A review on Raman finger prints of doping and strain effect in TMDCs

Iqbal, Muhammad Waqas; Shahzad, Kinza; Akbar, Rehan; Hussain, Ghulam

doi:10.1016/j.mee.2019.111152

Cited by 88 publications

(71 citation statements)

References 92 publications

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“…The electron doping effect can induce the frequency shifts of A 1g mode due to the strong electron–phonon interaction 47 . Consult to previous literature, the E 2g mode is not sensitive to the electron doping effect 47 , 48 . So it is assumed that the electron doping effect induced Raman shift of E 2g mode did not change with temperature, or the changes can be neglected.…”

Section: Resultssupporting

confidence: 56%

Thermal expansion coefficient of few-layer MoS2 studied by temperature-dependent Raman spectroscopy

Lin

Liu

Tian

et al. 2021

Sci Rep

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The thermal expansion coefficient is an important thermal parameter that influences the performance of nanodevices based on two-dimensional materials. To obtain the thermal expansion coefficient of few-layer MoS2, suspended MoS2 and supported MoS2 were systematically investigated using Raman spectroscopy in the temperature range from 77 to 557 K. The temperature-dependent evolution of the Raman frequency shift for suspended MoS2 exhibited prominent differences from that for supported MoS2, obviously demonstrating the effect due to the thermal expansion coefficient mismatch between MoS2 and the substrate. The intrinsic thermal expansion coefficients of MoS2 with different numbers of layers were calculated. Interestingly, negative thermal expansion coefficients were obtained below 175 K, which was attributed to the bending vibrations in the MoS2 layer during cooling. Our results demonstrate that Raman spectroscopy is a feasible tool for investigating the thermal properties of few-layer MoS2 and will provide useful information for its further application in photoelectronic devices.

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Section: Resultssupporting

confidence: 56%

Thermal expansion coefficient of few-layer MoS2 studied by temperature-dependent Raman spectroscopy

Lin

Liu

Tian

et al. 2021

Sci Rep

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“…Thus, the generation of active Co IV species that can participate in a fast and efficient OER process should lead to the observed red-shift of the Raman signals. In contrast, blue-shifts in Raman signals usually suggest lattice contraction and charge redistribution 64 , 69 . Unlike the more active Co 3 O 4 /CeO 2 , the pure Co 3 O 4 catalyst would go through substantial charge-accumulation surface reconstruction (Co III Co IV ↔ Co IV Co IV ) at ~1.62 V around the onset for OER.…”

Section: Resultsmentioning

confidence: 99%

Modifying redox properties and local bonding of Co3O4 by CeO2 enhances oxygen evolution catalysis in acid

et al. 2021

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Developing efficient and stable earth-abundant electrocatalysts for acidic oxygen evolution reaction is the bottleneck for water splitting using proton exchange membrane electrolyzers. Here, we show that nanocrystalline CeO2 in a Co3O4/CeO2 nanocomposite can modify the redox properties of Co3O4 and enhances its intrinsic oxygen evolution reaction activity, and combine electrochemical and structural characterizations including kinetic isotope effect, pH- and temperature-dependence, in situ Raman and ex situ X-ray absorption spectroscopy analyses to understand the origin. The local bonding environment of Co3O4 can be modified after the introduction of nanocrystalline CeO2, which allows the CoIII species to be easily oxidized into catalytically active CoIV species, bypassing the potential-determining surface reconstruction process. Co3O4/CeO2 displays a comparable stability to Co3O4 thus breaks the activity/stability tradeoff. This work not only establishes an efficient earth-abundant catalysts for acidic oxygen evolution reaction, but also provides strategies for designing more active catalysts for other reactions.

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“…Raman spectroscopy is an experimental technique which is directly sensitive to the crystal structure. [ 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 ] Previous Raman spectroscopy studies of the bulk 1 T ′‐MoTe 2 crystals indicate that in the high‐temperature 1 T ′ phase at T ≥ 250 K upon cooling (or at T ≥ 260 K upon warming), the out‐of‐plane vibration mode D around 125 cm –1 is Raman in‐active (i.e., only infrared active) and is absent in the Raman spectra due to the centrosymmetry of the monoclinic 1 T ′ structure, while in the low‐temperature T d phase at T < 250 K upon cooling (or at T < 260 K upon warming), the out‐of‐plane vibration mode D becomes both Raman‐ and infrared‐active and can be probed by Raman spectroscopy owing to the centrosymmetry breaking in the orthorhombic T d structure (see the two vibration modes D and E in the Raman spectra of the MoTe 2 bulk crystal with the orthorhombic T d structure measured at T = 80 K in Figure 2 a , the vibration mode e in the Raman spectra of the MoTe 2 bulk crystal with the monoclinic 1 T ′ structure at T = 300 K in Figure 2b , and the Raman spectra of the MoTe 2 bulk crystal in the energy range from 60 to 300 cm –1 in Figure S1 , Supporting Information). [ 35 , 36 , 37 , 38 , 39 , 40 ] Thus, the presence of the out‐of‐plane vibration mode D can be regarded as a spectroscopic signature of the temperature‐driven structural phase transition in MoTe 2 from the high‐temperature monoclinic 1 T ′ structure to the low‐temperature orthorhombic T d structure.…”

Section: Resultsmentioning

confidence: 99%

Persistence of Monoclinic Crystal Structure in 3D Second‐Order Topological Insulator Candidate 1T′‐MoTe₂ Thin Flake Without Structural Phase Transition

Huang

Hou

et al. 2021

Advanced Science

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A van der Waals material, MoTe 2 with a monoclinic 1T′ crystal structure is a candidate for 3D second-order topological insulators (SOTIs) hosting gapless hinge states and insulating surface states. However, due to the temperature-induced structural phase transition, the monoclinic 1T′ structure of MoTe 2 is transformed into the orthorhombic T d structure as the temperature is lowered, which hinders the experimental verification and electronic applications of the predicted SOTI state at low temperatures. Here, systematic Raman spectroscopy studies of the exfoliated MoTe 2 thin flakes with variable thicknesses at different temperatures, are presented. As a spectroscopic signature of the orthorhombic T d structure of MoTe 2 , the out-of-plane vibration mode D at ≈ 125 cm -1 is always visible below a certain temperature in the multilayer flakes thicker than ≈ 27.7 nm, but vanishes in the temperature range from 80 to 320 K when the flake thickness becomes lower than ≈ 19.5 nm. The absence of the out-of-plane vibration mode D in the Raman spectra here demonstrates not only the disappearance of the monoclinic-to-orthorhombic phase transition but also the persistence of the monoclinic 1T′ structure in the MoTe 2 thin flakes thinner than ≈ 19.5 nm at low temperatures down to 80 K, which may be caused by the high enough density of the holes introduced during the gold-enhanced exfoliation process and exposure to air. The MoTe 2 thin flakes with the low-temperature monoclinic 1T′ structure provide a material platform for realizing SOTI states in van der Waals materials at low temperatures, which paves the way for developing a new generation of electronic devices based on SOTIs.

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A review on Raman finger prints of doping and strain effect in TMDCs

Cited by 88 publications

References 92 publications

Thermal expansion coefficient of few-layer MoS2 studied by temperature-dependent Raman spectroscopy

Thermal expansion coefficient of few-layer MoS2 studied by temperature-dependent Raman spectroscopy

Modifying redox properties and local bonding of Co3O4 by CeO2 enhances oxygen evolution catalysis in acid

Persistence of Monoclinic Crystal Structure in 3D Second‐Order Topological Insulator Candidate 1T′‐MoTe₂ Thin Flake Without Structural Phase Transition

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A review on Raman finger prints of doping and strain effect in TMDCs

Cited by 88 publications

References 92 publications

Thermal expansion coefficient of few-layer MoS2 studied by temperature-dependent Raman spectroscopy

Thermal expansion coefficient of few-layer MoS2 studied by temperature-dependent Raman spectroscopy

Modifying redox properties and local bonding of Co3O4 by CeO2 enhances oxygen evolution catalysis in acid

Persistence of Monoclinic Crystal Structure in 3D Second‐Order Topological Insulator Candidate 1T′‐MoTe2 Thin Flake Without Structural Phase Transition

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Persistence of Monoclinic Crystal Structure in 3D Second‐Order Topological Insulator Candidate 1T′‐MoTe₂ Thin Flake Without Structural Phase Transition