Issue 6, 2024

Second-harmonic generation in 2D moiré superlattices composed of bilayer transition metal dichalcogenides

Abstract

Moiré superlattices (MSLs) in twisted two-dimensional van der Waals materials feature twist-angle-dependent crystal symmetry and strong optical nonlinearities. By adjusting the twist angle in bilayer van der Waals materials, the second-harmonic generation (SHG) can be controlled. Here, we focus on exploring the electronic and SHG properties of MSLs in 2D bilayer transition metal dichalcogenides (TMDs) with different twist angles through first-principles calculations. We constructed MSL structures of five TMD materials, including three single-phase materials (MoS2, WS2, and MoSe2) and two heterojunctions (MoS2/MoSe2 and MoS2/WS2) with twist angles of 9.4°, 13.2°, 21.8°, 32.2°, and 42.1° without lattice mismatch. Our findings demonstrate a consistent variation in the SHG susceptibility among different TMD MSLs as a response to twist-angle changes. The underlying reason for the twist-angle dependence of SHG is that the twist angle regulates the interlayer coupling strength, affecting the optical band gap of MSLs and subsequently tuning the SHG susceptibility. Through a comparison of the static SHG susceptibility values, we identified the twist angle of 9.4° as the configuration that yields the highest SHG susceptibility (e.g. 358.5 pm V−1 for the 9.4° MoSe2 MSL). This value is even twice that of the monolayer (173.3 pm V−1 for monolayer MoSe2) and AA′-stacked bilayer structures (139.8 pm V−1 for AA′ MoSe2). This high SHG susceptibility is attributed to the strong interlayer coupling in the 9.4° MSL, which enhances the valence band energy (contributed by the antibonding orbitals of chalcogen-pz and transition metal-dz2) and consequently leads to a small optical band gap, thus improving the optical transitions. The findings of this study provide a straightforward way to improve the SHG performance of bilayer TMDs and also throw light on the sensitive relationship between the twist angle, band structure and SHG properties of TMD MSLs.

Graphical abstract: Second-harmonic generation in 2D moiré superlattices composed of bilayer transition metal dichalcogenides

Supplementary files

Article information

Article type
Paper
Submitted
01 جمادى الأولى 1445
Accepted
21 جمادى الثانية 1445
First published
29 جمادى الثانية 1445

Nanoscale, 2024,16, 2913-2922

Second-harmonic generation in 2D moiré superlattices composed of bilayer transition metal dichalcogenides

X. Yang, X. Wang, M. Faizan, X. He and L. Zhang, Nanoscale, 2024, 16, 2913 DOI: 10.1039/D3NR05805K

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements