High-quality narrow black phosphorus nanoribbons with nearly atomically smooth edges and well-defined edge orientation.

Black phosphorus nanoribbons (BPNRs) with a tunable bandgap and intriguing electronic and optical properties hold strong potential for logic applications. However, efficiently producing high-quality BPNRs with precise control over their size and structure remains a great challenge. Here we achieved high-quality, narrow and clean BPNRs with nearly atomically smooth edges and well-defined edge orientation at high yield (up to ~95%) through the sonochemical exfoliation of the synthesized bulk BP crystals with a slightly enlarged lattice parameter along the armchair direction. The resulting BPNRs have widths centred at 32 nm and can be as narrow as 1.5 nm, with edges consistently aligned along the zigzag direction in measured BPNRs with widths ≤340 nm. The formation of one-dimensional BPNRs with zigzag edges is attributed to the introduction of pre-stress along the armchair direction of the grown bulk BP and the application of suitable sonication conditions. The BPNR bandgap increases as the BPNR width decreases from 83 nm to 13 nm, with a large bandgap of 0.64 eV for a 13-nm-wide BPNR. A typical graphene-contacted field-effect transistor fabricated with a 13-nm-wide and 10-nm-thick BPNR can achieve an on/off ratio of 1.7 × 10