The thermal expansion of 2H-MoS2, 2H-MoSe2and 2H-WSe2between 20 and 800°C

El-Mahalawy, S. H.; Evans, B.

doi:10.1107/s0021889876011709

Cited by 153 publications

(112 citation statements)

References 13 publications

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“…The redshift indicates a temperature-induced reduction of the band gap due to thermal expansion of the crystal lattice. The fact that the redshift is far less pronounced in the CVD-grown sample shows that the CVD-grown MoS 2 film strongly adheres to the SiO 2 substrate, which has a very small thermal expansion coefficient (α SiO 2 = 0.24 × 10 [28]. A very similar reduction of the spectral shift with temperature was observed in oxide-covered MoS 2 flakes on SiO 2 substrates [26].…”

Section: Photoluminescencementioning

confidence: 66%

A direct comparison of CVD-grown and exfoliated MoS₂using optical spectroscopy

Plechinger

Mann

Preciado

et al. 2014

Semicond. Sci. Technol.

106

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MoS 2 is a highly interesting material, which exhibits a crossover from an indirect band gap in the bulk crystal to a direct gap for single layers. Here, we perform a direct comparison between large-area MoS 2 films grown by chemical vapor deposition (CVD) and MoS 2 flakes prepared by mechanical exfoliation from mineral bulk crystal. Raman spectroscopy measurements show differences between the in-plane and out-of-plane phonon mode positions in CVD-grown and exfoliated MoS 2 . Photoluminescence (PL) mapping reveals large regions in the CVD-grown films that emit strong PL at room-temperature, and low-temperature PL scans demonstrate a large spectral shift of the A exciton emission as a function of position. Polarization-resolved PL measurements under near-resonant excitation conditions show a strong circular polarization of the PL, corresponding to a valley polarization.

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Section: Photoluminescencementioning

confidence: 66%

A direct comparison of CVD-grown and exfoliated MoS₂using optical spectroscopy

Plechinger

Mann

Preciado

et al. 2014

Semicond. Sci. Technol.

106

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“…Alternatively, one can understand the red shift of the exciton mode as a strain-induced effect owing to the hot temperatures in the furnace at which CVD growth takes place, while ML samples prepared by exfoliation at RT have very similar emission energies to one another. Since CVD ML are formed on the hot surface out of the vapor phase at elevated temperatures, the consecutive cooling after growth leads to tensions caused by the mismatch of the thermal expansion coefficients (TECs) of WSe 2 (in plane coefficient) TEC = (1.1 × 10 [69,70] and sapphire TEC = (5 × 10 −6 /K-8.3 × 10 −6 /K) [71] at the relevant temper atures (300-900 K), which differ by a factor of 1.5-2. Qualitatively, the TEC of sapphire is less than that of WSe 2 over this temperature range.…”

Section: Resultsmentioning

confidence: 99%

Influence of the substrate material on the optical properties of tungsten diselenide monolayers

et al. 2017

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Monolayers of transition-metal dichalcogenides such as WSe 2 have become increasingly attractive due to their potential in electrical and optical applications. Because the properties of these 2D systems are known to be affected by their surroundings, we report how the choice of the substrate material affects the optical properties of monolayer WSe 2 . To accomplish this study, pump-density-dependent micro-photoluminescence measurements are performed with time-integrating and time-resolving acquisition techniques. Spectral information and power-dependent mode intensities are compared at 290K and 10K for exfoliated WSe 2 on SiO 2 /Si, sapphire (Al 2 O 3 ), hBN/Si 3 N 4 /Si, and MgF 2 , indicating substrate-dependent appearance and strength of exciton, trion, and biexciton modes. Additionally, one CVD-grown WSe 2 monolayer on sapphire is included in this study for direct comparison with its exfoliated counterpart. Time-resolved micro-photoluminescence shows how radiative decay times strongly differ for different substrate materials. Our data indicates exciton-exciton annihilation as a shortening mechanism at room temperature, and subtle trends in the decay rates in correlation to the dielectric environment at cryogenic temperatures. On the measureable time scales, trends are also related to the extent of the respective 2D-excitonic modes' appearance. This result highlights the importance of further detailed characterization of exciton features in 2D materials, particularly with respect to the choice of substrate.

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“…In Fig. 4 we plot the a lattice constant assembling published data in the literature [35][36][37][38] in order to span the temperature range of interest for MoS 2 , MoSe 2 , and sapphire. The solid lines are secondorder polynomial fits which we use to calculate the strain versus temperature.…”

Section: B the Influence Of Strainmentioning

confidence: 99%

“…Strain modifies the ratio of the effective masses in the valence and the conduction bands giving rise to an intercellular [35][36][37][38]. Note that for the low temperature MoS 2 data, scatter was reduced by taking points corresponding to the linear fit to the data in Ref.…”

Section: B the Influence Of Strainmentioning

confidence: 99%

Magnetoexcitons in large area CVD-grown monolayerMoS2andMoSe2on sapphire

et al. 2016

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Magnetotransmission spectroscopy was employed to study the valley Zeeman effect in large area monolayer MoS 2 and MoSe 2 . The extracted values of the valley g factors for both A and B excitons were found to be similar with g v −4.5. The samples are expected to be strained due to the CVD growth on sapphire at high temperature (700• C). However, the estimated strain, which is maximum at low temperature, is only 0.2%. Theoretical considerations suggest that the strain is too small to significantly influence the electronic properties. This is confirmed by the measured value of the valley g factor, and the measured temperature dependence of the band gap, which are almost identical for CVD and mechanically exfoliated MoS 2 .

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The thermal expansion of 2H-MoS₂, 2H-MoSe₂and 2H-WSe₂between 20 and 800°C

Cited by 153 publications

References 13 publications

A direct comparison of CVD-grown and exfoliated MoS₂using optical spectroscopy

A direct comparison of CVD-grown and exfoliated MoS₂using optical spectroscopy

Influence of the substrate material on the optical properties of tungsten diselenide monolayers

Magnetoexcitons in large area CVD-grown monolayerMoS2andMoSe2on sapphire

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The thermal expansion of 2H-MoS2, 2H-MoSe2and 2H-WSe2between 20 and 800°C

Cited by 153 publications

References 13 publications

A direct comparison of CVD-grown and exfoliated MoS2using optical spectroscopy

A direct comparison of CVD-grown and exfoliated MoS2using optical spectroscopy

Influence of the substrate material on the optical properties of tungsten diselenide monolayers

Magnetoexcitons in large area CVD-grown monolayerMoS2andMoSe2on sapphire

Contact Info

Product

Resources

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The thermal expansion of 2H-MoS₂, 2H-MoSe₂and 2H-WSe₂between 20 and 800°C

A direct comparison of CVD-grown and exfoliated MoS₂using optical spectroscopy

A direct comparison of CVD-grown and exfoliated MoS₂using optical spectroscopy