Anomalous Raman scattering and lattice dynamics in mono- and few-layer WTe<sub>2</sub>

Kim, Young‐Hee; Jhon, Young In; Park, June; Kim, Jae‐Hun; Lee, Seok; Jhon, Young Min

doi:10.1039/c5nr06098b

Cited by 99 publications

(124 citation statements)

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“…Using the same approach, we also studied the evolution of the Raman-active phonon modes as a function of layer number. We find that the

A_{1}^{9}

should redshift from 211.36 cm −1 for monolayer material to 209.53 cm −1 for bulk, in agreement with our measurements and previous DFT studies [21, 31]. …”

Section: Characterization Of Monolayer 1t’-wte2 Flakessupporting

confidence: 93%

“…The flake was encapsulated with large-area graphene to avoid degradation during the measurements. Two main Raman peaks were observed: the in-plane

A_{1}^{7}

peak, and the

A_{1}^{9}

peak, which contains both in-plane and out-of-plane vibrations [21]. For the monolayer region, the

A_{1}^{7}

and

A_{1}^{9}

peaks were observed at 163.2 cm −1 and 214.7 cm −1 , respectively.…”

Section: Characterization Of Monolayer 1t’-wte2 Flakesmentioning

confidence: 99%

“…Bi-layer 1T’-WTe 2 is reported to be unstable under ambient conditions, as evidenced by a decay in the Raman signal intensity over the course of several hours [21]. If bi-layer samples decay in hours, one might expect that monolayer samples decay much more quickly.…”

Section: Degradation Of Monolayer 1t’-wte2 Under Ambient Conditionsmentioning

confidence: 99%

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Large-area synthesis of high-quality monolayer 1T’-WTe ₂ flakes

et al. 2017

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Large-area growth of monolayer films of the transition metal dichalcogenides is of the utmost importance in this rapidly advancing research area. The mechanical exfoliation method offers high quality monolayer material but it is a problematic approach when applied to materials that are not air stable. One important example is 1T’-WTe2, which in multilayer form is reported to possess a large non saturating magnetoresistance, pressure induced superconductivity, and a weak antilocalization effect, but electrical data for the monolayer is yet to be reported due to its rapid degradation in air. Here we report a reliable and reproducible large-area growth process for obtaining many monolayer 1T’-WTe2 flakes. We confirmed the composition and structure of monolayer 1T’-WTe2 flakes using x-ray photoelectron spectroscopy, energy-dispersive x-ray spectroscopy, atomic force microscopy, Raman spectroscopy and aberration corrected transmission electron microscopy. We studied the time dependent degradation of monolayer 1T’-WTe2 under ambient conditions, and we used first-principles calculations to identify reaction with oxygen as the degradation mechanism. Finally we investigated the electrical properties of monolayer 1T’-WTe2 and found metallic conduction at low temperature along with a weak antilocalization effect that is evidence for strong spin–orbit coupling.

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“…Using the same approach, we also studied the evolution of the Raman-active phonon modes as a function of layer number. We find that the

A_{1}^{9}

should redshift from 211.36 cm −1 for monolayer material to 209.53 cm −1 for bulk, in agreement with our measurements and previous DFT studies [21, 31]. …”

Section: Characterization Of Monolayer 1t’-wte2 Flakessupporting

confidence: 93%

“…The flake was encapsulated with large-area graphene to avoid degradation during the measurements. Two main Raman peaks were observed: the in-plane

A_{1}^{7}

peak, and the

A_{1}^{9}

peak, which contains both in-plane and out-of-plane vibrations [21]. For the monolayer region, the

A_{1}^{7}

and

A_{1}^{9}

peaks were observed at 163.2 cm −1 and 214.7 cm −1 , respectively.…”

Section: Characterization Of Monolayer 1t’-wte2 Flakesmentioning

confidence: 99%

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Large-area synthesis of high-quality monolayer 1T’-WTe ₂ flakes

et al. 2017

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“…[ 59 ] It was also shown that WTe 2 with more than six layers exhibits almost the same Raman frequencies as those in bulk WTe 2 , which are 118, 134, 164, and 212 cm −1 , respectively. [ 59 ] It was also shown that WTe 2 with more than six layers exhibits almost the same Raman frequencies as those in bulk WTe 2 , which are 118, 134, 164, and 212 cm −1 , respectively.…”

Section: Preparation Of Wte 2 Microfl Akesmentioning

confidence: 84%

Near‐Infrared Saturable Absorption of Defective Bulk‐Structured WTe₂ for Femtosecond Laser Mode‐Locking

Koo

Jhon

Park

et al. 2016

Adv Funct Materials

Self Cite

175

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Mono‐ and few‐layer transition metal dichalcogenides (TMDCs) have been widely used as saturable absorbers for ultrashort laser pulse generation, but their preparation is complicated and requires much expertise. The possible use of bulk‐structured TMDCs as saturable absorbers is therefore a very intriguing and technically important issue in laser technology. Here, for the first time, it is demonstrated that defective, bulk‐structured WTe2 microflakes can serve as a base saturable absorption material for fast mode‐lockers that can produce femtosecond pulses from fiber laser cavities. They have a modulation depth of 2.85%, from which stable laser pulses with a duration of 770 fs are readily obtained at a repetition rate of 13.98 MHz and a wavelength of 1556.2 nm, which is comparable to the performance achieved using mono‐ and few‐layer TMDCs. Density functional theory calculations show that the oxidative and defective surfaces of WTe2 microflakes do not degrade their saturable absorption performance in the near‐infrared range, allowing for a broad range of operative bandwidth. This study suggests that saturable absorption is an intrinsic property of TMDCs without relying on their structural dimensionality, providing a new direction for the development of TMDC‐based saturable absorbers.

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“…This novel scenario promises an abundance of unexplored experimental possibilities, such as the observation of magnetic breakdown in transport experiments [33]. Our theory and tight-binding models should serve as important resources for ongoing experimental efforts [34,35] focused on the synthesis and the study of MTe 2 monolayers.…”

Section: Introductionmentioning

confidence: 99%

Topological Nonsymmorphic Metals from Band Inversion

et al. 2016

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We expand the phase diagram of two-dimensional, nonsymmorphic crystals at integer fillings that do not guarantee gaplessness. In addition to the trivial, gapped phase that is expected, we find that band inversion leads to a class of topological, gapless phases. These topological phases are exemplified by the monolayers of MTe 2 (M ¼ W; Mo) if spin-orbit coupling is neglected. We characterize the Dirac band touching of these topological metals by the Wilson loop of the non-Abelian Berry gauge field. Furthermore, we develop a criterion for the proximity of these topological metals to 2D and 3D Z 2 topological insulators when spinorbit coupling is included; our criterion is based on nonsymmorphic symmetry eigenvalues, and may be used to identify topological materials without inversion symmetry. An additional feature of the Dirac cone in monolayer MTe 2 is that it tilts over in a Lifshitz transition to produce electron and hole pockets-a type-II Dirac cone. These pockets, together with the pseudospin structure of the Dirac electrons, suggest a unified, topological explanation for the recently reported, nonsaturating magnetoresistance in WTe 2 , as well as its circular dichroism in photoemission. We complement our analysis and first-principles band structure calculations with an ab-initio-derived tight-binding model for the WTe 2 monolayer.

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Anomalous Raman scattering and lattice dynamics in mono- and few-layer WTe₂

Cited by 99 publications

References 50 publications

Large-area synthesis of high-quality monolayer 1T’-WTe ₂ flakes

Large-area synthesis of high-quality monolayer 1T’-WTe ₂ flakes

Near‐Infrared Saturable Absorption of Defective Bulk‐Structured WTe₂ for Femtosecond Laser Mode‐Locking

Topological Nonsymmorphic Metals from Band Inversion

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Anomalous Raman scattering and lattice dynamics in mono- and few-layer WTe2

Cited by 99 publications

References 50 publications

Large-area synthesis of high-quality monolayer 1T’-WTe 2 flakes

Large-area synthesis of high-quality monolayer 1T’-WTe 2 flakes

Near‐Infrared Saturable Absorption of Defective Bulk‐Structured WTe2 for Femtosecond Laser Mode‐Locking

Topological Nonsymmorphic Metals from Band Inversion

Contact Info

Product

Resources

About

Anomalous Raman scattering and lattice dynamics in mono- and few-layer WTe₂

Large-area synthesis of high-quality monolayer 1T’-WTe ₂ flakes

Large-area synthesis of high-quality monolayer 1T’-WTe ₂ flakes

Near‐Infrared Saturable Absorption of Defective Bulk‐Structured WTe₂ for Femtosecond Laser Mode‐Locking