ISSN 1054660X, Laser Physics, 2011, Vol. 21, No. 4, pp. 818–822. © Pleiades Publishing, Ltd., 2011. Original Text © Astro, Ltd., 2011. 818 1 1. INTRODUCTION There is a growing interest toward metal nanopar ticles (NPs), owing to their peculiar optical, structural and electronic properties, which depend on their size, shape and their mutual aggregation properties [1]. In particular noble metal nanoparticles (Au, Ag, Pt) have been the object of intensive theoretical and experi mental research because they show unique character istics in their optical and magnetic properties besides antibacterial and catalytic activities [2]. In particular the search for production methods able to control their structural properties was extended to physical deposition methods usually adopted for the growth of bulk materials. This is the case of the pulsed laser abla tion (PLA) technique. The technique is based on the material removal (ablation) from a target by focusing a high energy laser on its surface. The interaction of the laser beam with the target produces a highly oriented material stream, usually ejected along the normal to the target surface. PLA is nowadays widely employed to grow a large class of materials, especially when such materials cannot be produced by alternative methods, 1 The article is published in the original. or when PLA gives superior results in terms of material quality [3, 4]; moreover pulsed laser irradiation can also be employed to modify the morphology and/or chemistry of the target surface [5] in a controlled way. Several experimental parameters can be varied in PLA in order to tune the properties of the resulting materi als: laser wavelength, laser pulse energy and duration, target to substrate distance, pressure and chemical composition of an ambient gas. In conventional PLA the use of an ambient gas during the deposition pro cess is usually required to correct an incongruent sto ichiometry transfer from the target to the deposited films, as in the case of superconductor oxides [6]; or when a foreign specie, not included in the target mate rial, is desired in the resulting material, as, for exam ple, in the case of carbon nitride thin films produced by ablating graphite in a nitrogen atmosphere [7]. The pressure values at which deposition takes place are determined by the need to incorporate in the growing films the desired quantity of the gaseous specie, yet avoiding to lower excessively the kinetic energies of the ablated species. Concerning this it was observed that the properties of the PLA deposited materials depend in a non trivial way on the ambient gas pressure. The ADVANCED LASER TECHNOLOGIES Synthesis by Pulsed Laser Ablation in Ar and SERS Activity of Silver Thin Films with Controlled Nanostructure 1 C. D’Andrea a , F. Neri a , P. M. Ossi b , N. Santo c , and S. Trusso d, * a Dipartimento di Fisica della Materia e Tecnologie Fisiche Avanzate, Università di Messina, Salita Sperone 31, 98166 Messina, Italy b Dipartimento di Energia and Centre for NanoEngineered MAterials and SurfacesNEMAS, Politecnico di Milano, Via Ponzio, 343, 20133 Milano, Italy c Centro Interdipartimentale di Microscopia Avanzata, Università degli Studi di Milano, Via Celoria 26, 20133 Milano, Italy d Istituto per i Processi ChimicoFisici del CNR, S. ta Sperone, C.da Papardo, Faro Saperiore, 98158, Messina, Italy *email: trusso@me.cnr.it Received April 22, 2010; in final form, July 25, 2010; published online March 4, 2011 Abstract—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/cm 2 , 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 easytomanage process parameters control the number density and the average size of the asdeposited 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. DOI: 10.1134/S1054660X11070048