Self-organized patterned arrays of Au and Ag nanoparticles by thickness-dependent dewetting of template-confined films Francesco Ruffino • M. G. Grimaldi Received: 5 March 2014 / Accepted: 29 April 2014 / Published online: 15 May 2014 Ó Springer Science+Business Media New York 2014 Abstract In this work we report on the formation of self- organized and multimodal sized patterned arrays of Au and Ag nanoparticles on SiO 2 surface exploiting the thickness- dependent solid-state dewetting properties of template- confined deposited nanoscale films. In this approach, the Au and Ag surface pattern order, on the SiO 2 substrate, is established by the template confined deposition on a mi- crometric scale, while the solid-state dewetting phenome- non is induced by thermal processes (below the Au and Ag melting temperature). The deposited films have not an uniform thickness. They, instead, present a controlled thickness due to shadowing mask effects during deposi- tions. Such an inhomogeneity can be further controlled by changing the deposition angle. After the dewetting process, scanning electron microscopy analyses allowed us to cor- relate the mean diameter hDi and spacing hsi of the formed nanoparticles by the thickness h of the deposited films. Despite the dewetting process of the Au and Ag films occurs in the solid state, relations describing the evolution of hDi and hsi with hhi typical of the linear hydrodynamic spinodal dewetting process of liquid films, hDi µ h 5/3 and hsi µ h 2 , were verified within a 20 % experimental error. As a consequence we call this process ‘‘pseudo-spinodal dewetting’’. Introduction Metallic micro- and nano-structures and thin films have attracted much interest because of their wide applications in many areas, such as in catalysis [1–4], sensing [5–8], data storage [9], optoelectronics [10], biological related areas [11], plasmonics and photovoltaics [12–14]. A common method for preparing metallic nanoparticles (NPs) over a large area is the process of dewetting a thin solid metal film on a poorly wetting flat substrate [15–20]. Thin metal films are rarely stable structures, but are instead kinetically frozen as a consequence of formation far from equilibrium. In general, the total free energy associated with the interfaces of a film is reduced if it agglomerates to form islands [21, 22]. Therefore, when films are heated so that atomic diffusion occurs, they, often, dewet to form arrays of islands. Dewetting can occur at temperatures well below the melting temperature of the film, so that the material remains in the solid state throughout the process, and it will occur upon heating if the surface energy of the metal is greater than one-half the work of adhesion in which a finite contact angle between the film and substrate is energetically favorable [22]. For example [15–25], thin Fe, Ni, Au, Cu or Co films and alloy films (AuPt, for example) deposited onto several substrates (silica, mica, …) break down into island arrays upon annealing at tem- peratures of several hundred degrees Celsius (500–900 °C). The dewetting of metallic thin films during heat treatment has been widely studied both theoretically and experi- mentally as a structure-directing mechanism providing the possibility for nanoscale patterning of the surfaces [22–36]. In a general dewetting phenomenon, a thin film breaks up into particles via one of three mechanisms [22, 37–39]: (1) heterogeneous nucleation, which initiates from a defect located at the film surface or the film-and-substrate F. Ruffino (&) Á M. G. Grimaldi Dipartimento di Fisica ed Astronomia-Universita ` di Catania, Via S. Sofia 64, 95123 Catania, Italy e-mail: francesco.ruffino@ct.infn.it F. Ruffino Á M. G. Grimaldi MATIS IMM-CNR, Via S. Sofia 64, 95123 Catania, Italy 123 J Mater Sci (2014) 49:5714–5729 DOI 10.1007/s10853-014-8290-4