The morphological regularity, thickness uniformity, and size controllability of two-dimensional materials play a crucial role in regulating their physicochemical properties. However, achieving a synergistic balance among these three factors remains a key challenge in the field. In this study, through a systematic investigation of 36 salt-assisted growth systems, we discovered that CsCl promotes the lateral growth of SnS2, while KI optimizes the crystal morphology. Using a CsCl/KI mixed salt system, we successfully grew triangular, ultrathin, large-area SnS2 nanosheets with a size exceeding 200 μm and a thickness of only 1.8 nm. Angle-resolved polarized Raman spectroscopy (ARPRS) revealed that SnS2 nanosheets transferred onto SiO2 substrates exhibit intrinsic in-plane isotropy. In contrast, SnS2 nanosheets grown directly on mica substrates display a 90° periodic variation in Raman peak intensity with polarization angle, indicating significant in-plane anisotropy. This anisotropy arises from interfacial stress induced by lattice mismatch between the mica substrate and SnS2, which breaks the intrinsic symmetry of the material. In addition, the transition of SnS2 nanosheets from in-plane optical isotropy to anisotropy were confirmed by the polarized optical microscopy characterization. These results demonstrate that the mixed salt-assisted growth strategy provides a new approach for synergistically controlling the size, shape and thickness of two-dimensional materials and offers a novel method for inducing anisotropic property in intrinsically isotropic two-dimensional materials through lattice mismatch.
Lian et al. (Thu,) studied this question.