Anomalous Raman spectra and thickness-dependent electronic properties of WSe<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mrow /><mml:mn>2</mml:mn></mml:msub></mml:math>

Şahin, Hasan; Tongay, Sefaattin; Horzum, Şeyda; Fan, Wen; Zhou, Jian; Li, J.; Wu, Junqiao; Peeters, F. M.

doi:10.1103/physrevb.87.165409

Cited by 463 publications

(363 citation statements)

References 30 publications

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“…In bulk 2H-WSe 2 , the E 1 2g and A 1g modes degenerate, giving rise to only a single Raman band. When the dimensionality is decreased, this peak splits into two, with the E 1 2g band at a frequency lower than that of the A 1g band and with greater intensity [79] Raman bands of mechanically exfoliated monolayer TMDCs show significant temperature dependence. The temperature coefficients (α) of the A 1g and E 1 2g modes of MoS 2 were found to be −0.0123 cm −1 K −1 and −0.0132 cm −1 K −1 , respectively [80][81][82].…”

Section: Raman Spectroscopymentioning

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: Raman Spectroscopymentioning

confidence: 99%

Two-dimensional inorganic analogues of graphene: transition metal dichalcogenides

Jana¹,

Rao²

2016

Phil. Trans. R. Soc. A.

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“…The discrepancy is partly due to the fact that some calculations neglect spin-orbit interactions. In bilayer WSe 2 , the two valleys are expected to be nearly degenerate 25 . Degeneracy of these valleys indicates increased probability for intervalley scattering of the carriers.…”

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confidence: 99%

Origin of Indirect Optical Transitions in Few-Layer MoS₂, WS₂, and WSe₂

et al. 2013

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It has been well established that single layer MX 2 (M=Mo,W and X=S,Se) are direct gap semiconductors with band edges coinciding at the K point in contrast to their indirect gap multilayer counterparts. In few-layer MX 2 , there are two valleys along the Γ-K line with similar energy. There is little understanding on which of the two valleys forms the conduction band minimum (CBM) in this thickness regime. We investigate the conduction band valley structure in

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“…During the cooling, the electronic temperature dynamically changes, modifying also the coupling strength. With a calculated energy difference of the conduction band minimum at K and Σ of 240 meVand optical phonon energies of 15-30 meV (at the corner of the BZ) [35], photoexcited electrons emit approximately ten phonons on average. The quantitative difference of the single-state lifetime and the measured q-dependent population dynamics is therefore in good agreement with expectations from a kinetic relaxation model.…”

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confidence: 99%

Momentum-Resolved View of Electron-Phonon Coupling in Multilayer WSe2

et al. 2017

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We investigate the interactions of photoexcited carriers with lattice vibrations in thin films of the layered transition metal dichalcogenide (TMDC) WSe 2 . Employing femtosecond electron diffraction with monocrystalline samples and first-principles density functional theory calculations, we obtain a momentumresolved picture of the energy transfer from excited electrons to phonons. The measured momentumdependent phonon population dynamics are compared to first-principles calculations of the phonon linewidth and can be rationalized in terms of electronic phase-space arguments. The relaxation of excited states in the conduction band is dominated by intervalley scattering between Σ valleys and the emission of zone boundary phonons. Transiently, the momentum-dependent electron-phonon coupling leads to a nonthermal phonon distribution, which, on longer time scales, relaxes to a thermal distribution via electron-phonon and phononphonon collisions. Our results constitute a basis for monitoring and predicting out of equilibrium electrical and thermal transport properties for nanoscale applications of TMDCs. DOI: 10.1103/PhysRevLett.119.036803 Semiconducting transition metal dichalcogenides combine crystal structures of chemically stable twodimensional layers with indirect band gaps in the visible and near infrared optical range. Their intrinsic stability down to monolayer thicknesses [1,2] in combination with the possibility to create artificial stacks [3,4] suggests them for electronic and optoelectronic applications like nanoscale transistors or photodetectors with atomically sharp p-n junctions [5][6][7]. In such devices, the electronic mobilities, electronic coupling, and heat conductivities within the layers and across interfaces are of central interest. Whereas macroscopic heat and electrical transport properties can be measured directly, the observation of the underlying microscopic processes, i.e., the scattering processes of carriers and of phonons, requires methods with time, momentum, and energy resolution to be understood in detail. Such information can be decisive in the correct determination of transport properties [8,9] or energy relaxation [10][11][12]. A momentum-resolved view of scattering processes will in addition be of uttermost importance in conceiving novel quantum technologies harnessing spin and valley degrees of freedom [13][14][15], as they utilize carrier populations at specific positions in momentum space. While time-and angle-resolved photoemission spectroscopy provides this level of detail for electron dynamics, see, for instance, Refs. [16,17], techniques for studying ultrafast structural dynamics have not yet reached the equivalent level of resolution. Recently, the investigation of the time-and momentum-resolved phonon population has been demonstrated with ultrafast x-ray and electron diffraction [18][19][20][21].This work reports a momentum-resolved study of scattering processes and the resulting energy transfer between photoexcited electrons and phonons in thin bulklike films of WS...

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Anomalous Raman spectra and thickness-dependent electronic properties of WSe2

Cited by 463 publications

References 30 publications

Two-dimensional inorganic analogues of graphene: transition metal dichalcogenides

Two-dimensional inorganic analogues of graphene: transition metal dichalcogenides

Origin of Indirect Optical Transitions in Few-Layer MoS₂, WS₂, and WSe₂

Momentum-Resolved View of Electron-Phonon Coupling in Multilayer WSe2

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Anomalous Raman spectra and thickness-dependent electronic properties of WSe2

Cited by 463 publications

References 30 publications

Two-dimensional inorganic analogues of graphene: transition metal dichalcogenides

Two-dimensional inorganic analogues of graphene: transition metal dichalcogenides

Origin of Indirect Optical Transitions in Few-Layer MoS2, WS2, and WSe2

Momentum-Resolved View of Electron-Phonon Coupling in Multilayer WSe2

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Product

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Origin of Indirect Optical Transitions in Few-Layer MoS₂, WS₂, and WSe₂