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Title: Interlayer Interactions in Twisted WSe2/WS2 Bilayer Heterojunctions: Synthesis, Characterization, and Modeling

Twisting adjacent layers in van der Waals solids can significantly alter their interlayer interactions for tunable optical and electronic properties. Here, we report theoretical calculations, fabrication, and detailed characterizations of WSe2/WS2 bilayer heterojunctions with various twist angles that were synthesized by artificially stacking monolayers of CVD-grown WS2 and WSe2. Density functional calculations predicted the formation of type-II heterojunctions for the stamped bilayers, with band structures that strongly depend on the interlayer twist angle. Raman spectroscopy reveals strong interlayer coupling with the appearance of a layer-number sensitive mode of WS2 at 311 cm-1 in WSe2/WS2 bilayers. This strong interlayer coupling resulted in a 1~2 order of magnitude quenching of the photoluminescence. The broadening and shifts were observed in micro-absorption spectroscopy of WSe2/WS2 bilayers, which resulted in a net ~10% enhancement in integrated absorption strength across the visible spectrum with respect to the sum of the individual monolayer spectra. The observed 24 4 meV broadening of the WSe2 A-exciton absorption band in the bilayers provided an estimate on the rate of charge transfer between the layers that ranged from 23 to 33 fs, and was supported by direct femtosecond pump-probe measurements. These results indicate that interlayer exciton formation and non-radiative decay channelsmore » dominate optical properties in these bilayers, which may be important for tunable future photovoltaics and detector applications.« less
Authors:
 [1] ;  [1] ;  [2] ;  [3] ;  [1] ;  [1] ;  [1] ;  [1] ;  [1] ;  [1] ;  [3] ;  [1] ;  [2] ;  [1]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  2. Univ. of Tennessee, Knoxville, TN (United States)
  3. Univ. of Kansas, Lawrence, KS (United States)
Publication Date:
OSTI Identifier:
1324084
Grant/Contract Number:
AC05-00OR22725
Type:
Accepted Manuscript
Journal Name:
ACS Nano
Additional Journal Information:
Journal Volume: 10; Journal Issue: 7; Journal ID: ISSN 1936-0851
Publisher:
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
Language:
English
Subject:
36 MATERIALS SCIENCE Charge transfer; Interlayer coupling; Twist angle; Van der Waals heterostructures