Pressure-induced semiconducting to metallic transition in multilayered molybdenum disulphide

Nayak, Avinash P.; Bhattacharyya, Swastibrata; Zhu, Jie; Liu, Jin; Wu, Xiang; Pandey, Tribhuwan; Jin, Changqing; Singh, Abhishek K.; Akinwande, Deji; Lin, Jung Fu

doi:10.1038/ncomms4731

Cited by 549 publications

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“…This reversible modulation of the band gap could be used to make wavelength tunable phototransistors 16 , or MoS 2 strain sensors that have a sensitivity comparable to their state of the art silicon counterparts 20 . Moreover it has been suggested that strain could also improve the performance of MoS 2 transistors 21 , or could be used to create broadband light absorbers for energy harvesting 22 .The effect of strain on the band gap of 2D TMD's has been reported in a number of studies [9][10][11][12]20,23,24 , including uniaxial strains of up to ~4 % 25 and biaxial strains of up to ~3 % produced in highly localized sub-micron areas 26 . 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 .…”

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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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“…This tradeoff might be mitigated by using high-quality h-BN gate dielectric where its atomic smoothness and high phonon energy are expected to enhance monolayer TMD mobilities as is the case for graphene 3,9 . Beyond bending studies, hydrostatic compressive strain of MoS 2 of about 15% has been recently reported to produce a semiconducting to metallic transition, which can enable new flexible or straintronic device or switch concepts 65 .…”

Section: Contemporary Flexible Performancementioning

confidence: 99%

Two-dimensional flexible nanoelectronics

2014

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represents the tenth anniversary of modern graphene research. Over this decade, graphene has proven to be attractive for thin-film transistors owing to its remarkable electronic, optical, mechanical and thermal properties. Even its major drawback-zero bandgap-has resulted in something positive: a resurgence of interest in two-dimensional semiconductors, such as dichalcogenides and buckled nanomaterials with sizeable bandgaps. With the discovery of hexagonal boron nitride as an ideal dielectric, the materials are now in place to advance integrated flexible nanoelectronics, which uniquely take advantage of the unmatched portfolio of properties of two-dimensional crystals, beyond the capability of conventional thin films for ubiquitous flexible systems.T wo-dimensional (2D) atomic sheets are atomically thin, layered crystalline solids with the defining characteristics of intralayer covalent bonding and interlayer van der Waals bonding 1-3 . The expanding portfolio of atomic sheets illustrated in Fig. 1a currently include the archetypical 2D crystal graphene 3-14 , transition metal dichalcogenides (TMDs) 1,2,15-21 , diatomic hexagonal boron nitride (h-BN) 3,[22][23][24][25] , and emerging monoatomic buckled crystals collectively termed Xenes, which include silicene 2,26,27 , germanene 2 and phosphorene [28][29][30][31] . These materials are considered 2D because they represent the thinnest unsupported crystalline solids that can be realized, possess no dangling surface bonds and show superior intralayer (versus interlayer) transport of fundamental excitations (charge, heat, spin and light). The portfolio is expected to grow as more elemental and compound sheets are uncovered.The outstanding properties of 2D crystals have generated immense interest for both conventional semiconductor technology and the nascent flexible nanotechnology because, amongst other considerations, these atomic sheets afford the ultimate thickness scalability desired in a variety of essential material categories, including semiconductors, insulators, transparent conductors and transducers 3,16,18 . In particular, flexible nanoelectronics stand to greatly benefit from the development of 2D crystals because their unmatched combination of device physics and device mechanics is accessible on soft polymeric or plastic substrates 17,18,32,33 , which can enable the long sought after large-area high-performance flexible devices that can be manufactured at economically viable scales. As a result, existing flexible technology is expected to be transformed from low-cost commodity applications, such as radio-frequency identification tags and sensors, to integrated nanosystems with electronic performance comparable to silicon devices, in addition to affording mechanical flexibility and manufacturing form-factor beyond the capability of conventional semiconductor technology 34 . Hence, a new era in integrated flexible technology founded on 2D crystals is emerging.

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“…Recently, both X-ray diffraction and Raman spectroscopy of ML (at ∼19 GPa) and bulk MoS 2 (between 20 and 30 GPa) under high pressure confirmed the above transitions. 99,120,148 Fig . 18(a) shows the Raman spectra of bulk MoS 2 at various pressures up to 57 GPa in both compression (denoted by c) and decompression (denoted by d) runs.…”

Section: E Pressure-induced Semiconductor To Metallic Transitionmentioning

confidence: 99%

Phonon and Raman scattering of two-dimensional transition metal dichalcogenides from monolayer, multilayer to bulk material

et al. 2015

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Two-dimensional (2D) transition metal dichalcogenide (TMD) nanosheets exhibit remarkable electronic and optical properties. The 2D features, sizable bandgaps, and recent advances in the synthesis, characterization, and device fabrication of the representative MoS2, WS2, WSe2, and MoSe2 TMDs make TMDs very attractive in nanoelectronics and optoelectronics. Similar to graphite and graphene, the atoms within each layer in 2D TMDs are joined together by covalent bonds, while van der Waals interactions keep the layers together. This makes the physical and chemical properties of 2D TMDs layer dependent. In this review, we discuss the basic lattice vibrations of monolayer, multilayer, and bulk TMDs, including high-frequency optical phonons, interlayer shear and layer breathing phonons, the Raman selection rule, layer-number evolution of phonons, multiple phonon replica, and phonons at the edge of the Brillouin zone. The extensive capabilities of Raman spectroscopy in investigating the properties of TMDs are discussed, such as interlayer coupling, spin-orbit splitting, and external perturbations. The interlayer vibrational modes are used in rapid and substrate-free characterization of the layer number of multilayer TMDs and in probing interface coupling in TMD heterostructures. The success of Raman spectroscopy in investigating TMD nanosheets paves the way for experiments on other 2D crystals and related van der Waals heterostructures.

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Pressure-induced semiconducting to metallic transition in multilayered molybdenum disulphide

Cited by 549 publications

References 66 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 flexible nanoelectronics

Phonon and Raman scattering of two-dimensional transition metal dichalcogenides from monolayer, multilayer to bulk material

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Pressure-induced semiconducting to metallic transition in multilayered molybdenum disulphide

Cited by 549 publications

References 66 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 flexible nanoelectronics

Phonon and Raman scattering of two-dimensional transition metal dichalcogenides from monolayer, multilayer to bulk material

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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