Scalable and Lithography‐Free Fabrication of High‐Aspect‐Ratio Diamond Nanowires for Photonic and Electrochemical Applications

The scalable integration of low‐dimensional diamond nanostructures into advanced technologies is fundamentally bottlenecked by the complexity and high cost of conventional lithography. Here we report a highly scalable, lithography‐free top‐down etching approach to produce densely distributed high‐aspect‐ratio (HAR) diamond nanowires across polycrystalline (PCD), single‐crystal (SCD), and boron‐doped diamond (BDD) substrates, including continuous fabrication on a full 2‐inch wafer. By correlating time‐dependent surface characterizations, transmission electron microscopy (TEM), energy‐dispersive x‐ray spectroscopy (EDS) elemental mapping, and 3D femtosecond laser tomography, we elucidate an Ag‐initiated, redeposition‐sustained secondary inorganic micromasking process: self‐assembled Ag nanoclusters initiate nanowire formation, while redeposited inorganic residues derived from the carrier wafer and chamber environment sustain anisotropic etching during prolonged reactive ion etching (RIE). The broad versatility of this method is validated through distinct functional demonstrations: PCD nanowires demonstrate a pronounced transition to hydrophobicity; SCD nanowires demonstrate spatial modulation and localized enhancement of ensemble nitrogen‐vacancy (NV) photoluminescence, while finite‐difference time‐domain (FDTD) simulations support nanowire‐assisted optical extraction; BDD nanowires provide an approximately 30‐fold increase in electrochemical double‐layer capacitance (C dl )‐derived accessible electrochemical surface area, achieving a 2.5‐fold enhancement in pollutant‐degradation kinetics with stable electrochemical operation. This study establishes a viable and scalable pathway for integrating diamond nanostructures into advanced sensing, photonics, and electrocatalysis.