Thickness‐Dependent Refractive Index of 1L, 2L, and 3L MoS2, MoSe2, WS2, and WSe2

Hsu, Chunwei; Frisenda, Riccardo; Schmidt, Robert; Arora, Ashish; Vasconcellos, Steffen Michaelis de; Bratschitsch, Rudolf; Zant, Herre S. J. van der; Castellanos-Gómez, Andrés

doi:10.1002/adom.201900239

Cited by 194 publications

(116 citation statements)

References 28 publications

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“…Several previous reports have shed light on the complex refractive index (or the complex dielectric function, where one can be calculated from the other) of monolayer and few-layer MoS 2 . [13][14][15][16][17] Many of these reports have been indirect calculations of the n and k values, whereas some direct measurements are performed only for a small bandwidth of the spectrum. Li et al reported the complex dielectric function of exfoliated monolayer TMDC materials, including MoS 2 , from reflection spectra using Kramers-Kronig analysis.…”

Section: Introductionmentioning

confidence: 99%

In‐Plane and Out‐of‐Plane Optical Properties of Monolayer, Few‐Layer, and Thin‐Film MoS₂ from 190 to 1700 nm and Their Application in Photonic Device Design

Islam

Synowicki

Ismael

et al. 2021

Advanced Photonics Research

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Monolayer, few‐layer, and thin‐film MoS2 is synthesized using chemical vapor deposition (CVD) and thermal vapor sulfurization (TVS) methods. The complex refractive index of these samples is assessed using variable angle spectroscopic ellipsometry (VASE) measurements over a broad spectral range between 190 and 1700 nm. The ellipsometry data are sensitive to birefringence effects in the thickest thin‐film sample. These birefringence effects are investigated, and an analysis method is developed to extract the in‐plane and out‐of‐plane optical properties. The complex refractive index is then used to calculate reflectance, transmittance, and absorption of the MoS2 films using the transfer‐matrix method (TMM) and is matched with experimentally measured transmittance of the same samples. The modeled results show that the monolayer, few‐layer, and thin‐film MoS2 absorbs 7.4%, 12.6%, and 32.4% of the incident light, respectively, between 300 and 700 nm. When normalized to per unit‐thickness absorption, they absorb 12.1%, 5.9%, and 1.1% nm−1, respectively, clearly showing superior light–matter interaction in the monolayer and few‐layer films. These new complex refractive index data are further used to design optical coatings for these films to either confine absorption in a narrow bandwidth for photodetector applications or enhance broadband absorption for photovoltaic applications.

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Section: Introductionmentioning

confidence: 99%

In‐Plane and Out‐of‐Plane Optical Properties of Monolayer, Few‐Layer, and Thin‐Film MoS₂ from 190 to 1700 nm and Their Application in Photonic Device Design

Islam

Synowicki

Ismael

et al. 2021

Advanced Photonics Research

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“… 21 To this respect, extensive studies are reported on the layer‐dependent optical properties of graphene 20 , 22 and MoS

. 23 , 24 The importance of optical contrast (O.C.) of CrCl

increases due to the reported Raman insensitivity on few layers.…”

Section: Introductionmentioning

confidence: 99%

Determination of the refractive index and wavelength‐dependent optical properties of few‐layer CrCl within the Fresnel formalism

Gunnella

Zannotti

Giovannetti

et al. 2021

Journal of Microscopy

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Based on previous reports on the optical microscopy contrast of mechanically exfoliated few layer CrCl 3 transferred on 285 nm and 270 nm SiO 2 on Si(100), we focus on the experimental determination of an effective mean complex refractive index via a fitting analysis based on the Fresnel equations formalism. Accordingly, the layer and wavelength-dependent absorbance and reflectance are calculated. Layer and wavelength-dependent optical contrast curves are then evaluated demonstrating that the contrast is significantly high only around welldefined wavelength bands. This is validated a posteriori, by experimental UV-Vis absorbance data. The present study aims to show the way towards the most reliable determination of thickness of the 2D material flakes during exfoliation.

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“…18,[27][28][29][30][31] The reflectance/transmittance contrast spectrum is introduced to measure the exciton energy without explicitly measuring the bandgap. 26,[32][33][34][35] Therefore, a robust measurement system is required to accurately measure the exciton energy and bandgap.…”

Section: Introductionmentioning

confidence: 99%

Unusually Large Exciton Binding Energy In Multilayered 2H-MoTe2

Jung

Park

Seo

et al. 2021

Preprint

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Although large exciton binding energies of typically 0.6–1.0 eV are observed for monolayer transition metal dichalcogenides (TMDs) owing to strong Coulomb interaction, multilayered TMDs yield relatively low exciton binding energies owing to increased dielectric screening. Recently, the ideal carrier-multiplication threshold energy of twice the bandgap has been realized in multilayered semiconducting 2H-MoTe2 with a conversion efficiency of 99%, which suggests strong Coulomb interaction. However, the origin of strong Coulomb interaction in multilayered 2H-MoTe2, including the exciton binding energy, has not been elucidated to date. In this study, unusually large exciton binding energy is observed through optical spectroscopy conducted on CVD-grown 2H-MoTe2. To extract exciton binding energy, the optical conductivity is fitted using the Lorentz model to describe the exciton peaks and the Tauc–Lorentz model to describe the indirect and direct bandgaps. The exciton binding energy of 4 nm thick multilayered 2H-MoTe2 is approximately 300 meV, which is unusually large by one order of magnitude when compared with other multilayered TMD semiconductors such as 2H-MoS2 or 2H-MoSe2. This finding is interpreted in terms of small exciton radius based on the 2D Rydberg model. The exciton radius of multilayered 2H-MoTe2 resembles that of monolayer 2H-MoTe2, whereas those of multilayered 2H-MoS2 and 2H-MoSe2 are large when compared with monolayer 2H-MoS2 and 2H-MoSe2. From the large exciton binding energy in multilayered 2H-MoTe2, it is expected to realize the future applications such as room-temperature and high-temperature polariton lasing.

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Thickness‐Dependent Refractive Index of 1L, 2L, and 3L MoS₂, MoSe₂, WS₂, and WSe₂

Cited by 194 publications

References 28 publications

In‐Plane and Out‐of‐Plane Optical Properties of Monolayer, Few‐Layer, and Thin‐Film MoS₂ from 190 to 1700 nm and Their Application in Photonic Device Design

In‐Plane and Out‐of‐Plane Optical Properties of Monolayer, Few‐Layer, and Thin‐Film MoS₂ from 190 to 1700 nm and Their Application in Photonic Device Design

Determination of the refractive index and wavelength‐dependent optical properties of few‐layer CrCl within the Fresnel formalism

Unusually Large Exciton Binding Energy In Multilayered 2H-MoTe2

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Thickness‐Dependent Refractive Index of 1L, 2L, and 3L MoS2, MoSe2, WS2, and WSe2

Cited by 194 publications

References 28 publications

In‐Plane and Out‐of‐Plane Optical Properties of Monolayer, Few‐Layer, and Thin‐Film MoS2 from 190 to 1700 nm and Their Application in Photonic Device Design

In‐Plane and Out‐of‐Plane Optical Properties of Monolayer, Few‐Layer, and Thin‐Film MoS2 from 190 to 1700 nm and Their Application in Photonic Device Design

Determination of the refractive index and wavelength‐dependent optical properties of few‐layer CrCl within the Fresnel formalism

Unusually Large Exciton Binding Energy In Multilayered 2H-MoTe2

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Product

Resources

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Thickness‐Dependent Refractive Index of 1L, 2L, and 3L MoS₂, MoSe₂, WS₂, and WSe₂

In‐Plane and Out‐of‐Plane Optical Properties of Monolayer, Few‐Layer, and Thin‐Film MoS₂ from 190 to 1700 nm and Their Application in Photonic Device Design

In‐Plane and Out‐of‐Plane Optical Properties of Monolayer, Few‐Layer, and Thin‐Film MoS₂ from 190 to 1700 nm and Their Application in Photonic Device Design