期刊
NANO LETTERS
卷 15, 期 10, 页码 6481-6489出版社
AMER CHEMICAL SOC
DOI: 10.1021/acs.nanolett.5b02683
关键词
two-dimensional materials; layered crystals; transition metal dichalcogenides; MoTe2; Raman spectroscopy; interlayer breathing and shear modes; force constants; Davydov splitting; surface effects
类别
资金
- Agence Nationale de la Recherche [12 JS10-001-01]
- CNRS
- Universite de Strasbourg
- National Research Fund, Luxembourg [INTER/ANR/13/20/NANOTMD, C14/MS/7731521/FAST-2DMAT]
N-layer transition metal dichalcogenides provide a unique platform to investigate the evolution of the physical properties between the bulk (three-dimensional) and monolayer (quasi-two-dimensional) limits. Here, using high-resolution microRaman spectroscopy, we report a unified experimental description of the F-point optical phonons in N-layer 2H-molybdenum ditelluride (MoTe2). We observe series of N-dependent lowfrequency interlayer shear and breathing modes (below 40 cm(-1), denoted LSM and LBM) and well-defined Davydov splittings of the mid-frequency modes (in the range 100-200 cm(-1), denoted iX and oX), which solely involve displacements of the chalcogen atoms. In contrast, the high-frequency modes (in the range 200-300 cm(-1), denoted iMX and oMX), arising from displacements of both the metal and chalcogen atoms, exhibit considerably reduced splittings. The manifold of phonon modes associated with the in-plane and out-of-plane displacements are quantitatively described by a force constant model, including interactions up to the second nearest neighbor and surface effects as fitting parameters. The splittings for the iX and oX modes observed in N-layer crystals are directly correlated to the corresponding bulk Davydov splittings between the E-2u/E-1g and B-1u/A(1g) modes, respectively, and provide a measurement of the frequencies of the bulk silent E-2u and B-1u optical phonon modes. Our analysis could readily be generalized to other layered crystals.
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