Layer-dependent dielectric and optical properties of centimeter-scale 2D WSe₂: evolution from a single layer to few layers

Abstract

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

Complete Dielectric Tensor and Giant Optical Anisotropy in Quasi-One-Dimensional ZrTe5

“…To further reveal the physical origins of the optical anisotropy of ZrTe 5 , we investigated the dielectric functions along crystal axes by combining the CP analysis and the first-principle calculations. As is known, the real part ε r of the dielectric functions can be transformed from the imaginary part ε i by the K−K relation (details in the SI, Equation S13), and ε i can be examined from the perspective of quantum mechanics: 16,43,44…”

“…21,24 With this powerful method, we comprehensively and quantitatively discuss the optical anisotropy in novel materials, such as the birefringence, dichroism, and optical activity, from the complete dielectric tensor and further deeply reveal the underlying physical mechanisms combined with first-principle calculations. 16,21,25 With prominent physical properties, such as the threedimensional quantum Hall effect, 26 superconductivity, 27 and Zeeman splitting, 28 ZrTe 5 is a promising candidate for advanced electronic and optoelectronic devices. Particularly, ZrTe 5 shows giant optically anisotropic properties due to its quasi-1D structure (space group Cmcm, No.…”

Thickness Scaling Effects on the Complex Optical Conductivity of Few‐Layer WSe2 Investigated by Spectroscopic Ellipsometry

“…These feature peaks A–H are relevant to different direct transitions from four highest valance bands to four lowest conduction bands along the Γ–K–M branch in the band structure of 2D WSe 2 , as detailed discussed in previous works. [ 23,27,29 ] It is obvious that real part of optical conductivity ( σ r ) increases with the increasing layer number of 2D WSe 2 , and imaginary part of optical conductivity ( σ i ) also exhibits a monotonous increase when the energy is less than 4 eV. The layer‐dependent increase of the complex optical conductivity of 2D WSe 2 can be explained as the gradually enhanced light absorption and propagation effects, which are expected to be sensitive to the thickness of materials.…”

“…[ 26 ] Gu et al, obtained the layer‐dependent dielectric function of centimeter scale 2D WSe 2 on sapphire substrate by SE, and proposed a systematic method based on critical point (CP) analysis and first‐principles calculations to identify the optical transitions at these CP, demonstrating the exciton, joint density of states, and band renormalization effect in 2D WSe 2 . [ 27 ] Ermolaev et al, measured the dielectric function of chemical vapor deposition (CVD)‐grown large area monolayer WS 2 and WSe 2 films on SiO2/Si substrates over the range of 300–1700 nm. [ 28 ] Except for these experimental methods, some scientists devote to perform some theoretical studies on the basic optical/electrical properties of 2D WSe 2 , which are mainly based on the first‐principle calculations.…”

“…[19][20][21] The optical/electrical properties of 2D WSe 2 have been extensively studied by multiple techniques, such as the microreflectance (absorption) spectrum method, differential reflection spectrum method, deterministic method based on reflection coefficients, spectroscopic ellipsometry (SE), and first-principles calculations. [22][23][24][25][26][27][28][29][30] Li et al, extracted the complex dielectric functions of four kinds of monolayer TMDCs (MoS 2 , MoSe 2 , WS 2 , and WSe 2 ) from their absolute reflectance spectra over the photon energies of 1.5-3 eV by the Kramers-Kronig constrained variational analysis. [22] Hsu et al, determined the complex refractive index spectra of 1-3 layer (L) mechanically exfoliated MoS 2 , MoSe 2 , WS 2 , and WSe 2 samples in the range of 400-850 nm by combining microreflectance spectroscopy with the Fresnel equations.…”