Symmetry Engineering Induced In-Plane Polarization in MoS2 through Van der Waals Interlayer Coupling

2D materials with low-symmetry exhibit anisotropic physical properties, making them promising candidates for various applications. However, the lack of matured synthesis methods in anisotropic 2D materials is still the main obstacle to their future applications. Given the mature synthesis method of transition metal dichalcogenides (TMDCs), manipulating anisotropy in 2D TMDCs becomes a promising way to tune or trigger functional properties. Herein, for the first time, a van der Waals symmetry engineering is reported to introduce in-plane polarization in MoS2 through contact with low-symmetric CrOCl. The emergence of asymmetric second harmonic generation pattern in MoS2/CrOCl heterojunction indicates the variation of lattice symmetry in MoS2. Furthermore, the theoretical simulation shows that such change stems from lattice-mismatch-induced uniaxial strain because of the strong interlayer interactions. The angle-dependent Raman and photoluminescence spectra further identify that the uniaxial strain gives rise to the in-plane polarization in MoS2. In addition, the polarized MoS2 exhibits excellent orientation-sensitive electrical characteristics with a conductance anisotropy ratio of approximate to 1.5. More importantly, the strong linear polarization-sensitive photodetection is realized, and the anisotropic ratio reached 1.25 with 532 nm. The results suggest that symmetric engineering potentially opens up a new field to endow high-symmetry 2D materials with anisotropic functionalities.

Automated summary

2D materials with low-symmetry exhibit anisotropic physical properties, making them promising candidates for various applications. However, the lack of matured synthesis methods in anisotropic 2D materials is still the main obstacle to their future applications. Herein, a van der Waals symmetry engineering is used to introduce in-plane polarization in MoS2 through contact with low-symmetric CrOCl. The change in lattice symmetry is shown through the emergence of asymmetric second harmonic generation pattern in MoS2/CrOCl heterojunction. Theoretical simulation and experimental results confirm that the lattice-mismatch-induced uniaxial strain is responsible for the in-plane polarization in MoS2.