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Title: Effects of lower symmetry and dimensionality on Raman spectra in two-dimensional WSe2
Authors: Luo, Xin
Zhao, Yanyuan
Zhang, Jun
Toh, Minglin
Xiong, Qihua
Quek, Su Ying
Kloc, Christian
Keywords: DRNTU::Science::Physics
Issue Date: 2013
Source: Luo, X., Zhao, Y., Zhang, J., Toh, M., Kloc, C., Xiong, Q., et al. (2013). Effects of lower symmetry and dimensionality on Raman spectra in two-dimensional WSe2. Physical review B - condensed matter and materials physics, 88(19), 195313-.
Series/Report no.: Physical review B - condensed matter and materials physics
Abstract: We report the observation and interpretation of new Raman peaks in few-layer tungsten diselenide (WSe2), induced by the reduction of symmetry going from three-dimensional (3D) to two-dimensional (2D). In general, Raman frequencies in 2D materials follow quite closely the frequencies of corresponding eigenmodes in the bulk. However, while the modes that are Raman active in the bulk are also Raman active in the thin films, the reverse is not always true due to the reduced symmetry in thin films. Here, we predict from group theory and density functional calculations that two intralayer vibrational modes, which are Raman inactive in bulk WSe2 in our experimental configuration become Raman active in thin film WSe2, due to reduced symmetry in thin films. This phenomenon explains the Raman peaks we observe experimentally at ∼310 and 176 cm−1 in thin film WSe2. Interestingly, the bulk B12g mode at ∼310 cm−1 that is Raman inactive can, in fact, be detected in Raman measurements under specific wavelengths of irradiation, suggesting that in this case, crystal symmetry selection rules may be broken due to resonant scattering. Both theory and experiment indicate that the E12g and B12g modes blueshift with decreasing thickness, which we attribute to surface effects. Our results shed light on a general understanding of the Raman/infrared activities of the phonon modes in layered transition metal dichalcogenide materials and their evolution behavior from 3D to 2D.
DOI: 10.1103/PhysRevB.88.195313
Rights: © 2013 American Physical Society. This paper was published in Physical Review B - Condensed Matter and Materials Physics and is made available as an electronic reprint (preprint) with permission of American Physical Society. The paper can be found at the following official DOI: []. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper is prohibited and is subject to penalties under law.
Fulltext Permission: open
Fulltext Availability: With Fulltext
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