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From Bulk to Monolayer MoS2: Evolution of Raman Scattering

Authors

  • Hong Li,

    1. Microelectronics Centre, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798, Singapore
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  • Qing Zhang,

    Corresponding author
    1. Microelectronics Centre, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798, Singapore
    • Microelectronics Centre, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798, Singapore.
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  • Chin Chong Ray Yap,

    1. Microelectronics Centre, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798, Singapore
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  • Beng Kang Tay,

    Corresponding author
    1. Microelectronics Centre, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798, Singapore
    • Microelectronics Centre, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798, Singapore.
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  • Teo Hang Tong Edwin,

    1. CINTRA, Research Techno Plaza, Nanyang Technological University, 50 Nanyang Drive, Singapore 639798, Singapore
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  • Aurelien Olivier,

    1. CINTRA, Research Techno Plaza, Nanyang Technological University, 50 Nanyang Drive, Singapore 639798, Singapore
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  • Dominique Baillargeat

    1. CINTRA, Research Techno Plaza, Nanyang Technological University, 50 Nanyang Drive, Singapore 639798, Singapore
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Abstract

Molybdenum disulfide (MoS2) is systematically studied using Raman spectroscopy with ultraviolet and visible laser lines. It is shown that only the Raman frequencies of equation image and equation image peaks vary monotonously with the layer number of ultrathin MoS2 flakes, while intensities or widths of the peaks vary arbitrarily. The coupling between electronic transitions and phonons are found to become weaker when the layer number of MoS2 decreases, attributed to the increased electronic transition energies or elongated intralayer atomic bonds in ultrathin MoS2. The asymmetric Raman peak at 454 cm−1, which has been regarded as the overtone of longitudinal optical M phonons in bulk MoS2, is actually a combinational band involving a longitudinal acoustic mode (LA(M)) and an optical mode (equation image). Our findings suggest a clear evolution of the coupling between electronic transition and phonon when MoS2 is scaled down from three- to two-dimensional geometry.

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