Scalable Fabrication of Highly Organized, Horizontally Aligned Sub-5 nm Silicon Nanowires via Chemical Vapor Etching.

Herein, the scalable fabrication of hierarchical silicon structures featuring high-density, horizontally super-aligned sub-5 nm silicon nanowires (SiNWs), is reported. These unprecedented, highly organized silicon architectures with tunable sizes and densities are fabricated using straightforward micro-patterned SiO₂/Si templates followed by a chemical vaporetching process. In time-resolved structural analysis, it is revealed that rapid, aggressive etching is crucial for creating an inhomogeneous spatial distribution of vapor etchants, inducing surface defects acting as preferential sites for localized anisotropic silicon etching along <111> direction. The efficacy of this unique structure is demonstrated as a single-molecule detectable surface-enhanced Raman scattering sensor, incorporating sub-10 nm silver plasmonic nanoparticles. Its distinct structural features-marked by quantum-confined dimensions, ultrahigh surface area, dual-scale roughness, and exceptional uniformity-enable significant enhancement of optical response and detection sensitivity down to 10^-11  m. These highly controlled sub-5 nm SiNW architecture can broaden the applications of quantum nanowires in chemical and bio-sensing and other emerging technologies.