Pillar-cap shaped arrays of Ag/SiO2 multilayers after annealing treatment as a SERS-active substrate

The “pillar-cap” shaped arrays of Ag/SiO2 multilayers were prepared on 2D PS template by sputtering Ag and SiO2 materials alternatively. Annealing under argon accelerated the interface diffusion between Ag and SiO2 sublayers. Some Ag nanoparticles squeezed into SiO2 sublayer through the pinholes in SiO2 sublayer and the corona-like structure consisting of SiO2-trapped Ag nanoparticles formed on the surfaces of the pillar-cap arrays. The sizes of Ag nanoparticles varied from 2 nm to 5 nm, depending on the annealing temperature. The separations of 1-2 nm SiO2 were generated between Ag particles and underlying Ag sublayer, which provided a lot of hot spot sites for SERS. This fabrication method could avoid the unnecessary and cumbersome stages in chemical surface modification, which made the substrate a promising candidate for the SERS detection.