Surface-Assisted Passivation Growth of 2D Ultrathin β-BiO Crystals for High-Performance Polarization-Sensitive Photodetectors.

2D nonlayered materials (NLMs) have garnered considerable attention due to unique surface structure and bright application prospect. However, owing to the strong interatomic forces caused by intrinsic isotropic chemical bonds in all directions, the direct synthesis of ultrathin and large area 2D NLMs remains a tremendous challenge. Here, the surface-assisted passivation growth strategy is designed to synthesize ultrathin and large size β-BiO crystals with the thickness down to 0.77 nm and the lateral size up to 163 µm. These results are primarily ascribed to the bonding between Se atoms and the unsaturated Bi atoms on the surface of β-BiO, resulting in the surface passivation and promoting the obtaining of ultrathin β-BiO. Strikingly, the photodetectors based on β-BiO flakes exhibit a high photoresponsivity of 71.91 A W, an excellent detectivity of 6.09 × 10 Jones, a remarkable external quantum efficiency of 2.4 × 10%, an outstanding anisotropic photodetection and excellent UV imaging capability at 365 nm. This work sheds light on the synthesis of 2D ultrathin NLMs and promotes their applications in multifunctional optoelectronics.