Chemically exfoliated 
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 layers: Spectroscopic evidence for the semiconducting nature of the dominant trigonal metastable phase

Pal, Banabir; Singh, Anjali; Sharada, G; Mahale, Pratibha; Kumar, A. V. Anil; Thirupathaiah, S.; Sezen, Hikmet; Amati, Matteo; Gregoratti, Luca; Waghmare, Umesh V.; Sarma, D. D.

doi:10.1103/physrevb.96.195426

Cited by 46 publications

(35 citation statements)

References 54 publications

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“…Similar features are also found in 1-5 layers of MoSe 2 using excitation wavelength 465 nm by Soubelet et al [31] but remain unresolved. Additional Raman modes observed in earlier Raman studies on exfoliated WS 2 and MoS 2 are assigned to different crystal structures embedded in parent hexagonal phase [16,21]. Therefore it is important to discuss XRD measurements before proceeding to further analysis of high pressure measurements.…”

Section: Resultsmentioning

confidence: 98%

“…Though the above studies on layered MoSe 2 show metallization of the sample without any structural transition under stress, a complete experimental characterization of the exfoliated MoSe 2 sample at high pressure is lacking. Exfoliated MoSe 2 layers can develop inherent surface strain similar to MoS 2 and WS 2 [16,21] and therefore a careful detailed high pressure study is needed to address the effect of strain in the structural and electronic behavior of exfoliated MoSe 2 .…”

Section: Introductionmentioning

confidence: 99%

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High pressure anomalies in exfoliated MoSe₂: resonance Raman and x-ray diffraction studies

Saha

Ghosh

Mazumder

et al. 2020

Mater. Res. Express

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Detailed high pressure Resonance Raman (RR) Spectroscopy and x-ray diffraction (XRD) studies are carried out on 3-4 layered MoSe 2 obtained by liquid exfoliation. Analysis of ambient XRD pattern and RR spectra indicate the presence of a triclinic phase along with its parent hexagonal phase. Slope change in the linear behavior of reduced pressure (H) with respect to Eulerian strain ( f E ) is observed at about 13 GPa in hexagonal phase and at about 17 GPa for the triclinic phase. High pressure Raman measurements using two different pressure transmitting media (PTM) show three linear pressure regions, separated by pressure values around which anomalies in the structure are observed. A broad minimum in the FWHM values of E g 2 1 mode at about 10-12 GPa indicate to an electron-phonon coupling. Above 33 GPa the sample completely gets converted to the triclinic structure, which indicates the importance of strain in structural as well as electronic properties of two dimensional materials.

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Section: Resultsmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

High pressure anomalies in exfoliated MoSe₂: resonance Raman and x-ray diffraction studies

Saha

Ghosh

Mazumder

et al. 2020

Mater. Res. Express

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“…A representative way of manipulating the polymorphs, particularly for group 6 TMDs (e.g., MoS 2 ), is chemical intercalation of electron‐donating alkali metals, such as Li, Na, and K, into the TMDs . Phase engineering by chemical intercalation has provided breakthroughs in various areas: improving the contact resistance of 2D field effect transistors, efficient exfoliation of the TMDs down to a monolayer, and improving the mechanical properties and electrochemical catalytic activity (e.g., hydrogen evolution reaction, HER) . In those studies, a key feature is the formation of mixed phase structures by inhomogeneous chemical phase transition in the TMDs .…”

Section: Introductionmentioning

confidence: 99%

Vertical Heterophase for Electrical, Electrochemical, and Mechanical Manipulations of Layered MoTe₂

Eshete

Ling

Kim

et al. 2019

Adv Funct Materials

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Phase engineering is a breakthrough for various electronic and energy device applications with transition metal dichalcogenides (TMDs). Chemical methods, such as lithium intercalation, are mostly used for phase engineering, which achieves atomically thin flakes and high catalytic performances in several group 6 TMDs including MoS 2 . However, chemical methods cannot be applied to MoTe 2 , a widely investigated group 6 TMD with intriguing semiconducting, topological, and catalytic properties. The lack of modifying MoTe 2 by chemical methods remains a puzzling issue considering the small energy difference between the polymorphs of MoTe 2 . Here, a convectionassisted lithium ion intercalation and phase transition is reported to achieve a vertical heterophase in a MoTe 2 crystal. The vertical heterophase in MoTe 2 reduces the Schottky barrier with metal electrodes down to 66 meV, enhancing the overall ion conductance for electrochemical hydrogen production. Moreover, the weakened adhesion of the 1T' phase layers on the top and bottom surfaces in the vertical heterophase, formed by the intercalation, enables a unique surface tension-driven exfoliation of MoTe 2 flakes. The heterophase chemical engineering suggests a new platform for hybrid catalysts and next-generation electronic devices based on 2D materials.

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“…Among the reported structural phases, 2H, 2H′ and 3R are semiconductors, 1T′ and 1T″ are narrow bandgap semiconductors and 1T is metallic 9 – 13 . The 2H is the most widely explored phase for device applications 5 , 14 – 18 .…”

Section: Introductionmentioning

confidence: 99%

“…The 2H phase belongs to the space group P 6 3 mmc with a trigonal prismatic coordination between Mo and S atoms and 1T belongs to space group with an octahedral coordination between the Mo and S atoms 26 . The 1T′ and 1T″ are distorted 1T phases 13 . The possibility of controllably and selectively engineering metallic 1T MoS 2 regions starting from the semiconducting 2H MoS 2 provides a new route for monolithic 2D circuits.…”

Section: Introductionmentioning

confidence: 99%

Stable and scalable 1T MoS2 with low temperature-coefficient of resistance

Sharma

Surendran

Varghese

et al. 2018

Sci Rep

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Monolithic realization of metallic 1T and semiconducting 2H phases makes MoS2 a potential candidate for future microelectronic circuits. A method for engineering a stable 1T phase from the 2H phase in a scalable manner and an in-depth electrical characterization of the 1T phase is wanting at large. Here we demonstrate a controllable and scalable 2H to 1T phase engineering technique for MoS2 using microwave plasma. Our method allows lithographically defining 1T regions on a 2H sample. The 1T samples show excellent temporal and thermal stability making it suitable for standard device fabrication techniques. We conduct both two-probe and four-probe electrical transport measurements on devices with back-gated field effect transistor geometry in a temperature range of 4 K to 300 K. The 1T samples exhibit Ohmic current-voltage characteristics in all temperature ranges without any dependence to the gate voltage, a signature of a metallic state. The sheet resistance of our 1T MoS2 sample is considerably lower and the carrier concentration is a few orders of magnitude higher than that of the 2H samples. In addition, our samples show negligible temperature dependence of resistance from 4 K to 300 K ruling out any hoping mediated or activated electrical transport.

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Chemically exfoliated MoS2 layers: Spectroscopic evidence for the semiconducting nature of the dominant trigonal metastable phase

Cited by 46 publications

References 54 publications

High pressure anomalies in exfoliated MoSe₂: resonance Raman and x-ray diffraction studies

High pressure anomalies in exfoliated MoSe₂: resonance Raman and x-ray diffraction studies

Vertical Heterophase for Electrical, Electrochemical, and Mechanical Manipulations of Layered MoTe₂

Stable and scalable 1T MoS2 with low temperature-coefficient of resistance

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Chemically exfoliated MoS2 layers: Spectroscopic evidence for the semiconducting nature of the dominant trigonal metastable phase

Cited by 46 publications

References 54 publications

High pressure anomalies in exfoliated MoSe2: resonance Raman and x-ray diffraction studies

High pressure anomalies in exfoliated MoSe2: resonance Raman and x-ray diffraction studies

Vertical Heterophase for Electrical, Electrochemical, and Mechanical Manipulations of Layered MoTe2

Stable and scalable 1T MoS2 with low temperature-coefficient of resistance

Contact Info

Product

Resources

About

High pressure anomalies in exfoliated MoSe₂: resonance Raman and x-ray diffraction studies

High pressure anomalies in exfoliated MoSe₂: resonance Raman and x-ray diffraction studies

Vertical Heterophase for Electrical, Electrochemical, and Mechanical Manipulations of Layered MoTe₂