Low-Frequency Interlayer Raman Modes to Probe Interface of Twisted Bilayer MoS2

Shengxi Huang, Liangbo Liang, Xi Ling, Alexander A. Puretzky, David B. Geohegan, Bobby G. Sumpter, Jing Kong, Vincent Meunier, Mildred S. Dresselhaus

Research output: Contribution to journalArticlepeer-review

191 Scopus citations

Abstract

van der Waals homo- and heterostructures assembled by stamping monolayers together present optoelectronic properties suitable for diverse applications. Understanding the details of the interlayer stacking and resulting coupling is crucial for tuning these properties. We investigated the low-frequency interlayer shear and breathing Raman modes (<50 cm-1) in twisted bilayer MoS2 by Raman spectroscopy and first-principles modeling. Twisting significantly alters the interlayer stacking and coupling, leading to notable frequency and intensity changes of low-frequency modes. The frequency variation can be up to 8 cm-1 and the intensity can vary by a factor of ∼5 for twisting angles near 0° and 60°, where the stacking is a mixture of high-symmetry stacking patterns and is thus sensitive to twisting. For twisting angles between 20° and 40°, the interlayer coupling is nearly constant because the stacking results in mismatched lattices over the entire sample. It follows that the Raman signature is relatively uniform. Note that for some samples, multiple breathing mode peaks appear, indicating nonuniform coupling across the interface. In contrast to the low-frequency interlayer modes, high-frequency intralayer Raman modes are much less sensitive to interlayer stacking and coupling. This research demonstrates the effectiveness of low-frequency Raman modes for probing the interfacial coupling and environment of twisted bilayer MoS2 and potentially other two-dimensional materials and heterostructures.

Original languageEnglish
Pages (from-to)1435-1444
Number of pages10
JournalNano Letters
Volume16
Issue number2
DOIs
StatePublished - Feb 10 2016

Funding

S.H., X.L., and M.S.D. acknowledge Grant DE-SC0001299 for financial support. The Raman measurements were conducted at the Center for Nanophase Materials Sciences, a DOE Office of Science User Facility. The theoretical work at Rensselaer Polytechnic Institute (RPI) was supported by NSF under grant EFRI--2DARE 1542707h. L.L. acknowledges the support from Eugene P. Wigner Fellowship at the Oak Ridge National Laboratory. The computations were performed using the resources of the Center for Computational Innovation at RPI.

FundersFunder number
DOE Office of Science
National Science FoundationEFRI--2DARE 1542707h
Oak Ridge National Laboratory

    Keywords

    • Molybdenum disulfide
    • density functional theory
    • interlayer coupling
    • interlayer phonon modes
    • low-frequency Raman spectroscopy
    • twisted bilayer

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