Optical properties of thickness-controlled MoS2 thin films studied by spectroscopic ellipsometry

Li, Dahai; Song, Xiongfei; Xu, Jun; Wang, Ziyi; Zhang, Rongjun; Zhou, Peng; Zhang, Hao; Huang, Renzhong; Wang, Song-You; Zheng, Yu‐Xiang; Zhang, David Wei; Chen, Liang‐Yao

doi:10.1016/j.apsusc.2016.09.069

Cited by 51 publications

(33 citation statements)

References 33 publications

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“…Photoluminescence studies also demonstrated that a reduction in thickness has a strong effect on the band structure of MoS2 and other semiconductor TMDCs, including a change in the band gap and a thickness mediated direct-toindirect band gap crossover [20][21][22][23][24]. The thickness dependent band gap can have a strong influence on other electrical [25] and optical properties, such as the absorption [25][26][27], and it has been also exploited to fabricate photodetectors where their spectral bandwidth is determined by the number of layers of the semiconductor channel [9,11]. However, the determination of the intrinsic quantum efficiency and the photoresponse of photodetectors based on semiconducting TMDCs, requires a comprehensive study of their reflectance and/or transmittance with different numbers of layers in a wide spectral range, which is still lacking.…”

Section: Introductionmentioning

confidence: 98%

Thickness-Dependent Differential Reflectance Spectra of Monolayer and Few-Layer MoS2, MoSe2, WS2 and WSe2

et al. 2018

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The research field of two dimensional (2D) materials strongly relies on optical microscopy characterization tools to identify atomically thin materials and to determine their number of layers. Moreover, optical microscopy-based techniques opened the door to study the optical properties of these nanomaterials. We presented a comprehensive study of the differential reflectance spectra of 2D semiconducting transition metal dichalcogenides (TMDCs), MoS2, MoSe2, WS2, and WSe2, with thickness ranging from one layer up to six layers. We analyzed the thickness-dependent energy of the different excitonic features, indicating the change in the band structure of the different TMDC materials with the number of layers. Our work provided a route to employ differential reflectance spectroscopy for determining the number of layers of MoS2, MoSe2, WS2, and WSe2.

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Section: Introductionmentioning

confidence: 98%

Thickness-Dependent Differential Reflectance Spectra of Monolayer and Few-Layer MoS2, MoSe2, WS2 and WSe2

et al. 2018

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“…However, these studies can hardly gain the basic optical constants, such as dielectric function, complex refraction index, etc., which play an important role in the quantitative design and optimization of those MoS 2 ‐based photoelectric devices . Beyond these researches, there are also some reports on the dielectric function of the 2D MoS 2 , where the techniques they used can be roughly divided into three types: ellipsometry, reflection (or absorption) spectrum method, and contrast spectrum or differential reflection (or transmission) spectrum method . By using of ellipsometry, Li et al investigated the optical properties of the monolayer and bulk MoS 2 , and identified some critical points (CPs) in their dielectric function spectra .…”

Section: Introductionmentioning

confidence: 99%

Layer‐Dependent Dielectric Function of Wafer‐Scale 2D MoS₂

Song

Fang

Chen

et al. 2018

Advanced Optical Materials

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layer-dependent bandgap, [10] valley selective circular dichroism, [11] high on/off ratio, [12] and high thermostability [12] of the 2D MoS 2 . The performance of these novel devices significantly depends on the intrinsic optical properties (especially the dielectric function) of the 2D MoS 2 , which exhibit an intriguing layer dependency due to the enhanced quantum confinement effect and the absence of inversion symmetry. Therefore, the effective characterization of the layer-dependent optical properties of MoS 2 is critical for the performance improvement and the optimal design of those photoelectric devices based on MoS 2 .Layer-dependent optical properties of MoS 2 , including absorbance, [1] photoluminescence spectra, [10] Raman spectra, [13] and second-harmonic generation effect, [14] have been measured and discussed previously. However, these studies can hardly gain the basic optical constants, such as dielectric function, complex refraction index, etc., which play an important role in the quantitative design and optimization of those MoS 2 -based photoelectric devices. [15] Beyond these researches, there are also some reports on the dielectric function of the 2D MoS 2 , where the techniques they used can be roughly divided into three types: ellipsometry, [16][17][18][19][20][21][22][23][24][25][26] reflection (or absorption) spectrum method, [27,28] and contrast spectrum or differential reflection (or transmission) spectrum method. [29,30] By using of ellipsometry, Li et al. investigated the optical properties of the monolayer and bulk MoS 2 , and identified some critical points (CPs) in their dielectric function spectra. [22] The frequency-dependent reflection (transmission) spectra and corresponding differential spectra of the monolayer MoS 2 were simultaneously measured by Morozov et al., then the dielectric function was extracted. [27] Li et al. measured the reflection spectra of the mechanical exfoliation monolayer MoS 2 flake and the bulk MoS 2 , then their dielectric functions were calculated combined with a Kramers-Kronig constrained variational analysis. [28] Nevertheless, these published experimental reports on the dielectric function of MoS 2 mainly focus on the monolayer and bulk counterpart and the spectral range is relatively narrow. Apart from these experimental studies, some researchers have also devoted to predict the dielectric properties of the 2D MoS 2 with the help of theoretical calculations. [31,32] For example, Johari et al. studied the dielectric properties of monolayer, bilayer, and bulk MoS 2 by computing the electron Wafer-scale, high-quality, and layer-controlled 2D MoS 2 films on c-sapphire are synthesized by an innovative two-step method. The dielectric functions of MoS 2 ranging from the monolayer to the bulk are investigated by spectroscopic ellipsometry over an ultra-broadband (0.73-6.42 eV). Up to five critical points (CPs) in the dielectric function spectra are precisely distinguished by CP analysis, and their physical origins are identified in the band structures with ...

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“…Moreover, Figure S1b, Supporting Information, shows peaks at 161.9 and 163.1 eV, which are ascribed to S 2p 3/2 and S 2p 1/2 , respectively. [ 29 ] This shows the formation of MoS 2 at the surface for the samples without and with CuO ILs. In addition, Figure S1c, Supporting Information, also demonstrates that after sulfurization Cu is present in the oxidation state of +1, whereas, XPS study of the as‐deposited CuO reveals that the oxidation state of Cu is +2.…”

Section: Resultsmentioning

confidence: 93%

“…Furthermore, the composition at the surface of Mo/SLG samples without and with CuO ILs was characterized using XPS after peeling off the CZCTS absorber layer (Figure S1, Supporting Information). The study reveals peaks located at 229.1 and 232.2 eV attributed to Mo 3d 5/2 and Mo 3d 3/2 , [ 29 ] respectively, as shown in Figure S1a, Supporting Information. Moreover, Figure S1b, Supporting Information, shows peaks at 161.9 and 163.1 eV, which are ascribed to S 2p 3/2 and S 2p 1/2 , respectively.…”

Section: Resultsmentioning

confidence: 99%

Solution‐Processed Pure Sulfide Cu₂(Zn_0.6Cd_0.4)SnS₄ Solar Cells with Efficiency 10.8% Using Ultrathin CuO Intermediate Layer

et al. 2020

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Herein, it is demonstrated that incorporating ultrathin p‐type cupric oxide (CuO) enhances the performance and stability of solution‐processed Cu2(Zn0.6Cd0.4)SnS4 (CZCTS)/CdS thin film solar cells. In sol–gel CZCTS/CdS thin film solar cells, nanoscale CuO films (4–32 nm) are deposited on top of molybdenum (Mo) by magnetron sputtering and this is used as an intermediate layer (IL). The CuO IL thickness has a significant effect on the short‐circuit current density (JSC) in CZCTS/CdS solar cell devices. As a result, a maximum power conversion efficiency (PCE) of 10.77% is measured for the optimized device with 4 nm CuO compared with 10.03% for the reference device without a CuO layer. Furthermore, the stability of the devices is enhanced significantly by incorporating the CuO IL. This work demonstrates that through proper design of the CuO IL thickness, both the back interface quality and optical property of the CZCTS absorber can be tuned to enhance the device performance.

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Optical properties of thickness-controlled MoS2 thin films studied by spectroscopic ellipsometry

Cited by 51 publications

References 33 publications

Thickness-Dependent Differential Reflectance Spectra of Monolayer and Few-Layer MoS2, MoSe2, WS2 and WSe2

Thickness-Dependent Differential Reflectance Spectra of Monolayer and Few-Layer MoS2, MoSe2, WS2 and WSe2

Layer‐Dependent Dielectric Function of Wafer‐Scale 2D MoS₂

Solution‐Processed Pure Sulfide Cu₂(Zn_0.6Cd_0.4)SnS₄ Solar Cells with Efficiency 10.8% Using Ultrathin CuO Intermediate Layer

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Optical properties of thickness-controlled MoS2 thin films studied by spectroscopic ellipsometry

Cited by 51 publications

References 33 publications

Thickness-Dependent Differential Reflectance Spectra of Monolayer and Few-Layer MoS2, MoSe2, WS2 and WSe2

Thickness-Dependent Differential Reflectance Spectra of Monolayer and Few-Layer MoS2, MoSe2, WS2 and WSe2

Layer‐Dependent Dielectric Function of Wafer‐Scale 2D MoS2

Solution‐Processed Pure Sulfide Cu2(Zn0.6Cd0.4)SnS4 Solar Cells with Efficiency 10.8% Using Ultrathin CuO Intermediate Layer

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Product

Resources

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Layer‐Dependent Dielectric Function of Wafer‐Scale 2D MoS₂

Solution‐Processed Pure Sulfide Cu₂(Zn_0.6Cd_0.4)SnS₄ Solar Cells with Efficiency 10.8% Using Ultrathin CuO Intermediate Layer