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 number. Other deposition parameters such as laser fluence, target to substrate distance and substrate temperature were kept fixed at 2.0 J/sm2, 35 mm and 297 K. Film morphologies were investigated by scanning and transmission electron microscopies. Surface features range from isolated nearly spherical nanoparticles to larger islands with smoothed edges. Cluster growth is favored by plume confinement 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 morphology as a function of laser pulse number and Ar pressure. These two easy-to-manage process parameters control the number density and the average size of the as-deposited nanoparticles. Surface enhanced Raman scattering measurements were performed by soaking the samples in rhodamine 6G aqueous over the concentration range between 1.0*10-4 M and 5.0*10-8 M. The dependence of the film SERS activity on their surface morphology is discussed