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This content will become publicly available on February 21, 2017

Title: Low-Frequency Interlayer Raman Modes to Probe Interface of Twisted Bilayer MoS 2

A variety of van der Waals homo- and hetero- structures 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. Twisted bilayer transition metal dichalcogenides offer a great platform for developing a precise understanding of the structure/property relationship. Here, we study the low-frequency interlayer shear and breathing Raman modes (<50 cm-1) in twisted bilayer MoS2 by Raman spectroscopy and first-principles modeling. Twisting introduces both rotational and translational shifts and 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 near 0 and 60 , where the stacking is a mixture of multiple high-symmetry stacking patterns and is thus especially sensitive to twisting. Moreover, for twisting angles between 20 and 40 , the interlayer coupling is nearly constant since the stacking results in mismatched lattices over the entire sample. It follows that the Raman signature is relatively uniform. Interestingly, unlike the breathing mode, the shear mode is extremely sensitive to twisting: it disappears between 20more » and 40 as its frequency drops to almost zero due to the stacking-induced mismatch. Note that for some samples, multiple breathing mode peaks appear, indicating non-uniform 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, showing negligible changes upon twisting. Our 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.« less
 [1] ;  [2] ;  [1] ;  [3] ;  [3] ;  [3] ;  [1] ;  [4] ;  [1]
  1. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
  2. Rensselaer Polytechnic Inst., Troy, NY (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  4. Rensselaer Polytechnic Inst., Troy, NY (United States)
Publication Date:
OSTI Identifier:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Nano Letters
Additional Journal Information:
Journal Volume: 16; Journal Issue: 2; Journal ID: ISSN 1530-6984
American Chemical Society
Research Org:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Sciences (CNMS)
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States