Formation of Armored\nSilicon Nanowires Array via High-Repetition-Rate\nFemtosecond Laser Oxidation for Robust Surface-Enhanced Raman Scattering\nDetection

Superhydrophobic nanostructures with dense hotspots and\nhigh concentration\nefficiency are of paramount importance for highly sensitive surface-enhanced\nRaman scattering (SERS) detection. However, their low mechanical strength\nmakes them susceptible to damage from external interferences, leading\nto hotspot loss and superhydrophobicity failure. In this study, robust\nSERS detection is achieved using an armored superhydrophobic silicon\nnanowires array. A micro/nanocross-scale oxide mask is created through\nhigh-repetition-rate femtosecond laser oxidation to fabricate the\narmored nanowires array. The underlying mechanisms of the nanoparticle\nlayer serving as a mask in deep reactive ion etching (DRIE) are analyzed\nto elucidate the formation of the silicon nanowires. The armored nanowires\narray SERS substrate exhibits a high contact angle of 158°, demonstrating\nexceptional analyte enrichment capability. Combined with the dense\nhotspots provided by the high aspect ratio nanostructures, the detection\nlimit for Rhodamine 6G is 10<sup>–13</sup> M, and the enhancement\nfactor (EF) is 4.35 × 10<sup>9</sup>. After undergoing various\nmechanical tests, the substrate maintains its superhydrophobicity\nalong with a stable Raman signal enhancement, demonstrating its resistance\nto potential external interference in SERS detection. The sensitive\ndetection of various analytes highlights the promising applications\nof the armored nanowires substrate in diverse SERS scenarios.