Synthesis by pulsed laser ablation in Ar and SERS activity of silver thin films with controlled nanostructure

--Thin silver films were deposited by pulsed laser ablation in a controlled Ar atmosphere and their SERS activity was investigated. The samples were grown at Ar pressures between 10 and 70 Pa and at different laser pulse numbers. Other deposition parameters such as laser fluence, target to substrate distance and sub strate temperature were kept fixed at 2.0 J/cm2, 35 mm and 297 K. Film morphologies were investigated by scanning and transmission electron microscopies (SEM, TEM). Surface features range from isolated nearly spherical nanoparticles to larger islands with smoothed edges. Cluster growth is favored by plume confine ment induced by background gas. After landing on the substrate clusters start to aggregate giving rise to larger structures as long as the deposition goes on. Such a path of film growth allows controlling the surface mor phology as a function of laser pulse number and Ar pressure. These two easytomanage process parameters control the number density and the average size of the asdeposited nanoparticles. We investigated the influ ence of substrate morphologies on their surface enhanced Raman scattering properties. Raman measure ments were performed after soaking the samples in rhodamine 6G aqueous solutions over the concentration range between 1.0 × 10-4 and 5.0 × 10-8 M. The sensitivity of the film SERS activity on the surface features is put into evidence.