van der Waals Epitaxy of MoS<sub>2</sub> Layers Using Graphene As Growth Templates

Shi, Yumeng; Zhou, Wu; Lu, Ang‐Yu; Fang, Wenjing; Lee, Yi-Hsien; Hsu, Allen; Kim, Soo Min; Yang, Hui Ying; Li, Lain‐Jong; Idrobo, Juan Carlos; Kong, Jing

doi:10.1021/nl204562j

Cited by 936 publications

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“…25). At the Γ-point, the bandgap transition is indirect for the bulk material, but gradually shifts to be direct for the monolayer 24,[73][74][75][76][77] . The direct excitonic transitions at the K-point remain relatively unchanged with layer number 32 .…”

Section: Electronic Structurementioning

confidence: 99%

“…In many of these methods, the final MoS 2 film thickness is dependent on the concentration or thickness of the initial precursor, although precise control of the number of layers over a large area has not yet been achieved. CVD growth of MoS 2 has also been demonstrated using previously CVD-grown graphene on Cu foil as a surface template, resulting in single-crystal flakes of MoS 2 several micrometres in lateral size 75 . These CVD reports are still relatively early results but hold promise that further work will lead to growth of materials other than MoS 2 , and production of uniform, large-area sheets of TMDCs with controllable layer number.…”

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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: Electronic Structurementioning

confidence: 99%

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confidence: 99%

Electronics and optoelectronics of two-dimensional transition metal dichalcogenides

et al. 2012

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“…Furthermore, for many applications, it is vital to manufacture high-quality epitaxial films with controllable methods such as chemical vapour deposition (CVD) or molecular beam epitaxy (MBE) 20,21 .…”

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“…Moreover, we find rather large spin-splitting (~180 meV) at the valence band maximum (VBM) of the monolayer Figure 1b shows the reflection high-energy electron diffraction (RHEED) pattern of our substrate of epitaxial bilayer graphene-terminated 6H-SiC(0001) 22 . The similar layered structure and chemically inert surface of graphene make it a perfect substrate for van der Waals epitaxial growth of two-dimensional layered materials 21,23,24 . We have successfully grown high-quality singlecrystal MoSe 2 films of large size (~5 mm× 2 mm), from monolayer up to 8 ML, with layer-by-layer control of thickness, by delicate control of the growth conditions.…”

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Direct observation of the transition from indirect to direct bandgap in atomically thin epitaxial MoSe2

et al. 2013

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The layered transition metal dichalcogenides (TMDs) MX 2 (M = Mo, W; X = S, Se, Te), a class of graphene-like two-dimensional materials, have attracted significant interest because they demonstrate quantum confinement at the single-layer limit 13 . As with graphene, these layered materials can be easily exfoliated mechanically to provide monolayers 3-7,14-16 and assume a hexagonal honeycomb structure in which the M and X atoms are located at alternating corners of the hexagons. However, unlike graphene, which has a gapless Dirac cone band structure, MX 2 has a rather large bandgap, making these materials more versatile as candidates for thin, flexible device applications and useful for a variety of other applications including lubrication 16 , catalysis 17 , transistors 18 and lithium-ion batteries 19 . Most interestingly, an indirect to direct bandgap transition in the monolayer limit has been predicted theoretically and supported experimentally by optical measurements [3][4][5]9,12 . Because of the direct bandgap, monolayer MX 2 is favourable for optoelectronic applications5 and field-effect transistors 15,16,18 . Furthermore, both the conduction and valence bands have two energy degenerate valleys at corners of the first Brillouin zone, making it viable to optically control the charge carriers in these valleys and suggesting the possibility of valley-based electronic and optoelectronic applications 3,6-8 .Despite these exciting developments, direct experimental verification of the novel band structure at the monolayer limit remains lacking. Furthermore, for many applications, it is vital to manufacture high-quality epitaxial films with controllable methods such as chemical vapour deposition (CVD) or molecular beam epitaxy (MBE) 20,21 .

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“…For vertical heterostructures in particular, layer-by-layer growth allows direct control of the constituent materials in a serial fashion, and typically these techniques can be scaled to large lateral dimensions in a way that is not possible with exfoliated materials. Hence, a great deal of e ort has gone into adapting epitaxial growth methods to form atomic layers of MoS 2 , MoSe 2 , WSe 2 , h-BN, and others on graphene, [50,52,68,75,76] as well as graphene on h-BN. [77,78] Graphene itself has been formed in large-area lms using CVD on metal foils with varying degrees of quality.…”

Section: Introductionmentioning

confidence: 99%

Layered Two-Dimensional Heterostructures and Their Tunneling Characteristics

Barrera¹

2017

Springer Theses

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van der Waals Epitaxy of MoS₂ Layers Using Graphene As Growth Templates

Cited by 936 publications

References 53 publications

Electronics and optoelectronics of two-dimensional transition metal dichalcogenides

Electronics and optoelectronics of two-dimensional transition metal dichalcogenides

Direct observation of the transition from indirect to direct bandgap in atomically thin epitaxial MoSe2

Layered Two-Dimensional Heterostructures and Their Tunneling Characteristics

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van der Waals Epitaxy of MoS2 Layers Using Graphene As Growth Templates

Cited by 936 publications

References 53 publications

Electronics and optoelectronics of two-dimensional transition metal dichalcogenides

Electronics and optoelectronics of two-dimensional transition metal dichalcogenides

Direct observation of the transition from indirect to direct bandgap in atomically thin epitaxial MoSe2

Layered Two-Dimensional Heterostructures and Their Tunneling Characteristics

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van der Waals Epitaxy of MoS₂ Layers Using Graphene As Growth Templates