Silver nanoclusters-decorated silicon nanostructures: Site specific active-spots confirmed by surface-enhanced Raman scattering

Conventional silicon (Si) wafers were used as base materials and etched Si nanostructures (eSi-NSs) were fabricated through metal catalysed electroless etching (MCEE) technique followed by decoration of silver nanoclusters (Ag-NCs). The nanopores and hills, at different etching conditions, were found to have higher surface area as well as enough space to possess highly populated SERS-active sites. For short term etching in MCEE technique, the vertical etching was found to be dominant making the nanostructures narrow, whereas for long term etching pore size increased due to accelerated top lateral etching. It was noted that smaller Ag-NCs with the size distribution of 29.04±5.69 nm were observed within eSi-NSs of shorter etching time, whereas comparatively bigger Ag-NCs with the size distribution of 51.36±11.21 nm were observed within those of longer etching time. Strong SERS-activity was observed in presence of Ag-NCs-decorated eSi-NSs using Rhodamine 6G. The SERS-enhancement was noted to be as high as 1 × 10⁶. SERS enhancements in presence of eSi-NSs with shorted etching time was noted to be nearly double of those with longer etching time. EM near-field distributions derived from finite difference time domain simulations validated the observations as well. A plausible explanation and correlation with the experimental observations have been amended.