M = Mo, W and X = S, Se) are direct gap semiconductors with relatively intense photoluminescence (PL), while bilayers and thicker multilayers exhibit indirect gap and weaker PL. 1,10−17 The peculiar nature of the excited states has stimulated intense research efforts to investigate exciton dynamics and radiative/nonradiative lifetimes in TMDs. 13,18−24 Recent time-resolved experiments found a range of characteristic times for exciton dynamics in monolayer TMDs, including fast (1−10 ps) recombination attributed to exciton trapping at defects, and slower processes on a 0.1−1 ns time scale interpreted as radiative exciton recombination. 18,20−22 However, the attribution of the observed signals to radiatiave and nonradiative processes can be ambiguous in time-resolved spectroscopies since defects and impurities can modulate the excited state dynamics. In TMDs, the interpretation of time signals and comparison among different experiments is further complicated by the use of micrometer-size flakes where the edges can play a significant role in exciton recombination. This situation has stimulated an ongoing quest for the intrinsic time scale of exciton recombinatio...

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supporting

confidence: 91%

supporting

confidence: 88%

mentioning

confidence: 98%

mentioning

confidence: 99%

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Exciton Radiative Lifetimes in Two-Dimensional Transition Metal Dichalcogenides

Palummo¹,

2015

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“…The behaviors of excitons and trions have strong influence on optical phenomena including absorption and light emission. Reported by many groups, spin‐orbit coupling effect induces the valence band edge of monolayer MoS 2 to split, and the maximum of split locates at the K point of the Brillouin zone, while the minimum of conduction band also locates at K point 38, 39, 40. At the K point of Brillouin zone, the split transition band corresponds to two strongly bound A exciton and B exciton, of which the split band transition energy in monolayer MoS 2 is approximately 1.92eV and 2.08eV, and induces two separated absorption peaks in red to near infrared region.…”

Section: Plasmonic Properties Of 2d Nanomaterialsmentioning

confidence: 99%

Plasmonics of 2D Nanomaterials: Properties and Applications

et al. 2017

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Plasmonics has developed for decades in the field of condensed matter physics and optics. Based on the classical Maxwell theory, collective excitations exhibit profound light‐matter interaction properties beyond classical physics in lots of material systems. With the development of nanofabrication and characterization technology, ultra‐thin two‐dimensional (2D) nanomaterials attract tremendous interest and show exceptional plasmonic properties. Here, we elaborate the advanced optical properties of 2D materials especially graphene and monolayer molybdenum disulfide (MoS2), review the plasmonic properties of graphene, and discuss the coupling effect in hybrid 2D nanomaterials. Then, the plasmonic tuning methods of 2D nanomaterials are presented from theoretical models to experimental investigations. Furthermore, we reveal the potential applications in photocatalysis, photovoltaics and photodetections, based on the development of 2D nanomaterials, we make a prospect for the future theoretical physics and practical applications.

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