Structure of Ni/SiO 2 films prepared by sol–gel dip coating B. Canut a , M.G. Blanchin a , V. Teodorescu b , A. Traverse c, * a Laboratoire de Physique de la Matie `re Condense ´e et Nanostructures, Universite ´ Claude Bernard Lyon I, 69622 Villeurbanne cedex, France b National Institute for Physics of Materials, Magurele, R-76900 Bucharest, Romania c Laboratoire de Chimie Physique, Ba ˆt. 201P2, Universite ´ Paris-Sud, 91405 Orsay cedex, France Received 25 October 2006; received in revised form 26 April 2007 Abstract The sol–gel dip coating technique has been used to deposit composite oxide films (NiO) x (SiO 2 ) 1x with x = 0.1 on silicon wafers. Sin- gle and multilayer coatings allowed a variation of the film thickness from 70 to 400 nm. Film morphology, atomic structure and atomic composition have been investigated by transmission electron microscopy (TEM) and Rutherford backscattering spectrometry (RBS). The local environment of the Ni atoms was characterized by extended X-ray absorption fine structure (EXAFS). The samples were stud- ied in the as-prepared state and after annealing in H 2 at 600 °C for 1 h. The structural and chemical state evolution of clusters present inside the silica matrix is discussed in terms of out-of-equilibrium reaction processes specific to low-dimensional objects and superficial effects. Ó 2007 Elsevier B.V. All rights reserved. PACS: 61.10.Ht; 68.37.Lp; 81.07.b; 81.20.Fw Keywords: Nanocrystals; Rutherford backscattering; TEM/SEM; Nano-clusters; Nanoparticles; Sol–gels (xerogels); X-ray absorption 1. Introduction Over the past ten years, a great deal of interest has been shown in the processing of metal-based particulated nano- composites. In addition to their fundamental interest, such systems open promising applications in optical [1], micro- electronic [2] and magnetic [3] fields. Concerning the magnetic properties, numerous studies have shown that ferromagnetic clusters embedded into insulating matrices exhibit specific properties such as superparamagnetism [4], giant magnetoresistance [5] and modification of the magnetic moment per atom [6]. Several methods have been used to process nanocom- posite layers: ion implantation [7], sputtering [8], co-evapo- ration [9] and the sol–gel route [10]. The latter method involves the synthesis from hydrolysis and condensation processes of both matrix and metal oxides, followed by a thermal treatment in a reducing atmosphere to induce the nucleation and growth of metallic clusters. Such a proce- dure was successfully applied to different systems like Fe (Co, Ni)–SiO 2 [11], Ni–Al 2 O 3 [12] or Fe–Al 2 O 3 [13]. In the quoted studies, the resulting composites were generally packaged as monolithic gels or sintered pellets of large thicknesses. For example, Estournes et al. [11] showed that, because of the high stability of SiO 2 , a selective reduction of NiO during annealing treatments in an H 2 atmosphere leads to Ni clusters. Depending on the annealing tempera- ture between 600 °C and 900 °C, Ni particles grow with magnetic diameters about two times less than the geomet- rical ones. We chose to select the sol–gel route by using the dip coating (SGDC) procedure which allows the deposition of single or composite thin films (thickness <1 lm) with a high control of composition, density and surface roughness [14]. Our purpose was to investigate the possibility of preparing metallic Ni nanoparticles embedded in a SiO 2 matrix in an attempt to obtain dense enough system to 0022-3093/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2007.05.009 * Corresponding author. Tel.: +33 1 64 46 88 26. E-mail address: agnes.traverse@clio.u-psud.fr (A. Traverse). www.elsevier.com/locate/jnoncrysol Journal of Non-Crystalline Solids 353 (2007) 2646–2653