Single- and few-layer WTe<sub>2</sub>and their suspended nanostructures: Raman signatures and nanomechanical resonances

Lee, Jae-Sung; Ye, Fan; Wang, Zenghui; Yang, Rui; Hu, Jin; Mao, Zhiqiang; Wei, Jian; Feng, Philip X.‐L.

doi:10.1039/c6nr00492j

Cited by 45 publications

(43 citation statements)

References 29 publications

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“…Thus, the shift of major peaks and the intensity ratio of the

A'_{1}^{} (1^{1})

and

A'_{1}^{} (2^{2})

peaks can be used as convenient measures to rapidly characterize thickness of GaSe layers. A similar effect has been observed in TMDs like WS 2 , WSe 2 , MoSe 2 , WTe 2 , NbSe 2 , PtSe 2 , GaS, etc …”

Section: Resultssupporting

confidence: 76%

Quantum Confinement and Gas Sensing of Mechanically Exfoliated GaSe

Zhang

Lee

et al. 2016

Adv Materials Technologies

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GaSe layers with thicknesses ranging from a monolayer to 100 nm are successfully mechanically exfoliated for use in gas sensing. In combination with density functional theory calculations, general guidelines to determine the number of layers using Raman spectra are presented. With decreasing layer numbers, quantum confinement induces a red-shift for out-of-plane modes and a blue-shift for in-plane modes. The relative Raman shifts of the out-of-plane vibrational modes A A ( (1 1 ) ′ ′ mode of monolayer GaSe (≈−1.99 × 10 −2 cm −1 K −1 ) being almost double that of 100 layer GaSe (≈−1.22 × 10 −2 cm −1 K −1 ). Finally, the exfoliated GaSe is used for gas sensing and shows high sensitivity, displaying a minimum detection limit of 4 ppm for NH 3 at room temperature, confirming the potential of mechanically exfoliated GaSe in high-sensitivity gas sensors.

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“…Thus, the shift of major peaks and the intensity ratio of the

A'_{1}^{} (1^{1})

and

A'_{1}^{} (2^{2})

Section: Resultssupporting

confidence: 76%

Quantum Confinement and Gas Sensing of Mechanically Exfoliated GaSe

Zhang

Lee

et al. 2016

Adv Materials Technologies

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“…Figure 1h displays the Raman spectroscopy of WTe 2 of 2 to 8 layers probed by a 532 nm wavelength laser. The bi-layer shows least peaks and lowest signal, with 6 distinct Raman bands observed around 86.7, 108.3, 120.0, 135.6, 164.2 and 215.3 cm -1 , respectively, in agreement of those reported in previous works [16][17][18]. All spectra are fitted via single Lorentzian and renormalized for visual clarity as seen in Fig.…”

supporting

confidence: 82%

Effect of aging-induced disorder on the quantum transport properties of few-layer WTe ₂

Liu

Chen

et al. 2016

2D Mater.

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Atomically thin layers of transition-metal dicalcogenides (TMDCs) are often known to be metastable in the ambient atmosphere. Understanding the mechanism of degradation is essential for their future applications in nanoelectronics, and thus has attracted intensive interest recently. Here, we demonstrate a systematic study of atomically thin WTe 2 in its low temperature quantum electronic transport properties. Strikingly, while the temperature dependence of few layered WTe 2 showed clear metallic tendency in the fresh state, degraded devices first exhibited a re-entrant insulating behavior, and finally entered a fully insulating state. Correspondingly, a crossover from parabolic to linear magnetoresistance, and finally to weak anti-localization was seen. Real-time Raman scattering measurement, together with transmission electron microscopy studies done before and after air degradation of atomically thin WTe 2 further confirmed that the material gradually form amorphous islands. It thus leads to localized electronic states and explains the low temperature Coulomb gap observed in transport measurements. Our study reveals for the first time the correlation between the unusual magnetotransport and disorder in few-layered WTe 2 , which is indispensable in providing guidance on its future devices application. [4,5]. Albeit a layered material, WTe 2 devices in the two-dimensional (2D) limit have been rarely reported, with its experimental investigations mostly restrained in the bulk regime. Unlike other transition-metal dichalcogenides (TMDCs), instead of 2H phase, Td-(also addressed as 1T'-) phase of bulk WTe 2 occupies the lower energy state, whose two nearly perfectly compensated electron and hole bands result in a large unsaturated classical magnetotransport, with a parabolic dependence of the applied magnetic field B [6]. Meanwhile, strong anisotropy was found in its bulk form, which gives rise to some exotic linear magnetoresistance in a specific measurement configuration [7]. Moreover, recent angle resolved photon electron spectroscopy (ARPES) studies showed subtleness of the band structure of bulk WTe 2 [8][9][10][11], intriguing possible peculiar electronic properties in the few layered scenario. In the 2D limit, electrostatic gate can, in principle, largely tune the carrier density, thus breaking down the electron-hole balance, leading to new opportunities.Despite the fact that WTe 2 can be readily exfoliated against the weak interlayer van-der-Waals bonding, atomically thin WTe 2 is proven to rapidly age in ambient atmosphere like many of the TMDCs [12]. Together with the extinction of optical contrast and Raman signal after air exposure [13], ultra thin WTe 2 flakes were reported to exhibit, rather than the so-called semi-metal state, an insulating behavior as a function of number of layers, with the lack of a systematic analysis of the aging effect on the quantum transport [14]. Such air instability therefore hampers the further possibilities for nanoelectronic devices of, for example, few-layered WTe 2 fi...

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“…Figure b shows the optical microscopy images of 1L, 2L, and 3L WTe 2 and Figure c shows the Raman spectra of corresponding regions in (b) in vacuum conditions. In our previous study, we have observed total 12 peaks in few‐layer WTe 2 . As number of layers decreases to 3L, many peaks' intensities decrease significantly and only four peaks remain robust due to space group evolution from bulk ( C 2v ) to 1L ( C 2h ) WTe 2 .…”

mentioning

confidence: 83%

“…In our previous study, we have observed total 12 peaks in few-layer WTe 2 . [7] As number of layers decreases to 3L, many peaks' intensities decrease significantly and only four peaks remain robust due to space group evolution from bulk (C 2v ) to 1L (C 2h ) WTe 2 . [6] We refer these four peaks as P1, P2, P3, and P4 hereafter (see Figure 1c).…”

mentioning

confidence: 99%

Environmental Instability and Degradation of Single‐ and Few‐Layer WTe₂ Nanosheets in Ambient Conditions

Lee

et al. 2016

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Single- and few-layer WTe₂and their suspended nanostructures: Raman signatures and nanomechanical resonances

Cited by 45 publications

References 29 publications

Quantum Confinement and Gas Sensing of Mechanically Exfoliated GaSe

Quantum Confinement and Gas Sensing of Mechanically Exfoliated GaSe

Effect of aging-induced disorder on the quantum transport properties of few-layer WTe ₂

Environmental Instability and Degradation of Single‐ and Few‐Layer WTe₂ Nanosheets in Ambient Conditions

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Single- and few-layer WTe2and their suspended nanostructures: Raman signatures and nanomechanical resonances

Cited by 45 publications

References 29 publications

Quantum Confinement and Gas Sensing of Mechanically Exfoliated GaSe

Quantum Confinement and Gas Sensing of Mechanically Exfoliated GaSe

Effect of aging-induced disorder on the quantum transport properties of few-layer WTe 2

Environmental Instability and Degradation of Single‐ and Few‐Layer WTe2 Nanosheets in Ambient Conditions

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Product

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Single- and few-layer WTe₂and their suspended nanostructures: Raman signatures and nanomechanical resonances

Effect of aging-induced disorder on the quantum transport properties of few-layer WTe ₂

Environmental Instability and Degradation of Single‐ and Few‐Layer WTe₂ Nanosheets in Ambient Conditions