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Title: Interlayer Interactions in Twisted WSe 2/WS 2 Bilayer Heterojunctions: Synthesis, Characterization, and Modeling

Abstract

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 WSe 2/WS 2 bilayer heterojunctions with various twist angles that were synthesized by artificially stacking monolayers of CVD-grown WS 2 and WSe 2. 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 WS 2 at 311 cm -1 in WSe 2/WS 2 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 WSe 2/WS 2 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 WSe 2 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.more » These results indicate that interlayer exciton formation and non-radiative decay channels 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:
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)
OSTI Identifier:
1324084
Grant/Contract Number:
AC05-00OR22725
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
ACS Nano
Additional Journal Information:
Journal Volume: 10; Journal Issue: 7; Journal ID: ISSN 1936-0851
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; Charge transfer; Interlayer coupling; Twist angle; Van der Waals heterostructures

Citation Formats

Wang, Kai, Huang, Bing, Tian, Mengkun, Ceballos, Frank, Lin, Ming-Wei, Mahjouri-Samani, Masoud, Boulesbaa, Abdelaziz, Puretzky, Alexander A., Rouleau, Christopher, Yoon, Mina, Zhao, Hui, Xiao, Kai, Duscher, G., and Geohegan, David B. Interlayer Interactions in Twisted WSe2/WS2 Bilayer Heterojunctions: Synthesis, Characterization, and Modeling. United States: N. p., 2016. Web. doi:10.1021/acsnano.6b01486.
Wang, Kai, Huang, Bing, Tian, Mengkun, Ceballos, Frank, Lin, Ming-Wei, Mahjouri-Samani, Masoud, Boulesbaa, Abdelaziz, Puretzky, Alexander A., Rouleau, Christopher, Yoon, Mina, Zhao, Hui, Xiao, Kai, Duscher, G., & Geohegan, David B. Interlayer Interactions in Twisted WSe2/WS2 Bilayer Heterojunctions: Synthesis, Characterization, and Modeling. United States. doi:10.1021/acsnano.6b01486.
Wang, Kai, Huang, Bing, Tian, Mengkun, Ceballos, Frank, Lin, Ming-Wei, Mahjouri-Samani, Masoud, Boulesbaa, Abdelaziz, Puretzky, Alexander A., Rouleau, Christopher, Yoon, Mina, Zhao, Hui, Xiao, Kai, Duscher, G., and Geohegan, David B. 2016. "Interlayer Interactions in Twisted WSe2/WS2 Bilayer Heterojunctions: Synthesis, Characterization, and Modeling". United States. doi:10.1021/acsnano.6b01486. https://www.osti.gov/servlets/purl/1324084.
@article{osti_1324084,
title = {Interlayer Interactions in Twisted WSe2/WS2 Bilayer Heterojunctions: Synthesis, Characterization, and Modeling},
author = {Wang, Kai and Huang, Bing and Tian, Mengkun and Ceballos, Frank and Lin, Ming-Wei and Mahjouri-Samani, Masoud and Boulesbaa, Abdelaziz and Puretzky, Alexander A. and Rouleau, Christopher and Yoon, Mina and Zhao, Hui and Xiao, Kai and Duscher, G. and Geohegan, David B.},
abstractNote = {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 channels dominate optical properties in these bilayers, which may be important for tunable future photovoltaics and detector applications.},
doi = {10.1021/acsnano.6b01486},
journal = {ACS Nano},
number = 7,
volume = 10,
place = {United States},
year = 2016,
month = 6
}

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Cited by: 12works
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  • 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 MoS 2 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 andmore » 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 20 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