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

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Abstract

Two-dimensional (2D) materials usually exhibit interesting layer-dependent dielectric and optical properties, which play important roles in structure optimization and performance improvement of related devices. Recently, 2D WSe2 has attracted considerable attention in atomically thin electronics and optoelectronics, due to its exotic photoelectric properties. In this paper, high-quality, continuous, and centimeter-scale 2D WSe2 with different layers on a sapphire substrate are prepared by an ultrafast ambient-pressure chemical vapor deposition method. We comprehensively investigate the evolution of the layer-dependent dielectric and optical properties of 2D WSe2 from a single layer to five layers by spectroscopic ellipsometry over an ultra-broad energy range (0.73–6.42 eV). We identify the critical points (CPs) in the dielectric function spectra of 2D WSe2 with different layers, and reveal physical origins of the corresponding optical transitions at these CPs by the CP analysis method and first-principles calculations. Results demonstrate that the center energies of these CPs exhibit intriguing layer-dependencies, which can be interpreted as the alternative domination of the decreasing exciton binding energy and the striking band renormalization. For the first time, we found that the imaginary part of the dielectric function of WSe2 at these CPs exhibits a valley-like shape versus the layer number, and the bottom appears at 3-layers. This non-monotonic evolution is explained as a competition between the layer-dependent decrease of the exciton effect and the layer-dependent increase of the joint density of states.

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

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Publication details

The article was received on 19 May 2019, accepted on 12 Aug 2019 and first published on 02 Sep 2019


Article type: Paper
DOI: 10.1039/C9NR04270A
Nanoscale, 2019, Advance Article
  • Open access: Creative Commons BY-NC license
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    Layer-dependent dielectric and optical properties of centimeter-scale 2D WSe2: evolution from a single layer to few layers

    H. Gu, B. Song, M. Fang, Y. Hong, X. Chen, H. Jiang, W. Ren and S. Liu, Nanoscale, 2019, Advance Article , DOI: 10.1039/C9NR04270A

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