Atomically Precise Bottom‐Up Fabrication of Ultra‐Narrow Semiconducting Zigzag BiP Nanoribbons

1D semiconductors with atomically precise edge and well‐controlled width hold significant promise as channel materials for next‐generation electronics. Here a method to fabricate the narrowest zigzag‐edged bismuth phosphide (BiP) nanoribbons (NRs) is presented, achieving widths of three atoms (≈0.7 nm), through molecular beam epitaxy on bismuthene in a wide P coverage range. Using scanning tunneling microscopy and first‐principles calculations, it is revealed that these BiP NRs exhibit a blue‐phosphorene‐like structure, with a theoretical bandgap of 0.38 eV. Notably, first‐principles calculations reveal spin‐polarized states located on the zigzag edges, presenting an option for spintronics applications. Formation of these uniform BiP NRs is attributed to tensile strain from lattice‐registry confinement. During epitaxial growth, P clusters act dually as feedstock and catalysts, suggesting a self‐catalyzed growth mechanism. The bottom‐up strategy offers an effective approach for the atomically precise fabrication of 1D BiP NRs, paving the way for the creation of diverse low‐dimensional binary materials with tailored chemical and electronic properties, facilitated by selecting suitable elemental 2D materials as substrates. The narrowest zigzag‐edged BiP nanoribbons are fabricated by MBE on β‐bismuthene. STM complemented with DFT calculation reveals a blue‐phosphorene‐like structure with three atoms wide, which exhibits spin‐polarized states located on the zigzag edges. P clusters serve both as a feedstock and catalyst, indicating a self‐catalyzed mode.