AFM and micro-Raman investigation on filters coated with silver colloidal nanoparticles

Rough silver surfaces are obtained by filtration of silver colloidal suspensions through aluminium oxide membranes. This technique leads to a deposited layer of nanostructured metal, which ensures an efficient surface enhanced Raman scattering (SERS) effect. As detected by atomic force microscopy (AFM), the surface is constituted by silver spheroids with 30 nm as average diameter. The Ag particles can assembly forming some isolated bumps higher than 200 nm. The micro-Raman investigation is here combined with the AFM measurements to analyse the surface morphology by evaluating the SERS enhancement of p-nitrobenzoic acid, as organic ligand. The SERS signal results strongly enhanced when the laser beam is focalised on the prominent metal clusters.