Gradient‐Mass‐Transfer Synthesis of 2D [Bi 2 CuO 3 ]SO 4 Crystals for Anisotropy Engineering

ABSTRACT The intrinsic physical anisotropy of low‐symmetry materials makes them highly promising candidates for polarization‐sensitive devices. However, their practical application remains constrained by the scarcity of single materials that can combine low symmetry with high performance. Here, we report a novel low‐symmetry [Bi 2 CuO 3 ]SO 4 crystal with an insulating nature, designed to enable symmetry control over conventional high‐performance semiconductors. We achieve controllable growth of layered [Bi 2 CuO 3 ]SO 4 nanosheets via a gradient‐mass‐transfer‐assisted chemical vapor deposition method, with thicknesses down to 1.43 nm. Alternating [Bi 2 CuO 3 ] 2+ cationic layers and SO 4 2− anionic layers, coupled with disparate ionic radii of Bi 3+ and Cu 2+ , endow the [Bi 2 CuO 3 ]SO 4 material with low structural symmetry, resulting in pronounced in‐plane optical anisotropy. Upon integration with high‐symmetry MoS 2 , [Bi 2 CuO 3 ]SO 4 induces interfacial symmetry breaking, driven by strong interfacial coupling and substantial charge redistribution. Notably, by fabricating devices along different crystallographic orientations of [Bi 2 CuO 3 ]SO 4 , tunable polarization ratios are exhibited, reaching a maximum of 5.44 along the a ‐axis and a minimum of 1.57 along the b ‐axis. This work establishes a reliable strategy for obtaining heterostructures with low symmetry and tunable anisotropy, advancing next‐generation directional optoelectronic devices.