Bandgap opening in few-layered monoclinic MoTe2

Keum, Dong Hoon; Cho, Suyeon; Kim, Jung Ho; Choe, Duk‐Hyun; Sung, Ha Jun; Kan, Min; Kang, Haeyong; Hwang, Jae-Yeol; Kim, Sung Wng; Yang, Heejun; Chang, Kee Joo; Lee, Young Hee

doi:10.1038/nphys3314

Cited by 866 publications

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References 29 publications

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“…Even at very high applied magnetic fields, MR in Td-WTe 2 does not saturate, which is attributed to a perfect balanced electron-hole resonance. Bulk monoclinic 1T -MoTe 2 with Mo-Mo zigzag chains (figure 15a) is semimetallic and also exhibits giant MR of 16 000% in a magnetic field of 14 T at 1.8 K (figure 15c) [168]. Pan et al [170] have reported pressure-driven dome-shaped superconductivity in Td-WTe 2 .…”

Section: Giant Magnetoresistance and Superconductivity In Distorted Tmentioning

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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Section: Giant Magnetoresistance and Superconductivity In Distorted Tmentioning

confidence: 99%

Two-dimensional inorganic analogues of graphene: transition metal dichalcogenides

Jana¹,

Rao²

2016

Phil. Trans. R. Soc. A.

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“…MoTe2 is an exfoliable transition metal dichalcogenide (TMD) which crystallizes in three symmetries; the semiconducting trigonal-prismatic 2H−phase, the semimetallic 1T ′ monoclinic phase, and the semimetallic orthorhombic T d structure [1][2][3][4] . The 2H−phase displays a band gap of ∼ 1 eV 5 making it appealing for flexible and transparent optoelectronics.…”

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confidence: 99%

Engineering the Structural and Electronic Phases of MoTe₂ through W Substitution

et al. 2017

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MoTe2 is an exfoliable transition metal dichalcogenide (TMD) which crystallizes in three symmetries; the semiconducting trigonal-prismatic 2H−phase, the semimetallic 1T ′ monoclinic phase, and the semimetallic orthorhombic T d structure 1-4 . The 2H−phase displays a band gap of ∼ 1 eV 5 making it appealing for flexible and transparent optoelectronics. The T d−phase is predicted to possess unique topological properties 6-9 which might lead to topologically protected non-dissipative transport channels 9 . Recently, it was argued that it is possible to locally induce phasetransformations in TMDs 3,10,11,14 , through chemical doping 12 , local heating 13 , or electric-field 14,15 to achieve ohmic contacts or to induce useful functionalities such as electronic phase-change memory elements 11 . The combination of semiconducting and topological elements based upon the same compound, might produce a new generation of high performance, low dissipation optoelectronic elements. Here, we show that it is possible to engineer the phases of MoTe2 through W substitution by unveiling the phase-diagram of the Mo1−xWxTe2 solid solution which displays a semiconducting to semimetallic transition as a function of x. We find that only ∼ 8 % of W stabilizes the T d−phase at room temperature. Photoemission spectroscopy, indicates that this phase possesses a Fermi surface akin to that of WTe2 16 .The properties of semiconducting and of semimetallic MoTe 2 are of fundamental interest in their own right, but are also for their potential technological relevance. In the mono-or few-layer limit it is a direct-gap semiconductor, while the bulk has an indirect bandgap 5,17,18 of ∼ 1 eV. The size of the gap is similar to that of Si, making 2H−MoTe 2 particularly appealing for both purely electronic devices 19,20 and optoelectronic applications 21 . Moreover, the existence of different phases opens up the possibility for many novel devices and architectures. For example, controlled conversion of the 1T ′ −MoTe 2 phase to the 2H−phase, as recently reported 22 , could

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“…[1,9,10,11,12] The 1T' or Td phase MX 2 are of the distorted 1T structure, which usually show semi-metallic behavior. [3,[13][14][15] Examples of the latter include WTe 2 and -MoTe 2 , which have drawn special interests lately following some recent revelations of, e.g., the large and unsaturated magnetoresistance, [4,15,16,17,18] pressure-driven superconductivity, [7,19] novel optical properties and characteristics, [11,12,17,18,20] and the topological insulator [14] and Weyl semimetal states. [6,7,21] Metallic TMDs are also good catalysts for hydrodesulfurization and hydrogen evolution reactions.…”

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confidence: 99%

“…This would lead to many new applications of the TMD thin films. [18] In this work, we report growths of both 2H and 1T' MoTe 2 ML by molecular beam epitaxy (MBE). We reveal a dramatic effect of Te adsorption on 1T' phase MoTe 2 formation and growth.…”

mentioning

confidence: 99%

Quantum Effects and Phase Tuning in Epitaxial Hexagonal and Monoclinic MoTe₂ Monolayers

et al. 2017

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Transition-metal dichalcogenides (TMDs) with the common formula MX 2 (M = Mo, W; X=S, Se, Te) exist in different phases such as the hexagonal (2H), octahedral (1T), monoclinic (1T') and orthorhombic (Td) structures. [1,2,[3][4][5][6][7] The 2H phase is most common including, for example, metal disulfides (MS 2 ) and diselenides (MSe 2 ), which are direct gap semiconductors for monolayer (ML) thin films. [1,8] They have attracted extensive research attention in recent years due to their appeals in microelectronic, optoelectronic, spin and valley electronic applications. [1,9,10,11,12] The 1T' or Td phase MX 2 are of the distorted 1T structure, which usually show semi-metallic behavior. [3,[13][14][15] Examples of the latter include WTe 2 and -MoTe 2 , which have drawn special interests lately following some recent revelations of, e.g., the large and unsaturated magnetoresistance, [4,15,16,17,18] pressure-driven superconductivity, [7,19] novel optical properties and characteristics, [11,12,17,18,20] and the topological insulator [14] and Weyl semimetal states. [6,7,21] Metallic TMDs are also good catalysts for hydrodesulfurization and hydrogen evolution reactions. [22] The large difference in electrical properties between 2H and 1T' (Td) phases of MX 2 further makes them promising for phase-change electronics. [23,24] Therefore, tuning and stabilizing the different phases of MX 2 can be of great scientific and application relevance.Among the various TMDs, MoTe 2 takes a special place as there is a small energy difference between its 2H and 1T' phases (~ 43meV per formula unit [5] ). The hexagonal phase of MoTe 2 is slightly more stable than 1T' MoTe 2 under ambient conditions, while the latter becomes more favorable at high temperature and/or under 3 tensile strain. [5,24] In any case, due to the small energy difference between the two structures, there is a high chance for one to obtain samples containing coexisting phases or to purposely tune the structure of MoTe 2 crystal by applying external constraints. This would lead to many new applications of the TMD thin films. [18] In this work, we report growths of both 2H and 1T' MoTe 2 ML by molecular beam epitaxy (MBE). We reveal a dramatic effect of Te adsorption on 1T' phase MoTe 2 formation and growth. By changing the conditions of MBE and by annealing, we can achieve effective tuning of the structural phase of MoTe 2 . Employing scanning tunneling microscopy and spectroscopy (STM/S), we establish unambiguously the structures and electronic characteristics of 2H and 1T' MoTe 2 ML such as the energy bandgap and the density of states (DOS). By consulting with the first principles calculations, we provide an explanation for the stabilization of the otherwise metastable 1T' phase MoTe 2 at the temperature and pressure condition, which is associated with Te adsorption on surface. Figure 2d. From the experimental STS data, we further derive an electronic energy gap of ~ 1.4 eV (refer to Supplementary), a value that is in qualitative agreement with that reported in li...

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Bandgap opening in few-layered monoclinic MoTe2

Cited by 866 publications

References 29 publications

Two-dimensional inorganic analogues of graphene: transition metal dichalcogenides

Two-dimensional inorganic analogues of graphene: transition metal dichalcogenides

Engineering the Structural and Electronic Phases of MoTe₂ through W Substitution

Quantum Effects and Phase Tuning in Epitaxial Hexagonal and Monoclinic MoTe₂ Monolayers

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Bandgap opening in few-layered monoclinic MoTe2

Cited by 866 publications

References 29 publications

Two-dimensional inorganic analogues of graphene: transition metal dichalcogenides

Two-dimensional inorganic analogues of graphene: transition metal dichalcogenides

Engineering the Structural and Electronic Phases of MoTe2 through W Substitution

Quantum Effects and Phase Tuning in Epitaxial Hexagonal and Monoclinic MoTe2 Monolayers

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Engineering the Structural and Electronic Phases of MoTe₂ through W Substitution

Quantum Effects and Phase Tuning in Epitaxial Hexagonal and Monoclinic MoTe₂ Monolayers