Twist angle-dependent interlayer coupling of MoS₂ bilayers

Chien-Ju Lee^1*, Fu-Hsien Chu¹, Li-Syuan Lu¹, Wei-Ting Hsu², Wen-Hao Chang^1,3

¹Department of Electrophyiscs, National Chiao Tung University, Hsinchu, Taiwan
²Department of Phyiscs, National Tsing Hua University, Hsinchu, Taiwan
³Research Center for Applied Sciences, Academia Sinica, Taipei, Taiwan

* Presenter:Chien-Ju Lee, email:chienju1016@gmail.com

Manipulating the interlayer coupling in two-dimensional (2D) van der Waals bilayers has emerged as a new route to engineer the properties of 2D quantum materials. Recent advances in the preparation of twisted bilayers of transition metal dichalcogenides (TMDs) has led to the demonstration of moiré excitons. The moiré superlattice formed by stacking two monolayer TMDs with lattice mismatch or rotational misalignment can modulate the electronic structure of the materials and confine excitons. Experimental evidence shows that domain reconstruction can occur when the twist angle is smaller than a critical value. It is expected that the structural and electronic properties of bilayer TMDs will be further influenced by the stacking configuration. In this work, taking advantage of the aligned monolayer MoS₂ grown by chemical vapor deposition, we prepared a series of MoS₂ bilayers by stacking aligned monolayers together. The twist angles of the stacked MoS₂ bilayers cover the range where domain reconstruction takes place with very fine steps. A systematic study of the interlayer coupling of bilayer MoS₂ as a function of the interlayer twist angle was conducted. Twist-angle-dependent indirect bandgap transition was observed. The energy blueshift in the indirect photoluminescence (PL) with the increasing twist angle is attributed to the increasing interlayer distance. Temperature dependent PL measurements show that the indirect transition of bilayer MoS₂ originates from the recombination of electrons at Q-point and holes at Γ-point. Compared to DFT calculations we are able to deduce the interlayer distance as a function of twist angles. Our results shed some light on the correlation between structural and electronic properties of MoS₂ twisted bilayers and provide a guide for designing new van der Waals structures for applications.

Keywords: 2D materials, twisted bilayer, indirect excitons, band structure