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From Bulk to Monolayer MoS 2 : Evolution of Raman Scattering
Author(s) -
Li Hong,
Zhang Qing,
Yap Chin Chong Ray,
Tay Beng Kang,
Edwin Teo Hang Tong,
Olivier Aurelien,
Baillargeat Dominique
Publication year - 2012
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.201102111
Subject(s) - materials science , raman spectroscopy , phonon , overtone , molybdenum disulfide , monolayer , raman scattering , coupling (piping) , molecular physics , ultraviolet , condensed matter physics , atomic physics , optoelectronics , optics , nanotechnology , spectral line , physics , astronomy , metallurgy
Molybdenum disulfide (MoS 2 ) is systematically studied using Raman spectroscopy with ultraviolet and visible laser lines. It is shown that only the Raman frequencies of $ E_{2{\rm g}}^1 $ and $ A_{{\rm 1g}}^{} $ peaks vary monotonously with the layer number of ultrathin MoS 2 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 MoS 2 decreases, attributed to the increased electronic transition energies or elongated intralayer atomic bonds in ultrathin MoS 2 . The asymmetric Raman peak at 454 cm −1 , which has been regarded as the overtone of longitudinal optical M phonons in bulk MoS 2 , is actually a combinational band involving a longitudinal acoustic mode (LA(M)) and an optical mode ( $ A_{{\rm 2u}}^{} $ ). Our findings suggest a clear evolution of the coupling between electronic transition and phonon when MoS 2 is scaled down from three‐ to two‐dimensional geometry.