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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 ...

The excitonic effect and JDOS dominated evolution in layer-dependent dielectric and optical properties of 2D WSe2 were investigated by spectroscopic ellipsometry.

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Accurate measurement of the Mueller matrix over a broad band is highly desirable for the characterization of nanostructures and nanomaterials. In this paper, we propose a general composite waveplate (GCW) that consists of multiple waveplates with flexibly oriented axes as a polarization modulating component in the Mueller matrix ellipsometer (MME). Although it is acommon practice to make achromatic retarders by combining multiple waveplates, the novelty of the GCW is that both the retardances and azimuths of fast axes of the single-waveplates in the GCW are flexible parameters to be optimized, which is different from the conventional design where single-waveplates are usually arranged in symmetrical layout or with their fast axes parallel or perpendicular to each other. Consequently, the GCW can provide many more flexibilities to adapt to the optimization of the MME over a broad band. A quartz triplate, as a concrete example of the GCW, is designed and used in a house-made MME. The experimental results on the air demonstrate that the house-made MME using the optimally designed quartz triplates has an accuracy better than 0.2% and a precision better than 0.1% in the Mueller matrix measurement over a broad spectral range of 200∼1000 nm. The house-made MME exhibits high measurement repeatability better than 0.004 nm in testing a series of standard SiO 2 /Si samples with nominal oxide layer thicknesses ranging from 2 nm to 1000 nm.

Abstract. Due to the rich information provided by the Mueller matrices when the most general conical diffraction configuration is considered, the Mueller matrix polarimetry has demonstrated a great potential in semiconductor manufacturing. As the configurations of the incidence and azimuthal angles have different influences on the measurement accuracy, it is necessary to select an optimal one among the multitude of possible options. We introduce the norm of a configuration error propagating matrix to assess the measurement accuracy for different measurement configurations. The optimal configuration for a Si grating sample was achieved by minimizing the norm of the configuration error propagating matrix. Experimental results show the agreement between the theoretically predicted optimal configuration and the experimental exhibited one obtained by using a dual-rotating compensator Mueller matrix polarimeter and thus demonstrated the validity of the proposed optimization method. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

The complex optical conductivities of two-dimensaionl (2D) materials are fundamental for extended applications of related optoelectronic devices. Here, we systematically investigate the layer-dependent evolutions in the complex optical conductivities of 1–6 layer 2D MoS2 over an ultrawide spectral range (0.73–6.42 eV) by spectroscopic ellipsometry. We identify five feature peaks (A–E) in the optical conductivity spectra, which present interesting layer dependencies due to the scaling effect. Results suggest that the center energies of peaks A and B are nearly layer-independent, while those of peaks C and D exhibit redshifts as the layer increases. We interpret these layer-dependent evolutions as the competition between the decreasing exciton effect and the prominent band shrinkage with the increasing layer number. Additionally, the applicability of the classical slab model and the surface current model in evaluating the optical conductivities of 2D MoS2 with different layers is discussed from an experimental perspective.

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