Nonblinking, Intense Two-Dimensional Light Emitter: Monolayer WS<sub>2</sub> Triangles

Peimyoo, Namphung; Shang, Jingzhi; Cong, Chunxiao; Shen, Xiaonan; Wu, Xiangyang; Yeow, Edwin K. L.; Yu, Ting

doi:10.1021/nn4046002

Cited by 298 publications

(348 citation statements)

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“…These nanocrystals, which are usually found during vapor transportation growth [18], can be assigned to WS 2 . The thickness of 1 L WS 2 can determined to be~0.8 nm from the line profile across the edge ( Figure S2b), which agrees well with the reported thickness of a 1 L WS 2 flake [19].…”

Section: Growth Of Ws 2 /Ti 3 C 2 T X Mxenesupporting

confidence: 87%

“…A Raman spectrum of 1 L WS 2 in Figure 1b is also shown for comparison. At a laser excitation wavelength of 532 nm, the Raman spectra of WS 2 flakes exhibit features of first-order and second-order blended Raman modes, which are similar to previous reports [19,24]. The Raman peak at 417.8 cm −1 can be assigned to A 1g (out-of-plane mode).…”

Section: Optical Characterization Of Ws 2 /Ti 3 C 2 T X Mxenesupporting

confidence: 85%

“…In previous reports of Kim et al [30], Gutierrez et al [3] and Peimyoo et al [19], different authors observed PL enhancement at edges and grain boundaries of CVD (chemical vapor deposition) deposited 1 L WS 2 flakes. They attributed this PL enhancement to the high density of sulphur vacancies at the edges and grain boundaries [3,19,30]. In our study, PL enhancement is observed inside 1 L flake, but absent at its edges (Figures 4a and S5).…”

Section: Optical Characterization Of Ws 2 /Ti 3 C 2 T X Mxenementioning

confidence: 89%

“…The peak at 351.3 cm −1 can be assigned to the blended modes of E 1 2g (in-plane mode) and 2LA mode (M point of first Brillion zone). The Raman peaks at 324.1 and 296.2 cm −1 can be assigned to second order Raman modes of 2LA − E 2 2g and 2LA − 2E 2 2g , respectively [19,24]. As the most distinguishable feature, the intensity of A 1g peak subsequently decreases from LT1 to LT5.…”

Section: Optical Characterization Of Ws 2 /Ti 3 C 2 T X Mxenementioning

confidence: 96%

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Growth of WS2 flakes on Ti3C2Tx Mxene Using Vapor Transportation Routine

Wang

et al. 2018

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Two-dimensional dichalcogenides (TMDs) and mxene junctions had been predicted to possess distinct tunable electronic properties. However, direct synthesis of WS 2 on Ti 3 C 2 T x mxene is still challenging. Herein, we successfully deposited WS 2 onto the surface of Ti 3 C 2 T x mxene by employing the vapor transportation (VT) routine. By modulating pressure and source-sample distance, multilayer and monolayer (1 L) WS 2 flakes were deposited onto the lateral side and top surface of Ti 3 C 2 T x flakes. The 1 L WS 2 flakes growing on lateral side of Ti 3 C 2 T x flake have much higher photoluminescence (PL) intensity than 1 L flakes growing on the top surface. Our study has the potential to benefit the design and preparation of novel electronic and electrochemical devices based on TMDs/mxene junctions.

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Section: Growth Of Ws 2 /Ti 3 C 2 T X Mxenesupporting

confidence: 87%

Section: Optical Characterization Of Ws 2 /Ti 3 C 2 T X Mxenesupporting

confidence: 85%

Section: Optical Characterization Of Ws 2 /Ti 3 C 2 T X Mxenementioning

confidence: 89%

Section: Optical Characterization Of Ws 2 /Ti 3 C 2 T X Mxenementioning

confidence: 96%

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Growth of WS2 flakes on Ti3C2Tx Mxene Using Vapor Transportation Routine

Wang

et al. 2018

Coatings

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“…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.…”

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confidence: 99%

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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Engineering Substrate Interactions for High Luminescence Efficiency of Transition‐Metal Dichalcogenide Monolayers

Cai

et al. 2016

Adv Funct Materials

173

171

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4733wileyonlinelibrary.com the infl uence of substrates. [ 2 ] It has been reported that substrates may affect the luminescence effi ciency of the monolayers by inducing strain, doping, or dielectric screening. [ 2 a, e-g, 3 ] However, despite the recent progress, many important questions about the substrate effect have remained to be answered. For instance, while it is known that substrates could affect the luminescence effi ciency through multiple ways, there is no quantitative understanding for the effect of each mechanism and no knowledge on which mechanism could be dominant. More importantly, it is not clear how the effect of substrates might depend on the nature of the substrate and the physical features of the monolayers. Answers to these questions would provide useful guidance for the realization of optimal luminescence effi ciency through engineering the substrate effects. Here we quantitatively evaluate the effect of substrates on the luminescence effi ciency of monolayers MoS 2 , WS 2 , and WSe 2 and demonstrate strategies of substrate engineering to improve the effi ciency by orders of magnitude. We fi nd that the main effects of the substrate lie in doping the monolayers and facilitating defect-assisted nonradiative exciton recombinations. The doping may be from substrate-borne water moisture and the substrate itself, the former of which is much stronger than the latter for WS 2 and MoS 2 but negligible for WSe 2 . Using proper substrates can substantially mitigate the doping effect on the photoluminescence (PL), such as mica for WS 2 and MoS 2 and hexagonal boron nitride (h-BN) or polystyrene (PS) for WSe 2 . The defect-assisted recombination depends on the interaction of the defects in the monolayer such as sulfur vacancies with the substrate and may be substantially suppressed by either removing the substrate or lowering the number of defects. In this work we largely ignore the optical resonance effects associated with the substrate's geometrical features. [ 4 ] Results and DiscussionWe start with comparing the PL of suspended MoS 2 , WS 2 , and WSe 2 monolayers to those of as-grown counterparts. The monolayers were synthesized on sapphire substrates using chemical vapor deposition (CVD) processes as described previously, [ 5 ] and the suspended monolayers were prepared by manually It is demonstrated that the luminescence effi ciency of monolayers composed of MoS 2 , WS 2 , and WSe 2 is signifi cantly limited by the substrate and can be improved by orders of magnitude through substrate engineering. The substrate affects the effi ciency mainly through doping the monolayers and facilitating defect-assisted nonradiative exciton recombinations, while the other substrate effects including straining and dielectric screening play minor roles. The doping may come from the substrate and substrate-borne water moisture, the latter of which is much stronger than the former for MoS 2 and WS 2 but negligible for WSe 2 . Using proper substrates such as mica or hexagonal boron nitride can substantially mitigat...

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Nonblinking, Intense Two-Dimensional Light Emitter: Monolayer WS₂ Triangles

Cited by 298 publications

References 74 publications

Growth of WS2 flakes on Ti3C2Tx Mxene Using Vapor Transportation Routine

Growth of WS2 flakes on Ti3C2Tx Mxene Using Vapor Transportation Routine

Exciton Radiative Lifetimes in Two-Dimensional Transition Metal Dichalcogenides

Engineering Substrate Interactions for High Luminescence Efficiency of Transition‐Metal Dichalcogenide Monolayers

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Nonblinking, Intense Two-Dimensional Light Emitter: Monolayer WS2 Triangles

Cited by 298 publications

References 74 publications

Growth of WS2 flakes on Ti3C2Tx Mxene Using Vapor Transportation Routine

Growth of WS2 flakes on Ti3C2Tx Mxene Using Vapor Transportation Routine

Exciton Radiative Lifetimes in Two-Dimensional Transition Metal Dichalcogenides

Engineering Substrate Interactions for High Luminescence Efficiency of Transition‐Metal Dichalcogenide Monolayers

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Nonblinking, Intense Two-Dimensional Light Emitter: Monolayer WS₂ Triangles