3D plasmonic hot spots network via gold decorated deep micro-porous silicon exhibiting ultrahigh-SERS enhancement with application to explosives detection

Microporous deep (12 µm depth) silicon substrate coated with optimum Au layer is fabricated for ultrahigh SERS enhancement factor and employed for explosives trace detection. Being microporous with quasi-periodicity, short lived extended plasmons can be excited via scattering and coupled to localized ones thus providing ultrahigh local optical field, and the SERS ultrahigh enhancement is achieved. SERS activity of the substrate is checked using 4-ATP monolayer immobilized over the proposed substrate and analyzed using two different methods including peak absolute intensity and peak ratios, to find best suitable method for higher reproducibility. The obtained enhancement factor for Raman signal is found to be the order of 10⁶–10⁷, explained due to the existence of 3D hot-spot network and coupling between localized to extended plasmons. The coupling is verified through the Rabi splitting observed in the reflectivity dip. A 2–3 times fewer signal variability is obtained using peak ratio between highest peak intensity of Raman receptor and that of the substrate. The substrate is then employed for picric acid sensing providing the detection limits of 7.48 nM and 2.87 nM, determined based on peaks height and ratio measurements respectively. The proposed work suggests deep micro-porous silicon coated with 200 nm Au layer deposited over a large area as promising candidate for SERS and sensing of ultra-trace amount of chemicals.