Silver films over silica microspheres (AgFOSM) as SERS substrates

Through the years, nanosphere lithography (NSL) has attracted a growing interest because of its potential to manufacture a wide variety of homogeneous arrays of nanostructures. In this work, NSL was used for the fabrication of Surface-Enhanced Raman Spectroscopy (SERS) substrates. The proposed Raman-SERS substrates consist of 50 nm or 120 nm thick silver thin films evaporated over a monolayer of silica microspheres (AgFOSM) onto silicon or quartz substrates. The samples were tested as SERS substrates using Rhodamine 6G as analyte. As a comparison and to determine the Raman enhancement factor, not only the AgFOSM samples were measured, but also we studied similar samples obtained when the Ag film is directly deposited onto the silicon or quartz substrate. Our results show that the R6G Raman signal is always more intense by two or three orders of magnitude for the AgFOSM samples than for the Ag maskless ones. In the case of the 120 nm thick Ag films, the calculated enhancement factors for the AgFOSM samples are of the order of 104 for both silicon and quartz substrates.