Ag nanocluster synthesis by laser ablation in Ar atmosphere: A plume dynamics analysis E. FAZIO, 1 F. NERI, 1 P.M. OSSI, 2 N. SANTO, 3 AND S. TRUSSO 4 1 Dipartimento di Fisica della Materia e Ingegneria Elettronica, Universita ` di Messina, Messina, Italy 2 Dipartimento Energia & Centre for NanoEngineered MAterials and Surfaces, NEMAS, Politecnico di Milano, Milano, Italy 3 Centro Interdipartimentale Microscopia Avanzata, Universita ` degli Studi di Milano, Milano, Italy 4 CNR-Istituto per i Processi Chimico-Fisici Sezione di Messina, Salita Sperone, Messina, Italy (RECEIVED 7 October 2008; ACCEPTED 5 January 2009) Abstract Ag thin films were deposited by pulsed laser ablation in a controlled Ar atmosphere. The deposition process was performed at different Ar pressure values in the range between 10 and 100 Pato investigate the influence of ambient gas pressure on the plasma expansion dynamics and on the film structural properties. Position, velocity and volume of the laser generated plasma as functions of time were obtained by time resolved fast photography. The morphological properties of the films were investigated by transmission electron microscopy which shows that film growth proceeds via aggregation on the substrates of nanoclusters formed in the expanding plume. The formation of nanoparticles takes place as a consequence of plasma confinement induced by the interaction with ambient gas species. Data from fast photography analysis were used as input parameters to calculate the size of the nanoparticles using a model that takes into account the collisional nature of the laser generated silver plasma. Keywords: Laser ablation; Plasma expansion; Silver clusters 1. INTRODUCTION In the last decade, nanostructured surfaces have been extensively studied, due to the predicted and in part observed unusual transport (electronic, optical), magnetic, and chemi- cal properties that characterize matter when its typical sizes are pushed to the nanometer scale (Jarrold, 1994). Much research activity was focused on noble metal nanoparticles (NPs), exploiting their optical properties of interest in surface enhanced spectroscopes and plasmonic, while their catalytic behavior finds application in the growth of nano- tubes and nanorods (Bailini et al., 2006; Bertoni et al., 2004). Among physical vapor deposition (PVD) techniques, that have been modified to produce nanostructured materials, in particular thin films, pulsed laser deposition (PLD) in a buffer gas is a promising approach to deposit nanoparticles of different materials over wide intervals of process con- ditions (Wang et al., 2007; Wolowski et al., 2007; Gamaly et al., 2000). In exemplary PLD depositions, including Au/glass (Irissou et al., 2003), Au/HOPG (Zenkevich et al., 2002), Ag/Si (Seal et al., 2003), Pt/HOPG (Dolbec et al., 2004) on the nucleation and coalescence of NPs on the substrate was reported. The synthesis of C nanoclusters in plumes propagating through He and Ar atmospheres at pressures up to 1 kPa was reported and modeled (Bolgiaghi et al., 2005), keeping into account the relevant role of ioniz- ation phenomena occurring in the interface region between the shock wave front and the buffer gas (Bailini et al., 2006a, 2006b). Recently, cluster-assembled W films were deposited in different atmospheres and pressure ranges (Di Fonzo et al., 2006; Baserga et al., 2007); the surface mor- phology, bond coordination, and oxidation path of the films, both when exposed to the ambient atmosphere after deposition, and when synthesized in dry air were systemati- cally studied and complemented a detailed high resolution transmission electron microscopy (HREM) analysis of struc- ture, size, and morphology of the deposited NPs (Ossi et al., 2008a, 2008b), whose sizes agree with those predicted by a model of cluster growth in a plume expanding through a buffer gas (Bailini & Ossi, 2007b). In this work, we investigate the synthesis and deposition of Ag NPs produced by PLD in a controlled inert gas (Ar) atmosphere. The films were prepared on polished ,100 . 281 Address correspondence and reprint requests to: S. Trusso, CNR-Istituto per i Processi Chimico-Fisici Sezione di Messina, Salita Sperone, C.da Papardo, Faro Superiore, 98158 Messina, Italy. E-mail: trusso@me.cnr.it Laser and Particle Beams (2009), 27, 281–290. Printed in the USA. Copyright # 2009 Cambridge University Press 0263-0346/09 $20.00 doi:10.1017/S0263034609000366