Vapor–Solid Growth of High Optical Quality MoS<sub>2</sub> Monolayers with Near-Unity Valley Polarization

Wu, Sanfeng; Huang, Chun-Ming; Aivazian, Grant; Ross, Joel; Cobden, David; Xu, Xiaodong

doi:10.1021/nn4002038

Cited by 408 publications

(370 citation statements)

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“…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 .…”

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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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Band Gap Engineering with Ultralarge Biaxial Strains in Suspended Monolayer MoS₂

et al. 2016

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“…The chemical reaction involved is (NH 4 ) 2 MoS 4 + H 2 → 2NH 3 + 2H 2 S + MoS 2 . Wu et al [46] have reported a vapoursolid (versus) growth method for synthesizing MoS 2 monolayer on insulating substrates such as Si wafer and sapphire, by physical vapour transport of MoS 2 powder at 900 • C (hot zone) under a low pressure of 20 Torr (figure 4f ,g). The substrates were placed in a cold zone at 650 • C [46].…”

Section: Synthesis and Characterizationmentioning

confidence: 99%

“…The substrates were placed in a cold zone at 650 • C [46]. Feng et al [52] have also reported the synthesis of uniformly distributed monolayer MoS 2(1−x) Se 2x alloys on SiO 2 /Si substrates through the direct evaporation of MoSe 2 [44], (d,e) adapted with permission from Li et al [45], (f ,g) adapted with permission from Wu et al [46] and (h) adapted with permission from Liu et al [47].…”

Section: Synthesis and Characterizationmentioning

confidence: 99%

Two-dimensional inorganic analogues of graphene: transition metal dichalcogenides

Jana¹,

Rao²

2016

Phil. Trans. R. Soc. A.

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The discovery of graphene marks a major event in the physics and chemistry of materials. The amazing properties of this two-dimensional (2D) material have prompted research on other 2D layered materials, of which layered transition metal dichalcogenides (TMDCs) are important members. Single-layer and few-layer TMDCs have been synthesized and characterized. They possess a wide range of properties many of which have not been known hitherto. A typical example of such materials is MoS 2 . In this article, we briefly present various aspects of layered analogues of graphene as exemplified by TMDCs. The discussion includes not only synthesis and characterization, but also various properties and phenomena exhibited by the TMDCs.This article is part of the themed issue 'Fullerenes: past, present and future, celebrating the 30th anniversary of Buckminster Fullerene'.

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“…[36][37][38][39] Although upscaling of the sulfurization method appears to be easier compared to the MoO 3 -based CVD, sulfurization tends to produce films of lower quality. [34,36,37] Other bottom-up techniques used for the deposition of thin MoS 2 films include sputtering, [40] physical vapor transport, [41] pulsed laser deposition, [42] and atomic layer deposition (ALD). [43][44][45][46][47][48][49][50][51][52] Atomic layer deposition is an inherently scalable technique that can be regarded as an advanced modification of CVD.…”

Section: Introductionmentioning

confidence: 99%

Atomic Layer Deposition of Crystalline MoS₂ Thin Films: New Molybdenum Precursor for Low‐Temperature Film Growth

Mattinen

Hatanpää

Sarnet

et al. 2017

Adv Materials Inter

106

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Compared to the most well-known 2D material, graphene, which is a semi-metal, the semiconducting 2H phase of MoS 2 is advantageous in having a band gap suitable for electronic applications. In bulk form, MoS 2 has an indirect band gap of 1.3 eV, which increases as a function of decreasing film thickness. In monolayer MoS 2 (thickness ≈0.6 nm), the band gap becomes direct with a width of 1.8 eV. [1] Importantly, to meet the requirements of different applications, properties of MoS 2 and other TMDCs can be tuned by controlling the thickness, [1] doping and alloying, [5][6][7][8] surface modification and functionalization, [9][10][11] strain, [12,13] and by creating heterostructures with other 2D materials. [6,[14][15][16] The appealing properties of TMDCs have led to a wide range of proposed applications. MoS 2 has been extensively studied as a channel material in conventional field-effect transistors, [17][18][19][20][21] as well as phototransistors and other optoelectronic devices. [16,21,22] The 2D structure of TMDCs plays a crucial role in possible applications relying on more exotic quantum phenomena, such as valleytronics. [23,24] MoS 2 has also shown promise in, for example, catalysis, [25] batteries, [26] photovoltaics, [27] sensors, [28] and medicine. [29] The production of high-quality, large-area MoS 2 films with a thickness controllable down to a monolayer, as required in many of the aforementioned applications, still remains a major challenge. Additionally, in many cases, the processing temperature should be kept as low as possible in order to avoid damaging sensitive substrates, such as polymers or nanostructures. Initially, flakes of monolayer MoS 2 were produced from natural MoS 2 crystals using micromechanical exfoliation, a topdown method capable of producing high-quality monolayers, albeit with poor throughput as well as limited control over flake thickness and dimensions. [4,30,31] Liquid-phase exfoliation of bulk crystals, on the other hand, offers good scalability, but often suffers from limited flake size, poor crystallinity, or contamination. [4,31,32] Bottom-up methods offer a more controllable way to produce MoS 2 films. High-quality MoS 2 thin films are most commonly deposited by chemical vapor deposition (CVD) or sulfurization of metal or metal oxide thin films. The most common Molybdenum disulfide (MoS 2 ) is a semiconducting 2D material, which has evoked wide interest due to its unique properties. However, the lack of controlled and scalable methods for the production of MoS 2 films at low temperatures remains a major hindrance on its way to applications. In this work, atomic layer deposition (ALD) is used to deposit crystalline MoS 2 thin films at a relatively low temperature of 300 °C. A new molybdenum precursor, Mo(thd) 3 (thd = 2,2,6,6-tetramethylheptane-3,5-dionato), is synthesized, characterized, and used for film deposition with H 2 S as the sulfur precursor. Self-limiting growth with a low growth rate of ≈0.025 Å cycle −1 , straightforward thickness control, and large-area uni...

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Vapor–Solid Growth of High Optical Quality MoS₂ Monolayers with Near-Unity Valley Polarization

Cited by 408 publications

References 36 publications

Band Gap Engineering with Ultralarge Biaxial Strains in Suspended Monolayer MoS₂

Band Gap Engineering with Ultralarge Biaxial Strains in Suspended Monolayer MoS₂

Two-dimensional inorganic analogues of graphene: transition metal dichalcogenides

Atomic Layer Deposition of Crystalline MoS₂ Thin Films: New Molybdenum Precursor for Low‐Temperature Film Growth

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Vapor–Solid Growth of High Optical Quality MoS2 Monolayers with Near-Unity Valley Polarization

Cited by 408 publications

References 36 publications

Band Gap Engineering with Ultralarge Biaxial Strains in Suspended Monolayer MoS2

Band Gap Engineering with Ultralarge Biaxial Strains in Suspended Monolayer MoS2

Two-dimensional inorganic analogues of graphene: transition metal dichalcogenides

Atomic Layer Deposition of Crystalline MoS2 Thin Films: New Molybdenum Precursor for Low‐Temperature Film Growth

Contact Info

Product

Resources

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Vapor–Solid Growth of High Optical Quality MoS₂ Monolayers with Near-Unity Valley Polarization

Band Gap Engineering with Ultralarge Biaxial Strains in Suspended Monolayer MoS₂

Band Gap Engineering with Ultralarge Biaxial Strains in Suspended Monolayer MoS₂

Atomic Layer Deposition of Crystalline MoS₂ Thin Films: New Molybdenum Precursor for Low‐Temperature Film Growth