Modified laser-etched silicon covered with bimetallic Ag–Au Alloy nanoparticles for high-performance SERS: laser wavelength dependence

The effect of etching laser wavelength on the performance of bimetallic alloy Ag–Au nanoparticles (Ag–AuNPs) SERS-active substrate was investigated. Two kinds of macro-P-Si structures were synthesized by a laser-assisted etching process using two laser wavelengths 650 and 532 nm. Ag–AuNPs/macro-P-Si SERS-active substrate was made up via the ion reduction process. The SERS-active substrates were investigated by utilizing XRD, FE-SEM microscope, EDS analysis and Raman microscope. P-Si surface modification process by bimetallic alloy Ag–AuNPs was carried out to form efficient and nearly uniformly distributed Ag–AuNPs hot spot regions with ultra-high specific surface areas. The morphological features of the deposited Ag–AuNPs on the P-Si layer prepared by 650 nm exhibited that the nucleation process is mainly concerted on the pore boundaries with a low tendency for aggregation, while for 532 nm, the Ag–AuNPs layer is mostly well ordered of high-density semi-uniformly distributed spherical nanoparticles initiate over the macro-P-Si. The SERS results of Ag–AuNPs/macro-P-Si exposed a strong dependence on the hot spot regions among bimetallic nanoparticles. The enhancement factor of the Raman signal of Ag–AuNPs/macro-P-Si modified with 532 nm is four orders of magnitude greater than that of modified with 650 nm, which is about 2.1×10¹² and 9.3×10⁸, respectively. (author)