From Bulk to Monolayer MoS 2 : Evolution of Raman Scattering

• Published in: Advanced functional materials Vol. 22; no. 7; pp. 1385 - 1390
• Main Authors: Li, Hong, Zhang, Qing, Yap, Chin Chong Ray, Tay, Beng Kang, Edwin, Teo Hang Tong, Olivier, Aurelien, Baillargeat, Dominique
• Format: Journal Article
• Language: English
• Published: 10.04.2012
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.201102111

Abstract 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.