A Raman and AFM investigation on metal surfaces SERS-activated by silver colloidal nanoparticles

The giant Raman enhancement observed by means of the SERS (surface-enhanced Raman scattering) technique upon adsorption of molecules on nanostructured Ag, Au or Cu surfaces allows widespread applications in materials science. The Raman intensities of the adsorbed molecules can be enhanced up to 107-fold upon going to the SERS spectra. Recently, the SERS spectroscopy has been applied to single-molecule detection, showing enhancement factors up to 1014-1015. In this work, by depositing silver colloidal suspensions on different metal surfaces, dry layers of Ag nanoparticles were obtained, as detected by atomic force microscopy (AFM) measurements. Hence, substrates, unable to give rise to the Raman enhancement of the adsorbate, become SERS-active, avoiding the roughening treatment of the metal surfaces.