Synthesis of Highly Anisotropic 2D Insulator CrOCl Nanosheets for Interfacial Symmetry Breaking in Isotropic 2D Semiconductors.

Chromium oxychloride (CrOCl), a van der Waals antiferromagnetic insulator, has attracted significant interest in 2D optoelectronic, ferromagnetic, and quantum devices. However, the bottom-up preparation of 2D CrOCl remains challenging, limiting its property exploration and device application. Herein, the controllable synthesis of 2D CrOCl crystals by chemical vapor deposition is demonstrated. The combination reaction of precursors together with the space-confined growth strategy, providing stable and stoichiometric growth conditions, enable a robust synthesis of high-crystallinity CrOCl nanosheets with regular rhombus-like morphology and uniform thickness. By tuning the growth temperature from 675 to 800 °C, the thickness of CrOCl nanosheets can be continuously modulated from 10.2 to 30.8 nm, with the domain size increasing from 16.9 to 25.5 µm. The as-grown CrOCl nanosheets exhibit significant structural/optical anisotropy, ultrahigh insulativity, and superior air stability. Furthermore, a MoS/CrOCl heterostructure with single-mirror symmetry stacking and ultrastrong interfacial coupling is built to realize interfacial symmetry breaking, a novel interface phenomenon that converts MoS from isotropy to anisotropy. Consequently, the MoS/CrOCl heterostructure device achieves polarization-sensitive photodetection and bulk photovoltaic effect, which are nonexistent in high-symmetry 2D materials. This work paves the way for the future exploration of CrOCl-based 2D physics and devices via symmetry engineering.