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Interlayer vibrational modes in few-quintuple-layer Bi2Te3 and Bi2Se3 two-dimensional crystals: Raman spectroscopy and first-principles studies

Zhao, Yanyuan
Zhang, Jun
Wu, Junxiong
Bai, Xuxu
Wang, Meixiao
Jia, Jinfeng
Peng, Hailin
Liu, Zhongfan
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Abstract
© 2014 American Physical Society. Layered materials, such as graphite/graphene, boron nitride, transition metal dichalcogenides, represent materials in which reduced size, dimensionality, and symmetry play critical roles in their physical properties. Here, we report on a comprehensive investigation of the phonon properties in the topological insulator Bi2Te3 and Bi2Se3 two-dimensional (2D) crystals, with the combination of Raman spectroscopy, first-principles calculations, and group theory analysis. Low frequency (<30cm-1) interlayer vibrational modes are revealed in few-quintuple-layer (QL) Bi2Te3/Bi2Se3 2D crystals, which are absent in the bulk crystal as a result of different symmetries. The experimentally observed interlayer shear and breathing mode frequencies both show blueshifts, with decreasing thickness in few-QL Bi2Te3 (down to 2QL) and Bi2Se3 (down to 1QL), in agreement with first-principles calculations and a linear chain model, from which the interlayer coupling force constants can be estimated. Besides, an intense ultralow (<12cm-1) frequency peak is observed in 2-4QL Bi2Te3, which is tentatively attributed to a substrate-induced interface mode supported by a linear chain model analysis. The high frequency Raman peaks exhibit frequency shifts and broadening from 3D to 2D as a result of the phonon confinement effect. Our studies shed light on a general understanding of the influence of dimensionality and crystal symmetry on the phonon properties in layered materials.
Keywords
Science & Technology, Technology, Physical Sciences, Materials Science, Multidisciplinary, Physics, Applied, Physics, Condensed Matter, Materials Science, Physics, ENHANCED THERMOELECTRIC PROPERTIES, TOPOLOGICAL INSULATOR NANORIBBONS, NANOPLATELET COMPOSITES, LATTICE-VIBRATIONS, GRAPHENE, SURFACE, SB2TE3
Source Title
PHYSICAL REVIEW B
Publisher
American Physical Society
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Date
2014-12-23
DOI
10.1103/PhysRevB.90.245428
Type
Article
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