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Nano Lett. 2017 Sep 13;17(9):5634-5640. doi: 10.1021/acs.nanolett.7b02513. Epub 2017 Aug 28.

Strain-Mediated Interlayer Coupling Effects on the Excitonic Behaviors in an Epitaxially Grown MoS2/WS2 van der Waals Heterobilayer.

Author information

1
Department of Engineering Science, University of Oxford , Parks Road, Oxford OX1 3PJ, United Kingdom.
2
Department of Chemistry and Department of Energy Engineering, Low-Dimensional Carbon Materials Center, Ulsan National Institute of Science and Technology (UNIST) , UNIST-gil 50, Ulsan 44919, Republic of Korea.
3
UNIST Central Research Facilities (UCRF), Ulsan National Institute of Science and Technology (UNIST) , 50 UNIST-gil, Ulsan 44919, Republic of Korea.
4
Division of Physics and Semiconductor Science, Dongguk University , Seoul 100-715, Republic of Korea.
5
Department of Engineering, University of Cambridge , 9 JJ Thomson Avenue, Cambridge CB3 0FA, United Kingdom.

Abstract

van der Waals heterostructures composed of two different monolayer crystals have recently attracted attention as a powerful and versatile platform for studying fundamental physics, as well as having great potential in future functional devices because of the diversity in the band alignments and the unique interlayer coupling that occurs at the heterojunction interface. However, despite these attractive features, a fundamental understanding of the underlying physics accounting for the effect of interlayer coupling on the interactions between electrons, photons, and phonons in the stacked heterobilayer is still lacking. Here, we demonstrate a detailed analysis of the strain-dependent excitonic behavior of an epitaxially grown MoS2/WS2 vertical heterostructure under uniaxial tensile and compressive strain that enables the interlayer interactions to be modulated along with the electronic band structure. We find that the strain-modulated interlayer coupling directly affects the characteristic combined vibrational and excitonic properties of each monolayer in the heterobilayer. It is further revealed that the relative photoluminescence intensity ratio of WS2 to MoS2 in our heterobilayer increases monotonically with tensile strain and decreases with compressive strain. We attribute the strain-dependent emission behavior of the heterobilayer to the modulation of the band structure for each monolayer, which is dictated by the alterations in the band gap transitions. These findings present an important pathway toward designing heterostructures and flexible devices.

KEYWORDS:

MoS2/WS2; band gap transition; interlayer interactions; strain engineering; van der Waals heterostructures

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