Pressure-Dependent Optical and Vibrational Properties of Monolayer Molybdenum Disulfide

Nayak, Avinash P.; Pandey, Tribhuwan; Voiry, Damien; Liu, Jin; Moran, Samuel T.; Sharma, Ankit; Tan, Cheng; Chen, Chang-Hsiao; Li, Lain‐Jong; Chhowalla, Manish; Lin, Jung‐Fu; Singh, Abhishek K.; Akinwande, Deji

doi:10.1021/nl5036397

Cited by 296 publications

(332 citation statements)

References 45 publications

(101 reference statements)

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“…Band gap shifts in MoS 2 of ~300 meV have been induced by using very large hydrostatic pressures 27 , and tensile strain has induced shifts of as much as ~100 meV 11 . However, the combination being both an ultrastrength material and having a band gap highly sensitive to strain imply that a much larger band gap tuning must be possible.…”

mentioning

confidence: 99%

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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confidence: 99%

Band Gap Engineering with Ultralarge Biaxial Strains in Suspended Monolayer MoS₂

et al. 2016

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“…This issue has been theoretically addressed either through LDA/GGA calculations [163,27,28,31], or the GW method [144]. The effect of hydrostatic pressure on the vibrational, electronic, and optical properties of bulk, multi-, and single layer MoS 2 was investigated by Nayak et al [33,34] by combining various experiments (high resolution transmission electron microscopy, electrical resistance measurements, laser Raman spectroscopy, synchrotron X-ray diffraction experiments under high-pressure) with DFT calculations. Interestingly, while the direct bulk band gap decreases with increasing pressure, the direct band gap of 1L-MoS 2 increases by 11.7% up to ∼ 12 GPa before it is reduced.…”

Section: Strain Effects In Single-layer Mosmentioning

confidence: 99%

“…Thus the pressure induced electronic transition from the semiconducting to a semimetallic state occurs at much larger pressures in the latter. [34] Being aware of the importance of substrate interactions, we investigated the strain effects on the electronic properties of 1L-MoS 2 within the GW approach and the model of free-standing 2D layers. Biaxial tensile strain has been realized by increasing the in-plane lattice constant of 1L-MoS 2 .…”

Section: Strain Effects In Single-layer Mosmentioning

confidence: 99%

“…The application of strain drives a direct-to-indirect band gap transition in single-layer MoS 2 [27,28,29,30,31,32]. Moreover, suitable hydrostatic pressure reduces the band gap of single-and multi-layer MoS 2 resulting in a phase transition from semiconductor to metal [33,34]. The group symmetry and the spin-orbit interaction in MoS 2 also raise interesting properties.…”

Section: Introductionmentioning

confidence: 99%

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Vibrational and optical properties of MoS2: From monolayer to bulk

Molina-Sánchez

Hummer

Wirtz

2015

Surface Science Reports

207

167

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Molybdenum disulfide, MoS 2 , has recently gained considerable attention as a layered material where neighboring layers are only weakly interacting and can easily slide against each other. Therefore, mechanical exfoliation allows the fabrication of single and multi-layers and opens the possibility to generate atomically thin crystals with outstanding properties. In contrast to graphene, it has an optical gap of 1.9 eV. This makes it a prominent candidate for transistor and opto-electronic applications. Single-layer MoS 2 exhibits remarkably different physical properties compared to bulk MoS 2 due to the absence of interlayer hybridization. For instance, while the band gap of bulk and multi-layer MoS 2 is indirect, it becomes direct with decreasing number of layers. In this review, we analyze from a theoretical point of view the electronic, optical, and vibrational properties of single-layer, few-layer and bulk MoS 2 . In particular, we focus on the effects of spinorbit interaction, number of layers, and applied tensile strain on the vibrational and optical properties. We examine the results obtained by different methodologies, mainly ab initio approaches. We also discuss which approximations are suitable for MoS 2 and layered materials. The effect of external strain on the band gap of single-layer MoS 2 and the crossover from indirect to direct band gap is investigated. We analyze the excitonic effects on the absorption spectra. The main features, such as the double peak at the absorption threshold and the high-energy exciton are presented. Furthermore, we report on the phonon dispersion relations of single-layer, few-layer and bulk MoS 2 . Based on the latter, we explain the behavior of the Raman-active A 1g and E 1 2g modes as a function of the number of layers. Finally, we compare theoretical and experimental results of Raman, photoluminescence, and optical-absorption spectroscopy.

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“…Therefore, photoluminescence properties of two-dimensional materials can be tuned through chemical doping when dopants cover its surface [27]. Pressure produces a shift in the band gap energy of the material and therefore widens its spectrum although it reduces the photoluminescence intensity [28]. Uniaxial tensile strain increases the photoluminescence peak intensity in a twodimensional material, due to that it guarantees the direct band gap [29].…”

Section: Photoluminescencementioning

confidence: 99%

Graphene against Other Two-Dimensional Materials: A Comparative Study on the Basis of Photonic Applications

Vargas-Bernal¹

2017

Graphene Materials - Advanced Applications

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Two-dimensional materials represent the basis of technological development to produce applications with high added value for nanoelectronics, photonics, and optoelectronics. In first decades of this century, these materials are impelling this development through materials based on carbon, silicon, germanium, tin, phosphorus, arsenic, antimony, and boron. 2D materials for photonic applications used until now are graphene, silicene, germanene, stanene, phosphorene, arsenene, antimonene, and borophene. In this work, the main strategies to modify optical properties of 2D materials are studied for achieving photodetection, transportation, and emitting of light. Optical properties analyzed here are refractive index, extinction coefficient, relative permittivity, absorption coefficient, chromatic dispersion, group index, and transmittance. The transmittance spectra of various two-dimensional materials are presented here with the aim of classifying them from photonic point-of-view. A performance comparison between graphene and other twodimensional materials is done to help the designer choose the best design material for photonic applications. In next three decades, a lot of scientific research will be realized to completely exploit the use of 2D materials either as single monolayers or as stacked multilayers in several fields of knowledge with a special emphasis in the optoelectronics and photonic industry in benefit of the industry and ultimately to our society.

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Pressure-Dependent Optical and Vibrational Properties of Monolayer Molybdenum Disulfide

Cited by 296 publications

References 45 publications

Band Gap Engineering with Ultralarge Biaxial Strains in Suspended Monolayer MoS₂

Band Gap Engineering with Ultralarge Biaxial Strains in Suspended Monolayer MoS₂

Vibrational and optical properties of MoS2: From monolayer to bulk

Graphene against Other Two-Dimensional Materials: A Comparative Study on the Basis of Photonic Applications

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Pressure-Dependent Optical and Vibrational Properties of Monolayer Molybdenum Disulfide

Cited by 296 publications

References 45 publications

Band Gap Engineering with Ultralarge Biaxial Strains in Suspended Monolayer MoS2

Band Gap Engineering with Ultralarge Biaxial Strains in Suspended Monolayer MoS2

Vibrational and optical properties of MoS2: From monolayer to bulk

Graphene against Other Two-Dimensional Materials: A Comparative Study on the Basis of Photonic Applications

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Product

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Band Gap Engineering with Ultralarge Biaxial Strains in Suspended Monolayer MoS₂

Band Gap Engineering with Ultralarge Biaxial Strains in Suspended Monolayer MoS₂