Metal-Iodide-Mediated CVT Growth of Form V Red Phosphorus Wires

One-dimensional phosphorus allotropes remain difficult to synthesize despite their promise for (opto)electronics. Form V red phosphorus (Hittorf's phosphorus), composed of tubular phosphorus chains, has mainly been obtained as platelets or bulk crystals, limiting studies of anisotropic growth and transport. Here, AgI-assisted chemical vapor transport enables on-substrate growth of high-aspect-ratio red-phosphorus wires extending hundreds of micrometers. SAED identifies multiple individual wires as Form V, while HRTEM-FFT analysis supports preferential [010] growth along the tubular chains. PXRD/GID and a weak Raman band near 486 cm^{- 1} provide complementary evidence, although the population-wide Form V fraction was not quantified. SEM analysis reveals a log-normal diameter distribution with a median of 433 nm (n = 175). EDX, XPS, and cross-sectional TEM-EDX detect residual Ag/I species enriched near wire surfaces. Together with AgI-free controls, these results support AgI-mediated heterogeneous nucleation, pending in situ verification. A two-terminal device on a ∼1.2 µm wire shows linear I-V behavior and an effective resistivity of 91.3 Ω cm, excluding continuous metallic Ag shorting, although contact and scattering contributions were not deconvoluted. This work establishes an on-substrate route to Form V red-phosphorus wires and a platform for future gate-dependent transport studies.