Electronic structure of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">MoSe</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>,<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">MoS</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>, and<mml:math xmlns:mml="http

Coehoorn, R.; Haas, C.; Groot, R.A. de

doi:10.1103/physrevb.35.6203

Cited by 402 publications

(183 citation statements)

References 21 publications

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“…The photoconductivity of TMDCs also reflects these band-structure features, with the photocurrent of MoS 2 increasing in steps with respect to photon energy corresponding to the direct and indirect gap energies 31 . The optical absorption spectrum of bulk MoS 2 shows two main peaks corresponding to exciton bands, the so-called A and B excitons: direct-gap transitions at the K-point of the Brillouin zone between the maxima of split valence bands and the minimum of the conduction band 31,32,129 (Fig. 5d).…”

Section: Optoelectronicsmentioning

confidence: 99%

Electronics and optoelectronics of two-dimensional transition metal dichalcogenides

et al. 2012

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699M any two-dimensional (2D) materials exist in bulk form as stacks of strongly bonded layers with weak interlayer attraction, allowing exfoliation into individual, atomically thin layers 1 . The form receiving the most attention today is graphene, the monolayer counterpart of graphite. The electronic band structure of graphene has a linear dispersion near the K point, and charge carriers can be described as massless Dirac fermions, providing scientists with an abundance of new physics 2,3 . Graphene is a unique example of an extremely thin electrical and thermal conductor 4 , with high carrier mobility 5 , and surprising molecular barrier properties 6,7 .Many other 2D materials are known, such as the TMDCs 8,9 , transition metal oxides including titania-and perovskite-based oxides 10,11 , and graphene analogues such as boron nitride (BN) 12,13 . In particular, TMDCs show a wide range of electronic, optical, mechanical, chemical and thermal properties that have been studied by researchers for decades 9,14,15 . There is at present a resurgence of scientific and engineering interest in TMDCs in their atomically thin 2D forms because of recent advances in sample preparation, optical detection, transfer and manipulation of 2D materials, and physical understanding of 2D materials learned from graphene.The 2D exfoliated versions of TMDCs offer properties that are complementary to yet distinct from those in graphene. Graphene displays an exceptionally high carrier mobility exceeding 10 6 cm 2 V -1 s -1 at 2 K (ref. 16) and exceeding 10 5 cm 2 V -1 s -1 at room temperature for devices encapsulated in BN dielectric layers 5 ; because pristine graphene lacks a bandgap, however, fieldeffect transistors (FETs) made from graphene cannot be effectively switched off and have low on/off switching ratios. Bandgaps can be engineered in graphene using nanostructuring [17][18][19] , chemical functionalization 20 and applying a high electric field to bilayer graphene 21 , but these methods add complexity and diminish mobility. In contrast, several 2D TMDCs possess sizable bandgaps around 1-2 eV (refs 9,14), promising interesting new FET and optoelectronic devices.TMDCs are a class of materials with the formula MX 2 , where M is a transition metal element from group IV (Ti, Zr, Hf and so on), group V (for instance V, Nb or Ta) or group VI (Mo, W and so on), and X is a chalcogen (S, Se or Te). These materials form layered structures of the form X-M-X, with the chalcogen atoms in two hexagonal planes separated by a plane of metal atoms, as shown in Fig. 1a. Adjacent layers are weakly held together to form the bulk crystal in a variety of polytypes, which vary in stacking orders and metal atom coordination, as shown in Fig. 1e. The overall symmetry of TMDCs is hexagonal or rhombohedral, and the metal atoms have octahedral or trigonal prismatic coordination. The electronic properties of TMDCs range from metallic to semiconducting, as summarized in Table 1. There are also TMDCs that exhibit exotic behaviours such as charge density waves ...

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Section: Optoelectronicsmentioning

confidence: 99%

Electronics and optoelectronics of two-dimensional transition metal dichalcogenides

et al. 2012

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“…The PL spectrum of 1L-MoS 2 exhibits two bands at 2eV and 1.8eV (Fig.1b) associated with excitonic transitions at the K point of the Brillouin zone[4]. The energy difference of 0.2eV has been attributed to the degeneracy breaking of the valence band due to spin-orbit coupling [4,7,8,22]. As compared to bulk MoS 2 , Fig.1b, 1L-MoS 2 does not have a peak at 1.4eV [3,4], associated with the indirect band gap [12].…”

Section: Molybdenum Disulphide (Mosmentioning

confidence: 99%

mentioning

confidence: 99%

“…A single layer of MoS 2 (1L-MoS 2 ) consists of two planes of hexagonally arranged S atoms linked to a hexagonal plane of Mo atoms via covalent bonds [3,[6][7][8][9]. In the bulk, individual MoS 2 layers are held together by weak van der Waals forces [6][7][8][9]. This property has been exploited in lubrication technology [10] and, more recently, has lead to the isolation of 1L-MoS 2 [2][3][4]11].…”

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Electroluminescence in Single Layer MoS₂

et al. 2013

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We detect electroluminescence in single layer molybdenum disulphide (MoS2) field-effect transistors built on transparent glass substrates. By comparing absorption, photoluminescence, and electroluminescence of the same MoS2 layer, we find that they all involve the same excited state at 1.8eV. The electroluminescence has pronounced threshold behavior and is localized at the contacts. The results show that single layer MoS2, a direct band gap semiconductor, is promising for novel optoelectronic devices, such as 2-dimensional light detectors and emitters. Here, we report electrically excited luminescence in 1L-MoS 2 FETs, and study the underlying emission mechanism. We find that the electroluminescence occurs via hot carriers and is localized in the contacts region. The observed photoluminescence and electroluminescence arise from the same excited state at 1.8eV. Molybdenum disulphide (MoS1L-MoS 2 crystals are produced by micromechanical cleavage of bulk MoS 2 (Structure Probe Inc.-SPI, Natural Molybdenite) on 100nm SiO 2 . As for the case of graphene [20], interference allows visibility and counting the number of layers, Fig.1a. Due to the different dielectric properties, an optimum thickness of 100nm SiO 2 is well suited for MoS 2 [21]. The presence of monolayers is then confirmed by performing PL measurements, Fig.1b. The PL spectrum of 1L-MoS 2 exhibits two bands at 2eV and 1.8eV (Fig.1b) associated with excitonic transitions at the K point of the Brillouin zone[4]. The energy difference of 0.2eV has been attributed to the degeneracy breaking of the valence band due to spin-orbit coupling [4,7,8,22]. As compared to bulk MoS 2 , Fig.1b, 1L-MoS 2 does not have a peak at 1.4eV [3,4], associated with the indirect band gap [12]. In addition 1L-MoS 2 exhibits a stronger PL intensity compared to bulk MoS 2 [3, 4] due to the direct band gap. Another evidence for 1L-MoS 2 comes from the analysis of the Raman spectrum, Fig.1d. The peak at∼385cm −1 corresponds to the in plane (E 1 2g ) mode [23], while that at ∼404 cm −1 is attributed to the out of plane (A 1g ) mode [23]. The E 1 2g mode softens and A 1g mode stiffens with increasing layer thickness[23], similar to what happens for other layered materials, where the bond distance changes with number of layers [24]. The frequency difference between these two modes can be used as a signature of 1L-MoS 2 [23].1L-MoS 2 flakes are then transferred onto glass substrates by using a poly(methyl methacrylate) (PMMA) based transfer technique, similar to that previously used to transfer graphene onto optical fibre cores [25]. This process involves spin coating two layers of 495K PMMA and one layer of 950K PMMA on the substrate where flakes are deposited. The samples are subsequently immersed in de-ionized (DI) water at 90 • C for 1h, resulting in the detachment of the polymer film, due to the intercalation of water at the polymer-SiO 2 interface. MoS 2 flakes stick to the PMMA, and can thus be removed from the original substrate and mechanically transferred onto glass substrates [2...

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“…The peaks at 598 and 648 nm (2.08 and 1.92 eV) correspond to the B 1 and A 1 exciton peaks, respectively. These bands have been attributed to the direct transfer at the K point of the Brillouin zone [29]. The spacing between these two exciton peaks is 0.16 eV, which corresponds to MoS 2 , and confirms the formation of MoS 2 .…”

Section: Methodsmentioning

confidence: 56%

Closed-cage clusters in the gaseous and condensed phases derived from sonochemically synthesized MoS₂ nanoflakes

Singh

Pradeep

Bhattacharjee

et al. 2007

J. Am. Soc. Mass Spectrom.

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The Mo 13 clusters we previously reported were derived from MoS 2 flakes prepared from bulk MoS 2 , although the nature of the precursor species was not fully understood. The existence of the clusters in the condensed phase was a question. Here we report the preparation of MoS 2 nanoflakes from elemental precursors using the sonochemical method and study the gas-phase clusters derived from them using mass spectrometry. Ultraviolet-visible (UV-vis) spectrum of the precursor is comparable to nano MoS 2 derived from bulk MoS 2 . High-resolution transmission electron microscopy (HRTEM) revealed the formation of nanoflakes of MoS 2 with 10-to 30-nm length and 3-to 5-nm thickness. Laser desorption ionization mass spectrometry (LDI-MS) confirmed the formation of Mo 13 clusters from this nanomaterial. Matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) points to the existence of Mo 13 clusters in the condensed phase. The clusters appear to be stable because they do not fragment in the mass spectrometer even at the highest laser intensity. Computational analysis based on generalized Wannier orbitals is used to understand bonding and stability of the clusters. These clusters are highly stable with a rich variety in terms of centricity and multiplicity of MoOMo There are several synthetic approaches such as gas-phase deposition [5,6], laser ablation [7,8], electron irradiation [9], and high-temperature chemical routes [10,11] for the synthesis of clusters. Nano forms of these materials have their own advantages over the corresponding bulk materials. Electrochemical deposition [12] and sonochemical routes [13,14] are some other methods adapted for the synthesis of nanostructured materials. Electrochemical methods result in the formation of nanomaterials as a film, whereas sonochemical methods produce free-standing nanoflakes of metal chalcogenides with controlled size.

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Electronic structure ofMoSe2,MoS2, and
R. Coehoorn
¹
,
C. Haas
²
,
R.A. de Groot
³

Abstract: Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.

Cited by 402 publications

References 21 publications

Electronics and optoelectronics of two-dimensional transition metal dichalcogenides

Electronics and optoelectronics of two-dimensional transition metal dichalcogenides

Electroluminescence in Single Layer MoS₂

Closed-cage clusters in the gaseous and condensed phases derived from sonochemically synthesized MoS₂ nanoflakes

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Electronic structure ofMoSe2,MoS2, andR. Coehoorn1, C. Haas2, R.A. de Groot3

Abstract: Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.

Cited by 402 publications

References 21 publications

Electronics and optoelectronics of two-dimensional transition metal dichalcogenides

Electronics and optoelectronics of two-dimensional transition metal dichalcogenides

Electroluminescence in Single Layer MoS2

Closed-cage clusters in the gaseous and condensed phases derived from sonochemically synthesized MoS2 nanoflakes

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Product

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About

Electronic structure ofMoSe2,MoS2, and
R. Coehoorn
¹
,
C. Haas
²
,
R.A. de Groot
³

Electroluminescence in Single Layer MoS₂

Closed-cage clusters in the gaseous and condensed phases derived from sonochemically synthesized MoS₂ nanoflakes