Raman Spectroscopy Study of Lattice Vibration and Crystallographic Orientation of Monolayer MoS<sub>2</sub> under Uniaxial Strain

Wang, Yanlong; Cong, Chunxiao; Qiu, Caiyu; Yu, Ting

doi:10.1002/smll.201202876

Cited by 418 publications

(465 citation statements)

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“…2c) 39,40 . The position of the A 1g peak is known to vary with doping 41 , however as this is not the case with the more strain sensitive E 1 2g mode, its peak position can be used as a reliable way to measure the internal strain of monolayer MoS 2 .…”

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Band Gap Engineering with Ultralarge Biaxial Strains in Suspended Monolayer MoS₂

et al. 2016

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We demonstrate the continuous and reversible tuning of the optical band gap of suspended monolayer MoS 2 membranes by as much as 500 meV by applying very large biaxial strains. By using chemical vapor deposition (CVD) to grow crystals that are highly impermeable to gas, we are able to apply a pressure difference across suspended membranes to induce biaxial strains. We observe the effect of strain on the energy and intensity of the peaks in the photoluminescence (PL) spectrum, and find a linear tuning rate of the optical band gap of 99 meV/%. This method is then used to study the PL spectra of bilayer and trilayer devices under strain, and to find the shift rates and Grüneisen parameters of two Raman modes in monolayer MoS 2 . Finally, we use this result to show that we can apply biaxial strains as large as 5.6% across micron sized areas, and report evidence for the strain tuning of higher level optical transitions.KEYWORDS: Strain engineering, MoS 2 , photoluminescence, bandgap, Raman spectroscopy, biaxial strain 3 The ability to produce materials of truly nanoscale dimensions has revolutionized the potential for modulating or enhancing the physical properties of semiconductors by mechanical strain 1 . Strain engineering is routinely used in semiconductor manufacturing, with essential electrical components such as the silicon transistor or quantum well laser using strain to improve efficiency and performance 2,3 . Nano-structured materials are particularly suited to this technique, as they are often able to remain elastic when subject to strains many times larger than their bulk counterparts can withstand 4 . For instance, bulk silicon fractures when strained to just 1.2%, whereas silicon nanowires can reach strains of as much as 3.5% 5 . Parameters such as the band gap energy or carrier mobility of a semiconductor, which are often crucial to the electronic or photonic device performance, can be highly sensitive to the application of only small strains. The combination of this sensitivity with the ultra-high strains possible at the nanoscale could lead to an unprecedented ability to modify the electrical or photonic properties of materials in a continuous and reversible manner.Monolayer MoS 2, a 2D atomic crystal, has been shown in both theory 6,7 and experiment [8][9][10][11][12] to be an ideal candidate for strain engineering. It belongs to the class of 2D transition metal dichalcogonides (TMD's), and as a direct-gap semiconductor 13 has received significant interest as a channel material in transistors 14 , photovoltaics 15 and photodetection 16 devices. It has a breaking strain of 6-11% as measured by nanoindentation, which approaches its maximum theoretical strain limit 17 and classifies it as an ultra-strength material. Its electronic structure has also proven to be highly sensitive to strain, with experiments showing that the optical band gap reduces by ~50 meV/% for 4 uniaxial strain 8,11 , and is predicted to reduce by ~100 meV/% for biaxial strain 18,19 . This reversible modulation of the band...

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Band Gap Engineering with Ultralarge Biaxial Strains in Suspended Monolayer MoS₂

et al. 2016

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“…However, these experiments have only been performed on exfoliated samples and a comprehensive study of the role of substrate and homogeneity on the transferred strain has not been explored. Most recently, the strain-induced bandgap changes in monolayer MoS 2 , using polymer substrates, has been demonstrated 26,[28][29][30] . However, because of the weak adhesion between MoS 2 and substrates, strain cannot be completely transferred to MoS 2 from the substrate, as exemplified in graphene strain-engineering studies 31,32 .…”

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Strain and structure heterogeneity in MoS2 atomic layers grown by chemical vapour deposition

et al. 2014

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Monolayer molybdenum disulfide (MoS 2 ) has attracted tremendous attention due to its promising applications in high-performance field-effect transistors, phototransistors, spintronic devices and nonlinear optics. The enhanced photoluminescence effect in monolayer MoS 2 was discovered and, as a strong tool, was employed for strain and defect analysis in MoS 2 . Recently, large-size monolayer MoS 2 has been produced by chemical vapour deposition, but has not yet been fully explored. Here we systematically characterize chemical vapour deposition-grown MoS 2 by photoluminescence spectroscopy and mapping and demonstrate non-uniform strain in single-crystalline monolayer MoS 2 and strain-induced bandgap engineering. We also evaluate the effective strain transferred from polymer substrates to MoS 2 by three-dimensional finite element analysis. Furthermore, our work demonstrates that photoluminescence mapping can be used as a non-contact approach for quick identification of grain boundaries in MoS 2 .

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“…40 The result of Raman scattering modes is shown in Figure 3, where all the modes, not the resonant second order or combinations of first order modes, are shown in the It is known that the Raman E' peak of monolayer MoS2 is sensitive to strain and strain could induce a red-shift in the E' modes that have been observed for MoS2 monolayer or multilayers in other reports. 33,[41][42][43] The red-shift of the MoS2 E' peak after the two layers are coupled (thermally treated)…”

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confidence: 99%

Spectroscopic Signatures for Interlayer Coupling in MoS₂–WSe₂ van der Waals Stacking

et al. 2014

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Stacking of MoS 2 and WSe 2 monolayers is conducted by transferring triangular MoS 2 monolayers on top of WSe 2 monolayers, all grown by chemical vapor deposition (CVD).Raman spectroscopy and photoluminescence (PL) studies reveal that these mechanically stacked monolayers are not closely coupled, but after a thermal treatment at 300 °C, it is possible to produce van der Waals solids consisting of two interacting transition metal dichalcogenide (TMD) monolayers. The layer-number sensitive Raman out-of-plane mode A 2 1g for WSe 2 (309 cm À1 ) is found sensitive to the coupling between two TMD monolayers. The presence of interlayer excitonic emissions and the changes in other intrinsic Raman modes such as E 00 for MoS 2 at 286 cm À1 and A 2 1g for MoS 2 at around 463 cm À1 confirm the enhancement of the interlayer coupling.

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Raman Spectroscopy Study of Lattice Vibration and Crystallographic Orientation of Monolayer MoS₂ under Uniaxial Strain

Cited by 418 publications

References 30 publications

Band Gap Engineering with Ultralarge Biaxial Strains in Suspended Monolayer MoS₂

Band Gap Engineering with Ultralarge Biaxial Strains in Suspended Monolayer MoS₂

Strain and structure heterogeneity in MoS2 atomic layers grown by chemical vapour deposition

Spectroscopic Signatures for Interlayer Coupling in MoS₂–WSe₂ van der Waals Stacking

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Raman Spectroscopy Study of Lattice Vibration and Crystallographic Orientation of Monolayer MoS2 under Uniaxial Strain

Cited by 418 publications

References 30 publications

Band Gap Engineering with Ultralarge Biaxial Strains in Suspended Monolayer MoS2

Band Gap Engineering with Ultralarge Biaxial Strains in Suspended Monolayer MoS2

Strain and structure heterogeneity in MoS2 atomic layers grown by chemical vapour deposition

Spectroscopic Signatures for Interlayer Coupling in MoS2–WSe2 van der Waals Stacking

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Product

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Raman Spectroscopy Study of Lattice Vibration and Crystallographic Orientation of Monolayer MoS₂ under Uniaxial Strain

Band Gap Engineering with Ultralarge Biaxial Strains in Suspended Monolayer MoS₂

Band Gap Engineering with Ultralarge Biaxial Strains in Suspended Monolayer MoS₂

Spectroscopic Signatures for Interlayer Coupling in MoS₂–WSe₂ van der Waals Stacking